Gassed Power Drawn by Each Impeller in Multiple Impeller Agitated Vessels

多段通氣攪拌槽中各段攪拌翼之功率消耗

呂維明(Wei-Ming Lu) ； 巫鴻章(Hong-Zhang Wu)

《Journal of the Chinese Institute of Chemical Engineers》 33卷6期 (2002/11) Pp. 541-553

https://doi.org/10.6967/JCICE.200211.0541

摘要

Power drawn by each impeller in gassed multiple impeller systems with different impeller combinations was examined in detail by considering the effects of non-uniform gas loading and the gas recirculation. By applying the developed numerical method (Wu and Lu, 2002) to the aerated stirred vessel, the local gas holdup distribution and the velocity profile of gas bubbles within the system were calculated and used to acquire the gas recirculation rate around each impeller. From the results obtained in this study, it is found that non-uniform gas loading results in the non-equivalent energy dissipation among the impellers in multiple impeller systems. This will lead to an erroneous result if the effect of gas recirculation is not considered. By relating (l-Pg/Pο)n to the modified aeration number based on the total gassing rate around each impeller, Qtn, the correlation equations for estimating the power drawn by any Rushton turbine impeller in a multiple impeller system can be obtained by
(l-Pg/Po)n=14.9NA'=14.9(Qtn/ND3), 　　　　　　　Qsn/ND3 ＜0.03,
(l-Pg/Po)n=4.69NA'+0.432=4.69(Qtn/ND3)+0.432, Qsn,/ND3＞0.03.
For a pitched blade impeller installed in a coaxial shaft in a multiple impeller system, two formulas based on the total gassing rate are also proposed to estimate the power drawn by any pitched blade impeller i.e.,
(l-Pg/Po)n=17.91NA'=17.91 (Qtn/ND3), Qsn/ND3 ＜0.03,
(l-Pg/Po)n=3.13NA'+0.605=3.13 (Qtn/ND3)+0.605, Qsn/ND3 ＜0.03.
Comparing the calculated power drawn by the Rushton turbine impeller using the formulas obtained in this study with the correlation proposed by Michel and Miller (1962), it is found that they agree quite well. By using the above correlation equations, the power drawn by each impeller in a multiple impeller system with various impeller combinations can be evaluated accurately

並列摘要

Power drawn by each impeller in gassed multiple impeller systems with different impeller combinations was examined in detail by considering the effects of non-uniform gas loading and the gas recirculation. By applying the developed numerical method (Wu and Lu, 2002) to the aerated stirred vessel, the local gas holdup distribution and the velocity profile of gas bubbles within the system were calculated and used to acquire the gas recirculation rate around each impeller. From the results obtained in this study, it is found that non-uniform gas loading results in the non-equivalent energy dissipation among the impellers in multiple impeller systems. This will lead to an erroneous result if the effect of gas recirculation is not considered. By relating (l-Pg/Pο)n to the modified aeration number based on the total gassing rate around each impeller, Qtn, the correlation equations for estimating the power drawn by any Rushton turbine impeller in a multiple impeller system can be obtained by
(l-Pg/Po)n=14.9NA'=14.9(Qtn/ND3), 　　　　　　　Qsn/ND3 ＜0.03,
(l-Pg/Po)n=4.69NA'+0.432=4.69(Qtn/ND3)+0.432, Qsn,/ND3＞0.03.
For a pitched blade impeller installed in a coaxial shaft in a multiple impeller system, two formulas based on the total gassing rate are also proposed to estimate the power drawn by any pitched blade impeller i.e.,
(l-Pg/Po)n=17.91NA'=17.91 (Qtn/ND3), Qsn/ND3 ＜0.03,
(l-Pg/Po)n=3.13NA'+0.605=3.13 (Qtn/ND3)+0.605, Qsn/ND3 ＜0.03.
Comparing the calculated power drawn by the Rushton turbine impeller using the formulas obtained in this study with the correlation proposed by Michel and Miller (1962), it is found that they agree quite well. By using the above correlation equations, the power drawn by each impeller in a multiple impeller system with various impeller combinations can be evaluated accurately

並列關鍵字

CFD simulation ； Gas recirculation ； Power consumption ； Multiple impeller ； Stirred vessel ； Gas loading