Journal
APPLIED THERMAL ENGINEERING
Volume 114, Issue -, Pages 1287-1299Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.applthermaleng.2016.10.012
Keywords
Heat transfer augmentations; Parabolic trough receiver; Mixed turbulent convection; Dimples; Non-uniform heat flux
Funding
- National Basic Research Program of China (973 Program) [2010CB227102]
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The fully-developed mixed turbulent convective heat transfer characteristics in dimpled tubes of parabolic trough receiver are numerically studied at a certain Reynolds number of 2 x 10(4) and different Grashof numbers ranged from 0 to 3.2 x 10(10) to produce substantial surface heat transfer augmentations with relatively small pressure drop penalties. The Boussinesq approximation is applied, in which variations in fluid properties other than density are ignored. The Realizable k-epsilon two-equation turbulence model with enhancement wall treatment is adopted. The influences of outer wall heat flux distributions and dimple depth on flow resistance and heat transfer rate are illustrated and analyzed. The results indicate that the average friction factor and Nusselt number in dimpled receiver tubes under non-uniform heat flux (NUHF) are larger than those under uniform heat flux (UHF). In most cases, the comprehensive performance of dimpled receiver tube under NUHF is also better than that under UHF. The deep dimples (d/D-i = 0.875) are far superior to the shallow dimples (d/D-i= 0.125) at a same Grashof number. (C) 2016 Elsevier Ltd. All rights reserved.
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