In this paper

simulation calculation of liquid mixing in downcomer is carried out by using eddy diffusion model and mixing pool model. The mixing quantity among pools and the eddy diffusivity De expressing the mixing degree are obtained. The results indicate that mixing in downcomer is actually incomplete. It is a correction to the assumption of complete mixing in downcomer which is generally made in simulation calculations. The plate efficiency at various degrees of mixing in downcomer is calculated by the use of two-dimensional eddy diffusion model.