Heat pipes applied to flat-plate solar collectors. Final report

Abstract

The objective of this program was to analytically and experimentally investigate the use of heat pipes in flat-plate solar collectors. Heat pipes are passive heat transport devices which utilize a closed evaporation-condensation cycle. Because of their high equivalent conductance, they appear to be well suited to transport heat from the solar absorber to an air or liquid distribution system. The program consisted of the following tasks: (I) Configuration Studies, (II) Parametric Performance Studies, (III) Economic Analysis, (IV) System Integration Studies, (V) Submodule Fabrication and Testing (in the laboratory), and (VI) Full-Scale Module Fabrication and Testing (using solar input). An additional Task VII, Feasibility Study of a Stationary Concentrator, was identified during the program and was also completed. In performing Tasks I through IV, various aspects of integrating heat pipes into flat-palte solar collectors were investigated. The results of these tasks were reported in the Annual Progress Report (Ref. 2) dated January 31, 1975. A summary of that program effort is included in the present report. The results of the experimental work conducted under Tasks V and VI are presented in this report. Under Task V, breadboard heat pipes were fabricated from sections of Roll-Bond panels and their heat transfer performance was evaluated in the laboratory. Three complete solar panels, two of which were heat pipe absorbers and one was a Roll-Bond control panel, were fabricated and solar tested during Task VI. Finally, under the new Task VII, a feasibility study of a stationary concentrator using heat pipes as thermal diodes was conducted. Results are presented and discussed.