共查询到17条相似文献,搜索用时 62 毫秒
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为了解双层流体系统上液层流体与下液层流体普朗特数(Pr)对热毛细对流的影响,通过线性稳定性分析,确定了上液层流体与下液层流体Pr比值从0.164~5.417时环形双层流体热毛细对流失稳的临界条件,预测了它们的4种流动失稳型式,即轮辐状的几乎占据了整个液层的"轮辐波"、轮辐状的热流体波与同波数共同旋向的靠热壁处流胞、径向... 相似文献
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数值研究了不同重力场下液池内耦合热-溶质毛细对流流动特性,模型中考虑了热毛细效应和溶质毛细效应相当这一特殊情况。计算结果显示,当重力加速度较大时液池内存在周期性迁移的对流涡,而当重力加速度较小时,液池内的对流涡迁移消失,因而重力加速度能够促使热-溶质毛细对流失稳。随着重力加速的减小,监测点的温度和浓度振荡幅度减小。常重力条件下自由表面速度分布受浮力对流控制;微重力条件下,自由表面的速度分布基本一致,随着重力加速度减小自由表面速度略微减小。 相似文献
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为了了解微重力条件下、水平温度梯度作用时,上部为固壁的环形腔内双层流体系统中液层厚度比对流动稳定性的影响,采用隐式重启Arnoldi方法(IRAM)对环形池内5cSt硅油/HT-70双层流体的热对流过程进行了线性稳定性分析,获得了不同液层厚度比下的临界Marangoni数、临界波数、临界相速度,并通过计算特征向量,得到了临界Marangoni数附近液-液界面的热流体波形态。 相似文献
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针对液封提拉法生长蓝宝石晶体的热毛细对流过程,通过二维数值模拟,获得了微重力条件下、上部为自由表面的环形双液池B2O3/蓝宝石熔体的R-Z截面的流函数、温度分布,以及监测点的速度和温度分布,揭示了流动失稳后的振荡流型.并且把B2O3/蓝宝石熔体的计算结果与5cSt硅油/HT-70进行了比较.结果表明:当Marangon... 相似文献
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讨论了混合对流条件下环形通道中浮升力对流动及传热的影响。实验时用LDA测量了水向下流过竖直环形通道时的平均流速和湍流强度。对于逆浮升力方向的流动情况,湍流速度脉动和湍流剪切应力都因浮升力的影响而增加,从而传热得到了增强。当浮升力的影响特别大时。靠近环形内壁的流动出现反向流,在这种情况下即使流动在无浮升力影响时是层流。湍流也会由于浮升力的存在而产生,传热维持较好的效果。 相似文献
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为了对高效大功率远端射频模块(RRU)的散热器设计提供依据,本文提出了两种强化直翅式竖直热沉自然对流散热的有效措施:对完整热沉在中间位置开缝同时在开缝处添加挡片,以及对开缝热沉存在的局部传热不利区域开孔来强化散热。本文采用了实验手段结合数值模拟的方法,研究了两种逐次递进的改进措施对给定几何结构参数的直翅式竖直热沉散热性能的影响。研究结果表明:当开缝宽度为10 mm时,中间开缝并添加挡片之后,竖直热沉散热性能显著提升;开缝从中间位置分别向上或向下平移时,散热性能均逐渐减弱。添加挡片后的中间开缝热沉肋间流场存在传热死区,通过对该区域内的翅片开孔能够有效减少传热死区的面积;开孔不仅改变了肋间空气的流向,而且形成了漩涡现象和扰流运动,从而进一步强化了热沉整体的散热性能。 相似文献
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M. Ould-Rouiss L. Redjem-Saad G. Lauriat A. Mazouz 《International Communications in Heat and Mass Transfer》2010
The effect of Prandtl number on the turbulent thermal statistics in fully developed annular pipe flow, with isoflux boundary conditions, is investigated by use of direct numerical simulation, for two values of Reynolds number. The Prandtl number has marked influence on the thermal field. With decreasing Pr, the conductive sublayer at both walls spreads from the walls to the core region, while the root mean square of temperature fluctuations and the turbulent heat fluxes are reduced near both walls. Asymptotic behaviours of these quantities are analyzed. 相似文献
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Lattice Boltzmann Simulation of Natural Convection in a Differentially Heated Square Enclosure Containing Heat Generating Low‐Prandtl Number Fluid
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Lattice Boltzmann simulations were conducted for the free convective flow of a low‐Prandtl number (Pr = 0.0321) fluid with internal heat generation in a square enclosure having adiabatic top and bottom walls and isothermal side walls. The problem of free convection with volumetric heat source has represented itself in connection with advanced engineering applications, such as water‐cooled lithium–lead breeder blankets for nuclear fusion reactors and liquid metal sources of spallation neutrons for subcritical fission systems. A single relaxation time (SRT) thermal lattice Boltzmann method (LBM) was employed. While applying SRT, a D2Q9 model was used to simulate the flow field and temperature field. Results have been obtained for various Rayleigh numbers characterizing internal and external heating from 103 to 106. Flow and temperature fields in terms of stream function and isotherms in the enclosure were predicted for these cases. The temperature of the fluid in the enclosure was found higher than the heated wall temperature at high values of internal Rayleigh numbers. The internal heat generation affected the rate of heat transfer significantly as two convection loops are observed in the enclosure. The average Nusselt number at the heated and cold wall was determined for all the cases. 相似文献
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In order to understand the influence of curvature on thermocapillary‐buoyancy convection in a differentially heated annular pool with an outer heated cylinder ($ro=40 mm$) and an inner cooled cylinder (ri=20 or 10 mm), a series of unsteady two‐dimensional numerical simulations using the finite‐volume method was conducted. The pool was filled with 0.65 cSt silicone oil (Prandtl number Pr=6.7); its depth changed from 0.5 to 1.5 mm. Simulation results show that the flows with different curvature are all stable at small temperature differences. Increasing the temperature difference, the flow transition to an oscillatory flows occurs. The critical temperature difference, depending on the curvature of annulus, is determined. It was found that there is a good agreement between the simulation and the experiment results on the critical temperature difference. ©2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(4): 187– 197, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20157 相似文献
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We examined the effects of Prandtl number on three‐dimensional mixed convection in a horizontal square duct with heated and cooled side walls numerically. Non‐dimensional governing equations were solved for Re = 100, Pr = 0.1–10, and Ri = 36.44 by the SIMPLE method. The numerical results show that the swirl flow was generated along the flow direction, and its pitch lengthened with the increase of Pr. We also examined the strength of swirl flow using the swirl number, S, and we discuss heat transfer behavior as it corresponded to the flow. Heat transfer was promoted by the swirl flow with all Pr, and the optimum value existed within these Pr. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20319 相似文献
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The effect of Prandtl number on natural convection heat transfer and fluid flow in triangular enclosures with localized heating has been analyzed by solving governing equations of natural convection in streamfunction–vorticity form with finite-difference technique. Solution of linear algebraic equations was made by Successive Under Relaxation (SUR) method. Bottom wall of triangle is heated partially while inclined wall is maintained at a lower uniform temperature than heated wall while remaining walls are insulated. Computations were carried out for dimensionless heater locations (0.15 ≤ s ≤ 0.95), dimensionless heater length (0.1 ≤ w ≤ 0.9), Prandtl number (0.01 ≤ Pr ≤ 15) and Rayleigh number (103 ≤ Ra ≤ 106). Aspect ratio of triangle was chosen as unity. It is observed that both flow and temperature fields are affected with the changing of Prandtl number, location of heater and length of heater as well as Rayleigh number. 相似文献
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Lucia Fontana 《热科学学报(英文版)》2014,23(6):586-592
Simultaneous free convection above and below a uniformly heated horizontal plate has been widely investigated,both in the case of an isothermal surface,and of a uniformly heated surface,but always assuming only air as fluid(Pr=0.7).Nevertheless,there are works dealing with horizontal plates whose results show that the Nu dependence on Pr may not be simply expressed by a power law with the same exponent of the Gr one.So it was considered useful to study the Prandtl number influence in the case of the isothermal horizontal strip.Results show that,while for the lower surface of the strip the Nu dependence in Gr can be expressed by a power law with an exponent close to the Gr one,for the upper surface the exponent is sensibly different.Correlating equations related to the investigated situations are proposed. 相似文献
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INTRODUCTIoNJetimpingementhasbeenextensivelyemployedintechnicalprocessestoproducerelativelyhighheat/massfluxes.Incomparisonwiththeheat/masstransferratesprovidedbyconventionaltechniqueswithfluidfiowsparalleltotheheat/masstransfersur-face,aremarkableincreaseintransfercoefficientscanbeobtainedinthisfashion.Inmostcasesairisusedastheworkingmedium.Examplesofairjetapp1icationsincludecoolingofturbinebladesandelectroniccom-ponents,annealingofmetallicandplasticsheets,dry-ingoftextilesandpaper,andtem… 相似文献