湿天然气凝结流动的双组分模型

基于气液相间滑移的影响,建立了适用于湿天然气凝结系统的水蒸气-甲烷双组分自发凝结流动数理模型,研究了水蒸气在以甲烷为载气的超声速流动中的凝结规律,对比了不考虑相间滑移的单流体模型与加入了相间滑移因素的双组分模型在自发凝结过程中的凝结规律的区别,分析了压力、温度对湿天然气在Laval喷管中自发凝结的影响.结果表明,湿天然气中相间滑移作用对凝结参数影响较大,本文建立的包含相间滑移因素的双组分模型能更准确的预测湿天然气的凝结特性;在凝结初始阶段相间滑移速度较大达到7.2 m/s,对湿天然气的自发凝结规律影响较大,随凝结过程的不断进行气液两相逐渐达到平衡,相间滑移速度逐渐降低至1.8 m/s;随入口温度的降低、入口压力的升高最大凝结成核率位置向入口方向移动。     

氩蒸气均匀核化与非均匀核化的分子动力学模拟

本文运用分子动力学模拟方法对氩蒸气的均匀核化和非均匀核化进行了研究.模拟氩蒸气的初始温度为30℃,冷却终温为-220℃.对均匀核化成核现象的团簇分析表明,蒸气凝结分为显热和潜热释放两个过程.提出了一个新的力函数模型,实现了非均匀核化过程的模拟.通过比较冷却速率为0.0002 m/s的均匀核化过程和非均匀核化过程,发现均匀核化的凝结核心是随机的,而非均匀核化的凝结核心以外界引入的核化点为核心.     

新型双蒸发两级压缩/喷射制冷系统性能分析

为提高两级压缩制冷系统性能,提出了一种新型双蒸发两级压缩/喷射制冷系统,建立了系统热力学计算模型,对不同工况下的系统性能进行了研究。结果表明:当低温蒸发器和高温蒸发器的蒸发温度升高时,新系统性能系数和单位容积制冷量都增大;当冷凝温度升高时,性能系数、制冷量和相对于传统系统的性能系数提升率都减小;当蒸发和冷凝温度固定时,随着中间温度的升高,性能系数先增大后减小。在低温蒸发器和高温蒸发器的蒸发温度分别为-10℃和0℃、冷凝温度为40℃的情况下,当中间温度为20℃时,性能系数达到最大值4.7,与传统系统相比新系统性能系数提升率均在17%以上。     

多孔细径微肋管内CO2流动蒸发换热特性的研究

对亚临界二氧化碳在带有微肋的微细通道内的蒸发换热特性进行了实验研究.实验段为长0.6 m,内径1.7 mm的八孔带0.16 mm高微肋的铝制扁管.实验中参数的变化为:蒸发温度1～15 ℃,质量流速100～300 kg/m2s,热流密度1.67～8.33 kW/m2,干度0.1～0.9.实验结果表明,二氧化碳在带有微肋的微细通道中的蒸发换热系数高于其在光滑微细通道内的换热.二氧化碳的流动蒸发换热系数主要受热流密度和蒸发温度的影响,基本上是换热系数随热流密度及蒸发温度的增加而增加,但同时临界干度前移及滞后,而质量流速对换热系数的影响较弱;压力损失随质量流速和热流密度的增加以及蒸发温度的降低而增加.     

"Ω"形微槽热管传热性能的实验研究

本文对一定型"Ω"形轴向槽道热管传热性能进行了实验研究,着重分析了该型热管在水平工况下的轴向温度分布、当量导热系数和总热阻、蒸发/凝结传热系数和最大传热能力.研究表明,该型热管元件具有良好的等温特性和导热性能,可实现高热流、长距离、低温差的热量传输;热管的最大传热能力受其工作温度影响较大,在工作温度较低时具有良好的传热能力,但在高温工况下,传热能力受到削弱.     

水平管降膜蒸发器传热特性研究

建立了水平管降膜蒸发和管内凝结传热实验台,通过对实验结果的归纳,获得了水平管降膜蒸发器总传热系数随喷淋密度、蒸发温度、传热温差和蒸汽入口流速的变化规律,以及管间距对传热特性的影响。结果表明,总传热系数随喷淋密度、蒸发温度的增大而增大,随传热温差的增大而减小,而蒸汽流速对传热系数影响较小;在本文研究的管间距范围内,当管间距为46.7 mm时,总传热系数最高。     

新型双蒸发制冷系统制冷剂的研究

研究了喷射器内部流体流动过程,应用质量守恒、动量守恒、能量守恒对两相喷射器建立了热力学模型,分析了不同制冷剂对新型双蒸发制冷系统性能的影响。计算结果表明:新型双蒸发系统中,当蒸发和冷凝温度相同时,R152a的性能系数高于其他4种制冷剂,R143a的喷射系数、喷射器的压缩效率、制冷量和性能系数提高率均高于其他4种制冷剂;当蒸发温度不变时,性能系数提高率随着冷凝温度的升高而降低,冷凝温度为30℃时,制冷剂为R143a,性能系数提高率达20%。     

CO2在细径管内蒸发换热的实验研究

对CO2在细径管内蒸发换热特性进行了研究。试验管为内径4 mm长为0.5 m的光滑紫铜管。实验中参数变化范围为,蒸发温度1-15℃,质量流速100-300 kg/m2s,热流密度2-18 kW/m2,干度0.1-0.9。实验结果表明CO2 蒸发换热系数高于氟利昂类制冷剂,蒸发温度和热流密度对换热系数影响显著,而质量流速的影响相对较弱,传统制冷剂的换热系数关联式不适用于CO2;二氧化碳的压力损失随着热流密度和质量流速的增加而增加,随着蒸发温度的上升而减小,CO2压力损失小于氟利昂类制冷剂。     

表面张力修正系数对非平衡凝结流动的影响

水滴表面张力以三次方的形式出现在成核率的指数项，对凝结参数影响显著。基于国内外研究现状，采用修正系数对平面表面张力模型进行修正，通过与实验数据的对比，分析了表面张力修正系数对计算精度的影响，并以各工况下工质进口压力、温度、过热度以及进出口压比四种参数与最佳表面张力修正系数的相关性为出发点，通过不同类型的拟合函数定量描述了其依变关系。结果表明：四次多项式函数对验证工况下工质进口压力的拟合误差分别为1.0519%、1.2443%，具有最佳的拟合效果。     

超音速蒸汽浸没射流凝结换热的实验研究

针对入口压力为0.20～0.50 MPa的饱和蒸汽在20～70℃过冷水中超音速浸没射流凝结换热进行了实验研究.结果表明入口蒸汽压力和过冷水温度是影响汽羽形状的主要因素.分子动力学理论得到的凝结换热系数在0.16～1.91 MW/(m2·℃)之间,随着过冷水温度的增加而增加;湍流强度理论得到的凝结换热系数在0.68～1.68 MW/(m2·℃)之间,随着过冷水温度的增加基本不变;对流换热理论得到的凝结换热系数在1.47～2.11 MW/(m2·℃)之间,随着过冷水温度的增加先增大后减小.     

H-H and C-H coupling constants in neutral and protonated azines

New measurements are reported of the density dependent depolarization ratio for argon, krypton, xenon, methane and sulphur hexafluoride, and the results are analysed to provide values for the second and third depolarization virial coefficients. The relationships between the second depolarization virial coefficient, the zeroth moment of the two-body Rayleigh spectrum and the second Kerr virial coefficient are considered, and it is shown that they now provide consistent results for the collision-induced pair polarizability anisotropy. Former inconsistencies are attributed to insufficient allowance for the effects of three-body interactions. Calculations of the second and third depolarization virial coefficients based on the DID model and using the Maitland-Smith potential are in excellent agreement with the experimental results for argon, krypton and xenon.     

Ion-cluster reactions initiated by an electron beam in mixtures of argon with methane and monosilane

The excitation of argon radiation in condensing supersonic jets of argon mixtures with methane, monosilane, and carbon dioxide upon electron-beam activation of the flow is investigated experimentally. It is found that, at certain condensation stages, the radiation intensity at some atomic argon lines increases anomalously. It is shown that the effect appears at the initial stages of condensation and is damped upon the formation of large mixed clusters.     

Thermodiffusion and Vaporization of Metal from Levitated Droplet V. Determination of Condensation Rate and Thermodiffusion Parameters of Mn, Fe, and Ni Vapours

In the present paper the experimental data of vaporization from levitated droplet for Mn, Co, Ni in the flow of argon obtained from the bibliography were evaluated by means of the new method published in the previous work [Czech. J. Phys. 50 (2000) 737]. The rate constants of condensation, thermodiffusion ratios, thermodiffusion coefficients and the corresponding temperature dependencies were determined together with other physical quantities for Mn vapour at the temperature 2000 K and for Fe, Ni at 2200 K. The rate constant of condensation and the thermodiffusion ratio are higher for Ni than for Fe. The value of thermodiffusion coefficient determined for Mn is rather high and the rate constant of condensation is higher than for Ni. The increase of vaporization resulting from condensation and thermodiffusion for Mn was only 2.7-times and for Fe and Ni (5.5-5.65)-times. The process of vaporization from a levitated droplet includes molecular diffusion and convective diffusion, molecular thermodiffusion with vapour condensation and condensation without thermodiffusion. The proportions of these processes were for Mn in the range (37-29) condensation dominated and its share was over 70 accurate experimental data and this is the reason why the evaluation of the Co vaporization was unsuccessful. The work also presents some proposals of experimental procedures leading to the data accuracy improvement.     

流速对混合蒸汽Marangoni凝结换热影响的实验研究

本文在蒸汽压力为47.36 kPa的条件下,通过实验研究了不同蒸汽流速(u=2、4、5 m/s)下纯水和不同酒精浓度水-酒精混合蒸汽沿重力方向流过竖直紫铜平板表面上的凝结换热特性,并实现了实验的可视化,同时分析了不同蒸汽流速下造成Marangoni凝结换热特性差异的原因.实验及分析结果表明,在相同蒸汽浓度、蒸汽压力和表面过冷度条件下,高流速下的凝结换热系数比低流速的大.且蒸汽流速对凝结换热的影响因混合蒸汽酒精浓度的不同而不同,低浓度0.5%和高浓度50%时流速的增加对凝结换热特性的影响较小,而在中间浓度2%时凝结换热强度随流速的增加明显.     

Kinetic boundary condition at a vapor-liquid interface

By molecular dynamics simulations, the boundary condition for the Boltzmann equation at a vapor-liquid interface is found to be the product of three one-dimensional Maxwellian distributions for the three velocity components of vapor molecules and a factor including a well-defined condensation coefficient. The Maxwellian distribution for the velocity component normal to the interface is characterized by the liquid temperature, as in a conventional model boundary condition, while those for the tangential components are prescribed by a different temperature, which is a linear function of energy flux across the interface. The condensation coefficient is found to be constant and equal to the evaporation coefficient determined by the liquid temperature only.     

水蒸气超高温热泵系统的实验研究

近年来以低温室效应(GWP)的制冷剂的蒸汽压缩式高温热泵一直是余热回收领域的研究热点。为获得更高的输出温度,本课题组搭建了一台采用自然工质水作为循环冷媒的超高温热泵样机并进行了实验测试。实验结果表明蒸发温度为80℃,冷凝温度从115℃升至145℃时,热泵的COP从4.88降至1.89。在85℃蒸发,117℃冷凝时,最高COP为6.1,制热量为285 kW,同时在85℃蒸发时,该热泵的最高冷凝温度可达到150℃,此时COP为1.96。在相同的温升下,热泵的COP和卡诺效率都随着输出温度的升高而增加,因此我们认为该热泵更适合高温输出的应用场合。     

Flow condensing heat transfer of R410A,R22, and R32 inside a micro-fin tube

An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m²s) and heat fluxes of 3–12 kW/m². The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed.     

低压蒸汽滴状冷凝传热性能的实验研究

实验研究了不同水蒸气压力条件下的滴状冷凝传热特性。10 kPa、40 kPa和70 kPa时的传热系数分别是常压下的56%,68%和81%。随着水蒸气压力的下降,液滴脱落直径变大,液滴生长周期延长,冷凝传热系数下降。通过液滴的动力学特性分析和基于界面效应的滴状冷凝传热模型,分析了低压对水蒸气冷凝传热的主要影响因素,压力变化主要影响了分子扩散率和气-液相际传热热阻,导致总冷凝传热系数随压力下降。     

液体蒸发率及表面温度测量

基于准稳态理论,建立了一套测量液体蒸发率及气液界面温度分布的实验装置,可用于测量常温下压力在0～1000 Pa区间的液体蒸发率及准稳态蒸发界面温度分布.该装置具有较高的实验精度,能够测量蒸发界面每0.02 mm范围内的温度变化.测量了水、甲醇和四氯化碳三种工质的蒸发流率及蒸发界面附近温度分布,并计算了相应的蒸发率,测量结果与文献值相一致.本文研究对揭示气液相变机理和工程实际应用具有理论意义和应用价值.     

Influence of the temperature modulation of an incident flux on the properties of films of cadmium selenotellurides synthesized under sharply nonequilibrium conditions

Results of structural and electrical investigations of the films of cadmium selenotellurides synthesized by evaporation and condensation in vacuum under sharply nonequilibrium conditions are presented. The modulating effect of a nonuniform thermal field on the vapor phase flux has been revealed. The possibility of controlling the stoichiometry of the film composition with the use of a thermal field applied on the path of the thermal phase from the evaporator to the substrate has been demonstrated. Curves of condensation and temperature dependences of the conductivity, Hall coefficient, and Hall mobility are presented.