Coupled Thermo Hydraulic Model And Calculation Method For Two Phase Flow Network

Two-phase network is widely exists in variety of thermodynamic system. Modeling and simulation of two-phase fluid network has been a focus for researchers. It has great significance to improve the simulation accuracy of the entire system by improving the simulation model. In most case, the fluid network system in the engineering field can be simplified as single-phase compressible fluid network. Compared with two-phase fluid network, the mathematical model of single-phase fluid network is simpler and the model solution is faster. Thus improving the single-phase fluid network simulation model is also necessary.In this paper, the networks simulation and computing of thermal fluid have been studied.For single-phase fluid, coupled thermo hydraulic network model and its calculation method are proposed. For two-phase network, the mathematical model based on traditional solution of enthalpy pressure matrix is established firstly. Then apply the coupled thermal hydraulic idea into the two-phase fluid network model. Thus the two-phase fluid network model coupled with thermal hydraulic idea is obtained.To solve the linear algebraic equations generated by the separation algorithm, LU decomposition method and Gaussian elimination method with pivoting was used. To solve the first-order differential equations generated by the coupling algorithm, the classical fourth-order Runge-Kutta method, fourth-order and fifth-order adaptive Runge-Kutta method and Treanor method which are used to solve stiff differential equations were used, and analyze the advantages and disadvantages of these methods.The method of using existing water and steam properties Dynamic Link Library to calculate water and steam properties was described in this paper. The IAPWS-IF97 formula is proposed through transforming program into a one-dimensional or two-dimensional table function. Water and steam properties are then calculated by linear interpolation method.Under the premise of ensuring the calculation accuracy, it can improve computational efficiency. Two methods are given to calculate water and steam properties partial derivative in the coupling algorithms (density on the pressure of the partial derivative and density on the enthalpy partial derivative). One way is to take partial derivative with respect to a two-dimensional table function; another way is derivate mathematically through the IAPWS-IF97 formula. From the above, two partial derivative formulas are derived; these two methods can also be used for other water and steam properties partial derivatives.Using visual modeling techniques, this paper has designed interface for graphical modeling, and has achieved automatic identification of fluid network topology, automatic numbering of fluid network elements. In the background of modeling interface, the common fluid network computing components based on fluid network mathematical model are designed. The computing components can obtain data directly from the modeling interface,and return the results to the screen in real-time display. Applying Multi-threading technology,thread synchronization device is designed to implement multiple drift parallel synchronous operation.Through analyzing typical flow network simulation, the dynamic response of the object system on a variety of disturbances has been tested,and then compares this method with the traditional pressure-enthalpy matrix separation algorithm. The results show that the algorithm takes into account the interaction between thermal and hydraulic calculation, thus the results are closer to reality.