基于污泥流变学的射流搅拌混合特性

Mixing characteristics of jet agitation based on sludge rheology

以市政污泥为研究对象,基于污泥流变学,考察了工业尺寸的液液喷嘴、气液喷嘴进行搅拌时射流的流动形态及喷嘴轴向速度分布,并考察了气液喷嘴不带气管进行液液混合时的情况。通过流变实验,确定实验污泥为屈服-胀塑性流体,有触变性,其稠度系数k=0.000 2,流动系数n=1.535 5,表明射流为紊流。且每种类型射流轴向速度衰减规律有一定的自相似性,气液喷嘴在安装气管时射流效果较好。对液液喷嘴、气液喷嘴进行流速场测定,分别考察了其全流场速度方差加权平均值、死区容积百分数随喷嘴安装高度、喷嘴入射流速的变化规律。结果表明,随着入射流速及喷嘴距池底安装高度的增加,搅拌槽内污泥流速均匀程度增加、污泥流动停滞区减少。并且喷嘴安装高度为2 m,入射流速4.95 m·s^(-1)时液液、气液喷嘴的混合效果最佳,2种喷嘴经济入射流速分别为4.95 m·s^(-1)和3.77 m·s^(-1)。

Based on sludge rheology,the flow pattern and axial velocity variation of full-scale jet mixing were investigated for municipal sewage sludge with liquid-liquid and gas-liquid jet nozzles. The gas-liquid jet nozzle was further studied with or without a windpipe. Through rheological measurements,the agitated sludge was determined to be a yield-dilatant fluid with thixotropic properties. The fluid consistency coefficient for sludge samples was 0. 000 2,and the fluid behavior index was 1. 535 5,based on which the jet flow was determined as turbulent. The axial velocity attenuation law for each kind of jet showed a certain self-similarity. A comparison of the outcomes for the gas-liquid jet nozzle with and without a windpipe showed that the nozzle with the windpipe performed better. Based on the velocity field for the liquid-liquid and gas-liquid jet nozzles,the change rule for the variance-weighted average of the flow rate and the dead volume fraction in the agitator bath versus the installation height and entering flow velocity of the jet nozzle were obtained. As a result,with increasing installation height,the sludge flow velocity uniformity coefficient increased and the physical stagnation zone decreased. The optimum mixing conditions for both jet nozzles were the same（ installation 2. 0 m above the bath bottom with an injection velocity of 4. 95 m·s-1）,and the economical injection velocities for the liquid-liquid and gas-liquid jet nozzles were 4. 95 m·s-1and 3. 77 m·s-1,respectively.