Junji Kurima

Choked flow of low density gas in a narrow parallel-plate channel with adiabatic walls

Abstract The continuum and slip choked flows of low-density air through a narrow parallel-plate channel with adiabatic walls are investigated by means of finite-difference numerical calculation, experiment and analytical solution. In the numerical calculation based on two-dimensional compressible viscous boundary layer equations, the previous method is improved to achieve a higher precision of the choked state by decoupling the pressure term from momentum equation. The numerical results of discharge coefficient, pressure distribution and surface temperature distribution agree well with the experimental data. As the upstream tank pressure drops, the numerical results of friction coefficient and recovery factor approach the asymptotic values for the incompressible developed flow.

Choked flow and heat transfer of low density gas in a narrow parallel-plate channel with uniformly heating walls

Abstract The discharge and heat transfer characteristics of the continuum and slip choked gas flows through a narrow parallel-plate channel with uniform heat flux walls are studied by experimental means, numerical simulation, and analytical approximate solution. The numerical results of the discharge coefficient and the wall surface temperature distributions agree relatively well with the experimental results. The effects of the heat transfer at the walls on the discharge coefficient can be correlated with the dimensionless heat input at the walls. Three kinds of Nusselt numbers which are defined by adiabatic wall, bulk mean, and total temperatures as a reference temperature, respectively, are proposed and the effects of the viscous heating on these Nusselt numbers are clarified.

Free convection heat transfer from vertical and horizontal short plates

Abstract Free convection heat transfer from vertical and horizontal short plates was numerically analyzed by the finite-difference method. The present results regarding average Nusselt number on vertical and horizontal thin plates can be closely approximated by the following equation: Vertical thin plate, Nul = 0.448 + 0.46Grl 1 4 , Pr = 0.72 and 15 ⩽ Grl ⩽ 27,000. Horizontal thin plate, Nuld = 0.353 + 0.509Grd 1 5 , Pr = 0.72 and 4 ⩽ Grd ⩽ 27,000. These relations between Nusselt and Grashof numbers show the same tendency as the experimental results and give slightly lower Nusselt numbers. The average Nusselt numbers on the vertical plate (height = l) with finite thickness (d) can be approximated by the above correlation for a thin vertical plate with an error within about 6% using characteristic length l + d in both Nusselt and Grashof numbers instead of l, in the range of L ⩾ 5 and D ⩽ 10. Where L is dimensionless plate height and D is dimensionless plate thickness.

Unsteady heat transfer and particle behavior around a horizontal tube bundle near an expanded bed surface of a gas fluidized bed: conditional sampling statistical analysis

The heat transfer augmentation by particles making contact with a heat transfer surface in a fluidized bed was studied. The instantaneous local heat transfer coefficient and particle packing around the tube were simultaneously measured at the same location. The measured results were analysed by the conditional averaging method, distinguishing between particle contact and no particle contact. The average local heat transfer coefficient in the periods during particle contact can be closely correlated by an exponential function of the average local particle packing.