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• 1.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
Ram pump hydraulic air test. Pressure conditions and flow measurements: Experimental research and case study2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

This study consists of the development of a ram pump, which will allow the pumping of water without the need of external energy sources. It is considered an analysis of interest since, once it is finished; it can be applied in reality improving and facilitating different activities related to agriculture and health.

Previous studies have been made related to the ram pump; however, in this case, it is intended to understand the system that has been built in the laboratory in order to find the best combination of parameters that will lead to obtain the highest possible efficiency.

The study will be carried out by studying scientific literature and by experimenting in the laboratory. Encompassing the experimental and literary field, it is expected to understand perfectly the advantages and disadvantages of the ram pump in order to determine if it is worth it to install in certain places.

After the study, the most favourable parameters for the operation of the Bruzaholms Bruk pump have been obtained. It has been found that the use of a longer drive pipe favours the operation of the system, as it is possible to obtain a higher efficiency, although it must be taken into account that the mentioned length needs to be controlled, as it could reduce the working rhythm of the pump. It has also been seen that the pump gives better results if the impulse valve is completely opened. Finally, it has been proven that, as long as the height difference between the two tanks is enough, increasing the height of the water source will favour the operation of the system.

• 2.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Environmental engineering.
Building Services LTH, Lund University, Lund, Sweden . Building Physics LTH, Lund University, Lund, Sweden. Building Services LTH, Lund University, Lund, Sweden .
Air infiltration into naturally ventilated apartments in multifamily dwellings2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, p. 34-40Conference paper (Refereed)

This study presents the ACH for ten apartments in naturally ventilated multifamily dwellings for two cases inlet vent manipulations: i) fully opened inlet vents; and ii) fully closed and taped inlet vents. Even with fully opened inlet vents the resulting ventilation is rather poor. The average ACH is 0.26±0.16 h-1. All apartments fall in the lower quartile in terms of ACH when compared to other multifamily dwellings in Sweden. A method using two different tracers A and B is presented that allow for measurement of the partial flow from the stairway zone and the partial flow from other pathways into the apartment. On the average 10-20% of the airflow into a typical apartment in a naturally ventilated multifamily dwelling seems to originate from the stairway zone when the inlet vents are fully opened. By closing and taping the inlet vents, the airtightness of the apartments have been investigated. The average direct leakage flow, i.e. not from the stairway zone, is 17 m3/h but the variation is large. Layout B seems to leak the most, followed by A and then C.

• 3.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Kan man styra luftfördelningen i en byggnad med hjälp av ventilationssystemet?2009In: Forskning, ISSN 1654-8876, no 4, p. 46-46Article, review/survey (Other (popular science, discussion, etc.))
• 4.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Detection and removal of wind turbine ice: Method review and a CFD simulation test2018Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis

Nowadays, the energy sector is facing a huge demand that needs to be covered. Wind energy is one of the most promising energy resources as it is free from pollution, clean and probably will arise as one of the main energy sources to prevent global warming from happening. Almost 10% of the global energy demand is coming from renewable resources. By 2050 this percentage is expected to grow to 60%. Therefore, efforts on wind turbine technology (i.e. reliability, design…) need to be coped with this growth.

Currently, large wind energy projects are usually carried out in higher altitudes and cold climates. This is because almost all of the cold climates worldwide offer profitable wind power resources and great wind energy potential. Operating with wind turbines in cold climates bring interesting advantages as a result of higher air density and consequently stronger winds (wind power is around 10% higher in the Nordic regions). Not only benefits can be obtained but extreme conditions force to follow harsh conditions. Low temperatures and ice accretion present an important issue to solve as can cause several problems in fatigue loads, the balance of the rotor and aerodynamics, safety risks, turbine performance, among others. As wind energy is growing steadily on icy climates is crucial that wind turbines can be managed efficiently and harmlessly during the time they operate.

The collected data for the ice detection, de-icing and anti-icing systems parts was obtained through the company Arvato Bertelsmann and is also based on scientific papers. In addition, computer simulations were performed, involving the creation of a wind tunnel under certain conditions in order to be able to carry out the simulations (1st at 0ºC, 2nd at -10ºC) with the turbine blades rotating in cold regions as a standard operation.

In this project, Computational Fluids Dynamics (CFD) simulation on a 5MW wind turbine prototype with ice accretion on the blades to study how CL and CD can change, also different measures of ice detection, deicing and anti-icing systems for avoiding ice accumulation will be discussed. Simulation results showed a logical correlation as expected, increasing the drag force about 5.7% and lowering the lift force 17,5% thus worsening the turbine's efficiency.

• 5.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science. Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building Engineering, Energy Systems and Sustainability Science, Energy Systems and Building Technology. Department of Physics and Astronomy, University of Bologna, Bologna, Italy.
The drag force distribution within regular arrays of cubes and its relation to cross ventilation – Theoretical and experimental analyses2019In: Journal of Wind Engineering and Industrial Aerodynamics, ISSN 0167-6105, E-ISSN 1872-8197, Vol. 189, p. 91-103Article in journal (Refereed)

A novel set of wind tunnel measurements of the drag force and its spatial distribution along aligned arrays of cubes of height H and planar area index λ p (air gap between cubes) equal to 0.028 (5H) to 0.69 (0.2H) is presented and analysed. Two different types of measurements are compared: one type where the drag force is obtained using the standard load cell method, another type where the drag force is estimated by measuring the pressure difference between windward and the leeward façades. Results show that the drag force is nearly uniformly distributed for lower λ p (0.028 and 0.0625), it decreases up to 50% at the second row for λ p = 0.11, and it sharply decreases for larger λ p (from 0.25 to 0.69) where the force mostly acts on the first row. It follows that for the lowest λ p the drag force typically formulated as a drag area corresponds to the total frontal area of the array, whereas for large λ p the drag area corresponds to the area of the first row. By assessing the driving pressure for ventilation from the drag force, the analysis is extended to estimate the cross ventilation as an example of application of this type of measurements.

• 6.
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Physics and Astronomy, University of Bologna, Bologna, Italy.
Direct measurements of the drag force over aligned arrays of cubes exposed to boundary-layer flows2017In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 17, no 2, p. 373-394Article in journal (Refereed)

Wind tunnel measurements of the total drag force for aligned arrays of cubes exposed to two different boundary-layer flows at three flow velocities are discussed. The drag force for eight different building packing densities λp (from 0.028 to 1) is measured with a standard load cell generating a novel dataset. Different λp are reproduced by increasing the number of buildings on the same lot area; this represents a real situation that an urban planner is faced with when a lot area of a given (fixed) size is allocated to the development of new built areas. It is assumed that the surrounding terrain is uniform and there is a transition from a given roughness (smooth) to a new roughness (rough). The approaching flow will adjust itself over the new surface within a distance that in general may be larger than the horizontal length covered by the array. We investigate the region where the flow adjustment occurs. The wide range of packing densities allowed us to analyse in detail the evolution of the drag force. The drag force increases with increasing packing densities until it reaches a maximum at an intermediate packing density (λp = 0.25 in our case) followed by a slight decrease at larger packing densities. The value of the drag force depends on the flow adjustment along the array which is evaluated by introducing the parameter “drag area” to retrieve information about the drag distribution at different λp. Results clearly suggest a change of the distribution of the drag force, which is found to be relatively uniform at low packing densities, while most of the force acts on first rows of the arrays at large packing densities. The drag area constitutes the basis for the formulation of a new adjustment length scale defined as the ratio between the volume of the air within the array and the drag area. The proposed adjustment length scale automatically takes into account the change in drag distribution along the array for a better parameterization of urban effects in dispersion models.

• 7.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Unsteady CFD simulations for prediction of airflow close to a supply device for displacement ventilation2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, p. 47-54Conference paper (Refereed)

Modern diffusers applied in the field of ventilation of rooms are often complex in terms of geometry, including perforated plates, dampers, guide rails, curved surfaces and other components inside the diffuser, with the intention to create satisfying thermal comfort for the occupants. Also connecting ducts can be different for the same diffuser in different situations, affecting the supply velocity profile. It is obvious that simulation of airflow and air temperature particularly in rooms with displacement ventilation is very troublesome, particularly if the near-zone of the diffuser is of interest. Experiments commonly indicate very high turbulence intensities in the near-zone of displacement ventilation supply devices, especially close to the floor where high mean flow gradient occurs. This indicates that the air flow from inlet devices designed for displacement ventilation might be very unstable; the position of the stream leaving the diffuser and entering the room is changing with time, hence diffusion of momentum and temperature are increased. This effect is not captured in RANS simulations, since it is performed with the assumption of time-independent conditions. In this paper URANS simulations were performed for prediction of velocity and temperature distribution close to a complex air supply device in a room with displacement ventilation. The presented study show that unsteady simulations with the realizable turbulence k-ε model generates too high eddy viscosity and therefore damps out the unsteadiness of the flow especially inside the diffuser.

• 8.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Energisystem.
Near-Field Study of Multiple Interacting Jets: Confluent Jets2015Doctoral thesis, comprehensive summary (Other academic)

This thesis deals with the near-field of confluent jets, which can be of interest in many engineering applications such as design of a ventilation supply device. The physical effect of interaction between multiple closely spaced jets is studied using experimental and numerical methods. The primary aim of this study is to explore a better understanding of flow and turbulence behavior of multiple interacting jets. The main goal is to gain an insight into the confluence of jets occurring in the near-field of multiple interacting jets.

The array of multiple interacting jets is studied when they are placed on a flat and a curved surface. To obtain the boundary conditions at the nozzle exits of the confluent jets on a curved surface, the results of numerical prediction of a cylindrical air supply device using two turbulence models (realizable $\kappa$$\epsilon$ and Reynolds stress model) are validated with hot-wire anemometry (HWA) near different nozzles discharge in the array. A single round jet is then studied to find the appropriate turbulence models for the prediction of the three-dimensional flow field and to gain an understanding of the effect of the boundary conditions predicted at the nozzle inlet. In comparison with HWA measurements, the turbulence models with low Reynolds correction ($\kappa$ − $\epsilon$ and shear stress transport [SST] $\kappa$ − $\omega$) give reasonable flow predictions for the single round jet with the prescribed inlet boundary conditions, while the transition models ($\kappa$$\kappa$$\iota$ − $\omega$ and transition SST $\kappa$$\omega$) are unable to predict the flow in the turbulent region. The results of numerical prediction (low Reynolds SST $\kappa$$\omega$model) using the prescribed inlet boundary conditions agree well with the HWA measurement in the nearfield of confluent jets on a curved surface, except in the merging region.

Instantaneous velocity measurements are performed by laser Doppler anemometry (LDA) and particle image velocimetry (PIV) in two different configurations, a single row of parallel coplanar jets and an inline array of jets on a flat surface. The results of LDA and PIV are compared, which exhibit good agreement except near the nozzle exits.

The streamwise velocity profile of the jets in the initial region shows a saddle back shape with attenuated turbulence in the core region and two off-centered narrow peaks. When confluent jets issue from an array of closely spaced nozzles, they may converge, merge, and combine after a certain distance downstream of the nozzle edge. The deflection plays a salient role for the multiple interacting jets (except in the single row configuration), where all the jets are converged towards the center of the array. The jet position, such as central, side and corner jets, significantly influences the development features of the jets, such as velocity decay and lateral displacement. The flow field of confluent jets exhibits asymmetrical distributions of Reynolds stresses around the axis of the jets and highly anisotropic turbulence. The velocity decays slower in the combined regio  of confluent jets than a single jet. Using the response surface methodology, the correlations between characteristic points (merging and combined points) and the statistically significant terms of the three design factors (inlet velocity, spacing between the nozzles and diameter of the nozzles) are determined for the single row of coplanar parallel jets. The computational parametric study of the single row configuration shows that spacing has the greatest impact on the near-field characteristics.

• 9.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
Evaluation of RANS models in predicting low reynolds, free, turbulent round jet2014In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 136, no 1, article id 011201Article in journal (Refereed)

In order to study the flow behavior of multiple jets, numerical prediction of the three-dimensional domain of round jets from the nozzle edge up to the turbulent region is essential. The previous numerical studies on the round jet are limited to either two-dimensional investigation with Reynolds-averaged Navier-Stokes (RANS) models or three-dimensional prediction with higher turbulence models such as large eddy simulation (LES) or direct numerical simulation (DNS). The present study tries to evaluate different RANS turbulence models in the three-dimensional simulation of the whole domain of an isothermal, low Re (Re = 2125, 3461, and 4555), free, turbulent round jet. For this evaluation the simulation results from two two-equation (low Re k-ε and low Re shear stress transport (SST) k-ω), a transition three-equation (k-kl-ω), and a transition four-equation (SST) eddy-viscosity turbulence models are compared with hot-wire anemometry measurements. Due to the importance of providing correct inlet boundary conditions, the inlet velocity profile, the turbulent kinetic energy (k), and its specific dissipation rate (ω) at the nozzle exit have been employed from an earlier verified numerical simulation. Two-equation RANS models with low Reynolds correction can predict the whole domain (initial, transition, and fully developed regions) of the round jet with prescribed inlet boundary conditions. The transition models could only reach to a good agreement with the measured mean axial velocities and its rms in the initial region. It worth mentioning that the round jet anomaly is still present in the turbulent region of the round jet predicted by the low Re k-ε. By comparing the k and the ω predicted by different turbulence models, the blending functions in the cross-diffusion term is found one of the reasons behind the more consistent prediction by the low Re SST k-ω.

• 10.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Division of Energy Systems, Department of Management and Engineering, Linköping University.
Investigation in the near-field of a row of interacting jets2015In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 137, no 12, article id 121202Article in journal (Refereed)

Multiple interacting jets (confluent jets) are employed in many engineering applications, and the significant design factors must be investigated. Computational fluid dynamics (CFD) is used to numerically predict the flow field in the proximal region of a single row of round jets. The numerical results that are obtained when using the low Reynolds k-∈ are validated with the experimental data that are acquired by particle image velocimetry (PIV). PIV was used to measure mean velocity and turbulence properties in the proximal region of a row of six parallel coplanar round air jets with equidistant spacing at low Reynolds number (Re = 3290). The low Reynolds k-∈ underpredicts the streamwise velocity in the onset of the jets' decay. The characteristic points are determined for various regions between two neighboring jets. The comparison of the merging point (MP) and the combined point (CP) computed from measurements and simulations shows good agreement in the different regions between the jets. In this study, a computational parametric study is also conducted to determine the main effects of three design factors and the interactions between them on the flow field development using response surface method (RSM). The influences of the inlet velocity, the spacing between the nozzles, and the diameter of the nozzles on the locations of the characteristic points are presented in the form of correlations (regression equations). CFD is used to numerically predict the characteristic points for a set of required studies, for which the design values of the simulation cases are determined by the Box-Behnken method. The results indicate that the spacing between the nozzles has a major impact on the flow characteristics in the near-field region of multiple interacting jets. The RSM shows that the inlet velocity has a marginal effect on the merging and CPs. All of the square terms are removed from the response equations of MP, and only one two-way interaction term between inlet velocity and spacing remains in the regression model with a marginal effect. The square of the nozzle diameter contributes in the regression equations of CP in some regions between the jets.

• 11.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy engineering. Division of Energy Systems, Department of Management and Engineering, Linköping University.
Numerical and experimental verification of initial, transitional and turbulent regions of free turbulent round jet2011In: 20th AIAA Computational Fluid Dynamics Conference 2011, 2011Conference paper (Refereed)

Three-dimensional simulation of the whole domain (initial, transition and fully developed regions) of round jet is essential in order to predict and to study the flow behavior of multiple jets (e.g. confluent jets). According to authors knowledge, numerical prediction of round jet with RANS models that has been presented by other researchers, are only in two-dimensional (axisymmetric) and mostly for the fully developed region. The inlet boundary conditions,  inlet velocity profile, turbulent kinetic energy and its dissipation rate at the diffuser exit has been governed from an earlier verified numerical simulation. In the present paper, results of three-dimensional modeling of isothermal, free, turbulent round jet with two two-equation (Low Re  and SST ), a transition three-equation ( ) and a transition four-equation (SST) eddy-viscosity turbulence models with resolved inlet profiles are compared and validated with hot-wire anemometry. This study shows that numerical simulation of round jet with SST  gives good agreement with measured mean longitudinal velocities, while transition models could only predict the initial region of round jet.

• 12.
Department of Mechanical Engineering, The University of Hong Kong, Hong Kong.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology. Department of Mechanical Engineering, The University of Hong Kong, Hong Kong. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.
Flow mechanisms and flow capacity in idealized long-street models2010In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 45, no 4, p. 1042-1053Article in journal (Refereed)

It is an open question whether a street network of a city has a certain flow capacity characterizing the flow that can pass through the street network. It s our hypothesis that at least the simple street network has a certain flow capacity. With the purpose of exploring this we studied numerically and experimentally the flow capacity in some idealized long-street models continuously lined with buildings and exposed to a parallel approaching wind. The height of all the models is the same (H = 69 mm). Three groups of models were studied: models with the same uniform street width (W = H) but different lengths (L = 21.7H, 43.5H, 72.5H); models with the same length (L = 43.5H) but different uniform width (W = H, 2H, 4H); and models with a change of width at half distance, L/2. In the last of the three cases, the width of the upstream half was always the same (W1 = H), but there was a wider (W2 = 1.25H, 1.5H, 2H) or narrower (W2 = 0.75H, 0.5H) downstream half. We normalized flow rates by a reference flow rate equal to the flow rate through an opening far upstream with the same area as the windward entry. The normalized flow rate through the windward entry was about 1.0 in all cases. For a sufficiently long-street models, a flow balance is established, creating a fully developed region with a constant horizontal flow (flow capacity) and zero vertical mean velocity. The street length does not affect the flow capacity but as expected the width of the street affects the flow capacity.

• 13.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China . Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China . Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy. Department of Physics and Astronomy, University of Bologna, Bologna, Italy .
City breathability in medium density urban-like geometries evaluated through the pollutant transport rate and the net escape velocity2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 94, no P1, p. 166-182, article id 4213Article in journal (Refereed)

This paper investigates pollutant removal at pedestrian level in urban canopy layer (UCL) models of medium packing density (λ<inf>p</inf> = λ<inf>f</inf> = 0.25) using computational fluid dynamics (CFD) simulations. Urban size, building height variations, wind direction and uniform wall heating are investigated. The standard and RNG k-ε turbulence models, validated against wind tunnel data, are used. The contribution of mean flows and turbulent diffusion in removing pollutants at pedestrian level is quantified by three indicators: the net escape velocity (NEV), the pollutant transport rate (PTR) across UCL boundaries and their contribution ratios (CR).Results show that under parallel approaching wind, after a wind-adjustment region, a fully-developed region develops. Longer urban models attain smaller NEV due to pollutant accumulation. Specifically, for street-scale models (~100 m), most pollutants are removed out across leeward street openings and the dilution by horizontal mean flows contributes mostly to NEV. For neighbourhood-scale models (~1 km), both horizontal mean flows and turbulent diffusion contribute more to NEV than vertical mean flows which instead produce significant pollutant re-entry across street roofs. In contrast to uniform height, building height variations increase the contribution of vertical mean flows, but only slightly influence NEV. Finally, flow conditions with parallel wind and uniform wall heating attain larger NEV than oblique wind and isothermal condition.The paper proves that by analysing the values of the three indicators it is possible to form maps of urban breathability according to prevailing wind conditions and known urban morphology that can be of easy use for planning purposes.

• 14. Holmberg, Sture
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö. University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Indoor Air Quality and climate control parameters in office environment – CFD calculaions and measurements2000In: Roomvent 2000 Conference, 2000Conference paper (Refereed)
• 15.
Danish Building Research Institute, Aalborg University, Copenhagen, Denmark .
Danish Building Research Institute, Aalborg University, Copenhagen, Denmark . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Indoor Environmental Engineering, Aalborg University, Aalborg, Denmark .
Discharge coefficient of centre-pivot roof windows2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 92, p. 635-643Article in journal (Refereed)

Use of centre-pivot roof windows is very common in single family houses in Nordic Europe. Unfortunately the wind-driven airflow characteristics of this kind of windows are missing in the scientific literature. In the present study, the airflow rate through the window was specified by using the discharge coefficient. Wind tunnel measurements using a modelled centre-pivot roof windowwas used in the present study. For smaller sash opening angles the value of discharge coefficientwas approaching unity and the discharge coefficient decreased with increase in the sash opening angle. The value of 0.6 was only obtained when the window was without sash. Hence, the inclusion of sash improved the airflow characteristics of the window due to increased value of the dischargecoefficient. The discharge coefficient also depended on turbulence in the flow. In the absence of external wind, the turbulence was described by the value of Re. Only for higher values of Re the still-air discharge coefficients became independent of the flow direction and the air velocity. Whereas for wind driven natural ventilation the ratio of average air speed within the opening and the reference wind speed (velocity ratio) was used to define the fully developed turbulent flow. Constant values of wind-driven discharge coefficients were obtained when the average air speed within the opening was equal to or greater than the reference wind speed i.e. the velocity ratio greater than unity. Moreover, when the velocity ratio was greater than unity, the still-air discharge coefficients became identical to the wind-driven discharge coefficients.

• 16.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University, Linköping, Sweden .
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University, Linköping, Sweden .
Numerical study of a ventilation system based on wall confluent jets2014In: ASHRAE Transactions, ASHRAE , 2014, p. 272-284Conference paper (Refereed)

This study presents a numerical investigation of an air supply device based on wall confluent jets in a ventilated room. Confluent jets can be described as multiple round jets issuing from supply device apertures. The jets converge, merge, and combine at a certain distance downstream from the supply device and behave as a united jet or so-called "confluent "jets. The numerical predictions of the velocity flow field of isothermal confluent jets with three Reynolds-averaged Navier-Stokes (RANS) turbulence models (RNG k-ε, realizable k-ε, and SST k - ω) are reported in the present study. The results of the numerical predictions are verified with detailed experimental measurements by hot-wire anemometer and constant-temperature anemometers for two airflow rates. The box method is used to provide the inlet boundary conditions. The study of the airflow distribution showed that a primary wall jet (wall confluent jet) exists close to the supply device along the wetted-wall and a secondary wall jet is created after the stagnation region along the floor. It is presented that the flow field of the primary and secondary wall jet predicted by turbulence models is in good agreement with the experimental data. The current study is also compared with the literature in terms of the velocity decay and the spreading rate of the primary and secondary wall jet, the results of which are consistent with each other. Velocity decay and the spreading rate of the secondary wall jet in vertical and lateral directions were studied for different inlet airflow rates and inlet discharge heights. The comparative results demonstrate that the flow behavior is nearly independent of the inlet flow rate. Inlet discharge height is found to have impact close to the inlet, where the velocity decays faster when the jet discharges at a higher level. The decay tendency is similar as the jet enters into the room for all discharge heights.

• 17.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Management and Engineering, Linköping University.
Numerical study of a ventilation system based on wall confluent jets2014In: HVAC & R RESEARCH, ISSN 1078-9669, E-ISSN 1938-5587, Vol. 20, no 8, p. 846-861Article in journal (Refereed)

This study presents numerical investigation of an air supply device based on wall confluent jets in a ventilated room. Confluent jets can be described as multiple round jets issuing from supply device apertures. The jets converge, merge, and combine at a certain distance downstream from the supply device and behave as a united jet, or so-called confluent jet. The numerical predictions of the velocity flow field of isothermal confluent jets with three Reynolds-averaged Navier-Stokes turbulence models (renormalization group k-epsilon, realizable k-epsilon, and shear stress transport k-omega) are reported in the present study. The results of the numerical predictions are verified with detailed experimental measurements by a hot wire anemometer and constant temperature anemometers for two airflow rates. The box method is used to provide the inlet boundary conditions. The study of the airflow distribution shows that a primary wall jet (wall confluent jet) exists close to the supply device along the wetted wall, and a secondary wall jet is created after the stagnation region along the floor. It is presented that the flow field of the primary and secondary wall jet predicted by turbulence models is in good agreement with the experimental data. The current study is also compared with the literature in terms of velocity decay and the spreading rate of the primary and secondary wall jet, the results of which are consistent with each other. Velocity decay and the spreading rate of the secondary wall jet in vertical and lateral directions were studied for different inlet airflow rates and inlet discharge heights. The comparative results demonstrate that the flow behavior is nearly independent of the inlet flow rate. Inlet discharge height is found to have impact close to the inlet, where the velocity decays faster when the jet discharges at higher level. The decay tendency is similar as the jet enters into the room for all discharge heights.

• 18.
Department of Atmospheric Science, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China.
Department of Atmospheric Science, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China. Department of Atmospheric Science, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China. Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong. Department of Atmospheric Science, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China. Department of Atmospheric Science, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Numerical investigation of wind-driven natural ventilation performance in a multi-storey hospital by coupling indoor and outdoor airflow2016In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 25, no 8, p. 1226-1247Article in journal (Refereed)

This study employed two ventilation indexes: local mean age of air and air change rate per hour, to investigate wind-induced natural ventilation of 260 wards of a multi-storey hospital building in suburb of Guangzhou using computational fluid dynamics simulations. Using the surface-grid extrusion technique, high-quality hexahedral grid cells were generated for the coupled outdoor and indoor airflow field. Turbulence was solved by the renormalisation group k-model validated against experimental data with grid independence studies. Homogeneous tracer gas emission was adopted to predict room age of air. The air change rate of cross ventilation and single-sided ventilation can reach 30-160 h-1 and 0.5-7 h-1, respectively. Due to different locations of room openings on the balconies, natural ventilation of a room can be greatly better than its neighbouring room. The wind-induced cross ventilation highly depends on the distance from the room opening to the stagnation point and on the resulting pressure distribution on the target building surface. Furthermore, it is significantly influenced by the upstream buildings, the bent shape of the target building, and the prevailing wind directions. The coupled computational fluid dynamics methodologies with integrated ventilation indexes are useful for assessing the natural ventilation performance in other complex built environments.

• 19.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Entrainment and its Implications on Microclimate Ventilation Systems: Scaling the Velocity and Temperature Field of a Round Free Jet2019In: Indoor Air, ISSN 0905-6947, E-ISSN 1600-0668, Vol. 29, no 2, p. 331-346Article in journal (Refereed)

Research on microclimate ventilation systems, which mostly involve free jets, point to delivery of better ventilation in breathing zones. While the literature is comprehensive, the influence of contaminant entrainment in jet flows and its implications on the delivery of supplied air is not fully addressed. This paper present and discuss entrainment characteristics of a jet issued from a round nozzle (0.05 m diameter), in relation to ventilation, by exploring the velocity and temperature fields of the jet flow. The results show a trend suggesting that increasing the Reynolds number (Re) reduces ambient entrainment. As shown herein, about 30% concentration of ambient air entrained into the bulk jet flow at Re 2541 while Re 9233 had about 13% and 19% for Re = 6537/12026 at downstream distance of 8 diameters (40 cm). The study discusses that “moderate to high” Re may be ideal to reduce contaminant entrainment, but this is limited by delivery distance and possibly the risk of occupant discomfort. Incorporating the entrainment mixing factor (the ratio of room contaminants entrained into a jet flow) in performance measurements is proposed and further studies are recommended to verify results herein and test whether this is general to other nozzle configurations.

The full text will be freely available from 2019-11-30 00:01
• 20.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Center for the Built Environment, University of California, Berkeley, USA.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Experimental evaluation of an intermittent air supply system: Part 1: Thermal comfort and ventilation efficiency2016In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 95, p. 240-250, article id 4263Article in journal (Refereed)

Spaces with high occupancy density e.g.; classrooms, auditoriums and restaurants, provide challenges to ventilate at a lower energy use due to elevated temperatures. To meet occupants’ thermal comfort requirements traditional systems use a lot of energy. Alternative ventilation strategies that optimize high air movements in the occupied zone allow human activities at elevated temperatures while attaining improve occupants’ perception and acceptance of the indoor climate at a low energy use. This paper presents an experimental evaluation of a novel ventilation strategy for high occupancy spaces that provides fresh air and thermal comfort in the sitting zone through a controlled intermittent air jet system. The strategy uses ceiling mounted high momentum air jet diffusers (AJD) made from ventilation duct fitted with nozzles that generate confluent jets. The jets coalesce into a single two-dimensional jet which is directed downwards in the sitting zone. This paper presents an experimental evaluation/analysis of the proposed system with regard to ventilation efficiency and thermal comfort measurements in a classroom mockup. Results show that the system qualifies to be used as a primary ventilation system and has local air change index > 1 inside the jet, and a ventilation efficiency > 50%. The system also provides better thermal climate than mixing and displacement ventilation at elevated temperatures.

• 21.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Investigation of flow pattern for a confluent-jets system on a workbench of an industrial space2014In: Indoor Air 2014: 13th International Conference on Indoor Air Quality and Climate, 2014, p. 192-199Conference paper (Refereed)

A new air supply terminal based on confluent jets was installed on a workbench, in vicinity of a CNC machine, of an industrial space. The flow pattern and temperature field was carried out by CFD calculations and infrared camera imaging technique. A main goal of this technique is to save energy therefore the jet should distribute the air where it is desired. This is possible because the confluent jets system uses the benefits of both mixing (high momentum for better spreading of the air jet) and displacement (cleaner air in occupied zone). The results show that thermal comfort and air quality analysis relies on consistent facts and is in good agreements with the existed standards. It was shown that the supply terminal is able to spread the fresh air to the needed work area. This is an advantage of the high momentum air distribution system used in this investigation.

• 22.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
Krafter på rörsystem vid transient flöde: En jämförelse mellan RELAP5 och Fluent2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

At Forsmarks Kraftgrupp AB (FKA) forces on pipe systems due to transient flow are frequently calculated as a step to verify their structural integrity. In nuclear industries these forces are often calculated with a one dimensional thermal-hydraulic analysis-code called RELAP5. When calculations regarding more complex geometries are needed, the three dimensional code Fluent is often used. This code is highly time consuming and requires large computational power.

This projects aim is to compare calculations of pressure, flow and forces carried out by RELAP5 and Fluent for an arbitrary pipe section during transient flow conditions. This has been accomplished by constructing a simple geometry for which a transient flow is simulated in both programs. Forces have been calculated via pressure difference over the pipe section and also by use of differentiated mass flow. In Fluent k-ω SST and VLES turbulence models have been used and also two different numerical schemes in order to investigate their influence on the results.

The results show that forces calculated with RELAP5 and Fluent are in parity. Small differences in mass flow and pressure appear when comparing between the codes. This probably stem from different handling of losses in RELAP5 and Fluent. The differences have no effect on forces calculated since the differentiated mass flow and pressure difference used are equivalent for both codes.

• 23.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Wind driven flow through openings: analysis of the stream tube2006In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 4, no 4, p. 323-336Article in journal (Refereed)

Wind approaching a building provided with openings on the windward and leeward sides has a choice, either it flows through the openings or flows around and above the building. This choice gives rise to a dominant stream tube containing the fluid flowing through the openings. In this paper the stream tube is analysed based on wind tunnel measurements and CFD simulation. A house model with dimensions 120 mm (Width)×120 mm (Height)×180 mm (Length) was provided with rectangular openings of equal size located opposite each other. The end walls were thin giving rise to a sharp edged opening. The size of the openings expressed as the porosity (opening area divided by the façade area) was 1.3 %, 5.2 %, 11.6 %, 20.7 % and 46.5 %. In the wind tunnel, velocity including velocity fluctuations and pressure were measured along the centre line through the openings. In the CFD prediction it was possible to visualize the stream tube by the method of “flying particles”. This made it possible to explore the change in shape of the stream tube and to calculate the cross-sections of the stream tube at different positions and to know the total pressure distribution within the stream tube cross section. Finally, the discharge coefficient based on stream tube analysis was compared to that from a conventional chamber method.

• 24.
Department of Architecture, School of Engineering, Osaka City University, Japan.
Department of Architecture, School of Engineering, Osaka City University, Japan. Department of Architecture, School of Engineering, Osaka City University, Japan. Kyoto Institute, Kinden Corporation, Japan. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Numerical investigation and accuracy verification of indoor environment for an impinging jet ventilated room using computational fluid dynamics2017In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 115, p. 251-268Article in journal (Refereed)

The impinging jet ventilation (IJV) system has been proposed as an air distribution strategy to provide a better thermal environment with a medium supply momentum than displacement ventilation (DV) system. However, no simplified prediction method that is practically applicable has been established to date. The ultimate goal of this study is to establish a calculation model to predict the vertical temperature profile in an IJV system. The authors aim to propose a one-dimensional model, where the room is divided into several control volumes. To perform this, the turbulent thermal diffusion between control volumes needs to be well understood. Therefore, a knowledge about the effect of each design factor such as the supply air velocity on the turbulent thermal diffusivity needs to be acquired through a parametric study. Computational Fluid Dynamics (CFD) is effective for this purpose. As a first step, the accuracy of CFD simulations is verified by conducting a full-scale experiment. The velocity profiles inside the impinging jet and the indoor temperatures are measured and compared with the CFD results. It is shown that the shear-stress transport k-ω model has a sufficient accuracy to analyse the target room, and an appropriate grid layout is established as well. The convection-radiation coupling CFD prediction where the external temperature is used as a boundary condition is adopted as the best method for the numerical study in this research. Finally, a parametric study on the supply air velocity is performed based on this setting and its effect on the thermal stratification is presented.

• 25.
Harbin Institute of Technology, School of Municipal and Environmental Engineering, China; School of the Built Environment, University of Reading, Reading, United Kingdom.
School of the Built Environment, University of Reading, Reading, United Kingdom . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Harbin Institute of Technology, School of Municipal and Environmental Engineering, China; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, China .
Revisiting the 'Venturi effect' in passage ventilation between two non-parallel buildings2015In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 94, p. 714-722Article in journal (Refereed)

A recent study conducted by Blocken et al. (Numerical study on the existence of the Venturi effect in passages between perpendicular buildings. Journal of Engineering Mechanics, 2008, 134: 1021-1028) challenged the popular view of the existence of the 'Venturi effect' in building passages as the wind is exposed to an open boundary. The present research extends the work of Blocken et al. (2008a) into a more general setup with the building orientation varying from 0° to 180° using CFD simulations. Our results reveal that the passage flow is mainly determined by the combination of corner streams. It is also shown that converging passages have a higher wind-blocking effect compared to diverging passages, explained by a lower wind speed and higher drag coefficient. Fluxes on the top plane of the passage volume reverse from outflow to inflow in the cases of α = 135°, 150° and 165°. A simple mathematical expression to explain the relationship between the flux ratio and the geometric parameters has been developed to aid wind design in an urban neighborhood. In addition, a converging passage with α = 15° is recommended for urban wind design in cold and temperate climates since the passage flow changes smoothly and a relatively lower wind speed is expected compared with that where there are no buildings. While for the high-density urban area in (sub)tropical climates such as Hong Kong where there is a desire for more wind, a diverging passage with α = 150° is a better choice to promote ventilation at the pedestrian level.

• 26.
Center for the Built Environment, University of California, Berkeley, CA, USA.
Center for the Built Environment, University of California, Berkeley, CA, USA. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Civil and Environmental Engineering, University of California, Berkeley, CA, USA.
Predicted Percentage Dissatisfied with Ankle Draft2017In: Indoor Air, ISSN 0905-6947, E-ISSN 1600-0668, Vol. 27, no 4, p. 852-862Article in journal (Refereed)

Draft is unwanted local convective cooling. The draft risk model of Fanger et al. (Energy and Buildings 12, 21-39, 1988) estimates the percentage of people dissatisfied with air movement due to overcooling at the neck. There is no model for predicting draft at ankles, which is more relevant to stratified air distribution systems such as underfloor air distribution (UFAD) and displacement ventilation (DV). We developed a model for predicted percentage dissatisfied with ankle draft (PPDAD ) based on laboratory experiments with 110 college students. We assessed the effect on ankle draft of various combinations of air speed (nominal range: 0.1-0.6 m/s), temperature (nominal range: 16.5-22.5 °C), turbulence intensity (at ankles), sex, and clothing insulation (< 0.7 clo; lower legs uncovered and covered). The results show that whole body thermal sensation and air speed at ankles are the dominant parameters affecting draft. The seated subjects accepted a vertical temperature difference of up to 8 °C between ankles (0.1 m) and head (1.1 m) at neutral whole body thermal sensation, 5 °C more than the maximum difference recommended in existing standards. The developed ankle draft model can be implemented in thermal comfort and air diffuser testing standards.

• 27.
School of Construction Management and Engineering, University of Reading, United Kingdom .
School of Construction Management and Engineering, University of Reading, United Kingdom; School of Municipal and Environmental Engineering, Harbin Institute of Technology, China . University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. School of Municipal and Environmental Engineering, Harbin Institute of Technology, China; State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, China.
Ventilation performance in a passage between two nonparallel buildings2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, p. 815-820Conference paper (Refereed)
• 28.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
Simulering av ett värmesystem i COMSOL Multiphysics: Pipe Flow Module2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis

Syftet med detta arbete är att simulera ett värmesystem i COMSOL Multiphysics, Pipe Flow Module, Non-Isothermal Pipe Flow som innehåller ekvationer och randvillkor för att modellera inkompressibel strömning och värmeöverföring i rör.

Data om processen och dess komponenter har samlats in från industrin där arbetet är utfört och i vissa fall modifierats för att bättre beskrivas i programmet.

Utifrån insamlad data har en modell byggts upp och två simuleringar har gjorts. En stationär för starten av systemet, den har sedan legat till grund för en dynamisk som simulerar förloppet från start till normaldrift.

Tiden det tar för det aktuella fallet att nå drifttemperatur är 16 timmar. En felströmning upptäcktes samt att en av pumparna inte kommer att klara en start från 20 °C.

• 29.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Displacement Ventilation in a Classroom: Influence of Contaminant Position and Physical Activity1998In: Proc. 19th AIVC Conference, Oslo, Norway., 1998Conference paper (Refereed)

This study describes how the air quality in a displacement ventilated classroom can be influenced by the position of a contaminating person, and by the activity of a person who walks around in the room. Tracer gas measurements have been performed in a full scale mock-up of a classroom, with person simulators at the student’s desks.

The spreading of contaminants from a person seems to be strongly dependent on the position of the person. The closer the contaminating person sits to the outlet terminal(s), the less of his/hers contaminants are spread in the room. Paradoxically, people sitting furthest away from the air supply were found to be provided with the least contaminated air. Physical activity, produced by a walking person, tends to increase the concentration of contaminants emitted from people in the room, whereas the air exchange efficiency actually can benefit from it. At all levels of activity tested in this study the displacement ventilation system provided significantly better air quality than a mixing system would. The temperature gradient in the occupied zone was rather high during these steady-state experiments, and it was only marginally affected by the movements of a person.

• 30.
University of Gävle, Department of Technology and Built Environment. Inomhusmiljö.
ON THE EFFICIENCY OF DISPLACEMENT VENTILATION, with Particular Reference to the Influence of Human Physical Activity1999Doctoral thesis, monograph (Other scientific)

The efficiency of room ventilation by the displacement principle was studied with respect to some influential factors, in particular that of physical activity. The study was experimental and performed in two full-scale test rooms, one of office-size and one of classroom-size. Physical (mainly walking) activity was executed in these rooms by person simulators and by humans. The ventilation efficiency was quantified by tracer gas measurements.

In the performed tests, the activity of a walking person generally proved detrimental to the ventilation efficiency. Particularly the air quality in the occupied zone was impaired, due to down-wash of air in the wake behind the moving person, causing transportation of relatively old and contaminated air from the upper part of the room down to lower levels. It appeared, however, that it takes a rather high level of physical activity to completely abolish the displacement effect. Especially the air quality in the breathing zone of non-moving occupants tended to remain significantly better than at perfect-mixing conditions. Completely mixed room air occurred nevertheless when the activity was intense, but the displacement flow pattern was re-established fairly quickly after ceasing of the activity.

The contaminant distribution showed substantial horizontal variations in the "classroom". A contaminant released in the occupied zone was effectively extracted from the room when the source was situated on the same side of the room as the extract terminal(s), whereas, when situated on the opposite side, the contaminant accumulated in the upper part of the room. It was further shown that the air supplied from displacement diffusers tends to reach all occupants fairly quickly, also in relatively large and densely populated rooms such as classrooms.

The temperature stratification of the room air, and free-convection currents along the walls are crucial for the appearing air flow pattern and contaminant distribution. Transfer and accumulation of heat in materials tend further to make the thermal conditions indoors more or less transient at all times. This entails, it was shown, that also the ventilation efficiency is time dependent. In tests where people suddenly entered the "classroom", the ventilation efficiency improved with time. This generally caused the highest contaminant exposures to occur at the beginning of the stay in the room.

Tests with two different ceiling heights showed lower ventilation efficiency with the higher ceiling, involving a higher contaminant exposure of the occupants. The reason for this appears to be enhanced down-flow along the walls, caused by a higher section of relatively low surface temperature, and possibly by the appearance of merging plumes, enhancing the vertical recirculation process.

A wall temperature deviating from that of the indoor air impaired the ventilation efficiency, whereas an increase in ventilation rate improved it. In all test cases in this study, however, the air quality in the breathing zone of seated occupants remained significantly better than that at perfect-mixing conditions – a sports-activity test being the only exception.

• 31.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Removal of airborne particles of different sizes in classrooms using portable air cleaners2007In: Roomvent 2007, 13-15 June 2007 Helsinki, Finland: Scanvac Conference : proceedings, abstract book, 2007Conference paper (Refereed)

Portable electrostatic air cleaners (precipitators) were tested in six different classrooms during ordinary lessons. The number concentration of airborne particles in the classrooms was measured using optical particle counters, which separated the particle recordings into six different size fractions in the range 0.3 μm to >25 μm. It was found that the effectiveness of the air cleaners in cleaning the classroom air was decreasing significantly with increasing particle size. For the smallest particles measured, 0.3-0.5 μm, the measured effectiveness was 76 %, whereas for the particle size fraction 10-25 μm it was only 33 %. This reduced effectiveness for the large particles can be explained by the removal process of particle deposition onto room surfaces. The removal rate due to deposition seems to be competitive with the removal rate of the air cleaners as regards large particles. It appears that the deposition effect often needs to be taken into account in effectiveness assessments for particulate air cleaners.

• 32.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
Testing local exhaust ventilation at controlled turbulence generation by using tracer gas and a 3-D anemometer2014Report (Other academic)

Local exhaust (LE) ventilation is a ventilation technique where contaminated air is locally extracted close to the contaminant source, usually with the purpose to reduce the exposure of a person doing work which involves the contaminant. There is a need for well-defined and appropriate methods to test the performance of LE constructions. The present study aims at contributing to the establishment of such tests. The study entails full scale experimental measurements that include 3-D air velocity measurements, tracer gas tests and controlled generation of air turbulence through physical movements of a vertical, human-sized plate. The tested exhaust hood (EH) was of circular, flat plate flanged type.

One part of the study concerned the task of determining the 0.4 m/s distance, x0.4, at the EH; i.e. the distance from the EH opening to a point where the air velocity has declined to 0.4 m/s. This is a currently used measure of “safe zone” at an EH. It was found that practicable measurements of good accuracy seem to be attained by using the following fairly simple correction equation:

x0.4=xm*rot(Vm/0.4)

where Vm is a provisionally measured air velocity, preferably within the zone where Vis within 0.35-0.45 m/s in front of the EH, and xm is the measured distance from the EH opening to the measuring point of Vm.

The tracer gas tests implied injection of a neutrally buoyant tracer gas through a perforated sphere placed in front of the EH. The amount of tracer gas that escaped from the suction flow was measured in the room air, thus yielding a sensitive method for measuring the capture efficiency (CE) of the EH. The CE is the percentage of injected tracer gas that is directly captured by the EH. Measurements of CE was performed at several test cases, were exhaust flow rate, gas release distance, turbulence level and EH arrangement were varied. The recorded CE values varied between 75 to 100% and the response to the different test cases appeared trustworthy.

The use of a 3-D sonic anemometer, that yielded both magnitude and direction of the air movement, proved very useful in analyzing the generated air turbulence. Its measurement data was also used to construct another measure of the local exhaust performance: Percentage Negative Velocities, PNV. This measure represents the percentage of the time when the air flow at the measuring point in front of the EH is directed away from the EH nozzle, i.e. when the velocity component in the direction towards the EH opening is negative. The recorded PNV values correlated well with the corresponding CE values, attained at the tracer gas tests. Thus, measuring PNV might be a convenient alternative or complement to tracer gas measurements.

• 33.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Vertical distribution of occupant-generated particles in a room with displacement ventilation2002In: Indoor Air 2002: 9th international conference on indoor air quality and climate, 2002, p. 509-514Conference paper (Refereed)

The vertical distribution of airborne particles in a room ventilated according to the displacement principle was measured using a vertically conveyed particle counter. The supply air was absolute-filtered and the particles generated through office-like activity of people. In general, particle concentrations increased with height, indicating a displacement effect. This effect improved with ventilation rate. A threshold-size of the particles could be discerned, above which the displacement effect started declining. The measured threshold-size agreed well with calculations based on the settling velocity of the particles and the hypothetical vertical piston-flow velocity of the room air (ventilation rate divided by floor area). At the ventilation rates tested (normal to high), the threshold-size was in the range 5-10 µm. Slightly negative concentration gradients were observed for large particles at the lowest ventilation rate. Hence, if hazardous substances are known to be associated with fairly large particles, the use of displacement ventilation is questionable.

• 34.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Mixing and displacement ventilation compared in classrooms; distribution of particles, cat allergen and CO22003In: Proceedings from Healthy Buildings 2003: 7th International conference, 2003, p. 458-464Conference paper (Refereed)

Mixing ventilation and displacement ventilation were compared in an intervention study in classrooms. Particles, cat allergen and CO2, were measured in classroom air at different levels above the floor, during regular lessons. With mixing ventilation, the particle concentration tended to decrease with height, with a stronger gradient occurring for larger particles. With displacement ventilation, the particle concentration increased with height, except for particles >25 µm. The displacement system thus tended to have a slight upward displacement effect on most of the particles. Significant correlations were found between concentrations of cat allergen and particles in the size fraction 1–10 µm. The particle and cat allergen concentration at breathing height did not, however, differ significantly between the two ventilation systems. CO2 was about 10% lower with displacement ventilation. A fairly high level of physical activity of the pupils is believed to have had significant dispersing effect on the airborne contaminants.

• 35.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för byggnadskvalitet.
Effect of Particulate Air Cleaners on the Content of airborne Dust and Cat Allergen in Classrooms2004In: Roomvent 2004: 9th international conference on air distribution in rooms, 2004Conference paper (Refereed)

Electrostatic air cleaners (precipitators) were tested in four classrooms during ordinary lessons for four weeks. Airborne dust in the classrooms was collected on filters using two different kinds of samplers: IOM-sampler and a new kind of ionizing sampler. The amount of collected dust was evaluated by visual inspection (“filter blackening”) and the content of cat allergen was measured using an amplified ELISA assay. It was found that the filter blackening was 64% lower when the air cleaners were active than when they where inactive (p<0.001). This suggests that the air cleaners were effective in reducing the content of airborne particulate matter. The reduction in cat allergen appeared however to be less substantial. The variance of the allergen data was unexpectedly large, presumably due to relatively few allergen-carrying particles in the sampled air. It is believed that larger sampling volumes are needed to get more reliable data of airborne cat allergen in spaces where the allergen is emitted indirectly.

• 36.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering.
Study of temperature raise in Gavleån river related to district cooling2010Independent thesis Advanced level (degree of Master (One Year)), 40 credits / 60 HE creditsStudent thesis

This project is a preliminary study in order to build a small power plant, located beside to Gavleån River. It has been designed with the aim of cooling a district of Gävle city, Sweden. That big project is carried out by the international consulting engineering company SWECO. The mentioned plant contains a thermodynamic cycle that takes water from the river and afterwards, it is returned back warmer. It will attempt to study the temperature raise downstream along the river due to the spill of hot water. In addition, it will try to quantify and weight which may be the importance of the increment of temperature compared to the entire river. This work could be vital for an environmental impact study. The thermo and fluid dynamic problem is going to be solved using typical procedure for numerical simulations. To do this, it will be used Computer Aided Design (CAD) to model Gavleån River path and Computational Fluent Dynamics (CFD) to predict the distribution of temperatures. Finally the results of the simulations will be analyzed and discussed to draw conclusions about the final temperature raise in Gavleån River.

• 37.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik. Department of Mechanical Engineering, Linköping University, Linköping, Sweden.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för energi- och maskinteknik. Department of Mechanical Engineering, Linköping University, Linköping, Sweden.
RSM and v̄2-f study on the flow behaviour of an impinging jet in a cross-flow on a wall-mounted cube2007In: Progress in Computational Fluid Dynamics, An International Journal, ISSN 1468-4349, E-ISSN 1741-5233, Vol. 7, no 6, p. 311-322Article in journal (Refereed)

The current trends of electronic devices are resulting in a steady increase in the dissipated heat from the components. One possible cooling method is to use an impinging jet and a low-velocity channel flow. The objective is to investigate the performance of the v(2) - f model and RSM in order to predict the time-average velocity and the Reynolds stresses. The case is a channel with a cube in the middle of the base plate and two inlets, one horizontal channel flow and one vertical impinging jet above the cube. The turbulence models are validated against earlier PIV measurement with identical set-up.

• 38.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.
Swedish University of Agricultural Sciences. University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.
Industrial nanoparticles health risks and advantages of a decent industrial ventilation system in reducing the related risks2012Conference paper (Refereed)

With the fast-growing use of nanoparticles (NPs) in a wide range of production andmanufacturing processes, and great health and environmental risks associated to NPs, it is important totreat the industry-produced NPs in a proper way. Ventilation of industrial workplaces lies within theconcept of sustainability challenges for the development of nanoproducts. Due to the decreased grainsize of material to nano limits and thus the appearance of either new or changed properties, health riskof workers in such environments is critical concerning the complicated and unknown characteristicsof nanoparticles. There is great evidence over the past few years that ultrafine particles and especiallyNPs in the breathing air are strong toxins. Different mitigation measures for air-borne nanoparticles inindustrial workplaces are substitution, engineering controls such as ventilation and provision of personalprotective equipment. In this paper selection criteria for ventilation systems and different ventilationmethods (hood ventilation and global enclosure/room ventilation systems) as engineering controlsof nanoparticles within industrial enclosures will be reviewed. Novel methods for improvement ofventilation efficiency in general and industrial work places with an eye on ventilation of nanoparticleswill be presented.

• 39.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.
Piv study of ventilation quality incertain occupied regions of a 2d room model with rapidly varying flow rates2012Conference paper (Refereed)

The use of supply jet flows is the most common type of air distribution for general ventilation inindustrial premises. Usually the supply flow rate is constant or slow varying (VAV-systems) to copewith a varying load. A novel air distribution method, with the potential to reduce stagnation and toincrease the ventilation efficiency, is to introduce rapid flow variations (pulsations). In the paper wereport on a fundamental study of this type of air distribution. The purpose of the study was to explorethe effect on stagnant zones and the levels of the kinetic energy and the relative turbulence intensity.The study was conducted in a small-scale, two-dimensional (2-D) room model with water as operatingfluid. The size of the model made it possible to investigate the 2-D velocity vector field in certainoccupied regions using Particle Image Velocimetry (PIV) method and further consequent analyseshave been done from the resulted vector fields. The comparison between cases of constant inflow andpulsated inflow (flow variations with frequency of 0.5 Hz) have been conducted for three domains,two belonging to the far-field occupied zone and one belonging to the near-field, downstream of thesupply wall jet.

• 40.
University of Gävle, Department of Technology and Built Environment.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö. University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för byggnadskvalitet. University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Numerical and experimental studies of wind environment in an urban morphology2005In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 39, no 33, p. 6147-6158Article in journal (Refereed)

The purpose of the paper is to examine the relation between urban morphology (three-dimensional structure) and windiness. We regard a city as a porous obstacle, which is open at the top. We consider the interaction between the atmospheric boundary layer and a city to be both a function of the overall shape (silhouette or skyline) and the internal resistance to the flow caused by the friction when the wind flows over the urban surfaces. We regard the street pattern as an interconnected flow network with the crossings as nodes. Flow, along the streets is generated by pressure differences.

We here use a highly idealized city model consisting of a circular block divided into two or four equally large sectors. Two types of cases are studied, the first with only one street through the city model with different angles between the street and the oncoming wind. The second case also contains a perpendicularly crossing street (through the center). Both wind tunnel experiments and numerical flow computations (computational fluid dynamics, CFD) are used and compared. The general agreement between the two is good and the CFD method offers new possibilities for quantifying the urban wind environment. (c) 2005 Elsevier Ltd. All rights reserved.

• 41.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
The confinement effects on jet kinetic momentum flux quantified by measuring the reaction force2014In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 13, no 3, p. 285-298Article in journal (Refereed)

A turbulent jet is the most important flow element in mechanical ventilation. Mixing ventilation is basedon the properties of turbulent jets. By entrainment into the jet the ambient air is set into motion. For ajet supplied within a room the enclosure may affect the jet in several ways, through: a) Coanda effect which is the tendency of a fluid to be attracted to a nearby surface. A free jet is turned into a wall jet and the momentum flux of the jet decreases by friction against the room surfaces.b) The jet collides with the opposing wall and the jet is transformed into a wall jet. c) The size of the cross sectional area relative to the supply opening will affect the flow pattern withinthe enclosure. One can expect the direction of the inflow (entrainment) to the jet to be affected. d) Location of supply and extract. The location of the supply is a factor that influences the pressure gradient within the room. This paper considers the items b), c) and d). The main characteristic of a jet is its momentum flux, but determining the momentum flux is not an easy task and has lead to contradicting results. Standard methods require velocity field measurements which have their restrictions and uncertainties. To overcome these problems a direct and more reliable method was used by recording the flow force, caused by an impinging jet, with a digital balance. Thetests were carried out both for unenclosed (free jet) and enclosed cases. In the latter case tests were conducted with supply and extract both located on the same wall and located on opposite walls. Detailed pressure measurements were conducted to describe the details of the reaction force. There was a clear effect of the confinement on the reaction force and a Reynolds number dependence.

• 42.
University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
I.N.Ri.M., Fluid Dynamics Group, Politecnico di Torino, Turin, Italy. University of Gävle, Department of Technology and Built Environment, Ämnesavdelningen för inomhusmiljö.
Experimental analysis of low-Reynolds number free jets: Evolution along the jet centerline and Reynolds number effects2009In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 47, no 2, p. 279-294Article in journal (Refereed)

The present paper analyzes the features of a low-Reynolds number free submerged jet with special regard to statistical quantities on the jet centerline. Measurements in an environment with very low disturbances allowed to observe details of turbulence and higher-order moments. Some peculiar features of the measured (natural) jet are shown to be in correspondence to observations referring to forced higher-Reynolds number jets. In particular, it is shown that, at low Reynolds numbers, the initial region of the jet is dominated by well-defined vortices in the shear layer. This result is substantiated by both the statistical moments and the spectral analysis. The presence of two distinct regimes is evidenced and discussed from a physical standpoint, also in relation to the mathematical analysis of the jet structure from the bibliography.

• 43.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China .
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system. Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China .
Assessment of air change rate and contribution ratio in idealized urban canopy layers by tracer gas simulations2014In: Indoor Air 2014 - 13th International Conference on Indoor Air Quality and Climate, 2014, p. 470-477Conference paper (Refereed)
• 44.
University of Gävle, Faculty of Engineering and Sustainable Development.
MOMENT BALANCE OF AN AXISYMMETRIC JET AND THE EFFECT OF AIR ENTRAINMENT FROM AMBIENT2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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