Experimental Investigation Of An Evacuated-Tube Solar Water Collector With Serpentine Through-Flow Pipe


The present work deals with experimental study of an evacuated-tube (all-in-glass) solar collector. The collector consists of 5 evacuated tubes filled with ordinary engine oil. An additional stainless steel pipe is integrated with the tubes to carry the working fluid (water). The steel pipe (through-flow pipe) is bent 5 times to form 5 U-shape turns. Each U-turn is immersed in a single evacuated tube. Oil acts as the heat transfer medium between tube inner surface and the stainless steel pipe outer surface. Experiments are carried out for several values of water mass flow rate and under various meteorological conditions (irradiance, ambient temperature). Results show that the collector exhibits high conversion efficiency and fast response to the affecting parameters (water inlet temperature changes, clouding, replacement of oil) compared to conventional flat-plate collectors. However, the limited number of tubes and the small diameter of the stainless steel pipe combined with its large length (14 m) caused some fluctuations in the water flow rate at the pipe exit. To enhance the performance of the system and make it suitable for higher loads (e.g. for producing superheated steam) the number of evacuated tubes should be increased and the stainless steel pipe diameter is increased and its length decreased.