共查询到18条相似文献,搜索用时 203 毫秒
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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. 相似文献
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高效传热管内凝结换热性能及阻力性能的实验研究 总被引:1,自引:0,他引:1
本文以HFC134a和HCFC22为工质对光管及两种不同槽型的强化传热管(DAE-2管与DAEC管)的水平管内凝结换热进行了对比实验研究、研究发现,DAE-2管平均换热系数比光管提高了140%~170%,而单位长度阻力损失增加了50%~100%,DAEC管平均换热系数比光管提高了160%~200%,同时单位长度阻力损失增加了70%~130%。此外,本文给出了DAE-2管和DAEC管平均换热系数及阻力损失的计算关联式,可用于冷凝器设计。 相似文献
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多孔介质内受迫对流凝结时两相共存区的非达西模型 总被引:2,自引:0,他引:2
本文提出多孔介质内受迫对流凝结时两相共存区的二维非达西流模型。分析了蒸气在多孔介质内沿水平平板和填充国管内受迫对流凝结时两相共存区的厚度。假定局部平衡和暂先假设蒸气为理想气体,化简了能量方程。 相似文献
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水平微肋管内基于分层流流型的沸腾传热理论模型 总被引:1,自引:1,他引:0
本文提出了基于气液分层流的水平螺旋微肋管内沸腾传热理论预测模型。在模型建立过程中,采用了与开发微肋管冷凝分层流模型类似的理论处理方法。在气液分界面以上区域,相邻微肋之间的沟槽内的半月形液面形状取决于重力和表面张力之间的静力平衡关系,其中半月形液面中的薄液膜区域的传热特性由先前提出的薄液膜蒸发模型预测;分层流液体中的传热特性由Mori等建立的基于实验数据的关联式确定。将模型理论预测值与已由的四种不同结构的微肋管、三种有机工质下得到的实验数据进行了比较,结果表明,只要不发生管内部分烧涸现象,在Fr0<2.5时,理论预测值和实验数据符合得相当好。 相似文献
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N─甲基吡咯烷酮两相闭式热虹吸管传热特性的实验研究 总被引:2,自引:0,他引:2
本文报道了用N—甲基吡咯烷酮(C5H9NO3)为工质以光滑管与三维内翅片管为管壳制成的两相闭式逆流热虹吸管的传热特性。实验结果表明在工作温度为220~350℃,热负荷为8.2~17.3kW/m2范围内光滑热虹吸管蒸发段与凝结段换热系数的积分平均值分别约为1700W/m2·℃和1600W/m2·℃。由于三维翅片的强化传热作用,使三维内翅片热虹吸管蒸发段与凝结段换热系数分别比光滑管增大了20%~40%和70%~160%。实验表明N—甲基吡咯烷酮综合传热性能优于萘,可望作为中温热管工质使用。 相似文献
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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. 相似文献
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内螺旋肋管流动与传热特性的实验研究 总被引:4,自引:0,他引:4
对六种内螺旋肋管进行了流动与传热的实验研究,实验管内径为16.25-16.69 mm,内螺旋肋高为0.28-0.44 mm,螺旋肋牙数为40-45,螺旋角为43°-45°.研究表明,内螺旋肋管可以有效地强化传热,本文所研究的管型的传热强化倍率为1.67-2.99.比较了两种评价内螺旋肋管性能的方法.用Webb模型及Ravigururajan模型对内螺旋肋管进行了性能预测并与实验值进行了比较.两个模型的预测值与本试验结果有较大偏差,相对而言,传热模型稍优. 相似文献
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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. 相似文献
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In this study, condensation of pure refrigerant R134a vapor inside a vertical 18° helical microfin tube was experimentally investigated. Tests were performed at saturation pressure of 5.7–5.9 bar with mass fluxes of 20–100 kg/m2s and heat fluxes of 1.7–5.3 kW/m2. The effects of mass flux and the temperature difference between the refrigerant and tube wall (ΔT) on the heat transfer performance were analyzed throughout experimental data. For experiments in which ΔT is more than 2.5°C, the average condensation Nusselt number showed a tendency to be independent from ΔT. Heat transfer enhancement ratio was found to be 1.59–1.71, which is always higher than the heat transfer area enhancement factor (1.55). Fins always act as a turbulence promoter in the given experimental data range. Finally, the most widely used heat transfer coefficient correlations for condensation inside microfin tubes were analyzed through the experimental data. Best fit was obtained with Yu and Koyama's correlation with an absolute mean deviation of 17% and Kedzierski and Goncalves's correlation with an absolute mean deviation of 19%. 相似文献
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全玻璃真空太阳能热水器强化换热机理分析 总被引:1,自引:0,他引:1
本文应用Ansys Fluent软件对加装导流板全玻璃真空太阳能热水器内自然对流流场进行三维数值模拟计算,并与实验进行对比分析,通过改变导流板长度和位置改善热水器内的流动和换热。结果表明,与无导流板结构相比较,加装导流板后管内涡流消失,流体流动稳定,有利于管内自然对流,增强了换热效果,水箱内温度分层效果明显,有助于提高换热效率;同时得出导流板长度最佳选择范围为1.4~1.6 m,导流板加装在玻璃管中间位置与距管中间位置偏下1/2之间范围内更有助于换热。 相似文献