CONTRIBUTION TO THE STUDY OF NANOFLUID FLOWS IN A SOLAR ENERGY CAPTURE UNIT INTEGRATING A PCM

Abstract

Thermal energy storage using phase change materials (PCMs) has emerged as a promising solution to compensate for the intermittency of solar radiation and to ensure the continuity of energy supply in solar-assisted thermal systems. However, the inherently low thermal conductivity of PCMs still represents a major scientific challenge that limits their thermal performance. The aim of this thesis is to improve the energetic performance of a solar domestic hot water production system by employing two thermal enhancement strategies: the addition of metallic fins and the incorporation of nanoparticles. The studied system consists of two interconnected parts. The first part concerns a flat-plate solar collector, for which a mathematical model was developed to evaluate its thermal efficiency as well as the outlet fluid temperature under the climatic conditions of the city of Tissemsilt during four representative days of the year’s seasons (July, December, April, and September). Nanoparticles were integrated into the collector in order to enhance its thermal performance. The outlet temperature obtained from this part represents an essential input parameter for the second part of the system, namely a latent thermal energy storage unit based on a triplex-tube heat exchanger. Within this heat exchanger, two enhancement techniques were simultaneously implemented: the addition of innovative metallic fins to intensify heat transfer, and the direct incorporation of nanoparticles into the RT82 phase change material. Numerical simulations carried out using ANSYS Fluent 18.1 were used to investigate the effect of the adopted strategies on the melting process of the phase change material. The results reveal a significant improvement in heat transfer, a reduction in melting time, and better thermal uniformity, confirming that the combined use of fins and nanoparticles is an effective approach for enhancing the storage efficiency of low-temperature solar thermal systems.