Thermal performance improvement of a spiral channel solar air heater: Numerical and experimental investigation in the desert climate of Gabes region

Abstract

Abstract This study focuses on improving the thermal performance of a Solar Air Heater (SAH) using a single-pass spiral-shaped ducts. The SAH is designed and tested under prevailing weather conditions of Gabes,TUNISIA (33°52.8876' N,10°5.892' E). The experimental measurements are carried out over four days. Similarly, a CFD model developed to study the fluid flow and the heat transfer inside the SAH using the commercial software “ANSYS Fluent 2021 R1”. The discrete ordinate (DO) radiation model and the k-ω Shear Stress Transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow in the SAH, respectively. The numerical model is validated against experimental data and the average error does not exceed 3.6 %. To improve the heat transfer phenomena, the ratio of horizontal baffle spacing “d” to vertical baffle spacing “p” (d/p) are numerically investigated. Moreover, the highest air outlet temperature during the test days is reached 81.1°C under a mass flow rate of 0.0077kg/s. The maximum efficiencies are 57%, 54%, 49% and 46% for the configurations d/p=1.5, d/p =2, d/p=1 and d/p =0.5 under a mass flow rate of 0.02 kg/s, respectively. The SAH design with d/p=1.5 is about 4-10% more efficient than the standard design with d/p=1 under a mass flow rate ranging from 0.0077kg/s to 0.025kg/s.