共查询到19条相似文献,搜索用时 171 毫秒
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提出一种新型的正反两个方向交替扭转的扭带模型,并基于ANSYS FLUENT软件在层流状态下(Re=400~18 00)对换热管中插入新型扭带的换热特性、流体阻力特性和综合性能指标进行数值模拟研究。对y=3.0,4.5,6.0三种扭率下的无缺口正反扭转扭带与传统单一方向扭带进行对比研究,并对扭率y=3.0的无缺口正反扭转扭带和带有三角、半圆及方形缺口的正反扭转扭带进行了对比计算。研究结果表明:插入不同扭率的扭带,换热管的努赛尔数Nu、摩擦系数f与综合性能PEC值均随着扭率的减小而增大;相同扭率下无缺口的正反扭转扭带在强化换热效果和综合性能表现上要优于传统扭带;扭率为3.0时,无缺口的正反扭转扭带比带三种缺口的正反扭转扭带换热效果好,而缺口的存在可以大幅度地降低插入扭带产生的摩擦阻力,且缺口的面积越大,摩擦和换热效果降低越多。 相似文献
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为了研究纳米流体在内置扭带外螺纹管内的流动与传热特性,在Re(雷诺数)为2 000~12 000的范围内,分别对质量分数为0.1%、0.2%、0.3%、0.4%、0.5%和0.6%的Cu、Al、A1_2O3、Fe_2O_3、多壁碳纳米管和石墨纳米流体在内置扭带外螺纹管内的流动与对流换热特性进行了实验研究。实验结果表明:在相同Re下不同纳米流体都存在最佳浓度比0.5%,其中Cu-水纳米流体的换热性能最好但是摩擦阻力较大,石墨的换热性能和摩擦阻力方面的综合性能最好。内置扭带外螺纹管较光管在换热性能方面提高了50.32%,但摩擦阻力系数也相应增加。根据实验数据对热性能系数进行了综合分析,得到了石墨纳米流体内置扭带外螺纹管对流换热以及摩擦阻力系数关联式,其计算值和实验值有较好的吻合度。 相似文献
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光管内插入扭带传热与流动阻力的试验研究 总被引:3,自引:1,他引:2
为了研究管内强化换热技术,对三根不同结构参数的扭带插入光管的换热特性和流体动力学特性进行了试验研究。试验以空气为工质,Re在8000~10^5之间,管外被水冷却。对大量实验数据用多元线性回归法得到了具有较高精度的扭带管的传热系数和摩擦系数的统计关联式,分析了扭带管的传热与流阻性能,为换热器的设计及改造提供了理论依据。 相似文献
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数值研究了空气在内置异形等间距扭带管内的传热与流阻特性,对模拟结果进行了实验验证,然后分析了结构对空气传热与流阻特性的影响;进一步通过对局部流场、温度场和绝对涡量的分析,揭示了其强化传热机制。结果表明:模型与实验值吻合较好,最大相对偏差约为8%,在大多数Re(雷诺数)范围内,异形等间距扭带相对传统等间距扭带提高了空气传热综合性能,在Re 10 000~20 000范围内,最大传热综合性能约为1.08,交错布置的等间距扭带对传热综合性能的提升没有其它等间距扭带明显。等间距扭带能够强化空气传热主要在于通过诱导二次流,加强了近壁区流体与主流区流体的置换程度,均化了流场,并且能够以自旋流的形式在下游维持较长的距离。 相似文献
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具有传热强化功能的自转螺旋扭带清洗防垢技术发展较快。应用激光测速仪LDV(Laser Doppler Velocimeter)实验研究自转清洗扭带管内流体的湍流特性。结果表明:在自转扭带竹带动下,管内流体的流动结构发生了反常态的变化。在近管壁环形区域内流体的轴向分速度明显比管中心区域的高,轴向湍流度比无白转扭带时大;切向分速度随半径的增大而增大,并且存在很大的径向湍流度。这些结果初步说明了自转螺旋扭带管对流传热强化的机理是:管内由扭带带动形成的强制旋流和轴向平行流叠加而形成的螺旋流动,以及近管壁环形区域内流速的增大,不仅加强了边界层流体的扰动以及边界层流体与主流流体的混合,并且使边界层厚度减簿,从而才使管内的对流传热得以强化。本文试验研究的结果为自转螺旋扭带管内对流传热强化机理的深入理论研究提供实验基础。 相似文献
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本文提出将一种正反扭转且带有双排半圆切口的新型扭带用在套管式换热器上在层流条件下对换热器其换热性能和流动特性进行实验研究并分析这种扭带的综合性能。实验工质为水,Re(雷诺数)变化范围为540~1 440。本实验采用4种不同长度扭带做对比,4种分别是全长、3/4长、半长和1/4长扭带。结果显示,插入全长、3/4长、半长和1/4长扭带的换热Nu(努塞尔数)分别是光管的1.92~3.80,1.69~3.20,1.60~2.62和1.48~2.23倍;f(摩擦阻力系数)分别是光管的3.69~6.30,3.30~5.51,2.72~4.67,2.33~3.55倍;对应的PEC(综合性能指标)分别为1.24~2.06,1.14~1.81,1.15~1.57和1.11~1.47。插入全长扭带在实验范围内达到了最优,插入其它长度扭带的PEC也都高于1,可以应用在压力较小的工况下。最后,本文还对该类型扭带拟合了实验关联式,通过对比实验值和预测值,Nu和f的误差均在10%以内,这为今后的研究提供了理论依据。 相似文献
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电站翅片热管空气预热器变壁温数值模拟 总被引:1,自引:0,他引:1
介绍了用数值模拟计算方法和FLUENT软件相结合,对带翅片热管空气预热器进行三维数值模拟的方法.模型采用标准κ-ε湍流模型,用数值模拟计算方法计算管壁温度,并将之作为模型的边界条件,用流固耦合法研究了翅片的温度场分布.研究结果表明:换热管翅片迎风面换热效果明显高于背风面;换热管下游存在回流区,背风侧气流速度急剧下降;换热管迎风侧压力高于背风侧相应点的压力,沿流动方向压力分布具有分段降低的特征;模拟结果与已有文献的试验结果吻合良好,所以该方法能有效地模拟预热器流场与温度场的细观信息,为空气预热器的进一步理论研究和推广应用提供了依据. 相似文献
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S. Eiamsa-ard P. Nivesrangsan S. Chokphoemphun P. Promvonge 《International Communications in Heat and Mass Transfer》2010
In this paper, heat transfer, friction factor and thermal performance behaviors in a tube equipped with the combined devices between the twisted tape (TT) and constant/periodically varying wire coil pitch ratio are experimentally investigated. The periodically varying three coil pitch ratios were arranged into two different forms: (1) D-coil (decreasing coil pitch ratio arrangement) and (2) DI-coil (decreasing/increasing coil pitch ratio arrangement) while the twisted tapes were prepared with two different twist ratios. Each device alone is also tested and the results are subjected for comparison with those from the combined devices. The experiments were conducted in a turbulent flow regime with Reynolds numbers ranging from 4600 to 20,000 using air as the test fluid. Compared to each enhancement device, the heat transfer rate is further augmented by the compound devices. Over the range investigated, the highest thermal performance factor of around 1.25 is found by using DI-coil in common with the TT at lower Reynolds number. In addition, the empirical correlations of the heat transfer (Nu) and pressure drop (f) are also presented. 相似文献
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In this paper, the effects of dual twisted tape inserts with different pitches on turbulent heat transfer and pressure drop are numerically investigated. A nanofluid is flowed inside a circular tube, which is under a constant heat flux condition. The Reynolds number varies from 5000 to 20 000 at a fixed Prandtl number of 7. Nine different cases are considered in the current study; three cases consist of a single twisted tape insert, three cases are related to twin twisted tapes with identical pitches, and the remaining cases consist of dual twisted tapes with different pitches for each insert. The predicted results indicate that inserting a dual twisted tape effectively increases the heat transfer 1.5 times more than that of the single insert with the penalty of high pressure drop. Also, the relative Nusselt number decreases with increase in Reynolds number for all the investigated cases. The heat transfer rates induced by dual inserts with different pitch ratios are higher than those with identical pitch ratios. Moreover, the maximum and minimum thermal performances belong to cases with Tr 1 = 2, Tr 2 = 3 and Tr 1 = 2, Tr 2 = 2, respectively. And finally, it is stated here that adding nanoparticles improves the thermal performance of all cases in all the investigated Reynolds numbers. 相似文献
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Smith Eiamsa-ard Chinaruk Thianpong Pongjet Promvonge 《International Communications in Heat and Mass Transfer》2006,33(10):886-1233
Experimental investigation of heat transfer and friction factor characteristics in a double pipe heat exchanger fitted with regularly spaced twisted tape elements, were studied. The inner and outer diameters of the inner tube are 50.6 and 25.8 mm, respectively and cold and hot water were used as working fluids in shell side and tube side. The twisted tapes were made of the stainless steel strip with thickness of 1 mm and the length of 1500 mm. They were inserted in the test tube section in two different cases: (1) full-length typical twisted tape at different twisted ratios (y = 6.0 and 8.0), and (2) twisted tape with various free space ratios (S = 1.0, 2.0, and 3.0). The results, obtained from the tube with twisted tape insert, were compared with those without twisted tape. The results show that the heat transfer coefficient increased with twist ratio (y). Whereas the increase in the free space ratio (S) would improve both the heat transfer coefficient and friction factor. The results from each case were correlated for Nusselt number and friction factor. Subsequently, the predicted Nusselt number and friction factor from the correlations were plotted to compare with the experimental data. It was found that Nusselt number was within ± 15% and ± 10% for friction factor. 相似文献
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Smith Eiamsa-ard Chinaruk Thianpong Petpices Eiamsa-ard Pongjet Promvonge 《International Communications in Heat and Mass Transfer》2010
The paper presents a comparative investigation of enhanced heat transfer and pressure loss by insertion of single twisted tape, full-length dual and regularly-spaced dual twisted tapes as swirl generators, in a round tube under axially uniform wall heat flux (UHF) conditions. The investigation encompassed the Reynolds number based on the inlet tube diameter (D) ranging from 4000 to 19,000. The experiments are performed using single twisted tapes and full-length dual twisted tapes with three different twist ratios (y/w = 3.0, 4.0 and 5.0) and also regularly-spaced dual twisted tapes with three different space ratios (s/D = 0.75, 1.5 and 2.25). The effects of major parameters on heat transfer and friction factor are discussed and the results from both single and dual twisted tape inserts are compared with those from the plain tube. The result shows that the heat transfer of the tube with dual twisted tapes is higher than that of the plain tube with/without single twisted tape insert. For both single twisted tape and full-length dual twisted tapes, Nusselt number (Nu) and friction factor (f) tend to increase with decreasing twist ratio (y/w). The average Nusselt number and friction factor in the tube fitted with the full-length dual twisted tapes at y/w = 3.0, 4.0 and 5.0, are respectively 146%, 135% and 128%; and 2.56, 2.17 and 1.95 times of those in the plain tube. For the regularly-spaced dual twisted tapes, the heat transfer rate is decreased with increasing space ratio (s/D). The average Nusselt numbers in the tube fitted with the regularly-spaced dual twisted tapes (s/D) of 0.75, 1.5 and 2.25 are respectively, 140%, 137% and 133% of that in the plain tube. With the similar trend mentioned above, all dual twisted tapes with free spacing yield lower heat transfer enhancement in comparison with the full-length dual twisted tapes (s/D = 0.0). 相似文献
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K. WongchareeS. Eiamsa-ard 《International Communications in Heat and Mass Transfer》2011,38(3):348-352
The thermohydraulic characteristics of the circular tubes equipped with alternate clockwise and counter-clockwise twisted-tapes (TA) for the Reynolds number ranging from 830 to 1990, are reported. In the experiments, the twisted tapes with three different twist ratios (y/W = 3, 4 and 5) were inserted individually into the uniform wall heat flux tubes where water was utilized as the working fluid. The plain tube and the tube inserted with twisted tape (TT) were also tested, for comparison. The obtained results reveal that, Nusselt number, friction factor and thermal performance factor associated by TA are higher than those associated by TT. Among the tapes examined, the one with the smallest twist ratio of y/W = 3 is found to be the most efficient for heat transfer enhancement. For the range studied, the applications of both TT and TA for heat transfer enhancement are found to be promising since the thermal performance factors determined under the same pumping power are all above unity. In addition, the empirical correlations for Nusselt number, friction factor and thermal performance factor have also been developed. The consequential results obtained from the correlations are found to be in good agreement with the experimental results within ± 8% variation for Nusselt number (Nu), ± 8% for thermal performance factor (η) and ± 5% for friction factor (f). 相似文献
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Enhanced heat transfer and pressure loss in a tube with loose-fit perforated twisted tapes were experimentally investigated. The effects of the twist ratio and the hole diameter ratio were also described. A constant twisted tape width of 52 mm, which is lower than the tube inside diameter of 56 mm, was used in order to reduce excessive pressure drops associated with full-width twisted tape elements. The tests were conducted using the tapes with three different ratios of pitch length of twisted tape to inner diameter of tube (twist ratios = 2, 2.5, 3) and three different ratios of hole to inner diameter (diameter ratios = 0.0714, 0.107, 0.143) in a range of Reynolds number 4860 to 24,130 under uniform heat flux conditions. The experimental findings revealed that the Nusselt number, friction factor, and thermal performance factor increase with decreasing twist ratio and hole diameter ratio. The maximum value of thermal performance factor of 1.27 was achieved for the case at a twist ratio of 2 and a hole diameter ratio of 0.0714. Eventually, the experimental results of Nusselt number, friction factor and thermal performance factor were correlated, and the deviations determined for Nusselt number, friction factor, and thermal performance factor were within ±7%, ±8%, and ±6%, respectively. 相似文献
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《International Journal of Thermal Sciences》2007,46(5):506-518
This paper presents an original experimental study on compound heat transfer enhancement in a tube fitted with serrated twisted tape. The serrations on two sides of the twisted tape with twist ratio of 1.56, 1.88, 2.81 or ∞ are the square-sectioned ribs with the identical rib-pitch and rib-height. The local Nusselt number and Fanning friction factor increase as the twist ratio decreases in the tube fitted with smooth or serrated twisted tape. In the Re range of 5000–25 000, heat transfer augmentation attributed to the serrated twisted tape falls in the range of 250–480% of the plain-tube level. That is about 1.25–1.67 times the heat transfer level in the tube fitted with smooth twisted tape. Fanning friction factors are respectively decreased and increased in the tubes fitted with smooth and serrated twisted tapes as Re increases. Based on the same pumping power consumption, the thermal performances of the tubes with smooth and serrated twisted tapes are compared. A set of empirical correlations that permits the evaluation of the Nusselt number and the Fanning friction factor in the developed flow region for the tubes fitted with smooth and serrated twisted tapes is generated for engineering applications. 相似文献
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S. Eiamsa-ard K. Wongcharee S. Sripattanapipat 《International Communications in Heat and Mass Transfer》2009,36(9):947-955
The article presents the application of a mathematical model for simulation of the swirling flow in a tube induced by loose-fit twisted tape insertion. Effects of the clearance ratio defined as ratio of clearance between the edge of tape and tube wall to tube diameter (CR = c/D = 0.0 (tight-fit), 0.1, 0.2 and 0.3) on heat transfer enhancement (Nu), friction factor (f) and thermal performance factor (η) are numerically investigated for twisted tapes at two different twist ratios (y/w = 2.5 and 5.0). The simulation is conducted in order to gain an understanding of physical behavior of the thermal and fluid flow in the tube fitted with loose-fit twisted tape under constant wall temperature conditions in the turbulent flow regime for the Reynolds number ranging from 3000 to 10,000. The Navier–Stokes equation in common with a energy equation is solved using the SIMPLE technique with the standard k–ε turbulence model, the Renormalized Group (RNG) k–ε turbulence model, the standard k–ω turbulence model, and Shear Stress Transport (SST) k–ω turbulence model. The numerical results show that the predictions of heat transfer (Nu) and friction factor (f) based on the SST k–ω turbulence models are in better agreement with Manglik and Bergles [R.M. Manglik, A.E. Bergles, Heat transfer and pressure drop correlations for twisted-tape inserts in isothermal tubes, part II: Transition and turbulent flows, Transaction ASME, Journal of Heat Transfer, 115 (1993) 890–896.] than other turbulence models. The mean flow patterns in a tube with loose-fit twisted tapes in terms of contour plots of velocity, pathline, pressure, temperature and turbulent kinetics energy (TKE) are presented and compared with those in a tube fitted with tight-fit twisted tapes. It is visible that the twisted tape inserts for y/w = 2.5 with CR = 0.0 (tight-fit), 0.1, 0.2 and 0.3 can enhance heat transfer rates up to 73.6%, 46.6%, 17.5% and 20%, respectively and increase friction factors up to 330%, 262%, 189%, and 160%, respectively, in comparison with those of the plain tube. The tube with loose-fit twisted tape inserts with CR = 0.1, 0.2 and 0.3 provide heat transfer enhancement around 15.6%, 33.3% and 31.6% lower than those with CR = 0.0 (the tight-fit twisted tape). The heat transfer augmentation is expected to involve the swirl flow formation between the tape and a tube wall. In addition, the simulation for thermal performance factor (η) of a tube with the loose-fit twisted tape and the tight-fit twisted tape under the same pumping power is also conducted, for comparison. 相似文献
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K. Nanan K. Wongcharee C. Nuntadusit S. Eiamsa-ard 《International Communications in Heat and Mass Transfer》2012
Forced convective heat transfer on the impinged plate associated with swirling impinging jets (SIJ) issuing from nozzles inserted by twisted tapes has been investigated. Swirling impingement jets with several swirl rates were generated by twisted tapes at different twist ratios (y/W = 3, 4, 5, and 6). The experiments were performed by locating nozzle at 4 different jet-to-plate spacings of L/D = 2, 4, 6 and 8. A jet Reynolds number varied between 4000 and 16000. Attributing to a high momentum transfer rate, an efficient heat transfer was obtained by using the jet with a small jet-to-plate spacing and the twist tape with a large twist ratio at high Reynolds number. At small jet-to-plate spacings (L/D = 2 and 4), swirling impinging jets gave higher heat transfer rate than conventional impinging jets while at large jet-to-plate spacings (L/D = 6 and 8), the opposed result was obtained. Over the range examined, only SIJ induced by the twisted tape at a twist ratio of 6 consistently provided higher average Nusselt numbers than CIJ. 相似文献