Modeling of Liquid Phase, Non-Ideal Flow Characteristics in Multiple Effect Evaporators with FLUENT

The use of FLUENT, a computational fluid dynamics modeling tool in the engineering design process has become increasingly popular in recent times as a result of beneficial outcomes from several studies. Sugar mill evaporators are likely to have non-ideal juice flow characteristics and design improvements could be realized if a suitable computational model were developed. The model would be a useful tool for predicting broad trends in fluid flow behavior when process equipment modifications are implemented. In this paper, a numerical model is presented for the single-phase fluid flow inside an evaporator vessel. The model is a one-quarter wedge of the entire vessel utilizing two planes of symmetry to reduce the size of the mesh required. The model presented here is capable of predicting trends in the fluid flow behavior for processing conditions normally experienced in the final vessel of a multiple-effect evaporator set. 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 predictions also 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.