Validation of Thermal Equilibrium Assumption in Transient Forced Convection Flow in Porous Channel

The validity of the local thermal equilibrium assumption in the transient forced convection channel flow is investigated analytically. Closed form expressions are presented for the temperatures of the fluid and solid domains and for the criterion which insures the validity of the local thermal equilibrium assumption. It is found that four dimensionless parameters control the local thermal equilibrium assumption. These parameters are the porosity , the volumetric Biot number Bi, the dimensionless channel length _max and the solid to fluid total thermal capacity ratio C _R. The qualitative and quantitative aspects of the effects of these four parameters on the channel thermal equilibrium relaxation time are investigated.     

Effect of thermal losses on the microscopic hyperbolic heat conduction model

The effects of radiative losses on the thermal behavior of thin metal films, as described by the microscopic two-step hyperbolic heat conduction model, are investigated. Different criteria, which determine the ranges within which thermal radiative losses are significant, are derived. It is found that radiative losses from the electron gas are significant in thin films having [(C_R e_e^4/₃ T_￥ ⁴ )/(k_e^1/₃ L^2/₃ G)] 3 4.6 ×10⁷{{C_R \epsilon _e^{{4 \over 3}} T_\infty ^4 } \over {k_e^{{1 \over 3}} L^{{2 \over 3}} G}}\geq 4.6 \times 10^7 for /_o > 4 and F_F < 1 and [(C_R e_e^3/₂ T_￥ ^9/₂)/(k_e^1/₂ L^1/₂ G)] 3 7.4 ×10¹⁰{{C_R \epsilon _e^{{3 \over 2}} T_\infty ^{{9 \over 2}}} \over {k_e^{{1 \over 2}} L^{{1 \over 2}} G}}\geq 7.4 \times 10^{10} for /_o < 4 and F_F > 1.     

Validation of the thermal equilibrium assumption in the transient conjugated forced convection channel flow

 The validity of the local thermal equilibrium assumption in the transient conjugated forced convection channel flow is investigated analytically. Closed form expressions are presented for the temperatures of the fluid and solid domains and for the criterion which insure the validity of the local thermal equilibrium assumption. It is found that three dimensionless parameters control the local thermal equilibrium assumption. These parameters are the Biot number Bi, the dimensionless channel length ξ_max and the solid to fluid total thermal capacity ratio C _R. The qualitative and quantitative aspects of the effects of these three parameters on the channel thermalization time are investigated. Received on 9 August 2000     

Thermal Equilibrium in Transient Forced Convection Porous Channel Flow

The validity of the local thermal equilibrium assumption in the transient forced convection channel flow is investigated numerically. Axial conduction in both fluid and solid domains is included. It is found that five dimensionless parameters control the local thermal equilibrium assumption. These parameters are the thermal diffusivity ratio _R, the volumetric Nusselt number Nu, the dimensionless channel length _max, Peclet number Pe, and the solid to fluid total thermal capacity ratio C _R. The qualitative and quantitative aspects of the effects of these five parameters on the channel thermalization time are investigated.     

Entropy generation due to cross-flow heat transfer from a cylinder covered with an orthotropic porous layer

 Entropy generation due to laminar forced convection heat transfer from an isothermal horizontal cylinder covered with an orthotropic porous layer was studied numerically. The study covered a wide range of Reynolds number and for different values of porous layer thickness, radial resistance, and tangential resistance. Increasing either or both of the porous layer thickness or resistance reduced the total entropy generation. The relative contribution of the thermal and viscous components to the total entropy generation depends on the Reynolds number and the cylinder diameter. The results can be used to asses the impact of adding a porous layer on the thermodynamic efficiency of the heat transfer from the cylinder. Received on 13 November 2000