Numerical Simulation Analysis Of The Combustion And Heat Transfer Processes For Forced-draft Water Heater

In previous numerical simulation, research on the heat transfer conditions of finned heat exchanger and combustion in the combustion chamber are separated. This research will combine gas water heater and finned heat exchanger to obtain interaction discipline which can give a detailed description of the heat transfer conditions of finned heat exchanger and combustion in the combustion chamber.This thesis clarifies the factors that can influence the efficiency of gas water heater by theoretical analysis. According to the experimental data, it's easy to find that the gas pressure is an important factor to affect the thermal efficiency of the water heater. With the increase of the gas pressure and temperature, the thermal efficiency of water heater becomes higher. From the experiments we can see that when the gas pressure reduces, the premixed gas mixture decreases due to constant air volume from the water heater fan, while secondary air volume increases.This will cause a bigger excess air coefficient, combustion temperature relatively stays lower than values in design.This numerical simulation based on energy conservationand mass conservation, established a gas water heater combustion chamber part premixed combustion model and flue gas erosion of convection heat model using numerical computation method. First, we can get the temperature distribution of water heater in the combustion chamber by solving part premixed combustion model. From the temperature distribution, it's easy to find that burning temperature decreases about 300℃,from the highest point to the entrance of the fin heat exchangers, reducing the height of the combustion chamber appropriately may raise the average temperature when the flue gas scours the fin heat exchangers .It won't increase the CO volume and will improve the thermal efficiency of water heater. Secondly, the temperature distribution of flue gas side in fin heat exchangers can be obtained by observing the temperature distribution in the pipe rendering wake zone .Such disorder flow has a great influence to convection heat and reduce the tube heat exchanger .Considering this phenomenon, the flow in Temperature wake zone can be changed by changing the shape of the fin. Finally, we can get quality distribution of NOx and CO in the entrance by the two solutions of above models, which is consistent with the household gas water heater GB6932-2006 on limiting the water heater CO emission and the grade of NOx emission, satisfying the requirements of the environmental performance of the water heater. When the flue gas contact the heat exchanger, the average temperature and velocity is calculated by fluent. Bringing the outcome into the empirical formula, you can get the value of heat exchange. Compared with the heating load of boiler, the relative error is less than 3%, which shows that the experiment of gas boiler is similar with the outcome of CFD.