عنوان مقاله [English]
Due to the high use of thermal desalination plants, there is a great tendency to simulate the behavior of these plants. Most of the researches are focused on modeling steady behavior, but to design control systems and evaluate their performance, we also need to study unsteady behavior modeling. Also, few researches have studied system shut down. In this paper, steady and unsteady modeling of industrial desalination plant with four effects has been studied. The unit also consists of a condenser and a TVC. The variable-step, variable-order method (VSVO) has been used to solve differential equations. Each evaporator is divided into three phases of vapor, tubes and brine, and for each of these phases the equations of mass and energy conservation is used. Results have been validated with real plant data. The variables of temperature, vapor flow rate, brine flow rate and brine height were studied in unsteady modeling in starting, shutting down and steady state conditions. It was found that the largest change in the brine flow rate after shutting down is in the last effect, which increases by 42%. Also, the biggest change in the height of the brine is in the first effect, which after 800 seconds will reach 11 times the steady state, that will cause the phenomenon of flooding and possible damages.