Modeling the ultrapurification of substances by simple distillation

This paper presents a mathematical model for the ultrapurification of substances in a closed vaporization–condensation system, where the evaporation rate is determined by the combined effect of the mechanisms behind vaporization, condensation, and vapor transport from the vaporization surface to the condensation surface, and the impurity distribution in the liquid is determined by the diffusion mechanism. The degree of purification is evaluated as a function of the vaporization and condensation temperatures and the main simple distillation apparatus design parameters by numerical simulation for a particular example: removal of barium impurities from selenium.     

Modeling Iron Pentacarbonyl Vaporization Accompanied by Vapor Condensation on a Flowing Down Liquid Film

Using iron pentacarbonyl distillation as an example, we analyze the vaporization process in a closed vaporization–condensation system where vapor condenses on a flowing down liquid film. We jointly analyze the mechanisms behind vaporization, vapor transport, condensation, and flowing of the condensate on the inner surface of a vertical tube. We calculate the thickness of the flowing down liquid film, determine the vaporization coefficient for a closed system using experimentally determined temperature dependences of the vaporization rate and saturated vapor pressure, and present the vaporization rate as a function of the vaporization and condensation temperatures, the radius and height of the condensation tube, and the vaporization area of the still residue.     

水平单管传热性能试验台设计与试验研究

基于测量单管换热性能的目的,设计一个以R134a为制冷剂,用于进行满液蒸发、管外冷凝与降膜蒸发试验研究的水平单管换热性能测试试验台,并介绍其系统原理和流程。通过光管蒸发、光管冷凝的验证性试验和重复性试验,进行管内和管外换热系数测试值与理论计算值的误差分析,并研究降膜蒸发工况制冷剂流量对换热系数的影响。试验结果表明:测试值与理论计算值的偏差均在要求范围内,试验台可以为试验研究提供准确、可靠的数据。     

Condensation and evaporation heat transfer of R410A inside internally grooved horizontal tubes

Heat transfer coefficient and pressure drop were measured for condensation and evaporation of R410A and HCFC22 inside internally grooved tubes. The experiments were performed for a conventional spiral groove tube of 8.01 mm o.d. and 7.30 mm mean i.d., and a herring-born groove tube of 8.00 mm o.d. and 7.24 mm mean i.d. To measure the local heat transfer coefficients and pressure drop, the test section was subdivided into four small sections having 2 m working length. The ranges of refrigerant mass flow density was from 200 to 340 kg/(m² s) for both condensation and evaporation of R410A and HCFC22, and the vapour pressure was 2.41 MPa for condensation and 1.09 MPa for the evaporation of R410A. The obtained heat transfer data for R410A and HCFC22 indicate that the values of the local heat transfer coefficients of the herring-bone grooved tube are about twice as large as those of spiral one for condensation and are slightly larger than those of spiral one for the evaporation. The measured local pressure drop in both condensation and evaporation is well correlated with the empirical equation proposed by the authors.     

The inclusion of the effect of the evaporation coefficient on the rate of variation of droplet radius

The paper deals with the investigation of the effect of the evaporation (condensation) coefficient of droplet substance on the rate of unsteady variation of the radius of a spherical aerosol droplet in the cases of direct and indirect inclusion of this coefficient. It is found in both cases that the effect of evaporation coefficient is most significant at the initial instant of unsteady-state process of evaporation and of condensation growth of the droplet. At this instant, the size of spherical droplet has hardly any impact on the rate of variation of its radius. As the unsteady-state process continues, the effect of the evaporation coefficient on the rate of variation of the droplet radius depends significantly on the droplet size. The larger the droplet under consideration, the lower the effect of the evaporation coefficient on the rate of variation of its radius. The rates of variation, calculated for the same values of the evaporation coefficient but for different ways of inclusion of this coefficient, differ less for larger aerosol droplets. These methods of inclusion of the evaporation coefficient are considered for the process of slow evaporation of a droplet.     

电动汽车引射空调系统性能实验研究

本文提出一种电动汽车引射空调系统,该系统将车内蒸发器设计成前后排分离形式,并在其间加入引射器,以提高压缩机吸气压力,形成梯级蒸发,从而优化系统性能.实验研究了在不同蒸发温度、冷凝温度工况下电动汽车引射空调系统的性能,并与传统空调系统进行了对比.实验结果表明:在不同制冷工况下,电动汽车引射空调系统性能始终优于传统空调系统...     

Wicking of liquid nitrogen into superheated porous structures

Evaporation in porous elements of liquid–vapor separation devices can affect the vapor-free cryogenic propellant delivery to spacecraft engines. On that account, the capillary transport of a cryogenic liquid subjected to evaporation needs to be understood and assessed. We investigate wicking of liquid nitrogen at saturation temperature into superheated porous media. A novel test facility was built to perform wicking experiments in a one-species system under non-isothermal conditions. A setup configuration enabled to define the sample superheat by its initial position in a stratified nitrogen vapor environment inside the cryostat. Simultaneous sample weight and temperature measurements indicated the wicking front velocity. The mass of the imbibed liquid nitrogen was determined varying the sample superheat, geometry and porous structure. To the author’s extent of knowledge, these are the first wicking experiments performed with cryogenic fluids subjected to evaporation using the weight–time measurement technique. A one-dimensional macroscopic model describes the process theoretically. Results revealed that the liquid loss due to evaporation at high sample superheats leads to only a slight imbibition rate decrease. However, the imbibition rate can be greatly affected by the vapor flow created due to evaporation that counteracts the wicking front propagation.     

环路热管钎焊制造技术及传热性能数值模拟

为解决环路热管中蒸发器结构连接难的问题,开展了1Cr18Ni9Ti不锈钢与LD10铝合金环路热管封闭结构的大面积软钎焊技术研究,研究了钎料添加方式和焊接温度对接头质量的影响,分析了接头微观组织,并且利用ANSYS有限元软件对蒸发器热传输性能进行了数值模拟,分析了不同程度的缺陷对蒸发器热传输性能的影响.结果表明:焊接温度220℃,采用方式B的焊接接头质量优异,钎着率达到100%,从而设计出一套完整环路热管蒸发器软钎焊的生产工艺流程.     

Filling of carbon nanotubes with selenium by vapor phase process

A vapor phase method was developed to fill different kinds of nanotubes (including multiwall and singlewall nanotubes), which inner diameters range from 200 down to 1.5 nm. Experiments were performed with selenium in a sealed reactor in order to control the selenium partial pressure. This process allows a full control of the nanotube filling (partial or complete), i.e., either a selective diameter filling or a full filling rate. The weight gain of all the samples was plotted for different reaction temperature as a function of selenium pressure. Experimental isotherms are characteristic of capillary condensation of selenium, which occurs at first in the smallest nanotube inner diameters. X-ray diffraction data show that selenium confined in nanotubes with diameters larger than 3 nm keeps its trigonal structure.     

An experimental comparison of evaporation and condensation heat transfer coefficients for HFC-134a and CFC-12

Experimental heat transfer coefficients are reported for HFC-134a and CFC-12 during in-tube single-phase flow, evaporation and condensation. These heat transfer coefficients were measured in a horizontal, smooth tube with an inner diameter of 8.0 mm and a length of 3.67 m. The refrigerant in the test-tube was heated or cooled by using water flowing through an annulus surrounding the tube. Evaporation tests were performed for a refrigerant temperature range of 5–15°C with inlet and exit qualities of 10 and 90%, respectively. For condensation tests, the refrigerant temperature ranged from 30 to 50°C, with et and exit qualities of 90 and 10%, respectively. The mass flux was varied from 125 to 400 kg m⁻² s⁻¹ for all tests. For similar mass fluxes, the evaporation and condensation heat transfer coefficients for HFC-134a were significantly higher than those of CFC-12. Specifically, HFC-134a showed a 35–45% increase over CFC-12 for evaporation and a 25–35% increase over CFC-12 for condensation.     

Liquid film and droplet flow behaviour and heat transfer characteristics of herringbone microfin tubes

Cross-sectional liquid flow rate distribution of vapour liquid two phase flow of R123 in different herringbone microfin tubes has been measured. Droplet and liquid film flow rates are calculated with the measured data and assumptions for droplet distribution and slip ratio. Heat transfer coefficients of evaporation and condensation in herringbone microfin tubes have been measured using R22. Heat transfer enhancement mechanism by the herringbone microfins is discussed by using the measured data and numerically obtained cross-sectional flow field of a single phase flow. Flow rate of thin liquid film flowing on tube sides is affected by the helix angle and fin height. Larger helix angle and higher fin give thinner film. Liquid film flow rates in tube top and bottom are higher than tube sides. Droplet flow rate is increased with increase of helix angle and fin height, although the effect of fin height is not as pronounced as helix angle. Droplet radial mass velocity to tube side walls is increased with helix angle.     

Experimental research on degradation of nanolubricant–refrigerant mixture during continuous alternation processes of condensation and evaporation

Nanolubricant–refrigerant mixture used in vapor-compressor refrigeration system undergoes continuous alternation processes of condensation and evaporation, during which it degrades gradually as a result of the nanoparticle deposition. This paper quantitatively evaluates the degradation of nanolubricant–refrigerant mixture during continuous alternation processes of condensation and evaporation, and investigates the effects of lubricant mass fraction, nanoparticle mass fraction, heating condition, and cooling condition on degradation. TiO₂/NM56/R141b is chosen as the nanolubricant–refrigerant mixture for experiments. The experimental conditions cover lubricant mass fraction of 5–20%, nanoparticle mass fraction of 0.2–1.0%, heating temperature of 50–80 ^oC, and cooling temperature of 5–15 ^oC. The experimental results show that nanolubricant–refrigerant mixture degrades by 28–77% after 20 alternation times under present experimental conditions; besides, the degradation in long-term period can be reduced at conditions of higher lubricant mass fraction, lower nanoparticle mass fraction, lower heating temperature, or lower cooling temperature.     

真空蒸发冷凝制备超细铜粉的研究

借助激光粒度分析仪、扫描电镜、辉光放电质谱仪和X射线衍射仪等手段研究了真空蒸发冷凝制备超细Cu粉的方法及规律。实验表明,金属Cu的蒸发速率受蒸发温度和真空度的影响较大,所得Cu粉为面心立方晶体,形状规则,平均粒径小于2μm,分散性好,而且在真空条件下有利于制备高纯Cu粉。考察了蒸发温度、真空度、保温时间和冷凝条件四个因素对超细Cu粉粒度和形貌的影响规律,并用成核理论进行了分析。     

Optical properties and photovoltaic device applications of InSe films

Films were formed by alternately evaporating InSe and Selenium from separate evaporation sources onto glass substrates kept at temperatures below 150°C with subsequent thermal annealing.The effects of the additional selenium on the properties of the films were investigated by structural investigations and photoconductivity measurements. It is found from the results of the present measurements that compositional changes occur in the films with increasing selenium/InSe ratio and that single-phase films containing only InSe are obtained at a certain critical ratio.The refractive indices and absorption coefficients of amorphous and crystalline InSe films in the spectral range 0.6–2.5 μm are determined by spectrophotometric reflectance and transmittance measurements. The minimum optical energy gap obtained from measurements of the absorption spectrum for the crystalline films is close to the value for single crystals.A heterostructure diode using crystalline InSe films as “window layers” was prepared and the fundamental photovoltaic properties were investigated. An absolute quantum efficiency of about 18% is obtained in the wavelength range 1.1–1.25 μm.     

The deposition of selenium coatings on beryllium foils

A technique for preparing selenium films on 50.8μm thick beryllium foils is described. The selenium was deposited in vacuum from a resistance heated evaporation source. A water-cooled enclosure was used to minimize contamination of the vacuum system and to reduce the exposure of personnel to toxic and noxious materials. Profilometry measurements of the coatings indicated selenium thicknesses of 5.5, 12.9, 37.5, 49.8 and 74.5 μm. The control of deposition rate and of coating thickness was facilitated using a commercially available closed-loop programmable deposition controller. The X-ray transmission of the coated substrates was measured using a tritiated zirconium source. The transmissivities of the film/substrate combination are presented for the range of energies from 4 to 20 keV.     

Droplet size distribution in a metal evaporated by high-current electron beam

The ablation of substance from an irradiated target as a result of liquid-vapor phase transitions is considered. Kinetic equations that describe the formation and growth of vapor bubbles in a melted metal are derived. The composition of products formed during ablation of a copper target under the action of a high-current electron beam has been studied. The droplet size distribution in the condensed phase has been determined, which can be used in solving the problem of nanopowder condensation. It is established that the dimensions of droplets in the ablated substance are determined by the kinetics of the evaporation process, rather than by the initial structure of the target material, and depend on the beam energy deposition rate. In the electron irradiation regimes studied, the droplet dimensions fall in the interval from several dozen to several hundred nanometers.     

微肋管内制冷剂流动沸腾换热研究进展

内微肋管是增强管内凝结与沸腾换热的重要技术之一,在制冷空调领域有着广泛的应用。本文基于对近年文献回顾,从实验和计算关联式两方面综述了微肋管中沸腾换热的研究现状,总结了质量流速、热流密度、干度、管道结构、润滑油等对换热系数和压降的影响,讨论了现有的沸腾换热关联式的适用性和准确性,并指出了需要进一步研究的问题。     

Low‐Cost Manufacturing of Bioresorbable Conductors by Evaporation–Condensation‐Mediated Laser Printing and Sintering of Zn Nanoparticles

Currently, bioresorbable electronic devices are predominantly fabricated by complex and expensive vacuum‐based integrated circuit (IC) processes. Here, a low‐cost manufacturing approach for bioresorbable conductors on bioresorbable polymer substrates by evaporation–condensation‐mediated laser printing and sintering of Zn nanoparticle is reported. Laser sintering of Zn nanoparticles has been technically difficult due to the surface oxide on nanoparticles. To circumvent the surface oxide, a novel approach is discovered to print and sinter Zn nanoparticle facilitated by evaporation–condensation in confined domains. The printing process can be performed on low‐temperature substrates in ambient environment allowing easy integration on a roll‐to‐roll platform for economical manufacturing of bioresorbable electronics. The fabricated Zn conductors show excellent electrical conductivity (≈1.124 × 10⁶ S m^?1), mechanical durability, and water dissolvability. Successful demonstration of strain gauges confirms the potential application in various environmentally friendly sensors and circuits.     

The regularities of growth and properties of epitaxial cadmium chalcogenide films condensed from a gas phase of controlled composition

Generalized data on the epitaxial growth of CdS, CdSe and CdTe films condensed in quasi-closed cells are presented. An analysis is made of the complicated curves which relate the film condensation rate to the substrate temperature over a wide range (from room temperature to 650°C). The energetic parameters of the evaporation of the starting materials and of the film condensation are estimated. A study is made of the influence of a deviation of the gas phase composition from the stoichiometric composition on the process of film growth at high substrate temperatures and close to equilibrium conditions. It is shown that regulation of the gas phase composition allows epitaxial cadmium chalcogenide films whose carrier mobility is equal to that of single crystals to be produced.Based on a study of the temperature dependence of the electrical conductivity of epitaxial CdSe films over the range 90–400 K, a physico-chemical model is proposed and a physical model is discussed; these models explain the sudden increase of the carrier mobility with carrier concentration changes.     

R404A与CO2复叠式制冷系统的理论分析

本文针对所建立的新型R404A／CO2复叠式制冷设备进行了理论研究,该系统可提供零下40℃以下的低温环境。根据R404A和CO2的物性特征及复叠式循环流程,通过数值模拟寻找一定工况下CO2低温级的最佳冷凝温度及二者的最佳质量流量比,分析冷凝蒸发器的工作温度、CO2侧蒸发温度、R404侧的冷凝温度等对R404A／CO2复叠式系统COP的影响。结果表明,为了提高循环效率并保证循环的安全运行,应尽可能地升高低温段蒸发温度、降低高温段冷凝温度,缩小冷凝蒸发器的传热温差,环保工质R404A和CO2的复叠式制冷系统在低温制冷条件下有良好的发展前景。