水平三维肋管管外凝结换热实验与分析(I实验研究)

本文对不同饱和蒸汽温度下R11在水平Thermoexcel-C管的管外凝结换热性能进行了实验研究。实验结果表明:随着饱和蒸汽温度的提高,C管的凝结换热系数下降。C管凝结换热强化的主要机理在于孤立三维齿结构增大了表面张力减薄凝结表面液膜厚度的作用,而C管凝液淹没区小于相同肋间距的低肋管,且在淹没区内的凝结换热大于低肋管。     

斜翅型冷凝强化换热管传热性能的实验研究

对一种斜翅型外翅片带内螺纹的冷凝强化换热管进行传热性能的实验研究。管外冷凝换热的制冷剂为R134a,管内对流换热的介质为水。分别在定热流密度与定水流速的条件下进行一系列工况的实验,得到相应的实验数据。在定热流密度条件下,利用Wilson图解法得到管内的换热系数数据及相应的计算关联式。在定水流速的条件下,利用分离方法得到管外冷凝换热系数数据及相应的计算关联式。将强化管换热系数数据与光管换热系数的理论计算值进行了比较,结果表明:冷凝强化换热管管内对流换热的强化倍率为2.4,管外凝结换热系数随壁面过冷度的增加而增大,管外凝结换热的强化倍率为:1.78～3.92。     

R407C在水平单管外凝结换热的实验研究

本文用实验方法研究了Ｒ４０７Ｃ在水平单管外的凝结换热,并与ＨＣＦＣ２２做了对比。试验管包括一根光管和两根双侧强化管。结果表明,Ｒ４０７Ｃ在水平管（包括光管和强化管）外的冷凝换热系数随着热流密度的增加而显著增加,而且,强化管增长的程度要比光管的强烈。在相同的冷凝温度与热流密度范围内,无论对于光管还是强化管,Ｒ４０７Ｃ的管外冷凝换热系数都远小于ＨＣＦＣ２２的值。对于所试验的两种强化管,ＨＣＦＣ２２的管外冷凝换热系数的强化效果比Ｒ４０７Ｃ更明显。     

R134a在板式换热器中的凝结换热实验研究

本文对R134a在板式换热器内的凝结换热特性进行了实验研究,通过测量换热器中冷却水及板壁温度获得了局部凝结换热系数随蒸气干度、质量流量及热流密度的变化关系.实验结果表明,凝结换热系数随着蒸气干度增加而增加.文章还将实验结果与部分文献数据进行了比较与分析.本文的研究为换热准则关系式的发展提供了实验数据.     

水平强化管外降膜蒸发特性的实验研究

降膜蒸发因其低充灌量和高换热性能在制冷行业逐渐受到关注。本文对三种具有不同强化表面的换热管,以R134a为工质进行了水平单管管外降膜蒸发实验。研究结果表明:强化管外换热系数不仅与热流密度有关,还与喷淋量有关,且在一定热流密度范围内,存在最优喷淋量;对于不同强化表面,降膜蒸发换热为管外多孔结构密度与齿化结构密度的综合表现,多孔结构密度与齿化结构密度越高,降膜换热系数也就越高。     

双侧强化传热高效冷凝传热管的实验研究

本文报道了双侧强化传热高效冷凝传热管DAC管的实验研究方法与结果。所用试验装置保证在同样蒸气状态下对光管和高效传热管同时进行直接对比的性能测定,测量本体电阻以确定具有复杂机械延伸面的管壁平均温度.R11蒸气凝结的实验结果表明:DAC管外侧凝结换热性能已达到国外先进强化传热管的水平,并且在小换热温差下具有更高的强化换热倍率.DAC管内侧冷却水的放热系数可比光管提高60～80％,总传热系数比光管提高3倍以上。     

蒸发冷却的管外换热性能的实验研究

将淋水填料与盘管组合,构成高效低耗的密闭式冷却塔,成为当前闭式塔的主流塔型.本文以此类设备的研发为背景,设计了一个用于蒸发冷却换热模块性能试验的小型风筒,在横流和逆流模式下就单纯管束换热模块与填料-管束结合型换热模块的管外换热性能进行了比较,并研究了淋水密度、风量对其换热性能的影响.试验表明,采用填料-管束结合型换热模块,在相同截面风速和淋水密度以及相同的控制壁温和空气湿球温度条件下,管外综合换热系数比单纯管束有明显提高;对相同换热模块,管外综合换热系数在试验范围内随淋水密度和截面风速的增大而增大.     

蒸气流速对存在温度梯度的竖直壁面Marangoni凝结换热的影响研究

本文以水一酒精混合蒸气为工质,对蒸气流速对存在温度梯度的竖直壁面Marangoni凝结换热特性的影响进行了实验研究.结果表明:混合蒸气凝结换热系数随蒸气流速的增加而增加,但换热系数对流速的敏感性随酒精蒸气浓度不同而有所区别,在酒精蒸气浓度较低时,流速使换热系数的增加较为明显.对比流速对溶质Marangoni凝结换热特性的的影响,流速对温度梯度和浓度梯度共同驱动的Marangoni凝结换热影响要弱一些.     

蒸汽流速对竖直管外Marangoni凝结换热特性影响的实验研究

本文在不同蒸汽流速下对水-酒精混合蒸汽在竖直管外Marangoni凝结换热特性进行了实验研究.结果表明:在相同蒸汽压力下,混合蒸汽在竖直管外凝结换热系数随蒸汽流速的增加而增加.当蒸汽酒精浓度较低时(1%、2%、5%),凝结换热系数随流速的增加而明显增加.当蒸汽酒精浓度较高时(20%、50%),流速的增加对凝结换热系数影响较小.这主要是由于蒸汽流速在低酒精浓度下对凝结扩散层热阻的影响大于在高酒精浓度下对扩散层热阻的影响.     

R410A和R22在水平内螺纹管内冷凝性能的实验研究

实验研究了环保替代制冷工质R410A和R22在冷凝温度40℃时在内螺纹强化管(外径为9.52mm)内的冷凝换热特性,对二者的冷凝换热性能进行了对比,并研究了测试管外冷却水流量对换热系数的影响。结果表明:在管外冷却水流量相同时,R22的总换热系数K普遍比R410a小,而管内传热系数hr比R410A大。R22与R410A的总传热系数K均随管外冷却水流量的增加而增加,当制冷剂流量Gm大于300kg.s-1.m-2时,管外冷却水流量对总传热系数K的影响变小。     

含不凝气体时煤油在水平管束外的冷凝

采用实验的方法,研究了在较宽的不凝气体含量范围内,煤油蒸汽在不同几何结构的螺旋扁管管束外的冷凝换热现象,得出了螺旋扁管的几何结构对冷凝换热的影响规律,并与同样条件下的光管管束的冷凝换热进行了分析比较。     

HEAT TRANSFER AND PRESSURE DROP MEASUREMENTS FOR IN-TUBE CONDENSATION OF CFC-113 USING MICROFIN TUBES AND WIRE INSERTS

Accurate, repeatable heat transfer and pressure-drop measurements have been made for condensation of CFC-113 with downflow inside enhanced microfin tubes and tubes containing twisted-wire inserts. In the latter case measurements have also been made for CFC-113/air mixtures. The heat transfer rate was calculated from the coolant flow rate and temperature rise, the latter measured using a 10-junction thermopile with careful attention paid to adequate coolant mixing and isothermal immersion of the thermopile leads. The surface temperature was found from thermocouples embedded in the tube wall. One plain tube, nine microfin tubes (with different fin heights, helix angles, and number of fins), and four twisted-wire inserts (with different wire densities) were tested. Enhancement ratios (i.e., vapor-side heat transfer coefficient for the enhanced tube divided by that for a smooth tube at the same vapor-side temperature difference and vapor inlet velocity) between 1.6 and 5.6 for the microfin tubes and between 1.2 and 1.6 for the twisted-wire inserts were found, with values depending on vapor-side temperature difference, vapor inlet velocity, and air inlet mole fraction in the case of CFC-113/air mixtures. The microfin tubes showed moderate pressure-drop penalties of around 50% compared to the plain tube, while the twisted-wire inserts showed increasing pressure-drop penalty with increasing wire density.     

水蒸汽在水平三维微肋管内的凝结换热及阻力特性

本文以水蒸汽为工质对水平三维微肋管内凝结换热及阻力特性进行了实验研究．与光管和二维管相比，在相同条件下，实验中效果最好的T3管全长平均凝结换热系数分别提高了113％～410％和20％～65％，同时，与二维管相比流动阻力增加较小，最大值不超过6．3％．比较另两种管型（T1，T2管）也证明三维管以较小的流阻增加为代价换取了明显的强化效果．     

Modeling of vapor condensation in a longitudinally finned minichannel

Heat transfer with vapor condensation inside a longitudinally finned tube is numerically studied. The proposed model considers vapor condensation on two initial flow areas, namely, annular and rivulet. The model allows prediction of pressure difference along the tube length, vapor velocity profiles in the central channel and an interfin groove, and also a velocity profile in the condensate rivulet at the bottom of the interfin channel, local heat transfer coefficients at different fin points, and average heat transfer coefficients over tube section and length. The calculations showed that in the case of vapor condensation in longitudinally finned tubes of a small diameter it is of fundamental importance to divide the flow tube section into a central channel and interfin channels. The governing vapor velocities in these channels may differ by more than an order of magnitude. The reduced vapor velocity, used in engineering calculations, does not reflect the character of dynamic vapor impact on a condensate film on the most part of the heat transfer surface. For tubes with relatively large fins the proposed model describes vapor condensation almost completely,meanwhile, the mass vapor quality by the time of filling of the grooves reaches 0.01–0.05. The highest heat transfer intensification was obtained for “sharp fins” with a high value of the fin head curvature. Comparison of results of calculation by the model with results of the known experiments on water vapor condensation yields a good qualitative and quantitative agreement for low vapor velocities at the channel inlet (under 30 m/s). The wall thermal conductivity coefficient value affects significantly the condensation efficiency.     

非共沸混合工质水平管内凝结换热折算因子的实验关联

1前言前文山提出了计算环状流和波状分层流型下非共沸混合工质在水平管内凝结的换热系数的折算方法。租界面温度Ti的取值对计算结果影响很大。现在常用的方法是根据液膜和气相区传热传质的经验公式确定问，不仅计算工作量大，且无公认的计算方式。这给工程计算带来许多不便。本文取Ti二（Tv十几w，即气相温度Tv和壁面温度见的算术平均值，以计算相界面上的平衡参数，并将前文中的折算因子计算式改为如下形式：对环状流将由于相界面温度的取法所引起的误差归于用实验数据确定的经验系数A、B与经验指数p、q。式中Ja为雅各布数，无量纲温度0…     

一种内螺纹强化管的冷凝实验研究

实验研究了环保替代制冷工质R410A、R22在水平强化管内冷凝换热特性,探索了热流密度、水流速度对换热特性、压降的影响。实验测试管为内螺纹强化管,长度为5.2 m,外径为9.52 mm。实验结果表明:制冷剂R410A、R22的传热系数和压降随热流密度的增大而增大,同时内螺纹管的换热系数还随管外冷却水流量的增加而升高,压降随冷凝温度的升高而降低,而R410A比R22有更好的换热效率和较小的压降。     

Flow condensing heat transfer of R410A,R22, and R32 inside a micro-fin tube

An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m²s) and heat fluxes of 3–12 kW/m². The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed.     

氨的添加引发水蒸气凝结换热强化的实验研究

研究了添加极少量氨时,氨-水混合蒸气在水平圆管上的凝结传热特性。结果表明:由于氨的添加引发的Marangoni效应,水蒸气的凝结换热在实验工况范围内基本上都得到了强化。随着表面过冷度的增加,凝结换热系数表现出有峰值点的非线性变化规律。当氨蒸气的浓度为0.38%时,混合蒸气的最大凝结换热系数可达纯水蒸气的1.9倍,从液膜热阻和扩散热阻的角度分析了强化换热的机理。     

Heat Transfer Characteristics for Condensation of R134a in a Vertical Smooth Tube

In this study, condensation of pure refrigerant R134a vapor inside a smooth vertical tube was experimentally investigated. The test section was made of a copper tube with inside diameter of 7.52 mm and length of 1 m. Experimental tests were conducted for mass fluxes in the range of 20–175 kg/m²s with saturation pressure ranging between 5.8 and 7 bar. The effects of mass flux, saturation pressure, and temperature difference between the refrigerant and tube inner wall (ΔT) on the heat transfer performance were analyzed through experimental data. Obtained results showed that average condensation heat transfer coefficient decreases with increasing saturation pressure or temperature difference (ΔT). In addition, for the same temperature difference (ΔT), heat can be removed from the refrigerant at a higher rate at relatively low pressure values. Under the same operating conditions, it was shown that average condensation heat transfer coefficient increases as mass flux increases. Finally, the most widely used heat transfer coefficient correlations for condensation inside smooth tubes were analyzed through the experimental data. The best fit was obtained with Akers et al.'s (1959) correlation with an absolute mean deviation of 22.6%.     

R134a在水平三维内微肋管内的沸腾换热

本文以 Ｒ１３４ａ为工质,在外径为 １６ ｍｍ的两种不同几何结构的水平三维微肋管内进行了沸腾换热实验,研究了质量流率、热流密度、蒸汽干度等因素对沸腾换热系数的影响。与相同工况下的水平光管比较, １＃微肋管的换热强化因子在１．５～２．１之间,２＃微肋管的换热强化因子在１．９～２．８之间。两种三维微肋管的比较结果显示,单位内表面积上具有更多的微肋数目的 ２＃管的平均沸腾换热系数比 １＃管增加了 ２８～４３％。