Gas Interchange between a Bubble and Continuous Phase in Gas-Soild Fluidised Bed

The mechanism of gas interchange between a bubble and the continuous phase was investigated by blowing a bubble of visible brown NO₂ gas into two dimensional fluidised bed. From this investigation, it was found that the gas interchange occurred by the diffusion and by the flow out of gas from the cloud which was caused by variations of velocity and diameter of bubble. Based on the above transfer mechanism, a model for gas interchange was suggested and the gas interchange coefficient was calculated. Furthermore, gas interchange coefficients were obtained by measuring the change of the concentration of a CO₂ gas bubble at two different heights in the bed. The gas interchange coefficients calculated from the model coincided well with that obtained from experiments

Studies on Through Flow Drying : I. Heat and Mass Transfer between Fluid and Solids in Packed Bed

The mechanisms of through flow drying were investigated experimentally and theoretically. Part I of this paper deals with heat and mass transfer during the constant drying period. The experimental data were obtained by measuring the rate of evaporation of water into a stream of air from wetted granules and packings during the constant drying rate period. The drying rates of a single layer of wetted porcelain particles packed between two layers of dry glass spheres were measured and those of random packed beds also were obtained. From a comparison of the transfer data with a single layer and with packed beds, the characteristic constants of the packings were determined and a correlation of the transfer coefficients was obtained. Furthermore, the discussion is extended to considerations of transfer phenomena in fluidized beds

Studies on Through Flow Drying : II. Simultaneous Heat and Mass Transfer in the Decreasing Drying Rate Period

Part II of this paper reports an investigation of the mechanism of the decreasing drying rate period for through flow drying. The moisture distribution in the packed bed during the decreasing rate period was obtained by measuring the moisture content of particles at arbitrary drying times. A theoretical discussion on simultaneous heat and mass transfer in the decreasing drying rate period is presented and basic rate equations are derived from theoretical considerations under several assumptions. The authors solved numerically the simultaneous equations by digital computer. The calculated results generally agreed with the experimental date of moisture distribution

Studies on Through Flow Rotary Dryer

The drying procedure in the through flow rotary dryer was investigated by experimental equipment. From the drying rate, the heat transfer capacity coef ficients of the through flow rotary dryer were calculated. The heat transfer capacity coefficients based on the dryer volume were 500-1800 (kcal/hr m3-dryer vol. °C) which were large values as compared with those generally obtained from rotary dryers. The experimental correlations of the heat transfer capacity coefficients against the Reynolds number were obtained by the equation haDp=0.476/fe0-8

The Liquid Fraction of Moisture Transfer in the Drying Process of a Bed of Granular and Powdered Materials

To investigate the mechanism of the moisture transfer in the drying process of a bed of non-adsorptive granular and powdered materials, the drying experiments of a bed of such materials containing the dilute NaCl solution were performed. The liquid fraction of moisture transfer was defined and calculated from the experimental data. The drying mechanism during the first falling rate period was deduced from these results

Analysis of the Drying Rate during the Falling Rate Period in the Drying of a Bed of Granular and Powdered Materials

Drying mechanism of a bed of granular and powdered materials during the first falling rate period was analysed. The drying rate curves obtained from the present analysis represent sufficiently the experimental drying rate curves. Drying mechanism during the second falling rate period was analysed from the same considerations. The drying mechanism must be analysed as the phenomena of a simultaneous heat and mass transfer. Drying periods of a bed of non-adsorptive granular and powdered materials are distinguished to constant rate period, first and second falling rate periods from experimental results. The drying mechanism during the second falling rate period was analysed from such consideration in our previous reports. In this report, we will discuss the mechanism for the first falling rate period. The same argument is applied to the second falling rate period also

Mass Transfer Through a Rarefied Gas Between Two Concentric Spheres

The present work was undertaken to derive a theoretical formula of mass transfer under a reduced pressure, especially the transition regime, through the gas kinetic-theory and compare it with the experimental results. The Maxwell moment method utilizing the two-sided Maxwellian distribution function having been proposed by Lees et al. was applied to the mass transfer between two concentric spheres. In the process of analysis, the accomodation coefficient for mass transfer was taken into account. The analytical solution in which the value of accomodation coefficient was evaluated as 0.9 showed in good agreement with the experimental results of sublimation of naphthalene

Temperature Distribution of the Bed during the Second Falling Rate Period of Drying

The temperature distribution of the bed of the granular materials at drying during the second falling rate period was calculated by the analytical solution of the equation of heat conduction. The equation of heat conduction during the second falling rate period became the differential equations with moving boundary. The heat-balance integral method was applied to solve this problem which consists of a variable heat flux at surface. The calculated results by the analytical solution were displayed and compared with the numerical solution and also with the experimental ones

The Temperature and Moisture Profile of Material by Drying during the Falling Rate Period and the Asymptotic Temperature of the Moist Part

Experimental investigations of drying of bed of granular and powdered materials were performed. Drying rate, moisture profile and temperature profile were measured. The asymptotic temperature of the moist part was defined. The mechanism of drying process during the falling rate period has been analysed from consideration of a simultaneous heat and mass transfer. The equation to calculate the second falling rate was suggested

The Motion of Particles Caused by a Bubble in Gas-solid Fluidised Bed

The motion of particles caused by a single bubble which is blown into a two-dimensional fluidised bed has been studied. A drift line which is shown when a bubble has passed through the bed is obtained as a generalized curve. The experimental results can be explained fairly well by the authors' model. The model is as follows. 1. The motion of particles is assumed as the motion of perfect fluid caused by the motion of a circular cylinder in the perfect fluid. 2. There is an imaginary wall at the distance of the diameter of bubble below from the center of the moving bubble and it moves upwards with the same velocity as the bubble