Thermal and thermohydraulic performances of solar air heater using transverse wire rib roughness with various gaps- An experimental study

• The maximum thermal efficiency of 85.5 % was achieved at Ng = 2 at the highest ṁ = 0.04229 kg/s. • The highest thermohydraulic performance parameter (THPP) of 2.12 was observed at Ng = 2. • The maximum average thermal efficiency of 81.63 % was obtained for Ng = 2. • Transverse wire ribs with gaps outperformed smooth and continuous ribs in SAH. In this experimental study, solar air heater (SAH) is modified with transverse wire ribs with various gaps, tested under varying geometrical and actual environmental conditions in Jagdalpur city, India. The parameters are relative roughness pitch (p/e) as 10, relative roughness height (e/D) as 0.043, width of gaps as 4 mm, diameter of circular wire rib as 2 mm, number of gaps (Ng) from 1 to 4 (in 4-step) and mass flow rate ( m ̇ ) from 0.0109 to 0.04229 kg/s (in 8-steps). The observation showed that the maximum and minimum range of ambient temperature, wind speed, relative humidity, and solar intensity is 21 °C to 33 °C, 0.3 to 4.9 m/s, and 23.3 % to 88.9 %, and 30 to 894 w/m 2 , respectively. The maximum thermal efficiency ( η ) and maximum average thermal efficiency ( η avg ) achieved is 85.5 % and 81.63 % for Ng = 2, respectively. Comparing η, the roughened duct with transverse wire rib with various gaps shows higher η than continuous and smooth duct under identical conditions. The optimal thermohydraulic performance (THPP) observed under present investigations is 2.12 for Ng = 2, e/D = 0.043, g = 4 mm, p/e = 10 and m ̇ = 0.03275 and 0.03621 kg/s. Also, the η , η avg and THPP is optimum for the present study compared with previous investigations under identical conditions.