周期性渐扩-渐缩通道层流流动与换热特性研究

以渐扩-渐缩通道内周期性充分发展的层流流动与换热为研究对象,采用SIMPLE算法,适体坐标网格及Amano周期性边界条件的实施方案对之进行数值模拟,计算了在层流范围内不同Re数下的流动与换热规律.结果表明,在Re=100~1000范围内,与平行平板通道相比,阻力增强了(10~200)%,换热增强了(40~320)%.     

周期性通道内非牛顿流体的流动与换热的实验研究

本文用实验方法研究了两种不同浓度的非牛顿流体（ＰＡＭ溶液）在不同温度下的流变曲线及其在周期性通道内的流动与换热规律。实验结果表明,两种ＰＡＭ溶液的稠度系数Ｋ随温度升高而减小,而流变指数ｎ则随温度升高而增加。两种浓度ＰＡＭ溶液在周期性通道内的换热强度和阻力损失均比水高。同时,在Ｒｅ 在１０～５０的范围内,通道内非牛顿流体的流动与换热规律可整理成形如 Ｎｕ＝ Ｃ１Ｒｅ＊ｍ１和 ｆ＝ Ｃ２Ｒｅ＊,ｍ２的形式。     

滑移流区内微环缝槽道中的层流流动与换热

本文针对微环缝槽道采用速度滑移和温度跳跃边界条件求解了不可压缩气体的Ｎ－Ｓ方程和能量方程,理论分析了微环缝槽道在单侧或双侧不同热流密度加热条件下的流动与层流换热特性,讨论了Ｋｎ数、内外径比对流动阻力及换热特性的影响。结果表明：滑移流区微环继通道内的流阻和Ｎｕｓｓｅｌｔ数明显低于连续流区;且随着Ｋｎ数的增加,流阻和Ｎｕｓｓｅｌｔ数均减小;但其随内外径比ｒ＊的变化趋势与连续流区相似。     

FC—72圆形射流冲击模拟电子芯片单相局部对流传热的实验研究

以最新微电子设备冷却剂ＦＣ－７２为工质，实验研究了自由和浸没情况下，圆形射流冲击５ｍｍ×５ｍｍ模拟电子芯片的局部对流换热情况。喷嘴直径ｄ＝０．９８７ｍｍ，Ｒｅ数范围为３４８８～４２６４４。测定了自由和侵没情况下驻点换热及换热系数的径向分布，讨论了雷诺数、喷嘴一传热面间距的影响。首次发现ＦＣ—７２自由射流在高Ｒｅ数下，随着喷射间距的增加，驻点换热得到加强，而浸没射流随喷射间距的增大，驻点换热出现非单调性变化；给出了喷射间距ｚ／ｄ＝４时驻点换热系数的关联式，并与其它工质的已有结果进行了比较；对换热系数径向分布的研究表明，与自由射流不同，浸没射流分布曲线上明显出现由层流向湍流过渡所引起的二次峰值。     

膜片管束通道传热性能的数值研究

以膜片管束通道为研究对象,通过数值模拟分别对通道的入口段和充分发展段建立非稳态数学模型。在不同Re下的通道入口段中不同几何周期的相应截面上设置无量纲速度和无量纲温度的监测点,分析了入口段的换热特性,并且重点探讨了流动与换热进入周期性充分发展段后,改变管束排列方式对换热Nu的影响。结果表明:Re不同时,流动和换热进入充分发展需要经过的几何周期数也不同;进入充分发展段后,Nu随着管间距的减小而逐渐增加,而且对于大间距排列管束,改变圆管竖直方向间距对Nu的产生的影响更显著。     

＝4．03GeV下τ~±→π~＋π~－π~±υ_τ衰变的测量

利用北京谱仪（ＢＥＳ）在４．０３ＧｅＶ正负电子对撞能量下获取的数据，［研究了，τ＋τ－产生过程．借助双标记方法分析了τ±→π＋π－π±υτ衰变事例．测定分支比Ｂｒ（τ±→ａ１±υτ→ρ０π±υτ，ρ０→π＋π－＝（７．３±０．５）％，Ｂｒ（τ±→Ｋ＊±υτ→Ｋｓ０π±υτ，Ｋｓ０→π＋π－）＝（０．６±１．５）×１０－３．并由Ｄａｌｉｚ投影分布的分析，确认ａ１的主要衰变方式ρπ．同时，也观察到ａ１衰变中以Ｓ波贡献为主的现象．采用Ｋｕｈｎ模型拟合实验数据，得到：ｍａ１＝１．２４±０．０２ＧｅＶ，Γａ１Ｔ＝０．５７±０．０７ＧｅＶ．     

地球几个常用物理量的计算

有关地球的几个物理量,如质量、半径、电容量等,是我们在实践中常常提及并用到的,学生了解这些知识是非常必要的．１地球质量Ｍ地 月球绕地球作圆周运动,周期Ｔ＝２７．３天,轨道半径 Ｒ＝３． ８ × １０８ｍ．由万有引力定律和圆周运动的知识得： 化简后 与相关资料的 ５． ９８ × １０２４ｋｇ,近似相等． 有必要说明,在计算中我们所采用的月球绕地球的周期Ｔ＝２７．３天,而不是通常所认为的Ｔ０＝２９． ５天,这是因为Ｔ０表示了月相变化的周期,这种周期是相对于日地连线而言的,而月球绕地球公转的周期应相应于月地连线,…     

蒸气在倾斜细小直径圆管内的流动凝结换热特性

细小管内的流动凝结换热具有许多超常换热特性,经典的Ｎｕｓｓｅｌｔ分析方法已不能满足需要。在以往研究的基础上,本文进一步通过实验探析换热温差和蒸气流量对不同直径的细小管内流动凝结换热的影响。研究表明,管径越小,换热温差对凝结换热系数的影响程度越低;通过流量和倾角对凝结换热数的影响,分析了重力引发的流动分层和剪切力对凝结液的排除两种因素对细管传热强化的作用机制。本文的实验结果和用于常规尺度下的通用关联式对比表明,采用细管,管内的流动凝结换热得到无可置疑的强化     

周期性锯齿型通道内流动和换热研究

用非稳态层流模型对锯齿型通道内周期性充分发展流动与换热进行了数值模拟．Re=600时数值结果已发生明显振荡,而从入口段算起的第9、10个几何周期的平均Nu数与用周期性充分发展条件计算得到的平均Nu数吻合良好;在此基础上,计算通道周期长度L与通道垂直高度b的比值及通道倾角α等几何结构尺寸对周期性充分发展流动和换热的影响,计算结果表明,增大α和减小L／b都易促使流动产生涡旋,从而增强换热．     

周期性矩形槽通道内对流换热的振荡

采用非稳态数学模型,通过数值模拟对周期性矩型槽通道内流动和换热的振荡特性进行了研究。结果表明:随着Re的增大,对流换热从入口后某一个几何周期开始振荡,振幅沿着通道逐渐增加,并经过若干周期后振幅基本不变;对于不同的Re开始振荡的几何周期数不同;当振幅基本不变时,各几何周期的平均Nu及相应点的速度按时间的平均值基本相等,表明振荡的流动和换热特征参数的时均值仍然具有周期性充分发展的特征;通道中突出物高度对振荡有显著影响,突出部分越高,开始振荡的几何周期数越小。     

周期性矩形槽通道入口流动与换热的数值分析

对周期性矩形槽流道入口的流动与换热进行了数值模拟。结果表明:在所考虑的参数条件下,流动和换热是非稳态的,并且随着Re的增大,这种随时间变化的特点越明显;当Re等于100、200时,经过1~2个几何周期,各周期的流速分布和无量纲温度的分布基本相同,流动和换热表现为明显的周期性充分发展特征。     

非稳态横掠管束周期性充分发展对流换热的数值模拟

本文采用非稳态数学模型对横掠管束的周期性充分发展流动与换热进行了数值模拟。结果显示,在所考虑的参数条件下,Re≥100以后流场和温度场随时间发生振荡,并且振幅随Re增加而增大;进一步增加Re到一定值后,在管束间会有交替出现的涡。计算得到的平均Nusselt数与现有文献中的实验关联式基本是吻合的。平均Nusselt数的计算值随流动方向管间距的增加而增加。     

锌锅中低Pr流体混合对流的数值模拟

以带钢连续热镀锌生产工艺为背景,对抽象出的低Pr数流体混合对流流动和换热模型进行了数值模拟,给出了在不同Re、Ra及Ri时的流场和温度场.数值结果表明,当Re、Ra都不等于0时,在所考虑的参数范围内,流动和换热受自然对流和强制对流两种机理控制.Re不变,增大Ri,自然对流作用加强,并且当Ri增加到一定值时,流动和换热发生振荡.所给出的速度相图显示,对应不同的Re、Ra及Ri,流动和换热会出现稳态解、周期性振荡解和混沌.     

带间断性矩肋的平行平板通道中三维流动与换热的数值模拟

1数学描述与计算方法周期性变化的几何结构是广泛应用的一种强化换热形式＊‘］。文献中有关的数值研究多限于二维清形，三维的研究相对较少。本文针对沿流向周期性布置矩肋的平行平板通道，对层流周期性充分发展的流动与换热进行了三维数值模拟。计算单元如图1所示。对于不可压缩流体，忽略体积力时的控制方程为：图1矩助通道计算单元表1式（l）中各乡变量的含义式中d取不同值的对应关系见表1。设通道几何周期长度为S，则对充分发展状态的计算单元进出边界有如下关系：据文献＊，周期性充分发展流动的压力可以分解为两部分：式中o为一个周…     

方形通道内非牛顿流体的强化传热

对非牛顿流体在小尺寸方形通道内的低雷诺数受迫对流传热进行了实验研究。实验用介质为１５００ｗｐｐｍＣａｒｂｏｐｏｌ－９３４中性水溶液。通道顶壁受到等热流加热。结果表明，流体粘弹性与传热的相互作用取决于雷诺数的大小。当表观雷诺数Ｒｅ＞１１．５时，非牛顿流体开始强化对流传热。Ｒｅ数越高，传热强化的程度越大。流体的阻力系数则几乎不受粘弹性的影响。     

Experimental Investigation of Mixed Convection in a Channel With an Open Cavity

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.     

Analysis of heat transfer and nanofluid fluid flow in microchannels with trapezoidal,rectangular and triangular shaped ribs

In the present study, the effect of triangular, rectangular and trapezoidal ribs on the laminar heat transfer of water-Ag nanofluid in a ribbed triangular channel under a constant heat flux was numerically studied using finite volume method. Height and width of ribs have been assumed to be fixed in order to study the effect of different rib forms. Modeling were performed for laminar flow (Re=1, 50 and 100) and nanofluid volume fractions of 0, 2% and 4%. The results indicated that an increase in volume fraction of solid nanoparticle leads to convectional heat transfer coefficient enhancement of the cooling fluid, whereas increasing the Nusselt number results in a loss of friction coefficient and pressure. Also, along with the fluid velocity increment, there will be an optimal proportion between heat and hydrodynamic transfer behavior which optimizes performance evaluation criteria (PEC) behavior. Among all of the investigated rib forms, the rectangular one made the most changes in the streamlines and the triangular form has the best thermal performance evaluation criteria values. For all studied Reynold numbers, heat transfer values are least for rectangular rib from. Therefore, trapezoidal ribs are recommended in high Reynold numbers.     

Experimental study and mathematical modelling of heat transfer processes in heat accumulating media

Experimental results on reversing non-stationary heat transfer are presented for filtration of an air flow through an immobile heat accumulating medium consisting of lead (D = 2.0, 3.5, and 4.5 mm) and glass (D = 3.2 mm) balls. The studied device imitated the cyclic modes of heat regeneration in the ventilation system for domestic and office rooms. Dependency between the time of flow switching and Re number was measured. The mathematical model describing heat transfer between a gas flow and an immobile layer of balls was developed. Good correspondence between the experimental data and calculation results is observed for high Reynolds numbers. For low Re numbers the effect of heat losses is considerable, and experimental time of flow switching is shorter than the calculation one. The work was financially supported by the President of the Russian Federation (Grant No. NSh 6526.2006.3), Russian Foundation for Basic Research (Grant No. 06-08-00982), Foundation “Global energy” and Program “Energy saving of SB RAS”.     

Numerical study of flow and heat transfer from a torus placed in a uniform flow

Forced convection heat transfer characteristics of a torus (maintained at a constant temperature) immersed in a streaming fluid normal to the plane of the torus are studied numerically. The governing equations, namely, continuity, momentum and thermal energy in toroidal coordinate system, are solved using a finite difference method over ranges of parameters (aspect ratio of torus, 1.4 ≤ Ar ≤ 20; Reynolds number, 20 ≤ Re ≤ 40; Prandtl number, 0.7 ≤ Pr ≤ 10). Over the ranges of parameters considered herein, the nature of flow is assumed to be steady. In particular, numerical results elucidating the influence of Reynolds number, Prandtl number and aspect ratio on the isotherm patterns, local and average Nusselt numbers for the constant temperature (on the surface of the torus) boundary condition. As expected, at large aspect ratio the flow pattern and heat transfer are similar to the case of flow and heat transfer over a single circular cylinder.     

Numerical Analysis of the Joule Heating Effect on Plasma Heat Transfer

The application of thermal plasmas particularly in the field of plasma chemistry and plasma material processing requires a basic understanding of the heat transfer process. This paper is concerned with an analysis of the heat transfer to a positively biased body exposed to a plasma flow. Because of the induced current flow due to the biasing potential, the plasma surrounding the biased body will experience an increase in temperature caused by Joule heating. The fraction ? of the dissipated heat which is transferred to the body is calculated for an atmospheric argon plasma flow at temperatures between 104 and 2 × 104K and Reynolds numbers of 40 and zero. The results indicate that ? increases with increasing plasma temperature for Re = 40 and decreases slightly with increasing plasma temperature for Re = 0. As the Re number increases at constant plasma temperature ? decreases.