ATTACK ANGLE EFFECT OF CONCAVE DELTA WINGLET VORTEX GENERATOR ON HEAT TRANSFER AUGMENTATION IN FIN-AND-TUBE HEAT EXCHANGER FOR EGR COOLER APPLICATION BY NUMERICAL SIMULATION

摘要

The cooled EGR (exhaust gas recirculation) is one of the effective methods to control NO_x emissions. The cooled EGR is usually used in the form of shell and tube heat exchanger with water as the cooling fluid of exhaust gas. It requires a larger space for water circulation. In addition, the shell and tube heat exchanger has a larger size than the type of compact heat exchanger for the same load. Therefore, in this study, it is tried to replace the shell and tube heat exchanger by the fin-and-tube type with air as the cooling fluid of exhaust gas. The objective of this research is to investigate the attack angle effect of concave delta winglet vortex generator on heat transfer augmentation in a fin-and tube heat exchanger for EGR cooler by numerical simulation. The thermal performance is improved by manipulating the flow using longitudinal vortex generator (LVG). The numerical calculation is carried out by modeling fluid flow in a gap between two fins that are mounted a concave delta winglet (CDW) LVG. The validity is performed by comparing the simulation results with the experimental ones of previous researchers for the same boundary conditions. The results show that the heat transfer coefficients of delta winglet (DW) VG are increased by 5.9, 16.9 and 30.0% for the attack angles of 10, 15 and 20° compared to the baseline, respectively. On the other hand, for the case of CDW VG, the heat transfer coefficients are respectively increased by 32.2, 35.6 and 32.4% for the same attack angles compared to the baseline. In addition, the value of pressure drop is increased by using VG. The values of pressure drop for using DW VG are respectively increased by 19.6, 30.9 and 35.5% for the attack angles of 10, 15 and 20° against the baseline. As for the case of CDW VG, the values of pressure drop are respectively increased by 44.6, 57 and 66.1% for the same attack angles against the baseline.