Non-azeotropic Mixtures Research Articles

Experimental analysis on the flow patterns and conversion mechanisms of condensing flow with non-azeotropic mixtures in spiral tube

The flow patterns have a significant impact on the flow and heat transfer characteristics of the working fluid, making it fundamental for the study of complex two-phase flows. To investigate the condensation flow pattern and flow pattern transformation mechanism with mixed hydrocarbon in a spiral tube, a two-phase flow pattern experimental system was designed. The effects of mass flux (196–540 kg/m−2·s−1), vapor quality (0–1), and operating pressure (2–4 MPa) on flow patterns of methane/ethane/propane/isobutane mixed fluid in spiral tubes were analyzed. The results showed that with the increase in vapor quality, flow patterns such as bubbly flow, intermittent flow, wavy-stratified flow, and annular flow were observed in sequence. Additionally, through a comparative analysis of the experimental observations with existing flow pattern maps, a new flow pattern map tailored for the condensation two-phase flow of mixed hydrocarbon working fluids has been established. Based on the influence of inertial force, surface tension, gravity, shear force and other forces, Martinelli number, Soliman We and Soliman Fr are selected for the development of flow pattern conversion criteria. The new flow pattern map accurately predicts the majority of flow patterns.

Flow Boiling Heat Transfer Characteristics and Delayed Dry-Out Ability of Non-Azeotropic Mixtures R245fa/R134a in Microchannels

Flow Boiling Heat Transfer Characteristics and Delayed Dry-Out Ability of Non-Azeotropic Mixtures R245fa/R134a in Microchannels

Investigation of Heat Transfer Performance in Deionized Water–Ethylene Glycol Binary Mixtures during Nucleate Pool Boiling

Pool boiling heat transfer is recognized as an exceptionally effective method, widely applied across various industries. The adoption of non-azeotropic binary mixtures aligns with the environmental objectives of modern industrial development and enhances the coefficient of performance (COP) in numerous systems. Therefore, investigating the boiling heat transfer characteristics of these mixtures is crucial to improving their industrial usability. In this study, mixtures of ethylene glycol and deionized water (EG/DW) in varying concentrations were chosen as the working fluids. A comprehensive experimental setup was developed, followed by a series of experiments to assess their pool boiling performance. Simultaneously, the thermophysical parameters of these mixtures underwent detailed examination and analysis. The research revealed that the concentration of EG in the mixture markedly affects its thermal properties and temperature glide, both of which are crucial in influencing the heat transfer coefficient. Additionally, six established heat transfer coefficient prediction correlations, primarily designed for pure fluids, have been employed. However, their application to non-azeotropic mixtures under experimental conditions revealed significant deviations. To address this issue, the present study modified existing correlations with the temperature slip characteristics of non-azeotropic mixtures. This process involved recalibrating the wall superheat values in the correlations to reflect the local temperature differential at the boiling point, thereby customizing them for application to non-azeotropic mixtures. The modified correlations highlighted the unique behaviors of non-azeotropic mixtures in boiling heat transfer, demonstrating improved compatibility with these mixtures in a deviation within a permissible 20% range compared with experimental results.

Effect of lubricating oil on non-azeotropic refrigerant in flow boiling: an entropy generation analysis

ABSTRACT Entropy generation analysis is a useful method for studying the relationship between heat transfer and pressure drop in flow boiling. The flow boiling process in an actual refrigeration system is inevitably affected by oil. Therefore, the effect of oil on entropy generation needs to be investigated. A new non-azeotropic ternary refrigerant mixture, R447A, was selected as working fluid. Subsequently, flow boiling entropy generation models of R447A with and without oil were established. The effects of individual parameters on entropy generation were investigated. The entropy generation per unit tube length under different conditions was proposed as the benchmark for comparison. The results show that there is an optimal mass flux corresponding to minimum entropy generation per unit tube length at a specific oil concentration, and optimal mass flux decreases with increasing oil concentration. The tube diameter also affects the optimal mass flux of the fluid with oil, which increases with decreasing tube diameter and is smaller than that without oil for the same diameter tube. When the oil concentration is 0–4.95%, the total entropy generation exhibits a decreasing trend. Therefore, within the scope of this research, the addition of oil is beneficial for reducing the entropy generation of heat exchangers.

Heat transfer in a channel with internal intensifiers during azeotropic mixture circulation

Today, the use of mixtures as refrigerants and coolants in various energy systems is widespread. The volatility coefficients for the components of a non-azeotropic binary mixture vary significantly. In an azeotropic binary mixture, the volatility coefficients for both components are the same. This paper presents the experimental results on the intensity of heat transfer to an azeotropic alcohol-water mixture during forced circulation in a round heated channel. Experiments are carried out both in a smooth channel and in a channel with a spiral intensifier. The inner diameter of the channel is D = 7.6 mm, the length is 2 m. The intensifier surface has a hydrophobic coating. The experiments are carried out at low (0.03 – 0.04 MPa) pressure in the system, in the range of mass velocities 36 < M < 376 kg/m2s and Reynolds numbers of 360 – 3700. The heat flux density in these experiments is 8000 W/m2. In the single-phase flow of an azeotropic alcohol-water mixture in the channel with a spiral intensifier, the heat transfer coefficient is up to 5–6 times higher than that in a smooth channel. In this case, the higher the mass flow velocity, the greater the excess of the heat transfer coefficient. In the two-phase flow of the mixture in the channel with a spiral intensifier, the heat transfer coefficient is up to 2–3 times higher than that in a smooth channel.

Forced boiling of nonazeotropic immiscible mixture in a supercapillary microchannel array for ultra-high heat flux removal with chip junction temperature below 85°C

Forced boiling of nonazeotropic immiscible mixture in a supercapillary microchannel array for ultra-high heat flux removal with chip junction temperature below 85°C

Multi-criteria refrigerant screening and performance optimization comparison of a basic and composition-adjustable dual cooling source system

Climate variability and staff mobility have exacerbated the vulnerability of the indoor environment, which calls for air-conditioning units capable of adapting to the active regulation demand of the changing heat and humidity loads. The identification of the refrigerant constitutes an essential sector of the air-conditioning system design. A composition-adjustable dual cooling source (CADCS) chiller has been proposed utilizing the characteristics of inefficient condensation of the non-azeotropic mixture. Separated flows of the working fluid with flexible mass fraction and flow rate respectively treat the waste heat and moisture. Multi-criteria screening mechanism for the working fluid is established involving: i) application field. The critical temperature is better restricted within 300 K to 400 K for application in air-conditioning. ii) environmental impact. The GWP of the candidate cannot exceed 800. iii) cycle architecture adaptability. The boiling point difference preferably exceeds 20 K. iv) liquid separation potential. The obvious temperature glide and substantial separation range allow for the integration of liquid separation technology. Thermodynamic performance optimization indicates that propane/isobutane outperforms all the candidates at a mass fraction of 0.5:0.5 characterized by obvious temperature glide and close to temperature change of the heat transfer medium. The maximum coefficient of performance (COP) is found to be up to 5.2 for the BDCS cycle and 4.42 during separation at vapor quality 0.436 for the CADCS cycle. The exergy loss of the evaporator is reduced by 17.1 %-73.7 % while the exergy efficiency is improved by 3 %-59.7 % due to temperature match refinement in the CADCS cycle. The refrigerant charge in the CADCS cycle can be saved by 5.54 %-15 %. The accumulating waste heat demands a lower vapor quality during separation, while the moisture load barely exerts an effect. Moreover, the effect of the subcooling degree on the cycle performance is analyzed and suggested at 1 °C. The CADCS cycle constitutes a promising prospect of dynamic treatment for thermal and humidity load in the air-conditioning room due to its flexible function and improved heat transfer match.

Heat Transfer in Circular Channel with Spiral Intensifiers during Circulation of Non-Azeotropic Alcohol-Water Mixture

Heat Transfer in Circular Channel with Spiral Intensifiers during Circulation of Non-Azeotropic Alcohol-Water Mixture

Experimental study of R448A flow boiling in a 24-port microchannel tube

R448A is a mixture to replace R404A in the thermodynamic cycle applications. R448A has a temperature glide of about 5°C and might exhibit thermal non-equilibrium in the microchannel tube. This study investigated the flow boiling heat transfer and pressure drop of R448A, a five-component non-azeotropic mixture, in a microchannel tube. Six heat transfer coefficients (HTC) and pressure gradients (dP/dz) of R448A were measured in one pass in a 24-port microchannel tube. The experimental conditions covered mass fluxes from 100 to 200 kg-m−2s−1, heat fluxes from 2 to 8 kW- m−2, and saturation temperatures from 10 to 30 °C. The study compared the experimental results of R448A with four of its component fluids (R134a, R1234yf, R1234ze(E), and R32). R448A had higher HTC and lower dP/dz than its component fluids, except for R32 which had higher HTC and dP/dz than R448A. Muller-Steinhagen and Heck was the best correlation for predicting the dP/dz of R448A, with a mean absolute error (MAE) of 8.78 % and a mean error (ME) of 7.47 %. A new correlation for predicting the HTC of R448A, based on modifying Liu and Winterton (Müller-Steinhagen and Heck, 1986), was proposed with an MAE of 6.01 % and an ME of 0.588 %.

Enhanced heat-integrated distillation processes: Simultaneous synthesis via structural modification utilizing the matrix method

The research on simultaneously synthesizing heat-integrated distillation (HID) processes has primarily focused on non-azeotropic mixtures, utilizing the Winn-Underwood-Gilliland shortcut method. However, there is still a lack of rigorous simultaneous synthesis methods and automated searches for HID processes, especially when dealing with azeotropic mixtures. To address this issue, this work proposes a novel design optimization approach method for HID processes. The proposed method simplifies the representation of a superstructure of HID processes by treating the condensers and reboilers as columns and rows in a matrix, respectively and the complexity of representing the superstructure is significantly reduced. By dynamically adjusting the heat integration structure, automated search of HID processes has been achieved. The method combines thermodynamic analysis to predict the liquefaction probability of the overhead vapor compression process and the temperature range of condenser and reboiler. These predictions facilitate the screening of effective candidate schemes and reduce the complexity of decision variables, leading to improved speed and robustness in the automated optimization process. The effectiveness of the proposed method is demonstrated through its application to two case studies, showcasing its capability in identifying economically attractive HID schemes.

Experimental study on heat transfer and flow pattern transition for R1233zd/FC72 mixtures across tube bundles

An experimental investigation was conducted to study the heat transfer and two-phase flow patterns of pure R1233zd and non-azeotropic R1233zd/FC72 mixtures (0.75/0.25, 0.5/0.5, and 0.25/0.75 by mass) across tube bundles. The test section of tube bundles was transparent to observe the flow pattern. The flow boiling heat transfer was measured. The experiments were carried out with vapor qualities of 0.1–0.9, mass flow rates of 3–5 kg/h and heat fluxes of 3000–7000 W/m2. Falling film flow, bubbly flow, bubbly-shear flow, and shear flow were observed. The flow pattern transition maps were presented for various conditions. Increasing the mass fraction of the volatile component R1233zd causes the flow pattern transitions occurring at lower vapor qualities. The heat transfer coefficient of mixtures is lower than that of pure R1233zd. With increasing vapor quality, the heat transfer coefficient increases for both pure R1233zd and the mixture with a R1233zd mass fraction of 75 %. However, for mixtures with R1233zd mass fractions of 50 % and 25 %, the heat transfer coefficient initially increases and then decreases with increasing vapor quality. For vapor qualities higher than 0.5, increasing the volatile component, R1233zd, significantly enhances heat transfer. The heat transfer coefficient increases with increasing mass flow rate and heat flux. The experimental data were compared with correlations in the literature with poor agreement. An improved heat transfer correlation for non-azeotropic mixtures flowing across tube bundles was proposed, which effectively predicted the experimental data.

Research on the thermodynamic properties of binary mixtures containing R1234ze(E) based on Helmholtz model

R1234ze(E) has excellent environmental protection properties, but the unsatisfactory latent heat of vaporization and volumetric cooling capacity impede its application. A mixture with excellent thermophysical properties and environmental performance can be obtained through blending R1234ze(E) with other working fluids. In this paper, the vapor-liquid equilibrium data of R1234ze(E)/R32, R1234ze(E)/R152a, R1234ze(E)/R290, and R1234ze(E)/R161 were correlated by Helmholtz equation of state combined with the mixing rule, and the calculation model of thermodynamic properties was established. On this basis, temperature glides, latent heats of vaporization, saturated vapor pressures, and other thermodynamic properties of binary mixtures containing R1234ze(E) were calculated and compared. The results indicate that the standard boiling points and critical temperatures of the four binary mixtures containing R1234ze(E) were similar to those of R22 in most mass concentration ranges. And their saturated vapor pressures at 298.15 K were all lower than that of R22 except for R1234ze(E)/R32 mixed in a few proportions. The latent heat of vaporization and specific heat capacity at a constant pressure of the four mixtures were larger than those of R1234ze(E) and adding the four pure refrigerants with excellent thermodynamic properties into R1234ze(E) helps to improve the latent heat of vaporization and specific heat capacity of the binary mixtures. Among the four mixtures, R1234ze(E)/R290 is an azeotropic mixture and R1234ze(E)/R152a is a non-azeotropic mixture. Finally, the recommended mixing ratios of R1234ze(E)/R32, R1234ze(E)/R152a, R1234ze(E)/R290, and R1234ze(E)/R161 to replace R22 were in the range of 0.56/0.44∼0.76/0.24, 0.58/0.42∼0.71/0.29, 0.27/0.73∼0.85/0.15, and 0.58/0.42∼0.84/0.16.

"THE POTENTIAL OF GEOTHERMAL SOURCES IN SOUTHERN KAZAKHSTAN FOR HEAT SUPPLY TO RURAL CONSUMERS, the case OF THE ZHAMBYL REGION"

"The article presents the characteristics of geothermal deposits in the south of Kazakhstan and the analysis of the potential of geothermal waters of the Zhambyl region. Moreover, the study carries out the review of various types and methods of using geothermal water for household and its needs. Consequently, it outlines information on thermal boreholes. During the elaboration, manufacture and testing of these combined power units, several scientific and technical issues, such as the choice of the optimal low-boiling working fluid for heat and hot water supply systems were solved. An overview of the refrigerants and vapor compression fluids currently available have been made. The classification and characteristics of secondary heat carriers of various types and temperatures of their use are given. Therefore, it is proposed to use non-azeotropic binary mixtures as working bodies of a closed heat-power circuit. Moreover, an analysis was carried out on the use of non-azeotropic mixtures for heat pumps. It is proposed to use mixtures of refrigerants as working bodies for the second circuit. The specific characteristics of refrigerants are outlined. As a result, a description of the operation scheme of a steam compression heat pump operating in the mode of heat and hot water supply is highlighted. "

Effect of flow direction on evaporation flow regime of R32/R1234ze(E) mixture inside multiple rectangular minichannels

This study visualized the evaporation flow regime of a non-azeotropic mixture R32/R1234ze(E) inside multiple vertical-upward and horizontal rectangular minichannels with a hydraulic diameter of 2 mm. The effects of the mass flux, vapor quality, heat flux, flow direction, and test refrigerant on the flow regime characteristics were explored. The flow regimes of the mixture were compared to those of R1234ze(E). The effect of flow direction on the flow regime was examined under low mass flux conditions. In the vertical-upward flow, three flow regimes: slug, slug-annular, and annular flow regimes were observed. The flow regime transition boundary of R1234ze(E) shifted to lower mass flux and vapor quality conditions compared to the mixture because of the higher vapor velocity of R1234ze(E). Boiling bubbles were generated in the liquid slug and channel corners around the vapor plug, and the number of boiling bubbles increased with an increasing heat flux. The size of the boiling bubble of the mixture was smaller than that of R1234ze(E), which is attributed to the mass transfer resistance of the non-azeotropic mixture. Only in the vertical-upward flow, the reverse flow was observed in some channels, where the slug flow was observed, because of the effect of gravity. The number of channels with reverse flow decreased with increasing vapor velocity. The annular flow did not appear in the horizontal flow, and the flow regime was observed only in two regimes: slug and slug-annular flow regimes. No difference in flow regime transition boundary between R1234ze(E) and R32/R1234ze(E) was observed.

Modeling analysis of non-azeotropic and immiscible binary mixed vapors condensation under natural convection

A calculation model describing the condensation heat and mass transfer process of non-azeotropic immiscible binary mixed vapors on the vertical wall under natural convection conditions was developed in this study. The model includes the two possible condensation modes of mixed vapors on the vertical wall as well as the conversion conditions between them. Cyclohexane and water were used as non-azeotropic immiscible mixtures. The reliability of the model was verified first, then the influence of vapor mass concentration and wall subcooling on the condensation mode and heat and mass transfer of the mixed vapors were analyzed. The results showed that the maximum deviation between the model results and the experimental results was less than 21%, confirming that the model was reliable. When the mixed vapors mass concentration was nearly eutectic or the wall subcooling was large, the condensation Mode B (Co-condensation) was more likely to occur than Mode A (Single condensation) due to the decrease in vapor-liquid interface temperature. The condensation mode may change from B to A as the wall length increased along the gravity direction of the condensation wall, and the condensation heat transfer coefficient and mass flux decreased. The thermal resistance of the vapor and liquid phases during condensation was also calculated. In Mode A, regulation of the thermal resistance of the vapor-liquid two phases can be achieved by adjusting the vertical length of the condensation wall and the vapor mass concentration. Condensation Mode B can only be realized by adjusting the wall subcooling. The results of this work may provide a workable reference for condensation heat transfer and enhancement of non-azeotropic immiscible mixed vapors in industrial environments.

On the pressure drop calculation during the flow of two-phase non-azeotropic mixtures

• The effect of changes in the properties of the liquid and vapor phase during the flow of zeotropic mixture on the pressure drop. • The use of the equations of state of the liquid and vapor phases of a zeotropic mixture in the calculation of flow acceleration. • The approach has been developed for calculating the pressure gradient distribution and phase composition during the flow of a vapor-liquid zeotropic mixture. This article discusses the distinctive features of non-azeotropic vapor-liquid flows. It is shown that for the correct calculation of the pressure drop, the change in the thermophysical properties of the liquid and vapor phase along the flow must be taken into consideration. A calculation method that allows one to take the effect of a change in the composition of phases on the pressure drop and reasonably select a friction model for a two-phase flow has been proposed. In this method, the change in flow acceleration is calculated using the equations of state of the mixture for the liquid and vapor phases under phase equilibrium conditions. The method was verified. The calculation results are compared with experimental data from open sources for a non-azeotropic mixture of methane-ethane.

Boiling heat transfer of binary and ternary mixtures in multiple rectangular microchannels

In this study, the boiling heat transfer of binary and ternary refrigerant mixtures in a horizontal multiport tube with multiple rectangular microchannels was investigated. The influences of the mass velocity, vapor quality, and heat flux on the heat transfer were evaluated for near- and non-azeotropic mixtures of R410A, R32/CF3I, R32/R1123, R32/R1234yf, R1123/R32/R1234yf, and CO2/R32/R1234yf. The obtained results were compared with those of pure refrigerants R1234yf and R32. For R1234yf at low mass velocity, the flow patterns were estimated as intermittent (plug) and slug-annular flows with an extremely thin liquid film. The heat transfer coefficient decreased when the heat flux was increased because dry patch areas formed and expanded on the sides of the noncircular microchannel. The near-azeotropic mixtures with small temperature glides exhibited heat transfer characteristics similar to those of the pure refrigerant. Conversely, the heat transfer coefficients deteriorated slightly under lower mass velocities. The heat transfer coefficients of binary and ternary mixtures with larger temperature glides were significantly different from those of pure refrigerants and near-azeotropic mixtures; they decreased with decreasing mass velocity owing to mass diffusion resistance. The heat transfer coefficients of binary mixtures with large temperature glides decreased monotonically as the mass velocity decreased, and the heat transfer noticeably deteriorated at lower mass velocities. The heat transfer model was developed for rectangular microchannels by considering the heat transfer contributions of thin liquid film evaporation due to surface force, forced convection, and nucleate boiling. Moreover, this model considers the flow pattern of multiple microchannels, heat transfer degradations due to dry patches and mass diffusion resistance, and dryout incipience quality. The results of the present model agree well with the heat transfer coefficients, including those of binary and ternary mixtures, in the pre- and post-dryout regions with a mean percentage error of 3.1%.

Experimental study on spray cooling heat transfer performance of R245fa/R142b mixture in boiling regime

In this paper, the combination of spray cooling technology and non-azeotropic mixture was proposed to achieve the precise temperature control of heated surface. Experiments were performed with R245fa/R142b as the working fluid to study the spray cooling heat transfer of non-azeotropic mixture in boiling region. With the phase Doppler anemometer (PDA), the spray characteristics of working fluid at different height and mixing ratio were studied. The results showed that the non-azeotropic mixture existed a mixing ratio, at which the smallest droplet Sauter mean diameter (SMD) and the largest droplet density were obtained. This is beneficial to spray cooling heat transfer, and the mixing ratio is defined as the optimal mixing ratio. Heat transfer experiments proved that the surface uniformity of spray cooling is the best under the mixing ratio corresponding to the optimal spray characteristics. Further studies found that, at low heat flow in the two-phase region, the spray heat transfer performance of the non-azeotropic mixture was significantly weakened compared with that of any single component. With the increase of heat flux, the heat transfer performance of the non-azeotropic mixture gradually exceeds that of the single component R142b, which is related to the effect of additional mass transfer resistance in different stages.

Condensation heat transfer of binary and ternary mixtures inside multiport tubes

This study investigated the condensation heat transfer of pure refrigerants and binary and ternary mixtures inside horizontal multiport tubes with multiple square minichannels. The effects of mass flux, vapor quality, heat flux, channel size, and channel shape were evaluated using pure refrigerants R32 and R1234yf; binary mixtures R32/R1234yf, R32/R1123, R32/R13I1, and R410A; and ternary mixtures R1123/R32/R1234yf and CO2/R32/R1234yf. For pure refrigerants, the heat transfer coefficient in the annular and churn flow regimes decreased monotonically with decreasing vapor quality. By contrast, the heat transfer coefficient in the plug flow regime was higher over a wide vapor quality range because of the thin condensate film formed by surface tension. Smaller channels exhibited higher heat transfer coefficients. The square minichannels exhibited higher heat transfer coefficients than the circular minichannels, except in the region with high mass flux and high vapor quality. For binary and ternary mixtures, the heat transfer coefficients significantly decreased with decreasing mass flux and vapor quality and were strongly deteriorated at lower mass fluxes. Compared with the annular and churn flow regimes, in the plug and slug-annular flow regimes, where heat transfer through the thin liquid film was dominant, the effect of mass diffusion resistance in deteriorating heat transfer was the most pronounced. A new heat transfer model for pure refrigerants inside multiport tubes with multiple rectangular minichannels was developed considering the contributions of vapor shear stress and surface tension. The proposed model was verified using a dataset of pure refrigerants, and a mean absolute percentage error (MAPE) of 11.5% was achieved. Furthermore, a new heat transfer model that considers the heat transfer deterioration of non-azeotropic refrigerant mixtures was proposed, which could predict 508 datapoints with an MAPE of 13.3%.

STUDY OF A SOLAR ENERGY KALINA CYCLE APPLIED IN BOM JESUS DA LAPA - BAHIA

Modern population’s needs increased demands for electricity in such a way that new energy sources were explored, in search of lower environment impacts and fossil fuels dependency. Renewable energy sources for electricity production, such as solar and wind energy, have significantly attracted attention and places as the west region of Bahia state has a good potential for its application. This location is characterized by high solar irradiance of 2136 kWh/m² a year, already having 4 photovoltaic power plants in operation and 2 more in project phases. Another possible application is the solar thermal energy and Kalina Cycle presents as a good possibility for employing it, since the non-azeotropic mixture of ammonia-water as working fluid allows low temperature heat sources utilization. Based on that, this research proposed the study of a Kalina power cycle, with steady state conditions, using thermal solar energy as low temperature heat source and applied to the solar irradiance of Bom Jesus da Lapa – BA. The thermodynamic cycle was developed and simulated with Engineering Equation Solver (EES®), thermal efficiency was analyzed by varying parameters such as: heat source temperature from 90 °C to 120 °C, high pressure line from 10 to 35 bar and ammonia mass fraction from 0.35 to 0.95. The final cycle presented a superheater before the turbine and a regenerator with poor ammonia-water mixture from the separator (as hot side) and ammonia-water mixture before entering the boiler (as cold side). Results indicated maximum efficiency of ~7.4%, with high pressure side of 35 bar, heat source temperature of 120 °C, superheater heat source temperature of 200 °C and ammonia mass fraction of 0.64 kg/kg.