Numerical investigation of heat transfer and pressure drop characteristics in the micro-fin helically coiled tubes

The design of a compact heat exchangers is the challenging work in heat transfer research area. The enhancement of heat transfer can be achieved by increasing the surface area of the heat exchanger and changing the direction of fluid flow. Thus, in this study, the heat transfer and pressure drop characteristic in the micro-fin helically coiled tubes are investigated numerically by using ANSYS FLUENT 19.2. The realizable k - epsilon turbulence with enhanced wall treatment model was applied. These studies are carried out at different coil diameter from 100 mm to 200 mm, coil pitch of 25 mm to 45 mm and, Reynolds number varying from 10,000 to 25000. Effects of Reynolds number, fin number, coil diameter, and coil pitches on Nusselt number and pressure drop are discussed. At the same operating condition, the Nusselt number and pressure drop increase with an increase of fin number and Reynolds number. Compared to the smooth helical coiled tube, the micro-fin helical coiled tube having fin number N-f = 12 provides higher Nusselt number and pressure drop in the percentage of 39-51% and 22-36%, respectively. The coil pitches of helical tube have a small effect on Nusselt number. At the same Reynold number of 20000, the Nusselt number of smooth helical coiled tube with coil pitch 25 mm is about 0.86% and 1.71% higher than that of the tube with coil pitch of 35 mm and 45 mm, respectively. Moreover, the performance factor of micro-fin helical coiled tube with 8 fin declines from 1.08 to 0.96 with an increase of the coil diameter from 100 mm to 200 mm, respectively.