Cleaner Engineering and Technology (Feb 2024)
Application of pulsating jet concept for efficiency improvement of solar-based air heaters
Abstract
This study employs transient numerical analysis to investigate the hydraulic and thermal performance of a jet solar air heater (JSAH) operating under turbulent pulsating flow conditions, juxtaposed with a conventional solar air heater (SAH). The absorber plate experiences a cross-flow generated by impinging jets intersecting the channel flow. Four airflow scenarios, encompassing the application of pulsating flow to jets, channel flow, both, or neither, are considered. The numerical simulations undergo validation through time-dependent analysis, enabling parametric studies to explore the influence of pulsating flow parameters, including Reynolds number (1e4 to 5e4), frequency (10 Hz–160 Hz), and amplitude (0.1–0.9). The findings underscore significant advancements in solar air heater technology. The application of pulsating flow, particularly at the jet inlets, yields substantial enhancement in Nusselt number of the SAH, with the highest improvement achieved when pulsating flow is implemented in both channel and jet inlets. However, this heightened heat transfer is accompanied by increased friction factor and pumping power, impacting the thermohydraulic performance parameter (THPP). The influence of pulsating flow frequency is pronounced, affecting the Nu number, friction factor, pumping power, and THPP. Higher frequencies enhance the Nu number but result in elevated friction factor and pumping power demands, leading to diminished THPP values. For example, in case 4, the Nu/Nus ratio increases by 4.1 % when the frequency is raised from 10 Hz to 160 Hz. Furthermore, increasing pulsation amplitude in the JSAH correlates with higher heat transfer coefficients and increased friction factors. The study also highlights that applying pulsating jets to a SAH is more effective at lower Reynolds numbers, as the heat transfer coefficient decreases with increasing Reynolds number for all cases. In summary, this research contributes crucial insights into optimizing solar air heater performance under turbulent pulsating flow conditions, providing a comprehensive understanding of the nuanced effects of pulsating flow parameters.
