Heat Transfer Enhancement of Crossflow Air-to-Water Fin-and-Tube Heat Exchanger by Using Delta-Winglet Type Vortex Generators

The aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a "common flow up" orientation. The effects of attack angles of 15 degrees, 30 degrees and 45 degrees on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 <= Re-Dh <= 400 and water side Reynolds number, based on inner tube diameter, was constant Re-di = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11-27%) and reduction in the air-side thermal resistance fraction (from 78.2-76.9% for Re-Dh = 176 to 76-72.4% for Re-Dh = 400) is achieved by using the DWD configuration with attack angle 45 degrees. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30 degrees provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2-15.4% over the range of Re-Dh studied.