Modeling of the microconvective contribution to wall heat transfer in subcooled boiling flow |
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| Authors: | Franz Ramstorfer Helfried Steiner Günter Brenn |
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| Affiliation: | 1. The Virtual Vehicle Competence Center, Inffeldgasse 21A, 8010 Graz, Austria;2. Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, Inffeldgasse 25F, 8010 Graz, Austria;1. Helmholtz-Zentrum Dresden – Rossendorf, Institute of Fluid Dynamics, Bautzner Landstr. 400, 01328 Dresden, Germany;2. Central South University, School of Energy Science and Engineering, Lushannan Road 932, 410083 Changsha, China;1. The Institute for Space and Nuclear Power Studies, University of New Mexico, Albuquerque, NM, USA;2. Nuclear Engineering, University of New Mexico, Albuquerque, NM, USA;3. Mechanical Engineering, University of New Mexico, Albuquerque, NM, USA;4. Chemical and Biological Engineering, University of New Mexico, Albuquerque, NM, USA |
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| Abstract: | In the present work, the two-phase turbulent boundary layer in subcooled boiling flow is investigated. The bubbles in the near-wall region have a significant effect on the dynamics of the underlying liquid flow, as well as on the heat transfer. The present work develops a single-fluid model capable of accounting for the interactions between the bubbles and the liquid phase, such that the two-phase convective contribution to the total wall heat transfer can be described appropriately even in the framework of single-fluid modeling. To this end, subcooled boiling channel flow was experimentally investigated using a laser-Doppler anemometer to gain insight into the bubble-laden near-wall velocity field. It was generally observed that the streamwise velocity component was considerably reduced compared to the single-phase case, while the near-wall turbulence was increased due to the presence of the bubbles. Since the experimentally observed characteristics of the liquid velocity field turned out to be very similar to turbulent flows along rough surfaces, it is proposed to model the near-wall effect of the bubbles on the liquid flow analogously to the effect of a surface roughness. Incorporating the proposed approach as a dynamic boundary condition into a well-established mechanistic flow boiling model makes it possible to reflect adequately the contribution of the microconvection to the total wall heat transfer. A comparison against the experimental data shows good agreement for the predicted wall shear stress as well as for the wall heat flux for a wide range of wall temperatures and Reynolds numbers. |
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