Condensation from a vapor-gas mixture on a plane surface

An approach is developed, which was previously suggested for the investigation of intensive condensation of pure vapor in application to a one-dimensional steady-state problem of condensation in the presence of a noncondensable component. Results are obtained, which make possible the estimation of the parameters of the limiting modes of condensation from a vapor-gas binary mixture.     

Experimental study and modelling of heat transfer during condensation of pure fluid and binary mixture on a bundle of horizontal finned tubes

An experimental investigation was conducted to measure the local heat transfer coefficient for each row in a trapezoidal finned horizontal tube bundle during condensation of both pure fluid (HFC 134a) and several compositions of the non-azeotropic binary mixture HFC 23/HFC 134a. The test section is a 13×3 (rows × columns) tube bundle and the heat transfer coefficient is measured using the modified Wilson plot method. The inlet vapour temperature is fixed at 40 °C and the water flow rate in each active row ranges from 170 to 600 l/h. The test series cover five different finned tubes all commercially available, K11 (11 fins/inch), K19 (19 fins/inch), K26 (26 fins/inch), K32 (32 fins/inch), K40 (40 fins/inch) and their performances were compared. The experimental results were checked against available models predicting the heat transfer coefficient during condensation of pure fluids on banks of finned tubes. Modelling of heat exchange during condensation of binary mixtures on bundles of finned tubes based on the curve condensation model is presented.     

Experimental measurements for condensation of downward-flowing R123/R134a in a staggered bundle of horizontal low-finned tubes with four fin geometriesMesures expérimentales de la condensation lors de l'éoulement vertical d'un mélange de R123 et de R134a sur un faisceau de tubes en quinconce munis de quatre types d'ailettes

Experiments were conducted to obtain row-by-row heat and mass transfer data during condensation of downward-flowing zeotropic mixture R123/R134a in a staggered bundle of horizontal low-finned tubes. The vapor temperature and the mass fraction of R134a at the tube bundle inlet were about 50°C and 14%, respectively. The refrigerant mass velocity ranged from 9 to 34 kg m⁻² s⁻¹, and the condensation temperature difference from 1.9 to 12 K. Four kinds of low-finned tubes with different fin geometry were tested. The highest heat transfer coefficient was obtained with a tube which showed the highest performance for R123. However, the diference among the tubes was much smaller for the mixture than for R123. The heat transfer coefficient and the vapor-phase mass transfer coefficient decreased significantly with decreasing mass velocity. The mass transfer coefficient increased with condensation temperature difference, which was due to the effect of suction associated with condensation. On the basis of the analogy between heat and mass transfer, a dimensionless correlation of the mass transfer coefficient was developed for each tube.     

Condensation from a vapor-gas mixture

A review of the possible approaches to calculation of vapor condensation from a binary vapor-gas mixture on a surface is presented. Emphasis is paid to justification of the application of molecular-kinetic theory methods for calculation of applied problems. Quantitative estimates for the parameters of the existence in principle of the regimes of one-dimensional stationary condensation are given.     

Influence of thermal resistance of condensate drops on heat and mass transfer in condensation of vapor from a vapor-gas mixture

Heat transfer to a solid wall during condensation of a vapor from a vapor-gas mixture in drops is discussed.     

Condensation heat transfer of a pure fluid and binary mixture outside a bundle of smooth horizontal tubes. Comparison of experimental results and a classical model

The condensation of pure HFC134a and different zeotropic mixtures with pure HFC134a and HFC23 on the outside of a bundle of smooth tubes was studied. The local heat transfer coefficient for each row was experimentally determined using a test section composed by a 13×3 staggered bundle of smooth copper tubes, measuring cooling water temperature in the inlet and the outlet of each tube, and measuring the vapour temperature along the bundle. All data were taken at the inlet vapour temperature of 40°C with a wall subcooling ranging from 4 to 26 K. The heat flux was varied from 5 to 30 kW/m² and the cooling water flow rate from 120 to 300 l/h for each tube. The visualisation of the HFC134a condensate flow by means of transparent glass tubes reveals specific flow patterns and explains the difference between the measured values of the heat transfer coefficient and the calculated values from Nusselt's theory. On the other hand, the experimental heat transfer data with the binary mixtures HFC23-HFC134a show the important effects of temperature glide and the strong decrease of the heat transfer coefficient in comparison with the pure HFC134a data. The measured values with the different zeotropic mixtures were compared with the data calculated with the classical condensation model based on the equilibrium model. An improvement of this model is proposed.     

R134a单元式风冷冷风机组冷凝器设计

单元式风冷冷风空调机组普遍采用波纹翅片管冷凝器。对冷凝器进行设计的关键是确定制冷工质在铜管内的冷凝换热系数及空气在翅片侧的表面换热系数，同时也需要考虑空气流过冷凝器的压降，以便选择风机。采用数学模型及换热关联式计算相关参数，在此基础上对R134a单元式风冷冷风空调机组的冷凝器进行设计。     

Optical investigation of heat and mass transfer in vapor condensation from vapor-gas mixtures

Experimental data on the temperature and concentration fields are obtained by an interferometric procedure in vapor condensation from a vapor-gas mixture and from a vapor-vapor mixture of six working media under natural convection conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 6, pp. 892–897, December, 1987.     

Condensation of downward-flowing HFC134a in a staggered bundle of horizontal finned tubes: effect of fin geometry

Experimental results are presented that show the effect of fin geometry on condensation of refrigerant HFC134a in a staggered bundle of horizontal finned tubes. Two types of conventional low-fin tubes and three types of three-dimensional fin tubes were tested. The refrigerant mass velocity ranged from 8 to 23 kg/m²s and the condensation temperature difference from 1.5 to 12 K. The effect of condensate inundation was more significant for the three-dimensional fin tubes than for the low-fin tubes. In most cases, the highest performance was obtained by the tube with a three-dimensional structure at the tip of low fins. In the case of high mass velocity and high condensate inundation rate, however, the highest performance was obtained by one of the low-fin tubes. The results were compared with previous results for bundles of smooth tubes and low-fin tubes.     

汽-气液滴形管与圆管外凝结换热的研究

为了研究管型对汽-气凝结换热的影响和强化汽-气凝结换热过程,建立了汽-气在液滴形管与圆管外凝结换热所形成的气液膜的厚度及换热系数沿管壁分布的综合数学模型。通过有限差分的方法,以天然气燃烧产生的烟气为例对两种管型进行了计算比较。在有效换热面积相等的情况下,与圆管相比,液滴形管上半部分管径小,压力梯度大,有利于排液,下半部分表面曲率大,亦有利于排液;液滴形管表面形成的气膜薄,液膜亦薄,珠状凝结区域大,液珠尺寸小,凝结换热系数大;液滴形管对显热传递亦有一定的强化作用。通过实验对计算结果进行了比较验证,结果表明该模型亦适用于椭圆管和其它汽-气混合流体种类。     

数据中心用蒸发冷却（凝）空调机组的设计及试验分析

本文提出一种新型数据中心用蒸发冷却(凝)空调机组,将蒸发冷却、蒸发冷凝、机械制冷技术三者结合,加大了自然冷源的应用时间。阐述其运行模式,并结合数据中心机房特点,介绍适合数据中心机房的机组运行模式。设计一台风量为20000 m 3/h的试验样机,并通过调节喷淋水流量,对其各功能段最佳性能进行了测定,得出该机组直接蒸发冷却段在水气比为0.37时,效率为97.22%;间接蒸发冷却段在水气比为0.28时,效率为62.98%。对其在乌鲁木齐、兰州、西安、上海4个典型城市的适应性分区进行了分析,并以新疆某数据中心为例,对比分析其年耗电量,采用该蒸发冷却(凝)空调机组年节电率为51.4%。     

Experimental study of condensation heat transfer of R-404A in helically coiled tubes

In this research, the heat transfer coefficients of R-404A vapor condensation inside helically coiled tubes are studied, experimentally. The effects of different coil pitches and curvature radii at different vapor qualities and mass velocities are considered. The vapor is condensed inside the helically coiled tubes by transferring heat to the cooling water flowing in annulus. Results show that the coil diameter has significant effect on condensation heat transfer coefficient. By decreasing the coil diameter or increasing the Dean number, the heat transfer coefficient is increased as the highest value is obtained at curvature radius of 4.35 cm which is 45% greater than the corresponding figure of curvature radius of 7.65 cm at mass velocity of 125 kg m⁻² s⁻¹. Also, at low vapor qualities, the coil pitch effect is more pronounced. Finally, based on the results, a new correlation is developed to evaluate the condensation heat transfer coefficient of R-404A inside helically coiled tubes.     

Acoustic waves in two-fraction bubble liquid with phase transformations

The propagation of acoustic waves in two-fraction mixtures of liquid with vapor-gas and gas bubbles of different sizes and compositions with phase transformations has been studied. A system of the differential equations of the motion of the mixture is presented, and the dispersion relation is deduced. Two local maxima in the frequency dependence of the attenuation coefficient for the case of the two-fraction mixture of water with vapor-gas bubbles of air and helium bubbles are revealed. The evolution of the weak pulsed perturbations of the pressure in this mixture was calculated numerically. It was established that the substitution of part of the vapor-gas bubbles in the monodisperse bubble mixture with phase transitions for inert gas bubbles can lead to both a decrease and an increase in the attenuation coefficient in the low-frequency region depending on the sort of gas.     

Condensation heat transfer coefficients of binary HFC mixtures on low fin and Turbo-C tubes

In this study, external condensation heat transfer coefficients (HTCs) are measured for nonazeotropic refrigerant mixtures (NARMs) of HFC32/HFC134a and HFC134a/HCFC123 on a low fin and Turbo-C tubes. All measurements are taken at the vapor temperature of 39 °C with the wall subcooling of 3–8 °C. Test results showed that condensation HTCs of NARMs on enhanced tubes were severely degraded from the ideal values showing up to 96% decrease. HTCs of the mixtures on Turbo-C tube were degraded more than those on low fin tube such that HTCs of the mixtures at the same composition were similar regardless of the tube. The mixture with larger gliding temperature differences (GTDs), HFC134a/HCFC123, showed a larger heat transfer reduction from the ideal values than the mixture with smaller GTDs, HFC32/HFC134a. Heat transfer enhancement ratios of the enhanced tubes with NARMs were almost 2 times lower than those with pure refrigerants and they decreased more as the GTDs of the mixtures increased.     

Condensation heat transfer coefficients of R22, R407C, and R410A on a horizontal plain, low fin, and turbo-C tubes

In this study, condensation heat transfer coefficients (HTCs) were measured on a horizontal plain tube, low fin tube, and Turbo-C tube at the saturated vapor temperature of 39 °C for R22, R407C, and R410A with the wall subcooling of 3–8 °C. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation HTCs were up to 50% lower than those of R22. For R407C, as the wall subcooling increased, condensation HTCs decreased on a plain tube while they increased on both low fin and turbo-C tubes. This was due to the lessening effect of the vapor diffusion film with a rapid increase in condensation rate on enhanced tubes. On the other hand, condensation HTCs of R410A, almost an azeotrope, were similar to those of R22. For all refrigerants tested, condensation HTCs of turbo-C tube were the highest among the tubes tested showing a 3–8 times increase as compared to those of a plain tube.     

Heat and mass transfer in chemically reacting media with decrease in partial pressures of vapor

We present a mathematical model of heat and mass transfer in a chemically reacting medium-multi-component vapor-gas mixture system with decrease in partial pressures of vapor-gas components in a free reactor volume. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 5, pp. 1012–1020, September–October, 2000.     

The flow of liquid past a plate with boiling and injection of gas

A classical model boundary layer problem is considered for the flow of liquid past a plate in view of injection of a vapor-gas mixture from its surface. The obtained self-similar solutions enable one to estimate the typical values of thickness of the vapor-gas layer, the value of heat-transfer coefficient as a function of temperature of liquid, intensity of injection and composition of mixture being injected, and the velocity of flow past the plate. In addition, the problem is considered of reducing the hydrodynamic drag owing to vapor and vapor-gas “lubrication” because of boiling of liquid and injection of vapor-gas mixture from the plate surface. The possibility is analyzed of the emergence of vapor film due to viscous friction forces in the case where the liquid is in the vicinity of the boiling point.     

Heat transfer associated with vapor condensation from vapor-gas mixtures

Reports results of a theoretical analysis and experimental investigation of heat transfer accompanying vapor condensation from vapor-gas mixtures. Gives a dimensionless equation for estimating the surface necessary for vapor condensation in the presence of an inert gas.     

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.     

New method of simulation of volume condensation of supersaturated vapor

A method of direct numerical solution of kinetic equation for the droplet size distribution function is suggested for the investigation of the process of volume condensation of supersaturated vapor. Use is made of analogy with the corresponding method of solution of kinetic Boltzmann equation. An advantage of the suggested approach is the absence of limitations on the Knudsen number. The method is tested using the example of simulation of the behavior of vapor under conditions of rapid development of the state of supersaturation in a vapor-gas mixture as a result of adiabatic expansion. The results are compared in a wide range of Knudsen number with the results obtained using the moments method in a version of a set of moments equations. Investigation is performed of the effect of the droplet size dependence of saturation pressure on the dynamics of the process of condensation relaxation of supersaturated vapor.