Thermo-hydraulic performance investigation of double pass solar air heater integrated with PCM-based thermal energy storage

The solar air heater (SAH) is one of the ways to utilize solar energy for the purpose of drying, greenhouse heating and air conditioning. However, the SAHs are unable to deliver reliable thermo-hydraulic performance as a result of the intermittent nature of solar energy and the low convective heat transfer coefficient. Thus, in the present study, a three-dimensional numerical investigation is performed to study the thermo-hydraulic performance of the double pass solar air heater (DPSAH) having semi-cylindrical PCM tubes and perforated baffles as roughness geometry. The parameters selected for this study include baffle height ratio (eb/H) from 0.4 and 0.8, tube radius ratio (rt/H) from 0.2 and 0.5, and Reynolds numbers (Re) from 3000 and 13,000. Experimental validation has been conducted to verify the numerical results, and it has been found to be well-validated with mean absolute errors of 6.5 % and 1.2 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number (Nur) is found to be 200.08 at Re of 13,000, while the maximum friction factor (fr) is measured to be 0.6290 at Re of 3000, which corresponds to eb/H of 0.8 and rt/H of 0.3. The maximum heat transfer enhancement (Nur/Nus) in comparison to the smooth duct is found to be 5.08 times with a maximum friction factor increment (fr/fs) of 65.80 times, which corresponds to eb/H of 0.8, Re of 13,000 and rt/H of 0.3. The maximum thermo-hydraulic performance parameter (THPP) is observed to be 1.83 at Re of 13,000, rt/H of 0.2 and eb/H of 0.4. This study contributes to the design and optimisation of SAHs by incorporating thermal energy storage and roughness geometries.