用饱和核态池沸腾换热机理模型预测加热壁面活化核心密度

活化核心密度是核沸腾过程的重要参数,但其描述方法至今尚未统一,为了避免核心密度直接测量的困难,提出根据核沸腾换热机理模型预测沸腾表面的活化核心密度,预测得到的六种表面的核心尺度分布曲线与表面活化核心的分形分布相一致,证明了活化核心尺度分布具有分形特征这一结论具有普遍意义。     

沸腾两相流动中的动力学特征量

采用频域和相空间方法分析沸腾两相流系统。用实测的声压信号重构相空间，并用最大Lyapunov数和相关维数对重构的相空间进行量化。分析这些量化参数与实际实验过程中观察到的流型变化之间的关系。结果表明：声压信号的功率谱和相空间的量化参数均与沸腾流体中的流型变化有关，有可能作为流型变化的特征参量。     

高低热导率相间表面强化饱和池沸腾的格子玻尔兹曼模拟

采用格子玻尔兹曼方法模拟高低热导率相间表面的饱和池沸腾过程,研究不同表面高低热导率区域热导率比值、低热导率区域宽度和深度对沸腾换热性能的影响。对比均匀热导率表面与高低热导率相间表面的沸腾曲线发现：高低热导率相间表面的沸腾过程可被分为5个阶段,并且其临界热流密度最高可达均匀表面的12倍;高低热导率相间可促使表面维持一定的温度差异,从而保持明显的气液流动;随着低热导率区域宽度增大,气液分离更加明显,低热导率区域宽度存在一个最优值,其与毛细长度的量级接近;随着低热导率区域的深度增大,表面过热度的差异更加明显。     

微纳结构铜表面低液位池沸腾实验研究

采用两步电镀法,在改变电流密度的情况下制备出具有不同微纳结构和润湿特性的A、B两个表面,并应用于低液位饱和池沸腾的实验研究中.通过与铜表面对比,发现两个表面在低热流密度情况下,传热系数要高于铜表面,但液位降低时传热系数提升幅度较小,原因在于铜表面沸腾气泡较大,液位降低气泡脱离有很大影响,而表面A、B沸腾气泡较小,液位降...     

沸腾传热的分形学分析

分形论是当代兴起的非线性科学的一个重要组成部分。简要地阐述了分形论形的特征，解释了几何学中的维和物理学中的量纲的不同涵义。把分形论分数维的概念扩展应用到沸腾传热中的非线性问题的分析中，结合沸腾传热的操作特征和基本原理，以沸腾传热中的推动力△Tsat作为一个动力学维，进行了q-△Tsat^Df的标绘；对Df的物理意义作了分析和探讨。     

凹坑缺陷医用氧气瓶应力分布特性研究

随着新冠疫情在全球肆虐,医用氧气作为重要的医疗资源用量急剧增加,医用氧气瓶作为医用氧气的重要载体其安全使用对病人的救治至关重要.针对带有凹坑缺陷的气瓶和完整气瓶的应力分布特性进行了数值模拟,发现在额定压力下正常气瓶的最大应力在瓶身下部,长轴40 mm、短轴20 mm、深2 mm的椭球面凹坑缺陷的最大应力远远超过材料的许...     

强润湿性液体池沸腾传热的实验研究和机理分析

对强润湿性液体的池沸腾传热实验而言,本文提出了行之有效的实验程序,并严格按照实验程序进行了R113池沸腾传热的实验研究,具体研究了表现老化和液体过冷度对池沸腾传热曲线及起沸点的影响,实验中观察到了三个反常现象,最后,从强润湿性液体的沸腾传热机理的角度对其给出了相应的解释。     

表面亲疏水性改性多层铜网的池沸腾换热特性研究

通过化学处理金属铜网,制备了具有不同层数和湿润性的多层铜网样品。以去离子水作为液态工质,在相同的条件下,对制备的多组样品进行可视化池沸腾实验,分析了池沸腾换热特性和气泡动力学行为。研究结果表明：在低热流密度下,疏水结构换热性能略优;在大热流密度下,亲水结构换热性能更优;对于多层铜网结构,厚度可以增大换热面积和成核点位,但过厚会增大气泡逃逸阻力。实验中5层的亲水铜网换热性能最优,换热系数峰值可达7.4×10～4 W/（m²·K）,是相同热流密度下光滑铜表面沸腾换热系数的2.10倍。     

多孔表面强化沸腾传热的研究

一、前言 当前全世界普遍重视节省能源,降低产品能耗已成为重要的研究课题。构成节能对象的机器设备中,有众多的热交换器,因此,研究提高现有传热设备的性能和探求新的强化方法,对于降低能耗具有重要意义。     

电化学方法制备多孔微纳结构表面的池沸腾传热性能研究

电化学表面处理一直以来都是池沸腾传热强化领域的一种重要的表面改性方法。然而,在光滑表面通过不断沉积生长枝晶结构的同时,结构底层会形成不必要的堆积层,从而增加了底层的热阻,不利于表面沸腾传热系数（HTC）的提升。因此,本文通过结合电化学表面处理手段中的电化学腐蚀与电化学沉积两方面的工艺,制备了“电腐蚀+沉积”表面,来探究经预先腐蚀处理后的表面与直接沉积表面沉积形貌及沸腾传热性能的差异。SEM图像表明,相较于在未处理铜板上直接进行沉积的表面,“电腐蚀+沉积”表面具有更长的枝晶结构、更深的孔结构及较少的底层堆积,结构的整体粗糙度更大。稳态池沸腾实验结果表明,在未处理铜板上直接进行电沉积的表面,其临界热流密度值较未处理铜板提升141%,而“电腐蚀+沉积”表面的临界热流密度值相较于未处理铜板提升了193%,并且其整体的沸腾曲线相较于直接沉积表面左移。对表面沸腾过程中汽泡行为的观测及表面铺展速率测试结果表明,“电腐蚀+沉积”表面具有更强的回液能力,能更好地促进表面气泡的脱离过程。     

Effect of tube bundles on nucleate boiling and critical heat flux

In order to elucidate boiling heat transfer characteristics for each tube and the critical heat flux (CHF) for tube bundles, an experimental investigation of pool and flow boiling of Freon-113 at 0.1 MPa was performed using two typical tube arrangements. A total of fifty heating tubes of 14 mm diameter, equipped with thermocouples and cartridge heaters, were arrayed at pitches of 18.2 and 21.0 mm to simulate both square in-line and equilateral staggered bundles. For the flow boiling tests the same bundles as were used in pool boiling were installed in a vertical rectangular channel, to which the fluid was supplied with an approach velocity varying from 0.022 to 0.22 m/s. It was found in this study that the boiling heat transfer coefficient of each tube in a bundle was higher than that for an isolated single tube in pool boiling. This enhancement increases for tubes at higher locations, but decreases as heat flux is increased. At heat fluxes exceeding certain values, the heat transfer coefficient becomes the same as that for an isolated tube. As the heat flux approaches the CHF, flow pulsations occurred in the pool boiling experiments although the heat transfer coefficient was invariant even under this situation. The approach velocity has an appreciable effect on heat transfer up to a certain level of heat flux. In this range of heat flux, the heat transfer coefficient exceeds the values observed for pool boiling. An additive method with two contributions, i.e., single phase convection and boiling, was used to predict the heat transfer coefficient for bundles. The predicted results showed reasonable agreement with the measured results. The critical heat flux in tube bundles tended to increase as more bubbles were rising through the tube clearance. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(4): 312–325, 1998     

Characteristics of heat transfer coefficients during nucleate pool boiling of binary mixtures

Experimental studies were made on heat transfer on a horizontal platinum wire during nucleate pool boiling in nonazeotropic refrigerant binary mixtures at pressures of 0.25 to 0.7 MPa and at heat fluxes up to CHF. The boiling features of the mixtures and the single-component substances were observed by photography. The relationship between the boiling behavior and the reduction of heat transfer coefficients in binary mixtures is discussed in order to propose a correlation useful for predicting the present experimental data over a wide range of low to high heat fluxes. It is shown that the correlation is applicable to alcoholic mixtures. The physical meaning of k, which was introduced to evaluate the effect of heat flux on the reduction of a heat transfer coefficient, is clarified based on measured nucleate pool boiling heat transfer data and visual observations of the boiling features. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(7): 535–549, 1998     

Features of boiling on an artificial surface — Bubble formation, wall temperature fluctuation and nucleation site interaction

The artificial surfaces are applied to study the pool boiling features, including the bubble behaviors, the surface temperature fluctuation, the heat transfer characteristics and nucleate site interaction. Three sets of experiments are carried out to investigate the influences of cavity shape, cavity size, cavity spacing on the boiling phenomena. Experimental results reveal that bubbling from the cylindrical as well as reentrant cavity is generally stable. The influence of cavity diameter on the bubble behaviors and the temperature fluctuation seems very weak while the effect of cavity depth cannot be neglected. As for the two cavity conditions, the bubble behaviors show the different features depending on the dimensionless cavity spacing. Three significant factors (thermal interaction, hydraulic interaction, bubble coalescence) control the nucleation site interaction, and the competition and dominance of the factors yield four interaction regimes.     

Features of Boiling on an Artificial Surface—Bubble Formation, Wall Temperature Fluctuation and Nucleation Site Interaction

The artificial surfaces are applied to study the pool boiling features, including the bubble behaviors, the surface temperature fluctuation, the heat transfer characteristics and nucleate site interaction. Three sets of experiments are carried out to investigate the influences of cavity shape, cavity size, cavity spacing on the boiling phenomena. Experimental results reveal that bubbling from the cylindrical as well as reentrant cavity is generally stable. The influence of cavity diameter on the bubble behaviors and the temperature fluctuation seems very weak while the effect of cavity depth cannot be neglected. As for the two cavity conditions, the bubble behaviors show the different features depending on the dimensionless cavity spacing. Three significant factors (thermal interaction, hydraulic interaction, bubble coalescence) control the nucleation site interaction, and the competition and dominance of the factors yield four interaction regimes.     

Experiment Analysis of Pool Boiling Heat Transfer in Bead Packed Porous Layers

The heat transfer of pool boiling in bead packed porous layers was experimentally investigated to analyze the effects of the bead material, bead diameter and the layer number of the porous bed on the transport of flux and the heat transfer coefficients. The glass and copper bead, the bead sizes of 4 mm and 6 mm as well as the bead packed porous structures ranging from one to three layers were chosen in the experiments. The pool boiling heat transfer in the bead packed porous structures and that on the plain surface were compared to analyze the enhancement of pool boiling heat transfer while the bead packed porous layers were employed. The maximum relative error between the collected experimental data of the pure water on a plain surface and the theoretical prediction of pool boiling using the Rohsenow correlation was less than 12%. Besides, the boiling bubble generation, integration and departure have a great effect on the pool boiling and were recorded with a camera in the bead stacked porous structures of the different layers and materials at different heat flux. All these results should be taken into account for the promotion and application of bead packed porous structures in pool boiling to enhance the heat transfer.     

Enhancement of nucleate boiling on composite surfaces

A composite heating surface composed of materials with different thermal conductivities can be expected to enhance heat transfer in nucleate boiling. This is because the end surface, with higher conductivity, will attain a higher temperature and as a result will serve to provide preferential nucleation sites. To confirm this idea, several composite surfaces were fabricated by uniaxially imbedding thin copper cylinders in the heat flow direction on a stainless steel circular plate 30 mm in diameter and 5 mm thick. The imbedded copper cylinders ranged from 1 mm to 4 mm in diameter and one to 77 in number. The heat transfer performance of these composite surfaces was investigated for pool boiling of saturated water at atmospheric pressure. It was confirmed that the copper cylinder surfaces exposed to water functioned as local hot spots to initiate preferential nucleate boiling, leading to higher boiling heat transfer coefficients than those on a homogeneous stainless steel surface. The measured void fraction above the heating surface verified intensive bubble generation on the surface of the copper cylinders. This situation continued up to a certain heat flux level and was then followed by nucleation on the mother surface of stainless steel around the copper cylinders. A numerical analysis of heat conduction within a composite wall simulated the temperature distribution within the wall and the variation in surface heat flux at the time of boiling incipience. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(3): 216–228, 1998     

水平窄空间沸腾传热的实验研究

通过对五种尺寸的窄空间试验元件分别以水和乙醇做工质进行实验。研究了窄空间间距、窄空间尺寸、不同工质及不同热流密度对窄空间沸腾性能的影响。结果表明：当窄空间尺寸与热流通等因素组合恰当时。其换热系数可比大空间池沸腾提高3～6倍;临界热流密度有所降低。     

Investigation of Enhanced Boiling Heat Transfer from Porous Surfaces

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