平板结霜过程数值模拟及热泵机组结霜特性分析

【作者】 陈歆儒；

【导师】 廖胜明；

【作者基本信息】 中南大学 ， 供热、供燃气、通风及空调工程， 2007， 硕士

【摘要】 结霜的问题是一个复杂的热质传递问题，导热系数、密度、厚度及霜表面温度等都会随着霜层生长而变化。本文在综述国内外相关研究文献的基础上，研究了结霜工况下各特性参数之间的关系及霜层的生长规律。(1)通过建立冷平板结霜的一维饱和模型，利用有关结霜的经验关联式，对霜层比热、水蒸气质量百分比以及霜层厚度这三个因素进行数值模拟计算。同时，引入过饱和度的经验关联式，假定霜层表面水蒸气处于过饱和状态，结合其他研究者的实验数据，得出了有较高精度的霜层厚度计算方法。(2)运用适合模型的弯曲因子经验关系式，对霜层表面和内部的传质过程进行了数值模拟，研究了潜热传热率LHR、霜层导热系数增长率以及霜生长率的变化规律。研究表明，弯曲因子变动14％对总导热率的影响要小于3.3％；霜层导热系数在一小时内的变化仅为2％；传质过程中大于90％的量用于增加霜层厚度。(3)通过采用正则摄动法对翅片管换热器进行换热计算，分析了结霜工况下热泵机组翅片管换热器的传热特性，得出了达到最大肋片传热量的条件方程，并得出了翅片的最优设计尺寸。本文的研究结果，对了解霜层成长规律以及热泵的结霜融霜控制，有一定的参考价值。更多还原

【Abstract】 Frost formation is a complex heat and mass transfer process. The thermal conductivity, density and frost surface temperature keep changing during this process. In this paper, a one-dimensional saturated model for cold plate frost was set up. The relations among various characteristic parameters under frost operating mode were studied numerically. The variations of the frost specific heat, the weighting factor and frost thickness were analyzed based on the existed correlations. Meanwhile, a method to calculate the frost thickness based on the supersaturation degree concept and the supersaturation model was proposed.Then, an analysis of the mass transfer on and within frost layer was carried out. The latent heat transfer ratio, the thermal conductivity change ratio and frost growth ratio were analyzed numerically base on a rational tortuosity factor. The result shown that the error for total heat transfer rate with 14% variation of tortuosity factor is less than 3.3%; the frost thermal conductivity changes less than 2% for an hour; and more than 90% of the mass transfer goes to increasing the frost thickness.Finally, a heat transfer analysis for the fin-tube heat exchanger was carried out base on the Perturbation Methods. An equation for predicting the highest heat transfer rate of ribs in fin-tube heat exchanger of the heat pump unit was derived and optimal sizes of the wing pieces were obtained.The results of this paper are of use for understanding frost formation processes and for the optimal design of air-source heat pumps.更多还原