Thermo-hydraulic performance of a heat exchanger tube with discrete corrugations

Heat exchangers are omnipresent in every thermal system receiving or rejecting heat with its surroundings. Thermal performance of a system is highly dependent on the heat exchangers ability to transfer heat which is governed by distinct fluid flow characteristics in the tube passages. Use of corrugated tube results in higher heat exchange rates at the cost of additional power lost in friction. In search of thermo-hydraulically superior corrugation geometry, the present study investigates the effect of (modified tube surface) discrete corrugated rib roughened tube on heat transfer and frictional losses under varied fluid flow rates. Heat exchanger tubes having corrugated rib roughness with different number of gaps have been tested for pitch to rib height ratio (P/e) of 6-14 by operating under a wide range of flow Reynolds number (Re) from 7500 to 50,000. The maximum enhancements in Nusselt number and friction factor are found to be 2.73 and 2.78 corresponding to (P/e) of 10, (e/D) of 0.044 for the corrugated tube with five number of gaps. Thermo hydraulic performance parameter (eta) lie between 1 and 1.76, 1.02-1.82 and 1.05-1.95 for type-1, type-2 and type-3 corrugated tube respectively. Experimental results show that type-3 corrugated tube with (P/e) of 10 is thermo-hydraulically superior than other configurations at the flow Reynolds number of 7343. (C) 2014 Elsevier Ltd. All rights reserved.