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喷雾冷却瞬态传热过程及特性试验研究
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/9/4 8:14:24  

摘要:喷雾冷却具有冷却表面温度均匀、工质需求量少、换热效率高等优点,是较有应用前景的电子器件散热新技术之一。但现有研究往往专注于喷雾冷却稳态传热过程,总结单一传热区域的传热过程及特性,并拟合相应的传热关联式,缺少对喷雾瞬态冷却传热过程的系统探索。鉴于现有研究的不足,本文通过实验研究典型冷却需求下的喷雾冷却的瞬态传热过程,建立准确描述喷雾冷却瞬态过程的实验曲线;分析工质特性、蒸发压力、流量、初始表面温度等因素的影响,探寻喷雾冷却瞬态过程下的传热规律,揭示喷雾冷却瞬态过程的传热机理。所得研究成果可以为喷雾冷却在电子器件散热方面的应用提供实验数据和理论支撑。具体研究内容及结论如下:

(1)无内热源下喷雾冷却的瞬态过程研究。研究了R134a、R22和R410a三种制冷工质在不同蒸发压力的瞬态传热过程,建立了喷雾冷却瞬态传热曲线,分析了各突变点数值的变动规律。研究结果表明:穿越膜态沸腾区的耗时决定着整个冷却过程冷却速率的快慢,且冷却速率随着蒸发压力增加而减少;喷雾冷却瞬态传热过程在过渡沸腾区存在表面温度突变点,标志着整个冷却过程中传热能力增强的开始,随着蒸发压力的增大,对应温度值不断增大。

(2)恒定热源下喷雾冷却的瞬态过程研究。研究了冷却初始表面温度、加热功率及工质种类对瞬态传热过程及特性的影响。研究结果表明:恒定加热功率下,喷雾冷却的瞬态传热曲线随着初始表面温度的变化展现3种典型冷却趋势,且受工质特性及恒定功率大小的影响。

(3)热源功率突变下喷雾冷却的瞬态过程研究。分析了突变功率大小及流量对瞬态过程及传热特性的影响。研究结果表明:不同制冷剂在经历冷却失效时表面温度的变化规律基本相似,增大制冷工质蒸发压力,可以延缓达到温度突变的时间;突变加热功率越大,被冷面表面温度越容易发生突变,且冷却失效后能达到的极限温度越大。

Spray cooling technology has gotten an application potential in the field of electronic device cooling due to its advantages of uniform cooling surface temperature, less working fluid demand and high heat transfer performance. However, the existed study tends to focus on the steady-state heat transfer process of spray cooling. The process and characteristics of single heat transfer region were investigated with the fitted heat transfer dimensionless correlations. but there is no systematic study on the transient heat transfer process of spray cooling. According to the deficiency of the existed research, we carried out the experimental studies of the spray cooling transient heat transfer process under typical cooling requirements in this paper. An accurate experimental curve was established to describe the process. The influences of the refrigerant characteristics, the evaporation pressure, the mass flow rate, the initial surface temperature and other factors were analyzed to investigate the heat transfer rule and mechanisms under spray cooling transient process. The conclusions of this paper provides experimental and theoretical support for the promotion and application of spray cooling. The specific research contents and experimental results are as the following:

(1) The transient spray cooling process without internal heat source. The transient heat transfer processes of R134a, R22 and R410a refrigerants at different evaporation pressures were analyzed. The variation rules of each abrupt point was shown by transient heat transfer curve. The results show that the cooling rate of the whole cooling process is determined by the time consuming through the film boiling region, and the cooling rate decreases with the increase of evaporation pressure. During the transient heat transfer process of spray cooling, there is Surface a Temperature Discontinuity in the transition boiling region, which indicates the beginning of the enhancement of heat transfer capacity during the whole cooling process. With the increase of evaporation pressure, the value of the transient heat transfer process increases continuously.

(2) The transient spray cooling process with constant heat source. The factors of the refrigerant characteristics, the initial surface temperature and the heating power on the transient process and heat transfer characteristics were studied. The results show that under constant heating power, the transient heat transfer curves of spray cooling display three typical cooling trends with the change of initial surface temperature, which affected by the characteristics of refrigerant and the heating power.

(3) Transient spray cooling process with an abrupt change in heating power. The factors of heating power and mass flow rate on transient heat transfer process and characteristics were analyzed. The results show that the surface temperature curves of different refrigerants after cooling failure are almost similar, and the increase of refrigerant evaporation pressure can delay the time of temperature sudden change. A higher abrupt heating power is more likely lead to an abrupt change in surface temperature, and the greater the limit temperature can be obtained after the cooling failure.

关键词:喷雾冷却;瞬态过程;传热特性;工质特性;冷却失效

spray cooling; transient process; heat transfer characteristics; refrigerant characteristics; cooling failure

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