Effect of longitudinal vortex generator on heat transfer in rectangular channels

摘要

Average convective heat transfer on the top and bottom surfaces of a plain plate and four plates with a pair of delta winglet longitudinal vortex generator punched directly from the plates at attack angles of 15°, 30°, 45° and 60° respectively, is experimentally and numerically studied in the present paper. The plate fixed horizontally in the center of the tested channel is designed to simulate the forced heat transfer on the both surfaces of a single piece of fin in a fin-tube heat exchanger. Experimental results show that the average Nusselt number on the surfaces of plate increases with the increase of the attack angle of delta winglet pair compared with that of plain plate without delta winglet pair in the test range. The average Nusselt number of the plate with attack angle of 60° is slightly higher than that of plate with attack angle of 45°, yet may bring larger pressure drop. Strong longitudinal vortices are visualized when air flow across the leading-edges of the winglet pair. And a portion of air stream flows into the lower channel through the punched holes on the plates after rushing at the frontal face of delta winglet, and disturbs the flow field of the lower channel further. The heat transfer in the tested channel of five cases is also numerically investigated. Variance of average Nusselt number between the numerical results and experimental results for the five cases are all less than 10%, validating the present models and methods used for the simulation of fin channel flow with punched vortex generators feasible and reliable. The computed velocity and temperature fields are analyzed to understand the details of fin channel flow with longitudinal vortex generator. The experimental and numerical results reveal that the transverse flow of air stream through the punched holes disturbs the air flow in the lower channel, enhancing the heat transfer on the under surface of fin.