Design And Optimization Of Condensing Gas Water Heater Heat Exchanger

With the wide application of natural gas,gas water heater,as a common equip-ment for domestic heating and domestic hot water,is widely used in daily family life.The condensing gas water heater can recover the latent heat of the water vapor in the natural gas flue gas after combustion and save more energy.At present,in the use of condensing gas water heaters,the main problems are corrosion and complex processing.Therefore,based on the problems faced by the gas water heater,this paper designs a new type of heat exchanger for the gas water heater,which adopts stainless steel flat tube in the high temperature section and polytetrafluoroethylene tube in the low temperature section to design the low temperature section,which can solve the corrosion problems faced by the heat exchanger in the low temperature section and effectively extend the service life of the heat exchanger.The influence of structural parameters on the performance of high temperature heat exchanger is studied by numerical simulation.The control variable method is used to simulate the coil gap,coil width,coil height and coil radius of the heat ex-changer in high temperature section.The numerical simulation results show that the heat transfer factor is reduced by 35.1%and the friction factor of flue gas is reduced by 70%when the coil gap of heat exchanger increases from 2 mm to 6 mm.The height of the coil(oblate ellipse)increases from 3mm to 5mm,the heat transfer factor decreases by 8.1%,and the friction factor increases by 1.225 times.With the increase of coil width from 25 mm to 30 mm,the heat transfer factor and friction factor in-creased by 17.28%and 53.04%,respectively.With the increase of coil radius from 70mm to 100mm,the heat transfer factor and friction factor more than doubled.At the same time,the control variable method is used to simulate the longitudinal and trans-verse spacing of the heat exchanger in the low temperature section.The numerical simulation shows that the heat transfer factor and friction factor decrease by 24%and double with the increase of the longitudinal distance of the coil from 2 mm to 6 mm.The heat transfer factor and friction factor increased by 9.8%and 3.9%,respectively,with the increase of the transverse spacing of polytetrafluoroethylene coil from 5 mm to 10 mm.The response surface design method is used to quantify the structural parameters of the heat exchanger in the high-temperature section,the objective function parame-ters J factor,f factor and Ft factor are functionalized,the appropriate response surface function model is selected to establish an approximate relationship between the struc-tural parameters and the objective function,the multi-objective genetic algorithm is used to optimize the structure of the heat exchanger in the high-temperature section,and the optimal structural parameters under the 12L/min condition are obtained Among them,the optimized structural parameters are:the coil gap is 2mm,the coil height is 3mm,the coil radius is 100m,and the comprehensive performance factor is increased by 34.96%.For the low-temperature heat exchanger,the optimized longitu-dinal spacing is 4mm,and the transverse spacing is 7.5mm.The optimized structure,the comprehensive performance factor is increased by 28.69%.For the optimized model,numerical simulation and experiment are used to simu-late and test the whole heat exchanger.The influence of variable flow on the perfor-mance of the heat exchanger is studied.The experimental results show that the de-signed heat exchanger can meet the requirements of rated heat load and meet the de-sign requirements.