管带式冷凝器数学模型与实验研究/Mathematical Model and Experiment Investigation on Serpentine Co

2018-09-04 21:13:41

model 本文 heat 冷凝器 condenser



建立数学模型预测换热器性能不仅可以缩短产品开发周期,降低成本,还可以深入研究换热器内部流动、传热机理。本文对汽车空调用管带式五孔口琴管冷凝器进行了计算模型和实验研究。通过引入当地参数的概念,并对冷凝传热采用两相流理论分析,本文采用控制容积格式建立了一种全新的分布参数模型。模型考虑了U形管弯头对传热和压降的影响,并通过分气相折算系数计算出两相摩擦系数,将单相区和两相区控制方程统一起来。本文对该模型采用顺序求解方法,只需对单个控制体进行迭代计算,然后沿工质流动方向逐步推进,避免了全场迭代求解或高斯消元求解导致的模型不收敛问题。为研究冷凝器空气侧性能,本文对波纹百叶翅片分别提出一个j因子和摩擦系数f的计算关联式。为验证模型,本文采用美国TESCOR公司设计生产的两器(冷凝器和蒸发器)试验台对桑塔纳2000汽车空调冷凝器进行了变风量实验。通过模型计算值和实验数据的对比,本文建立的模型在迎面风速3.0m/s~5.5m/s、换热量7000W~9000W的变化范围内,换热量预测值误差约为1%,制冷剂侧压降误差在0.5%以内,空气侧压降误差在10%以内,这表明本文建立的数学模型合理。通过模型计算,本文还对管带式冷凝器参数沿管长的分布进行了研究。研究表明,管带式冷凝器内参数分布极不均匀,采用传统的集中参数模型计算很不合理。通过是否考虑弯头对传热和压降的影响,本文得出结论:不考虑弯头影响时管带式冷凝器出口压力增大约2%,换热量增加约1%。通过对其传热热阻分析,本文发现管带式冷凝器空气侧的热阻大约是制冷剂侧的27.5倍,故影响其换热的主要热阻在空气侧。本文最后还研究了控制体划分数目对模型计算结果的影响,指出100个控制体对换热器模型计算已经足够。

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.