Hydrodynamic Analysis Of Heat Exchange Network System Based On Modelica

With the development of national urbanization and the progress of social science and technology,the heating area in China is increasing year by year.As an important energy facility,the heat exchange pipe network has attracted much attention due to its high efficiency of energy utilization,good economic benefits and wide application in many fields.Due to the complex topology of the heat exchange pipe network and the lack of corresponding engineering management and operation regulation technologies,the workload of hydraulic calculation of the pipe network is increased,resulting in serious hydraulic imbalance and safety problems in the operation of the pipe network.It is difficult to obtain accurate hydraulic operation conditions and hydraulic characteristics of the pipe network,which directly affects the working efficiency of the heat exchange pipe network.Therefore,in order to ensure the safe operation of the heating pipe network,the hydraulic state of the heating pipe network can be better reflected.it is necessary to analyze the hydrodynamic characteristics of the heat exchange pipe network system during its operation through computer modeling and simulation technology.The focus of this paper includes the following aspects:First of all,this paper analyzes the structure of the heat exchange pipe network system,proposes a method to simplify the hydrodynamic system of the heat exchange pipe network with different structural forms into a directed graph,and describes the topological structure of the hydrodynamic system of the pipe network with the matrix form of "nodes" and "pipe sections".Among them,steam water separator,tee pipe and other components with the function of distributing working medium are regarded as "nodes",and the connecting part between the two nodes is regarded as "pipe section".According to the structural connection between nodes and pipe sections,the characteristic matrix of the heat exchange pipe network system is obtained by using the directed flow diagram,and the hydrodynamic calculation model of the heat exchange pipe network is established.Secondly,through the analogy between the heat exchange pipe network system and the DC circuit system,it is found that the circuit system principle is similar to the fluid pipe network calculation theory,and the hydrodynamic calculation of the heat exchange pipe network can be solved by analyzing the circuit.Therefore,combining Kirchhoff’s law with the characteristic matrix of the directed flow diagram,the nonlinear equations of the nodal mass flow and loop pressure drop of the heat exchange pipe network system are obtained;Based on the mass conservation and momentum conservation laws of the fluid in the pipe network,the resistance characteristic coefficients of the single-phase flow and the twophase flow of the working medium in the pipe network are derived respectively,and the pipe characteristic equation is obtained.The two equation groups of node mass flow and loop pressure drop are established simultaneously.By simplifying the correlation between flow and pressure drop,the equation group is linearized,and the efficient solution method of the equation group is obtained.The mathematical model for the analysis of hydrodynamic characteristics of the heat exchange pipe network is established.Thirdly,according to the hydrodynamic calculation model and solution algorithm of the heat exchange pipe network obtained from the research,the pipes,pumps,valves,steam water separators and other components in the heat exchange pipe network system are modeled based on Modelica language and Dymola software.During the modeling process,it was found that the pipes in the tube panel components have a complex structure of series and parallel connection,and it is difficult to directly establish the corresponding Modelica model through the Dymola software standard library.Because Dymola software and Microsoft Visual Studio compiler have the ability to communicate with each other,C#programming language is used to describe the structural connection relationship of complex pipes in the heat exchange pipe network,that is,the code implementation of the pipe panel model.The Modelica model of the pipe panel is established,and then the Modelica model of each component in the pipe network system is combined with the Dymola software standard library to simulate and establish a Modelica model library of the heat exchange pipe network system-Modelica boiler.Finally,according to the actual project case,the Modelica system model of the actual heat exchange pipe network is built,and the hydrodynamic characteristics are simulated and verified by using Dymola software.Under BMCR(boiler maximum continuous rate)working condition,through the comparison between simulation and actual operation,it is found that the total relative deviation is less than 3%,which can achieve the accuracy of engineering calculation.Then,the hydrodynamic circulation parameters such as the working pressure difference of the pipeline,the circulation ratio and the steam content of the pipeline under different operating conditions of the case are simulated and calculated to analyze whether there will be hydrodynamic safety problems such as circulation stagnation,backflow and heat transfer deterioration,so as to obtain the hydrodynamic characteristics of the pipe network and realize the reliability verification of the heat exchange pipe network system.