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Ducts with a square cross-section are widely used in many industrial applications because of their high compactness, easy forming, and low pressure drop. But the thermal performance of a duct will be reduced when the circular cross-sectional shape is not used. In this study, the convective heat transfer for a CuO/water nanofluid through a square cross-section duct in the turbulent flow regime has been investigated. The Nusselt number of nanofluids for different nanoparticle concentrations, as well as various Peclet numbers, was obtained. The results show considerable enhancement in the heat transfer coefficient and Nusselt number by increasing the nanoparticle concentrations as well as the Peclet number. 相似文献
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Laminar convective heat transfer enhancement of cuprous oxide (Cu2O)/water nanofluid flowing through a circular tube was investigated experimentally in the present work. A continuous closed loop was designed to measure heat transfer coefficients and pressure drop associated with the flow of Cu2O/water nanofluid over a wide range of laminar flow conditions. Comparison of the nanofluid experimental results with those of pure water have shown significant enhancement for heat transfer coefficients. On average, a 10% increase in heat transfer coefficient was observed with 16% penalty in pressure drop. 相似文献
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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. 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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In this study, steady-state laminar forced flow and heat transfer in a horizontal smooth trapezoidal duct having different corner angles were experimentally investigated in the Reynolds number range from 102 to 103. Flow is hydrodynamically fully developed and thermally developing under a uniform surface temperature condition. Based on the present experimental data of laminar flow in the thermal entrance region, new engineering correlations were presented for the heat transfer and friction coefficients for each corner angle. The results have shown that as the Reynolds number increases heat transfer coefficient increases but Darcy friction factor decreases. Also, it is observed that average Nusselt number increases while average Darcy friction factor decreases with increasing corner angle of the duct. 相似文献
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Abstract Heat transfer characteristics of water-based nanocrystalline alumina (Al2O3) nanofluids flowing through a uniformly heated tube under a fully developed laminar and turbulent flow regime is investigated experimentally in the present work to explore the heat transfer mechanism in nanofluids. In a laminar flow, the increase in Nusselt number was attributed to the thermophysical properties of the nanofluid. The movement of nanoparticles, along with the turbulent eddies in the turbulent core region and diffusion mechanism, such as thermophoresis, in the laminar sublayer are believed to be the reasons for enhanced heat transfer in turbulent region. The compatibility of Al2O3/water nanofluids was also examined by monitoring its color. 相似文献
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Thermal dispersion model has been used here to simulate heat transfer of water–Al2O3 nanofluid. A new form for dispersion thermal conductivity has been introduced in which non-uniform concentration distribution is applied on the model. It was observed that the non-uniformity of concentration increases at greater Reynolds numbers and average concentrations. An experimental set-up was made, and an experimental study was conducted to find the empirical coefficient in the dispersion thermal conductivity. The obtained results show that the developed dispersion model is able to properly simulate heat transfer of the nanofluid and provides more accurate results in comparison with a homogenous model. 相似文献
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The objective of this work is to provide a correlation between the heat transfer coefficient and the Nusselt Number with the flow Reynolds number for a truncated cylindrical probe in cross-flow, a configuration that has not previously been well defined. In the experiment, thermally stabilized, dry air was discharged into the test section across a heated probe that was instrumented with thermocouples and exhausted to atmosphere. Experimental data were recorded for several run conditions. A correlation between the probe heat transfer coefficient and the Reynolds number was developed with a calculated uncertainty of 1.24%. 相似文献
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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. 相似文献
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The present study is carried out to see the thermal-diffusion (Dufour) and diffusion-thermo (Soret) effects on the mixed convection boundary layer flow of viscoelastic nanofluid flow over a vertical stretching surface in a porous medium. Optimal homotopy analysis method (OHAM) is best candidate to handle highly nonlinear system of differ-ential equations obtained from boundary layer partial differential equations via appropriate transformations. Graphical illustrations depicting different physical arising parameters against velocity, temperature and concentration distributions with required discussion have also been added. Numerically calculated values of skin friction coefficient, local Nusselt and Sherwood numbers are given in the form of table and well argued. It is found that nanofluid velocity increases with increase in mixed convective and viscoelastic parameters but it decreases with the increasing values of porosity parameter. Also, it is observed that Dufour number has opposite behavior on temperature and concentration profiles. 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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以水为介质,建立了液体流动的混合物多相流模型及空化模型,运用CFD方法对水平圆管内伴随有水力空化现象的受迫对流换热过程进行了数值研究,详细分析了管道入口压力、入口温度和限流孔与管道直径比等因素对水力空化及对流换热过程的影响规律。数值模拟结果表明,空化现象出现在圆管喉部(限流孔)壁面附近区域;与相同流量下无空化时的传热相比,在发生空化现象的区域,传热壁面被蒸汽所覆盖导致传热急剧恶化,而在远离空化发生区域的下游位置,由于空化的扰流作用使得加热壁面与流体之间的传热得到明显改善。 相似文献
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Heat transfer performances of viscoelastic fluid, water-based Cu nanofluid, and viscoelastic-fluid-based Cu nanofluid flows in a circular pipe at a Peclet number of 40,000 were experimentally studied. It indicates that the viscoelastic fluid turbulent flow gives great heat transfer reduction, while the water-based Cu nanofluid flow shows significant heat transfer enhancement. The viscoelastic-fluid-based Cu nanofluid also exhibits heat transfer enhancement as compared with viscoelastic base fluid flow. The effects of nanoparticle volume fraction, mass concentration of viscoelastic base fluid, and temperature on local convective heat transfer coefficient and possible heat transfer enhancement mechanisms of nanofluid flows were discussed. 相似文献
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The experimental and numerical investigation of convective heat transfer in a rectangular cavity of aspect ratio (L/H) = 5 has been presented in this study. The comparison of experimental results is done with a two-dimensional numerical model considered with steady and turbulent flow conditions. Six different arrangements (bottom/bottom/bottom, top/top/top, right/top/left, bottom/top/right, bottom/top/left, and bottom/right/left) were considered. The lowest and highest hotspot temperatures were observed in bottom/bottom/bottom and bottom/right/left arrangements, respectively. For similar configurations, the bottom/bottom/bottom arrangement displays better heat transfer performance, while heat transfer performance is inferior for the bottom/right/left arrangement than all other configurations. 相似文献
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In this article, the effect of applying an electric field on the performance of a two-phase closed thermosyphon is investigated experimentally. A CuO/water nanofluid is used as the working fluid in the present investigation; 40% of the evaporator volume is filled with the working fluid during the tests. An electric field in various voltages ranging from 5 to 20 kV is applied to the system. Also, the input power supplied to the evaporator varies between 60 to 120 W. The thermal efficiency and the thermal resistance of the two-phase closed thermosyphon are evaluated in various strengths of electric field and different volume fractions. It is found that using the nanofluid and applying an electric field could increase the thermal efficiency by up to 30% as compared with the case in which the working media is pure water and no electric field is applied. To illustrate the effect of the electric field on the heat transfer enhancement, the augmentation Nusselt number, defined as the ratio of the Nusselt numbers after and before applying the electric field, is discussed. The results show that utilizing an electric field is more advantageous when the input power applied to the system is lower. 相似文献
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An experimental investigation was made to study heat transfer in a pipe which is oscillated about an axis that is parallel to, but offset from, the pipe axis. Air was used as working fluid. The experimental setup was designed so as to provide oscillating motion of a test pipe. The measurement systems were installed on the oscillating section. For both steady and oscillating flows, the bulk air temperature and wall temperature, pressure drop, and frequency were measured. The parameters for this study were chosen as Reynolds number from 5,000 to 20,000 and oscillating frequencies from 10 to 20 Hz. The variations of Nusselt number versus these parameters were determined and presented graphically. Heat transfer enhancement of 42% was achieved at constant pumping power for oscillatory flow. 相似文献