Characterization of Thermal Losses in an Evacuated Tubular Solar Collector Prototype for Medium Temperature Applications

AbstractDesign, construction and characterization of an evacuated 1.3 m long, tubular solar collector are presented. The collector is open at both ends for input and output of the fluid to be heated, and at one end a commercial, stainless steel bellows is soldered at the metal-glass seal, which allows for the higher thermal expansion coefficient of the steel tube as compared to the glass jacket. A selective coating of Ni/NiOwas electrochemically deposited on the stainless steel tubecollector using a two-step process. Collector losses are characterized up to 200 oC as a function of pressure in the space between the borosilicate glass and the stainless steel tube. A16-channel thermocouple system was used to characterize the dynamic thermal behavior of the collector. The suppression of convection as a heat transport mechanism in the vacuum zone is demonstrated for a pressure of 10-4Torr. The absorption characteristics of the collector were studied by placing it outside on a sunny day. A critical analysis of the possibilities of using thesolar collector in food industry is presented