Yasuo Katoh

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.

The Airflow Stagnation Zone Effect of Convective Heat Transfer on Adjacent Indoor Wall

The reduction of heat loss through buildings envelopes, i.e. outdoor walls and vertical window areas by means of active control of indoor airflow along adjacent surface areas is described in this work. The aim was to cause air layers adjacent to the room‐faced glass surface to slow down their movement and partly divert themselves, so they would form an additional stand‐still air area. The convective heat transfer occurring within the laminar as well as turbulent air layer adjacent to inner vertical surface would decrease as showed on a computational 2‐dimensional model and experimental data.

Condensate Migration Dynamics into Porous Bed in a Nonperforated Chamber

Due to complexity of condensate-migration into a porous-bed, the analytically simplified studies using uniform-flow assumption need enhancement through performing experiments. This study is conducted by maintaining saturated vapor-air over porous-alumina-balls and glass-beads-bed in a nonperforated chamber. Walls of the chamber are controlled isothermally. By evaluating on subcooling-, diffusive-, and porous perturbation-parameter, it is known that condensate migrates in Darcian regime. In this regime, based on visualized evidence and proposed Lyapunov-exponent-base series, this migration study finds that there are periodic- and unperiodic-dominant subregimes, where a temporal chaotic-migration case is found in the unperiodic-dominant subregime.

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.

Flow visualization around the rotating straight grinding wheel using the smoke wire method

In this report, the velocity vector field around the rotating straight grinding wheel were visualized by a smoke-wire method and an image analysis such as a gradient method developed by Miike et al. Consequently, we found that the each method for visualization were avilable to estimate the velocity vectors quantitatively. We also found that the air flow behavior around rotating straight grinding wheel was suggested complicated flow pattern such as the suction and injection which were caused by the internal flow of the porous body. The effect of thermal convection on the heat transfer should be considered in the calculation of heat balance in grinding.

High-speed Temperature Sensing in Microscopic area. Relationship between Impulse Signal and Abrasive Grain Diameter with Temperature of Grinding Wheel Surface.

A new type of infrared radiation thermometer with an optical fiber that has fast response time (3μs) and microscopic measurable area (φ110μm) was developed for thermal analysis of the grinding phenomenon. The obtained signals are made up of impulse signals and base signals. In order to elucidate why the impulse signals occur, we undertook some examinations. As a result, this impulse signal was found to correspond to the grain size. Its interval time seems to also correspond to the time between successive cutting points on the grinding wheel. The smaller the grain size is, the smaller is the heat production per grain. When the measurable area is larger than that targetted, the output signal indicates the shape of a plateau. On the other hand, when the measurable area is smaller than that targeted, the output signal indicates a chevron shape.