Correlation of the boiling points of mixtures

A modified Swietoslawski equation has been developed to correlate the boiling points of mixtures. Vapor—liquid equilibrium data have been determined at 760 mm for the binary systems normal butanol-tertiary butanol and normal butanol-secondary butanol. Both systems present slight negative deviations from ideal solution behavior. The boiling points of the two binaries and of several other non-ideal systems were satisfactorily correlated by means of the above equation. Prediction of ternary boiling points from binary data and simplifications in the correlation which are useful for practical applications are also discussed.     

Forced convection subcooled boiling of binary mixtures

A mode based on an additive mechanism of heat transfer is proposed for forced convection subcooled boiling of binary mixtures. The contributing modes of heat transfer are: (i) the heat transferred as latent heat by the rising bubbles, (ii) the heat transferred as the heat contained in the superheated thermal layer that is removed from the surface in the wake of the rising bubbles and (iii) the single phase forced convection heat transfer from the heating surface not influenced by the bubbles. Experimental data from the literature on binary systems show good agreement with the model, validating the postulated mechanism.     

Heat transfer in boiling of multicomponent mixtures

Pool boiling data of multicomponent mixtures show that the heat transfer coefficients can be considerably lower than those of a corresponding pure fluid with the same physical properties as the mixture. The proposed model, which assumes maximum mass transfer resistance in the liquid boundary layer, is confirmed by the comparison between calculated and experimental data. The model allows the prediction of heat transfer coefficients in pool boiling of mixtures using only single component properties and vapour-liquid equilibrium data. Judging by experience with a number of different systems, the method should be sufficiently accurate for most practical applications.     

Crisis during the boiling of binary mixtures of liquids

The existing notions on the crisis of the boiling of binary mixtures are analyzed. It is shown that the maximal values of the critical thermal load coincide with the so-called singular points corresponding to defined compounds. The search for new binary systems with similar properties can be based on the investigation, first of all, of these binary points.     

Flow boiling and pool boiling critical heat flux in water and ethylene glycol mixtures

Flow boiling and saturated pool trailing were studied in water, and in ethylene glycol and aqueous antifreeze solutions. Boiling took place from an electrically heated cast iron surface at pressures close to atmospheric. In the flow boiling tests, velocities and subcoolings were varied up to 3 m/s and 36°C respectively, and effects of changes in flow passage geometry were examined. In 50 weight percent antifreeze mixtures the pool boiling critical heat flux increased relative to pure ethylene glycol in aqueous solution. Both critical heat flux and heat transfer coefficients decreased as percent water in the mixtures tested was reduced.     

A study of microlayer evaporation for three binary mixtures during nucleate boiling

Microlayer evaporation was studied both experimentally and theoretically for the binary solutions: 50 mol % methanol in water, 10 mol % methanol in water, and 3 mol % 1-butanol in water. Surface temperatures beneath the evaporating microlayer were measured as the solution was boiled on Pyrex. These were compared with temperatures calculated from a mathematical model. This model considered mass diffusion within the liquid layer and heat diffusion in the Pyrex and across the microlayer. The agreement between the experimental and calculated results demonstrates that mass transfer has a significant effect on the evaporation of the microlayer for these three cases.     

双组分混合制冷工质沸腾换热理论研究

基于单组分工质池沸腾动态微液层预测模型,提出了预测双组分混合工质沸腾换热系数的理论模型。该模型认为沸腾换热的机理主要是由于在气泡的周期生长过程中所形成微液层的蒸发。模型中考虑了气泡生长过程中液体传质对传热的影响,给出了气泡生长过程中传热面上气液固接触的动态构造。利用本模型所得预测结果与实验结果能够较好地符合。     

水平细圆管内非共沸混合工质的流动沸腾

以非共沸混合工质R32/R134a为实验工质,进行了水平细圆管内流动沸腾换热实验.在获取大量实验数据的基础上,分析了质量干度、热通量和质量通量密度对沸腾换热的影响,讨论了各种工况下的换热机理,比较分析了细圆管和常规管道内流动沸腾换热性能.实验结果表明：在本实验范围内,水平细圆管内流动沸腾换热主要受热通量的影响,绝大部分实验工况下核态沸腾占主导地位.尺度效应是引起微细通道内流动沸腾换热特性不同于常规管道的主要原因.     

Errors associated with the measurement of dew-point loci for wide boiling mixtures

The normal practice to measure the dew-point locus of a mixture is to use a static phase equilibrium still. In this technique, the condensate needed to observe cloud formation completely changes the composition of the mixture, leading to inaccurate dew-point measurements. A careful analysis is made in this work to show the extent of the error in the dew-point measurement using the static phase equilibrium still.     

Enhanced flocculation of colloidal dispersions by polymer mixtures

Bridging flocculation and electrolyte coagulation of negatively charged colloidal dispersions in the presence and absence, respectively, of uncharged polymers and polymer mixtures were studied. The relative coagulation and flocculation rates of particles in the presence of electrolyte and small polymer amounts were measured and the stability ratios have been calculated at various ionic strengths. Also, the structure of polymer layers formed in individual adsorption of polymers and in simultaneous competitive adsorption from binary polymer mixtures at particle/solution interfaces was investigated. The electrophoretic mobility and the diffusion coefficient of particles with and without adsorbed polymer were measured by laser Doppler-electrophoresis and photon correlation spectroscopy, respectively, and the electrophoretic and the hydrodynamic thickness of adsorbed polymer layers have been calculated. It was found that the adsorbed polymers may enhance or diminish the rate of successsful encounters between particles, even at low surface coverages, depending on the magnitude of the interparticle electrostatic repulsion. In addition, competitive adsorption of chemically different polymers for particle surfaces may result in considerable alteration in the conformation of macromolecules in the mixed adsorption layer. Close correlation was found between the effectiveness of polymers as flocculants and the thickness of adsorbed polymer layers formed at optimum polymer dosages on the particle surfaces. Binary mixtures of suitable polymers proved to be very efficient flocculants for the dispersions. The enhanced flocculating effect of some mixtures can be ascribed to extended polymer layers formed in competitive adsorption of chemically different macromolecules at particle/solution interfaces. These findings have relevance in many environmental technologies and offer a way of improving the effectiveness of solid–liquid separation processes.     

A computation of differential distillations from true boiling data for hydrocarbon mixtures

A functional equation that relates a true boiling point distillation with a differential distillation, as defined by Rayleigh's Equation, is derived. It is a nonlinear integral equation which is solved by numerical computation. The calculation is applied to data on gasoline and hydrocarbon mixtures.     

氧化石墨烯表面的饱和池沸腾强化传热实验

利用氧化石墨烯（GO）纳米片沸腾自组装法（self-assembly）制备出GO纳米表面,以蒸馏水为液体工质,对常压下GO纳米表面和光滑铜平面的饱和池沸腾换热特性进行了对比实验研究,并用高速摄像机拍摄了汽泡的动态行为。结果表明,GO纳米表面降低了换热壁面的过热度,其临界热流密度（CHF）和换热系数（HTC）分别达到了208W/cm²和7.25W/(cm²?K),较光滑铜平面分别提高了66.4%和86.9%。分析认为,是铜基底表面沉积的润湿性优异的高导热二维GO层状结构促使了CHF提高。汽泡可视化观察发现,相比于光滑铜平面,较低热流密度时,相同热流下GO纳米表面上汽泡脱离直径较小,脱离频率较高,汽化核心增多;较高热流密度时,光滑铜平面汽泡合并现象更严重,即GO纳米表面能延缓导致CHF产生的表面蒸汽膜的出现。     

Design of hybrid distillation/melt crystallisation processes for separation of close boiling mixtures

Hybrid separations combining distillations and crystallisations have a significant potential for process intensification. To address the large number of degrees of freedom in the design of hybrid separations, a three-step approach is utilised. However, it can only be applied if all parameters for the rigorous modelling of crystallisation and cost functions are known a priori, which is often not the case. In this paper, we propose a four-step design method which can be applied in early process development stages when not all model parameters are available. In the first step, different process variants are generated. In the second step, the variants are evaluated using rigorous models, wherein the unknown model parameters are varied to quantify their influence on the process performance. If hybrid separations appear to be compatible, experiments are performed to determine the unknown parameters in the third step. In the last step, an optimisation is performed to find the optimal process, when necessary in dependence of unknown cost parameters. The developed tools and the feasibility of the approach are illustrated with the separation of a binary mixture of long-chain isomeric aldehydes.     

丙烷在水平微肋管内的沸腾传热强化特性

为了分析质量流速、热流密度和管径对丙烷在水平微肋管内的沸腾传热强化特性的影响,定义了表示微肋管沸腾传热强化程度的强化因子,在饱和温度为11℃的工况下,分别采用水平光滑管和微肋管进行沸腾传热特性实验。结果表明:干度为0.1时,不同质量流速下强化因子几乎相等;干度大于0.1时,强化因子随质量流速的增加而增大;高质量流速下强化因子随干度增加而增大,而低质量流速下则随干度增加先减后增,且高热流密度下更早出现强化因子急剧增大现象。此外,管径越小的微肋管内沸腾传热的强化因子越大,强化传热效果更佳。     

Hybrid separations combining distillation and organic solvent nanofiltration for separation of wide boiling mixtures

Membrane assisted hybrid separations offer tremendous potential for process intensification which aims at increasing resource efficiency as well as decreasing operating and capital costs. Design of such processes is challenging due to large number of degrees of freedom but also due to large experimental effort necessary for membrane screening and for characterising membranes in whole operating range. To address these issues, this paper elaborates a four-step design method for combination of organic solvent nanofiltration (OSN) and distillation in a hybrid separation of wide boiling mixtures. The design method is applied in a case study which is the separation of small amounts of heavy boiler from a mixture containing a mid- and a light-boiler. In the first step, different process options are generated based on heuristics and engineering judgement and screened for feasibility. In the second step, the options are evaluated based on quantitative metrics using rigorous models. In this step the unknown key parameters are identified, and their influences on the process performance are quantified in a detailed a priori process analysis. If hybrid separations with OSN show to be promising when compared to stand-alone distillation, experiments are conducted to (i) identify the best membrane for the operating window in which the hybrid process operates and (ii) to perform model validation and parameterisation in the third step. In the last (fourth) step, an optimisation is performed to identify the best (cost optimal) process using the experimental data gained in step three.     

Enhanced separation of highly non-ideal mixtures with extractive heterogeneous-azeotropic distillation

The distillation based separation can be extremely complex if highly non-ideal mixtures are to be separated. In spite of different successfully applied unit operations there is still a possible way to improve the distillation technique and widen its toolbar. A new improvement in this area is the development of the extractive heterogeneous-azeotropic distillation (EHAD). This unit operation includes the merits of extractive- and heterogeneous-azeotropic distillations in one unit without extra material addition. Our work supports EHAD features with successful experiments compared with modelling and comparison with other separation structures proving that the application of EHAD makes the separation of extremely non-ideal mixtures possible on an easy, powerful, energy saving, and cost efficient way.     

Film boiling of discrete droplets of mixtures of coal and water on a horizontal brass surface

The effect of coal on the evaporation of water from mixtures of coal and water was studied in a Leidenfrost-type experiment. Pulverized bituminuous coal was mixed with water in volume concentrations of 14% and 26%, with corresponding total droplet volumes of 0.052 cm³ and 0.055 cm³, respectively. Evaporation times were recorded by videotape over a range of plate temperatures from just above the Leidenfrost point of water to 670°K. The test surface used in all the experiments was brass, and the pressure was kept constant at atmospheric.Three stages in the evaporation lifetime of the coal/water droplets were observed: (1) evaporation of levitated sessile shaped drops; (2) a regime in wResults showed that evaporation times of water were lower in the presence of coal than for a pure water droplet containing the same volume of water as     

Enhanced heat transfer under conditions of liquid boiling in a thin layer at reduced pressure

The problem of heat transfer intensification by increasing the surface of heat transfer is considered. Estimations of an increase in interfacial area are performed when structures in the shape of funnels appear in the thin layer of a boiling liquid under the effect of the reactive force of phase transition. The work of the formation of a single funnel at the interface is estimated.     

纳米制冷剂TiO2/HFC134a水平管内流动沸腾换热实验研究

对纳米制冷剂TiO₂/HFC134a在水平管内的流动沸腾换热性能进行了实验研究,纳米颗粒的浓度为0.01、0.025和0.05 g•L^-1,并与纯质HFC134a的结果相比较。结果发现：TiO₂/HFC134a工质的流动沸腾传热系数得到一定的强化,强化程度与颗粒浓度有关,实验过程中发现的纳米颗粒在换热表面的沉积可能是主要的影响因素。