Shape Thermal Performance Analysis of a Triangular‐Tube Solar Air Heater With Impingement‐Return Flow

This work presents a numerical investigation of an advanced, high‐efficiency solar air heater featuring a nine‐tube array with triangular ducts in an integrated impingement‐return flow configuration. A comprehensive three‐dimensional computational fluid dynamics model, solving for conjugate heat transfer, turbulence, and radiation, was developed to analyze its performance. A direct comparison is made with an equivalent collector using circular tubes. The design employs an extended absorber plate within each triangular tube to create two flow channels, facilitating a 180° flow reversal. Under the solar irradiance of 800 W/m 2 and at a high air mass flux of 0.03 kg/s, the triangular tube achieves a remarkable thermal efficiency of 95%, significantly outperforming the circular tube (78%). This performance reverses at a lower flow of 0.01 kg/s, where the circular tube's efficiency (63%) surpasses that of the triangular one (60%), a finding attributed to the differing flow regime dependence of each geometry.