عنوان مقاله [English]
Due to the high use of thermal desalination plants, there is a great tendency to simulate their behavior. Most of the research is focused on modeling steady behavior, but to design control systems and evaluate their performance, we also need to study unsteady behavior. Also, few researchers have studied the system shutdown. In this paper, steady and unsteady modeling of an industrial multi-effect desalination plant with four effects, one condenser, and a Thermo compressor has been studied. The variable-step, variable-order method has been used to solve differential equations. Each evaporator is divided into three phases of vapor, tubes, and brine then the equations of mass and energy conservation are used. Results have been validated with real plant data. The variables of temperature, vapor flow rate, brine flow rate and brine level 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 level of the brine is in the first effect, which after 800 seconds will reach 11 times the steady state that will cause the flooding phenomenon.