共查询到18条相似文献,搜索用时 234 毫秒
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本文提出了基于气液环状流的水平螺旋微肋管内沸腾传热理论预测模型.在模型建立过程中,假设环状流液膜是由基底液膜和叠加扰动波液膜单元组成,将无量纲准则数Fr0=G/[gdeρv(ρl-ρv)]0.5作为汽液两相流环状流理论模型的判据建立的模型理论预测值与已由的四种不同结构的微肋管、三种有机工质下得到的实验数据进行了比较,结果表明,在Fr0>4.0时,提出的环状流预测值理论值或者和预测值符合得较好,或者大幅度改善了原有分层流模型的预测效果,充分说明了提出的环状流理论模型的合理性. 相似文献
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对背面有热流输入的矩形毛细微槽群横截面上的气液分界面形状进行了理论分析,在一定条件下对Wayner蒸发模型进行简化,根据等壁温条件推出蒸发薄液膜区域热流密度近似为定值,通过流体动力学理论推导出了微槽横截面薄液膜区域液膜厚度变化的关系式,并与Wayner蒸发模型的计算结果进行了比较。进一步提出了全新的交界线区域长度的判定方法,根据蒸发薄液膜区域总换热量计算得到蒸发薄液膜区域的长度,交界处接触角,以及固有弯月面区域的曲率半径,从而最终得出了微槽横截面整个气液分界面的形状曲线,理论分析表明:槽宽、热流密度、过热度等因素对蒸发薄液膜区域长度、接触角以及固有弯月面曲率半径等参数有较大的影响。 相似文献
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气-液两相流设备的性能受限于临界热流密度,开展流动微液膜动力学特性及其稳定性的相关研究是深入理解沸腾危机及临界热流密度机理的关键。采用光学玻璃制成的矩形通道作为实验段,使用微流量齿轮泵驱动去离子水,使其在实验通道入口处与在其上部流动的压缩空气接触形成同向流动的分层流。利用共轭光学探测器对流动微液膜的厚度进行了测量,利用高速摄像机对气-液两相分层流波动特性进行了可视化观测。研究表明,在绝热情况下,当液速一定时,液膜的平均厚度随着气速增加而减小,当气速增加到某一阈值时会导致液膜破裂。 相似文献
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采用了一种新的边界条件来求解微槽内蒸发薄液膜的控制方程。这种新的边界条件保证在毛细微槽中,本征弯液面区域的液面弯曲中心位于微槽的中心线上,从而消除了传统微槽薄液膜计算模型中产生的物理矛盾。计算结果显示随着过热度的增加,本征弯液面部分的曲率半径不是恒定的,而是逐渐增加的,这导致了本征区域毛细吸力的降低。计算结果同时表明在本征区域的较薄位置,存在一个狭窄的热流密度相当大的子区域。在数值研究中,如果将此子区域用恒定半径的区域来替代,从理论上来讲是不合理的。 相似文献
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毛细管内薄液膜轮廓和传热特性研究 总被引:2,自引:0,他引:2
本文认为毛细管的相变传热机理为液膜的导热和表面蒸发;表面蒸发受蒸汽温度、汽液界面的温度以及汽液压力差的共同控制。汽液流动机理为流动受脱离压力梯度、毛细力梯度支配。汽液相互作用机理为存在由于蒸发导致的动量转移切应力和由于汽液流速不同产生的摩擦切应力。提出的物理模型中较为全面地考虑了毛细管内传热、汽液流动及其相互作用。对毛细管半径和传热功率对薄液膜轮廓和传热特性影响程度的计算结果表明,随着毛细管半径的减小、传热功率的增大,蒸发界面区的长度会有所减小,这是针对微小空间得出的不同于常规情况的结论。 相似文献
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水平螺旋槽管壁面升膜形成机理的研究 总被引:3,自引:1,他引:2
对驱动升膜形成的润湿力进行分析,建立单组分流体的数学模型,得出壁面液膜蒸发时的速度和厚度分布。基于此得到蒸发过程中水平螺旋槽管管外壁升膜的形成机理和流动特性,并给出液膜润湿整个管壁面的临界条件。 相似文献
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Heat transfer at evaporation of falling films of Freon mixture on the smooth and structured surfaces
The paper presents the results of experimental investigation of heat transfer and hydrodynamics of falling films of binary
mixtures of R21 and R114 freons on the surfaces with complex configuration. The vertical tubes of 50-mm diameter with the
smooth and structured surfaces, made of D16T alloy, were used as the working sections. The range of film Reynolds number at
the inlet to the working section was Re =10÷155. The image of wave surface of the falling liquid film was visualized and recorded
by a high-speed digital video camera. At evaporation the heat transfer coefficients on the smooth and structured surfaces
are determined by the liquid flow rate and weakly depend on the heat flux. At low liquid flows, the heat transfer coefficients
on the structured surface decrease in comparison with the smooth surface because of liquid accumulation and enlargement of
efficient thickness in microtexture channels. At high liquid flows, a change in the structure of the wave film surface leads
to an increase in heat transfer coefficients in comparison with the smooth surface. 相似文献
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Jun-Jie Zhao Yuan-Yuan Duan Xiao-Dong Wang Bu-Xuan Wang 《Journal of nanoparticle research》2011,13(10):5033-5047
A thin film evaporation model based on the augmented Young–Laplace equation and kinetic theories was developed to describe
the nanofluid effects on the extended evaporating meniscus in a microchannel. The nanofluid effects include the structural
disjoining pressure, a thin porous coating layer at the surface formed by the nanoparticle deposition and the thermophysical
property variations compared with the base fluid. The results show that the nanofluid thermal conductivity enhancement mainly
due to the Brownian motion tends to greatly increase the liquid film thickness and the thin film heat transfer. The structural
disjoining pressure effect tends to enhance the nanofluid spreading capability and the thin film evaporation. The nanoparticle-deposited
porous coating layer improves the surface wettability while significantly reducing the thin film evaporation with increasing
layer thickness due to the thermal resistance across this layer. The nanofluid thermal conductivity enhancement together with
the structural disjoining pressure effect can not counteract the thermal resistance effects of the porous coating layer when
the coating layer thickness is sufficiently large. 相似文献
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本文应用近似解析方法对双组分混合液在竖直平壁上的膜态沸腾换热进行了理论分析,得到了其平均膜态换热系数的解析计算式,并通过三种典型的双组分混合液例证了传质过程对换热的影响。 相似文献
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Heat transfer from a horizontal heated rotating disk to a thin water film flowing over it was investigated. A series of experiments were carried out to determine Nusselt numbers on the disk both with and without evaporation from the liquid film surface. The Nusselt number increased with increasing disk rotation rate, water temperature, and water flow rate, while evaporative cooling from the liquid film surface only had a moderate effect on the Nusselt number magnitude. Functional dependence of the Nusselt number from an accompanying semi-analytical model and experimental data were used to develop semi-empirical correlations for the Nusselt number. 相似文献