共查询到20条相似文献,搜索用时 15 毫秒
1.
Koji Hasegawa Yutaka Abe Akiko Fujiwara Yuji Yamamoto Kazuyoshi Aoki 《Microgravity science and technology》2008,20(3-4):261-264
One of the major recent advances for experiments in containerless processing is acoustic levitation. Although there are a lot of previous studies for acoustic levitation, characteristic of external flow of an acoustically levitated droplet is not experimentally examined enough. In this study, external flow field has been observed by using high speed camera and Particle Image Velocimetry. In the case of any levitated droplet at a velocity antinode of standing wave, toroidal vortex are generated around levitated droplet. It is found that toroidal vortex around a levitated droplet is strongly affected by viscosity of levitated samples and input voltage. In terms of water droplet, as input voltage is decreased, location of toroidal vortex is moved from bottom to top of levitated samples. 相似文献
2.
Yuji Yamamoto Yutaka Abe Akiko Fujiwara Koji Hasegawa Kazuyoshi Aoki 《Microgravity science and technology》2008,20(3-4):277-280
Under the microgravity environment, products of new and high quality materials solidified into homogeneous crystal by under cooling solidification have been the subject of much interest. Manufacture of material under the microgravity environment can be performed more static than that under the normal gravity. Handling technology of molten metal is important for such processes to hold in the limit space. However, when a large levitated droplet exists in the limit space, internal flow can be appeared remarkably. Elucidation of the effect of the internal flow of the levitated droplet is required in order to establish the containerless processing for new material under the microgravity environment. In current research, the internal flow of a levitated droplet was investigated by Zhao et al. (J Acoust Soc Am 106:589–595, 1999a and 106:3289–3295, 1999b) and Trinh et al. (Phys Fluids 12(2):249–251, 2000). These studies were analyzed numerically and theoretically. However, experimental study about the internal flow of the levitated droplet is not enough. According to our study Abe et al. (Microgravity Sci Technol 19(3–4):33–34, 2007), the authors observed internal flow of the water and glycerol droplet in normal gravity environment. In the water droplet, which is a low viscosity fluid, internal flow of both left and right hand rotation was observed. On the other hand, in the glycerol droplet, which is a high viscosity fluid, only rigid body rotation was observed. This research measured only two dimensional flows. It is thought that internal flow in the water is not two-dimensional but three-dimensional flow. Then, in order to investigate a three-dimensional flow structure in levitated water droplet in detail, we try to measure the three-dimensional flow in the levitated droplet. In the present study, test fluid with different viscosity is levitated. And, multidimensional PIV measurement is conducted to investigate the internal flow structure in a levitated droplet. Stereo images at equatorial plane of a levitated droplet are observed for measuring the three-dimensional component of velocity in the levitated droplet. As a result, the velocity of z direction is observed in the water droplet. On the other hand, the v z is hardly observed in the glycerol droplet. The three dimensional structures of water and glycerol are differed. The difference of such flow structure is supposed to be due to the influence of the viscosity. 相似文献
3.
Masanori Kawakami Yutaka Abe Akiko Kaneko Yuji Yamamoto Koji Hasegawa 《Microgravity science and technology》2010,22(2):145-150
Under the microgravity environment, new and high quality materials with a homogeneous crystal structure are expected to be
manufactured by undercooling solidification, since the material manufacturing under the microgravity environment is more static
than that under the normal gravity. However, the temperature change on the interface of the material in space can affect on
the material processing. The purpose of the present study is to investigate effect of the temperature change of interface
on the large levitated droplet interface. A water droplet levitated by the acoustic standing wave is heated by YAG laser.
In order to heat the water droplet by the laser heating, rhodamine 6G is solved in it to achieve high absorbance of the laser.
The droplet diameter is from 4 to 5.5 mm. The deformation of the droplet interface is observed by high speed video camera.
The temperature of droplet is measured by the radiation thermometer. It is noticed that the larger droplet under the higher
sound pressure tends to oscillate remarkably by the laser heating. 相似文献
4.
Masanori Kawakami Yutaka Abe Akiko Kaneko Koji Hasegawa 《Microgravity science and technology》2010,22(3):353-359
Under the microgravity environment, new and high quality materials with a homogeneous crystal structure are expected to be
manufactured by undercooling solidification, since the material manufacturing under the microgravity environment has no effect
of gravity. However, the temperature change on the interface of the material in space is expected to affect on the material
processing due to the changing of physical property corresponding temperature. The purpose of the present study is to investigate
effect of the laser heating on surface deformation of large levitated droplet. A water droplet levitated in the acoustic standing
wave is heated by YAG laser. In order to increase the water droplet temperature, rhodamine 6G is solved in it to achieve high
absorbance of the laser. Droplet from 2.5 to 5.5 mm in diameter were levitated and heated. The deformation of the droplet
interface has been observed by high speed video camera. We used the radiation thermometer for the measurement of the temperature
of droplet surface. It is noticed that the heated droplet deforms with its resonance frequencies. The experimental result
of shape oscillation makes it possible to simulate the oscillation. 相似文献
5.
S. R. Berry R. W. Hyers L. M. Racz B. Abedian 《International Journal of Thermophysics》2005,26(5):1565-1581
The natural oscillation frequency of freely suspended liquid droplets can be related to the surface tension of the material,
and the decay of oscillations to the liquid viscosity. However, the fluid flow inside the droplet must be laminar to measure
viscosity with existing correlations; otherwise the damping of the oscillations is dominated by turbulent dissipation. Because
no experimental method has yet been developed to visualize flow in electromagnetically levitated oscillating metal droplets,
mathematical modeling can assist in predicting whether or not turbulence occurs, and under what processing conditions. In
this paper, three mathematical models of the flow: (1) assuming laminar conditions, (2) using the k−ɛ turbulence model, and (3) using the RNG turbulence model, respectively, are compared and contrasted to determine the physical
characteristics of the flow. It is concluded that the RNG model is the best suited for describing this problem when the interior
flow is turbulent. The goal of the presented work was to characterize internal flow in an oscillating droplet of liquid metal,
and to verify the accuracy of the characterization by comparing calculated surface tension and viscosity values to available
experimental results. 相似文献
6.
Yanxia Du Guangming Xiao Yewei Gui Lei Liu Lina Zhang Mingxing Yu 《International Journal of Thermophysics》2014,35(8):1577-1589
The objective of the study was to investigate the heat transfer characteristics of a phase-change energy storage unit for thermal management. Considering the conduction in the solid and natural convection in the liquid, a physical and mathematical model for heat transfer was formulated. The governing conservation equations were solved using the finite-volume method on fixed grids. An enthalpy-porosity method was used for modeling the melting phenomenon of a phase-change energy storage unit. The time and space movement of the phase front, the temperature distribution, and the heat dissipation rate have been analyzed based on the model. The influence of the unit geometry, heat source location, and types of phase-change materials on the thermal performance of the energy storage unit were investigated. The model and numerical method were evaluated by comparing the numerical predictions with the experimental results. There was found to be excellent agreement between the calculation and experiment, indicating that the numerical method for heat transfer simulation of a phase-change energy storage unit is accurate. The results from the analysis elucidate the thermal performance of the phase-change energy storage unit and will provide the basis for the design and optimization of thermal management systems. 相似文献
7.
针对应用于电站直接空冷凝汽器的蛇形翅片扁平单排管,对其空气侧的流动及换热特性进行了数值模拟。给出了该管件基本结构的雷诺数和欧拉数随迎面风速的变化关联式;结果显示,同一迎面风速下,随着翅片间距、高度的增大,换热变差,流动变好。但当间距增加到一定程度时,风速与间距对换热流动性能的影响都变得很小。风速越大,换热性能对翅片间距、高度越敏感,而流动则相反,需根据实际工况来选择合适的翅片间距及高度。 相似文献
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相变传热凭借其良好的传热能力和较低的能耗的特点在航空航天领域的电子设备冷却尤其是蒸发制冷循环系统中得到应用。飞行器在机动飞行或进出大气层都会遇到超重状态。超重状态下的两相流的流动及传热特性相对于静止状态时候发生了很大的变化。以流动水为介质,通过搭建旋转平台对超重状态下两相流系统进行了实验研究,得到流体在过载时流动特性和传热特性的初步变化规律。结果显示超重对流动和换热都会产生显著影响。试验结果对于飞行器上相变换热器的理论分析和设计积累了有价值参考资料。 相似文献
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冰浆流体流动与换热研究综述 总被引:4,自引:0,他引:4
介绍了冰浆流体的特点、应用以及固液两相流体等效比热的概念及其在冰浆流体中应用的困难;概述目前国内外冰浆流体的传热性能、流变模型和流态以及粘性和流动阻力的研究成果,指出由于固液两相密度的不同导致了在不同流速下冰水分层的现象;同时对冰浆流体的的研究进行了综述,最后提出了关于冰浆流体的进一步研究建议. 相似文献
11.
本文对水平细通道内CO_2流动沸腾换热过程中流态及其转变特性进行理论分析和可视化实验研究。根据可视化实验结果,更新了CO_2在低蒸发温度下的理论流动状态预测模型。实验工况为:热流密度(7. 5~30 k W/m2)、质量流率(50~600kg/(m2·s))、饱和温度(-40~0℃)、干度(0~1)、内径(1. 5 mm)。理论分析表明:质量流率对换热过程中经历的流态形式有决定性作用,热流密度对环状流-干涸区域、干涸区域-雾状流边界转变曲线影响较大,饱和温度对流态转变具有重要影响。可视化研究表明:基于理论流态图对于CO_2在细通道内流动沸腾换热的流态能够较好的预测,也能反映不同工况下流态的变化趋势,但理论流态图对干涸区域和雾状流区域预测偏差较大;在实验数据的基础上,增加了液气黏度比的无量纲因子,并提出一种新的临界热流密度预测模型。在考虑质量流率和热流密度影响的情况下,根据更新后临界热流密度预测模型和实验数据,引入沸腾数Bo对理论流态图中环状流-干涸区域、干涸区域-雾状流及间歇流/弹状流-环状流边界转变曲线进行了更新,可视化研究获得的流态数据中89. 4%符合更新后的CO_2理论流态预测模型。 相似文献
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为实现微小空间高效散热,本文以去离子水为工质,实验研究了工质流经高度和直径均为500μm的微圆柱组成的叉排微柱群通道时的饱和沸腾换热特性,并采用高速摄像机记录了通道内不同加热功率的气液两相流型,实验参数设定质量流速为341~598.3 kg/(m~2·s),热流密度为20~160 W/cm~2,蒸气干度为0~0.2。结果表明:随着热流密度增大,局部沸腾换热表面传热系数近似单调递减。在低干度区,局部沸腾换热表面传热系数随着质量流速的增加而增大,随着蒸气干度的增加而减小;受过冷沸腾气泡影响,工质进口温度越低,局部沸腾换热表面传热系数越大;随着热流密度增大,微柱群通道流动沸腾气泡流型依次为:泡状流、环状流,且泡状流区的局部沸腾换热表面传热系数明显高于环状流区。 相似文献
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介绍了强化管内流动沸腾换热国内外的研究现状,分析了微肋管内流动沸腾换热的影响因素,并且给出了几个实用的微肋管内沸腾换热关联式,最后对微肋管内沸腾换热的研究方向进行了讨论. 相似文献
15.
An integrated numerical model is presented for free surface phenomena and Marangoni fluid flows in electrically levitated droplets under both terrestrial and microgravity conditions. The model development is based on the boundary element solution of the Maxwell equations simplified for electrostatic levitation applications and the free surface deformation that is primarily caused from the surface Maxwell stresses resulting from the applied electric fields. The electric and free surface model is further integrated with a finite element model for the surface-tension-induced fluid flows in the levitated droplets. Both 2-D and 3-D fluid flow structures may be developed in the electrically levitated droplets depending on the applied laser heating sources. The integrated model is applied to study the electric field distribution, free surface deformation, and 2-D and 3-D internal fluid flow structures in normal and microgravity for single, symmetric two-beam, four-beam, and six-beam laser heating arrangements. Among these arrangements, the six-beam arrangement with equal heating intensity gives the smallest temperature difference and the smallest maximum velocity. 相似文献
16.
采用Level Set-VOF模拟单液滴撞击壁面的铺展行为及液滴初速度、初始直径及液膜厚度对液滴撞壁传热特性的影响。研究表明:液滴初始速度较大,撞击壁面后发生强烈反弹,液滴在表面回缩破碎及铺展破碎能力加强,导致表面传热系数随之增大;随着液滴初始直径增大,液滴铺展破碎的发生,将对表面传热起促进作用;初始液膜越厚,撞击后液滴溅射能力被削弱且在表面铺展趋势延缓,因此不利于热量迅速传递。 相似文献
17.
陈忠杰 《制冷空调与电力机械》2004,25(6):27-30
应用重力热管是解决青藏铁路建设中冻土路基冻融问题的一个较为实际的方法.本文通过分析重力热管的热阻网络,提出了重力热管的传热模型,并利用现有的热管内部传热的经验关系式,对不同倾角、不同管径以及不同冷凝管长度条件下的传热量进行模拟计算. 相似文献
18.
采用SES软件分析了地铁联络线中空气的流动和换热特性,讨论了联络线长度、断面积以及距车站距离对联络线中空气的流动和换热特性的影响。结果表明:联络线中空气的流向呈周期性正反交替变化,一个周期内两正线通过联络线的空气交换量为196m3;正线流入联络线的热流量也呈周期性正反交替变化,一个周期内两正线通过联络线的热交换量为2579kJ;三种影响因素中联络线距车站距离的影响最大,联络线长度的影响次之,断面积的影响最小。 相似文献
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