| Energy saving and efficiency elevation are both important for domestic economic development. In the recent years, many incidents such as lack of electricity in large area of the country, abnormal price increase of LPG and oil, etc, have shown that there's something wrong with domestic economic development model. This demonstrates that we should attach more importance to energy saving and efficiency. To improve thermal efficiency of common water heaters, this paper mainly focused on high efficiency, energy saved and environment benefit product of condensing water heater.In this paper, a device to guide gas-fired exhaust was designed to solve problems of disposal of CWH's new heat exchanger and the formal construction, as well as condensing water collection. After that, exhaust properties fired from both natural gas and LPG were calculated, for the analysis of exhaust dew point temperature, outlet temperature of water heater, exceed coefficient of air and effect of different inlet gas. Experiment on the two condensing heat exchanger disclosed that the heat efficiency during rating condition can be improved up to 99.6%. Heat input during different level was also discussed which revealed the law of thermal efficiency, volume fraction of carbon monoxide in these conditions. Then, according to the experiment data, a numeric equation of Nu, Re, Ln and Pr was elicited by the calculation result of a number of thermal equations. At last, PHOENICS was used to simulate the thermal process of the exhaust between two fins. Using hydrodynamics and heat transfer theory to analysis the simulation result, a proposal to improve the design of heat exchanger was put forward.
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