Effect of base angle of an isosceles trapezoidal solar air heater duct on flow and thermal characteristics - A numerical investigation

This paper reports the computational results of fluid flow and thermal characteristics in isosceles trapezoidal solar air heater (SAH). By varying the base angle of the trapezoidal duct from 90° to 45°, six different models of solar air heater ducts are obtained, namely: a rectangular, four isosceles trapezoids and one triangular duct geometries. The absorber plate width and the duct heights are maintained constant for all the six models of SAH, i.e. 160 mm and 80 mm respectively. The SAH is subjected to a constant and uniform heat flux value of 1000 W/m2 and Reynolds numbers varied from 5,000 to 28,000. For this investigation, a three dimensional computational model has been developed and simulations are carried out by using a commercially available ANSYS fluent software. The numerical results are validated with the standard correlations & literature data and a suitable model has been identified for the turbulence closure. A detailed analysis of the Nusselt number and temperature distribution over the SAH, friction factor across the SAH duct is done. Empirical correlations for the estimation of heat transfer and friction factor have been developed as functions of the base angle of the duct and Reynolds number. An overall performance factor is adopted to get the combined effect of friction factor and Nusselt number with an intension to arrive at the optimum base angle of the SAH duct and optimum geometry is identified.