A Comparative Study of Cooling radiator Coatings with Nanomaterials as a Function of Time and Solar Radiation in Baghdad

Abstract

This study investigates the thermal performance of cooling radiator coated with an epoxy-based nanocomposite containing aluminum oxide (Al₂O₃) and titanium dioxide (TiO₂) nanoparticles, compared with pipes coated with epoxy only. Experiments were conducted under real outdoor solar conditions in Baghdad during February and March. Outlet water temperature, surface temperature, ambient temperature, and solar radiation intensity were measured at different times of the day. Surface temperature data were analyzed using the Stefan–Boltzmann radiation model to estimate the relative emissivity of the coatings. The results reveal a dual thermal behavior of the nanocoated pipes: enhanced heat absorption at moderate solar radiation and increased radiative heat losses at higher irradiance levels. A relative emissivity ratio of approximately 1.05–1.08 was obtained for the nanocoating compared with epoxy, explaining the reduced net heat transfer to water at peak solar radiation. These findings confirm that emissivity plays a key role in determining the thermal efficiency of nanocoated pipes in solar thermal applications.