多孔表面的制造方法及其强化沸腾传热效果的比较

主要对用于强化沸腾传热的多孔表面的制造方法进行了介绍,对各种多孔表面强化沸腾传热的特性进行了比较和分析。最后探讨了多孔表面强化沸腾传热研究的发展方向。

复合金属丝网表面强化沸腾传热的研究进展

综述了复合金属丝网多孔表面的强化沸腾传热现状。介绍了复合金属丝网多孔表面的结构特性、强化沸腾传热特性;分析了丝网层内的传热传质过程。研究表明,烧结金属丝网多孔表面是一种很有工业应用前景的强化沸腾传热表面。

微通道流动沸腾过程中异态相干沸腾的强化传热研究

随着电子器件的集成化和小型化,其散热量超过10 MW/m2将成为现实,这超出了目前大功率系统中使用的单相冷却方案的上限,所以必须再次开发新的冷却方案.克服单相传热局限性的一种方法是转变为两相沸腾传热,而临界热流密度又是所有沸腾传热的上限值.因此,为了提高微通道内流动沸腾传热的临界热流密度,本文设计开发了非均匀导热性传热板.通过将两种不同导热性能的材料(铜和聚四氟乙烯)交替布置在靠近传热表面的传热板内,实现了传热表面的非均匀温度分布和异态相干沸腾模式(核态沸腾与膜态沸腾共存且相互干涉的状态).同时搭建了微通道流动沸腾实验系统,其微通道截面尺寸为1.84 mm×70.00 mm,通道长度为280.0 mm,传热板表面尺寸为10.0 mm×10.0 mm,流体工质为去离子水.在不同入口流速v=0.1 m/s、0.2 m/s、0.4 m/s和不同过冷度ΔTsub=10.0 K、20.0 K、30.0 K条件下,研究了非均匀导热性传热板在微通道流动沸腾中的传热强化效果.结果表明,相对于单纯的核态沸腾状态,异态相干沸腾状态能够有效地提升流动沸腾传热的临界热流密度.此外,改变入口流速和过冷度对临界热流密度有明显影响且趋势相同,减小入口流速和过冷度都会增大临界热流密度的提升比例.在本文的实验条件范围内,在水的流速v=0.1 m/s、过冷度ΔTsub=10.0 K的条件下,实现了最高约43.4%的临界热流密度提升比例.

多级复合芯结构的强化沸腾传热研究

采用固相烧结技术制备了均匀多孔层、复合16芯和复合32芯三种多孔结构,并且建立了池沸腾传热测试系统来研究不同芯数量、粒径与结构高度对多孔结构沸腾传热性能的影响。实验结果表明,在测试范围内复合层高1 mm的多孔复合32芯结构传热性能较强,临界热通量(CHF)最高为386 W/cm^(2),传热系数最高达到9.5 W/(cm^(2)·K)。同时利用高速摄影观察气泡行为来研究强化沸腾传热机理。可视化数据表明,相比于光滑表面,在高热通量下多孔复合表面上气泡周期更短,脱离更快,气泡的离开带来了更多的液体补充,进而不断提升传热性能,获得更高的CHF值。

工程热物理所在石墨烯自组装表面强化沸腾传热研究中取得进展

石墨烯等碳纳米材料有优异的力学、热学性质及化学稳定性,近些年在强化沸腾传热方面引起了学者的极大关注。基于碳纳米材料的沸腾强化技术主要可分为纳米流体技术和纳米涂层技术。纳米流体技术是利用含有碳纳米材料的纳米流体代替水作为液体工质来增强沸腾传热性能。

北京:在石墨烯自组装表面强化沸腾传热研究中取得进展

沸腾传热是一种极其高效的相变传热技术,具有取热热流密度高、过热度低和均温性好等优势,因此在热能的传递、转换和管理系统中起着至关重要的作用,被广泛应用于发电、海水淡化、冶金、高功率密度电子器件冷却、大功率激光器热管理、食品加工等化工、航空航天及军事等领域。提高沸腾传热性能在改善能源系统的效率、安全性及降低系统花费等方面具有重要意义,能够有效地实现节能减排。

碳钢-水热虹隙管内部强化传热机理研究

在微层蒸发模型的理论基础上，对热虹吸管内部设置分流管结构强化沸腾传热进行机理分析。建立分流管强化热虹吸管内部沸腾传热模型，同时选择七种不同的分流管开孔结构，与光滑管进行对比实验研究，寻得最佳分流管结构。并综合大量实验数据建立强化沸腾传热准数方程式。

T型管管束的沸腾传热性能

Ｔ型管管束的沸腾传热性能刘进荣（内蒙古工业大学化学工程系，呼和浩特０１００６２）沈自求徐维勤（大连理工大学化学工程研究所，大连１１６０１２）关键词水平管管束Ｔ型管沸腾传热强化卧式再沸器１引言水平管管束沸腾传热广泛应用于石油化工、制冷等工业部门，如蒸...

金属纤维多孔表面换热管换热性能研究

采用烧结法制备沸腾换热用不锈钢纤维多孔表面换热管,并对其制备方法和沸腾换热性能进行了测试研究。结果表明:采用逐次套管、限位烧结工艺,实现了金属纤维多孔表面换热管孔隙度精准控制,并通过施加过渡层,有效增强了金属纤维和基管间的冶金结合;当过热度小于20℃时,孔隙度小于90%的金属纤维多孔表面换热管的换热性能比光管好,其中85%孔隙度换热管的传热系数最高可达2 400 W/(m^2·K),比光管的传热系数增大1倍。

Fabrication and testing of phase change heat sink for high power LED

A novel phase change heat sink was fabricated for packaging cooling of high power light emitting diode （LED）. 3D structures as enhanced boiling structure in the evaporation surface were composed of a spiral micro-groove along circumferential direction and radial micro-grooves which were processed by ploughing-extrusion （P-E） and stamping, respectively. Meanwhile, the cycle power of refrigerant was supplied by wick of sintered copper powder on internal surface of phase change heat sink. Operational characteristics were tested under different heat loads and refrigerants. The experimental results show that phase change heat sink is provided with a good heat transfer capability and the temperature of phase change heat sink reaches 86.8 ℃ under input power of 10 W LED at ambient temperature of 20 ℃.

Pool boiling performance of porous surface tubes under vacuum conditions

Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.

不锈钢管表面多孔层真空制备工艺试验研究

为确定不锈钢表面多孔层的烧结工艺参数,通过改变粉末类型、粒径以及烧结气氛等因素,在不同烧结温度下进行了烧结试验,最终确定了合适的工艺。结果表明:烧结气氛是决定烧结结构以及母材性能的关键因素,真空烧结可保证烧结过程的顺利进行;随着烧结温度的升高,烧结时间的延长,烧结结构的结合强度升高,而孔隙率则呈急剧下降的趋势;粉末粒径不是影响孔隙率的主要因素,但是孔隙的当量直径随粒径的增大有变大的趋势,而混合粒径的粉末得到的烧结结构能得到孔隙当量直径分布较宽的烧结结构。另外,烧结管可有效提高沸腾传热系数,降低沸腾温差。

轻柴油汽提塔底T形翅片管重沸器工艺设计与应用

介绍了T形翅片管用于重沸器中强化沸腾传热的机理及其性能特点,建立了T形翅片管重沸器设计计算模型。与HTRI计算光管重沸器相比,T形翅片管管外沸腾传热系数提高了约5倍,总传热系数提高了80.4%,重沸器面积裕量由原-26.58%增加为31.2%,工业应用证明T形翅片管重沸器很好地满足了装置提负后的生产要求,为T形翅片管重沸器工业设计提供了理论依据。

Enhanced Pool Boiling Heat Transfer on Copper Foam Welded Surfaces

Enhanced pool boiling heat transfer of the porous structure is critical to the thermal management technology.In this paper,pool boiling heat transfer experiments are performed on copper foam welded surfaces in de-ionized water to investigate the effects of basic parameters of copper foam on heat transfer enhancement.Boiling phenomenon is observed to facilitate the understanding of enhancement mechanism.The results show that copper foam welded surfaces can significantly enhance the pool boiling heat transfer performance,reduce the boiling incipience temperature by 7-9℃,and reach two times heat transfer coefficient compared with smooth plain surfaces due to numerous nucleation sites,extended surface areas,and enhanced turbulent effect.Pore density and thickness of foam have two side effects on heat transfer.

Tabooed Universal Characteristic Length and Misled Boiling Heat Transfer Research

The paper presents the next step within multiyear fruitless efforts of the author to overcome the absurd situation in boiling heat transfer research. The focus is made on the problem of the characteristic length of the process most clearly exhibiting the consequences of half a century ignoring the basic MTD （Model ＂theater of director＂）, the UC （Universal correlation） and some other boiling fundamentals. Echoing control of boiling heat transfer by nucleation, the MTD-UC identifies universal characteristic length, the AER （Average effective radius） of nucleation sites, equally workable at the macro- and microscale. Inefficiency of the generally accepted, so called MTA （theater of actors） is particularly pronounced just in the confusion with the characteristic length. Traditional and potential candidates, departure diameter of vapor bubble and transverse internal size of the channel hardly can be adjusted to independence of developed boiling HTC on mass acceleration, subcooling, liquid convection and the heating surface geometry. At the same time, even such a problem has not prevented many authors to develop tens or even hundreds of helpless MTA-based correlations. The ignoring the MTD-UC-AER has also led to the incompleteness of the standard boiling heat transfer experiment, which is usually done without studying nucleation sites （there are available only very few comprehensive experimental works including the data on the AER）. The only exception was made for the problem of boiling heat transfer enhancement： over the past decades enhanced boiling surfaces were developed in direct accordance with the principle defined by the MTD-UC （just through the AER）. Another thing is that the basic role of the MTD-UC-AER in substantial progress of the relevant R＆D activities passed over in silence in the corresponding publications. Enviable unity and coherence of heat transfer community in preventing real scientific debate on the problem is also remarked.

Investigations on Heat Transfer Enhancement in Pool Boiling with Water-CuO Nano-Fluids

The main focus of the present work is to investigate Critical Heat Flux (CHF) enhancement using CuO nanofluid relative to CHF of pure water. To estimate the effect of nanoparticles on the CHF, pool boiling CHF values were measured for various volume concentrations of CuO nanofluid and compared with pure water. CHF enhancement of 130% was recorded at 0.2 % by volume of CuO nano-fluids. Surface roughness of the heater surface exposed to three measured heating cycles indicated surface modifications at different volume concentrations of nanofluid. SEM image of the heater surface revealed porous layer build up, which is thought to be the reason for CHF enhancement.

Vertically oriented TiO_2 nanotube arrays with different anodization times for enhanced boiling heat transfer

Pool boiling of saturated water on a plain Ti surface and surfaces covered with vertically-oriented TiO2 nanotube arrays(NTAs) has been studied.The technique of potentiostatic anodization using non-aqueous electrolytes was adopted to fabricate three types of TiO2 NTAs distinguished by their anodization time.Compared to the bare Ti surface,the incipient boiling wall superheat on the TiO2 NTAs was decreased by 11 K.Both the critical heat flux and heat transfer coefficient of pool boiling on the TiO2 NTAs were higher than those from boiling on a bare Ti surface.The measured maximum critical heat flux and heat transfer coefficient values were 186.7 W/cm2 and 6.22 W/cm2K,respectively.Different performances for the enhancement of heat transfer by the three types of TiO2 NTAs were attributed to the different degrees of deformation in the nanostructure during boiling.Long-term performance of the nanomaterial-coated surfaces for enhanced pool boiling showed degradation of the TiO2 NTAs prepared with an anodization time of 3 hours.