A Model for Predicting the Performance of Domestic Gas-Fired Water Heaters
The paper outlines a model for predicting the performance of downward-firing, gas-fired, domestic water heaters employing horizontal high-finned tubes. The model includes radiative heat transfer in the combustion zone, convective heat transfer for flow over side channels of the combustion zone and the tube bank, and condensation where the surface temperature is lower than the dew point of the combustion gas mixture. The inputs to the model are the inlet gas temperature, pressure, flow rate and composition (mainly air and methane), the water flow rate, inlet temperature and flow path arrangement, as well as details of the geometry. The model calculates the heat-transfer rates:- (a) by radiation to the combustion zone side channels and top tube row, (b) by convection to the combustion zone side channels and to each tube row and (c) by condensation on those surfaces for which the wall temperature is below the dew point of the combustion gases. Predictions of the model are compared with experimental data obtained from measurements on an instrumented commercially-available heater. Predictions for alternative designs are given.
KeywordsCombustion Zone Side Channel Finned Tube Condensation Rate Condensation Heat Transfer
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