A study on thermal characteristics of the solar collector made with a closed loop thermosyphon

The natural circulation type and the closed loop type thermosyphon systems are widely used for solar domestic hot water systems(SDHWS). Of these, the closed loop type thermosyphon system, which hires the concept of a wickless heat pipe, is extensively studied in the present analysis. The system under consideration consists of a rectangular shape solar collector and a circular cylindrical shape storage tank, the most common design of a natural circulation type SDHWS. A closed circulation loop runs through these units carrying heat from the collector to the storage tank. The working fluid(heat transfer medium) makes infinite number of roundtrips via this loop as long as the sun's energy hit the collector area and delivers the fuel needed for the trip. This paper reports the experimental results obtained in a series of tests where the operational characteristics of various working fluids are examined along with the whole performance of the system. The working fluids experimented in the present study are ethanol, water, and a binary mixture of ethanol and water(ethanol/water). Various amounts of working fluid were tested where the working fluid occupies 30%, 40%, 50%, 60% or 70% of the loop volume. Among these, in the cases of 30% and 40%, dry-out phenomena were observed. Also investigated in this study were the flow patterns and the mechanism of heat transfer within the loop. Flow patterns of the binary mixture of working fluid near the entry of the storage tank were analyzed where they were recorded with the aid of a high speed camera. (C) 2003 Elsevier Science Ltd.