Optimization Design And The Phase Change Heat Transfer Of The Compact Heat Exchange

Foam metal, a new type of com pact and enhanced surface, can greatly improve the heat transfer performance, and at the same time reduce the volume and weight of the heat exchanger. The single factor analysis and the multi-objective optimization of composite cycle analysis were conducted, the enchancing heat transfer mechanism of foam metal was analy zed. The h eat transfer characteristics of the wave-fin tube exchanger on wet condition was surveyed. Main work and conclusions are as follows:(1) The numerical model of the conventi onal wave-fin tube heat exchanger and the foam metal fin heat exchanger were established. After the evaluation of the model and the grid, the conjugate heat transfer model based on the lam inar flow was used for numerical simulation of the c ommon wave-fin and the f oam metal heat exchangers; PEC=(j/j0)/(f/fo)1/3 was chosen as the main evaluation index. Based on the sim ulation results, it shows that the porous structure m akes the fluid distributing more uniform ly; the metal framework has better therm al conductivity properties. Under the sam e operating conditions, the PEC of the f oam metal is 1.06～1.6 better than that of the common corrugated fin.(2) There are m any parameters influencing the flow and heat transfer, such as geometric parameters, material parameters, operator param eters. Considering the single parameter, it can be found that the PEC declines gradually with the increase of the pipe diam eter and the channel width; the PEC increases gradually with the enlarging of the channel length, the pore diam eter, the solid m aterial thermal conductivity, the surrounding temperature. The PEC reaches peak when the ratio of the tube positon on the left and right of the 1 ength of the channel is 2.8, or the porosity is 0.94-0.96.(3) The combined cycle m ulti objective optimization method based on genetic algorithm was established. Th e objective functions are Nu、f、PEC. It shows that these parameters has great influence on the o bjective functions, mainly the inlet velocity, the up distance of the tube on long itudinal, the down distance of the tube on longitudinal, the tube diam eter, the left di stance of the tube on transverse, the tub e distance of the tube on the transverse. The PEC of the optimal design point is 1.1436, when the width of the channel is 15.6 mm, the length of the channel is 34.71mm, the diam eter of the tube is 8.92 mm; the operate p arameters are Vin=3.09m/s,Tin =307.55K,Ttube= 278.97K.The datum of 80 design points are fitted and the correlation equations for heat transfer and flow were obtained.(4) The ph ase-change heat transfer char acteristic of the w ave-fin tube heat exchanger was built and the field was analyzed. It can be found that the jh factor decreases with the increase of the inlet velocity and the inlet relative humidity.