Condensation Of Mixture Research Articles

Experimental evaluation of the in-tube condensation heat transfer of pure n-pentane/R245fa and their non-azeotropic mixture as an ORC working fluid

The existence of temperature gliding in non-azeotropic mixture working fluids provides a promising opportunity for greatly improved resource utilization in organic Rankine cycle (ORC) systems for geothermal applications. The condensation heat transfer degradation associated with working fluid mixtures is an unavoidable penalty that may reduce the utilization and system benefits by necessitating larger heat exchangers. The objective of the current study is an experimental investigation of condensation heat transfer for R245fa, n-pentane, and a composition of their mixture. Quasi-local condensation heat transfer coefficients are measured in a straight horizontal smooth tube with flow conditions at mass flux G=100 and 150kg(m2s)−1, local equilibrium quality x=0.05–0.80, and reduced pressures Pr=0.05–0.15. The reduced condensation heat transfer coefficients from the test are compared with the predictions from already established mixture correction methods in the literature. Pure components R245fa and n-pentane condensation heat transfer data are well predicted by Shah (1979) correlations for all test conditions. However, their non-azeotropic mixture condensation heat transfer data require additional correction parameter to account for the heat transfer degradation. This correction parameter is correlated by the temperature gliding gradient of mixture fluids. Test data with mixture working fluids from current study are reasonably well predicted by the corrected in-tube correlation.

The analysis of thermal and flow characteristics of the condensation of refrigerant zeotropic mixtures in minichannels

Abstract The paper presents the results of experimental heat transfer and pressure drop during condensation of the single component refrigerant R134a and zeotropic mixtures R404A, R407C, and R410A in tube minichannels of internal diameter from the range 0.31-3.30 mm. The local values and the average of heat transfer coefficient and pressure drop in the whole range of the change in mass quality were measured. On the basis of the obtained test results there was illustrated the influence of the change of mass vapor quality, the mass flux density, and the inner diameter of channel on the studied parameters. These results were compared with the calculation results based on the relations postulated by other authors. The discrepancy range was ± 50%. On the basis of given test results own correlation was developed to calculate the heat transfer coefficient and pressure drop of tested refrigerants which presents the obtained results in a range of discrepancy of ±25%.

Modeling of In-Tube Condensation of Zeotropic Mixtures

Studies in the literature have shown that zeotropic mixture condensation rates are lower than those predicted using a pure-fluid approach. This has been attributed to the decrease in fluid temperature that occurs with zeotropic mixtures and to the development of concentration gradients in the vapor-phase that limit the condensation heat transfer. The decrease in the apparent heat transfer coefficient is not consistent across mass fluxes, tube diameters, fluid combinations, saturation pressures, and concentrations. Several modeling techniques exist, which allow engineers to model the decrease in heat transfer rates. This study provides guidelines on when the mass transfer effects can be neglected and when it is appropriate to apply established models in the literature. A condensation database containing fluid combinations of pairs of hydrocarbons, ammonia and water, and synthetic refrigerants across large changes in operating conditions, tube diameters, and concentrations is used to validate the approach. The proposed framework predicts that the Bell and Ghaly (1973, “An Approximate Generalized Design Method for Multicomponent/Partial Condensers,” AIChE Symp. Ser., 69, pp. 72–79) approach is valid for mid- and high-reduced pressures, i.e., above 0.40, while explicitly accounting for mass transfer is necessary at lower reduced pressures, i.e., below 0.40, where the influence of the temperature glide in the Bell and Ghaly method is weighted too strongly.

Optimization of a cascade refrigeration system using refrigerant C3H8 in high temperature circuits (HTC) and a mixture of C2H6/CO2 in low temperature circuits (LTC)

This paper discusses the multi-objectives optimization of a cascade refrigeration system using refrigerant C3H8 in high temperature circuits (HTC) and a mixture of C2H6/CO2 in low temperature circuits (LTC). The evaporator temperature, condenser temperature, C2H6/CO2 mixture condensation temperature, cascade temperature differences, and the CO2 mass fraction are chosen as the decision variables. Whereas cooling capacity, cold space temperature, and ambient temperature are taken as the constraints. The purpose of this research is to design a cascade refrigeration system whose optimum performance are defined in terms of economics and thermodynamics. Accordingly, there are two objective functions that should be simultaneously optimized including the total annual cost which consists of the capital and operational cost and the total exergy destruction of the system. To this aim, the optimum operating temperature of the system and CO2 fraction should be determined so that the system has minimum exergy destruction and annual cost. Results show that, the optimum value of the decision variables for this system can be determined by trade-off between annual cost and exergy destruction.

Condensation of the air-steam mixture in a vertical tube condenser

This paper deals with the condensation of water vapour in the presence of non-condensable air. Experimental and theoretical solutions of this problem are presented here. A heat exchanger for the condensation of industrial waste steam containing infiltrated air was designed. The condenser consists of a bundle of vertical tubes in which the steam condenses as it flows downwards with cooling water flowing outside the tubes in the opposite direction. Experiments with pure steam and with mixtures of steam with added air were carried out to find the dependence of the condensation heat transfer coefficient (HTC) on the air concentration in the steam mixture. The experimental results were compared with the theoretical formulas describing the cases. The theoretical determination of the HTC is based on the Nusselt model of steam condensation on a vertical wall, where the analogy of heat and mass transfer is used to take into account the behaviour of air in a steam mixture during the condensation process. The resulting dependencies obtained from the experiments and obtained from the theoretical model have similar results. The significant decrease in the condensation HTC, which begins at very low air concentrations in a steam mixture, was confirmed.

Nonlinear effect of surface disturbances on mass flux and its modeling in Marangoni dropwise condensation

We study Marangoni dropwise condensation of a binary vapor mixture in the framework of the long-wave model. The model equations for the film thickness of a condensate and the condensation mass flux are derived and numerically solved as an initial value problem. In the dropwise state, rupture of the liquid film is prevented by the effect of mass gain due to condensation, which is enhanced at the troughs of the liquid. The average mass and heat fluxes increase with respect to those in the flat-film state. By simplifying the model equation, we reveal that an increase in the average mass flux arises mainly from nonlinear coupling of the disturbances of the mass flux and the film thickness. Furthermore, we propose a simple expression for the average mass flux. The ratio of the average mass flux to that in the flat-film state becomes larger at smaller ambient vapor concentrations of the lower-boiling-point component, around the bubble point temperature, for thicker condensates or for thinner boundary layers, consistent with experimental results in literature. Our model of the average mass flux is a good approximation for that obtained from the original equation unless the concentration becomes sufficiently small or the temperature approaches that of the bubble point.

Study of aerosol behaviour in filmwise condensation processes with the presence of inert gas

The appearance of aerosols in condensation processes may result in a loss of condensate mass, a reduction of efficiency, pollution and damage to equipment. The presence of inert gases in condensation is frequent and can lead to the formation of aerosol particles. Equipment used in industrial condensation, gas cleaning, the removal of pollutants or the recovery of valuable substances comprise some examples of interest. The complexity of the physical phenomena occurring simultaneously makes the study of these systems difficult and it is thought that modelling might help to better understand their behaviour. A model has been developed in this study that includes the condensation of the gaseous mixture and phenomena related to the presence of liquid particles. The model solves the conservative equations for species continuity, energy and the number of liquid particles. It also includes the precipitation of liquid particles via thermophoresis, diffusiophoresis and gravitational deposition, homogeneous nucleation and coagulation induced by the Brownian movement of the particles. A condenser presenting a simple shell-and-tube geometry was selected and subjected to a unidimensional spatial discretization. The particle size interval of the aerosol population was discretized following a sectional method of moving intervals. The interaction between continuous and discrete phases was calculated as condensational growth in non-dilute and non-ideal media. Some cases were solved for water liquid particles and vapour mixed with air and a comparison was carried out using experimental data from a previous study from the literature providing a good fit. It was observed that the condensation rate is not radically altered by the presence of particles, although the persistence of remaining growing droplets dispersed in the gas could produce the aforementioned undesirable effects.

Condensation of a hydrocarbon in the presence of a non-condensable gas: Heat and mass transfer

This paper presents experimental study for horizontal tubeside and shellside condensation of kerosene in the presence of a wide range of non-condensable gas. Using the heat and mass transfer analogy model, the heat and mass transfer mechanism of the condensate film and the vapor-gas phase has been analyzed. Convective condensation of hydrocarbon mixtures in the presence of non-condensable gases in shear-controlled flow is strongly dependent on the diffusion of the vapor molecules through the non-condensable gas onto the condensate film. The mass transfer resistance increases as the non-condensable gas concentration increases, and the interfacial temperature decreases as the less volatile components condense. Our experimental results demonstrate that the heat transfer performance is influenced by the non-condensable gas, vapor, condensate Reynolds numbers, Schmidt number and Jacob number. Comparisons of a newly developed heat transfer correlation based on the heat and mass transfer analogy with experimental data show a good agreement. The correlations can be applied to tubeside and shellside condensation of mixtures with non-condensable gases.

An experimental investigation of pure steam and steam–air mixtures condensation outside a vertical pin-fin tube

A set of condensation experiments in the steam–air and pure steam conditions has been conducted to evaluate the heat removal capacity of a vertically pin-fin tube under free convection. Condensation heat transfer coefficient and heat transfer rate have been obtained. The bulk temperature, wall temperature and temperature near tube surface are measured in detail. As a reference, a smooth tube is tested under the same condition. For pure steam case, the pin-fin tube generates restrictions on the condensation heat transfer process in low wall subcooling region. With a higher wall subcooling, the pin-fin tube shows a larger condensation heat transfer coefficient than smooth tube does. For steam–air mixtures case, the result of the temperature measurement demonstrates that there is an air rich region near the pin-fin tube. Compared with the smooth tube, the pin-fin tube generates reduction effect on the condensation heat transfer process under low air mass fraction situation. As air mass fraction increasing, the condensation heat transfer coefficient of the pin-fin tube becomes larger than that of the smooth tube.

Visualization study of condensation of ethanol–water mixtures in trapezoidal microchannels

A visualization experiment is carried out to investigate the ethanol–water vapor mixtures condensation flow patterns in an array of microchannels under a wide range of concentration (2–60%). The text microchannel is a trapezoidal silicon channel with a hydraulic diameter of 165.87μm and a length of 50mm. Along the flow direction, annular, annular-streak, annular-streak-droplet, churn, injection, droplet-injection and bubble flow patterns are observed in the vapor mixtures condensation under different inlet ethanol mass concentration (60%, 31%, 20%, 6%, 4% and 2%), which is obviously different from pure steam condensation. The equivalent surface free energy differences under various vapor conditions and vapor–surface temperature differences are calculated quantitatively. The experimental results show that flow patterns are closely related to the equivalent surface free energy differences. A correlation based on the critical quality is proposed to indicate the injection two-phase flow patterns transition.

Two-phase pressure drop and condensation heat transfer of R32/R1234ze(E) non-azeotropic mixtures inside a single microchannel

Much attention has been paid in the recent years to the possible use of fluorinated propene isomers for the substitution of high global warming potential refrigerants. Among the fluorinated propene isomers, R1234ze(E) may be a substitute of R134a for refrigeration applications. R1234ze(E) has a global warming potential lower than 1 (considering a period time of 100 years), and it is receiving some attention also as a component of low global warming potential mixtures. In this article, a mixture of R1234ze(E) and R32 has been investigated at two different mass compositions (23/77% and 46/54% by mass) with regard to the performance at the condenser. The local heat transfer coefficients during condensation in a single microchannel with 0.96 mm diameter are measured and analyzed. The frictional two-phase pressure drop in the same channel is also investigated. The present tests are carried out on the experimental apparatus available at the Two-Phase Heat Transfer Lab of the University of Padova. The new experimental data are compared to those of pure R1234ze(E) and R32. This allows the heat transfer penalization due to the mass transfer resistance occurring during condensation of these zeotropic mixtures to be analyzed and suitable predicting models to be assessed. The knowledge of heat transfer coefficient and pressure drop allows evaluation of the overall performance of these mixtures when used in condensers.

Forces of Change: Mechanics Underlying Formation of Functional 3D Organ Buds

3D organ buds that can recapitulate organ function have myriad applications for regenerative and personalized medicine. Here, Takebe etal. (2015) describe a generalized method for organ bud formation, demonstrating that mechanosensitive mesenchymal stem cells drive condensation of heterotypic cell mixtures to create buds from diverse organs.

Condensation Heat Transfer Enhancement on Surfaces with Interlaced Wettability

This study investigated the effect of surfaces with interlaced wettability on steam–air mixture condensation. Experiments were conducted on various types of surface with different modified strip widths. In general, surfaces exhibiting high hydrophobic wettability yield a high condensation heat-transfer rate because dropwise condensation is easily formed. However, the experimental results of this study revealed that surfaces with interlaced wettability demonstrated superior condensation heat-transfer performance to those with homogeneous high hydrophobic wettability. Such an observation implies that the configuration of surface modification can enhance condensation heat transfer. In addition, the data indicated an optimal area ratio of modified surfaces to unmodified surfaces.

PERSONAL REFLECTIONS ON FIFTY YEARS OF CONDENSATION HEAT TRANSFER RESEARCH

This paper discusses some of the experimental and theoretical work on condensation heat transfer with which I have been involved over many years. The explosion in publications in recent years precludes a comprehensive survey of the general field. The paper is based on an unpublished presentation I gave at the 8th Experimental Heat Transfer, Fluid Mechanics and Thermodynamics Conference (ExHFT-8) held in Lisbon, Portugal, in 2013. It focuses on the topics of dropwise condensation, which has recently again become fashionable after many years, and condensation of metals. In both of these fields the interface temperature discontinuity plays a crucial role. Also discussed is work on condensation on integral finned tubes, in microchannels, and finally on Marangoni condensation of mixtures.

Numerical Study of the Condensation Length of Binary Zeotropic Mixtures

Abstract Heat exchangers are the main components in refrigeration and liquefaction systems, particularly in the liquefaction of natural gas, where the gas being condensed is a multicomponent mixture. The study of the two-phase condensation region is important for the design of heat exchangers. This paper studies heat and mass transfer characteristics of zeotropic mixtures condensation by four different models, including equilibrium and non-equilibrium conditions. The effects of heat and mass transfer resistances on the condensation process are analyzed, and the required pipe lengths are compared. It is found that the mass transfer resistance in the vapor phase has a significant influence on the condensation length, and that it overweighs heat transfer resistance in the vapor phase in the present case study.

低GWP混合冷媒R 32/R 1234ze(E)の水平ら旋溝付管内凝縮および蒸発特性

低GWP混合冷媒R 32/R 1234ze(E)の水平ら旋溝付管内凝縮および蒸発特性

Theoretical analysis of air-fuel mixture formation in the combustion chambers of the gas engine with two-stage combustion system

Abstract The results of theoretical analysis of a mixture formation process during the compression stroke in a prechamber of the IC (internal combustion) gas engine with the stratified mixtures two-stage combustion system were presented in the paper. The course of excess air-fuel ratio changes in prechamber at ignition time λkz in function of degree of the mixture condensation during the compression stroke φ expressing quotient of a temporary cylinder and prechamber volume and maximal value of the volume were estimated. Research concerning λkz sensitivity on changes of rich combustible mixture composition delivered to the prechamber by the additional fuel supply system λko, mixture composition in cylinder _c and degree of filling a prechamber with the rich combustible mixture ξ were performed. According to numerical calculations it was proved that the real gas engine with the two stage combustion system at equal degree requires exact regulation of the three analysed values.

Plasma treatment with nickel of vanadium carbide and nitride

X-ray, scanning probe, and high-resolution translucent electron microscopy techniques were used to investigate the structural and morphological features of super- and nanodispersed powders produced by the plasma chemical repeated condensation of mixtures of vanadium carbide or nitride with nickel in low-temperature (4000–6000°C) nitrogen plasma.

Direct-contact Condensation of Hydrocarbon Mixtures in a Structured Packing Bed

This article deals with experimental research of the direct-contact condensation in column with structured packing. Lots of experiments have been performed in a column of 257 mm inner diameter with Topic 125 Y structured packing using hydrocarbon mixtures. The influences of the vapor and liquid flow rate as well as liquid temperature at vacuum pressure have been investigated. A new empirical correlation was developed to predict the heat transfer coefficient for structured packings, which can be applied to both design and simulation of distillation columns in petroleum refinery.

Thermal-hydraulic evaluation of passive containment cooling system of improved APR+ during LOCAs

Various reactor concepts and technologies have been devised and evaluated to ensure the integrity of the core and the containment under a prolonged station blackout. After the successful validation of the passive auxiliary feedwater system (PAFS) of Advanced Power Reactor Plus (APR+), Korea is considering an improved APR+ with a passive containment cooling system (PCCS). In a previous paper, we suggested a PCCS design based on APR+ and performed a scoping analysis. We performed a MARS simulation for the thermal hydraulic evaluation of the system behavior, including natural circulation through the Passive Condensation Cooling Tank (PCCT) water pool and inside PCCS tubes as well as steam–air mixture condensation inside the containment. Through a simulation using the MARS system code, we investigated the effect of air holdup tanks (AHTs) on reduction of the air fraction in the containment, the effects of several steam–air mixture condensation models, the role of heat structures, and the flow instability inside the PCCS tubes. We found that the presence of AHT reduced the number of required PCCS tubes by more than half and the heat resistance of the steam–air mixture side is dominant in terms of governing the overall performance of PCCS. The embedded MARS condensation model and Uchida's correlation gave lower heat transfer coefficients than Dehbi's correlation, and heat structures removed more decay heat than PCCS tubes. Finally, intense flow instability inside the PCCS tubes was observed and was mitigated by placing orifice plates at the inlet of the PCCS tubes, increasing the height of the return nozzle, or increasing the tube angle.