Enhancement mechanism of high alcohol surfactant on spray cooling: Experimental study
Enhancement mechanism of high alcohol surfactant on spray cooling: Experimental study
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DOI：
10.1016/j.ijheatmasstransfer.2018.05.130
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发表时间：
2018-11
影响因子：
5.2
通讯作者：
Wei-Wei Zhang-Wei;Yi-Yi Li-Yi;Wenjun Long;W. Cheng
中科院分区：
文献类型：
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作者：
Wei-Wei Zhang-Wei;Yi-Yi Li-Yi;Wenjun Long;W. Cheng
添加表面活性剂具有用量少、效果显著、性能稳定等优点，被认为是喷雾冷却强化传热的重要手段。近年来的研究发现，高醇表面活性剂对喷雾冷却过程中的传热有显著的影响。本文以水为工质，研究了正庚醇、正辛醇、异辛醇和正癸醇四种高级醇表面活性剂对喷雾冷却换热的影响。结果发现，存在一个最佳的浓度为每种表面活性剂，以实现最佳的传热性能。在本实验条件下，正庚醇的最佳添加量为0.3‰，散热通量达到180.9 W/cm 2，传热量提高了20.9%，正辛醇的最佳添加量为0.3‰，散热通量达到200.8 W/cm 2，传热量提高了34.2%;异辛醇的最佳添加量为0.5‰，散热通量达到185 W/cm 2，传热量提高了23.7%;正癸醇的最佳添加量为0.1‰，散热通量达到180.7 W/cm 2，传热量提高了20.8%。为了进一步分析表面活性剂的强化机理，本文还研究了表面活性剂浓度对工质物性和喷雾特性的影响。实验结果表明，表面活性剂对饱和蒸汽压的影响较小，温度越高，饱和蒸汽压的变化越明显。表面张力随表面活性剂浓度变化明显，在较低浓度时表面张力迅速下降。动态粘度随表面活性剂的种类和浓度变化不大。实验中还得到了物理性质与浓度的关系。加入表面活性剂后，液滴数比水少，液滴在不同高度的分布更均匀。液滴直径在一定范围内减小，但由于局部碰撞和熔融，在区域边缘处液滴直径增大。液滴速度变化不明显。本文还提出了不同工质的物理性质与其浓度的关系，以及预测喷雾液滴直径和速度的关联式。
The addition of surfactant is considered as an important method for heat transfer enhancement in spray cooling based on numerous advantages such as less demand, significant effect and stable performance. Recent studies have found that high alcohol surfactant has a significant effect on the heat transfer in spray cooling. In this study, the effect of four kinds of high alcohol surfactants, 1-heptanol, 1-octanol, isooctanol and n-decanol, on spray cooling heat transfer using water as the working medium was studied experimentally. It was found that there exists an optimal concentration for each surfactant to achieve the best heat transfer performance. Under the experimental conditions, the optimal value of 1-heptanol was 0.3‰, heat dissipation flux reached 180.9 W/cm2, and the heat transfer increased by 20.9%; the best value of 1-octanol was 0.3‰, heat dissipation flux reached 200.8 W/cm2, and the heat transfer increased by 34.2%; the best value of isooctanol was 0.5‰, heat dissipation flux reached 185 W/cm2, and the heat transfer increased by 23.7%; the best value of n-decanol was 0.1‰, heat dissipation flux reached 180.7 W/cm2, and the heat transfer increased by 20.8%. To further analyze the enhancement mechanism, this paper also studied the influence of surfactant concentration on physical properties of working fluid and the spray characteristics. The experimental results showed that the effect of surfactant on saturated vapor pressure was small, and the change became obvious at higher temperature. The tension changed obviously with the surfactant concentration, and the surface tension decreased rapidly at lower concentration. The dynamic viscosity did not vary much with the type and concentration of the surfactant. The relationship between physical properties and concentration was also obtained in experiments. After adding surfactant, droplet number was lower than that of water, the distribution of droplets at different heights was more even. Droplet diameter reduced in certain area, however it increased in the edge of the area due to local impact and fusion. The change of droplet velocity was not obvious. This paper also put forward relations between the physical properties of different working fluids and their concentration and correlations which can predict diameter and velocity of spray droplet.