CFD modeling of a tubular three-pass solar air heater with phase change material: Investigating heat transfer enhancement and energy efficiency

The present study introduces a novel solar air heater design featuring a tubular surface with three passes arranged in a counter-flow configuration, aimed at improving compactness and enhancing heat transfer characteristics. The research involved the development and validation of a computational fluid dynamics (CFD) model, which was utilized to accurately depict the distribution of solar flux through the system components by comparing the model results with experimental data. The study involved conducting a comparative analysis between the tubular three-pass solar air heater with phase change material (TTPSAH_PCM) and conventional flat plate solar air heaters (FPSAH) to ascertain the superior design characteristics. A thorough investigation was carried out, encompassing evaluations of energy, exergy, outlet temperature, convection heat transfer coefficient, and useful heat gain. The findings indicate that the TTPSAH_PCM outperforms alternative geometries. For instance, when operating at a mass flow rate of 0.006 kg/s, the TTPSAH_PCM demonstrates substantial enhancements in several key metrics, including an 11.4 % increase in the system's daily thermal efficiency, a 17 % improvement in exergy efficiency, and a 4 % rise in outlet air temperature. The convection heat transfer coefficient of TTPSAH_PCM exhibited a 155.6 % increase compared to the FPSAH type. Moreover, the system being investigated demonstrates an 8.5 % rise in useful heat gain. The results underscore the enhanced efficacy of the TTPSAH_PCM system in contrast to alternative solar air heater arrangements, and its applicability for both drying operations and indoor heating applications.