The Experimental Study And Numerical Analysis Of Steam Condensation Characteristics In Inclined Tube

At present, the direct air-cooling technology is widely applied in China where it is rich in coal but short of water resource,and steam condensing in its core components,the condenser determines the heat exchange efficiency of the air cooling unit.However, literatures of studies on condensation heat transfer in air-cooled condenser(ACC) are very rare up to now. In this thesis, experiment and numerical simulation on steam condensation in two smooth inclined tubes has been investigated in order to provide reference for future heat transfer research on steam condensation in more complex and larger cross section inclined tubes.The steam condensation in tubes relates to a complex gas-liquid two-phase flow. Therefore, the primary objective of this thesis is to design and establish a new exprimental setup for investigating the condensation heat transfer characteristics in the inclined tubes,and the distribution of the steam temperature and condensation heat transfer coefficient reduce along the orientation of steam flow are acquired.The condensation heat transfer coefficient has few relationship with cooling water temperature. Steam flow speed, heat transfer temperature difference and inclination angle influence significantly on the condensation heat transfer coefficient. In some degree, the heat transfer coefficient increases with the increase of the steam flow speed but decreases with the increase of the temperature difference in heat transfer.Furthermore, there exists an optimum angle corresponding to the best condensation heat transfer coefficient, and the optimum angle is 60o in this range of experimental conditions. The heat transfer coefficient of inclined smooth circular tube is obviously higher than that of horizontal circular tube,Based on comparison of the test results and the prediction results from several correlations, a new correlation is presented, and most deviations of the prediction results from the new correlation to experimental data are less than 15%.Through analysis of the steam condensation heat transfer and flow characteristics,and segmenting the inclined tube, the heat transfer and flow resistance coupling differential equations for differential section of condensation are established on basis of the experimental data and the developed correlation, so that the numerical study on steam condensation characteristics in inclined tubes is to be carried out. In steam condensation process, the vapor quality is not transformed linearly, the integral average dry degree in smooth inclined tube can't be calculated according to the arithmetic average method, and steam pressure gradient decreases gradually along the tube, so the steam pressure along the tube decreases more slowly. The effects of shear stress recede in the steam flow process and friction resistance is gradually decreased.Based on two-phase flow theory, pipe flow has been studied;through the application of two-phase mixture model and user-defined functions(UDF), the flowtube steam condensation heat transfer process of inclined tubes, considering the affect of different inlet steam flow, tube bundles for the tilt angle and other parameters, was numerically simulated, the results show that: along the inner tube the heat exchanger intensity decreases, pressure drop increases; the same angle of inclination, the influence of heat transfer coefficient with inlet steam flow is related to the size of tube dip, the flow pressure drop becomes larger as inlet steam traffic increasing; With the increase of pipe inclination,tube heat transfer coefficient increases first, then levels off,the flowing pressure drop first decreases, then levels off, the most suitable tube bundle angle is around 60°,The variation law of steam condensation heat transfer characteristics in tube is consistent with the experimental results.The results of flow patterns, pressure drop, and heat transfer characteristics for steam condensation in inclined tubes of this thesis could be the reference to performance study, design and optimization of the direct air-cooled condenser in power plants.