Chemical conditioning is commonly used before the mechanically dewatering process for sewage sludge. The flow field distribution of conditioning tank has a significant effect on conditioning when paddles are operating. Moving reference frame-volume of fluid model was used for simulating flow field distribution of a sludge conditioning tank with the inner diameter of 40 cm by CFD (computational fluid dynamics) technology

and the gas-liquid two-phase distribution was verified. The results showed that in the single straight blade paddle conditioning tank

the optimium ratio of paddle diameter to tank diameter was 1:1.75 and the optimum ratio of baffle width to tank diameter was 1:20. Under these optimum conditions

the fluid swirl could be effectively eliminated and the turbulent action could be enhanced. Furthermore

the flow field distribution simulation was conducted for pilot-scale conditioning tank with the inner diameter of 110 cm and the simulation results were compared with test results. Moving reference frame-volume of fluid model used in this study can provide references for design and optimization of similar sludge conditioning tank.