Friction factor and heat transfer coefficient of liquid flow with variable properties can significantly differ from that with constant properties. Existing equations obtained by regression analysis of experimental dat...Friction factor and heat transfer coefficient of liquid flow with variable properties can significantly differ from that with constant properties. Existing equations obtained by regression analysis of experimental data use correction factors to account for variable property effect. They are limited to specific kind of fluid and low or medium temperature differences. The correction factors of the equations for heating and cooling conditions are different. New explicit friction factor and Nusselt number equations for laminar forced convection of liquid with variable properties are derived with a first order approximation of dynamic viscosity-temperature variation. The new equations are applicable to all kinds of liquids and can be used for large temperature differences. Governing equations of laminar forced convection of water and ethanol are numerically solved using computational fluid dynamics(CFD)method and the results are used to verify the derived equations. The derived equations show good predictions of friction factors and Nusselt numbers for both heating and cooling conditions and show more accurate predictions than the existing equations. A dimensionless number is also introduced based on theoretical analysis to evaluate property variation effects on friction factors and heat transfer coefficients.展开更多
利用有限元软件ANSYS建立热机直接耦合作用下的轮轨滑动接触热弹塑性有限元模型。采用与温度相关的变摩擦因数和材料参数,运用热机直接耦合法,考虑轮轨间非稳态热传导及轮轨与环境间热对流和热辐射的影响,考虑扣件系统对轮轨接触的影响...利用有限元软件ANSYS建立热机直接耦合作用下的轮轨滑动接触热弹塑性有限元模型。采用与温度相关的变摩擦因数和材料参数,运用热机直接耦合法,考虑轮轨间非稳态热传导及轮轨与环境间热对流和热辐射的影响,考虑扣件系统对轮轨接触的影响,分析了不同扣件垂向刚度和扣件间距对钢轨受力和变形的影响。结果表明：轮轨接触斑附近钢轨的最大等效应力和弹性应变出现在钢轨接触表面上;在车轮滑过区域,钢轨最大等效应力和弹性应变发生在钢轨次表面上;钢轨的等效应力、最大变形和车轮垂向加速度在扣件垂向刚度为50 k N/mm时最小;从钢轨的应力、应变、变形和温升方面考虑,扣件间距在0.6~0.725 m间取值均较合理,车轮垂向加速度在扣件间距为0.6 m时最小。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51576103)the National S&T Major Project(Grant No.ZX06901)
文摘Friction factor and heat transfer coefficient of liquid flow with variable properties can significantly differ from that with constant properties. Existing equations obtained by regression analysis of experimental data use correction factors to account for variable property effect. They are limited to specific kind of fluid and low or medium temperature differences. The correction factors of the equations for heating and cooling conditions are different. New explicit friction factor and Nusselt number equations for laminar forced convection of liquid with variable properties are derived with a first order approximation of dynamic viscosity-temperature variation. The new equations are applicable to all kinds of liquids and can be used for large temperature differences. Governing equations of laminar forced convection of water and ethanol are numerically solved using computational fluid dynamics(CFD)method and the results are used to verify the derived equations. The derived equations show good predictions of friction factors and Nusselt numbers for both heating and cooling conditions and show more accurate predictions than the existing equations. A dimensionless number is also introduced based on theoretical analysis to evaluate property variation effects on friction factors and heat transfer coefficients.
文摘利用有限元软件ANSYS建立热机直接耦合作用下的轮轨滑动接触热弹塑性有限元模型。采用与温度相关的变摩擦因数和材料参数,运用热机直接耦合法,考虑轮轨间非稳态热传导及轮轨与环境间热对流和热辐射的影响,考虑扣件系统对轮轨接触的影响,分析了不同扣件垂向刚度和扣件间距对钢轨受力和变形的影响。结果表明：轮轨接触斑附近钢轨的最大等效应力和弹性应变出现在钢轨接触表面上;在车轮滑过区域,钢轨最大等效应力和弹性应变发生在钢轨次表面上;钢轨的等效应力、最大变形和车轮垂向加速度在扣件垂向刚度为50 k N/mm时最小;从钢轨的应力、应变、变形和温升方面考虑,扣件间距在0.6~0.725 m间取值均较合理,车轮垂向加速度在扣件间距为0.6 m时最小。
