VALIDATION OF SIMULATION MODELS FOR DIFFERENTLY DESIGNED HEAT-PIPE EVACUATED TUBULAR COLLECTORS

Differently designed heat-pipe evacuated tubular collectors have been investigated theoretically and experimentally. The theoretical work has included development of two TRNSYS [1] simulation models for heat-pipe evacuated tubular collectors utilizing solar radiation from all directions. One model is developed for heat-pipe evacuated tubular collectors with flat fins and one model is developed for heat-pipe evacuated tubular collectors with curved fins. The models are characterized by detailed calculations of the heat transfer processes in the fins, by detailed shadow modeling and by fins with selective coating on both sides. The input to the models is thus not a simple collector efficiency expression but the actual collector geometry. In this study, the TRNSYS models are validated with measurements for four differently designed heat-pipe evacuated tubular collectors. The collectors are produced by the Chinese collector manufacturer SUNDA Technology Co. The collectors have either flat or curved fins inside the evacuated tubes, the tubes have different diameters and the fins have selective coating on both sides. The collectors’ thermal performances have been measured side-by-side under the same operation conditions in an outdoor test facility. For periods with different operation conditions – such as weather conditions and inlet temperatures – measured and calculated thermal performances are compared for the four collectors. Further, the measured and calculated dynamic behaviors are compared. In all four cases, a good degree of similarity between measured and calculated results is found. With these validated models detailed parameter analyses and collector design optimization are now possible. Key words: Evacuated tubular collector, Heat pipe, Thermal performance, TRNSYS simulation.