Modeling And Practice Of The Low Temperature Multiple Effect Desalination System

In this work, design of high-efficiency solar desalination system was systemically studied with the focus of5tons/day low temperature solar desalination system, of which the experiment platform was well designed. The control system of plate heat exchanger and low temperature high-efficiency solar desalination system were analyzed in detail with dynamic modeling and simulation based on Maltab software. The details are shown as follows:(1) In allusion to the characteristics of low temperature high-efficiency solar desalination system, based on its operating principle, the system can be divided into eight modules, that is, heat source system, steam system, fresh water system, brine system, feed water system, vacuum system, pretreatment system and control module. By analyzing their operational process, the operating principle of low temperature high-efficiency solar desalination system was mathematically modeled. Combining the first and second law of thermodynamics, the model for delivery of energy in plate heat exchanger was proposed, and the low temperature high-efficiency solar desalination system was also dynamically modeled.(2) Based on the technical background of low temperature high-efficiency solar desalination system, its general framework was carefully designed, which consists of three parts, that is, the secondary heat exchange module, low temperature multiple effect desalination modules and power supply control module. By analyzing the principles of each module, the principled framework was carefully designed. This work focused on the former two modules in which the process parameters were designed with circuit’s framework in order to make the process parameters real-time detected. With carefully design of each module, the design of high-efficiency solar desalination system with the experimental platform was proposed(3) Based on its principle, a method for dynamically modeling plate heat exchanger was proposed with differential equations. The modeling process is shown as follows:Firstly, with the physical basis of plate heat exchanger, the system was transformed to a physical model with thermal resistance and capacity. Secondly, with the theory of thermodynamics, the dynamic mathematical model of control system was established. At last, with the proposed mathematical model and Matlab software platform, the model parameters were selected and numerically soluted to verify the reliability of the model.(4) With the design of low temperature high-efficiency solar desalination system and its specific module, dynamic modeling system identification method was proposed. Considering the uncertainties inside the system model, uncertain functions of the system model were firstly set with the proposition of Black-box modeling method. Secondly, with the Black-box modeling and the specific parameters of low temperature high-efficiency solar desalination system, parameter model was proposed. In the end, dynamic model parameters can be systematically identified with augmented least-square method.