水平螺旋槽管壁面液膜特性的研究

研究水平螺旋槽管壁面液膜的形成机理及流动特性。通过建立单组分流体的物理和数学模型，得出了液膜的速度、厚度解析解，并分析了水平螺旋槽管的几何条件对壁面液膜形成的影响。结果表明：液膜的形状主要受表面张力和槽道表面几何形状的影响，在槽道谷底处较厚，而在槽道起始处较薄。相对于光滑直管，水平螺旋槽管壁面液膜具有更均匀的厚度分布，故具有更好的传热传质性能。     

水平螺旋槽管壁面液膜传热特性的研究--流体性质对液膜厚度的影响

考虑到薄膜表面张力和重力的影响，利用流体力学的基本方程建立了小流量液体在水平螺旋槽管外管壁形成壁面液膜的流动和强化传热的拟线性模型，得到了液膜厚度的解析表达式，进而分析了流体性质对壁面液膜厚度的影响。结果表明：对于同一种喷淋液体水，随着温度的升高，液膜厚度受表面张力和槽道表面曲率的影响逐渐减弱，液膜厚度趋向于均匀一致，具有更好的传热传质性能；用水作喷淋液体和煤油、原油相比较，有其特殊的优点，所以工业上常用水作为喷淋式换热器的喷淋液。     

水平微槽管壁面升膜形成的研究

对蒸发状态下水平螺旋槽管管外壁面升膜的形成机理和流动特性进行了研究。对驱动液膜形成的润湿紧力进行分析，建立单组分流体的数学模型，对拟线性方程数值求解，得出壁面液膜蒸发时的速度和厚度分布，并对影响水平螺旋槽管升膜的流动特性的因素进行分析。得出水平螺旋槽管有益于形成连续均匀的液膜，有更好的流动特性，增强传热传质效果。     

水平螺旋槽管降膜流动和传热特性研究

对水平螺旋槽管壁面降膜形成及传热特性进行了理论和实验研究,得到了液膜厚度及速度的解析及数值解.结果表明,降膜液膜特性主要受槽道结构和液膜表面张力控制.管壁温度沿周向向下逐渐升高,而且在定热流密度下保持不变,而液膜温度则沿周向逐渐上升.相比光管,螺旋槽管降膜具有更高的传热系数.     

水平螺旋槽管壁面二元混合液体升膜形成的试验研究

对二元液体混合物在蒸发状态下水平螺旋槽管管外壁面形成升膜进行了试验研究．实测了水平螺旋槽管壁面二元混合液体升膜的速度场和表面温度场,分析了水平螺旋槽管壁面热流密度和流体性质对壁面液膜特性的影响。结果表明：同一升膜工质,螺旋槽管的热流密度越大．液膜的爬升速度越大;流体性质对升膜的流动特性和温度分布特性有显著的影响,酒精溶液的浓度越高．液膜的流动性越好,表面总体温度越低,换热系数越小。     

气汽混合流体凝结液膜传热特性研究

液膜厚度对凝结传热具有较大影响,且传热管管型影响着凝结液膜形成及排除。为了通过改变管型降低液膜厚度达到强化传热的目的,对圆管、椭圆管及滴形管等三种管型凝结液膜建立了相应的物理及数学模型,并计算了液膜沿管壁的厚度分布及传热系数;分析了三种管型对液膜传热的影响。结果表明:在气汽混合流体凝结传热过程中,不同管型其凝结液膜厚度差别较大;壁面温度和混合流体速度对液膜传热均有影响;相同条件下滴形管管壁上所形成的液膜,其平均厚度较薄,传热系数较高,因此滴形管传热性能优于其他管型。     

调峰型气化炉内换热区换热行为模拟研究

基于两相流的欧拉壁膜模型和组分输运模型耦合的方法,针对1种调峰型的气化炉壳侧内部进行建模,研究了烟气垂直向上流动时,螺旋盘管管壁外表面的相变行为及液膜的形成过程和分布情况。计算结果表明:当烟气通过管道外壁面时,烟气中水蒸气在管道外壁发生相变。首先在底部盘管壁面发生凝结形成液膜,随着时间的推进,凝结过程持续进行。底部盘管表面先凝结形成的液膜最厚,上部盘管表面后冷凝形成的液膜逐渐变薄,在内圈盘管形成的液膜厚度要比外圈厚。烟气进入换热区域直至盘管外壁全部覆盖液膜用时2.4 s,液膜厚度达2.57×10~(-5) m,各测量点烟气温度与实验测值误差在5%以内,排烟温度310～330 K,含水量为6.2%,为新型气化炉结构的优化设计提供理论依据。     

水平翅片管外混合气体对流冷凝传热的理论研究

以Nusselt理论为基础,结合修正的膜理论,对含湿混合气体横掠水平翅片管外时的翅片表面对流冷凝传热机理进行研究。建议了分区处理方法,建立了翅片侧壁和光管上的液膜流动和传热模型。得到了管壁温度、烟气进口温度和雷诺数对总凝结液量的影响,以及翅片侧壁液膜的厚度分布。     

环形布膜器垂直管内R113降膜蒸发换热特性数值研究

通过建立垂直管内降膜蒸发物理数学模型,对环形插头型布膜器管内R113的气液两相逆流降膜蒸发换热特性进行二维非稳态数值研究,分析了管内液膜流动分布以及壁面温度和液膜表面温度分布,对比了加热前后液膜厚度的变化.结果表明:随着降膜蒸发过程的进行,液膜下端开始出现液滴飞溅,且不断向上端发展;R113在管内降膜蒸发过程中壁面温度和液膜表面温度沿流动方向逐渐升高,气相温度变化趋势则相反;从壁面到管中心,温度沿径向逐步降低,在近壁面1mm前后其分布趋势相反;加热后液膜厚度明显减小,且下游液膜厚度变得相对均匀.     

水平刻槽管壁面二元溶液升膜蒸发传热试验研究

对水平刻槽管壁面二元溶液升膜形成过程进行了分析.在同一热流密度下,不同升膜工质在管壁面的分布状态也不相同.由于刻槽管特殊的几何结构,液膜表面能实现欠热蒸发和过冷沸腾.实测了水平刻槽管壁面水和不同质量分数的NaCl溶液液膜内温度分布、周向换热系数和厚度分布.试验结果表明:NaCl溶液比水更易形成升膜,并且升膜的速度比水的大,所以换热效果比水的好,溶液质量分数对换热系数和温度分布存在影响.质量分数越大,溶液的换热系数也就越大,液膜内的温度变化也就越明显.对于一定质量分数的溶液,溶液的换热系数只与液膜的厚度分布有关.     

黏性流体在光滑横管外壁成膜机理研究

采用低雷诺数、小流量模型对黏性流体在水平管外形成的薄液膜的流速以及膜厚分布进行分析和计算；给出了边界层坐标系的二维边界层方程，求得了其相似性解；根据液膜自由表面上的运动学边界条件，给出关于膜厚的一阶偏微分方程，利用特征线法求得了膜厚分布的数值解。结果表明：重力驱动在光滑横管外壁面白发形成均匀的液膜是不可能实现的，必须外加一个能产生特殊流场的气刀来改变其原有受力情况，才有可能实现均匀液膜。在某一确定的时刻，膜厚沿着x轴逐渐增厚；随着时间的推移，各处膜厚逐渐减小。这些对于确定气刀的结构和安装的位置是十分重要的。     

Study of rising liquid film on surface of horizontal metallic mesh tube

The formation of a rising liquid film on the surface of a horizontal metallic mesh tube in the presence of a temperature field is investigated. A numerical model is established to study the behavior of the rising liquid film. For thermocapillary flow, the velocity distribution of the liquid film is obtained numerically and the influences of wall temperature, geometry of the metallic mesh, and diameter of the tube on the formation of the rising liquid film are also investigated. The results indicate that the velocity of the rising liquid film is influenced by the diameter of the tube and the gap between the tube and the metallic mesh. The velocity of the rising liquid is obviously promoted due to the influence of thermocapillary flow. An experimental system was developed and comparisons between numerical solution and experimental results were made. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20270     

The formation of rising liquid thin film on the fluted surface of a horizontal tube

The purpose of this study is to investigate the mechanism of the formation of the rising liquid thin film and its flow characteristics on the fluted surface of a horizontal tube. By analyzing the wetting behaviors of the fluted tube, which was primarily responsible for the formation of the rising liquid thin film, a numerical model of one‐phase fluid was established to analyze the distribution of the velocity and thickness of the rising liquid thin film during its evaporation. The behaviors of the flow characteristics were discussed and the results showed that geometric properties of the fluted surface of a horizontal tube and surface tension of the fluid were essential for the formation of a continuous and uniform liquid thin film. Theoretical analysis suggested that the capillary force created by the fluid surface tension was a key value for the formation of the thin film. The heat and mass transfer characteristics of the formed thin film also had an effect on the formation of the rising film. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(6): 396–406, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20075     

逆向气流条件下半椭圆管外水平降膜厚度分布研究

为研究半椭圆管水平降膜厚度的分布规律,搭建逆向气流条件下水平降膜实验平台,并结合数字图像处理技术,研究逆流风速(0～5 m/s)和喷淋流量(0.025～0.221 L/min)对液膜厚度的影响。研究表明:逆向气流会对管外水膜产生影响,并存在临界速度;当逆流风速低于临界速度,液膜厚度沿圆周方向先减小后增大,与无空气流动时相似;当逆流风速超过临界速度时,液膜分布严重不均甚至被吹飞;随着逆流风速增大,平均液膜厚度先增大后减小;随着喷淋流量增大,平均液膜厚度持续增大;当喷淋流量减小、逆流风速增大时,平均液膜厚度减小。     

The flow characteristics of an upward gas‐liquid two‐phase flow in a vertical tube with a wire coil: Part 2. Effect on void fraction and liquid film thickness

An experimental study has been carried out to clarify the characteristics of the void fraction and the liquid film thickness of the air‐water two‐phase flow in vertical tubes of 25‐mm inside diameter with wire coils of varying wire diameter and pitch. The flow pattern in the experiment on the average void fraction and the local void fraction distribution in cross section was a bubble flow, and the liquid film thickness was in the region of semiannular and annular flows. It is clarified from these experiments that the average void fraction in tubes with wire coils is lower than that in a smooth tube and decreases with the wire diameter owing to the centrifugal force of the swirl flow which concentrates bubbles at the center of the tube, that the local liquid film thickness becomes more uniform with a decrease in the pitch of the wire coil, and that the liquid film becomes thicker after the passage through the wire coil with an increase in the wire diameter. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 652–664, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10067     

Experimental study on combined buoyant-thermocapillary flow along with rising liquid film on the surface of a horizontal metallic mesh tube

Temperature distribution and variation with time has been considered in the analysis of the influences of the initial level of immersion of a horizontal metallic mesh tube in the liquid on combined buoyant and thermo-capillary flow. The combined flow occurs along with the rising liquid film flow on the surface of a horizontal metallic mesh tube. Three different levels of immersion of the metallic mesh tube in the liquid have been tested. Experiments of 60 min in duration have been performed using a heating metallic tube with a diameter of 25 mm and a length of 110 mm, sealed outside with a metallic mesh of 178 mm by 178 mm, and distilled water. These reveal two distinct flow patterns. Thermocouples and infrared thermal imager are utilized to measure the temperature. The level of the liquid free surface relative to the lower edge of the tube is measured as angle q. The results show that for a smaller q angle, or a low level of immersion, with a relatively low heating power, it is possible to near fully combine the upwards buoyant flow with the rising liquid film flow. In this case, the liquid is heated only in the vicinity of the tube, while the liquid away from the flow region experiences small changes in temperature and the system approaches steady conditions. For larger q angles, or higher levels of immersion, a different flow pattern is noticed on the liquid free surface and identified as the thermo-capillary (Marangoni) flow. The rising liquid film is also present. The higher levels of immersion cause a high temperature gradient in the liquid free surface region and promote thermal stratification; therefore the system could not approach steady conditions.