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Comparison of Dynamic PTC Thermal Models Using Semi-Analytical and Finite Volume Methods

Bayer, Özgür
Uzgoren, Eray
Resource potential estimation of concentrating solar power (CSP) applications with parabolic through collectors (PTC) needs to address time-dependent heat transfer fluid (HTF) temperature at collector field's outlet. HTF temperature distribution depends on several time-dependent variables; i.e., HTF temperature at PTC inlet, direct beam radiation, HTF flow rate and its properties, and PTC parameters, i.e., overall heat transfer coefficient. The present paper develops a time-dependent one-dimensional thermal model for PTCs using the analytical solution of governing partial differential equation assuming time-invariant material properties, inlet temperature, and incident irradiation. Time-dependency component is then integrated into the analytical solution using a time advancing numerical scheme. The results are presented in a generalized non-dimensional form, which features familiar parameters, i.e., NT U. It is shown that in contrast to the developed semi-analytical method, mesh-based methods suffer from an additional error source due to smoothening around t* = 1. As a result, it is also showed that the developed method can use time steps 10 to 25 times larger than mesh-based methods that achieve similar accuracy levels. In addition, developed method's each time-step is found to be about 13 times faster. The combined speed-up is identified as 130-325 for PTC simulations that have high variations in inlet temperature. (C) 2017 American Institute of Chemical Engineers