Heat Transfer Measurement in a Rectangular Channel of Solar Air Heater With Winglet-Type Ribs Using Liquid Crystal Thermography

Abstract

Abstract This paper deals with the study of heat transfer in solar air heater consisting of winglet-shaped roughness on the absorber plate using liquid crystal thermography technique. The winglet-type roughness element was placed on the absorber surface of a rectangular channel solar air heater having an aspect ratio of 4. The absorber surface was heated uniformly by a constant heat flux of 800 W/m2. The non-dimensional roughness parameter considered was relative roughness pitch, i.e., P/e, and its values range between 5 and 12 with Reynolds number (Re) ranges between 6500 and 22,000. The value of angle of attack, i.e., alpha and relative roughness width (W/w) was kept constant, and the relative roughness pitch was varied to measure the heat transfer coefficient. The enhancement in heat transfer has been compared, and it is observed that at P/e of 8 for angle of attack (α) of 60 degrees resulting its optimum value. The enhancement of heat transfer with the increase in Reynolds number is also noted.