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Experimental Study of Natural Convection from Electrically Heated Vertical Cylinders Immersed in Air
Abstract An experimental study of laminar steady-state natural convection heat transfer from electrically heated vertical cylinders immersed in air has been undertaken. Three stainless steel (316 SS) test sections of different slenderness ratios were employed. Surface temperature profiles along the vertical cylinders were obtained using miniature thermocouples when the cylinders were heated with different power levels resulting in different total wall heat fluxes. After the mandatory corrections for the radiation heat fluxes were made, three correlation equations relating the local Nusselt number Nuy with the local modified Rayleigh number Ra* y and the position-to-cylinder diameter y/d were developed. The correlation equations are valid for Ra* y ≤ 2 × 1012. 相似文献
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Mixed convection in an open cavity with a heated wall bounded by a horizontally unheated plate is investigated experimentally. The cavity has the heated wall on the inflow side. Mixed convection fluid flow and heat transfer within the cavity is governed by the buoyancy parameter, Richardson number (Ri), and Reynolds number (Re). The results are reported in terms of wall temperature profiles of the heated wall and flow visualization for Re = 100 and 1000, Ri in the range 30–110 (for Re = 1000) and 2800–8700 (for Re = 100), the ratio of the length to the height of cavity (L/D) is in the range 0.5–1.5, and the ratio of the channel height to cavity height (H/D) is in the range of 0.5 and 1.0. The present results show that the maximum dimensional temperature rise values decrease as the Reynolds and the Richardson numbers decrease. The flow visualization points out that for Re = 1000 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 plume from the heated plate wall into the upper channel. Nusselt numbers increase when L/D increase in the considered range of Richardson numbers. 相似文献
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Transient heat transfer of liquid methane under forced convection in a 1.8 mm × 1.8 mm asymmetrically heated square channel was investigated. This study is aimed at understanding the heat transfer behavior of cryogenic propellant in cooling channels of a regeneratively cooled rocket engine at the start-up condition. To simulate high heat load conditions representative of regeneratively cooled rocket engines, a high heat flux test facility with cryogenic liquid handing capabilities was developed at the Center for Space Exploration Technology Research. The time history of inlet and outlet fluid temperatures and test section channel wall temperatures were measured at high heat flux conditions (from 1.19 to 3.80 MW/m2) and a Reynolds number (Re) range of 1.88 × 105 to 3.45 × 105. The measured wall temperature data point toward possible film boiling within the test section during certain tests, particularly with higher heat fluxes and lower Reynolds number conditions that resulted in higher wall temperatures. The transient average Nusselt numbers (NuL) of the channel obtained from the experimental measurements are lower than those calculated from the Sieder–Tate correlation (NuO); however, the ratio (NuL/NuO) increases with the increase in Reynolds number. The ratio is around 0.25 at the lower end of Re and then increases to 0.7 at the maximum Re studied in the present investigation. 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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A theoretical and experimental study was carried out on the thermal performance of a pin fin array heat sink. A theoretical model was utilized based on the success of prior research that has the capability of predicting the influence of various geometrical, thermal, and flow parameters on the effective thermal resistance of the heat sink. An experimental investigation was carried out for measuring the thermal performance of the heat sink, and the overall convective heat transfer coefficient for the fin bundle, including the thermal and flow bundle effect. Utilizing the new empirical correlations, theoretical predictions were made and experimentally validated for a wide range of parameters for combined forced and natural convection in the assisting flow configuration. Both the theoretical model and experimental data indicated the existence of optimal fin spacing. 相似文献
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自然对流下LED集成芯片整体式热管散热器性能实验研究 总被引:2,自引:2,他引:0
为解决LED集成芯片光源的散热问题,提出一种整体式热管散热器,并在不同的热源功率、充液率、倾角下进行了自然对流散热实验研究。结果表明:散热器的热管最佳充液率为30%。热功率较小时,0°~50°倾角对热管传热影响不大;倾角达到75°时,各功率下的热管传热及散热器热阻都明显恶化。散热器启动时间约为30 min,且几乎不受功率大小影响;但75°倾角下,需要更多时间达到稳定。相比于常见的平行板和太阳花翅片散热器,采用整体式热管散热器散热的芯片结温可得到更有效控制。 相似文献
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采用SIMPLE算法,QUICK差分格式,对底部加热三维长方体腔内空气的自然对流进行了数值模拟。根据模拟结果,探讨了方腔内流体流动与换热的静态分岔与振荡等非线性现象。数值结果显示,在固定的几何尺寸和不同Ra的情况下,当初始场不同时,会出现若干不同的解,即存在解的静态分岔;在固定的几何尺寸和相同的初始场情况下,低Ra时流动和换热处于稳态,当Ra超过某一临界值时,流动和换热就会随时间振荡,并通过倍周期分岔过渡到混沌;当方腔的几何尺寸不同时,分岔点的特征值Ra也发生变化。 相似文献
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封闭圆内开缝圆自然对流的非线性特性研究 总被引:2,自引:0,他引:2
本文通过数值计算对封闭圆内开缝圆自然对流的非线性特性进行了研究。数值计算以整个流场为计算区域,采用非稳态数学模型和具有QUICK差分格式的SIMPLE算法。计算结果表明,在不同参数下流动和换热存在稳态定常解、周期性振荡解、拟周期性振荡解和非周期性振荡解。稳态定常解的相图是一个点;周期性振荡解的相图是一个极限环,对应功率谱含一个基频及其谐波;拟周期性振荡解的相图为环面,对应功率谱含两个不相关的频率及它们的线性组合频率;非周期性振荡解的功率谱为无规则的宽带连续谱。 相似文献
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Valentin Roussellet Xiaodong Niu Hiroshi Yamaguchi & Fré dé ric Magoulé s 《advances in applied mathematics and mechanics.》2011,3(1):121-130
In this article, natural convection of a temperature-sensitive magnetic fluid
in a porous media is studied numerically by using lattice Boltzmann method. Results
show that the heat transfer decreases when the ball numbers increase. When the
magnetic field is increased, the heat transfer is enhanced; however, the average
wall Nusselt number increases at small ball numbers but decreases at large ball
numbers due to the induced flow being more likely confined near the bottom walls
with a high number of obstacles. 相似文献
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建立自然对流作用下融化的格子Boltzmann双分布函数模型,根据非线性对流扩散方程的格子Boltzmann模型理论提出一个新的表征融化温度场的分布函数演化方程,并通过变松弛时间方法处理固液两相变热物性传热问题.应用模型对热传导融化及自然对流融化特别固液变热物的融化过程进行模拟.模拟结果与分析解、经典的关联式结果吻合较好,模型的正确性得到了验证.模拟结果表明,自然对流对融化传热过程有着重要的影响,此外固相热传导也对融化传热、融化速率及固液两相温度分布都有一定影响. 相似文献
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Saeed Ullah Jan Sami Ul Haq Syed Inayat Ali Shah Ilyas Khan Muhammad Atif Khan 《理论物理通讯》2019,71(6):647-657
This work is focused on the effect of heat and mass transfer with unsteady natural convection flow of viscous fluid along with ramped wall temperature under the assumption of the slip wall condition at the boundary. Analytical solutions are obtained by using Laplace transformation to the non-dimensional set of governing equations containing velocity, temperature and concentration. Moreover, the expression for skin-friction is derived by differentiating the analytical solutions of fluid velocity. Numerical tables for Skin-friction, Sherwood number and Nusselt-number are examined. For the physical aspects of the flow, we use various values of involved physical parameters such as Prandtl number (Pr), slip parameter ($\eta$), Schmidt number (Sc), buoyancy ratio parameter ($N$), Sherwood number (Sh), and time $(t)$. Additionally, the general solutions are plotted graphically and a comprehensive theoretical section of numerical discussions is included. 相似文献
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In this paper, we propose an adaptive defect-correction method for natural convection (NC) equations. A defect-correction method (DCM) is proposed for solving NC equations to overcome the convection dominance problem caused by a high Rayleigh number. To solve the large amount of computation and the discontinuity of the gradient of the numerical solution, we combine a new recovery-type posteriori estimator in view of the gradient recovery and superconvergent theory. The presented reliability and efficiency analysis shows that the true error can be effectively bounded by the recovery-based error estimator. Finally, the stability, accuracy and efficiency of the proposed method are confirmed by several numerical investigations. 相似文献