Thermal performance assessment in a fin-and-oval-tube heat exchanger with delta winglet vortex generators

Thermal performance assessments, flow configurations and heat transfer characteristics in a fin-and-oval-tube heat exchanger with the delta winglet vortex generators are examined numerically. Delta winglet vortex generators like V-ribs are placed on fin surfaces with Vtip pointing upstream called 'V-Upstream'. The effects of the flow attack angles (α = 15 .deg., 30 .deg., 45 .deg. and 60 .deg.) and the distances between Vtip to the center of the oval tube in transverse line (Transverse pitch, a = 3.77, 4.77 and 5.77 mm) on heat transfer, flow structure and thermal performance are studied for Reynolds number based on the hydraulic diameter of the test channel, Re = 500 - 2500. The numerical results are presented in four parts: validations of the base case, flow configurations, velocity field, heat transfer and thermal performance assessment. It is found that the use of the delta winglet vortex generators can help to improve heat transfer rate in the heating system by creating vortex flow and swirl flow over the test channel. The heat transfer and pressure loss appeared to be higher than the plain fin for all case studies. The augmentation of the flow attack angle results in the rise of heat transfer rate and friction loss, while differences in transverse pitch produced similar values in terms of the Nusselt number and friction loss. In addition, augmentations are found around 1.15 - 1.55 and 1.5 - 3.4 times over the base case for heat transfer and friction factor, respectively. At Re = 2500, a = 5.77 mm and α = 15 .deg. , the maximum thermal enhancement factor is found to be around 1.12.