Condensation Heat Transfer Correlations Research Articles

Numerical investigation on flow condensation in zigzag channel of printed circuit heat exchanger

The printed circuit heat exchanger (PCHE) has a great potential for the application in various compact energy systems. However, the there is no existing heat transfer and pressure drop correlations on condensation in PCHE zigzag semicircular channel. In this study, the flow and heat transfer characteristics of condensation in the PCHE zigzag semicircular channel were analyzed numerically. The flow patterns of annular flow, annular wavy flow and plug flow were observed in the channel, and the flow pattern transition line correlations were developed. As the mass flux increases, the transition vapor quality from annular flow to intermittent flow decreases gradually. Both the condensation pressure drop and the heat transfer coefficient reach their peaks as the vapor quality is around 0.78, and the pressure drop decreases with the increase of saturation temperature. The heat transfer coefficient decreases as the saturation temperature increases when the vapor quality is less than 0.6, while it increases slightly as the saturation temperature increases when the vapor quality is greater than 0.6. New correlations for condensation pressure drop and heat transfer in PCHE zigzag semicircular channel are developed. The average errors of the developed condensation pressure drop and heat transfer correlations are 11.0 % and 7.9 %, respectively.

Flow condensation heat transfer correlation development of R32-oil mixture inside a micro-fin tube

The air-conditioners employ R32 as refrigerant because it has low GWP. The heat transfer performance of R32 in the heat exchangers would be influenced by the lubricating oil cycled with R32. In order to obtain the quantitative effect of oil on the flow condensation heat transfer characteristics, flow condensation heat transfer correlation of R32-oil mixture is needed. In this study, an experimental rig for testing the flow condensation heat transfer coefficients of R32-oil mixture is established. The test conditions covering the actual working conditions of air-conditioners are designed, including the condensation temperature ranging from 40 to 50 °C, mass flux ranging from 100 to 400 kg m − 2 s − 1, vapor quality ranging from 0.1 to 0.9 and oil concentration ranging from 0 % to 5 %. The results show that the flow condensation heat transfer coefficients decrease with the increasing of oil concentration because of the high viscosity of the oil. A new condensation heat transfer correlation is developed based on the enhanced structure of the micro-fin tube and physical properties of the working fluid, and it agrees with 82 % of the experimental results within a deviation of ± 20 %.

A simulation study on the condensation flow and thermal control characteristics of mixed refrigerant in a dimpled tube

In this study, the condensation flow and heat transfer characteristics of ethane/propane in the dimple tube have been numerically investigated, and the liquid droplet entrainment caused by the dimple structure was considered. The effects of operation and structure parameters on flow and heat transfer were analyzed, including different dimple depths, helical pitch, and dimple pitch. The results showed that the dimple tube had a higher heat transfer coefficient compared to the smooth tube, which increased with the increase in the mass flow rate and the decrease in the saturation temperature. The effect of dimple depth on heat transfer is greater than that of the dimple pitch or helical pitch, and the dimple depth will cause the local mass transfer rate to increase under high vapor quality. Meanwhile, the existing heat transfer correlations for smooth tubes were compared, and a condensation heat transfer correlation suitable for the mixed refrigerant in the dimple tubes was proposed with an average deviation of 6.3%.The conclusions obtained can provide support for the optimization design of liquefied natural gas plants.

A universal correlation for flow condensation heat transfer in horizontal tubes based on machine learning

Accurate and universal prediction of in-tube condensation heat transfer coefficients (HTCs) is vital for designing compact condensers. This study presents machine learning (ML) methods for predicting flow condensing HTCs inside horizontal tubes based on an assembled database. The database contains 6064 experimental data of 28 pure fluids and covers broad operating conditions. Furthermore, the database is serviced to train and evaluate five ML models based on K-nearest neighbors (KNN), artificial neural network (ANN), convolutional neural network (CNN), random forest (RF), and Extreme gradient boosting (XGBoost) algorithms. The designed ML models show excellent predictive performances for 1213 test data points with the best mean absolute relative deviation (MARD) of 5.82% achieved by CNN and the coefficient of determination (R2) of 0.98 or higher for both XGBoost models. Based on the parametric importance analysis conducted by the trained XGBoost models, a new universal correlation is developed by incorporating several key parameters to characterize condensation heat transfer. This correlation shows reliable predictions for all data points in the consolidated database with the mean relative deviation (MRD) of −1.77% and MARD of 19.21%. An additional excluded database is collected to validate the universality of the new correlation and these ML models. It illustrates that ML models are effective predictive tools for HTCs, and can also help develop the heat transfer correlation with high accuracy and universality.

Extension of the CIRCE methodology to improve the Inverse Uncertainty Quantification of several combined thermal-hydraulic models

The Inverse Uncertainty Quantification (IUQ) of physical correlations used in thermal-hydraulic system codes is a crucial issue in the BEPU (Best Estimate Plus Uncertainty) framework for the licensing and safety analyses of nuclear reactors. The CIRCE methodology is one of the most widely applied IUQ methods. It estimates the (log-)normal probability distribution of a multiplicative factor applied to the reference closure model used in thermal-hydraulic computer codes. CIRCE can jointly estimate the uncertainty of several physical models. However, in some particular cases, a problem of identifiability may occur resulting in less accuracy and precision of the estimated uncertainties.For this reason, in this work, the methodology is improved under the name of CIRCE 2-Steps. This new approach aims at improving the quantification of the model uncertainties when experiments with more than one physical phenomena interacting simultaneously on the output of interest has to be used. In a first step, the uncertainties of the least influential models are evaluated with classic CIRCE methodology using experiments for which only one physical phenomenon is dominant. Then, these uncertainties are properly taken into account when quantifying the remaining uncertainties on the experimental database. This approach is proven to provide more accurate and precise results on several analytical test cases where the uncertainties of two models has to be jointly estimated. The study of the impact of the relative importance of the two models shows that the biggest gain in precision is obtained when the hierarchy of models is such that one model is significantly more influential than the other.Finally, the newly developed methodology is applied to estimate the uncertainties of two condensation heat transfer correlations in the cold leg of a pressurised nuclear reactor.

Condensation Heat Transfer Correlation for Micro/Nanostructure Properties of Surfaces.

Condensation, which can be observed in nature as a phase change heat transfer phenomenon, is a critical phenomenon in industrial fields such as power generation, water desalination, and environmental control. Many existing studies have applied surfaces with different wettability by controlling the surface topology to enhance condensation heat transfer. However, the industrial applicability is close to zero due to the limited size and shape of surfaces and low supersaturation conditions. Here, we regulate the surface topology of large-area copper tubes, which are representative industrial metals. We fabricated four copper tubes with different surface structures. We analyzed the condensation phenomenon of the modified tube under specific supersaturation conditions by measuring the overall heat transfer coefficient. We analyzed the condensation phenomenon by measuring the condensation heat transfer coefficient. We have recognized that there is a difference between the maximum droplet radius and the droplet detaching frequency depending on the size and shape of the structure. We measured the contact angle and contact angle hysteresis to accurately analyze the droplet behavior on each surface. As a result, we show that there is a correlation between contact angle hysteresis (CAH) and the total heat transfer coefficient, indicating heat transfer performance. These findings can be applied when evaluating surfaces with excellent condensation heat transfer performance for use in real industrial environments, which can dramatically reduce time and cost.

Experimental study on condensation heat transfer characteristics of steam in rectangular channels rotating about a parallel axis

• Nu in rotating channel increases with Re but decreases with steam temperature. • Pressure drop in rotating channel increases with Re and steam temperature. • Propose a new heat transfer correlation for steam condensation in rotating channel. In the papermaking industry, a kind of new cylinder dryer with multiple small and rectangular channels are employed to enhance the drying efficiency of drying machine. In practical working conditions, the multi-channel cylinder dryer runs under rotating states that could affect the heat transfer characteristics of the inside two-phase flow. However, the fluid heat transfer characteristics in the multi-channel at rotating states have not been well explored. In this study, a set of rotating experimental system is established to investigate the condensation characteristics and pressure drop changes of steam in rotating rectangular channels. Firstly, the experimental apparatus and the data processing method are described in detail. Then the effects of rotation speed, mass flux and steam temperature on the heat transfer coefficients and pressure drop are studied through experiment. The results show that when Re is small, the heat transfer coefficient first increases and then decreases with the increased Re ω ; when Re is large, the heat transfer coefficient increases with the increased Re ω . Moreover, the heat transfer coefficient decreases as the steam temperature increases. In addition, the pressure drop decreases with the increased Re ω while increases with the increased Re and steam temperature. Finally, a heat transfer model of two-phase flow condensation under rotating states is developed to predict the heat transfer coefficient of steam in rotating multiple channels.

Design and modeling of novel two-phase heat exchangers for a home cooling system with ice energy storage

In this study, a novel three-fluid micro-channel evaporator is designed and modeled for a home cooling system with ice energy storage. A two-fluid condenser with similar heat duty is also modeled using micro-channels. Thermal resistance network is used to model the overall heat transfer coefficient of the heat exchangers. The heat transfer model considers the non-symmetric nature of the three-fluid micro-channel evaporator and includes detailed two-phase boiling heat transfer analysis. Similar detailed condensation two-phase heat transfer analysis is conducted for the condenser using the Universal Correlation. The study also conducted extensive code validation for the two-phase boiling and condensation heat transfer correlations before using the code for evaporator and condenser design and analysis. The design conditions for the evaporator and condenser including superheat and subcooling are gathered from ASHRAE standards. The models are expected to accurately predict the heat exchanger sizes for a design requirement, and calculates the fluid outlet temperatures and heat duty for a heat transfer analysis. When combining with the system model of the home cooling system, the evaporator and condenser models can more accurately predict the overall system performance under variable operating conditions. The discretization method results a 62.4 cm length evaporator and a 42.4 cm condenser, which are required to run a 17-kW home-cooling system based on the detailed assumptions and two-phase correlations.

A comprehensive Bayesian framework for the development, validation and uncertainty quantification of thermal-hydraulic models

The development, validation and uncertainty quantification of closure laws used into thermal–hydraulic system codes is a key issue before applying the BEPU (Best Estimate Plus Uncertainty) methodology for safety studies and licensing of nuclear reactors. The assessment of those physical models requires tuning some parameters against available experimental data. This paper presents a methodology called Bayesian calibration, which allows a more robust and reliable assessment, selection and uncertainty quantification of physical models.In this work, the experimental and predicted values are linked by means of a multiplicative random variable which represents the model uncertainty. This hypothesis is suitable for models scaling across many orders of magnitude as it is the case in nuclear thermal–hydraulic. Several empirical models, which describe the same physics with different formalisations, are calibrated. Then, the one which is the best-suited according to different statistical indicators is selected. A statistical validation is performed with a Leave One Out (LOO) technique which allows using the same database for both assessment and validation of the physical model. Finally, the uncertainty on the selected best-fitting model is assessed.This framework is applied to condensation heat transfer correlations for safety injection based on the COSI (COndensation at Safety Injection) experiments.

Effect of Tube Expansion on Heat Transfer and Pressure Drop Characteristics During Condensation in Micro-Fin Tubes

Despite of the large number of research dedicated to condensation heat transfer and pressure drop characteristics in pristine micro-fin tubes, experimental investigation on effects of tube expansion have not been reported in the open literature. The paper reports measured cross-sectional dimensions, condensation heat transfer and pressure drop data of R1234ze(E) in pristine (5.10 mm OD) and expanded (5.26 mm OD) micro-fin tubes with mass fluxes from 100 to 300 kg/(m2·s). Effects of mass flux, vapor quality and tube expansion on the heat transfer coefficients and friction pressure gradients were investigated in the study. When the mass flux is 100 kg/(m2·s), the heat transfer coefficient and pressure drop of R1234ze(E) decrease after tube expansion. However, when the mass fluxes are 200 and 300 kg/(m2·s), tube expansion effects on the heat transfer coefficient and pressure drop are not notable. In addition, the experimental results are analyzed based on the existing condensation heat transfer and pressure drop correlations.

Effects of Experimental Parameters on Condensation Heat Transfer in Plate Fin Heat Exchanger

This study aims to provide an experimental investigation and comparison of the condensation heat transfer characteristics in a plate–fin heat exchanger (PFHE). The heat flux, mass flux, and saturation pressure were adjusted as experimental parameters to verify the effects on the condensation heat transfer. In addition, condensation heat transfer correlation of two-stream PFHEs was provided based on the experimental data for utilization as a design reference for the heat exchanger. The turbulence is the most influential in heat transfer. One of the ways to foster turbulence is to increase shear stress. The higher flow velocity results in the higher shear stress. That was why increasing mass flux or the flow with higher vapor quality showed the higher heat transfer coefficient (HTC). Refrigerant properties such as viscosity and specific volume of vapor changed according to the saturation pressure. It is expected they affect the degree of turbulence too in similar manners. The mass flux was more influential than the heat flux and saturation pressure. Thus, the equivalent mass flux of the refrigerant is dominant in the derived correlation model. The average difference between experimental and calculated HTC from correlations was about 6.5%. Multi-stream PFHE comprises an additional heat transfer surface, which implies a more active droplet formation. The average pressure drop in the multi-stream is 15% larger than that of the two-stream.

Evaporation/Condensation Heat Transfer and Pressure Drop of R1336mzz (E) and Its Mixture Working Fluid for High-temperature inside Horizontal Microfin Tubes

Research is currently in progress on developing and improving efficiency of high-temperature heat pumps and organic Rankine cycle power systems, both of which generate high-temperature steam by effectively utilizing low-quality heat sources from ship engines and factories for industrial purposes. From an environmental point of view, development efforts are also underway to replace low-pressure working fluids used in these systems with new alternative working fluids with low global warming potentials (GWPs). The purpose of this study is to experimentally clarify the evaporation and condensation flow characteristics of alternative low-GWP working fluids inside two types of horizontal microfin tubes with outer diameters of 9.5 mm. The Hydrofluoroolefin (HFO) working fluids R1336mzz(E) and R1336mzz(Z), both of which are expected to replace the working fluid R245fa that is used widely at present, two pure components and their mixture were used as test fluids in this study. In this experiment, the authors measured the evaporation and condensation heat transfer coefficients and pressure drop under the conditions of 50-300 kg/(m2s) mass velocity, a saturated evaporation temperature of 40 °C and a saturated condensation temperature of 60 °C. The results of the experiment clarified the effects of mass velocity and fin geometries on the evaporation and condensation heat transfer and pressure drop characteristics of R1336mzz(E), R1336mzz(Z) and their mixture working fluid. In addition, comparisons were made between the evaporation and condensation heat transfer coefficients and pressure drop of these working fluids and those of R245fa to highlight differences in their performance. Furthermore, the measured values were correlated with previous correlations for evaporation and condensation heat transfer for microfin tubes to verify the applicability of these predicted correlations.

Tube-in-Tube 미세관내 R-22 및 R-407C의 응축열전달 특성

This paper focuses on the results of an experimental study of condensation heat transfer coefficients with the refrigerants R-22 and R-407C, and looks at the pressure gradient and heat transfer coefficients of horizontal tube-in-tube heat exchangers with the use of small tubes with inner diameters of 4 mm, 3 mm and 2 mm, in a 16.91 mm tube and length of 3,000 mm. Experiments were performed at an inlet saturation temperature of 35 to 45℃ and mass flux ranges from 200 to 600 kg/m²s. The use of an inner tube with a diameter of 4.0 mm resulted in a pressure gradient that was 2.5 times higher than that of an inner tube with a diameter of 8.0mm. In tube-in-tube HEX, the pressure gradients of R-22 measured higher than those of R-407C. The condensation heat transfer coefficients increase with an increase in mass flux, but they decrease with an increase in saturation temperature. Condensation heat transfer coefficients of R-407C were a little higher than those of R-22, and the condensation heat transfer coefficients of double tube HEX were about 40% higher than those of tube-in-tube HEX. The experimental results of this study were also compared with five existing correlations. New condensation heat transfer correlations were developed, and successfully predicted the experimental results with mean deviations of 10.6% and 10.1%, and average deviations are -0.92% and -0.31%, for R-22 and R-407C, respectively.

Condensation heat transfer and pressure drop correlations in plate heat exchangers for heat pump and organic Rankine cycle systems

An accurate prediction method of flow condensation heat transfer in plate heat exchangers is important for the design of condensers. The existing prediction methods are semi-empirical correlations, whose applicability highly rely on the range of original test data used for the correlation development. In this study, prediction methods of frictional pressure drop and heat transfer coefficient of flow condensation in a plate heat exchanger which were tailored for the applications in heat pump and organic Rankine cycle systems, were developed. We conducted a comprehensive experimental investigation, building a database including 283 data points for both pressure drop and heat transfer. We tested seven working fluids, classified by hydrofluorocarbons – R134a, R236fa and R245fa, hydrofluoroolefins – R1234ze(E) and R1233zd(E), and hydrocarbons – propane and isobutane, for a wide range of condensation temperatures varying from 30 °C to 90 °C. Two dimensionless numbers, the density ratio of liquid phase to vapour phase and the Bond number, were involved for developing the new prediction methods. The paper presents data for higher temperatures than those presented in previous works, and novel analysis and prediction methods. The new correlations achieve an improved prediction, enabling an 8.9% and a 10.3% mean absolute percentage deviation for heat transfer and pressure drop data, respectively.

Condensation heat transfer of R1234yf in a small diameter smooth and microfin tube and development of correlation

Condensation heat transfer of R1234yf inside smooth and microfin tube with 2.5 mm outer diameter are studied experimentally. The experiments are carried out at a saturation temperature of 20°C and 30°C, mass velocity ranging from 50 to 200 kg m−2s−1 and vapor quality ranging from 0-1. The effects of mass velocity, vapor quality, and saturation temperature on condensation heat transfer coefficient are analyzed with R1234yf and R134a. Condensation heat transfer correlation for smooth tube is developed considering present experimental data and other researchers’ data. Correlation is developed using experimental data for 2.5 mm to 10 mm outer diameter tubes and refrigerants are R134a, R1234yf, R123 and R1234ze (E) by including other researchers’ data. Newly developed correlation is successfully predicted experimental data and other sources data within mean deviation of 15 %. Experimental data are also compared with previous correlations proposed for smooth and microfin tube.

An improved heat transfer correlation for condensation inside inclined smooth tubes

To date, there has been no robust model that can satisfactorily predict the condensation heat transfer coefficients in smooth tubes when oriented at some angles other than horizontal and vertical. Therefore, it was the motivation of this investigation to develop a universally acceptable model capable of predicting the heat transfer coefficients during convective condensation inside inclined tubes subject to diabatic conditions. An extensive database of experimental results collected from our previous studies was used in the development of the proposed model. The database consisted of five hundred and fifty-nine data sets for tube orientation varying between - 90o and + 90o, mass velocities 100 kg/m2s to 400 kg/m2s, mean vapour qualities 10% to 90% and saturated condensing temperatures 30 °C to 50 °C. The proposed model showed a magnificient agreement with the experimental data within an global average and mean absolute deviations of −5.74% and 1.13% respectively. The performance of the new empirical model was validated with inclined flow data from three sources in the open literature and was found to predict them with high accuracy.

A general heat transfer correlation for flow condensation in single port mini and macro channels using genetic programming

• Evaluated previous flow condensation heat transfer coefficient correlations. • Proposed a new correlation for condensation heat transfer in mini and macro channels. • Verified the model with 6521 data points from 40 published papers. • Discussed the effects of the input parameters on the heat transfer coefficient. A new general explicit correlation is proposed to predict the heat transfer coefficient of fluids condensing in conventional and mini channels. The expression has been developed by correlating the Nu mix number with Re mix , Pr mix , phase density ratio, P res , We GT , and Fr L using genetic programming for the two-phase flow. The model has been validated with a big dataset consisting of 6521 data samples, covering a wide range of fluids used in refrigeration and heat pump industries, cross-sectional geometries (different diameters), mass fluxes, and saturation temperatures. The new generalized correlation fits the wide range of data points used with an average relative error of 17.82 %. The same database has been used to compare predictions of eight correlations available in the literature, but they failed to give a reasonable estimation of the present experimental results.

Condensation heat transfer of R290 in micro-fin tube with inside diameter of 6.3 mm

ABSTRACT An experimental investigation on condensation heat transfer of R290 with inside diameter of 6.3 mm in horizontal micro-fin tube was presented. Effects of each case on the condensation heat transfer coefficient of R290 were analyzed at saturation temperatures of 40°C, 50°C, and 55°C with heat flux ranging of 3–8 kW/m2, mass flux ranging of 100–250 kg/(m2·s) and vapor quality up to 1.0. The results show that the condensation heat transfer coefficients increase with mass flux and heat flux, however decrease with saturation temperature. In addition, compared with the smooth tube, the condensation heat transfer coefficients of R290 in the micro-fin tube increase by about 25%. Comparing the experimental data, the condensation heat transfer correlations of Yu et al. has high accuracy.

Flow condensation heat transfer in a smooth tube at different orientations: Experimental results and predictive models

The present study aims to better analyze the influence of body force on flow condensation heat transfer by conducting tests at multiple orientations in Earth’s gravity. Dielectric FC-72 is condensed in a smooth stainless-steel tube with 7.12 mm diameter and 574.55 mm condensing length by counterflow of cooling water across the outer surface of the tube. Test conditions span FC-72 mass velocities of 50.3–360.3 kg/m2 s, test section inlet pressures of 127.0–132.1 kPa, and test section inlet thermodynamic equilibrium qualities of 0.13–1.15. A subset of data gathered corresponding to axisymmetric, annular condensation heat transfer is identified and a detailed methodology for data reduction to calculate heat transfer coefficient presented. Uncertainty analysis is also presented and indicates channel average heat transfer coefficients are calculated within ±3.6% to ±26.7% (depending on operating conditions). Analysis of parametric trends for condensation heat transfer reveals the dominant influence of mass velocity (flow inertia), secondary influence of vapor mass fraction (thermodynamic equilibrium quality), and strong dependence on orientation (body force) at low mass velocities. At higher mass velocities results for all orientations investigated begin to converge, indicating body force independent annular condensation heat transfer is achieved. Separated Flow Model predictions of vertical downflow condensation heat transfer provide reasonable agreement with experimental results, evidence by a Mean Absolute Error (MAE) of 31.2%. Evaluation of condensation heat transfer correlations for horizontal flow reveal most correlations struggle for cases with high liquid content. Specific correlations are identified for superior accuracy in predicting the measured data.

Condensation heat and mass transfer of steam with non-condensable gases outside a horizontal tube under free convection

The condensation heat and mass transfer of steam-He, steam-N2 and steam-CO2 mixtures on a horizontal tube under free convection was studied experimentally and theoretically. A model was developed to predict the total condensation heat transfer coefficient of these mixtures and the model considered the effects of suction, fog formation and the variation of the mixture density and molecular weight across the diffusion layer. The experiments were conducted to investigate the effects of noncondensable gas component, concentration and surface subcooling. The condensation heat transfer coefficients are significantly reduced due to the presence of noncondensable gases. The condensation heat transfer coefficient decreases slowly as the surface subcooling increases and the subcooling effect decreases with increasing noncondensable gas concentration. For a given noncondensable gas mole fraction and a given surface subcooling, the steam-He mixture has the highest measured condensation heat transfer coefficient, followed by the steam-N2 mixture and the steam-CO2 mixture has the lowest measured condensation heat transfer coefficient. But for a given noncondensable gas mass fraction and a given surface subcooling, the measured condensation heat transfer coefficient of the steam-He mixture is the lowest, followed by the steam-N2 mixture, CO2 mixture. The model predicts the relative errors of the total condensation heat transfer coefficients of these mixtures within ±30%. A condensation heat transfer correlation was developed based on the experimental data and the correlation achieved an uncertainty of less than 20%.