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The modified film model combined with Nusselt's condensation theory are used for the study of convective condensation heat transfer on a horizontal tube with moist mixed horizontal gas flows at a given speed. A theoretical model considering gas boundary layer separation was set up. The liquid film flows and the heat transfer on the tube are presented. The effects of the flow direction on condensation heat transfer are discussed. The results predict that the condensate film is so thin that the liquid phase heat resistance can be ignored. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20238 相似文献
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This paper discusses the convective condensation of a gas mixture in a vertical tube. A mathematical model was derived by combining a modified film model and Nusselt's condensation theory. The effect of wall temperature on film thickness and interfacial temperature was predicted and film thickness was calculated. When compared with the gas phase resistance method, the film model is better. The phenomenon of SO2 absorption into condensate is illustrated and discussed. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(4): 219–228, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20011 相似文献
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《Applied Thermal Engineering》2014,62(2):671-679
The heat transfer model of stable dropwise condensation for saturated vapor on a horizontal tube is developed based on previous theoretical models. Through a comprehensive analysis of all the contributing thermal resistances, the convection effect inside the droplet itself is taken into consideration in the model. For the stable dropwise condensation process in dynamic conservation, a method of double integration of heat flux through numerous inclined plates with different inclination angles is introduced to obtain the overall heat flux through the horizontal tube surface. The model can predict the variation of heat transfer of stable dropwise condensation with different contact angles outside a horizontal tube. The influences of contact angle, temperature difference, and other typical parameters on both a single droplet and the whole condensation process are discussed. The results indicate that a high contact angle can cause a size reduction of falling droplets from condensing surface and thus taking more heat away. The adsorbed condensate film adds an extra thermal resistance and its thickness plays a significant role on the dropwise condensation heat transfer. 相似文献
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The convection‐condensation heat transfer of vapor‐gas mixtures in a vertical tube was studied theoretically and experimentally. The effects of the condensation of a small amount of water vapor (8 to 20%) on heat transfer in a vertical tube were discussed. Comparisons show that theoretical solutions obtained through modified film model and experimental results are in good agreement. The results show that the condensation heat transfer of a small amount of water vapor and single‐phase convection heat transfer in the vapor‐gas mixtures are of the same order of magnitude, and these two modes of heat transfer could not be neglected. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 531–539, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10055 相似文献
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基于Nusselt凝结传热理论,沿肋片管圆周方向划分有限个微元角,建立了每个微元角内肋侧壁、肋间基管及肋顶三个区域的凝结传热模型,通过求解非淹没区和淹没区总传热量,推导管外平均传热系数计算式。计算不同肋片高度、肋密度时,R134a饱和蒸汽的管外平均凝结传热系数。结果表明:随肋密度的增加,平均传热系数先增大后减小,肋密度为25fpi时传热最佳;高肋片管的平均凝结传热系数大于低肋片管的,肋片高度达到一定值时,平均传热系数几乎不随肋高增加而增加。当R134a饱和蒸汽为20℃时,两种不同翅片密度的管外平均凝结传热系数随温差的增大而减小,并通过所建模型得到的计算值与Beatty-Kate模型进行了比较,平均误差分别为约16.1%和8.3%,故所建模型基本反映肋片管外蒸汽凝结传热机理。 相似文献
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采用修正的膜模型与Nusselt凝结理论结合的方法,对含湿混合气体自上而下横掠水平管外时的对流冷凝换热机理进行研究,建立了液膜流动和传热模型,进行数值求解并分析了雷诺数、壁面温度及水蒸汽浓度等因素对混合气体冷凝换热的影响。计算结果表明:水管外壁液膜厚度分布很大程度上受气体边界层对液膜剪切力的影响。而局部努谢尔数不同于纯蒸气的的冷凝换热,它受气相热阻的影响很大,其分布状况类似于单相气体管外的对流换热。 相似文献
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水平单管内换热实验研究 总被引:1,自引:1,他引:0
利用隔膜泵作为系统动力输出源,搭建了单管内传热和流动测试实验台,对制冷剂R22在水平单管内的换热性能进行了实验研究,考察了不同蒸发温度和不同冷凝温度对总传热系数、制冷剂表面换热系数和管内压降的影响.实验结果表明:总传热系数和制冷剂表面换热系数均随着蒸发温度和冷凝温度的上升而增大;管内压降随着蒸发温度的上升而减小,随着冷凝温度的上升而增大;对于同一根实验管,在相同的冷却水流量和制冷剂质量流量下,最佳蒸发工况为10℃;冷凝实验中,总传热系数和制冷剂表面换热系数在40℃时高于其他两种冷凝温度时的值,但35℃冷凝时,管内压降高于其他两种工况. 相似文献
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An experiment has been conducted in detail to study the turbulent heat transfer in horizontal helically coiled tubes over a wide range of experimental parameters. We found that the enhancement of heat transfer in the coils results from the effects of turbulent and secondary flows. With Reynolds number increasing to a high level, the contribution of the secondary flow becomes less to enhance heat transfer, and the average heat transfer coefficient of the coil is closer to that in straight tubes under the same conditions. The local heat transfer coefficients are not evenly distributed along both the tube axis and the periphery on the cross section. The local heat transfer coefficients on the outside are three or four times those on the inside, which is half of the average heat transfer. A correlation is proposed to describe the distribution of the heat transfer coefficients at a cross section. The average cross-section heat transfer coefficients are distributed along the tube axis. The average value at the outlet section should not be taken as the average heat transfer coefficient. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 395–403, 1999 相似文献
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采用数值模拟方法,对径向错列翅片管内含不凝结气体水蒸气的凝结对流换热及阻力特性进行了综合分析。将编写的自定义函数(UDF)导入ANSYS FLUENT软件,对新型强化管传热性能和阻力性能进行了数值模拟,并根据管长方向壁面上蒸汽质量分数的变化情况,讨论分析了凝结过程中翅片管传热性能的变化规律。分析结果表明:与光管相比,内翅片管的强化传热效果随翅数增多、翅片换热接触面积增大而更加显著;另一方面,翅片管的流动阻力相应增大,对管路换热产生不良影响。在所研究翅型范围内16翅y=2x~2型翅片管综合强化换热效果更优;此外随着换热过程的持续,蒸汽凝结逐渐放缓;入口速度增大导致水蒸气凝结不充分,对换热效果的提升有一定制约。 相似文献
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介绍了各种类型的管外冷凝强化换热管,分析了其强化机理及结构特点,并总结得出:管外冷凝强化管的换热系数与管型有关,且各管型的结构参数对强化传热具有重要的作用.对国内外管外冷凝强化技术研究工作进行分析,结果表明,目前管外冷凝强化换热管的研究主要集中于翅片形状、翅片密度、翅片高度等结构参数对换热性能的影响.强化换热管的冷凝传热性能不仅与翅片结构参数有关,而且也与管材的表面特性和导热系数有关.管外冷凝强化换热管的研究重点是开发新型三维结构翅片的双侧强化管并研究其传热关联式,以及研究不锈钢等低成本材料制造的强化管换热管的传热性能和强化结构的优化. 相似文献
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为深入研究液膜内的微观传热机理,对水平管外降膜蒸发的传热特性进行了数值模拟,获得了液膜厚度、液膜流动速度和传热系数等热力参数在液膜内的分布特性。通过与实验数据的对比验证了数学模型的准确性。研究结果表明:在饱和蒸发温度62℃、传热温差2.8℃、管外径25.4mm和液膜入口速度0.071~0.15 m/s条件下,沿圆周方向,液膜厚度减小,传热系数增加,直至达到液膜热力发展区,膜厚和传热系数趋于稳定;受液膜内温度变化的影响,液膜内的粘度、表面张力和导热系数的变化对液膜传热特性产生显著影响。 相似文献
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Katsuhide Ohira 《亚洲传热研究》2001,30(7):542-560
There have been a number of experimental investigations on condensing heat transfer to cryogenic fluids. The investigations with nitrogen and oxygen have shown reasonable agreement between experimental data and those predicted by Nusselt's theory. On the other hand, in the previous investigations with much colder fluids, such as hydrogen, deuterium, and helium, the experimental condensing heat transfer coefficients are smaller than those predicted by Nusselt's theory, and these differences become much larger when the film Reynolds number or decreasing temperature difference across the condensate film is decreased. In the present investigation, hydrogen and nitrogen were condensed inside a vertical tube (d = 15 mm, L = 30 mm) under steady‐state conditions, respectively, and condensing heat transfer coefficients were precisely measured. From the experimental results, the condensing heat transfer coefficients for saturated hydrogen and nitrogen vapors agree with those predicted by Nusselt's theory within ±20%. The results of the present study suggest that deuterium and helium might also behave as predicted by Nusselt's theory. © 2001 Scripta Technica, Heat Trans Asian Res 30(7): 542–560, 2001 相似文献
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Spirally corrugated tubes with different helix angles have been used in experiments on the characteristics of condensation heat transfer and flow resistance. The result of the experimentation shows that the helix angle plays a vital part in the spirally corrugated tube during the process of condensation heat transfer. This paper analyzes the mechanism of how the helix angle influences the characteristics of condensation heat transfer and flow resistance, and presents an experimental correlation formula of condensation heat transfer which takes the helix angle into account as a factor. ©2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(5): 275–282, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20208 相似文献
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Enhancement of condensation heat transfer using a nonuniform electric field was experimentally investigated for horizontal smooth and low‐finned tubes. In the experiments, a wire electrode parallel to the tube was placed beneath the tube. The experimental parameters were the distance and voltage between the wire electrode and the tube, and the condensation heat flux. Results of the present experiment for the low‐finned tube indicate that, as the applied voltage increases, the enhancement ratio increases steeply at a certain voltage and it reaches 2.4. It was observed that the condensate flow pattern falling down from the bottom of the tube changed from a flat film to circular columns at a critical voltage. © 2000 Scripta Technica, Heat Trans Asian Res, 29(4): 269–279, 2000 相似文献
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