This paper presents several simulator models allowing studying the behavior of different types of thermal desalination plants [1]. Three types of evaporators have been distinguished in thermal desalination plants: horizontal falling film evaporators (HFF), vertical falling film evaporators (VFF) and vertical rising film evaporators (VRF). An in depth study of the correlations adopted to calculate the heat transfer coefficients (HTC) of the selected evaporator/condenser has been made, in order to predict the plant performance of dual-purpose plants. Once the sensitivity analysis of the possible HTC has been done, the selected HTC has been implemented in a complex simulation model of MSF and MED/VC/TVC desalination units. Validation (if possible) of the calculated HTC was also done with the real data encountered in the literature.