This paper proposes a mathematical model for estimating the overall heat transfer coefficient for the optimal design of a multiple effect evaporator system taking into account various parameters (type of flow during the evaporation, length of each flow zone, temperature profile, turbulence, etc.). The predictions of the model have been compared with the experimental data reported in literature [18]. A good agreement has been observed between predicted values and the reported data. Subsequently the applicability of this model has been checked in the design and dynamic study of multiple-effect evaporator system. A good agreement has been observed between the estimated values and the experimental data reported by HOLLAND and LIAPIS [1]. This study confirms that the proposed model would give more flexibility to the designer than existing models in fixing the length of the evaporator tubes so as to increase effective heal transfer area. As the model is rather simple and fairly accurate it would enable optimal design with comparatively low computational cost.