Experimental Measurement of Heat Collection Element Thermal Resistance for Concentrating Parabolic Solar Troughs

摘要

Heat Collection Elements (HCE's) mounted in the focal line of parabolic troughs are a common solution for sunlight energy capture in concentrated solar power (CSP) systems. The typical HCE is a composite device consisting of a steel pipe mounted inside an evacuated glass tube. The inner pipe is covered with a high-absorptivity coating that encourages retention of incident concentrated sunlight. The tube's vacuum must typically be maintained below the Knudsen conduction limit to mitigate thermal convection and convection losses between the inner pipe and outer glass tube. We tested an HCE 1921 mm long with a 35-mm-diameter coated steel pipe receiver mounted inside a 100-mm-diameter borosilicate glass envelope. In our static tests, heated working fluid (water) filled the HCE. An array of thermocouples mounted inside the tube measured the fluid spatial temperature profile as a function of time while the HCE was exposed to a constant temperature ambient environment. These static tests evaluated the HCE's heat transfer performance by experimtnally measuring the thermal resistance it provided. Results from the static tests inform design improvments for an experimental parabolic solar trough simulator.