Study Of Performances Of Thermosyphon Flat Plate Solar Water Heaters With Mantle Heat Exchangers

The exploitation and utilization of solar energy is a important part of that of new and renewable energy. The development and generalization of solar water heaters accord with sustainable development policy in China. At first, current situation of solar water heaters, freeze protection techniques, and some common heat exchangers used in solar water heaters and their characteristics are introduced in this paper. A successful technique for freeze protection is based on the use of a heat exchangers separating the potable water from the working fluid in collector-heat exchangers loop. The mantle heat exchanger has been used extensively in other countries as it has some advantages, such as high heat transfer rates, simplicity of construction and low manufacturing costs.In this paper, based on the principle of thermosyphon-type solar hot water systems which are advanced in foreign countries, mantle heat exchanges in thermosyphon flat plate solar water heaters have been designed, and a theoretical analysis and experimental study of mantle heat exchangers and thermal performance in thermosyphon flat plate solar water systems has been undertaken. We analyzed the effect on the collector efficiency of using a heat exchanger and determined a "heat exchanger penal factor" . The heat transfer performance of mantle heat exchanges was tested in the condition of different width of mantle gap and different quantity of working fluid in a mantle gap, and total heat transfer coefficient of mantle heat exchangers was determined. Experiment results show that there is a correlation between the value of total heat transfer coefficient and the width of mantle gap, the heat transfer performance of mantle heat exchanges is better when the width of mantle gap is smaller, and the value of total heat transfer coefficient ofmantle heat exchanges with 15 mm gap is up to 110W/m~2, and the more quantity of working fluid in a mantle gap is, the better heat tranf er performance of mantle heat exchanges is, and the heat transfer performance ofmantle heat exchanges will be improved obviously if there is a board in a mantle gap. A lot of outdoor tests of thermal performance of the solar water heating systems have been taken, and a mathematical model of the systems has been established, and simulating computation has been done. Experiment results show that average daily efficiency of thermosyphon flat plate solar water heaters with mantle heat exchanges with 15 mm gap is up...