强制对流传热的换热表面结垢特性实验研究

An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance was set up for the present experiments. The fouling behavio（s were examined under different factors including fluid velocity, hardness,alkalinity, solution temperature, and wall temperature. Asymptotic fouling curves varying with time were obtained. The fouling rate and asymptotic fouling resistance increased and the induction periods were shortened with the fluid velocity decreasing, hardness andalkalinity increasing, and solution temperature and heat transfer surface temperature increasing. Thecomponents of fouling that formed on the heat transfer surface included crystallization fouling and particulate fouling. The thermal performance parameter of fouling,ρfhf, varied from 380 to 2600 kg·W·（m^4·K）^-1, increasing with growing velocity and decreasing solution temperature, hardness or alkalinity. Furthermore, the thermal conductivity of fouling, λf, varied from 1.7 to 2.2 W·（m·K）^-1 .     

Effect of dissolved gases on subcooled flow boiling heat transfer

The influence of various dissolved gases (He, N₂, Ar, CO₂, C₃H₈) on subcooled boiling heat transfer was investigated for flow of water and of heptane in an annulus with a heated core. Flow velocity, liquid bulk temperature, system pressure, gas partial pressure and heat flux were all varied over a wide range.In comparing the measured heat transfer coefficients with those for subcooled boiling of the corresponding degassed liquids, it was found that the coefficients were always increased owing to the desorption of the dissolved gases. The extent of the increase depended on the solubility of the given gas in the given liquid and could be as much as several hundred per cent. In addition, the solid surface temperature required for the inception of bubble formation was reduced considerably, in some cases far below the saturation temperature of the pure liquid.Attempts were made to extend the prediction of incipient boiling temperatures to cases where gases are dissolved in the liquid.     

池式沸腾条件下CaSO4污垢生成的实验研究

在池沸腾装置中,100℃下CaSO4饱和溶液以及热通量55—300 kW/m2,研究了传热表面性质对硫酸钙污垢沉积的影响。通过现代表面处理技术,例如动态混合离子注入和动态混合磁控溅射技术,对若干加热器表面进行处理,以减小金属表面的表面能。研究表明,表面能低的表面,即经离子注入或磁控溅射的表面具有良好的抗垢性能。     

换热表面Ni-W-P镀层抗垢特性

通过调整Ni-W-P化学镀镀液中钨酸钠浓度,获得了钨元素含量不同的三元Ni-W-P镀层。进一步的实验研究表明,随着三元Ni-W-P镀层中钨元素含量的增加,其热稳定性得到显著改善,同时,镀层晶粒转变的激活能值呈增大趋势。三元Ni-W-P镀层的抗垢性随着镀层中钨元素含量的增加而降低,而与镀层表面自由能以及表面粗糙度没有必然的联系。     

Mathematical modelling of mixed salt precipitation during convective heat transfer and sub-cooled flow boiling

The main purpose of this investigation was to study the mechanisms of mixed salt crystallisation fouling on heat transfer surfaces during convective heat transfer and sub-cooled flow boiling conditions. In the present investigation, the effects of various operating parameters such as solution composition and hydrodynamics of the system, on crystallisation fouling of mixtures of calcium sulphate and calcium carbonate have been studied experimentally. After clarification of the effects of operating parameters on the deposition process, the results of the experiments were used to develop a mechanistic model for prediction of fouling resistances, caused by crystallisation of mixed salts, under convective heat transfer and sub-cooled flow boiling conditions. Model predictions were compared with the measured experimental data when calcium sulphate and calcium carbonate form deposits on the heat transfer surface simultaneously. Deviations ranging from 6% to 25% were observed which confirm the suitability of the model.     

连通微通道内过冷流动沸腾传热强化机理分析

连通微通道（平行主通道由支流通道连通）流动沸腾传热具有优越的换热性能,但其传热传质强化机理尚不够明确,限制了其实际应用。鉴于此,本文基于流体体积函数（VOF）方法,对连通微通道内过冷流动沸腾进行二维非稳态数值模拟,研究了流场扰动、脱落汽泡与壁面间的薄液膜分布对微通道当地传热系数的影响规律。结果表明,连通微通道存在两种强化换热机理：支流通道脱落汽泡可增强主通道流场扰动,进而促进了通道热边界层再发展;脱落汽泡与热壁面间可形成薄液膜,该薄液膜减小了换热热阻。同时研究了支流通道倾角（θ）对连通微通道强化换热的影响,结果发现,不同θ时,连通微通道整体平均传热系数提高10.51%~17.66%,单个主通道平均传热系数最高可提升27.94%,且θ=45°时连通微通道具有最佳换热特性。该研究有望为芯片高效冷却结构的设计提供指导。     

表面工程技术应用于蒸发器的防垢及沸腾传热强化的研究进展

对传统的表面工程技术和纳米表面工程技术在蒸发器等换热设备的防垢和沸腾传热强化方面的研究进展进行了综述。分析了采用磁控溅射、离子注入、化学复合镀、分子自组装等表面工程技术制得的低能表面,包括纳米涂层传热表面的防垢或强化沸腾传热的功效。认为应用表面工程技术的难点在于如何制备既能防垢又能强化沸腾传热的优良传热表面;高黏物系的污垢形成规律和表面抗垢机理研究,应用纳米表面工程技术进行防垢和强化沸腾传热研究是今后的重要研究方向。     

Thermal resistance of steam‐generator tube deposits under single‐phase forced convection and flow‐boiling heat transfer

Measurements were made of the thermal resistance of porous deposits of various thicknesses under both single‐phase forced convection and flow‐boiling conditions. Both synthetic deposits and deposits on tubes removed from operating steam generators were used in this investigation. The thermal resistance was modeled as the sum of two components: one associated with conduction through the porous deposit and a second associated with the effect of surface roughness. The conductive component of the thermal resistance was always positive, whereas surface roughness made a negative contribution to the thermal resistance, i.e., roughness enhanced the rate of heat transfer. Thermal conductivity of the porous deposits was higher for single‐phase forced convection, whereas the effect of deposit roughness on thermal resistance was higher under flow‐boiling conditions. The results are discussed in terms of the effect of composition, morphology, surface roughness, and the mode of heat transfer on the thermal resistance of porous deposit.     

电火花改性表面池沸腾换热特性

通过电火花成型加工技术在铜基换热表面制备微纳结构改性表面,以自制换热表面性能测试装置进行改性表面的池沸腾换热性能实验。改性表面随加工电流改变而具有不同粗糙度、孔隙率和粗糙度因子,表面接触角范围在117.4°~133.5°。实验结果表明,改性表面的微纳结构提高换热面的池沸腾换热效果,临界热流密度较光滑铜表面提高了26%~87.8%,最大传热系数提高了48.1%~213%。改性表面的传热系数随着粗糙度增大而减小,而临界热流密度则是先增大后减小;孔隙率的增大使得改性表面的传热系数也随之增大,临界热流密度则是随着孔隙率的增大而先增大后减小;临界热流密度随着粗糙度因子的增大而降低,传热系数则是先增大后降低。粗糙度对沸腾换热的强化效果较小,孔隙率和粗糙度因子是强化池沸腾换热的关键,孔隙率和粗糙度因子分别影响了气泡核化密度和实际接触面积,提高了气泡脱离频率,带走更多的热量,但两者间存在互相制约的平衡关系。     

加热面倾斜角对过冷沸腾中汽泡生长-冷凝行为的影响

采用高速摄影的方式,对矩形通道内过冷沸腾时的汽泡在倾斜状态下的行为进行了可视化研究,分析了加热面倾斜角度对汽泡生长-冷凝速率以及平均汽泡最大直径与对应生长时间的影响。结果表明:在同一入口工况参数下,汽泡的最大直径与寿期均随角度的增加而上升,且与倾斜角度近似呈正比;不同倾斜条件下的汽泡最大直径与对应生长时间基本满足0.5次幂的函数关系,其系数与倾斜角度呈正比;采用Zuber量纲1形式表示后,不同倾角时的平均汽泡生长-冷凝曲线在生长阶段随倾角增加而增加,而在冷凝阶段则与角度无明显关联。     

梯度表面能材料表面上滴状凝结换热

采用气相沉积（CVD）的方法,以十二烷基三氯硅烷和辛基三氯硅烷为扩散工质,制备了梯度表面能材料表面。对空气中水滴在水平梯度表面能材料表面上的运动现象和表面倾角为0°、30°、60°和90°情况下,梯度表面能材料表面上的水蒸气滴状凝结换热进行了可视化实验,研究了凝结液滴的长大、聚并、运动和脱落现象。结果表明：直径大于1 mm的凝结液滴峰值运动速度达到110 mm·s-1,远大于空气中液滴的运动速度。通过图像分析,分别讨论了壁面过冷度、凝结表面倾角和表面能梯度对换热和液滴运动的影响。结果表明：随着壁面过冷度的增加,凝结表面传热系数先增加后减小;当凝结表面倾角大时,由于重力作用加大,凝结表面传热系数也高;当表面能梯度较大时,运动液滴尺寸更小,速度更快,凝结表面传热系数更高。     

稠油开采污水蒸发结垢过程传热传质计算方法

蒸发器是一种根据热法脱盐原理,利用稠油热采地面系统废热驱动,实现污水脱盐软化,进而回用锅炉实现水资源循环利用的装置。但是,由于油田污水水质的特殊性,使得其极易在蒸发器表面发生结垢行为。通过对污水水质分析,得出其结垢类型主要为碳酸钙垢。建立了碳酸钙垢在强制对流传热和过冷流动沸腾情况下于换热表面结垢的传热传质模型,计算了污水在蒸发过程中析晶污垢形成的数量,得出了与实验数据符合较好的计算模型。对稠油污水在蒸发器中的结垢情况可以进行较好的预测,并对安全生产和设备高效利用有一定参考价值。     

液氮过冷沸腾壁面换热特性的数值研究

应用计算流体力学(CFD)研究手段,对液氮过冷沸腾过程进行了模拟。系统分析了过冷沸腾壁面换热过程中存在的各传热模式,得到3部分热流沿管长的分布规律。计算结果表明,在过冷沸腾后期,蒸发热流成为壁面换热的主要模式。同时,就壁面热流密度的变化对3部分热流的影响进行了分析。随着壁面热流的增加,过冷沸腾出口处淬火热流和对流热流将减小,只有蒸发热流增大,且所占总热流份额绝对占优,壁面热流的增加促进了沸腾换热。     

超疏水/亲水性结构表面流动沸腾传热实验研究

用激光烧蚀方法在抛光后的铜上制备出四种无需涂覆修饰即可获得超疏水/亲水性的规则微阵列结构表面。基于流动可视化与温度数据结果,分析了表面浸润性和过冷度对流动沸腾传热性能的影响,与经典汽化核心密度关联式进行了对比。结果表明：疏水表面可削弱单相对流传热,大幅强化沸腾传热,最大传热系数提高了75.5%,沸腾起始点提前3.5 K,且汽化核心数目较裸铜表面提高了5倍以上,但有较低的临界热通量。超亲水表面可增强单相对流传热、小幅度提升流动沸腾传热。对比亲水表面与疏水表面的气泡生长过程,发现疏水表面尾端气泡容易汇聚,生长周期较长;而亲水表面没有发生明显的气泡汇聚行为,气泡生长周期较短。     

纳米管阵列表面流动沸腾传热特性的实验研究

利用阳极氧化法在钛换热管内表面制备出了一层管阵列结构纳米薄膜。以该纳米管阵列表面管为传热元件,蒸馏水为工质,采用管外电加热竖管强制循环工艺,在恒质量流速下考察了纳米管阵列表面管的流动沸腾传热性能。在实验的基础上,得出了纳米管阵列表面管流动沸腾传热系数关联式。实验结果表明,与光滑表面管相比,流动沸腾传热温差降低了30%～55%,在没有增加阻力的情况下,沸腾传热系数提高了1.5～2.2倍。     

在过冷流动沸腾期间硫酸钙污垢形成过程研究

在过冷流动沸腾条件下 ,对硫酸钙的沉积过程进行了研究 ,考查了不同流速和不同加热器表面条件下硫酸钙的结垢状况。研究表明 ,表面能对污垢沉积有显著影响 ,采用现代表面处理技术 ,对金属表面进行磁控溅射 ,可以降低金属表面能 ,抑制污垢在加热器表面上的沉积。同时 ,操作的工艺条件对硫酸钙结晶垢的形成也有一定影响 ,在一定流速范围内 ,提高流速 ,可减少污垢的形成 ,提高传热系数     

The effect of bond formation on the tack of polymers

The tack of polymers to be used as adhesives is measured by a two-stage process of bond formation and bond separation. Bond formation is governed by the contact time, the contact force, the roughness of the surfaces, surface and interfacial tensions, and the mechanical or viscoelastic properties of the adhesive and substrate. This paper presents experimental studies of the contact formation of various model polymers on steel surfaces with well-defined and different degrees of roughness. The tack was measured with an instrument of the probe tack type, which determines the adhesive (interfacial) fracture energy per unit of interface as a measure of the tack and by means of which the most important parameters during bond formation and separation, such as the contact time, contact force, rate of separation, and temperature, can be adjusted and measured over sufficiently wide ranges. In the typical time interval for the contact time, the polymers are found in the plateau range of their viscoelastic spectrum. This means that entanglements strongly affect their bonding behaviour. Good agreement was found between the experimental results presented in this study and a model of contact formation on rough surfaces, published recently by Creton and Leibler [1], especially concerning the dependence of the adhesive fracture energy on the contact force and the contact time for smooth and rough substrate surfaces. The influence of the surface roughness becomes significant at low contact forces, where full contact is not yet developed on a rough substrate surface, and for polymers with comparatively high moduli. The fracture energy increases with the contact time and shows the same time dependence as the reciprocal modulus.     

改性纳米碳酸钙表面性质的研究

用树脂和硬脂酸改性纳米碳酸钙。IR分析显示包膜剂与碳酸钙间以离子键结合;TEM照片显示改性的碳酸钙在环己烷中有更好的分散性能;沉降体积和接触角的测定结果说明改性碳酸钙在非极性介质中的润湿性得到了提高。     

换热器用多孔管沸腾传热物理模型比较

多孔管是一种新型高效强化沸腾传热的换热管,对其沸腾传热的物理模型的研究是深刻理解其强化传热机理和今后改进该技术的前提。通过总结国内外相关研究工作,介绍了烧结型和机加工型多孔管沸腾传热的物理模型。重点分析了多孔层特征参数(多孔层厚度、当量半径和孔隙率)对强化传热的影响。同时对各种模型的优缺点进行了分析归纳,探讨了多孔管沸腾传热物理模型研究的发展方向,对今后的发展提出了自己的建议。     

颗粒多孔表面强化沸腾传热动力学研究

通过对颗粒多孔层几何结构、沸腾两相流及传热的理论分析，提出了微型通道薄膜环状蒸发物理模型和沸腾传热机理，建立了颗粒多孔表面强化沸腾传热动力学模型。该动力学模型与实验数据吻合良好，可用于工程设计。