Heat Transfer in a Tube Fitted with Vertical and Horizontal Wing-Cut Twisted Tapes

This article reports an experimental investigation on the heat transfer, friction factor, and thermal enhancement factor of a tube equipped with vertical wing-cut twisted tapes, horizontal wing-cut twisted tapes, and plain twisted tapes with twist ratios of y = 2.0, 4.4, and 6.0. The obtained results reveal that the heat transfer rate, friction factor, and thermal enhancement factor in the tube equipped with horizontal wing-cut twisted tapes are significantly higher than those in the tube fitted with vertical wing-cut twisted tapes, plain twisted tapes, and a plain tube. An empirical correlation is subsequently derived from the experimental results.     

Laminar Heat Transfer Augmentation through A Square Duct and Circular Tube Fitted with Twisted Tapes

Experimental studies on friction factor and heat transfer characteristics for the laminar flow of ethylene glycol in a square duct fitted with twisted tapes of different twist ratios under nearly uniform wall temperature conditions are reported in this article. The Nusselt numbers were found to be 5.44–7.49 and 2.46–4.87 times that of plain square duct forced convection values based on constant flow rate and constant pumping power criteria, respectively, for y = 2.66. The augmented friction factor and Nusselt number for a square duct is about 1.9 and 2.10 times higher than that for an augmented circular tube.     

Thermal Performance Evaluation of Heat Exchanger Tubes Equipped with Coupling Twisted Tapes

The present work has been conducted to investigate the effect of coupling twisted tapes on heat transfer enhancement in a heat exchanger. The effects of (1) twisted tape orientation (co-coupling twisted tapes or counter-coupling twisted tapes), (2) width ratio, and (3) twist ratio were also examined. Results of coupling twisted tapes were also compared to those of a typical twisted tape. Experimental results showed that the use of counter-coupling twisted tapes resulted in higher heat transfer, friction loss, and thermal performance factor than that of co-coupling twisted tapes and typical twisted tapes. Thermal performance factor increased as twist ratio and Reynolds number decreased while width ratio increased.     

内置螺旋片的强化传热管的数值模拟研究

本文采用数值计算的方法,以水为流动介质,对内置螺旋片的强化传热管进行流动与传热特性的分析.结果表明,在管内插入螺旋片可以有效提高换热与流动的综合性能,雷诺数Re在300O～12000之间时,其PEC值在1.60～2.40之间.     

Numerical Simulation Study on Flow Laws and Heat Transfer of Gas Hydrate in the Spiral Flow Pipeline with Long Twisted Band

The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3–4 times farther than that of the straight flow.     

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,...     

Experiments on New Arrangements of Convex and Concave Corrugated Tubes through a Double-pipe Heat Exchanger

The main scope of this article paper is to experimentally clarify the effects of outer-tube and inner-tube corrugations on thermal and frictional characteristics in a horizontal double-pipe heat exchanger. Nusselt number, friction factor, and thermal performance factor are evaluated for new various arrangements of convex and concave corrugated tubes. Smooth tubes were corrugated by means of a special machine. Findings indicate that the arrangement type of corrugated tubes has a significant effect on the mentioned parameters. The best performance was obtained for a heat exchanger made of a concave corrugated outer tube and a convex corrugated inner tube.     

Heat Transfer and Pressure Drop Characteristics of Graphene Oxide/Water Nanofluid in a Circular Tube Fitted with Wire Coil Insert

In this work, heat transfer and pressure drop characteristics of graphene oxide/water nanofluid flow through a circular tube having a wire coil insert were studied. The required graphene oxide was synthesized via the Hummer method and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (SRD), and scanning electron microscope (SEM) methods. Dispersing graphene oxide in the water, nanofluids with 0.02, 0.07, and 0.12% volume fraction were prepared. An experimental set-up was designed and made to investigate the heat transfer performance and pressure loss of nanofluids. All experiments were carried out in the constant heat flux at tube wall conditions. The volumetric flow rates of the nanofluid were adjusted at 6, 8, and 10 L/min. Thermal conductivity, specific heat, density, and viscosity as thermophysical properties of the nanofluid were calculated using graphene oxide and water properties at the average temperature via appropriate relations. These properties were applied to calculate the convective heat transfer coefficient, Nusselt number, and friction factors for each experiment. Finally, the constant and exponents of Duangthongsuk and Wongwises's correlations for Nusselt number and friction factor were corrected by experimental results. The achieved experimental data have shown good agreement with those predicted. The results have shown that 0.12 vol% of graphene oxide in the water can enhance convective heat transfer coefficient by about 77%. As a result, it can be concluded that the graphene oxide/water can be used in the heat transfer devices to achieve more efficiency.     

Experimental Investigation of Local Heat Transfer in a Square Duct With Continuous and Truncated Ribs

In the present study, the turbulent heat transfer and fiction in a square duct roughened by continuous and truncated ribs on one wall has been investigated experimentally. The ribs are oriented transversely to the main stream in a periodic arrangement. For both cases, the rib height-to-hydraulic diameter ratio is 0.15, the rib pitch-to-height ratio is fixed at 12, and the Reynolds number varies from 8,000–20,000. Liquid crystal thermography is applied to demonstrate detailed distribution of heat transfer coefficient between a pair of ribs. The results show that the horseshoe vortices produced by truncated ribs are quite different from the flow structures altered by continuous ribs. It is noted that continuous ribs give higher heat transfer augmentation and pressure drop than truncated ribs. Moreover, the truncated ribs cannot be employed to eliminate hot spots which occur in the corresponding continuous types.     

大空间和毛细管内液氮池沸腾传热的实验研究

文中以直径50μm,长20mm的磷青铜丝作为加热丝和测温元件,采用控制热流密度的方式测量了0°,30°,60°和90°倾角下大空间和玻璃毛细管内液氮的沸腾曲线,分析了毛细管对核态沸腾传热的影响以及管径和倾角对临界热流密度的综合影响。结果表明,在实验管径内,毛细管对于核态沸腾传热有明显的强化作用;并存在一最佳管径,可在30°~90°倾角范围内获得最大的CHF值,并且其值高于大空间时的CHF。     

超临界CO2-丙烷混合物管内传热特性数值研究

采用SST k-w湍流模型对超临界CO₂/丙烷混合工质水平管内的传热特性进行数值模拟研究。管径d=4 mm,加热段L₂=800 mm;混合工质浓度配比为100/0、95/5、90/10、85/15、80/20、75/25;质量流速为150～250 kg·m^?2·s^?1;热流密度为30～40 kW·m^?2,入口温度293 K,入口压力7.5～30 MPa。随着丙烷浓度的增加,CO₂/丙烷二元混合工质的临界压力降低,临界温度升高,丙烷浓度从5%增加到25%,换热系数峰值降低6.19%～31.45%,但增加丙烷浓度可提高拟临界温度后的换热效果。P=7.5～8.5 MPa,换热系数有明显峰值;P=20～30 MPa,换热系数变化规律无明显峰值,并随压力的升高而减小。混合工质的换热系数随质量流速的增大而增大。同一流体温度所对应的换热系数,随着热流密度的增加而减小。     

超临界CO2-丙烷混合物管内传热特性数值研究

采用SST k-w湍流模型对超临界CO₂/丙烷混合工质水平管内的传热特性进行数值模拟研究。管径d=4 mm,加热段L₂=800 mm;混合工质浓度配比为100/0、95/5、90/10、85/15、80/20、75/25;质量流速为150～250 kg·m^?2·s^?1;热流密度为30～40 kW·m^?2,入口温度293 K,入口压力7.5～30 MPa。随着丙烷浓度的增加,CO₂/丙烷二元混合工质的临界压力降低,临界温度升高,丙烷浓度从5%增加到25%,换热系数峰值降低6.19%～31.45%,但增加丙烷浓度可提高拟临界温度后的换热效果。P=7.5～8.5 MPa,换热系数有明显峰值;P=20～30 MPa,换热系数变化规律无明显峰值,并随压力的升高而减小。混合工质的换热系数随质量流速的增大而增大。同一流体温度所对应的换热系数,随着热流密度的增加而减小。     

超临界CO2-DME混合物竖直圆管内传热特性数值研究

本文采用RNG k-ε湍流模型对超临界CO₂/DME(二甲醚)二元混合工质在竖直圆管内的传热特性进行了数值模拟研究。管径4 mm,管长为1000 mm;CO₂/DME浓度配比分别为97/3、95/5、92/8、90/10、85/15、以及70/30;质量流速为125～200 kg·m^-2.s^-1;热流密度为15～30 kW.m^-2,入口温度295～308 K,入口压力8～15 MPa。不同浓度配比的混合工质在各自临界压力下应用时,随着DME浓度的增加,换热系数的峰值逐渐减低,但在温度大于310 K时混合工质的换热系数会高于纯CO₂。压力相同时,随着DME浓度的增大,拟临界温度升高,换热系数峰值点也随之向温度升高的方向移动。混合工质的换热系数随质量流速的增大而增大。在拟临界点前,增大热流密度及降低压力对管内传热有利,而在拟临界点之后,换热系数随热流密度的升高以及压力的降低而降低。     

喷雾冷却换热机理和影响换热性能的因素

基于目前国内外相关研究结果,分析了喷雾冷却的传热特性,阐述了喷雾冷却换热机理,给出了强化方法,研究了影响换热性能的因素,并给出一些理论临界热流密度（CHF）模型。最后结合高功率激光器件的散热需求,提出了喷雾冷却的发展方向。     

喷雾冷却换热机理和影响换热性能的因素

 基于目前国内外相关研究结果,分析了喷雾冷却的传热特性,阐述了喷雾冷却换热机理,给出了强化方法,研究了影响换热性能的因素,并给出一些理论临界热流密度（CHF）模型。最后结合高功率激光器件的散热需求,提出了喷雾冷却的发展方向。     

泡沫金属对含油制冷剂管内流动沸腾换热特性的影响

实验研究了制冷剂-润滑油混合流体在内嵌泡沫金属圆管内流动沸腾的换热特性。泡沫金属为10ppi、90%孔隙率;制冷剂为R410A,润滑油为VG68,油浓度为0～5%。实验结果表明:纯制冷剂工况下,泡沫金属强化流动沸腾换热系数,换热系数提高30%～120%;含油工况下,泡沫金属只强化流动沸腾换热系数20%以下,在低质流密度或者高质流密度的高干度情况下出现恶化换热的情况。润滑油总是恶化制冷剂在内嵌泡沫金属圆管内流动沸腾的换热系数,换热系数最多恶化71%,且在低质流密度下对换热的恶化比在高质流密度工况下严重。     

叶顶单一气膜孔位置传热特性的数值研究

本文采用数值模拟的方法对凹槽叶顶前缘气膜孔的位置进行了研究,通过改变前缘第一气膜孔位置来分析叶顶区传热。数值模拟结果表明,由于冷却气对该区域没有提供足够的保护,肩壁表面的平均绝热效率远低于凹槽底面,平均传热系数远高于凹槽底面。叶顶第一气膜孔向前缘移动使肩壁表面的平均传热系数先升高再降低,叶顶前缘低绝热冷却效率区逐渐消失...     

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.     

含不同形状内热源的圆管内纳米流体自然对流及换热数值研究

采用格子玻尔兹曼方法对有三种恒温热源(圆形、三角形、方形)参与的圆管内纳米流体(铜-水)自然对流进行数值研究.主要研究瑞利(Ra)数,纳米颗粒体积分数以及热源几何形状等控制参数对纳米流体的流动与传热的影响.结果发现纳米颗粒体积分数的增加有利于强化传热,且在Ra数较小时,平均努塞尔(Nu)数增加的幅度要优于Ra数较大的情...