Condensation Of Mixture Research Articles

On the heat transfer deterioration during condensation of binary mixtures

Heat transfer processes involving binary- and multicomponent mixtures are ubiquitous in nature, particularly in several industries like the chemical and petrochemical ones. Condensation of binary mixtures inside pipes has been extensively studied during the past decades for unraveling the physical mechanisms controlling heat transfer. In particular, it has been observed that the heat transfer coefficient of mixtures is lower than the ones corresponding to its single–component constituents. This puzzle has motivated a vast research, and this heat transfer deterioration has been attributed to a dominant thermal resistance at the liquid-vapor interface. However, no suitable model has been found to be capable of accurately predicting experimental heat transfer coefficients during flow condensation. We show that the heat transfer deterioration observed during condensation of binary mixtures can be attributed to the change in the physical properties of the multicomponent mixture, and in fact the heat transfer coefficient remains equivalent to the one corresponding to the single-component, contrary to all the existing theories.

Fast photogenerated electron transfer in N-GQDs/PTI/ZnO-QDs ternary heterostructured nanosheets for photocatalytic H2 evolution under visible light

The efficiency of photogenerated charge transport is one of the critical factors determining the photocatalytic performance in heterostructured photocatalysts. In this work, a two-dimensional conjugated polytriazine imide (PTI)-based photocatalyst was developed to achieve fast photoexcited electron transfer. These heterostructured nanosheets were synthesized by a one-pot condensation of a precursor mixture of cyanamide and N-doped graphene quantum dots (N-GQDs) in ZnCl2 containing salt melts. The ionothermal synthetic approach results in the N-GQDs/PTI in-plane heterostructured nanosheets, loaded with well-dispersed ZnO quantum dots (ZnO-QDs). Especially, the N-GQDs are coupled with PTI through the nitrogen atoms at the edge of triazine rings, forming new π-p-π conjugated connection units. Therefore, the obtained ternary heterostructured nanosheets can synchronously promote photoelectron transport through the new π-p-π conjugated networks as well as extend the optical response. Importantly, it exhibits approximately 230 and 3.6 times enhancement of H2 evolution over pure PTI and the PTI/ZnO-QDs heterostructure under visible light irradiation, respectively.

Numerical study of condensation flow regimes in presence of non-condensable gas in minichannels

A numerical research on flow regime of R134a in horizontal minichannels was conducted. The model was on the basis of the volume of fluid approach, and inserted user-defined routines which cover condensation mass and heat transfer. The observed annular flow, injection flow and intermittent flow of pure steam condensation, and annular (annular-wavy) flow, injection flow, annular-intermittent flow and intermittent flow of gas mixture condensation were qualitatively compared against experimental data. Flow patterns of lower non-condensable gas mole concentration show similar with that of pure steam, while the fluctuation of gas-liquid interface in annular flow and the noticeable annular-intermittent flow of higher non-condensable gas mole concentration were noted. Besides, injection flow characters with larger head volume and longer neck, and intermittent flow characters with larger slug sizes in existence of non-condensable gas were found. Furthermore, the influence of mole concentration of non-condensable gas and operating conditions on flow pattern transition lines were analyzed after validating the flow pattern transition. The results showed that the injection flow transition point has a relative fixed point at pure vapor condensation, while various in presence of NCG. Besides, lower non-condensable gas mole concentration, smaller inlet gas mass flux and larger wall heat flux could lead to earlier flow pattern regime.

Condensation of ternary low GWP zeotropic mixtures inside channels

The condensation heat transfer coefficient and two-phase frictional pressure drop of ternary zeotropic mixtures R455A (R32, R1234yf and R744 at 21.5/75.5/3.0% by mass composition) and R452B (R32, R1234yf and R125 at 67.0/26.0/7.0% by mass composition) have been measured inside a minichannel (0.96 mm diameter) and a conventional tube (8.0 mm diameter). The effects of tube diameter, mass velocity, vapor quality and saturation-to-wall temperature difference have been investigated. A comparison between the experimental data of the tested mixtures and the condensation heat transfer of the pure components R32 and R1234yf has been performed. The two-phase pressure drop and condensation heat transfer data are compared to predictions of correlations available in the literature. In the prediction of the heat transfer coefficient, the models are adapted to account for the additional mass transfer resistance occurring during condensation of zeotropic mixtures.

Condensation heat transfer enhancement using steam-ethanol mixtures on horizontal finned tube

Condensation of steam-ethanol mixtures was investigated experimentally on instrumented, finned copper tube. The tube had length 70 mm, fin root diameter 12.7 mm. Height, thickness and inter-fin space was of rectangular fins was 1.6 mm, 0.5 mm and 0.6 mm. Concentration of ethanol by mass in the boiler when cold prior to the start-up were 0.025, 0.05, 0.1, 0.5 and 1.0%. Experiments were conducted over a range of vapor-to-surface temperature difference at three pressures of 14 kPa, 55 kPa and atmospheric. Maximum upstream vapor velocity on condensing finned test tube at atmospheric pressure and 14 kPa was 7.5 and 15.0 m/s respectively. Heat transfer enhancement as compared to pure steam of around 3 times was obtained over a range of vapor to surface temperature difference. Results have been compared with the available data for pure steam condensation on finned tube and steam-ethanol condensation on the smooth tube under same conditions of pressure, vapor velocity and vapor to surface temperature difference. Photographs showing increase of retention angle due to ethanol are included in the paper.

A new simplified model for condensation heat transfer of zeotropic mixtures inside horizontal tubes

Simple and accurate prediction models are highly demanded for industrial design of heat exchangers using refrigerant mixtures. This paper presents some data taken during condensation of R32/R1234ze(E) and proposes a new method to predict condensation heat transfer coefficient of zeotropic mixtures inside horizontal tubes. The method is developed based on the heat transfer model by Cavallini et al. (2006) for pure fluids by including additional heat transfer resistances during zeotropic mixtures condensation. The heat transfer resistances are modified from the Bell and Ghaly (1973) method by considering the effect of interfacial roughness and non-equilibrium phenomena, following the approach by Del Col et al. (2005). This new model is easy to implement and requires low computational effort. The predicted results by the model show a satisfactory agreement with experimental data covering various mixtures and a wide range of working conditions.

PQ, KD to expand Asia polyolefin catalysts

The condensation mechanism of alkanes is an essential foundation for improving the liquefaction efficiency of natural gas. However, a microscopic understanding of this mechanism is still lacking. This study analyzes the homogeneous and heterogeneous condensation characteristics of methane and explores the influence mechanisms of n-hexane molecules. The results reveal that higher initial pressures cause more intense nucleation stages with more latent heat released. Moreover, changes in the monomer temperature lag behind changes in cluster temperature, which is particularly pronounced in low supersaturation systems. Trace amounts of n-hexane can greatly improve the nucleation rate and liquefaction ratio of methane. The pre-condensed n-hexane clusters serve as a surface for heterogeneous methane nucleation, lowering the nucleation barrier significantly. As the number of n-hexane molecules increases, the nucleation promotion effect is further enhanced. With increased subcooling, the promotion effect lg (J/J0) drops from 17 to approximately 2. Furthermore, the heterogeneous condensation of n-hexane and methane mixture comprises three processes: n-hexane condensation with methane molecular adhesion, methane aggregation on n-hexane nuclei, and surface growth of methane clusters accompanied by n-hexane dissolution. Moreover, methane with lower surface tension always dominates in the cluster surface region.

Numerical simulation of air–steam mixture condensation flows in a vertical tube

In this study, a fully compressible three-phase numerical model for steam condensation flow in the presence of air is presented. The model solves the Reynolds-averaged Navier–Stokes equation coupled with two interface advection equations. The Lee condensation model was applied to simulate the mass and energy transfer processes via interfaces. Several test cases were simulated for the air–steam mixture condensation flow in a vertical tube with different air mass fractions to verify the numerical model. The validity was demonstrated through comparisons of the centerline temperatures along the tube and experimental data; the results were in good agreement with experimental data. A detailed radial profile of the temperature, species mass fraction, and velocity was analyzed. A developing thin condensate water film along the tube and the thickest film layer at the outlet tube wall of approximately 4.0 mm were observed. Air accumulation at the steam–water interface was also represented. In addition, the effects of air mass fraction on the characteristics of the condensation rate were investigated.

Experimental study on two-phase flow pressure drop during ethanol–water vapor mixture condensation in microchannels

Ethanol-water vapor mixtures condensation shows different flow patterns in microchannels due to the equivalent surface free energy differences. The transition point of streak flow pattern was introduced in the paper which was found closely related to the frictional pressure drop of ethanol–water vapor mixtures condensation flow in microchannels. Characteristics of two-phase pressure drop for ethanol–water vapor mixtures condensation flow in silicon microchannels of streak and smooth annular flow pattern were investigated. Four types of multi-port trapezoidal and triangular microchannels with hydraulic diameter in the range of 126–155 μm were employed. The pressure drop was determined under steam mass flux between 259.2 and 504.8 kg m−2 s−1 when the inlet ethanol weight concentration varied from 1% to 60%. The experimental pressure drop results were compared with existing correlations of flow condensation. The transition point basing on the streak flow pattern of binary vapor condensation was proposed to replace the traditional Reynolds number criterion of the laminar flow state to turbulent flow state for the frictional factor and the C parameter for Kim and Mudawar’s universal pressure drop model, which is in good agreement with the results the experiment results.

Mathematical Model of Plate Heat Exchanger for Utilisation of Waste Heat from Condensable Gaseous Streams

The mathematical model of vapour condensation from the mixture with noncondensing gas in Plate Heat Exchanger (PHE) channels is presented. The model accounts for the change of process parameters along the heat transfer surface and local features of heat and mass transfer processes in PHEs channels with plates of different corrugations geometry. It consists of the system of ordinary differential equations with considerably nonlinear right parts. The software for its solution by finite difference method is developed. The validity of the model is confirmed by comparison with the experiment for steam-air mixture condensation in a PHE channel sample.

New cooling approach using successive evaporation and condensation of a liquid film inside a vertical mini-channel

In this paper, the successive evaporation and condensation of water-ethanol and water-methanol liquid film mixtures for cooling purpose is investigated. The simulations are achieved using a finite difference model to describe the heat and mass transfer during this process. The studied process relies on the absorption of energy at the evaporator and then the release of this energy at the condenser. The evaporation and heat exchange abilities of the mixtures composition are analysed to identify the appropriate mixture for the new proposed cooling approach. The results indicate that more energy equilibrium occurs with high concentration of water in the mixture with the advantage of having low bulk and interface temperature.

Numerical investigation on flow condensation of zeotropic hydrocarbon mixtures in a helically coiled tube

A numerical investigation was carried out to study the condensation flow and heat transfer coefficient of methane/propane and ethane/propane mixtures in a helically coiled tube. Two-phase heat transfer simulations had been performed at saturation pressures of 0.3–3.7 MPa with mass flux of 200, 300, 400 kg/(m2 s) and heat flux of 5 kW/m2. The effects of mass flux, saturation pressure, vapor quality and component ratios on the heat transfer coefficient were examined. In addition, annular/non-annular flow patterns were obtained by numerical simulations and experiments, and a new flow pattern transitional line for annular/non-annular flows was proposed. Meanwhile, the results were compared with the existing condensation heat transfer correlations, and the improved heat transfer correlation was proposed and well coincided with the data with a mean absolute relative deviation (MARD) of 9.2%.

Performance investigation of a novel zeotropic organic Rankine cycle coupling liquid separation condensation and multi-pressure evaporation

The decrease in fossil energy reserves and the increase in energy costs have resulted in a strong interest in power generation using renewable heat sources or waste heat. Organic Rankine cycle (ORC) is a promising heat-to-power conversion technology. Although the ORC using zeotropic mixture is superior to ORC using pure fluid in thermodynamic performance due to low irreversibility during the evaporation and condensation of zeotropic mixture, the improvement in thermodynamic performance is usually achieved at the cost of poor economic performance. The studies on improving the thermo-economic performance are limited. In the present study, a novel zeotropic ORC coupling liquid separation condensation and multi-pressure evaporation is proposed. Multi-pressure evaporation is presented to improve heat match between the heat source and working fluid. Liquid separation condensation is applied to control the composition of the mixtures that enter the evaporation processes. Thermodynamic analysis and optimization model of the novel ORC is developed. The superiority of the proposed novel ORC over the traditional simple zeotropic ORC and traditional multi-pressure evaporation zeotropic ORC is elaborated for different mixtures. The contribution of mixture composition adjustment and condensation enhancement through liquid-vapor separation on the cycle performance improvement is investigated. Sensitivity analysis of heat-sink inlet temperature, heat source inlet temperature, vapor quality, heat source specific heat capacity, and heat-sink temperature rise on the cycle performance are conducted. The case results show that net power output of the novel ORC is 13.05–26.18% higher than that of the simple zeotropic ORC. The contribution of mixture composition adjustment on improving the net power output can be up to 3.57% compared with traditional multi-pressure evaporation ORC for mixture R245fa–R365mfc. When the heat transfer enhancement through liquid separation is incorporated into the thermodynamic optimization, the net power output of the novel zeotropic ORC can be increased by 8.22% compared with the traditional multi-pressure evaporation ORC under the same economic constraint.

Capillary Condensation of Binary and Ternary Mixtures of n-Pentane-Isopentane-CO2 in Nanopores: An Experimental Study on the Effects of Composition and Equilibrium.

Confinement in nanopores can significantly impact the chemical and physical behavior of fluids. While some quantitative understanding is available for how pure fluids behave in nanopores, there is little such insight for mixtures. This study aims to shed light on how nanoporosity impacts the phase behavior and composition of confined mixtures through comparison of the effects of static and dynamic equilibrium on experimentally measured isotherms and chromatographic analysis of the experimental fluids. To this end, a novel gravimetric apparatus is introduced and validated. Unlike apparatuses that have been previously used to study the confinement-induced phase behavior of fluids, this apparatus employs a gravimetric technique capable of discerning phase transitions in a wide variety of nanoporous media under both static and dynamic conditions. The apparatus was successfully validated against data in the literature for pure carbon dioxide and n-pentane. Then, isotherms were generated for binary mixtures of carbon dioxide and n-pentane using static and flow-through methods. Finally, two ternary mixtures of carbon dioxide, n-pentane, and isopentane were measured using the static method. While the equilibrium time was found important for determination of confined phase transitions, flow rate in the dynamic method was not found to affect the confined phase behavior. For all measurements, the results indicate qualitative transferability of the bulk phase behavior to the confined fluid.

Numerical study on condensation heat transfer and pressure drop characteristics of ethane/propane mixture upward flow in a spiral pipe

Spiral wound heat exchanges (SWHE) has been the most widely used in large-scale liquid natural gas (LNG) plants. However, few studies have been focused on the condensation heat transfer and pressure drop for hydrocarbon mixture refrigerant in SWHE tube side. In this paper, the condensation heat transfer and pressure drop characteristics for ethane/propane mixture upward flow in a spiral pipe were numerically investigated. The numerical model was established and verified based on the existing experimental results and new flow pattern observation experiments. It discussed the variation trends of void fraction, frictional pressure drop, heat transfer coefficient and heat and mass transfer resistance with various parameters, such as, vapor quality, mass flux, heat flux, saturation pressure and inclination angle. Comparing with the existing correlations, the results showed that Steiner’s correlation, modified Fuchs’s correlation, Boyko’s correlation could better predict the void fraction, frictional pressure drop, film heat transfer coefficient with mean absolute deviation of 6.08%, 10.67% and 13.06%, respectively. Meanwhile, modified Silver approach was used to modify the mixed effects of ethane/propane mixture on heat transfer. The study provides some constructive instructions to understand the condensation of zeotropic mixtures in the spiral pipe, and is helpful in designing more effective SWHE.

Effect of flow velocity on the process of air-steam condensation in a vertical tube condenser

This article describes the influence of flow velocity on the condensation process in a vertical tube. For the case of condensation in a vertical tube condenser, both the pure steam condensation process and the air-steam mixture condensation process were theoretically and experimentally analyzed. The influence of steam flow velocity on the value of the heat transfer coefficient during the condensation process was evaluated. For the condensation of pure steam, the influence of flow velocity on the value of the heat transfer coefficient begins to be seen at higher speeds, conversely, this effect is negligible at low values of steam velocity. On the other hand, for the air-steam mixture condensation, the influence of flow velocity must always be taken into account. The flow velocity affects the water vapor diffusion process through non-condensing air. The presence of air significantly reduces the value of the heat transfer coefficient. This drop in the heat transfer coefficient is significant at low velocities; on the contrary, the decrease is relatively small at high values of the velocity.

Condensation of binary mixtures on horizontal tubes

The two most common models to describe the condensation of binary mixtures are the equilibrium model by Silver (Trans Inst Chem Eng 25:30–42, 1947) and the film model by Colburn and Drew (Transactions of the American Institute of Chemical Engineers 33:197–215, 1937), which is stated by Webb et al. (Int J Heat Mass Transf 39:3147–3156, 1996) as more accurate. The film model describes the outer heat transfer coefficient by subdividing it into two separate resistances against the heat transfer. The resistance of the liquid condensate film on the tube can be calculated with equations for the condensation of pure substances for the analogous flow pattern and geometry using the property data of the mixture. The resistance in the gas phase can be described by a thermodynamic parameter Z and the single phase heat transfer coefficient αG. In this work measurements for condensation of the binary mixtures n-pentane/iso-octane and iso-propanol/water on horizontal tubes for free convection are carried out. The obtained results are compared with the film model by Colburn and Drew (Transactions of the American Institute of Chemical Engineers 33:197–215, 1937). The comparison shows a rather big deviation between the theoretical model and the experimental results. To improve the prediction quality an own model based on dimensionless numbers is proposed, which describes the experimental results of this work significantly better than the film model.

Synthesis of metallocomplexes of water soluble bisquinolinylporhyrins as potential antimicrobial agents

At present, extensive research is being carried out on the phenomenon of resistance of microbes to antibiotics, including the newest of them. Among the most promising drug candidates for treatment such superbugs is derivatives of 5,15-disubstituted water-soluble porphyrins developed and patented by Destiny Pharma, UK. Here, we continued of our investigation of quinolinylporphyrins and report about synthesis of 5,15-di(n-propyl)-10,20-di(3-quinolinyl)porphyrine and its isomer - 5,10-di(n-propyl)-15,20-di(3-quinolinyl)porphyrine and their complexes with Fe and Mn. The porphyrins was obtained by mixed aldehydes condensation of mixture quinoline-3-carbaldehyde and n-butyraldehyde with pyrrole in propionic acid with small amount propionic anhydride. Above mentioned porphyrins was separated and purified by column chromatography on silica gel and their Fe and Mn complexes was synthesized in refluxing DMF by treatment respectively FeCl3 and Mn(CH3CO2)2. Water-soluble form of the metalloporphyrines was obtained by quaternization of nitrogen atom of quinolinyl substituents by methyl-paratoluenesulfonate for further investigation their antimicrobial properties.

Heat transfer degradation during condensation of non-azeotropic mixtures

International organizations call for a reduction of the HFCs production and utilizations in the next years.Binary or ternary blends of hydroflourocarbons (HFCs) and hydrofluoroolefins (HFOs) are emerging as possible substitutes for high Global Warming Potential (GWP) fluids currently employed in some refrigeration and air-conditioning applications.In some cases, these mixtures are non-azeotropic and thus, during phase-change at constant pressure, they present a temperature glide that, for some blends, can be higher than 10 K. Such temperature variation during phase change could lead to a better matching between the refrigerant and the water temperature profiles in a condenser, thus reducing the exergy losses associated with the heat transfer process. Nevertheless, the additional mass transfer resistance which occurs during the phase change of zeotropic mixtures leads to a heat transfer degradation. Therefore, the design of a condenser working with a zeotropic mixture poses the problem of how to extend the correlations developed for pure fluids to the case of condensation of mixtures. Experimental data taken are very helpful in the assessment of design procedures. In the present paper, heat transfer coefficients have been measured during condensation of zeotropic mixtures of HFC and HFO fluids. Tests have been carried out in the test rig available at the Two Phase Heat Transfer Lab of University of Padova. During the condensation tests, the heat is subtracted from the mixture by using cold water and the heat transfer coefficient is obtained from the measurement of the heat flux on the water side, the direct measurements of the wall temperature and saturation temperature. Tests have been performed at 40°C mean saturation temperature. The present experimental database is used to assess predictive correlations for condensation of mixtures, providing valuable information on the applicability of available models.

Heat transfer during condensation of steam from steam-gas mixtures in the passive safety systems of nuclear power plants

A theoretical model for calculation of heat transfer during condensation of multicomponent vapor-gas mixtures on vertical surfaces, based on film theory and heat and mass transfer analogy is proposed. Calculations were performed for the conditions implemented in experimental studies of heat transfer during condensation of steam-gas mixtures in the passive safety systems of PWR-type reactors of different designs. Calculated values of heat transfer coefficients for condensation of steam-air, steam-air-helium and steam-air-hydrogen mixtures at pressures of 0.2 to 0.6 MPa and of steam-nitrogen mixture at the pressures of 0.4 to 2.6 MPa were obtained. The composition of mixtures and vapor-to-surface temperature difference were varied within wide limits. Tube length ranged from 0.65 to 9.79m. The condensation of all steam-gas mixtures took place in a laminar-wave flow mode of condensate film and turbulent free convection in the diffusion boundary layer. The heat transfer coefficients obtained by calculation using the proposed model are in good agreement with the considered experimental data for both the binary and ternary mixtures.