Heat transfer characteristics and entropy generation for wing-shaped-tubes with longitudinal external fins in cross-flow

摘要

A numerical study is conducted to clarify heat transfer characteristics, effectiveness and entropy generation for a bundle of wingshaped-tubes attached to Longitudinal fins (LF) at downstream side. The air-side Rea ranged from 1.8 x 10(3) to 9.7 x 10(3). The fin height (h(f)) and fin thickness (delta) have been changed as: (2 mm a parts per thousand currency sign h(f) a parts per thousand currency sign 12 mm) and (1.5 mm a parts per thousand currency sign delta a parts per thousand currency sign 3.5 mm). The analysis of entropy generation is based on the principle of minimizing the rate of total entropy generation that includes the generation of entropy due to heat transfer and friction losses. The temperature field around the wing-shaped-tubes with (LF) is predicted using commercial CFD FLUENT 6.3.26 software package. Correlations of Nu(a), St(a), and Bejan number (Be), as well as the irreversibility distribution ratio (I broken vertical bar) in terms of Re-a and design parameters for the studied bundle are presented. Results indicated that, installing fins with heights from 2 to 12 mm results in an increase in Nua from 11 to 36% comparing with that of wing-shaped tubes without fins (NOF). The highest and lowest values of effectiveness (epsilon) at every value of the considered Re-a range are occurred at h(f) = 6 mm and (NOF), respectively. The wing-shaped-tubes heat exchanger with h(f) = 6 mm has the highest values of (epsilon), efficiency index (eta) and area goodness factor (G (a)) and also the lowest values of I broken vertical bar and hence the best performance comparing with other arrangements. The minimum values of I broken vertical bar are occurred at h(f) = 6 mm. (Be) decreases with increasing Re-a for all studied h(f). The heat transfer irreversibility predominates for (1800 a parts per thousand currency sign Re-a a parts per thousand currency sign 4200) while the opposite is true for (6950 < Re-a a parts per thousand currency sign 9700). delta has negligible effect on Nu(a) and heat transfer irreversibility. Comparisons between the experimental and numerical results of the present study and those, previously, obtained for similar available studies showed good agreements.