共查询到19条相似文献,搜索用时 140 毫秒
1.
2.
工质热物性显著影响脉动热管的流动与传热特性。本文通过理论计算及实验研究,定性分析了工质热物性对临界直径、毛细滞后阻力、启动运行及传热极限等方面的影响。研究表明,为保证脉动热管的运行性能,在设计阶段应综合考虑工质、管材及管径大小等因素。首先,根据使用场合的热流密度及运行温度高低合理选取工质种类;然后,选用合适的管壁材料,尽可能减少液塞与管壁之间前、后接触角不同引起的毛细滞后阻力;最后,确定管内直径范围。本文工作旨在为脉动热管的设计和选用提供一些依据和参考。 相似文献
3.
4.
5.
6.
7.
8.
《工程热物理学报》2018,(12)
开展了矩形槽道铝-乙醇小型重力热管的传热特性的实验研究,分析讨论了充液率对壁面温度分布、气液两相分布、热阻等热管传热性能的影响。研究表明,充液率对高热负荷工况的两相流动状态和传热特性有显著影响。两相脉动是高热负荷工况小型重力热管特有的两相流动现象.低充液率时,液塞易被气流冲破形成环状流,壁面温度几乎无波动。中等充液率时,在蒸汽和液塞的交替冲刷作用下,热管各段壁面温度均表现出脉动特性。高充液率时,液塞脉动速度的减小削弱了液塞对壁面的冲刷作用,壁面温度未出现明显波动.并且,中等充液率工况下气液两相的快速脉动增强了热管的传热性能,使得均温性和传热极限均优于低充液率和高充液率的情况. 相似文献
9.
《工程热物理学报》2017,(7)
本文通过实验研究了工质类型和工质充液率对竖直式脉动热管换热特性的影响。采用了去离子水、甲醇和乙醇三种液体作为工质,加热功率为5~80 W。结果表明,脉动热管的换热特性与工质充液率密切相关。当去离子水充液率为50%时,脉动热管内能够形成稳定的气柱和液塞流动,具有最佳的换热表现,获得的最低热阻为80 W加热功率下的0.47K/W。在较小的加热功率下,乙醇和去离子水具有比甲醇更小的热阻,随加热功率增加,采用甲醇时加热段温度上升波动剧烈,而采用去离子水和乙醇时温度上升平缓,具有更好换热效果。甲醇和乙醇做工质时获得的最小热阻分别为80 W加热功率下的0.56 K/W和0.48 K/W。 相似文献
10.
11.
Capillary Forces between Submillimeter Spheres and Flat Surfaces at Constant Liquid Volumes 下载免费PDF全文
We investigate the capillary forces between submillimeter spheres and flat surfaces at constant liquid volumes theoretically and experimentally. An iterative method is used to estimate the capillary force with contact angles as the boundary conditions and the constant volume as a constraint. The theoretical analysis shows that the maximum capillary force between them decreases with the increase of the liquid bridge volume at small contact angles. The experimental results show that the force is smaller than the theoretical values at the initial separation distances. It is also observed that the force first increases and then decreases with an increasing separation distance in some cases. These phenomena of capillary forces hysteresis are explained according to the wetting hysteresis. 相似文献
12.
利用落塔的短时微重力条件, 实验研究了与容器连通的毛细管中的流体在微重力条件下的毛细流动过程, 并通过理论分析建立了相应的毛细管中弯月液面高度随时间变化的微分方程. 结果表明, 对于不同的接触角和不同的容器/毛细管参数, 由建立的理论公式得到的数值解结果都与实验结果在定量上较为一致. 此外, 实验中发现, 改变乙醇和去离子水混合液的比例可以明显地改变接触角参数, 但对毛细流动的影响很小, 建立的理论公式也对这一现象给出了合理的解释. 该研究对于预测和分析微流道及空间微重力条件下的毛细流动行为具有明显的应用价值. 相似文献
13.
《Surface Science Reports》2014,69(4):325-365
A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, wetting has been studied using contact angles of drops on solids for more than 200 years, the question remains unanswered: Is wetting of a rough and chemically heterogeneous surface controlled by the interactions within the solid/liquid contact area beneath the droplet or only at the three-phase contact line? After the publications of Pease in 1945, Extrand in 1997, 2003 and Gao and McCarthy in 2007 and 2009, it was proposed that advancing, receding contact angles, and contact angle hysteresis of rough and chemically heterogeneous surfaces are determined by interactions of the liquid and the solid at the three-phase contact line alone and the interfacial area within the contact perimeter is irrelevant. As a consequence of this statement, the well-known Wenzel (1934) and Cassie (1945) equations which were derived using the contact area approach are proposed to be invalid and should be abandoned. A hot debate started in the field of surface science after 2007, between the three-phase contact line and interfacial contact area approach defenders. This paper presents a review of the published articles on contact angles and summarizes the views of the both sides. After presenting a brief history of the contact angles and their measurement methods, we discussed the basic contact angle theory and applications of contact angles on the characterization of flat, rough and micropatterned superhydrophobic surfaces. The weak and strong sides of both three-phase contact line and contact area approaches were discussed in detail and some practical conclusions were drawn. 相似文献
14.
15.
Up to now, measured results of the contact angle on rough surfaces have been explained usually based on the Wenzel equation (1936) and the Cassie-Baxter equation (1944). However, these equations do not take into account considerations of liquid wetting behaviors on rough surfaces, and this leads to poor understanding of the mechanisms of contact between liquid droplets and rough surfaces (e.g. contact angle hysteresis). We propose a new model for the contact angle of liquid droplets. By means of the present model, we can well understand the evperimental data which could not be well explained by the Wenzel equation and the Cassie-Baxter equation. 相似文献
16.
Hyväluoma J Koponen A Raiskinmäki P Timonen J 《The European physical journal. E, Soft matter》2007,23(3):289-293
The behaviour of liquid droplets on inclined heterogeneous surfaces was simulated by the lattice-Boltzmann method using the
Shan-Chen multiphase model. The effect of topography of the surface on the contact angle hysteresis was investigated. It is
shown in particular, by using anisotropic rough surfaces, how surface topography and thereby the continuity of the three-phase
contact line, affect this hysteresis. Our results clearly indicate that the superhydrophobicity of a surface cannot be judged
by the contact angle alone. 相似文献
17.
脉动热管的毛细管结构和尺度效应实验研究 总被引:3,自引:0,他引:3
脉动热管的毛细管结构变化如何影响其性能是研究者关注的问题.本文对毛细管截面为正方形和正三角形,水力直径范围为1 mm左右的回路型脉动热管的传热性能进行了实验研究.结果表明,角管脉动热管的倾角变化时,底加热明显优于顶加热;三角形截面脉动热管的热阻比正方形截面脉动热管的热阻更低.脉动热管在水力直径为1.5 mm时比1mm时的性能要好.实验研究为理论分析打下了基础. 相似文献
18.
19.
Nano-structured polyurethane/organoclay composite films were fabricated by dispersing moisture-curable polyurethanes and fatty amine/amino-silane surface modified montmorillonite clay (organoclay) in cyclomethicone-in-water emulsions. Cyclomethicone Pickering emulsions were made by emulsifying decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6) and aminofunctional siloxane polymers with water using montmorillonite particles as emulsion stabilizers. Polyurethane and organoclay dispersed emulsions were spray coated on aluminum surfaces. Upon thermosetting, water repellent self-cleaning coatings were obtained with measured static water contact angles exceeding 155° and low contact angle hysteresis (<8°). Electron microscopy images of the coating surfaces revealed formation of self-similar hierarchical micro- and nano-scale surface structures. The surface morphology and the coating adhesion strength to aluminum substrates were found to be sensitive to the relative amounts of dispersed polyurethane and organoclay in the emulsions. The degree of superhydrophobicity was analyzed using static water contact angles as well as contact angle hysteresis measurements. Due to biocompatibility of cyclomethicones and polyurethane, developed coatings can be considered for specific bio-medical applications. 相似文献