Analysis of convection heat transfer mechanism in nanofluids

Abstract

Energy shortage and environment pollution are the major and large problems presently encountered by human all over the world. It is an effective way to save energy and reduce emission of polluted gas by using the nanofluids technology. There has been not a widely recognized theory which can explain flow and heat transfer of nanofluids until now. So the mechanism of flow and heat transfer of nanofluids is not clear. Considering the Brownian motion of nanoparticles in nanofluids, a mechanism model for heat transfer by heat convection is proposed based on the fractal distribution of nanoparticle. No additional/new empirical constant is introduced. The proposed fractal model for heat flux of nanofluids is found to be a function of temperature, average nanoparticle size, concentration, fractal dimension of nanoparticles, fractal dimension of active cavities on boiling surfaces and basic fluid property in pool boiling. The model predictions are compared with the existing experimental data, and fair agreement between the model predictions and experimental data is found for the cases of different nanoparticle concentrations and different average nanoparticle diameters. The analytical model can reveal the physical principles for convection heat transfer in nanofluids. 考虑在纳米流体中纳米颗粒做布朗运动引起的对流换热,基于纳米颗粒在纳米流体中遵循分形分布,本文得到纳米流体对流换热的机理模型.本解析模型没有增加新的经验常数,从该模型发现纳米流体池沸腾热流密度是温度、纳米颗粒的平均直径、纳米颗粒的浓度、纳米颗粒的分形维数、沸腾表面活化穴的分形维数、基本液体的物理特性的函数.对不同的纳米颗粒浓度和不同的纳米颗粒平均直径与不同的实验数据进行了比较,模型预测的结果与实验结果相吻合.所得的解析模型可以更深刻地揭示纳米流体对流换热的物理机理.