Simulations of fixed beds having column to particle diameter ratio （D/dp） of 3, 5 and 10 were performed in the creeping, transition and turbulent flow regimes, where Reynolds number （dpVLρL/μL） was varied from 0...Simulations of fixed beds having column to particle diameter ratio （D/dp） of 3, 5 and 10 were performed in the creeping, transition and turbulent flow regimes, where Reynolds number （dpVLρL/μL） was varied from 0.1 to 10,000. The deviations from Ergun＇s equation due to the wall effects, which are important in D/dp 〈 15 beds were well explained by the CFD simulations. Thus, an increase in the pressure drop was observed due to the wall friction in the creeping flow, whereas, in turbulent regime a decrease in the pressure drop was observed due to the channeling near the wall. It was observed that, with an increase in the D/dp ratio, the effect of wall on drag coefficient decreases and drag coefficient nearly approaches to Ergun＇s equation. The predicted drag coefficient values were in agreement with the experimental results reported in the literature, in creeping flow regime, whereas in turbulent flow the difference was within 10-15%.展开更多
We investigate the drop formation dynamics of shear-thinning liquids from a drop-on-demand piezoelectric inkjet printhead numerically using the volume-of-fluid(VOF)method.The influence of key liquid properties such as...We investigate the drop formation dynamics of shear-thinning liquids from a drop-on-demand piezoelectric inkjet printhead numerically using the volume-of-fluid(VOF)method.The influence of key liquid properties such as zero-and infinite-shear viscosity,power-law index,and surface tension on filament ejection and pinch-off,filament contraction,and drop formation are systematically explored.In the parameter range studied,we find that the early stages of ejection are unaffected by the liquid properties,and only surface tension critically governs the pinch-off length and pinch-off time during the late stages of ejection.The filament growth rate during ejection and its contraction post-pinchoff for shear-thinning liquids match those of Newtonian fluids with viscosity equal to the infinite-shear viscosity,provided the power-law index remains below a threshold.展开更多
基金One of us (Rupesh Kumar Reddy Guntaka) acknowledges the fellowship support given by the university Grant Commission (UGC),Government of India
文摘Simulations of fixed beds having column to particle diameter ratio （D/dp） of 3, 5 and 10 were performed in the creeping, transition and turbulent flow regimes, where Reynolds number （dpVLρL/μL） was varied from 0.1 to 10,000. The deviations from Ergun＇s equation due to the wall effects, which are important in D/dp 〈 15 beds were well explained by the CFD simulations. Thus, an increase in the pressure drop was observed due to the wall friction in the creeping flow, whereas, in turbulent regime a decrease in the pressure drop was observed due to the channeling near the wall. It was observed that, with an increase in the D/dp ratio, the effect of wall on drag coefficient decreases and drag coefficient nearly approaches to Ergun＇s equation. The predicted drag coefficient values were in agreement with the experimental results reported in the literature, in creeping flow regime, whereas in turbulent flow the difference was within 10-15%.
文摘We investigate the drop formation dynamics of shear-thinning liquids from a drop-on-demand piezoelectric inkjet printhead numerically using the volume-of-fluid(VOF)method.The influence of key liquid properties such as zero-and infinite-shear viscosity,power-law index,and surface tension on filament ejection and pinch-off,filament contraction,and drop formation are systematically explored.In the parameter range studied,we find that the early stages of ejection are unaffected by the liquid properties,and only surface tension critically governs the pinch-off length and pinch-off time during the late stages of ejection.The filament growth rate during ejection and its contraction post-pinchoff for shear-thinning liquids match those of Newtonian fluids with viscosity equal to the infinite-shear viscosity,provided the power-law index remains below a threshold.
