粗糙度对微细通道纳米流体临界热流密度(CHF)和不稳定性的影响

Effect of surface roughness on nanofluid critical heat fluxes(CHF) in rectangular microchannels and instability

分别以去离子水和质量分数为0.3%的Al2O3-H2O纳米流体为实验工质,在水力直径为1.24mm的矩形微细通道内进行饱和流动沸腾传热实验研究。首先运用酸性抛光技术对矩形微细通道的壁面粗糙度进行处理,再采用SFS法获得壁面粗糙度的显微图像,然后借助MATLAB对图像进行灰度化处理,从而获得粗糙度分别为25.3、38.7、51.2的3种实验矩形微细通道。对比研究了去离子水和0.3%Al2O3-H2O(质量分数)纳米流体在饱和流动沸腾传热过程中不同壁面粗糙度对临界热流密度(CHF)和纳米流体流动不稳定性的影响。研究结果表明:相同工况下,0.3%Al2O3-H2O纳米流体的CHF比去离子水可提高18.37%~226.28%;随着壁面粗糙度的增大,两种工质的CHF均略有增大,但相比去离子水,0.3%Al2O3-H2O纳米流体CHF随壁面粗糙度增大而增大的趋势更为明显;通过对大量实验数据综合评估分析,发现微细通道壁面粗糙度的增大会使微细通道内流体流动的不稳定性增大。

Saturated flow boiling heat transfer in rectangular microchannels with a hydraulic diameter of1.24mm was experimentally investigated.Deionized water and0.3%Al2O3-H2O nanofluid were selected respectively as the working fluids.Rectangular microchannels’surface roughness was disposed firstly by acidic polishing process,further sonic frequency system(SFS)method was adopted to obtain the microscopic images of surface roughness,and then these images were gray-scale processing by means of MATLAB.Accordingly,three experimental rectangular microchannels whose surface roughness was25.3、38.7and51.2respectively were acquired.Contrastive study on the effect of different surface roughness on nanofluid critical heat fluxes(CHF)and instability in the process of saturated flow boiling heat transfer of deionized water and0.3%Al2O3-H2O nanofluid was carried out.Results indicated that under the same experimental conditions,the CHF of0.3%Al2O3-H2O nanofluid can be increased by18.37%-226.28%than deionized water.With the increase of surface roughness,the CHF of both of them increases slightly,but the rising tendency of0.3%Al2O3-H2O nanofluid shows more obvious.Through the comprehensive evaluation and analysis of massive experimental data,it was found that the increase of microchannels’surface roughness can make the instability of fluid in the microchannels increase.