旋转状态对板式换热器冷凝换热特性的影响

发布时间：2019-04-08 20:25

【摘要】：蒸发制冷循环系统作为机载环控系统的重要组成部分,对其冷凝换热机理的研究具有十分重要的意义。本文以垂直旋转状态下板式换热器为研究对象,利用实验和数值模拟相结合的方法,研究了旋转状态下板式换热器的冷凝换热特性。选取R22作为制冷剂,设计单级压缩制冷剂循环系统,并搭建旋转换热实验台。通过改变换热器的放置角度、R22进口流量、冷却水进口流量、转速等条件,对不同工况下R22的冷凝换热过程进行研究。运用数值模拟方法,分析不同转速下板片流道内R22冷凝换热过程。当换热器处于静止状态时,R22进口流量从18 m3/h增加到28 m3/h,R22侧换热系数、冷却水侧换热系数以及总传热系数都呈增长趋势。为研究重力对换热的影响,对0~180°放置的板式换热器内流体的换热特性进行实验分析,得到R22侧出口压力、温度及换热系数受重力影响的变化范围均在4%以内,冷却水侧换热系数几乎不受影响。由于旋转过程中板式换热器向周围环境的散热方式为强化对流换热,旋转导致的热量损失不可忽略。本文提出了两种热损失量计算公式,由两种公式计算得出:热损失量变化值为0.20~2.29 kW,二者差值的变化范围为-0.57~2.75 kW,最大偏差约为总换热量的5%。当板式换热器处于垂直旋转状态时,R22和冷却水的换热性能会受到R22进口流量、冷却水进口流量以及转速等因素的影响。转速为0~60 rpm,旋转对R22进出口压差变化范围为0.2~0.6 MPa。转速的增加对冷却水进口流量影响较小,转速从0 rpm增加到60 rpm,冷却水进口流量从13 m3/h下降到12.97 m3/h。R22进口参数以及冷却水进口参数确定的情况下,转速由0 rpm增加到60 rpm过程中,R22侧换热系数增加了83.98~129.49 W/(m2·K),增长率为4.42~8.26%;冷却水侧换热系数增加了433.17~435.73 W/(m2·K),增长率为5.00~6.99%。根据R22出口冷凝液的雷诺数、普朗特数与努塞尔数之间的关系,对适用于本文实验条件的R22冷凝换热实验关联式进行拟合。在静止状态下实验关联式的基础上,引入旋转数Ro,拟合垂直旋转状态下R22冷凝换热的实验关联式,该实验关联式拟合精度较高,偏差在±5%以内。利用CFX模拟计算了板式换热器单元流道模型在0~350 rpm的转速范围内的冷凝换热过程。在低转速(0~60 rpm)数值模型与实验结果验证的基础上,得出高转速(120~350 rpm)对R22在板式换热器通到内的冷凝换热过程产生了更大的影响,尤其是对R22沿程压降的影响显著。
[Abstract]:Evaporative refrigeration system, as an important part of airborne environmental control system, is of great significance to the study of condensation heat transfer mechanism. In this paper, the condensation heat transfer characteristics of plate heat exchangers in rotating state are studied by means of experiment and numerical simulation, taking the plate heat exchanger under vertical rotation as the research object. R22 was selected as refrigerant to design a single stage compression refrigerant circulation system and set up a rotating heat transfer test bed. The condensation heat transfer process of R22 under different working conditions was studied by changing the setting angle of the heat exchanger, the inlet flow rate of R22, the inlet flow rate of cooling water, the rotational speed and so on. The condensation heat transfer process of R22 in plate channel at different speeds was analyzed by numerical simulation. When the heat exchanger is in static state, the inlet flow rate of R22 increases from 18 m3 / h to 28 m3 / h, and the heat transfer coefficient of R22 side, cooling water side and total heat transfer coefficient all show an increasing trend. In order to study the effect of gravity on heat transfer, the heat transfer characteristics of fluid in plate heat exchanger placed at 0 掳were analyzed experimentally. The variation range of outlet pressure, temperature and heat transfer coefficient of R22 side affected by gravity was less than 4%. The heat transfer coefficient on the side of cooling water is almost unaffected. The heat loss caused by rotation can not be ignored because the heat dissipation from plate heat exchanger to the surrounding environment is enhanced convective heat transfer. In this paper, two formulas for calculating the heat loss are presented. The results show that the maximum deviation of the difference between the heat loss and the heat loss is about 5% of the total heat transfer in the range of-0.57? 2.75 kW,. The variation of the difference between the two is 0.20? 2.29?. When the plate heat exchanger is in a vertical rotating state, the heat transfer performance of R22 and cooling water will be affected by the inlet flow rate of R22, the inlet flow rate of cooling water and the rotational speed. The range of pressure difference between R22 and R22 is 0.2 渭 0.6 MPa. when rotating speed is 0 / 60 rpm,. The increase of rotating speed has little effect on the inlet flow rate of cooling water. When the rotating speed increases from 0 rpm to 60 rpm, the inlet flow rate of cooling water decreases from 13 m3 / h to 12.97 m3/h.R22 / h and the inlet parameters of cooling water are determined. In the process of increasing rotation speed from 0 rpm to 60 rpm, the heat transfer coefficient of R22 side increased by 83.98? 129.49 W / (m2 路K),) to 4.42? 8.26%. The heat transfer coefficient of cooling water increased 433.17 / 435.73 W / (m2 路K),) to 5.00 渭 6.99%. According to the relationship between Reynolds number, Plantt number and Nussel number of R22 outlet condensate, the experimental correlation of R22 condensation heat transfer suitable for the experimental conditions in this paper is fitted. Based on the experimental correlation in static state, the rotation number Ro, is introduced to fit the condensation heat transfer of R22 in vertical rotation state. The fitting precision of the experimental correlation is higher and the deviation is less than 卤5%. The condensation heat transfer process of the flow channel model of plate heat exchanger unit in the speed range of 0 ~ 350 rpm was simulated by CFX. Based on the verification of the numerical model of low speed (0? 60 rpm) and the experimental results, it is concluded that the high speed (120? 350 rpm) has a greater effect on the condensation heat transfer process of R22 in the plate heat exchanger, especially on the pressure drop along the path of R22. The experimental results show that the high speed (120? 350 rpm) has a greater effect on the condensation heat transfer process of R22 in the plate heat exchanger.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：V245.3

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