Chaotic heat transfer for heat exchanger design and comparison with a regular regime for a large range of Reynolds numbers
APPLIED THERMAL ENGINEERING
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An experimental comparison is made over a large range of Reynolds numbers (from 30 to 30,000) between two shell-and-tube heat exchangers having the same heat-transfer area and same number of bends, but different configurations: one has a helical configuration (regular flow), the other has a chaotic one (chaotic advection flow). Both are composed of 33 bends with circular tube cross section (inside diameter 23 mm) and are immersed in a closed shell. The working fluids are Newtonian with different Prandtl numbers (820, 230, 75 and 6.5) in order to cover the large-Reynolds-number range. The comparison is made by using a criterion L that takes into account thermal performance and energy expenditure. The results show that at low Reynolds numbers, heat transfer is higher and heating more homogeneous for chaotic advection flow, with no increase in energy expenditure. At high Reynolds numbers, the configuration has no influence on heat transfer. When the Prandtl number increases, the heat transfer increases. The flows have also been visualized by laser-induced fluorescence to assess the improvement of mixing in the chaotic configuration. (C) 2000 Elsevier Science Ltd. All rights reserved.