Studies in two-phase gas-solids flow



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Turbulent gas-solids flow was studied in a horizontal 2-inch I.D. smooth tube. Pressure drop measurements were made under specific conditions of flow pattern in the range of Reynolds numbers from about 20,000 to 71,000 and solids to gas loading ratios from 0.03 to 14.0. The results demonstrated the importance of the saltation velocity as a governing factor for an accurate prediction of the pressure drop. The introduction of apparent viscosity in the pressure drop model of Julian and Dukler illustrated the effect of particle collisions on the modified Von Karman constant and hence on the friction factor. An analytical model based on the principles of similarity was developed and tested. Momentum equations were developed for turbulent gas-solids flow in an attempt- to interpret various terms which contribute to the pressure drop. A new technique called the momentum-isokinetic technique was developed to measure the local mean phase velocities and particle concentration distributions simultaneously. A probe based on this technique was designed and tested in dispersed phase flow. The local properties were calculated from data obtained undei1 non-isokinetic conditions and by accurate setting of isokinetic conditions. The significance of the entrance region pressure loss was recognized for this purpose. Within the range investigated, the air velocity profiles showed a decrease in velocity gradient near the wall accompanied by an increase in pressure drop over single phase flow. A negligible slip between gas and solids was observed at the center of the tube. The slip velocity remained constant for uniform solids distribution, and it increased towards the wall for non-uniform solids distribution.