Nanofluid cooling in photovoltaic thermal systems: Influence of thermal radiation, MHD, Joule heating, and carbon nanotubes

The integration of cooling systems into photovoltaic (PV) technology has led to the development of photovoltaic-thermal (PV-T) systems. These systems simultaneously generate electricity and recover waste heat for additional thermal applications. However, the performance of PV-T systems is highly sensitive to their operating temperature. Therefore, effective thermal management is essential to prevent overheating and maintain optimal efficiency. This study investigates the non-Newtonian nanofluid based cooling system for the PV-T structures. Fluid flow and heat transfer characteristics of nanofluids containing single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) within a magnetohydrodynamic environment between two parallel plates are studied. The research employs the Casson fluid model to describe the non-Newtonian behavior of the nanofluid, incorporating the effects of rotation, thermal radiation, magnetic fields, heat sources, and viscous dissipation. The governing equations are solved numerically using boundary value problem fourth order collocation method (BVP4C). The results indicate that SWCNT based nanofluids outperform their MWCNT counterparts by 10-25% in terms of both heat transfer and velocity enhancement. In particular, under the influence of thermal radiation, SWCNT nanofluids demonstrate approximately 20% better thermal regulation, and under internal heat generation, they show 10%-15% smaller temperature increases compared to MWCNT nanofluids. These findings highlight SWCNT nanofluids as generally more effective for thermal regulation in PV-T systems, although MWCNT outperform in high-rotation regimes where convective mixing dominates.