共查询到20条相似文献,搜索用时 15 毫秒
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H.A. Mohammed G. BhaskaranN.H. Shuaib R. Saidur 《Superlattices and Microstructures》2011,50(3):215-233
This paper reports a numerical analysis of the performance of a counter-flow rectangular shaped microchannel heat exchanger (MCHE) using nanofluids as the working fluids. Finite volume method was used to solve the three-dimensional steady, laminar developing flow and conjugate heat transfer in aluminum MCHE. The nanofluids used were Ag, Al2O3, CuO, SiO2, and TiO2 and the performance was compared with water. The thermal, flow fields and performance of the MCHE were analyzed using different nanofluids, different Reynolds numbers and different nanoparticle concentrations. Temperature profile, heat transfer coefficient, pressure profile, and wall shear stress were obtained from the simulations and the performance was discussed in terms of heat transfer rate, pumping power, effectiveness, and performance index. Results indicated enhanced performance with the usage of nanofluids, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The increase in nanoparticle concentration also yielded better performance at the expense of increased pressure drop. 相似文献
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H.M. Deylami N. Amanifard F. Dolati R. Kouhikamali K. Mostajiri 《Journal of Electrostatics》2013,71(4):656-665
Forced convection heat transfer enhancement with electrohydrodynamic (EHD) technique of turbulent flow inside a smooth channel has been numerically investigated. A two dimensional numerical approach has been chosen to evaluate the local and average heat transfer coefficient. In addition, the swirling flow pattern in the presence of an electric field has been studied. To achieve higher enhancement while using multiple electrodes, variety of electrode arrangements have been examined for specified values of Reynolds number, applied voltage, and wire radius. The results demonstrate that different electrode arrangements cause significant improvement of the heat transfer coefficient. 相似文献
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In this paper, a numerical method is presented to investigate the Electrohydrodynamic effect using micropolar fluid model. The EHD flow for the forced convection heat transfer in a smooth channel is simulated. The computed results were compared with the fully turbulent flow approach. It is found that the micropolar model can be used to simulate the hydraulically laminar flow. In addition, the heat transfer enhancement has the same efficiency for both the micropolar and the k-ε models. The change of the applied voltage and the Reynolds number caused various deviations of the results obtained from the two approaches up to a maximum of 20.79%, and a minimum of 0.03%. 相似文献
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采用由SRK方程计算得出的混合工质物性参数,将具有相变两相流体物性分三部分处理,得出混合工质分段物性数据拟合曲线,并输入FLUENT软件的材料物性数据文件中,作为数值模拟物性参数数据。在上述物性数据处理的基础上,对混合工质天然气液化装置中换热器采用分段方式进行稳态数值模拟研究,得到沿长度方向一定温度下传热系数、压力梯度的变化曲线。通过与MUSE软件数据比较,计算结果有一定合理性,所得结论为有相变换热的混合工质低温板翅式换热器的设计和优化提供一定参考。 相似文献
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Ultrasound is considered to be an effective active heat transfer enhancement method, which is widely used in various fields. But there is no clear understanding of flow boiling heat transfer characteristics in micro/mini-channels under ultrasonic field since the studies related are limited up to now. In this paper, a novel minichannel heat exchanger with two ultrasonic transducers inside the inlet and outlet plenum respectively is designed to experimentally investigate the impacts of ultrasound on flow boiling heat transfer enhancement in a minichannel heat sink. Flow visualization analyses reveal that ultrasound can promote rapid bubble motion, bubble detachment from heating wall surface and thereby new bubble generation, and decrease the length of confined bubble. Furthermore, the flow boiling experiments are initiated employing working fluid R141b at different ultrasonic parameters (e.g., frequency, power, angle of radiation) and heat flux under three types of ultrasound excitations: no ultrasound (NU), single inlet ultrasound (IU), inlet and outlet ultrasound (IOU). The results indicate that ultrasound has obvious augmentation effects on flow boiling heat transfer even though the intensification effects will be limited with the heat flux increases. The higher ultrasonic power, the lower ultrasonic frequency and the higher ultrasonic radiation angle, the better intensification efficiency. The maximum enhancement ratio of have in the saturated boiling section reaches 1.88 at 50 W, 23 kHz and 45° under the experimental conditions. This study will be beneficial for future applications of ultrasound on flow boiling heat transfer in micro/mini-channels. 相似文献
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Nanofluids, because of their enhanced heat transfer capability as compared to normal water/glycol/oil based fluids, offer the engineer opportunities for development in areas where high heat transfer, low temperature tolerance and small component size are required. In this present paper, the hydrodynamic and thermal fields of a water–γAl2O3 nanofluid in a radial laminar flow cooling system are considered. Results indicate that considerable heat transfer enhancement is possible, even achieving a twofold increase in the case of a 10% nanoparticle volume fraction nanofluid. On the other hand, an increase in wall shear stress is also noticed with an increase in particle volume concentration. 相似文献
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Intriguingly high convective heat transfer enhancement of nanofluid coolants in laminar flows 总被引:1,自引:0,他引:1
We reported on investigation of the convective heat transfer enhancement of nanofluids as coolants in laminar flows inside a circular copper tube with constant wall temperature. Nanofluids containing Al2O3, ZnO, TiO2, and MgO nanoparticles were prepared with a mixture of 55 vol.% distilled water and 45 vol.% ethylene glycol as base fluid. It was found that the heat transfer behaviors of the nanofluids were highly depended on the volume fraction, average size, species of the suspended nanoparticles and the flow conditions. MgO, Al2O3, and ZnO nanofluids exhibited superior enhancements of heat transfer coefficient, with the highest enhancement up to 252% at a Reynolds number of 1000 for MgO nanofluid. Our results demonstrated that these oxide nanofluids might be promising alternatives for conventional coolants. 相似文献
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Roughness effect on the heat transfer and pressure loss performances of microscale tubes and channels are investigated through a finite element CFD code. Surface roughness is explicitly modelled through a set of random generated peaks along the ideal smooth surface. Different peak shapes and distributions are considered; geometrical parameters are representative of tubes in the diameter range from 50 to 150 μm. The use of a fine enough mesh allows the direct computation of tube performances under the assumption of incompressible fully developed flow. As a result, a significant increase in Poiseuille number is detected for all of the configurations considered, while the effect of roughness on heat transfer rate is smaller and highly dependent on the tube shape. 相似文献
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热管技术已在电子设备散热领域得到广泛应用。热管的传热能力虽然很大,但不能无限加大热负荷。文中讨论了热管的主要极限如沸腾极限、毛细极限、粘性极限、声速极限、携带极限等的理论表达式,就一种实验用微槽平板热管进行了理论计算,得出了毛细极限是实验热管主要传热极限的结论。 相似文献
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Turbulent forced convection in a corrugated tube with spring tape is investigated experimentally, for Reynolds numbers from 10,000 to 50,000. The working fluid is air. Experiments are performed for different pitch and spring ratios. Results show that Nusselt numbers can be increased considerably, depending on pitch and spring ratios. An overall assessment, considering the friction losses, is achieved using the thermo-hydraulic performance parameter. The latter is observed to take values larger than unity for all cases, where quite high values around 2.8 occur for cases with smallest pitch and spring ratios. Predictive Nusselt number and friction factor correlations are proposed. 相似文献
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用三维数值的研究方法对带有纵向涡发生器的翅片管流动和传热进行了数值研究。研究发现,使用了45°冲角的矩形小翼纵向涡发生器可以使得翅片管的传热增加10.4-24.6%,同时相应的压力损失增加30.5-57.2%。研究了不同的冲角(a=30,45,60)对于管翅间换热和流动的影响,结果显示冲角为30°时效果最好。 相似文献
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In this article we study the electro-thermal convection in a dielectric liquid layer placed between two electrodes and subjected to the simultaneous action of an electric field and a thermal gradient. The full set of equations describing the electro-thermo-convective phenomena is directly solved using a finite volume method. We first heat the liquid from below at time t = 0, wait for the thermal steady state and then inject the electric charges by applying the electric potential. The development of the electro-convective motion is analysed in detail in two cases: 1) strong injection from the lower electrode, 2) strong injection from the upper one. We also study the heat transfer enhancement due to electro-convection. The evolution in time of the Nusselt number Nu for different combinations of the two usual non-dimensional parameters associated to the electro-thermo-convection phenomena (Rayleigh number Ra and the electrical parameter T) is also given and analysed. 相似文献
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A computational and experimental approach is undertaken to study the enhancement of convective heat transfer in fully-developed internal flows by an electrically-induced secondary flow field. Using longitudinal flat electrodes along a parallel-plate configuration, the corona discharge is employed to generate an electrically induced secondary flow on the cross section of the flow passage. The electrically-induced secondary flow forms a swirling flow field in the fully-developed condition and enhances the heat transfer significantly. The flow field was solved computationally and the results were verified and validated by grid refinement study and computational error analysis. 相似文献
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Sidi El Bcaye Maïga Cong Tam Nguyen Nicolas Galanis Gilles Roy 《Superlattices and Microstructures》2004,35(3-6):543
In the present work, we consider the problem of the forced convection flow of water– γAl2O3 and ethylene glycol– γAl2O3 nanofluids inside a uniformly heated tube that is submitted to a constant and uniform heat flux at the wall. In general, it is observed that the inclusion of nanoparticles has increased considerably the heat transfer at the tube wall for both the laminar and turbulent regimes. Such improvement of heat transfer becomes more pronounced with the increase of the particle concentration. On the other hand, the presence of particles has produced adverse effects on the wall friction that also increases with the particle volume concentration. Results have also shown that the ethylene glycol– γAl2O3 mixture gives a far better heat transfer enhancement than the water– γAl2O3 mixture. 相似文献
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在内径为2mm曲率为0.057的螺旋管内进行了超临界氮的对流换热实验,研究探讨了螺旋管入口温度、壁面热流密度对沿程壁面温度分布以及平均换热系数的影响,与前人关于螺旋管内常规流体流动换热的平均Nu的经验关系式进行了比较。并基于FLUENT软件进行了数值计算,并与实验结果进行了比较。分析表明,数值计算对壁面温度的预测有一定的适用性。 相似文献