Resumo

VAN DER VYVER, S.  e  MEYER, J.P.. Heat transfer augmentation in the annulus of a heat exchanger consisting of a round tube inside a twisted square tube. R&D j. (Matieland, Online) [online]. 1997, vol.13, pp.77-82. ISSN 2309-8988.

The potential of a very simple and inexpensive method of heat augmentation that could be used by small manufacturing companies is investigated. It consists of an aluminium heat exchanger comprising a round tube inside a twisted square tube. The aim is to increase the heat transfer between the flow in the inner tube and the flow in the annulus by increasing the heat transfer coefficient in the annulus. This investigation was conducted with measurements on five different heat exchanger configurations: the first without any twist and the rest with the square tube twisted at angles of 45°, 60°. 90°, and 105° per metre, respectively. The Nusselt number and friction factor in the annulus of each case study were measured as functions of the Reynolds number, while the Prandtl numbers were kept constant; and for each heat exchanger configuration an equation was deduced that describes this functional relationship. The relationships are shown in graphical format. It was found in general that the heat transfer and pressure drop increase with twist angle and Reynolds number. Furthermore that for a twist angle of 60° and a Reynolds number lower than 4 000, the heat transfer rate per unit pumping power is the highest while for higher Reynolds numbers a twist angle of 90° gives the highest heat transfer per unit pumping power.

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