tailieunhanh - Computational Fluid Dynamics 2011 Part 12

Tham khảo tài liệu 'computational fluid dynamics 2011 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 324 Computational Fluid Dynamics well with the experimental values. It can also be seen from the table that the suspension performance in terms of power number is different for different impeller designs. The lowest power consumption was observed for A315 hydrofoil impeller and highest for Rushton turbine impeller. This indicates that the impeller which directs the flow downward having mainly axial component and has the least power number is most energy efficient. Impeller type Power number Experimental CFD 6-Rushton turbine 6-PBTD 4- A315 Hydrofoil downward Table 5. Experimental and predicted values of Power number Solid suspension in gas-solid-liquid mechanically agitated reactor The critical impeller speed for gas-liquid-solid mechanically agitated contactor obtained by CFD simulation based on the criteria of both standard deviation approach and cloud height is validated with our experimental data. The bubble size distribution in the mechanically agitated reactor depends on the design and operating parameters and there is no experimental data available for bubble size distribution. It has been reported by Barigou and Greaves 1992 that their bubble size distribution is in the range of mm for the higher gas flow rates used in their experiments. Also in the recent simulation study on a gas-liquid stirred tank reactor carried out by Khopkar et al. 2005 a single bubble size of 4 mm was assumed. Since the gas flow rates used in our experiments are also in the same range a mean bubble size of 4 mm is assumed for all our simulations. Off-bottom suspension CFD simulations have been carried out for 6 blade Rushton turbine impeller DT and 4 blade pitched blade turbine with downward pumping PBTD at different impeller speeds. The air flow rate for this simulation is vvm and the solid phase consists of ilmenite particles of size 230 pm and the solid loading is 30 by weight. Figure 6 shows the variation of the standard deviation