Masahide Miyamoto

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.

The Effects of Particle Size on Particle Behavior and Heat Transfer around Horizontal Tube in a Fluidized Bed.

The effects of particle size on the particle behavior and heat transfer coefficient around a horizontal tube in a gas-solid fluidized bed were quantitatively investigated. Three kinds of glass beads with different average diameters (0.2, 0.42, and 1.0 mm) were used in this experiment. The local particle behavior and instantaneous heat transfer coefficient on the tube surface were simultaneously measured. Comparing the experimental results with the existed theoretical heat transfer model, the differences of the heat transfer mechanisms between the different particle sizes were made clear.

Bubble and Particle Behavior around Horizontal Tube in Fluidized Bed

The effects of cohesiveness and subsequent agglomeration of particles on the particle behavior and heat transfer characteristics around the horizontal tubes were experimentally studied. The inter-particle cohesive forces due to a liquid bridge were controlled by changing the humidity of the fluidizing air. The behavior of the particles and the bubbles on the tube surface were visualized by throwing a laser light sheet from the inside. This proposed visualization method can clearly distinguish the particles making contact with the tube surface from the bubble.

Image Analysis with SFM for the Particle Velocity at the Center of Cross Section in a Circulating Fluidized Bed

This paper described the study for the image analysis with SFM (Spatial Filtering Method) which was velocimetry for the particle velocity at the center of crosssection in a circulating fluidized bed. For image analysis as SFM, there are some problems caused by difficult conditions such as the high particle density and velocity. This timee we repaired the image pictures for image processing to reduce the particle numbers per image frame. The results also depended on selection of tracer particle which indicated us offering the good image pictures as well. We reconfirmed that SFM was successful method for measuring particle velocity at the center of cross section in a circulating fluidized bed.

SFM Image Analysis on the Particle Velocity of Multiphase Upward Flow

This paper describes SFM(Spatial Filtering Method) which is image analysis velocimetrp for measuring the particle velocity of solid-air multiphase upward flow like that in the riser of CFB. For image analysis as SFM, there are some difficult conditions such as the high particle density and the high particle velocity. This time we developed in the image processing and image analysis program, further repairing in the number of image frames per time. The results also depended on selection of tracer particle which indicated us offering the good image pictures. We reconfirmed that SFM was successful method for measuring particle velocity.

Characteristics of the falling particles velocity in the air with image analysis

This paper describes the characteristics of the falling particles velocity in the air with the image analysis. Glass beads in a mean diameter 200 micrometers were dropped from an exit of a small nozzle. An application of a new image analysis such as a spatial filtering method based on dynamic image processing with a sequential image data obtained by a high speed video system was carried out. A specified frequency was obtained by the spectrum analysis with the reduced signals. Once a specified frequency was reached, we could calculate the velocity of a particle using the following equation, Vo equals f X (lambda) . These values were compared with the other values obtained by the optical fiber sensor method which was dual light source/receiver type sensor. Consequently, there were slight differences between them.

Image Analysis with Spatial Filtering Method for Fluidizing Particle Velocity in a Circulating Fluidized Bed

This paper describes an application of a new measuring technique; the spatial filtering method based on dynamic image processing and a sequential image data obtained by a high speed video system for measuring the velocity of flowing particle in a circulating fluidized bed(CFB). The particle velocity was too high and the contained particle numbers too many. Therefore, it was very difficult to specify the peak of frequency by spectrum analysis. As a result, we confirmed that it was possible and successful to basically apply the technique for measuring the velocity of fluidizing particle in a circulating fluidized bed.