共查询到20条相似文献,搜索用时 203 毫秒
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针对水平管降膜蒸发器运行和优化设计中存在的流动与传热问题,建立了水平管降膜蒸发器实体的三维分布参数模型,采用数值模拟方法对蒸发器内海水流场、温度场等特性进行了深入研究,获得了相应热力参数分布的详细信息,直观地刻画了蒸发器内部的工作过程以及复杂流动与换热现象。通过数值解与实际值的比较,对模型进行了验证,结果表明:第1、2管程蒸汽进口区总传热系数最大,海水表现出喷淋密度上高下低、盐度上小下大等细观规律;供入海水流量在280~370 t/h范围内变化对二次蒸汽与加热蒸汽的温差影响较大,而对二次蒸汽产量没有明显的影响,说明海水流量偏离设计值会造成整个海水淡化系统无法正常运行。 相似文献
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为了研究冷却水入口压力和空气流速对喷嘴成膜特性的影响,以喷射式凝汽器喷嘴为研究对象,采用可视化实验方法对凝汽器喷嘴出口液膜的流动形态进行了拍摄,采用数字图像处理手段提取了液膜面积与喷射长度,并与数值模拟中不同的湍流模型的计算结果进行了对比,最终选取了Realizable k-ε湍流模型。基于Fluent求解器,耦合Realizable k-ε湍流模型与VOF方法,数值计算了凝汽器内部的流场。结果表明:当喷嘴入口压力从3 kPa升高到25 kPa时,布液板近壁面的速度随入口压力的升高逐渐增加,且液膜厚度也呈逐渐减小的趋势。对于DN15和DN13喷嘴,空气从静止状态变化到30 m/s流速时液膜面积略微减小,空气流速从30 m/s提高到150 m/s时液膜面积迅速减小。 相似文献
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据《Теплоэнергетика》2013年12月刊报道,全俄热工研究所的专家研究并分析了在高蒸汽含量下蒸燃联合装置余热锅炉低压蒸发器内侵蚀性-腐蚀性磨损的特点。分析表明,在蒸发器内工质的压力小于1 MPa并且质量含汽量x≈0.5时,体积含汽量接近1,在蒸发器出口几乎是干饱和蒸汽流动并且没形成液膜。在这种情况下,盘管式蒸发器出口段磨损具有如下侵蚀特性。 相似文献
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The falling film evaporation of R134a with nucleate boiling outside a triangular-pitch (2-3-2-3) tube bundle is experimentally investigated, and the effects of saturation temperature, film flow rate and heat flux on heat transfer performance are studied. To study the effect of cross vapor stream on the falling film evaporation, a novel test section is designed, including the tube bundle, liquid and extra vapor distributors. The measurements without extra vapor are conducted at the saturation temperature of 6, 10 and 16°C, film Reynolds number of 220 to 2650, and heat flux of 20 to 60 kWm?2. Cross vapor stream effect experiments are operated at three heat fluxes 20, 30, and 40 kWm?2 and two film flow rates of 0.035 and 0.07 kgm?1s?1, and the vapor velocity at the smallest clearance in the tube bundle varies from 0 to 2.4 ms?1. The results indicate that: film flow rate, heat flux and saturation temperature significantly influence the heat transfer; the cross vapor stream either promote or inhibit the falling film evaporation, depending on the tube position, film flow rate, heat flux and vapor velocity. 相似文献
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Yuanyuan Zhou Jianlin Yu Yanzhong Li 《International Journal of Heat and Mass Transfer》2012,55(23-24):7218-7222
In this study, a mathematical model for the laminar falling film is presented in order to simulate the evaporation heat transfer characteristics in falling liquid oxygen films. The model takes into account the effect of the interfacial shear. The values of the film thickness, the heat transfer coefficient as well as the interfacial shear are obtained under given conditions by solving the model with an iteration method. The influences of the inlet Reynolds number, channel length and the interfacial shear on the flow and heat transfer characteristics of the falling film evaporation are analyzed in detail. Effects of key factors on the circulation ratio of the inlet fluid mass flow rate to the generated vapor mass flow rate, an important design parameter for reboilers/condensers, are particularly analyzed. In addition, the variations of the average vapor velocity and interfacial film velocity are also discussed. The analysis results could provide theoretical guidance for the simulation and design of downflow reboilers/condensers applied in air separation units. 相似文献
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ABSTRACTIn this paper, a new two-dimensional simulation model was developed for the falling film flow under low Reynolds number (below 20). The phase-field multiphase lattice Boltzmann model was developed to simulate the flow pattern of the two-phase falling film with high density ratio. The approaches to treating the liquid-gas interface with high density ratio (up to 775), surface tension, gravity, inlet and outlet open boundary conditions as well as solid-liquid interface considering contact angle were developed firstly, and then implemented in the model. The dynamic characteristics of the film flow, including the development of the liquid-gas interface and the film thickness, were simulated under the Reynolds numbers between 1.0 and 20. The results show that the film is fully laminar under low Reynolds numbers. The falling film flow model developed in this study lays the foundation for the study of heat and mass transfer in the falling film based liquid desiccant dehumidifier. 相似文献
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S.P. Aktershev S.V. Alekseenko 《International Journal of Heat and Mass Transfer》2005,48(6):1039-1052
The linear stability of condensate film flowing on an inclined isothermal plate under action of gravity and turbulent vapor flow was the subject of study. The cases of cocurrent and countercurrent flow of two phases were considered at an arbitrary inclination of the plane. The first part of this work deals with stationary film flow. The impact of vapor flow on the film is described by a given shear stress on the interface with account for the transverse mass flux due to phase transition. The integral method gives the analytical solution for distribution of film thickness along the plane (with and without account for film inertia) at different inclination angles. The second part of paper deals with linear stability of stationary film flow. The fluctuation of shear stress on the surface was calculated using the quasilaminar model. The two-wave equation for film thickness with phase transition and dispersion formulas were derived. The results of effect of condensation on film stability are presented for a wide range of flow parameters. 相似文献
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《International Journal of Thermal Sciences》2002,41(9):891-898
In the absorbers of air-cooled water–lithium bromide absorption chillers, the absorption process usually takes place inside vertical tubes with external fins. In this paper we have carried out an experimental study of the absorption of water vapour over a wavy laminar falling film of water–lithium bromide on the inner wall of a smooth vertical tube. The control variables for the experimental study were; absorber pressure, solution mass flow rate, solution concentration and cooling water temperature. Relatively high cooling water temperatures were selected to simulate air-cooling thermal conditions. The parameters considered to assess the performance of the absorber were; the mass absorption flux, the outlet solution degree of subcooling and the falling film heat transfer coefficient. The results indicate that in water cooling thermal conditions the mass absorption fluxes are in the range 0.001–0.0015 kg·m−2·s−1, whereas in air-cooling thermal conditions the range of mass absorption values decreases to 0.00030–0.00075 kg·m−2·s−1. 相似文献
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Numerical Simulation of Laminar Film Condensation in a Horizontal Minitube with and Without Non-Condensable Gas by the VOF Method 总被引:1,自引:0,他引:1
Zhan Yin Yanling Guo Bengt Sunden Qiuwang Wang 《Numerical Heat Transfer, Part A: Applications》2013,63(9):958-977
Based on the volume of fluid (VOF) method, a steady three-dimensional numerical simulation of laminar film condensation of water vapor in a horizontal minitube, with and without non-condensable gas, has been conducted. A user-defined function defining the phase change is interpreted and the interface temperature is correspondingly assumed to be the saturation temperature. An annular flow pattern is to be expected according to a generally accepted flow regime map. The heat-transfer coefficient increases with higher saturation temperature and a smaller temperature difference between the saturation and wall temperatures, but varies little with different mass flux and degree of superheat. The existence of a non-condensable gas will lead to the generation of a gas layer between vapor and liquid, resulting in a lower mass-transfer rate near the interface and higher vapor quality at the outlet. In consequence, the heat-transfer coefficient of condensation with a non-condensable gas drops sharply compared with that of pure vapor condensation. Meanwhile, the non-condensable gas with a smaller thermal conductivity would cause a stronger negative effect on heat flux as a result of a higher thermal resistance of heat conduction in the non-condensable gas layer. 相似文献
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Wei QuTongze Ma Jianyin MiaoJinliang Wang 《International Journal of Heat and Mass Transfer》2002,45(9):1879-1887
The physical and mathematical models are established to account for the formation of evaporating thin liquid film and meniscus in capillary tubes. The core vapor flow is due to gradient of vapor pressure, which is mainly contributed by the shear stress at vapor-liquid interface. The liquid film flow is owing to gradients of capillary pressure and disjoining pressure. The heat transfer is composed of liquid film conduction and evaporation at vapor-liquid interface. The mass balance of vapor flow is considered to obtain the vapor velocity, this can evade directly solving the rarefied gas velocity field.In regard to the capillary tubes of micron scale, the calculation results show that, the bigger the inner radius or the smaller the heat flow, the longer the evaporating interfacial region will be. There only exists meniscus near the wall, and nearby the axial center is flat interface. While as to the capillary tubes of scale about 100 μm, the evaporating interfacial region will increase with heat flux. Compared with capillaries of micron scale, the meniscus region will extend to the center of capillary axis. These can be tentatively explained as strong influence of the thin liquid film.For the capillary tubes of radius about 100 μm, the experimental results indicate that the apparent contact angles and meniscus profiles can almost coincide with those of the theoretical values. 相似文献