微细管内气体流动特性实验研究及影响因素分析

实验研究了直径范围50-200 μm微细光滑圆管及粗糙管内气体阻力特性。结果表明所研究光滑微细管内阻力特性与常规管基本符合,从层流到素流的转捩Re也未明显提前,而粗糙管阻力要远大于理论值。由于尺度效应,一些非常规因素对微尺度流动将产生明显影响。综合前人研究结果,对影响微尺度阻力特性研究结果的相关因素进行了探讨。     

壁面轴向导热对微细管内对流换热的影响

本文通过数值解析的方法研究了考虑壁面轴向导热时微细管内的对流换热。结果表明,当管外为对流换热边界条件时,管内充分发展对流换热的Nu依然在3.66～4.36之间。但若忽略壁面轴向导热,采用一维热阻模型整理微细管内对流换热的实验数据将会导致错误的结论。     

蒸气在倾斜细小直径圆管内的流动凝结换热特性

细小管内的流动凝结换热具有许多超常换热特性,经典的Ｎｕｓｓｅｌｔ分析方法已不能满足需要。在以往研究的基础上,本文进一步通过实验探析换热温差和蒸气流量对不同直径的细小管内流动凝结换热的影响。研究表明,管径越小,换热温差对凝结换热系数的影响程度越低;通过流量和倾角对凝结换热数的影响,分析了重力引发的流动分层和剪切力对凝结液的排除两种因素对细管传热强化的作用机制。本文的实验结果和用于常规尺度下的通用关联式对比表明,采用细管,管内的流动凝结换热得到无可置疑的强化     

基于微通道的热泵空调应用基础研究

微通道换热器具有集成度高、换热效率高及成本低等特点,本文归纳微通道换热器应用于热泵空调时制冷剂充注量、系统COP等性能参数,并与传统热泵空调进行对比,同时还就热泵空调应用微通道时空气侧的阻力与传热的影响因素进行了分析讨论。结果表明,将微通道换热器替代常规换热器,其换热系数及系统COP均有大幅度提升,且缩减了制冷剂充注量,因此将微通道换热器替代常规尺度换热器对于节能降耗意义十分重大。     

圆管内熔融盐强迫对流换热的实验研究

为了验证现有的经典对流换热关联式是否仍然适用于高温熔融盐管内强迫对流的换热规律,搭建了熔融盐传热蓄热循环实验台进行实验研究.实验台系统已经在实验室安全成功运行了上千小时,实验中,设计了熔融盐-导热油换热器,通过测量熔融盐进出口温降和导热油进出口温升得到了换热器的总传热效率,然后利用最小二乘法对管内熔融盐对流换热系数进行分离,拟合出了熔融盐管内过渡流和充分发展紊流的实验关联式.通过和经典的传热关联式进行比较发现,熔融盐管内强迫对流换热特性仍然适用于Sieder-Tate方程,Petukhov方程,Hausen方程以及Gnielinski方程.     

螺旋槽管换热器管内流动和换热特性的实验研究

以水为介质,对螺旋槽管管内流体的流动特性、换热特性进行了实验研究。分析了流速、温度对流动特性,换热特性的影响。在该实验研究中,进行了实验测得摩擦压降与经典公式拟合得出的计算结果误差分析,验证了实验结果的准确度;进行了Nu的值与迪图斯-贝尔特公式拟合得出的计算结果误差分析,验证了实验结果的准确度;提出了预测套管式换热器热工性能的新方法。螺旋管换热器在管内流体Re范围为41000-58000时,换热器的热工性能较好。     

低温发电用翅片管换热器传热特性的数值模拟分析

为了深入研究低温余热发电系统用翅片管换热器的传热特性,文中建立了翅片管换热器计算模型,对工质R123在翅片管换热器内的传热性能进行数值模拟,比较管内工质R123在不同流速与温度时的换热特性,利用最小二乘法原理,对烟气侧和工质侧的换热关联式进行了拟合,得到了二者的换热准则方程,此外,利用实验方法对模拟结果进行验证。     

伴随有水蒸气凝结的烟气对流换热的实验研究

本文通过实验研究了冷凝式燃气热水器中烟气伴随有水蒸气凝结的受迫对流换热过程。着重介绍实验系统、测试方法和对塔板式换热器和肋片板式换热器的实验研究结果。实验表明,有水蒸气凝结时的烟气对流换热系数远大于无凝结时的换热系数,可提高数倍。在冷凝式换热器中,塔板式换热器的换热系数大于肋片板式换热器。     

双壳程连续螺旋折流板换热器的数值模拟

本文提出了一种新型的双壳程连续螺旋折流板换热器。采用数值模拟方法对双壳程、单壳程连续螺折流板换热器,以及弓形折流板换热器壳侧流动与传热持性进行了对比研究。结果表明,同质量流量和对流换热系数近似相等的情况下,双壳程连续螺旋折流板换热器壳程压降比弓形折流板换热器低17.7%～23.5%,同质量流量和壳程压降近似相等的情况下,其对流换热系数比单壳程连续螺旋折流板换热器高7.1%～12.6%。     

微细管内超临界二氧化碳冷却换热研究

本文对超临界二氧化碳在微细管内冷却对流换热进行数值模拟研究,分析不同流动方向和管径大小对超临界二氧化碳对流换热的影响,考察管内局部流体温度、管壁温度以及无量纲温度分布的变化。湍流模型采用低雷诺数YS模型。研究表明,在LPV范围比较大的截面,超临界二氧化碳局部换热系数达到最大值,同时管内传热受流动方向和管径的影响均较大。     

油基钻屑螺纹推进式换热器流动传热特性

对油基钻屑在螺纹推进式换热器内的流动换热过程进行了数值模拟,研究了螺杆转速、油基钻屑雷诺数Re和螺纹截面形状对流动换热的影响。结果表明:随着螺杆转速增加,传热系数、油基钻屑出口温度均增大;同时发现,当雷诺数Re<250时,壳侧Nusselt数随雷诺数Re增大而迅速增大,此后雷诺数对Nusselt数影响较小;Nusselt数随曲率比d_i/D增大而增大。为方便工程设计,利用数值结果给出了油基钻屑的流动换热关系式。     

Heat Transfer Characteristics in a Double-Pipe Heat Exchanger Equipped with Coiled Circular Wires

An experimental investigation has been carried out to study the enhancement in heat transfer coefficient by inserting coiled wire around the outer surface of the inner tube of the double-pipe heat exchanger. Insulated wires, with a circular cross-section of 2 mm diameter, forming a coil of different pitches (p = 6, 12, and 20 mm), were used as turbulators. The investigation is performed for turbulent water flow in a double-pipe heat exchanger with cold water in the annulus space for both parallel and counter flows. The experiments were performed for Reynolds numbers ranging from 4,000 to 14,000. The experimental results reveal that the use of coiled circular wires leads to a considerable increase in heat transfer coefficients compared with a smooth wall tube for both parallel and counter water flows. The mean Nusselt number increases with Reynolds number and pitch. The convective heat transfer coefficient for a turbulent water flow increases for all coiled wire pitches, with the highest enhancement of about 450% for counter flow and 400% for the parallel flow. New correlations for mean relative Nusselt numbers at different coiled wire pitches are provided.     

采用铜铝复合管的翅片管换热器性能试验研究

针对铜铝复合管(ACC管)在空调用翅片管换热器中替代铜管应用进行了试验研究。分别对Ф7.94mm型管的全铜管、过冷段铜铝复合管、全铜铝复合管三种换热器进行了性能比较和成本分析。研究结果表明,在风速和风量不变的情况下,过冷段铜铝复合管换热器能力为8634.22W,高于全铜铝复合管的换热器的8389.36W,低于全铜管换热器的8989.07W。制冷剂侧能力测试中,过冷段铜铝复合管换热器平均值为8.885kW,与全铜铝复合管换热器平均值8.775kW相比高1.24%,与全铜管换热器平均值9.101kW相比低2.37%,与能力测试结果基本一致。与原换热器铜管相比,在相同条件下,铜铝复合管可以降低管材成本29.5%。综上所述,过冷段采用铜铝复合管的换热器能够取代铜管换热器应用在空调中,在不影响其换热性能的基础上,降低成本效果明显。     

周向重叠三分螺旋折流板换热器壳侧性能试验研究

对倾斜角为20°、24°、28°和32°的单头以及32°的双头周向重叠三分螺旋折流板换热器和弓形折流板换热器的传热和压降性能进行了测试,换热器采用公共壳体和可更换管芯结构。采用壳侧轴向雷诺数和轴向欧拉数分别作为反映壳侧流量和阻力系数的无因次参数。试验结果显示在试验范围内周向重叠三分螺旋折流板换热器壳侧换热系数、壳侧压降和综合性能指标都随着倾斜角增大而减小;倾斜角20°方案的性能指标最佳,其平均壳侧努塞尔数和轴向欧拉数与弓形折流板方案的数值之比分别为1.123和0.45;双头螺旋折流板方案的换热系数和压降都大于同样倾斜角的单头螺旋折流板方案,但两者的综合性能较接近。     

Performance of shell-and-dimpled-tube heat exchangers for waste heat recovery

This paper presents an experimental study of waste heat recovery shell-and-tube heat exchangers. The exchanger heat duty, overall heat transfer coefficient, effectiveness and tubeside friction factor are investigated as functions of the tube surface geometry (plain or dimpled), the flow type (counter or parallel), the tube Reynolds number and the shellside heat capacity rate. Water and the exhaust gases of a Diesel engine are passed inside the tube and the shell, respectively.The heat transfer characteristics increase with an increase in tube Reynolds number and the shellside heat capacity rate, for all the flow types and the surface geometries examined. The counter-flow, shell-and-dimpled-tube heat exchanger, compared with that exchanger having a plain tube, increases the heat duty and the overall heat transfer coefficient by 80%, and the heat exchanger -effectiveness increases by 35%. For the parallel-flow, shell-and-dimpled-tube heat exchanger, the heat duty, the overall heat transfer coefficient and the effectiveness increase by 30, 55, and 25%, respectively. At the same time the dimpled tube increases the tubeside friction factor by 600% over that of the plain tube. The rate of waste heat recovered from the exhaust gases of the Diesel engine by the counter-flow, shell-and-dimpled-tube heat exchanger is equal to 10% of the maximum brake power of the engine running at 1500 rpm, and the tube Reynolds number equal to 8875.     

流向对管束外混合对流影响的数值模拟

用格子玻尔兹曼方法对微圆管管束外混合对流的换热情况进行了数值模拟研究。在充分验证程序正确性的基础上,对混合流动绕流时不同壳侧进液角度,不同雷诺数Re以及瑞利数Ra等方面对传热的影响进行模拟研究,对衡量传热效果的Nu数及温度场进行了对比,总结出了换热规律。为高效微管换热器的开发提供了理论指导。     

Study on Heat Transfer Performance of Skin Heat Exchanger

Cooling technology is facing new challenges with the increase of electronic equipment power onboard aircraft. The traditional heat sink based on high-altitude bleed air does not satisfy this increase of cooling demands. In this article, an air/air-type skin heat exchanger is studied for cooling aircraft electronic equipment. It uses outside high-altitude cold air rather than bleed air as a heat sink. This cooling technology can effectively remove the heat load of high-power electronic devices without greatly increasing aircraft performance penalty. To assess its high-altitude heat transfer performance, an experimental prototype was designed and made. Some experiments were conducted on a ground experimental test. The heat transfer criteria formulas were obtained for both the side air in the skin heat exchanger and its convective heat transfer coefficients. Based on these experimental analyses, the heat transfer performances of the skin heat exchanger in a high-altitude cruise condition are deduced when it is assumed to be installed at an unfavorable position and a favorable position, separately. This work tries to provide a technical support for its future onboard application.     

非均匀热流边界条件下螺旋管内换热特性

对均匀和非均匀热流边界条件下螺旋管内湍流换热进行了数值模拟,结果表明:当螺旋管表面加热功率一定时,相同Re数下均匀热流边界条件时螺旋管截面周向局部Nu数高于非均匀热流边界条件;非均匀热流边界下充分发展段的平均Nu数小于均匀热流边界;相同的De数下,曲率较小的螺旋管换热系数大。     

POD方法在扁管管翅式换热器研究中的应用

针对复杂流动与传热现象的扁管管翅式换热器板芯结构构建特征正交分解（POD）低阶模型,数值分析不同参数组合的传热特性并与有限容积法（FVM）计算结果进行比对.结果表明：POD计算结果与FVM计算结果间的相对偏差平均值在5.25%以内,但计算速度比FVM提高了164.78~2 021倍.所得结论对于扁管管翅式换热器结构参数设计和运行优化有理论参考价值.     

热交换器表面镀层对传热性能的影响

采用化学镀的方法对热交换器表面进行表面改性,使其换热表面沉积一层表面能不同的均匀镀层。传热实验表明,随着磷含量的增大,凝结传热系数增大。进一步可视化实验研究表明,镀层换热表面均表现为珠膜共存状态,增大镀层的磷含量,换热表面促进珠状凝结的效果更加明显。这归于镀层降低了传热表面的表面能值。