Analysis On Flow Models Of Steam-water Two-phase Flow In Pipelines

At present, studies on gas-water two-phase flow mainly concentrate on that withinpipelines. With the increasing dependence on the natural gas and oil in terms of thedevelopment of industrial production and social life in the past ten years, more andmore scholars focused on two-phase flow problems associated with transport ofpetroleum and natural gas, however, researches on steam-water two-phase flowgradually reduce, this was mainly because of the fact that the existing research findingscould really solve some practical engineering problems. In fact, there are still manyproblems need to be solved when concerning steam-water flow during production, e.g.characteristics of vapor or water’s flow and heat transfer in conventional thermal powerplant, design of drain pipes after the DC boiler steam water separator, heater drain pipesand the working medium of the second loop pipeline is also in the wet steam state innuclear power station, the analysis method of two-phase flow should be used to describeits working process and calculate the related parameters.Drift-flux Model (DFM) is one method between homogeneous and two-phasemodel, in this system, the differences of each phase velocity are taken into accountwhich not only overcome the shortcomings of homogeneous model, but also avoid theheavy computing task caused by complex relationship between phase interface inseparated model. In view of the advantage of DFM, according to the domestic andinternational research results of two-phase flow, this dissertation put forward asimplified drift model which was based on the complete hydraulic model, the influencesof pipe angle on void fraction distribution parameter Coand drift velocity Vgjwasconsidered, on the basis of IAPWS-IF97, a module computing steam-water propertieswas gained followed by which a computing program using FORTRAN was carried outin terms of adiabatic and uniform heated vapor-water flow in pipelines, then an examplewithin thermal pipelines of nuclear power station was given.The main research results were as follows:①A comparison of the results in simplified model against the test results wasgiven under the same conditions, both agreed well with each other which provedserviceability of the simplified model.②In order to compare the difference between the common calculation method offlow in steam-water pipe and the model of this thesis, under condition of the test above, void fraction and distribution of pressure drop were predicted. It was found that thedifferences were existed between the predicted results from different models, and thebetter predicted results could be got when some parameters were calculated by usingthe model of this thesis. The relative errors between calculated value and measuredvalue of the pressure drop by use the methods were5.18%,6.72%,8.13%and9.19%respectively to the model of this thesis, slip ratio model, Friedel model and M-N model.For the predicted results of void fraction, the relative errors were5.07%,7.40%and8.39%respectively to the model of the thesis, slip ratio model and homogeneous phasemodel.③It was found that the working medium in a part of drain pipes and steamextraction pipes of a certain nuclear plant was under the condition of vapour-liquidtwo-phase flow. Calculation of the flow with two-phase method was finished, whencompared with the single-phase method, differences between these two method werereally exsit. This thesis could give reference for the condition.