Measurements of solids motion in a fluidized bed have been made in a computer‐aided particle tracking facility. A radioactive tracer particle, dynamically identical to the solid particles to be studied, was mixed with the solids in the bed. The gamma radiation from the tracer was continuously monitored by a large number of scintillation detectors located around the bed, providing information on the tracer's instantaneous location. Prudent use was made of the purposely introduced redundant distance data to achieve improved accuracy. The recognition of the existence of secondary emission due to the interaction of the primary radiation and other system materials and the subsequent devising of a scheme to mitigate its effect contribute much to the success. Results for a bed with a uniform air distributor plate show the existence of two counter‐rotating toroidal vortices whose relative sizes and strengths vary with the fluidizing velocity. Fluctuating motions at low frequencies ranging from 1.6 to 16 Hz have been observed at various locations in the bed.

The mechanics of vapor bubble collapse under spherically symmetrical conditions is examined to ascertain the relative importance of the effects of liquid inertia and heat transfer on the collapse rate. A dimensionless parameter, Beff, is identified to characterize the mode of collapse. Discriminating values of this parameter are suggested for the simple case where the collapse is initiated by a step change in pressure or temperature. For heat transfer controlled collapse, a model is also proposed to account for the influence of a permanent gas present in the bubble. Experimental results for bubbles with initial radii ranging from 0.3 cm to 0.9 cm collapsing in water and ethyl alcohol at atmospheric pressure levels and under free fall conditions are presented. The pressure difference ranges from 12 cm Hg to 63 cm Hg and the corresponding degrees of subcooling are 5 deg C to 45 deg C. Data are also given for water vapor bubbles containing significant amounts of nitrogen, helium, and xenon. When compared with theory, reasonable agreements are obtained. For slowly collapsing bubbles, the significance of small translational velocities is brought to attention. Photographic evidences are also given for bubble instability under suitable conditions.

A restrictive analysis based on a new model is presented for the prediction of thermal contact resistance in a vacuum environment. It is demonstrated that, for many surfaces commonly encountered in engineering practice, the macroscopic constriction has a commanding influence. Extensive results are given for brass, magnesium, stainless steel, and aluminum surfaces which show the effects of material properties and the degree of conformity of mating surfaces under load. Limited results are presented to show the influence of surface films, surface roughness, creep, additional interstitial material, mean interface temperature, etc. Good agreement between the measured and predicted values of the thermal contact resistance was found over wide ranges of the applied load and other system variables.

An analysis is made for the transient response behavior of thermal or concentration boundary layers of a fluid sphere moving at constant velocity with internal circulation in another fluid of large extent under the condition of large Reynolds and Peclet numbers. The disturbance is initiated by a step change in temperature or solute concentration of either the continuous or disperse region fluids. The governing energy or mass conservation equations are solved using similarity transformations. The result shows that the growth of the boundary layers is independent of the fluid properties but is governed by a single parameter; namely, the product of the translating speed and time divided by the droplet radius. For all practical purposes, the transients will die out when the value of that parameter attains unity.

No abstract