Optimization of thermal efficiency on solar parabolic collectors using phase change materials — experimental and numerical study

Abstract

Solar energy is a one-of-a-kind renewable energy source that has many uses, and in the thermal applications, it is receiving more attention and is becoming more feasible. The present work presents numerical and experimental studies to investigate the performance of a parabolic trough solar concentrator (PTC) integrated with a thermal energy storage system. A new receiver design is built that stores thermal energy using phase change material (PCM). A concentric absorber tube with two different kinds of PCM -MgCl 2 •6H 2 O and erythritol (filling the annular-space of absorber tube)were used to construct a PTC, and its thermal performance and thermal efficiency were investigated under two different HTF flow rates of 0.005 kg/s and 0.033 kg/s. Solar energy is transformed into heat, which is then used to store in the PCM before being discharged to cold water, which is the final heat transfer fluid in the receiver's inner pipe. The simultaneous studies of the PTC with and without PCM are investigated. A commercial Mat Lab's operating model through an imperialist competitive algorithm of the entire PTC system is presented, and the numerical results were compared to the experimental results, which were carried out with and without PCM in PTC. With the PCM in PTC (0.005 kg/s and 0.033kg/s), the HTF exhibited gain in peak temperatures of 11°C (erythritol) and 9°C (MgCl2• 6H2O) at 0.05 kg/s, whereas the peak temperatures further increase to 14°C (erythritol) and 12°C (MgCl2•6H2O) respectively at 0.033 kg/s, as compared to HTF without PCM. Average thermal efficiency of PTC with HTF flow rate of 0.033 kg/s was highest with usage of erythritol (40.6%), among all the cases. The experimental and predicted thermal efficiency performance indices for different flow rates and PCM are found to be with a deviation of around ± 1.9%, demonstrating the accuracy of the developed numerical model.