Research On Inverse Optimization Of Condensing Heat Exchanger Of Gas Water Heater

In the process of energy utilization,a large amount of energy utilization needs to be realized through the heat transfer process.Therefore,the development of efficient heat transfer enhancement technology has important theoretical and practical value for realizing efficient use of energy and reducing pollutant emissions.Condensing heat exchanger as the core component of condensing water heater,this paper first analyzes the development trend of condensing heat exchangers at home and abroad.The gas water heater test bench and numerical simulation technology were used to verify the structural optimization and multi-objective operation optimization scheme of the condensing heat exchanger.Based on computational fluid dynamics,combined with genetic algorithm,artificial neural network,field synergy theory and low temperature condensation anticorrosion,etc.And then an inverse design method is proposed.The main achievements were as follows:The condensing gas water heater experimental platform was used to study the flow,heat transfer,pollutant emission and low temperature corrosion of the heat exchanger.It was found that when the excess air ratio is 1.3,the high thermal efficiency and the lower NO_x and CO emission concentrations can be achieved.Then BPNN and GRNN are used to predict the thermal efficiency and pollutant emission concentration of water heaters under different load rates.At 90%¹00%load rate,higher heat exchanger efficiency and lower NO_x and CO emission concentrations are achieved.By using CFD to study the flow and heat transfer characteristics in the heat exchanger,the local resistance loss in the heat exchanger accounts for 89.7%of the total water flow resistance loss.In the high temperature zone,the temperature range of the flue gas accounts for 80%of the change in the overall temperature of the flue gas.The simulation results of various working conditions are fitted to obtain the analytical expressions of the heat transfer dimensionless Nu number of the flue gas and water side,which can be expressed as:Nu_w?28?1.04 Re_w⁰.⁴Pr_w^0.36?Pr_w/Pr_s?^0.25and Nu_g?28?C_gRe_g⁰.⁶Pr_g^0.36?Pr_g/Pr_s?^0.25.Based on the field synergy theory,the flow passage and fin structure of the heat exchanger were reformed.The heat exchange fins are added on the parallel flow passage to improve the heat exchange capacity of the heat exchanger,which maximum increases the heat transfer capacity of the water side of the heat exchanger by 3.6%.Reusing the application field synergy theory,the cylindrical fins were optimized into elliptical cylindrical fins,and the overall heat transfer capacity of the fins was improved by 10.2%maximum after optimization.The inverse design method based on double genetic algorithm and artificial neural network coupling is used to optimize the operating parameters of the condensing heat exchanger.The inverse design improves the design efficiency by 70%and reduces the calculation error by 24%.The flow resistance of the heat exchanger decreases by 3.7%and the thermal efficiency increases by 5.1%under the combined action of the optimization of the flow passage and the fin structure.At the same time,The optimized heat exchanger can also reduce the exhaust gas temperature from the original 60?C to about 40?C,thus realizing the high efficiency,energy saving and anti-corrosion operation of the heat exchanger.