固気液三相流

The optimum design and operation of a gas liquid solid flow system depend on the ability to accurately predict the fundamental properies of the hydrodynamics, heat and mass transfer and so on. Identification of the flow regimes is also needed to understand the overall system performance. This comprehensive review describes both the experimental and modeling studies of the fundamental characteristics of gas-liquid-solid three phase flow.

Three-phase flows are encountered in air-lift pumps, preheaters and reactors, and other industrial plants. It is necessary to clarify not only macroscopic characteristics such as pressure drops and volume fractions of each phase but also local characteristics such as spatial distnbutions of local volume fractions and local velocities of each phase. In the present review, measurement techniques of volumetric fluxes and volumetric fractions of each phase, radial distributions of gas and solid volume fractions and liquid velocities were described for the three-phase bubbly flow. Those of length and velocities of large bubble liquid slug and film thickness of large bubble were also described for the three-phase slug flow Furthermore, application of measurement techniques for two-phase flows to three-phase flows were examined.

Computational methods to simulate gas-solid-liquid flows in chemical reactors such as agitators, bubble columns and fluidized beds are reviewed. In addition, their problems are discussed, keeping in mind the present technical level and future problems of related commercial software.

Expantion of foods during cooking sometimes causes crack and burst. Burst is undesirable, while crack is desirable in some cases. Karinto with no sugar occasionally causes burst involving danger and cracks in doughnuts are generally favorable. Crack during deep frying is caused when the internal pressure of sample exceeds the cracking pressure of outer layer. Factors of internal pressure of samples are temperature increase and expanding ratio, and those of cracking pressure are thickness, tensile strength, and size and shape of the sample. The value of both internal pressure and cracking pressure can be calculated by using these data. The predicted timing of cracks in doughnut were confirmed in the experiment under various conditions. Mechanism of burst and crack during deep frying was proposed and it was expected to be applicable to the prediction and control of crack in food processing.