Research On Coupling Hydraulic & Thermal Calculation For Steam Pipe Network Theory & Its Application

Such problems were studied as the sharp changes of flow parameters in steam pipes, saturation temperature reducing caused by pressure dropping and the difference between computed and actual operating conditions by current computing methods. Computing model of steam pipe networks was established with hydraulic and thermal characteristic coupled, which has been implemented in software developed by the author. The research work is part of the science and technology development project"The Large-scale Steam Pipe Network Thermal-hydraulic Calculation Model and The Application Research"funded by Shandong Province Education Department. Fundamental of engineering thermodynamics, heat transfer and hydromechanics theory were used in the research work. The computation methods of steam thermodynamic properties are concluded. The heat loss of steam pipe network is analyzed. The actual operating conditions of city steam pipe network were tested. The main works are listed as follows:1 Thermal Computing model of steam pipe network were built with good match to actual operating dataThe thermal calculation model of steam pipe network was established according to the steam pipe network heat transfer characteristics and the thermal equilibrium principle,. It includes steam temperature drop expression, the expression of per unit length heat loss when steam pipe laying in different ways and total heat transfer coefficient expression. The factors influencing total heat transfer coefficient were analyzed by heat loss formula such as different laying ways of steel-encased steel steam insulated pipeline, the heat loss of different pipe diameters. The results showed that the accuracy of new steam pipe network thermodynamic calculation was improved by the built model and it is suitable for thermal calculation of new built steam pipe network.An approach to analyze the actual steam pipe network was presented and an integrated calculation formula was derived to compute steam pipe network heat loss. The operating data of three typical steam pipe networks in Jinan City were tested. Heat loss is analyzed from the data. Comparison showed the consistency of the calculated results and testing data. It can be applied into the thermal-hydraulic calculation of steam pipe network and also heat loss calculation of actual projects. 2 Researches on Choice of Computational Methods of Steam Thermal PropertiesSteam state parameters varies in a wide scope in the process of delivery, while they are usually taken as ideal gas or saturated steam by existing methods, which results in serious calculation error and bad continuity especially for wet steam state parameters. Through the analysis of three state equations with high precision to calculate steam state parameters: the Morrill state equation, Milutinovic uka state equation and the IAPWS-IF97 formula, this dissertation has carried on the comparison to the precision of computing results with those state equations. The suitable applied scope of each method are given. Steam pipe network thermodynamic properties can be chosen properly based on above work.3 Establishing of Thermal-Hydraulic Coupling Mathematical Computing ModelThe computing model is composed of the steam motion equation (obtained through the research on the characteristics of the flowing and heat transfer in the process of steam delivery), the steam state equation, the continuity equation and the energy conservation equation. The model generally considered many factors of the flowing steam such as condensability, change of state, the friction and heat transfer. It was proposed for the first time internationally that Hydraulic & Thermal computation of steam pipe network could be done by the coupled iteration computation. The big error would be caused between actual result and computation result when the impact of heat loss on the pressure change is not considered completely. Especially when running under little load, pressure drop is mainly caused by heat loss instead of flow loss.4 Solving of thermal-hydraulic coupling mathematical modelEffective simplification was made to the model since the thermal hydraulic coupling mathematical model was too complicated to be solved. The standard fourth-order Runge-Kutta method is used to solve the differential equations. The comparison between computed result and actual result showed good consistence. The model could be used to the thermal hydraulic coupling computation of steam pipe network and could be applied to actual projects to settle the existing computation inaccurate problem.5 The development of calculation software for thermal-hydraulic coupling mathematical modelThe development of thermal-hydraulic calculation software of steam pipe network had been completed under Visual C++6.0 environment. Intelligence cartography is adopted, the initial material is input through visualization contact surface dialog box type. Convenient cartography, quick the initial datum input, the document result output, quick computation speed, high precision and good stability are all the advantages of the software.6 The application in actual projectsThe simulating of thermal and hydraulic conditions of a typical steam heating pipe network of Jinan city was carried on. The comparison between calculated results and actual operating data showed that the software could be used in design and operation of the steam pipe network.