Numerical Simulation On Flow Boiling Heat Transfer Of Surfactant Aqueous Solution In Vertical Microchannel

Flow boiling heat transfer has been extensively concerned due to its good heat transfer performance, but for the integrated and miniaturized electronic device cooling,there are many problems that differ from conventional channels. Adding a small amount of surfactant, by changing interface wetting ability, surface tension, physical and chemical properties of solution, could improve flow boiling heat transfer behavior and enhance heat transfer effect. Therefore, it is conductive to develop new boiling heat transfer enhancement technique, achieve efficient heat transfer rate of high heat flux in small space and meet the integration and miniaturization requirement, by studying flow boiling heat transfer of surfactant aqueous solution in microchannel.In this paper, computational fluid dynamics software Fluent was performed for numerical simulation on flow boiling of Alkyl(8-16) Glycoside non-ionic surfactant aqueous solution in vertical microchannel. Flow boiling heat transfer model was established based on the VOF model and supplemented by User-Defined Function.Flow boiling heat transfer characteristics of water and surfactant aqueous solution,especially for the difference of bubbles’ behavior, were emphasized, including the number of nucleation sites, bubble size and departure during boiling process.The main conclusions are as follows:(1) Compared the heat transfer characteristics of the ONB and subcooled boiling stage between surfactant aqueous solution and water. It is found that nucleate boiling is more accessible for surfactant aqueous solution, and appears more nucleation sites. In the case of Tin=368K, v=0.5m/s and qw=200k W/m2, in 0.2mm×20mm vertical rectangular channel, the ONB is earlier 3.8ms than water, and nucleate sites are as twice as that in water at the distance 10~15mm from the inlet. In subcooled stage, as for surfactant aqueous solution, the period is longer, the temperature of heating wall and vapor volume at the outlet have great variation. At the distance 10~15mm from the inlet, bubble diameter and departure size for surfactant aqueous solution are both smaller, bubble’s number is also more than water. Besides, the heating wall superheat temperature for surfactant aqueous solution is lower, which can guarantee reliable heat transfer and operation for electronics.(2) Studied the influence of solution concentration on the ONB and subcooled boiling heat transfer characteristics. Under the same velocity, The ONB is constant with the increase of concentration between 100 ppm and 300 ppm. But from 0.3m/s to0.7m/s, nucleation sites at the ONB on the heating wall rise with the increase ofconcentration. In addition, concentration has different influence on the period of subcooled boiling stage in various cases, but in general, with the increase of concentration, the number of bubble and the percentage of small bubbles get a rise while there is little impact on the heating wall superheat temperature.(3) Analyzed heat transfer effect between surfactant aqueous solution and water during saturated boiling stage, and studied the impact of concentration on heat transfer effect. It is showed that flow boiling heat transfer effect of surfactant aqueous solution is better than water. In the case of Tin=368K, v=0.5m/s and qw=200k W/m2, at the distance 15~20mm from the inlet, the Nu of heating wall of 300 ppm surfactant aqueous solution is fluctuated in a small range, while it drops sharply and waves with a large scale for water. Under the same velocity, the average Nu of heating wall of surfactant aqueous solution rises by the concentration increasing, which indicates that heat transfer effect improves.(4) Discussed heat transfer reliability between surfactant aqueous solution and water during saturated boiling stage, and researched the impact of concentration on heat transfer reliability. It is found that surfactant aqueous solution is easier to maintain saturated boiling, and the heat transfer is more reliable. In the case of Tin=368K, v=0.5m/s and qw=200k W/m2, the superheat of 300 ppm surfactant aqueous solution is relatively low during saturated boiling stage, the local superheat temperature of water is 1.5 times of surfactant aqueous solution, the superheated locations are difficult to occur on the heating wall for surfactant aqueous solution. But the influence of concentration on heat transfer reliability is complex, and needs to be explored further.