钎焊板式换热器传热与压降性能实验

钎焊板式换热器具有高效、紧凑、节能、节材且密封性好等特点受到许多行业的青睐.文中介绍对钎焊板式换热器进行的水-水传热性能实验和根据实验结果测得的传热系数和压降的性能曲线.     

螺旋管紧凑式换热器传热性能分析

数值模拟研究了紧凑式小管螺旋管换热器的流动换热特性.螺旋管换热器由35个单管(直管和弯管)构成,管外为空气冷却,管内流过不同温度的液体工质R141B.模拟结果表明,各单根螺旋管内外对流传热系数、温度分布和传热性能,主要受内外流体温度梯度、回流条件、外部空气流速和单根管的传热表面积等因素的影响.     

多套型套管式换热器传热与流阻性能试验研究

多管型套管式换热器是在大尺寸外管的内部布置多根仙管所构成的换热设备，与单根内管的套管式换热器相比，流量大幅增加，选用螺纹内管和管间折流板可以强化传热。对于多管型套管式换热器的传热性能试验，采用修正威尔逊法进行试验计算，得出了两种多套型套管式换热器的传热与流动阻力性能试验结果。     

流动参数对双级螺旋套管换热器传热性能的数值分析

高效热泵系统性能研究一直是热泵空调领域普遍关注的热点问题,针对设计开发的双级套管串联式热泵系统。采用3D有限容积法和可实现的k-ε模型,数值分析入口流体温度、流动速度对换热系数以及内外管努塞尔数的影响规律。结果表明,降低入口水温或者增加入口制冷剂温度能够提高整体传热性能,Nui随着水和制冷剂流率的增加有所增加,而Nuo随着水流率的增加而增加,但随着制冷剂流率则增加而减小,Nui 和Nuo都随着水温的减小或制冷剂温度的增大而增大。     

管壳式换热器壳程强化传热技术研究

介绍了管壳式换热器壳程强化传热方面所展开的研究工作及取得的成果，指出了强化传热技术的研究方向。     

修正威尔逊法在管壳式换热器传热性能试验中的应用

该文介绍了修正威尔逊法的原理及其在管壳式换热器传热性能试验中的应用,并讨论了该方法的应用条件。     

板壳式换热器传热与流动特性研究

对圆形板片板壳式换热器内的传热流动特性进行了数值模拟及实验研究。采用SOLIDWORKS软件对单个流道进行了无简化、全尺度的实体建模,采用ICEM软件进行了网格划分,采用FLUENT软件进行求解,并通过中试规模的水—水传热实验来验证模拟结果。实验样机采用与数值模拟几何结构完全相同的板片,板片数目122片。通过对比发现,在雷诺数Re为200-7 000的范围内,数值模拟结果与实验结果误差在15%以内。模拟结果可以作为该类产品工业应用中设计选型及优化的依据。     

多级并联相变管壳式换热器传热性能分析

在管壳式换热器中并联填充多级相变材料或填充单相变材料,比较两种传热装置的传热性能,分析相变材料在两种换热器的换热过程中的熔化特性、换热速率。结果显示：对于相变材料三级并联填充的换热器,相变材料完全熔化时间沿换热内管（热工质流体）轴心往外逐渐增加;在所有相变材料均完成相变之前,其三级并联相变材料的熔融前沿呈曲线状;相变材料三级并联填充的换热器的最高换热速率是单相变材料填充的1.03倍;热工质流体入口温度不变时,增加热工质流体流量可以在一定限度上增加相变材料三级并联填充的换热器的换热效率;但热工质流体流量过大会在一定限度上降低相变材料三级并联填充的换热器的换热效率。     

地下水渗流条件下埋地换热器传热性能的实验研究

建立了根据地温分布确定地下水流动特性的简化数学模型。针对一个实际工程钻孔进行了地温分布测量,并测试了局部地下水渗流条件下埋地换热器的传热性能。结果表明,上述理论模型具有较好的预测精度。在该文实验条件下,地下水渗流对埋地换热器的传热性能具有明显的强化作用,埋地换热器的换热量平均提高11.35%。     

板壳式换热器板片流动与传热性能的数值模拟

针对板壳式换热器的人字形板片建立了单流道物理模型,并利用数值模拟软件分析了其重要结构参数波纹夹角的变化引起的模型流场、速度场和温度场的变化情况,以及对其传热性能的影响。结果显示:换热板片波纹夹角的变化使得流体的流动状态发生了变化,随着波纹夹角的增大,流体的流态由十字交叉流逐渐转变为曲折流。随着波纹角度的增大,流体的扰动程度加强,湍流程度提高,与此同时,努塞尔数和传热因子增大,传热性能增强。模拟结果表明波纹夹角对板壳式换热器流动和传热性能具有较大的影响,可以成为板壳式换热器优化设计的一个重要方向。     

Heat transfer and entropy analysis for a transparent gas flowing in a tube

Heat transfer by forced convection and radiation in tubes is very important for high‐temperature heat exchangers, which find wide applications in power plants. In addition, the entropy analysis gives insight into the qualitative measure of the heat transfer processes. Consequently, in the present study, forced convection and radiation heat transfer in flow through a tube is considered. The wall and fluid sides temperature rise are predicted for different tube lengths. The entropy analysis is carried out and the influence of tube length and heat transfer coefficient on the volumetric entropy generation are examined. It is found that the wall temperature and the volumetric entropy generation increases as the tube length increases. The point of maximum volumetric entropy generation moves close to the tube inlet as the tube length increases. In addition, the maximum volumetric entropy generation becomes independent of tube length for high heat transfer coefficients. Copyright © 1999 John Wiley & Sons, Ltd.     

Numerical investigation for improved heat transfer characteristics in micro‐fin tubes

Generally, internal micro‐fin tubes are used for increasing the life and performance of electronic devices. The micro‐fins enhance the heat transfer rate by increasing the surface area with an increase of the pressure drop. In this study, heat transfer and pressure drop are analyzed by varying Reynolds number with the increase in the number of fins in tubes. Heat transfer and pressure drop, together with turbulence kinetic energy of micro‐fin tubes (helical and straight) and a smooth tube, have been evaluated for different Reynolds numbers (60 000, 40 000, 20 000, and 2000) at a constant temperature of 350 K, which clearly establishes laminar to turbulent flow. It is observed that the helical micro‐fin tube has a better result compared with the straight micro‐fin tube and smooth tube at Reynolds numbers 60 000, 40 000, and 20 000 at velocity 2, 1, and 0.5 m/s, respectively. This study is an attempt to establish a comparison of different micro‐fin geometries with varying Reynolds numbers, concluding that a high Reynolds number is suitable for the same.     

Heat transfer on peristaltically induced Walter's B fluid flow

This paper look at the effects of heat transfer on peristaltic flow of Walter's B fluid in an asymmetric channel. The regular perturbation method is used to solve the governing equations by taking the wave number as the small parameter. Expressions for stream function, temperature distribution, and heat transfer coefficient are presented in explicit form. Solutions are analyzed graphically for different values of arising parameters. It has been found that these parameters affect considerably the considered flow characteristics. Results show that with an increase in the Eckert and Prandtl numbers, the temperature and heat transfer coefficient increase. Further, the absolute value of the heat transfer coefficient increases with an increasing viscoelastic parameter. Comparison with published results for viscous fluid is also presented. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21021     

Heat transfer augmentation in 3D internally finned and microfinned helical tube

Experiments are performed to investigate the single-phase flow and flow-boiling heat transfer augmentation in 3D internally finned and micro-finned helical tubes. The tests for single-phase flow heat transfer augmentation are carried out in helical tubes with a curvature of 0.0663 and a length of 1.15 m, and the examined range of the Reynolds number varies from 1000 to 8500. Within the applied range of Reynolds number, compared with the smooth helical tube, the average heat transfer augmentation ratio for the two finned tubes is 71% and 103%, but associated with a flow resistance increase of 90% and 140%, respectively. A higher fin height gives a higher heat transfer rate and a larger friction flow resistance. The tests for flow-boiling heat transfer are carried out in 3D internally micro-finned helical tube with a curvature of 0.0605 and a length of 0.668 m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D internally micro-finned helical tube is increased by 40-120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance is increased by 18-119%, respectively.     

Heat transfer and flow characteristics of flow boiling of CO2‐oil mixtures in horizontal smooth and micro‐fin tubes

Experiments were carried out on the flow pattern, heat transfer, and pressure drop of flow boiling of pure CO₂ and CO₂‐oil mixtures in horizontal smooth and micro‐fin tubes. The smooth tube is a stainless steel tube with an inner diameter of 3.76 mm. The micro‐fin tube is a copper tube with a mean inner diameter of 3.75 mm. The experiments were carried out at mass velocities from 100 to 500 kg/(m²·s), saturation temperature of 10 °C, and the circulation ratio of lubricating oil (PAG) was from 0 to 1.0 mass%. Flow pattern observations mainly showed slug and wavy flow for the smooth tube, but annular flow for the micro‐fin tube. Compared with the flow patterns in the case of pure CO₂, an increase in frequency of slug occurrence in the slug flow region, and a decrease in the quantity of liquid at the top of the tube in the annular flow region were observed in the case of CO₂‐oil mixtures. With pure CO₂, the flow boiling heat transfer was dominated by nucleate boiling in the low vapor quality region, and the heat transfer coefficients for the micro‐fin tube were higher than those of the smooth tube. With CO₂‐oil mixtures, the flow boiling heat transfer was dominated by convective evaporation, especially in the high vapor quality region. In addition, the heat transfer coefficient decreased significantly when the oil circulation ratio was larger than 0.1 mass%. For the pressure drop characteristics, in the case of pure CO₂, the homogeneous flow model agreed with the experimental results within ±30% for the smooth tube. The pressure drops of the micro‐fin tube were 0–70% higher than those predicted with the homogeneous flow model, and the pressure drops increased for the high oil circulation ratio and high vapor quality conditions. The increases in the pressure drops were considered to be due to the increase in the thickness of the oil film and the decrease in the effective flow cross‐sectional area. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20287     

Heat Transfer Characteristics of Laminar Flow in Internally Finned Tubes under Various Boundary Conditions

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Heat transfer analysis of lateral perforated fin heat sinks

In this article fluid flow and conjugate conduction-convective heat transfer from a three-dimensional array of rectangular perforated fins with square windows that are arranged in lateral surface of fins are studied numerically. For investigation, Navier–Stokes equations and RNG based k − ε turbulent model are used. Finite volume procedure with SIMPLE algorithm is applied to coupled differential equations for both solid and gas phases. Computations are carried out for Reynolds numbers of 2000–5000 based on the fin thickness and Pr = 0.71. Numerical model is first validated with previous experimental studies and good agreement were observed. Based on a valid numerical model, numerical solution is made to find fluid flow and temperature distribution for various arrangements. For each type, fin efficiency of perforated fins is determined and compared with the equivalent solid fin. Results show that new perforated fins have higher total heat transfer and considerable weight reduction in comparison with solid fins.     

三维微肋螺旋管内R134a沸腾环状流区的传热与关联式

首次实验研究了制冷剂R134a在三维微肋螺旋管内流动沸腾环状流区的流动与传热性能。对流型的可视化观察发现：当质量流速大于100kg／(m^2s)时。螺旋管内才开始出现环状流。环状流的起始干度为0．3、0．4。在流型图上给出了环状流区与其它主要流型的分区。回归了实验环状流区的传热实验数据，得到的传热关联武计算值与实验值的平均绝对误差为9．1％。     

Heat transfer in channel flow around a rectangular cylinder

Heat transfer and flow visualization experiments have been made in a channel with a rectangular cylindrical section having various width-to-height ratios. Vortices were observed to shed periodically from the cylinder and then reattach to the channel wall. This reattachment of the vortices induces a periodic fluctuation in heat flux at the wall and enhances the heat transfer in the downstream region of the cylinder. The streamwise position of the maximum Nusselt number moves downstream with decreasing width-to-height ratio, b/h, of the cylinder. When b/h = 2.0, however, the heat flux periodicity disappears because the wake narrows intermittently owing to reattachment of the separated flows to the upper and lower surfaces of the cylinder. © 1998 Scripta Technica. Heat Trans Jpn Res, 27(1): 84–97, 1998     

Heat transfer augmentation in a helical-ribbed tube with double twisted tape inserts

Turbulent convective heat transfer characteristics in a helical-ribbed tube fitted with twin twisted tapes have been investigated experimentally. The experiment was carried out in a double tube heat exchanger using the helical-ribbed tube having a single rib-height to tube-diameter ratio, e/D_H = 0.06 and rib-pitch to diameter ratio, P/D_H = 0.27 as the tested section. The insertion of the double twisted tapes with twist ratio, Y, in the range of 2.17 to 9.39 is to create vortex flows inside the tube. The inserted ribbed tube is arranged in similar directions of the helical swirl of the twisted tape and the helical rib motion of the tube (called co-swirl). Effects of the co-swirl motion of the ribbed tube and the double twisted tapes with various twist ratios on heat transfer and friction characteristics are examined. The results obtained from the ribbed tube and the twin twisted tape insert are compared with those from the smooth tube and the ribbed tube acting alone. The experimental results reveal that the co-swirling inserted tube performs much better than the ribbed/smooth tube alone at a similar operating condition. The co-swirl tube at Y ≈ 8 yields the highest thermal performance at lower Reynolds number (Re). In addition, the correlations of Nusselt number and friction factor as functions of Re, Pr and Y are also proposed.