Despite the large amount of research conducted on PTC performance analysis, few and rare numbers of research have considered the design optimization of PTCs. In the present work, a novel multiobjective-optimization model is developed for design optimization of PTCs. The objective functions are the thermal and exergetic efficiencies because they are the most important performance indicators (PIs) of PTCs. The design variables are the inlet temperature, and the outlet and inlet diameters of the PTC receiver tube. The PTC material volume (refers to the volume of the PTC receiver and collector) is kept constant throughout the optimization process to enhance the PTC performance without incurring additional cost (material). A parametric analysis is conducted before the optimization. The inlet-mass flow-rate effect is found to be negligible in contrast to the inlet temperature. Therefore, the latter is considered as a design parameter in the optimization process. Nine thermal fluids are used in the present optimization, which include pressurized water, Therminol, molten salt, liquid sodium, Syltherm, air, carbon dioxide, helium and hydrogen. The present optimization model is found to be efficient in maximizing both the thermal and exergetic efficiencies. Water achieves maximum optimal thermal efficiency, whereas helium achieves maximum optimal exergetic efficiency. Liquid sodium exhibits the best PI (60.725).
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