Vapor Mass Flow Rate Research Articles

A novel characterization methodology for vapor-injected compressors: A comparative analysis with existing black-box models

In regions characterized by high temperature gradients, vapor compression systems often necessitate operation at very high pressure ratios resulting in a reduction in system capacity. Economized vapor injection compressors are used to avoid these issues, yet a precise predictive map for various compressor technologies with minimal data and relatively better performance remains unclear. This paper establishes a black-box compressor model to accurately predict compressor power, injection mass ratio, and evaporator mass flow rate in compressors with a single vapor injection port. This model is compared against three legacy models from literature and the ANN model, for reference. All five models are evaluated based on their ability to predict the aforementioned metrics. The proposed black-box model can predict the relevant metrics all within 5 % Mean Absolute Percentage Error (MAPE). Additionally, a refrigerant sensitivity analysis is performed with the black-box models. The model is trained using data from R410A and then used the coefficients to predict the performance of the same compressor when using R454B, and vice versa. It can estimate the evaporator mass flow rate with an accuracy within 3 %, the power within 2 %, and the injection mass ratio with MAPE less than 3 %.

A method to calculate the two-phase distribution in a microchannel heat exchanger

Maldistribution seriously impacts the heat transfer performance of the microchannel heat exchanger (MCHX). Fully understanding the two-phase distribution in the heat exchanger is important for advancing academic research and engineering applications. This study introduces a novel method for quantifying two-phase distribution in a microchannel heat exchanger. An experimental setup was developed to measure the local vapor mass fraction in the heat exchanger header. Capacitance signals were measured under inlet vapor mass fractions from 0 to 1, and inlet flow rates of 10, 15, and 25 g s−1 corresponding to a mass flux of 17.47, 26.2, and 43.66 kg m−2s−1, respectively. The local vapor mass fraction in the header was estimated using the capacitance measurements. The mass flow rate in the header, the microchannel tube, and the vapor mass fraction in the tube were calculated using the proposed model. The calculation model was validated against literature data, and the results were analyzed. The analysis reveals the characteristics of vapor mass fraction and mass flow rate distribution in the MCHX and further elaborates on the effects of phase separation, entrainment ratio, and pressure drop balance on the distribution. The proposed method can evaluate distribution in the header and tubes of microchannel heat exchangers, and it is also applicable to other types of two-phase flow devices.

Operational characteristics and performance optimizations of the organic Rankine cycle under different heat source/condensing environment conditions

The fluctuating heat sources and seasonal condensing environments are critical to the operation of Organic Rankine Cycle (ORC) under off-design conditions. This paper presents a comprehensive steady-state mathematical model developed using a newly built experimental platform. Focusing on the operational characteristics, including the evaporation pressure, condensation temperature, mass flow rate, and the performance of key equipment during the regulation of the expander, working fluid pump, and cooling water pump. Results show that the net efficiency initially increases before decreases, with both evaporation pressure and mass flow rate rising alongside the working fluid pump frequency. The quasi-two-stage single screw expander achieves an isentropic efficiency above 65 %. Additionally, flexible adjustments to the cooling water pump effectively regulate the cooling system, with timely cleaning of cooling pipelines enhancing net efficiency by up to 3.27 %. Optimization using the particle swarm algorithm improves system performance, achieving net efficiency enhancements of 1.8 % and 12.3 % under specific conditions. The novelty of this study lies in directly regulation of the expander, working fluid pump, and cooling water pump, significantly enhancing the off-design performance. This research provides valuable insights for researchers and designers, enabling flexible regulation of ORC operations to ensure efficient performance under varying conditions.

APPLICATION OF AN EXACT SOLUTION OF SPECIAL TYPE OF THERMOSOLUTAL CONVECTION EQUATIONS FOR THE INVESTIGATION OF EVAPORATIVE THREE-DIMENSIONAL FLOWS

The characteristics of gas-liquid flows with evaporation at the thermocapillary interface in an infinite rectangular duct, with a linearly distributed thermal load being applied on the upper and lower walls, are studied. The theoretical research of the three-dimensional convective flows is carried out within the framework of a two-sided model of evaporative convection based on the Navier-Stokes equations in the Oberbeck-Boussinesq approximation. A solution of a special type of governing stationary equations is used for describing the heat and mass transfer in a system of two immiscible fluids. We investigate the influence of the working (equilibrium) temperature of the system and intensity of the external thermal load on the structure of the velocity and temperature fields, as well as on changes in the evaporation mass flow rate and vapor content in the gas phase. The simulations are performed for the ethanol-air system. Based on the comparison of the calculated and experimental data, an effective way of nondimensionalization is proposed that allows one to consistently take into account the impact of the gas pumping velocity being a controlled parameter in experiments. It provides correct matching of the mathematical model to the experiment conditions, as well as a better qualitative and quantitative agreement between theoretical and measured values of evaporative mass flow rate. The results of the present study can aid in developing a theoretical basis for experimental research methods of evaporative convection and also in designing equipment for thermal coating or drying.

Hybrid Heat Pipe Shutdown Rod as a Novel Concept of Passive Safety System for Microreactor

Ensuring the structural integrity of the monolithic core, which houses critical components such as heat pipes and fuel rods, is crucial for the safety of a microreactor. This research introduces a hybrid heat pipe shutdown rod as a novel passive safety system to address potential temperature rises in the monolithic core during accidents. It is designed to perform a dual function under accident conditions. It simultaneously absorbs neutrons and removes heat through structural modifications to the existing shutdown rod. Specifically, this system provides a heat transfer path within the monolithic core without increasing the size of the microreactor. By selecting cesium as the working fluid, we aimed to achieve rapid operation of the heat pipe to quickly reduce the temperature gradient in the monolithic core under accident conditions. The hybrid heat pipe was fabricated and evaluated and found to develop continuous flow even at temperatures around 205.1°C. However, its unique structure causes a pronounced converging–diverging effect, resulting in a temperature drop from about 70–170°C in the evaporator region, followed by a slight recovery to below 50°C in the condenser. This effect arises from changes in the cesium vapor mass flow rate due to phase changes and variations in the flow area between the evaporator and condenser. Despite these effects, the use of liquid cesium as the working fluid enables the hybrid heat pipe to operate under natural convection, avoiding startup problems that could cause flow blockage.

On the coupling between direct numerical simulation of nucleate boiling and a micro-region model at the contact line

During the past years, numerical simulations of Nucleate Boiling have attracted increasing attention. If significant advances have already been performed on the conception of accurate numerical schemes accounting for jump conditions at a non-isothermal interface, further studies are required on the modeling of the heat flux in the vicinity of the contact line. Especially, at very low scale (<500 nm) the formation of a micro-region can be assumed, since the observed apparent contact angle can be higher than the microscopic contact angle and depend on the wall superheat. This variation of the apparent contact angle can be related to a temperature discontinuity between the saturation temperature and the local wall temperature at the contact line inducing a micro-region heat flux and an evaporation mass flow rate. Whereas this micro-region acts at very low scale, existing theoretical models suggest a strong influence of the micro-region heat flux on the global heat flux, and so on the overall bubble growth phenomenon. However, the numerical description of this micro-region in the framework of Direct Numerical Simulation (DNS) of nucleate boiling is a major issue due to the large range of spatial scales involved in the whole process. In the present paper, we propose a coupling methodology between an existing micro-region theoretical model and a larger scale DNS solver for Nucleate Boiling in axisymmetric configurations. Several benchmarks are proposed to show the consistency and the accuracy of the proposed method and to highlight the quantitative effect of the micro-region at the bubble scale.

Modeling of stratified two‐phase flows with non‐uniform evaporation based on the exact solution of convection equations

Within the framework of the Oberbeck–Boussinesq approximation, the exact solution of equations of thermoconcentration convection is studied, which has the group origin. The issue of applicability of the exact solution for describing steady‐state convective flows of a liquid and a co‐current gas flux under the conditions of inhomogeneous evaporation of the diffusive type in a flat horizontal channel is discussed. Algorithms for obtaining analytical representations of the required functions for various types of the boundary conditions for the temperature function on the outer channel wall are proposed. The influence of the external thermal load and boundary thermal conditions on the structure of the velocity and temperature fields, evaporation mass flow rate, and vapor content in the gas layer is investigated at an example of the HFE‐7100–nitrogen system. The solution correctly predicts hydrodynamical, temperature, and concentration parameters of convective regimes appearing in the two‐phase system. The main characteristics are compared with the characteristics of the system in the case of uniform evaporation with a constant intensity.

An experimental investigation on the influence of condenser bypass area for the transient and steady-state heat-transfer performance of heat pipes

Fundamentally, an effective method for improving the performance of transient and steady-state heat transfer is reducing the flow resistance at the phase-change interface based on the counter flow of vapor and liquid within a typical heat pipe. The flow resistance at such an interface is proportional to the volume flow rates of liquid and vapor. Therefore, the flow resistance at the interface can be reduced by limiting the mass flow rate of vapor or liquid. In this study, experiments were performed on a liquid bypass to improve the steady-state thermal performance of heat pipes. A separate bypass tube allowed some liquid to be subcooled in the condenser to bypass the evaporator without passing through the heat pipe. Three liquid-bypass ports were designed and fabricated in a condenser to experimentally investigate the influence of the bypass port area on the thermal performance of the heat pipe under steady-state operation. An on/off valve was attached to each bypass tube port in the condenser to control the bypass flow rate. The results showed that the thermal resistance, an evaluation index of the performance of steady-state heat transfer, generally decreased with an increase in the bypass port area of the condenser. The thermal resistance of a heat pipe with a horizontal tilt angle and one at an inclination angle of 50° decreased by up to 25.5% and 51.6%, respectively.

Pressure drop characterization on cryogenic multiphase flow in spiral wounded heat exchanger under high mass flow conditions

In order to clarify the influence of dryness, working medium and mass flow rate on pressure drop characteristics in shell side of spiral wound heat exchanger, a simplified test section has been analyzed in this study. The model is with a coiled section under compact design: 1 mm layer spacing of and 2 mm tube spacing in the main structure. The mixed alkane composed of methane, ethane, propane and others are used as working fluid. The current study is focused on the pressure drop behaviors and the effects of multiphase flow in different stages of cooling process in the cryogenic heat exchanger. Systematic numerical model has been established in this study to investigate the pressure behaviors, which are also verified against newly constructed experimental system. Operating conditions range from vapor quality of 0.1–0.9, mass flux of 60–120 kg·(m2·s)−1, under the operation pressure of 0.25 MPa and temperature from −27 °C to −170.6 °C. The absolute error of pressure measurement is less than 1.5 kPa and the absolute error of pressure drop measurement is less than 25 Pa, and the relative error is 0.25 % for the current test. The experimental results show that the friction pressure drop increases with the increase of vapor quality from 0.1 to 0.9 and mass flux from 60 to 120 kg·(m2·s)−1, and the growth gradient of friction pressure drop decreases with the increase of vapor quality. A set of pressure drop correlation has been established to reflect the influence of factors such as vapor quality and mass flow rate, and the deviation between predicted pressure drop and experimental data was within ±20 %.

Development of a cooling and power generation prototype integrating an axial micro-turbine in an absorption chiller

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously within the same cycle. This technology holds great potential to harness low-temperature heat sources more efficiently than production with separate cycles. However, very few experimental studies on absorption combined cooling and power production cycles can be found in literature. In order to achieve an in-depth understanding of this technology and of the interactions between power and cooling production sides of the circuit, the integration of an expander into a single stage ammonia water absorption chiller was undertaken through the development of an experimental pilot plant. The peculiar characteristics of the expansion device, as well as the use of a newly developed combined desorber avoiding the presence of a rectifier make the prototype built unique. Design and integration of the expander proved to be very challenging, mainly due to the small size of the application and corrosiveness of the ammonia water mixture. Significant electricity generation losses experienced lead to maximum electrical efficiency of 7% and corresponding maximum power production around 33 W at a lower than expected rotational speed of 20′000 rpm.Despite these difficulties, first experimental measurements have been obtained, giving interesting insights on the functioning of the cycle. Indeed, the impracticability of regulating the ratio between cooling and power production was highlighted, due to the characteristics of the impulse turbine. Opening of the turbine line in the nominal point leads to a reduction of the mass flow rate passing through the cooling line of 65% (i.e., split ratio of 0.35) and a cooling power output decrease of around 57% (from 4.9 to 2.1 kW). Additionally, diverting some of the desorbed vapour to the power production line has important effects on the pressure equilibrium and circulating vapour mass flow rate, increasing from 16.1 kg/h in the simple absorption working mode to 31.1 kg/h in the combined mode in the nominal operating point. Feedback from the pilot plant will be very useful for the further development of the technology.

Experimental research on the separation performance of a compound T-junction for two-phase zeotropic mixtures

In this paper, the mixture composition separation performance of a compound T-junction for vapor–liquid two-phase zeotropic mixtures R134a/R245fa was experimentally investigated. The effect of inlet vapor quality and mass flow rate on the separation performance were investigated. The composition separation performance of compound T-junction and simple T-junction were compared. The separation models for simple T-junction and compound T-junction were also discussed. During the experiments, the composition ratio of the zeotropic mixture was 0.429/0.571 (R134a/R245fa). In order to represent the degree of actual separation to the ideal separation, the composition separation efficiency was defined as the ratio of the actual degree of composition separation to the ideal degree of composition separation. The inlet vapor quality varied from 0.09 to 0.19, and the composition separation efficiency increased from 38.34% to 86.86%. When the mass flow rate increased from 10 g/s to 13 g/s, the composition separation efficiency could be increased by up to 40%. Compared with simple T-Junction, composition separation efficiency of compound T-Junction was improved by about 10%. Furthermore, the separation model of the compound T-junction was developed based on the experimental results. And the coefficient of determination is 0.9662.

Crystallization-free and low-cost deep eutectic solvents for absorption thermal battery utilizing ultra-low-grade energy

Absorption thermal batteries (ATBs) play a significant role in balancing the mismatch between ultra-low-grade renewable/waste energy supply and building energy demand. Working fluids are critical to the high performance and reliability of ATBs, but conventional salt-based mixtures suffer from crystallization risks, while the popular ionic liquid-based mixtures are quite expensive. Therefore, crystallization-free and low-cost deep eutectic solvents (DESs) are proposed to achieve reliable and affordable ATBs. The property estimation based on the NRTL model and the cycle model based on mass and energy conservation are established and verified with high accuracies, which are used to investigate the energy storage performance of five H2O/DESs and four NH3/DESs. A comprehensive comparison between the emerging DES-based and traditional working fluids from multifaceted viewpoints (efficiency, compactness, exergy, response rate, applicability, heat transfer, reliability, and economics) is conducted. For a basic ATB with inferior operating conditions (generation temperature < 72 °C, evaporation temperature < 1 °C, or absorption temperature > 40 °C), NH3/Glyceline yields the highest energy storage efficiency (ESE) and exergy efficiency (EXE), outperforming the traditional refrigerant/salts. A compression-assisted ATB is further adopted, enabling NH3/DESs to utilize ultra-low-grade heat as low as 40 °C. NH3/Glyceline yields the highest ESE of 0.752 and EXE of 0.599 at a generation temperature of 50 °C. It also exhibits a rapid response rate with the highest maximum vapor mass flow rate of 5.4 g/s and the shortest discharging time (73.22 min). NH3/Glyceline exhibits the widest applicability, with an applicable operating range ratio of 87.72%, much higher than that of H2O/LiBr (23.72%). The compression-assisted ATB using NH3/Glyceline is the most promising for large-scale applications owing to the lowest levelized cooling capacity cost of 0.239 $/kWh, which is 41.89% lower than that of H2O/LiBr and 96.58% lower than that of H2O/[EMIM][OAc].

Integration of geothermal-driven organic Rankine cycle with a proton exchange membrane electrolyzer for the production of green hydrogen and electricity.

Engineers and scientists are increasingly interested in clean energy options to replace fossil fuels in response to rising environmental concerns and dwindling fossil fuel resources. There has been an increase in the installation of renewable energy resources, and at the same time, conventional energy conversion systems have improved in efficiency. In this paper, several multi-generation systems based on geothermal energy are modeled, assessed, and optimized which employ an organic Rankine cycle and a proton-exchange membrane electrolyzer subsystem in five different configurations. Based on the results, the evaporator mass flow rate and inlet temperature, turbine efficiency, and inlet temperature are the most influential parameters on system outputs, namely, net output work, hydrogen production, energy efficiency, and cost rate. In this study, the city of Zanjan (Iran) is selected for a case study, and the results of system energy efficiency for changes in ambient temperature are examined during the four seasons of the year. To determine the optimal values of the objective functions, energy efficiency, and cost rate, NSGA-II multi-objective genetic algorithm is employed, and a Pareto chart is derived. The system's irreversibility and performance are gauged by energy and exergy analyses. At the optimum state, the best configuration yields an energy efficiency and cost rate of 0.65% and 17.40 $/h, respectively.

Reduced modeling of liquid desiccant falling film absorbers

Liquid desiccant falling film absorbers are an energy-efficient solution for humidity control and dehumidification in buildings and cold stores. This work presents a reduced one-dimensional physics-based modeling approach for this technology and compares it to a high-fidelity three-dimensional computational fluid dynamics (CFD) model. Both models capture the complex heat and mass transfer mechanisms of vertical falling films on two opposing walls and a horizontal crossflow of air. Additionally, both models were verified against experimental data from previous work, and the results showed good agreement within the uncertainties of the measurement equipment. A parameter variation study was also performed, comparing the results of both models under conditions relevant to cold store applications. The reduced model was found to be over 400 times faster than the high-fidelity model, while still achieving an average difference of less than ±0.14K, ±1.3%, and ±3.9% for the calculated air outlet temperature, absorbed water vapor mass flow rate, and air-side pressure drop, respectively. The reduced model is suitable for optimization studies and easy to implement in system simulations, making it a valuable tool for the design and optimization of liquid desiccant systems.

EXPERIMENTAL INVESTIGATION OF TWO-PHASE PRESSURE DROP IN THE STRAIGHT ADIABATIC TUBES

The pressure drop is the significant constraint in designing the single or multiphase flow systems. Innovative technologies, such as nuclear power plants and enhanced oil recovery processes, can be designed more efficiently with the knowledge of the multiphase pressure drop phenomenon. The higher pressure drop induces the lower system efficiency. There is a scarcity of literature representing the steam-water flow at atmospheric system pressure in the adiabatic tubes. The experiments are performed to get the two-phase pressure drop in the adiabatic tube for the effective design of heat transfer equipment used for diverse applications. The adiabatic tubes of 8, 13.7, and 18 mm diameter, having 15 &amp;times; 10&lt;sup&gt;2&lt;/sup&gt; mm length, are experimented for 32-495 kg/m&lt;sup&gt;2&lt;/sup&gt;s mass flux and 0-1 vapor quality. The pressure drop in the adiabatic tubes increases nonlinearly with the increase of vapor quality. The pressure drop is influenced significantly by the diameter of the tube. The pressure drop is lesser in the 18 mm tube compared to the 8 and 13.7 mm tubes for constant vapor quality and mass flow rate. The increase of the mass flux increases the pressure drop monotonically. The pressure drop is higher at higher mass flux and higher vapor quality in the lesser diameter tube. The experimental pressure drop is compared to various correlations. A correlation is suggested to measure the two-phase pressure drop during steam-water flow at atmospheric system pressure in the adiabatic tubes.

Quantification of flow distribution and heat capacity potential of a microchannel evaporator

Maldistribution of fluid among the ports reduces the heat capacity of a microchannel heat exchanger. It is essential to understand the maldistribution mechanism to optimize the design of the heat exchanger. Quantification of the distribution helps analyze the maldistribution issue. This study proposes a method to quantify the flow distribution and capacity potential in the microchannel heat exchangers by integrating a microchannel heat exchanger model and infrared thermography. The method calculates the liquid and vapor mass flow rate at the inlet of each microchannel tube by comparing the wall temperature of a heat exchanger from simulation and the infrared image. The method is validated with tests of a 49-tube horizontal microchannel evaporator with R134a. The exit region of the top tubes has an extremely high surface temperature, which forms a superheat region. More liquid flows to the tubes located at the center of the heat exchanger. The total mass flow rate is low when the tube has a long superheat region. The heat capacity of the tested evaporator has 9.6–21.3% improvement potential when uniformly distributed. When the refrigerant outlet superheats of the evaporator is lower, the improvement potential is higher. In the superheat region, the heat flux is much lower than the average value. This quantification method provides a tool for a more profound investigation of the maldistribution issue of a microchannel evaporator, and it can be expanded to heat exchangers with different structures.

Heat transfer and pressure drop of CO2/R32 mixture in mini-channel

In this study, we investigated the condensation heat transfer characteristics of the CO2/R32 mixture in a mini-channel with a diameter of 2 mm. The experimental conditions were as follows: mass flow rate of 50–400 kg·m−2·s−1, vapor quality of 0–1, and a condensation temperature of 35–45 °C. The experimental data were then compared with the heat transfer correlations. The higher the CO2 content, the smaller the annular flow area. The convective heat transfer coefficient decreases rapidly and then increases slowly with an increase in CO2. The minimum value was obtained when the CO2 content was approximately 55%. In addition, the convective heat transfer coefficient decreased with an increase in the condensation temperature. Higher vapor quality and mass flow rate conditions correspond to higher convective heat transfer coefficients. The prediction correlations applicable to the in-tube condensation heat transfer have low prediction results for CO2/R32, and the model of Shah is recommended as the prediction model. The experimental results of the condensation pressure drop were analyzed, and the results showed that the pressure drop increased linearly with the mass flow rate but decreased with an increase in the condensation temperature. The lower the CO2 content, the more clear the effect of the condensation temperature. The correlation of Kim and Mudawar is recommended for the CO2/R32 two-phase condensation friction pressure drop. This study provides theoretical support for the analysis of the condensation heat transfer mechanism of a CO2/R32 mini-channel.

Performance Analysis of Externally Pressurized Gas Journal Bearing Lubricated with Vapor of R134a in Centrifugal Compressor

The performance of an externally pressurized gas journal bearing lubricated with R134a vapor used in an oil-free refrigeration centrifugal compressor is calculated by solving Reynold equations with the finite difference method (CFD). The load capacity, stiffness and mass flow rate of refrigerant vapor under conditions of various operational parameters are obtained and compared with that in air gas bearings. In addition, the influences of the average clearance, eccentricity ratios and supply vapor pressure on the static characteristics of journal bearings are investigated and discussed in detail. It concluded that the optimal operation parameters of gas journal bearings lubricated with R134a vapor are different with air journal bearings. These factors should be considered in the design process of R134a refrigerant vapor gas journal bearings.

Experimental study on condensation flow patterns and heat transfer characteristics of non-azeotropic and immiscible binary mixed vapors

The condensation phenomenon of non-azeotropic and immiscible mixed vapors always occurs in the waste heat recovery process of biomass gasification gas. During the condensation process, the immiscible condensation products, such as tar and water, have a different flow pattern from the pure working fluid, which can affect the waste heat recovery efficiency and the service life of the heat exchanger. However, the relationship between the flow pattern of immiscible condensates and condensation heat transfer is not clear at present. In this paper, water and cyclohexane were used as non-azeotropic and immiscible working fluids. The effects of different mixed vapors mass ratios, cooling water inlet temperatures, and vapor mass flow rates on the condensation heat transfer characteristics of the binary mixed vapors on the vertical wall were studied. And the condensate flow patterns were combined for analysis and discussion. The experimental results showed that the condensation on the wall surface of the mixed vapors presented a film-drop flow pattern comparing with the filmwise condensation of water vapor or cyclohexane vapor. The film-drop flow pattern was manifested as that the cyclohexane condensate was attached on the condensation wall in the form of liquid film, and the water condensate was attached on the cyclohexane film in the form of droplets. And the flow of water droplets on the cyclohexane liquid film can enhance the condensation heat transfer of the mixed vapors. In addition, different from water vapor and cyclohexane vapor, the heat transfer coefficient of the mixed vapors decreased with the increase of the cooling water inlet temperature, which was related to the film-drop condensation flow pattern.

Experimental and analytical investigation of CO2/R32 condensation heat transfer in a microchannel

Previous research has shown that CO2 mixtures can improve the thermal performance of CO2 refrigeration systems. Moreover, the use of a microchannel heat exchanger can reduce the refrigerant charge and improve the heat transfer coefficient. Therefore, in this experimental study, we investigated the condensation heat transfer characteristics of CO2/R32 in a porous flat microchannel with a hydraulic diameter of 0.715 mm. According to the results, the convective heat transfer coefficient decreased rapidly then increased slowly with an increase in the CO2 mass fraction. The minimum value was achieved when the CO2 mass fraction was approximately 55%. In addition, the convective heat transfer coefficient decreased with an increase in the condensation temperature. Higher vapour quality and mass flow rate conditions corresponded to higher convective heat transfer coefficients. The prediction correlations applicable to the in-tube condensation heat transfer exhibited low prediction results for CO2/R32, with a heat transfer coefficient prediction error for the newly established prediction model of 16.77%. This study provides theoretical support for analysis of the CO2/R32 condensation heat transfer mechanism in microchannels and the future design of microchannel condensers.