Abstract: A numerical simulation for frost formation and growth on the surface of finned-tube vaporizer was carried out based on the diffusion limited aggregation model of fractal theory,and images of frost formation and growth at different stages were obtained by experimental observations.For the frost layer profile on the surface of vaporizer,fractal dimension of pore area distribution and fractal porosity were calculated.The simulation results are in good agreement with experiments.Then the fractal model for heat conduction through the frost layer was established and the thermal resistance method was used to get an expression for thermal conductivity of frost layer.The result shows that the calculated thermal conductivity of frost layer falls in the range of measured data.Compared with other thermal conductivity models,the introduction of profile area distribution fractal dimension into the thermal conductivity model is appropriate,which is a new method for the theoretical study for thermal conductivity of frost layer.

Key words: finned-tube vaporizer, frost layer, thermal conductivity, fractal model, numerical simulation

摘要： 基于分形理论的DLA模型,数值模拟了翅片管气化器表面霜层生长过程,同时对霜层生长形态进行了实验观测,得到了不同时刻的霜层生长图像。计算了气化器表面霜层剖面孔隙面积分布分形维数与分形孔隙率,模拟图像与实验图像的对比表明两者取得良好的一致,验证了数值模拟的合理性。在此基础上建立了霜层导热的分形模型,采用热阻法给出了霜层热导率表达式。计算结果表明,用该方法确定的霜层热导率与实测得到的霜层有效热导率值域范围是相符的。并通过与其他导热模型的比较,验证了将剖面面积分布分形维数引入导热模型以确定霜层热导率的可行性,从而为霜层热导率的理论研究开辟了一条新路。

关键词: 翅片管气化器, 霜层, 热导率, 分形, 数值模拟