Heat transfer enhancement of fin-tube heat exchangers using punched triangular ramp vortex generator on the fin surface

摘要

Existence of the vortices in a flow field strongly affects the heat transfer. In this study, effect of newly proposed punched triangular ramp vortex generator (PRVG) on heat transfer performance for a fin-tube heat exchanger was investigated numerically. Normalized ramp height (H/d=0.196 and 0.161) and ramp angle (α_r=20° and 35°) were examined as the geometric parameter. Numerical computations were carried out under turbulent flow conditions (5000≤Re≤20000). RANS equations were solved using ANSYS Fluent by using SST k-ω) turbulence model. Nusselt (Nu) number, friction factor and Performance Evaluation Criterion (PEC) were comprehensively examined quantitatively. Flow characteristics were also investigated for elucidating the underlying physics of enhancement heat transfer by the PRVG winglet. Results were compared with the flat smooth fin surface (baseline case). Results showed that overall heat transfer on the entire channel wall increases up to 43.66% for Re=5000 by H/d=0.196 and α_r=35°. The influence of ramp angle on thermo-hydraulic performance was more significant compared to ramp height. Furthermore, PEC results showed that the most feasible geometric design of PRVG winglet for the fin-tube heat exchanger is H/d=0.161 and α_r=20°. Furthermore, decreasing flow speed in the channel increases the effectiveness of the vortex generator according to PEC results.