Performance enhancement of heat pipe-based solar tube collectors using graphene nanofluids: Experimental analysis and thermal optimization

This study uses graphene nanofluids to improve heat pipe-based solar tube collector thermal performance. The use of graphene nanofluids in varying quantities and flow rates to improve heat pipe-based solar tube collectors is novel in this study. This study uses graphene nanoparticles distributed in deionized water to improve solar tube collector thermal performance, unlike previous studies that focused on metallic or oxide-based nanofluids. The study introduces graphene nanoparticles into deionized water at volumetric concentrations of 0.1 %, 0.2 %, and 0.3 % at flow rates of 1.5–4.5 L/min to overcome the constraints of conventional heat transfer fluids. SEM and X-ray Diffraction were used to study graphene's structural and morphological properties, while Zeta potential studies confirmed the nanofluids' stability, showing no sedimentation for 30 days. Experimental results show that graphene improves STC system thermal conductivity and heat absorption. At a flow rate of 1.5 L/min with 0.3 % volumetric concentration, the maximum temperature differential was 9.2 °C. At 4.5 L/min, the highest temperature gain of 52.94 % and thermal performance increase of 41.3 % were obtained. However, the collector using only deionized water performed only 25 % under similar conditions.