Performance Optimization of a Thermosyphon Flat Plate Solar Water Heater

Abstract

Conventional flat plate solar water heaters which are widely used to convert solar energy to thermal energy and transfer that heat to circulating water have low efficiency of less than 60%. In addition, they require high manufacturing cost, they utilize expensive copper material and selective surface coatings. Flat plate solar water heater (FPSWH) lose 30-50% of the total harnessed heat through the top glazing glass via convection, radiation and conduction. Convection heat loss accounts for the bigger percentage of this heat loss due to the presence of air in between the absorber plate and the top glass. Radiative heat loss is a function of emissivity and shape factor of the absorber plate. In addition, the total heat loss is enhanced by poor heat transfer between the circulating water and the absorber plate. Poor heat transfer is contributed by tube pitch, type of bond between the tubes and the absorber plate as well as the thickness of the absorber plate. The aim of this research was to reduce the heat losses in flat plate solar water heaters through re-design and material selection. Hence a partially evacuated, V-grooved corrugated collector was fabricated and its performance tested under various conditions, air gaps, different number of glazing, flow rates etc in order to obtain its optimal performance. Its absorber plate was made of galvanized iron with v-groove channels of 700 and painted black using carbon black matte paint. Optimizing performance of Flat Plate Solar Water Heater,(FPSWH), was realized through a v-groove redesign and partial evacuation of air at 300-2500 pa. The new design improved heat transfer ability, reduced heat loss and eliminated need for laser beam welding but still maintained the merits of FPSWH of being cheap, easy to fabricate and easy to maintain. With partial evacuation of air at 2.5×103 pa, efficiency of 80-85% and operating temperatures of 80-1000C were obtained. The findings of this research work are applicable in FPSWH manufacturing industry and Jua Kali sector whereby efficient and affordable FPSWH can be produced and availed to households, institutions and industries. Since optimized FPSWH have high efficiency, their application can go beyond heating water to producing processing steam for businesses and industries.