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This article presents an investigation on heat transfer enhancement in a round tube inserted with a helically twisted tape. The effects of a helically twisted tape with alternate axis (HTT-A) on heat transfer, friction factor, and thermal performance factor behaviours are reported for the turbulent regime. HTT-A geometries are tape pitch to tube diameter, P/D = 1.0, 1.5, and 2.0; alternate length to pitch length, l/P = 1.0, 1.5, and 2.0; twisted length to tape width, y/W = 3.0; and tape width to tube diameter, w/D = 0.2. The experiment has been performed by varying the volumetric air flow rate in order to adjust Reynolds number ranging from 6 000 to 20 000. The wall of the testing tube is uniformly heated as a constant heat flux while the tests are covered with thermal insulations to reduce heat loss to surroundings. Thermal performance is evaluated by comparing the present experimental results with the results of the modified HTT-A and also those obtained from previous study (conventional helically twisted tape, HTT). The thermal performance of tested tube with HTT-A is evaluated to obtain the degree of heat transfer enhancement and friction factor induced by HTT-A with respect to the plain tube under the same test conditions. Evenly, it is interesting to observe that the tube with HTT-A consistently possesses higher heat transfer and thermal performance factor than those with the HTT around 14.1% and 1.9%, respectively. The HTT-A with the smaller pitch ratio and adjacent twist length provides higher heat transfer rate and friction factor than the one with larger pitch ratio and alternate length as a result of a larger contact surface area, stronger swirl intensity and, thus, better fluid mixing near the tube wall. In the range determined, the tubes with the largest pitch ratio (P/D = 2.0) and smallest alternate length (l/P = 1.0) give the highest thermal performance factor at around 1.35. In addition, the empirical correlations of the Nusselt number, friction factor, and thermal performance factor are also described. 相似文献
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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. 相似文献
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This article communicates the thermal performance, heat transfer rate, and friction factor of Al2O3/DI water nanofluids at different concentrations in a micro-finned tube with tube helical inserts for different twist ratios. The thermal performance, heat transfer coefficient, and friction of the present study is also compared with a plain tube for validation. From the study, it is identified that the micro-finned tube with tube insert performance is higher as compared with a plain tube. Similarly, an empirical relation for Nusselt number (Nu) and friction factor (f) is estimated for straight twisted tube and left-right combination. The deviation between experimental and theoretical values for left-right twist and straight twist is found as 3 and 7% for Nusselt number and 7 and 9% for friction factor, respectively. Similarly, while analyzing the thermal performance, it was found that the maximum performance achieved was with a micro-fin tube with left-right twist with nanofluid concentration of 0.2%. 相似文献
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小通道扁管内纳米流体流动与传热特性 总被引:2,自引:0,他引:2
建立了测量小通道扁管内纳米流体流动与对流换热性能的实验系统,测量了不同粒子体积份额的水-Cu纳米 流体的管内对流换热系数和摩擦阻力系数,实验结果表明,在相同雷诺数条件下,小通道扁管内纳米流体的对流换热系数 大于纯液体,且随粒子的体积份额的增加而增大,而纳米流体的阻力系数并未明显增大。 相似文献
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M. M. K. Bhuiya J. U. Ahamed M. A. R. Sarkar B. Salam H. H. Masjuki M. A. Kalam 《实验传热》2013,26(4):301-322
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. 相似文献
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Experiments are undertaken on the isotope separation by DC discharge through a narrow capillary of gaseous neon, argon and krypton of natural isotopic abundance. It is confirmed that the heavier isotopes become enriched in the region of cathode, and the lighter isotopes in that of anode. The effect on the obtainable separation factor brought by differences in experimental conditions is examined by changing the capillary tube diameter, tube length, discharge current and discharge pressure. The separation factor improves with increasing the tube length and the discharge current, and with decreasing the discharge pressure and the tube diameter. Ion density and electron temperature are measured in the positive column to compare the present experimental results with existing theories. The order of the isotope enrichment factor is well explained by the theory of the ion diffusive friction force onto isotopically different neutral molecules, together with the theory of the ionization degree of the different isotopic species. 相似文献
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本文利用传热传质之间的比拟关系研究了错排环布圆管换热板芯的平均传热特性及阻力特性。实验中我们采用了三种翅片间距(Tp)、三种管排数(Nrow)以及三种管数(Ntube)组成的27种板芯结构,传质实验采用萘升华的方法来进行。然后通过三种限制条件对不同翅片间距、不同管排数和不同管数下的换热板芯的传热性能进行了比较。最后利用最小二乘法得出了具有工程指导意义的准则关联式。 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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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. 相似文献
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D. Magesh Babu P. K. Nagarajan B. Madhu S. Ravishankar 《Journal of Engineering Thermophysics》2017,26(4):567-579
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. 相似文献
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ABSTRACTPresent study investigates the heat transfer and friction characteristics of heat exchanger tube fitted with perforated twisted tape (PTT) insert having V cuts. A copper tube of 1 m length and 0.032 m inner diameter is used as test section to collect the experimental data by varying the twist ratio of PTT from 2 to 6 for the Reynolds number range of 2,700–23,400. V cuts are introduced in the PTT and the V-cut relative pitch ratio is varied from 1 to 2. The maximum thermo-hydraulic performance parameter is found to be 1.58. 相似文献
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Experimental investigations had been conducted to study the forced convective heat transfer and pressure drop characteristics of the hydrodynamic fully developed turbulent flow in horizontal equilateral triangular ducts fabricated with Ike same length and hydraulic diameter but different surface roughness of 1.2, 3.0, and 11.5 μm. The experiments were performed with hydraulic diameter-based Reynolds number ranging from 7,000 to 20,000. The entire inner wall of the duct was heated uniformly, while the outer surface was thermally insulated. It was found that the variation of Stanton number (St) with friction factor (f) can be expressed by a relationship of St = C * f, where the constant (C) increases from 0.41 to 0.50 when the surface roughness is increased from 1,2 to 11.5 μm. It was also concluded that the duct with a higher surface roughness will have better heat transfer performance. Nondimensional expressions for the determination of the heat transfer coefficient and friction factor of the equilateral triangular ducts with different surface roughness were also developed. 相似文献