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  • 1.
    Jahedi, Mohammad
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Berntsson, Fredrik
    Department of Mathematics, Linköping University, Linköping, Sweden.
    Wren, Joakim
    Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem. Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Transient inverse heat conduction problem of quenching a hollow cylinder by one row of water jets2018Inngår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 117, s. 748-756Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, a two-dimensional linear transition inverse heat conduction problem (IHCP) was solved using the Generalized Minimal Residual Method (GMRES) in quenching process by water jets. The inverse solution method was validated by set of artificial data and solution sensitivity analysis was done on data noise level, regularization parameter, cell size, etc. An experimental study has been carried out on quenching a rotary hollow cylinder by one row of subcooled water jets. The inverse solution approach enabled prediction of surface temperature and heat flux distribution of test specimen in the quenching experiments by using measured internal specimen temperature. Three different boiling curves were defined in the quenching process of a rotary cylinder. Result obtained by the inverse solution showed clear footprint of rotation in surface temperature and heat flux on each revolution of cylinder and temperature variation damping from quenching surface toward interior of specimen.

  • 2.
    Jahedi, Mohammad
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik.
    Moshfegh, Bahram
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för byggnadsteknik, energisystem och miljövetenskap, Energisystem och byggnadsteknik. Department of Management and Engineering, Linköping University.
    Quenching a rotary hollow cylinder by multiple configurations of water-impinging jets2019Inngår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 137, s. 124-137Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experiments have been conducted to analyze quenching of a hot rotary hollow cylinder by one and two rows of water-impinging jets. Sub-cooled water jets (ΔTsub = 45–85 K) with flow rate 8006 to 36,738 impinged on hollow cylinder with rotation speed 10 to 70 rpm at various initial wall superheat temperatures from 250 to 600ºC. Jet-to-jet and jet-to-surface spacing varied between 4 to 10d and 1.5 to 7d respectively and angular position of impinging jets were tested from 0 to 135º. Effectiveness of the defined parameters on stagnation point’s local average heat flux was found lower in the film and nucleate boiling compare to transition boiling regime where rotation speed had the highest impact. Characteristic of maximum heat flux (MHF) at stagnation point and upwash flow point were analyzed based on surface heat flux, time and temperature corresponding to MHF. Same maximum heat flux levels were captured in the both points which reveals importance of the flow behavior at the upwash flow point. The effectiveness of the parameters to improve average heat transfer was studied based on cooling area of each water impingingjet in the multiple configurations. Higher average heat transfer was obtained by increasing flow rate and subcooling temperature and lower initial wall superheat temperature corresponding to onset of transition boiling regime.

  • 3.
    Rundström, Daniel
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för energi- och maskinteknik. Department of Management and Engineering, Linköping Institute of Technology, Sweden.
    Moshfegh, Bahram
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för energi- och maskinteknik. Department of Management and Engineering, Linköping Institute of Technology, Sweden.
    Large-eddy simulation of an impinging jet in a cross-flow on a heated wall-mounted cube2009Inngår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 52, nr 3-4, s. 921-931Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A large-eddy simulation (LES) is performed in order to predict the mean velocity field, the turbulence characteristics and the heat transfer rate of an impinging jet in cross-flow configuration on a heated wall-mounted cube. The WALE model was used to model the subgrid-scale tensor. The results from the LES are compared with a Reynolds stress model (RSM) and against earlier measurements with identical set-up. A comparison between the results from the predictions and the measurements shows that in general the LES has better agreement with the measurements compared to the RSM and particularly in the stagnation region of the impinging jet. (C) 2008 Elsevier Ltd. All rights reserved.

  • 4.
    Yin, Shi
    et al.
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region.
    Sandberg, Mats
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Energisystem.
    Lam, Kit-Ming
    Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong Special Administrative Region.
    Li, Yuguo
    Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region.
    Near-field merging and penetration of triple starting plumes from volumetric heat sources in a calm environment2017Inngår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 115, nr Part B, s. 1321-1333Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the buoyancy effect on near-field evolution of triple equal starting thermal plumes from volumetric heat sources, with a focus on merging process, velocity evolution, and stream-wise penetration. Instantaneous velocity fields and corresponding vorticity distribution, temporal evolution of centerline axial velocities, temporal penetrating rates and heights are examined by 2-D particle image velocimetry (PIV) at three different source heat strengths of 180 W, 90 W, and 30 W. A four-stage merging process is demonstrated to be independent of heat strength. Normalized starting and terminating times of each developing stage are also unified regardless of the heat strength, i.e., t/t∗ = 1.7–2.5 for stage i (relatively isolated development), t/t∗ = 2.5–3.3 for stage ii (bending wall flows), t/t∗ = 3.3–3.9 for stage iii (development after a self-merged state), and t/t∗ > 3.9 for stage iv (evolution with global merging). The axial velocity at a specific centerline point usually involves three distinct developing periods: a “centerline-silent” period ending at a normalized transportation time tt_n when heat is just transported to the measuring points, a fast rising period, and a fluctuating period starting at a normalized endurance time te_n. The buoyancy-independent tt_n is approximately 1.5, 2.2, 3.0, and 3.2 at a normalized downstream distance of 1.5, 2.5, 3.5, and 4.5, respectively. The time te_n, independent of buoyancy and axial height, is about 3.6 for all measuring points in this study. The maximum axial velocity above the middle heat source exhibits three linearly developing periods with different acceleration rates successively: a quicker rate as the wall flow develops, a slower rate due to enhanced lateral interaction, and the fastest rate as the global merging happens. In different periods, the proportional coefficients of linear fitted functions vary from 0.48 to 2.98. The downstream distance where axial velocity is maximum shows similar power-law increasing during t/t∗ = 1.5–3.2 at Q = 180 and 90 W, but exhibits significant fluctuations at Q = 30 W. Normalized overall penetration based on global velocity fields is notably faster and higher at the lowest buoyancy (Q = 30 W) than that at the higher buoyancy (Q = 180 and 90 W), probably due to the weaker lateral interaction and turbulent mixing together with the more dedicated vertical rise at Q = 30 W.

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