管带式冷凝器数学模型与实验研究/Mathematical Model and Experiment Investigation on Serpentine Co
By predicting the performance of heat exchanger with mathematical model, the product development period could be shortened and the product cost could be decreased. The mechanism of flow and heat transfer inside heat exchanger could also be studied deeply by this. The mathematical model and experiment on serpentine condenser used in automobile air conditioner are researched in this paper. A new distributed parameter model with control volume scheme has been raised by introducing the concept of local parameter and analyzing the condensation heat transfer with two-phase flow theory. In this model, the effects of U-bends on pressure drop and heat transfer are considered and the parameters are computed in single-phase region and two-phase region with one group of control equations by calculating the friction factor in two-phase region with frictional multipliers. All control volumes in the model are calculated in sequence, so the iteration is only processed in single micro-element and the non-convergence problem arisen from the N-R iteration in whole fields and the Gaussian elimination routine are avoided. In order to study the performance on air-side of condenser, the coefficients of J-factor and friction factor correlations for louver fins are decided respectively. A condenser used in automobile SANTANA2000 is tested in the condenser and evaporator test-bed produced by TESCOR Inc. in America when air volume flow is changed. By comparing the experimental data with the predicted result, the error of predicted heat capacity is 1% and the errors of predicted pressure drop on refrigerant-side and air-side are within 0.5% and 10% respectively when the air velocity and heat capacity are changed in the range from 3.0m/s to 5.5m/s and from 7000W to 9000W, respectively. These results have shown that the math model raised in this thesis is legitimate. The parameter distributions of the serpentine condenser along the pipe length are researched with the results calculated with the model. The research indicates that the parameters, including coefficient of heat transfer, temperature and pressure, distribute widely inside the serpentine condenser in non-uniform condition. So the predicted results with traditional mean-parameter model for serpentine condenser are illegitimate. By analyzing the condenser performance with considering the effect of bens , the outlet pressure and the heat capacity of serpentine condenser are found to increase about 2% and 1% , respectively, when the effect of bends is neglected. With studying the resistance of heat transfer, it has been found that the resistance of heat transfer of serpentine condenser on air-side is 27.5 times as large as the one on refrigerant-side and the main resistance of condenser heat transfer is on air-side. Finally, the effect of the number of control volume on the model calculation result is studied in the paper and the conclusion is that the precision of model calculation is sufficient when the heat exchanger is divided into 100 control volumes.