Evaluating the Effect of Fluid Temperature and Flow Rate on the Pressure Drop Across Direct Flow Evacuated Tubular Collector

Abstract

The objective of this study is to determine the effect of water temperature and volume flow rate on the pressure drop across an Evacuated Tubular Collector (ETC) with direct flow configuration. The findings are expected to be useful for pump selection and to determine the pumping power required for operating an ETC based solar thermal plant during the day. A detailed mathematical model is developed, utilizing correlations found in previous literature. An experimental investigation was carried out on a Linuo–Ritter CPC1518 ETC solar collector installed in BITS–Pilani, India for water temperature at 25 ℃, 55 ℃ and 85 ℃ and the volume flow rate is varied in the range of 0.4–1.6 m3⁄ℎr with a step of 0.2 m3⁄ℎr. Further, the developed mathematical model is validated with results obtained from the experimental setup within 5% error. Results showed that the pressure drop across the ETC unit becomes lower as the water temperature increases. It was also observed that the pressure drop is a quadratic function of the volume flow rate of water. Hence at higher flow rates, minor changes produce large pressure drop across the ETC unit.