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上游边界层对向上散热的水平热板自然对流换热影响的研究 总被引:1,自引:0,他引:1
论文对具有上游边界层场合的水平加热表面向上对流换热的自然对流进行了实验研究,采用全息干涉法测定温度场,对侧壁高度为50,100,150毫米三种情况进行了实验测定,发现其边缘效应与无侧壁时的水平板情况不同,在6×10~3相似文献
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本文采用M-Z干涉测量的方法,研究了半三角形翼片纵向涡发生器强化换热方案对矩形通道内气体流动换热的影响,获得了安装纵向涡发生器前后对流换热温度场的M-Z干涉图像.通过对实验获得的干涉图像进行分析处理,表明安装纵向涡发生器后,通道内入口段流动的热边界层明显变薄,反映了纵向涡对流动换热的强化作用,验证了将M-Z干涉测量方法应用于纵向涡强化换热研究的可行性. 相似文献
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本文对热面向上水平小尺寸平板的自然对流换热进行了实验研究。改进了现有文献的试验方法,提高了测量精度。用激光干涉技术测定了局部换热系数,并用热平衡法测定了平均换热系数。实验表明,平板上的流动和换热呈现随机不稳定性特征,但这种随机不稳定性随瑞利数减小而减弱,直至消失。拟合了热面向上水平小尺寸平板的对流换热关系式,填补了现有文献的空白。本文结果对微电子器件冷却的设计有参考价值。 相似文献
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The simulation and optical visualization of the refraction effects in an axisymmetric temperature field was undertaken in the case of free convection from a heated horizontal down-facing disk. Temperature and related refractive index fields have been calculated using a mathematical model based on the coupled flow and heat transfer equations. To avoid the complex and time-consuming computation of ray trajectory using the differential ray equation, we developed a simple method based on the application of the standard Snell law at each surface isotherm in the medium. Using this technique, we plotted the trajectory of rays bundle traveling in the medium and calculated the deflection angle. Comparison with shadowgraph images showed a good agreement with the simulation and explained the existence of a caustic induced by the thermal boundary layer acting as a schlieren lens. 相似文献
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Predictions are given on stability conditions for experiments in standard and reduced-gravity conditions when the Soret effect is operating in a horizontal binary liquid layer heated from below and open to the ambient air. 相似文献
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Mahfoud El fagrichHassan Chehouani 《Optics and Lasers in Engineering》2012,50(3):336-344
In this work, we describe a simple method of Abel inversion for temperature measurement in a natural convection axisymmetric flow. The essence of the method is that the measured lateral fringe shift profile is fitted with a polynomial with only even powers and then Abel inverse integral is evaluated analytically. This technique is compared with recent existing methods to test the accuracy and error propagation using a simulated interferogram of natural convection flow below a downward-facing heated horizontal disk in air. For this comparison, lateral fringe profiles are simulated using temperature fields computed by solving Navier Stokes and energy equations. Through random-number generation, noise profile is artificially added to the simulated noise-free lateral fringe shift profile. The results showed that the proposed technique for Abel inversion leads to accurate temperature profiles when the lateral fringe shift profile is fitted with even-power polynomials having degrees ranging from 20 to 30. 相似文献
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Air-coupled ultrasonic capacitance transducers operating at frequencies of up to 1 MHz have been employed in a fan-beam configuration for the cross-sectional tomographic imaging of temperature fields and flow fields in air, and the location of solid objects. Separate transmitter and receiver transducers were manufactured using thin polymer dielectric membranes and polished metal backplates, and used to acquire through-transmission data. The fan-beam reconstruction was developed in LabVIEW using a re-bin routine combined with a filtered backprojection algorithm and a difference technique to generate the cross-sectional images. The system was first used to reconstruct images showing the locations of solid objects positioned within the scanned region through interpretation of the arrival time of the transmitted ultrasound. The technique was then extended to image the temperature fields produced in air above a small heat source and the flow field produced by a nozzle connected to a regulated compressed air source. Reconstructed temperatures were within 4% of the measured background air temperature and 9% of the air temperature measured above the heat source. Reconstructed images of the flow field above a small nozzle were also presented, showing that the horizontal component of the flow velocity could be resolved using this method. 相似文献
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The natural convection flow phenomena that occur inside an enclosed space are very interesting examples of complex fluid systems
that may yield to analytical, empirical and numerical solutions, and many reports have looked into this basic problem. In
the present study, heat transfer and fluid flow for natural convection in a horizontal rectangular container with a free surface
are investigated using infrared thermography. The temperature field was measured and visualized at a gas-liquid (air — silicon
oil) interface using infrared thermography. The heat transfer phenomena were also investigated by statistically analyzing
the temperature data. The applicability of the infrared thermography to quantitative heat transfer measurement at the gas-liquid
interface was evaluated. It is revealed that infrared thermography is effective not only in visualization of a gas-liquid
interface but also in heat transfer measurement. A new heat transfer correlation is proposed for the gas-liquid interface
of this flow system. The coefficient of heat transfer can be summarized by a specific heat transfer correlation formula regardless
of several conditions, including container aspect ratio, fluid viscosity and fluid layer depth. 相似文献
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Atul Srivastava Atanu Phukan P. K. Panigrahi K. Muralidhar 《Optics and Lasers in Engineering》2004,42(4):73
The present study is concerned with the quantitative imaging of buoyancy-driven convection in a fluid medium that is confined in a horizontal differentially heated rectangular cavity. The horizontal surfaces of the cavity provide a temperature difference, for initiating convection in the fluid. The vertical side walls are thermally insulated. Three imaging techniques, namely laser interferometry, schlieren, and shadowgraph have been utilized. Experiments have been conducted in a cavity of length 447 mm and 32 mm vertical height. The cavity is square in cross-section, and the imaging direction is parallel to its longer side. Convection in air and water have been investigated. Temperature differences in the range of 5–50 K for air and 3–10 K for water have been employed in the experiments. Quantities of interest are the temperature profiles in unsteadiness in the thermal field. At lower temperature differences across the fluid region, temperatures as recorded by interferometry and schlieren are in good agreement with each other. Further, they match the numerical predictions, as well as correlations available in the literature. Imaging based on shadowgraph is not as satisfactory at lower temperature differences. At larger cavity temperature differences, the shadowgraph images become clear enough for quantitative analysis, but the flow becomes time-dependent. The three techniques reveal similar trends in terms of the spatial distribution of temperature gradients and the time scales of unsteadiness. The schlieren and shadowgraph are more suitable for high gradients and interferometry is suitable for low gradients and all these three techniques are not flow visualization tools alone but are appropriate for quantitative imaging of thermal field. 相似文献
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Abstract In this article, mixed convection in an open cavity with a heated wall bounded by a horizontal unheated plate is investigated experimentally. The heated wall is on the opposite side of the forced inflow. The results are reported in terms of wall temperature profiles of the heated wall and flow visualization. The range of pertinent parameters used in this experiment are Reynolds numbers (Re) from 100 to 2,000 and Richardson numbers (Ri) from 4.3 to 6,400. Also, the ratio between the length and the height of cavity (L/D) ranges from 0.5–2.0, and the ratio between the channel and cavity height (H/D) is equal to 1.0. The lack of experimental results on mixed convection in a channel with an open cavity below was an impetus for investigating this configuration when one cavity vertical wall is heated at uniform heat flux. The present results show that at the lowest investigated Reynolds number, the surface temperatures are lower than the corresponding surface temperatures for Re = 2,000 at the same ohmic heat flux. The flow visualization shows that for Re = 1,000, there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100, the effect of a stronger buoyancy determines a penetration of thermal plumes from the heated plate wall into the upper channel. Moreover, the flow visualization shows that for lower Reynolds numbers, the forced motion penetrates inside the cavity, and a vortex structure is adjacent to the unheated vertical plate. At higher Reynolds numbers, the vortex structure has a larger extension while L/D is held constant. 相似文献
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Temperature and velocity fields in unsteady non-penetrative turbulent thermal convection of a horizontal fluid layer are measured in horizontal and vertical planes simultaneously using the combined liquid-crystal thermometry and stereo particle image velocimetry (PIV) with high spatial and temporal resolution. The result shows the formation of convection pattern across the fluid layer, which originates from the spoke structure over the heated surface. The upward fluid motion is generated from the intersection of the bursting lines of the spoke structure, while the downward motion is induced by the low temperature fluid directing toward the center of the spoke structure. Thus, the large-scale convective motion is produced in the fluid layer through the motion of spoke structure. The POD analysis of the temperature and velocity eigenfunctions shows the existence of large-scale motion in the fluid layer, which supports the observed convection pattern near the heated boundary and in the middle of the fluid layer. 相似文献
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Guenter Ahlers Christopher W. Meyer David S. Cannell 《Journal of statistical physics》1989,54(5-6):1121-1131
The pure conduction state of a horizontal layer of fluid heated from below becomes unstable with respect to a convecting state when the temperature difference exceeds a critical value. We examine the question of how real, physical systems evolve from conduction to convection. Most experimental cells contain geometric or thermal inhomogeneities which render the bifurcation to convection imperfect. In that case the pure conduction state never exists and the convecting state evolves continuously and smoothly as the temperature difference is raised. When a sufficiently perfect experimental cell is constructed to eliminate this route to convection, then dynamic imperfections will usually prevail. When the temperature difference across the cell is raised, the vertical gradients in the sidewalls evolve at a rate which differs from that in the fluid. The resultingtransient horizontal thermal gradients initiate the convective flow. This phenomenon can be eliminated by providing sidewalls which have the same thermal diffusivity as that of the fluid. When that is done, the convective flow is started by random noise which exists in any experimental system. Analysis of experiments shows that the noise source is considerably stronger than thermal noise, but its origin is unclear at this time. 相似文献
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Two-dimensional measurement of density,velocity, and temperature in turbulent high-speed air flows by UV rayleigh scattering 总被引:2,自引:0,他引:2
Instantaneous cross-sectional images of turbulent air flows with densities on the order of one atmosphere or less can be obtained in a straightforward manner using far ultraviolet Rayleigh scattering. These images give quantitative values for the air density and show the details of turbulent structure, shock structure, and shock wave/boundary layer interactions. Two-dimensional spatial correlations taken from multiple images give the shape and extent of average turbulent structure as well as the coupling between turbulent structure and other flow features. This technique may be extended to observe velocity fields by either double pulsing the illumination source or by using a narrow linewidth atomic or molecular filter window in front of the detector array. The latter approach also yields temperature. Used in conjunction with flow marking techniques such as RELIEF, coupling between turbulent structure and velocity fluctuations can also be determined. These diagnostic techniques can be extended to combusting flows to observe instantaneous structure, mixing, flame front location, and velocity fields. 相似文献