叶轮搅拌非牛顿流体时的功耗特性研究

The Study on Power Consumption Characteristics of Impeller Mixing Non-Newtonian Fluids

发酵液搅拌是沼气工程不可或缺的工艺过程,合理的搅拌对提高沼气的产气率具有重要的意义.由于发酵过程中的沼液呈非牛顿流体特性,其粘度随剪切速率变化而变化致使在沼液搅拌过程中的功耗特性预测一直是一个研究难点.文中考察了Metzner&Otto广义雷诺数ReMO,Metzner&Reed广义雷诺数ReMR及Chhabra广义雷诺数ReCH与功率准数Ne的相互关系.采用上述三种方法基于不同尺寸搅拌叶轮及不同浓度非牛顿流体的搅拌系统所测得的数据来预测搅拌系统的功耗特性,发现每一种方法都不能完全准确的预测从层流到转捩过程的功耗特性.因此,文中通过分析非牛顿流体的本构方程,在上述三种方法的基础上推导了一个适用于预测从层流到转捩过程功耗特性的广义雷诺数Renew.研究发现,相比已有的预测方法,新的广义雷诺数能很好的预测该搅拌系统的功耗特性,为进一步研究奠定了坚实的基础.

Fermentation broth mixing is an indispensable process in biogas engineering.Reasonable stirring is of great significance to improve the biogas production rate.Because the biogas slurry in the fermentation process is Non-Newtonian fluid,its viscosity changes with the shear rate,so the prediction of power consumption characteristics in the process of biogas slurry mixing has always been a tough research topic.In this paper,the relationship between Metzner&Otto generalized Reynolds number Re_(MO),Metzner&Reed generalized Reynolds number Re_(MR)and Chhabra generalized Reynolds number Re_(CH) and power number Ne is investigated.Based on the experimental data of the mixing system with different impeller sizes and different concentrations of Non-Newtonian fluids,the above three methods are used to predict the power consumption characteristics of the mixing system.It is found that each method cannot accurately predict the power consumption characteristics from laminar flow to transition process.Therefore,by analyzing the constitutive equations of Non-Newtonian fluids,a generalized Reynolds number Re_(new),which can be used to predict the transition process from laminar flow to transition,is derived on the basis of the above three methods.It is found that compared with the existing prediction methods,the new generalized Reynolds number can well predict the power consumption characteristics of the stirring system,which lays a solid foundation for further research.