Heat Transfer Fluids for Parabolic Trough Solar Collectors - A Comparative Study

In this work we compared three heat transfer fluids (HTFs) for parabolic trough solar collectors (PTCs), namely, Syltherm 800, Therminol VP-1, and Dowtherm Q. For the assessment, we adopted and simplified a previously developed mathematical model of a parabolic trough solar receiver comprising an outer cover, annular space, abosrber, and heat transfer fluid, and discretized the governing equations using the finite difference method. Subsequently, we validated the model with the experimental data available in the literature and employed it to study the following: (1) the effects of annular pressure on the collector performance for the three HTFs and (2) collector performance subject to different concentration ratios (i.e., aperture area) and inlet HTF temperatures. Simulation results demonstrate the meager thermal performance of Syltherm 800 compared to Therminol VP-1 and Dowtherm Q that achieve similar performance. In addition, we show that there is an optimal aperture area and inlet fluid temperature for Syltherm 800 that yield maximum collector efficiency. Henceforth, we anticipate this work to provide a rough guideline on the selection of an appropriate HTF for future PTCs from the thermal standpoint.