水平内微肋管局部凝结换热性能实验与数值求解

以Ｒ１１为工质，蒸汽凝结压力为１４７－２６５ｋＰａ，质量流率４ｔｙ１５３ｋｇ／ｍ２ｓ，本文对二维内微肋管和三维内微肋管水平管内凝结分层流区局部换热系数进行了系统的实验。与光管比较，二维内微肋管和三维内微肋管局部凝结换热系数分别提高了１４７－７８３％和２６１－９９７％。本文首次从理论分析入手建立了二维内微肋管水平管内凝结分层流区局部换热系数分析模型并进行了数值求解。计算结果与本文实验相当吻合。     

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％。     

非均匀加热条件下内插扭带管强化传热模拟分析

以水为工作介质,采用欧拉多相流模型和非平衡沸腾模型,当流速在0.3~0.7m·s^-1范围内、工作压力为4.5MPa、热流密度为2MW·m^-2时,数值模拟了内插扭带管和光管管内流动过冷沸腾传热。对比了两种管道的换热系数、气泡份额、流动速度、流场流线、固体组件温度和压降,分析了内插扭带管的综合性能。结果表明,与光管相比较,内插扭带管的换热系数提高约6%~90%,压降增大约200%~250%,得到流速在0.4~0.6m·s^-1范围内时内插扭带管的综合性能评价因子η为1.1~1.3。     

Forced Convective Condensation of R134A Vapor Inside a Vertical Microfin Tube

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%.     

催化剂薄层内甲烷水蒸气重整反应强化管内对流换热的数值模拟

本文以竖直圆管内壁催化剂薄层内发生甲烷水蒸气重整反应强化对流换热作为研究对象,对其进行了数值模拟．结果发现,催化剂薄层内的吸热化学反应可以有效地强化对流换热,降低流体和壁面温度,从而对壁面起到保护作用;极限热流密度的大小与流体的入口温度有关,存在最佳入口温度使极限热流密度最大．     

内插弹簧转子的管内换热及转子旋转特性

管内插入物是强化管内换热的有效方法,内插可旋转结构在强化换热的同时还具有良好的除垢抑垢效果。实验研究了内插螺旋弹簧转子的管内换热以及转子的转动特性。结果表明,与光管相比,换热增强30%,但流动阻力增加5倍左右,转子的参数需要进一步优化以减小阻力。转子的转速与来流速度呈线性递增关系,与入口处转子相比,下游转子的转速逐渐降低,单螺旋转子转速降低的幅度大于双螺旋转子。双螺旋结构连续稳定运行半年以上,该转子强化换热及除垢抑垢性能稳定。     

非共沸混合物微翅管内强制对流蒸发换热计算

分析了非共沸混合物在水平微翅管内强制对流蒸发换热的传热传质的特点,考察了影响非共沸混合工质强制对流蒸发换热的主要影响因素,建立了考虑相界面传质阻力和微翅管二次流效应的换热系数的计算模型,利用本文模型的计算结果与实验数据进行了比较,吻合较好。在高质量流量和高干度(x>0.3)下,理论预测值与实验值的平均偏差不大于10％。     

原表面回热器换热阻力特性试验研究

本文对研制加工的适用于 100 kW 微型燃气轮机的 CW(Cross Wavy) 原表面回热器进行了试验研究,通过对两侧流体进、出口温度、压力等的测量,重点分析了燃气流量、入口温度及空气进口压力变化对换热阻力的影响,得出了在变工况下回热器的流动与换热性能规律,结果表明:所研制的 CW 原表面回热器空、燃气两侧换热均匀,提高了换热效率,两侧压降都有不同程度降低,并得出了有工程应用价值的 Nu-Re 及 f-RE 准则关系式,可为原表面回热器的设计制造提供参考.     

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.     

毛细管内薄液膜轮廓和传热特性研究

本文认为毛细管的相变传热机理为液膜的导热和表面蒸发;表面蒸发受蒸汽温度、汽液界面的温度以及汽液压力差的共同控制。汽液流动机理为流动受脱离压力梯度、毛细力梯度支配。汽液相互作用机理为存在由于蒸发导致的动量转移切应力和由于汽液流速不同产生的摩擦切应力。提出的物理模型中较为全面地考虑了毛细管内传热、汽液流动及其相互作用。对毛细管半径和传热功率对薄液膜轮廓和传热特性影响程度的计算结果表明,随着毛细管半径的减小、传热功率的增大,蒸发界面区的长度会有所减小,这是针对微小空间得出的不同于常规情况的结论。     

Experimental investigation on thermal-hydraulic characteristics of a tube equipped with modified vortex-generator inserts

The heat transfer, pressure drop, and overall performance specification of a straight circular tube fitted with vortex-generator inserts are investigated experimentally. To modify the thermal-hydraulic performance, the longitudinal spacing of winglets is varied along the flow direction. The experiments are performed in the turbulent regime (7,470 ≤ Re ≤ 18,670). Good agreement is obtained when the results are compared and validated with previous correlations proposed for the plain tube. The results show that the use of vortex-generator inserts inside the tube yields a higher heat transfer coefficient and pressure drop than the plain tube, and these parameters augment with increasing the number of winglets. The effect of variation of longitudinal spacing of winglets along the vortex-generator inserts on the heat transfer coefficient is higher that the pressure drop. It is also detected that the variation of this parameter affects each arrangement of winglets exclusively.     

三维内肋管内插入螺旋扭带的强化传热实验

本文分别以水和乙二醇为工质，在Ｒｅ数范围为：６００～４００００，Ｐｒ数范围为：５．５～１１０之间，对四根分别插入三种不同扭率螺旋扭带的三维内助管内的换热和流阻特性进行了实验研究。结果表明：三维内肋管内加装扭带的强化传热技术适用于低Ｒｅ数下高Ｐｒ数工质的管内对流换热强化。根据实验值得到了流阻和换热关联式。     

R134a过热蒸汽在三维内微肋管内的凝结换热特性

本文对三维内微肋管内进口区段R134a过热蒸汽的凝结换热过程进行了实验研究。结果表明;微肋管内过热蒸汽过热度降低的速率明显高于光管,且主要受质量流率和管望过冷度的影响.本文得到的过热蒸汽凝结换热计算式与实验的偏差在±15％以内。     

Heat transfer behaviour of nanofluids in a uniformly heated circular tube fitted with helical inserts in laminar flow

The CFD simulation of heat transfer characteristics of a nanofluid in a circular tube fitted with helical twist inserts under constant heat flux has been explained using Fluent version 6.3.26 in laminar flow. Al₂O₃ nanoparticles in water of 0.5%, 1.0% and 1.5% concentrations and helical twist inserts of twist ratios 2.93, 3.91 and 4.89 has been used for the simulation. All thermophysical properties of nanofluids are temperature dependent. The heat transfer enhancement increases with Reynolds number and decreases with twist ratio with maximum for the twist ratio 2.93. By comparing the heat transfer rates of water and nanofluids, the increase in Nusselt number is 5%–31% for different helical inserts and different volume concentrations. The maximum heat transfer enhancement is 31.29% for helical insert of twist ratio 2.93 and for the volume concentration of 1.5% corresponding to the Reynolds number of 2039. The data obtained by simulation match with the literature value of water with the discrepancy of less than ±10% for plain tube and tube fitted with helical tape inserts for Nusselt number.     

扁平管外蛇形翅片空间的流动换热性能数值模拟

扁平管外纤焊蛇形翅片是直接空冷凝汽器翅片管的一种常见形式,研究扁平管外蛇行翅片空间的空气流速和温度分布规律,对指导直接空冷凝汽器的设计和运行具有重要意义.针对不同空冷凝汽器管束夹角、不同空气温度以及不同空气入口流速,分别对空气侧流场和温度场进行了数值模拟,得到了空冷器外流场和温度场,以及对流换热Nu和摩擦系数f随Re和空冷器夹角的变化规律.数值模拟结果表明,不同的空冷器管束夹角显著影响其流动和换热特性,夹角越大,凝汽器空冷效果越好.     

Experimental investigation of heat transfer and friction coefficient of the water/graphene oxide nanofluid in a pipe containing twisted tape inserts under air cross-flow

The water/graphene oxide nanofluid effect in a pipe equipped by twisted tape inserts under air cross-flow is investigated and the optimal tape geometry is determined. The range of internal and external Reynolds numbers are: 3800<Re_o<21500 and 550<Re_i<2000. Heat transfer and pressure drop increase by increasing Re and inserts width and heat transfer performance coefficient increased up to 1.4, indicating enhanced heat transfer compared to undesirable pressure drop. On the other hand, the heat transfer coefficient is 26% higher when compared with water in a plain tube. According to the results, this method is a good alternative in heat exchangers.     

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．     

Heat Transfer and Pressure Drop Characteristics in Turbulent Flow Through a Tube

An experimental investigation has been carried out for turbulent flow through a tube with perforated strip inserts. Strips were of mild steels with circular holes of different diameters. Flow varies, with ranging Reynolds numbers from 15,000 to 47,000. Air velocity, tube wall temperatures, and pressure drops were measured for a plain and strip-inserted tube. The heat transfer coefficient and friction factor were found to be 2.80 times and 1.8 times, respectively, that of the plain tube. The heat transfer performance was evaluated and found to be 2.3 times that of the plain tube based on constant blower power.     

Experimental evaluation of friction factor and heat transfer enhancement of twisted tape inserts using TiO<Subscript>2</Subscript>–water nanofluids

This paper studies the experimental evaluation of TiO₂ nanofluids in enhancing the heat transfer rate and friction factor on a micro-finned tube fitted with twisted tape inserts. Results show that the enhancement in heat transfer and pumping power completely depends on the concentration ratio of nanoparticles, pitch ratio and the type of pitch. Comparisons were made with the previous study with different operating parameters such as twist ratio and twist type. Viscosity of nanofluid increases with an increase in the concentration, which leads to increased pressure drop and pumping power. For the Reynolds number (Re = 4000), the maximum performance ratio was found as 2.1, 2, for concentration of 0.1 and 0.05, respectively. The addition of microfin arrangement inside the circular tube enhanced the performance ratio with minimum concentration of TiO₂ nanofluid.     

组合式发动机进气道的冷却研究

针对空天飞机组合发动机进气道的冷却要求，采用冲击－对流复合冷却技术对进气道进行强化冷却试验，按照得出的冷却结构各部分传热经验公式，用温度200K，压力1MPa低温氢作冷却剂，算出进气道的冷却热流密度，证明所用结构可以满足进气道冷却要求。