CFD model development for sugar mill evaporators

Abstract

A numerical model is presented for the single-phase fluid flow inside a sugar mill evaporator vessel. The model incorporates the effect of temperature and sugar concentration on the fluid properties. The model is a quarter wedge of the evaporator where the vertical heating tubes III the calandria section are modelled through a momentum source term in three directions. Although the use of the momentum source term in the calandria section did not result in fluid flow being completely restricted to the vertical direction, the predictions show reasonable agreement when compared with measurements taken from the actual vessel. The model presented here is capable of predicting trends in the fluid flow behaviour for processing conditions normally experienced in the final vessel of a multiple-effect evaporator set. The predictions show that the design of the juice distribution system at the inlet to the vessel has a major influence on the flow field in the remainder of the vessel. A large amount of mixing was found to occur at the inlet resulting in the calandria region being exposed to juice with properties close to the outlet stream, which is detrimental to performance.