This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with di...This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with diameters of 0.4 mm and 10 mm in length. The surface roughness of the microchannels is R= 0.86, 0.92, 1.02 lm, and the Reynolds number ranges from 150 to 2800.Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt numbers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant theoretical value for macrochannels. The Reynolds number for the transition from laminar to turbulent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number.展开更多
运用VOF(volume of fluid)模型与用户自定义函数,数值模拟研究水在加热壁面上V形、梯形、方形和燕尾形凹槽微通道内的流动沸腾,分析凹槽形状对气泡成核、生长、脱离及聚并等行为的影响.研究结果表明:在热流密度为300 kW·m^(-2)时,...运用VOF(volume of fluid)模型与用户自定义函数,数值模拟研究水在加热壁面上V形、梯形、方形和燕尾形凹槽微通道内的流动沸腾,分析凹槽形状对气泡成核、生长、脱离及聚并等行为的影响.研究结果表明:在热流密度为300 kW·m^(-2)时,凹槽均被激活为沸腾核化点,与其他形状凹槽相比,水在燕尾形凹槽微通道内的起始沸腾时间相对较早;在核态沸腾阶段,与梯形凹槽相比,气泡在燕尾形凹槽微通道内的生长和脱离时间分别缩短为7.50和6.70 ms,气泡脱离频率从33.8 s^(-1)提高至66.7 s^(-1),有利于水在微通道内的流动沸腾换热强化;脱离气泡在微通道内的聚并与拉伸行为增大液膜蒸发区域,气泡对液相的扰动增强,但会造成加热壁面上发生局部干涸,降低沸腾换热的稳定性与可靠性.展开更多
文摘This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with diameters of 0.4 mm and 10 mm in length. The surface roughness of the microchannels is R= 0.86, 0.92, 1.02 lm, and the Reynolds number ranges from 150 to 2800.Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt numbers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant theoretical value for macrochannels. The Reynolds number for the transition from laminar to turbulent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number.
