Chaotic heat transfer for heat exchanger design and comparison with a regular regime for a large range of Reynolds numbers

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 sa me heat-transfer area and same number of bends, but different configuration s: one has a helical configuration (regular flow), the other has a chaotic one (chaotic advection flow). Both are composed of 33 bends with circular t ube cross section (inside diameter 23 mm) and are immersed in a closed shel l. The working fluids are Newtonian with different Prandtl numbers (820, 23 0, 75 and 6.5) in order to cover the large-Reynolds-number range. The compa rison is made by using a criterion L that takes into account thermal perfor mance and energy expenditure. The results show that at low Reynolds numbers , heat transfer is higher and heating more homogeneous for chaotic advectio n flow, with no increase in energy expenditure. At high Reynolds numbers, t he configuration has no influence on heat transfer. When the Prandtl number increases, the heat transfer increases. The flows have also been visualize d by laser-induced fluorescence to assess the improvement of mixing in the chaotic configuration. (C) 2000 Elsevier Science Ltd. All rights reserved.