The analysis of thermal efficiency of a passive solar water heater is presented. The heater which has potential applications in agro-industries and homes, consisted of a single-glazed flat plate solar collector made up of an absorber plate and a transparent sheet of glass; water storage tanks and the stand. The absorber plate was made of mild steel which is a very good conductor of heat. Copper tube was used to form a loop on the mild steel absorber. Water in the loop is heated by the radiant energy trapped by the absorber. The system was tested experimentally under daytime load conditions at Nsukka, Nigeria, over the ambient temperature range of 21 to 31°C, and a daily global irradiation range of 8.3 to 17.4 MJ m-2. Peak temperature rise of the heated water was about 83°C, while the maximum daily average useful efficiency was about 42%. It was deduced that the system can be operated successfully for agro-industries and home applications.
Key words: Solar, water, efficiency, temperature.
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