Experimental Condensation Heat Transfer Research Articles

Condensation characteristics of flows in newly developed three-dimensional enhanced heat transfer tubes

Condensation heat transfer characteristics were studied experimentally in order to evaluate the heat transfer performance of horizontal copper heat transfer tubes (smooth and enhanced). Using R410A and R32 as refrigerants, condensation heat transfer experiments were carried out for a saturation temperature of 45 °C; inlet vapor quality of the tube was 0.8 and outlet quality was 0.2; refrigerant mass flow rate range was in the range from 68 to 371 kg/(m2·s). Single-phase heat balance verification found that the heat loss is less than 6 %, with the deviation between single-phase experimental results and various correlations being less than 15 %. The condensation heat transfer coefficient increases with an increase in mass flow; as the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient (HTC) increases. Experimental results determined that the performance factor ratio (enhanced tube/smooth tube) of the three-dimensional surfaces investigated here are greater than 1. Tubeside heat transfer enhancement factor (EF) of the HB/D tube is the highest (max 1.76); its performance is closely related to increasing fluid turbulence and improving drainage. Performance factor (PF) of the HB/D tube (max 1.38) is the highest for most of the flowrates. All this indicates excellent thermal performance. Flow model-based analysis was performed in order to develop a correlation for the condensation heat transfer coefficient and the pressure drop for the enhanced surface tubes. Both prediction models accurately predicted all data points within a limited margin of error.

A novel strategy to enhance heavy oil Recovery: Condensation heat transfer calculation and 2-D visualized physical simulation

High carbon emissions and low efficiency in thermal utilization are pivotal challenges in heavy oil development. Addressing the urgent need to enhance heavy oil production, this paper introduces an innovative approach in which aerogel and flue gas serve as supplementary additives in steam thermal recovery. To investigate the mechanisms behind the improved heat transfer and oil recovery facilitated by the combination of aerogel and flue gas, condensation heat transfer experiments and 2-D visual oil displacement experiments were carried out. The condensation heat transfer coefficient, oil displacement performance, and heat utilization efficiency were analyzed and compared. The results showed the porous structure of the aerogel enhances its thermal insulation properties by adsorbing flue gas, thereby reducing the steam-to-cold object condensation heat transfer coefficient by 60.6%. The cementation between aerogel nanoparticles (NPs) retained in the formation and rock particles formed an insulating layer that impedes the upward propagation of steam heat. Combined with efficacy of flue gas foam in improving fluid flow, this promoted the horizontal expansion of the steam chamber, resulting in an 8.2% and 3.4% increase in the steam chamber’s extent compared to using steam and a combination of steam with aerogels, respectively. Moreover, the profile control and thermal insulation impacted following the NPs, lowering the water cut in the produced fluid and enhancing the oil recovery by 7.9%. Upon the application of flue gas, this enhancement in recovery extended to 9.3%.

Condensation enhancement experiment investigation of pure steam and steam-air mixture over the chrome-plated tube with different plating thickness

The condensation enhancement research of pure steam and steam with non-condensable gas is of great significance for reactor safety. In this study, to evaluate the influence of chrome-plated tubes on condensation enhancement, pure steam and steam with air condensation heat transfer experiments are conducted, and the plating thicknesses of 1 μm (tube #1) and 10 μm (tube #2) are considered. The results show that dropwise condensation (DWC) occurred in the part of tube #1 surface, while tube #2 surface is filmwise condensation (FWC). For the pure steam condition, the steam condensation heat transfer coefficient (HTC) of tube #2 is higher than that of tube #1, and both are greater than the theoretical analysis of Nusselt. Thus, the condensation enhancement effect of the chrome-plated tubes is remarkable. For the steam with air condition, a new condensation HTC expression is proposed, which is related to gas pressure, wall subcooling, and air mass fraction. Compared with the widely used experimental correlations and the experimental data of polishing tubes, it is found that the condensation enhancement performance is not significant. This is because the dominant thermal resistance affecting heat transfer is the air layer at the gas-liquid interface. Thus, enhancing the disturbance of the gas layer is the key to the condensation enhancement of steam with non-condensable gas.

Condensation Heat Transfer Experiments of R410A and R32 in Horizontal Smooth and Enhanced Tubes

Abstract A horizontal smooth copper tube and two enhanced tubes (a dimpled tube and a diamond-shaped tube) with a length of 2 m and an outer diameter of 9.52 mm were studied in a two-phase condensation experiment using R410A and R32 as heat transfer working fluids. The condensation heat transfer performance of different heat transfer tubes at various mass fluxes ranging from 150 to 400 kg/(m2s) and different vapor qualities ranging from 0.8 to 0.2 was studied experimentally. For R410A, the heat transfer coefficients (HTCs) of the dimpled tube and the diamond-shaped tube were found to be 1.39–1.52 times and 1.30–1.35 times higher than those of the smooth tube, respectively. For R32, the HTCs were found to be 1.46–1.59 times higher for the dimpled tube and 1.26–1.35 times higher for the diamond-shaped tube than for the smooth tube. The diamond-shaped tube was found to be effective in directing the flow of the liquid phase and in thinning the liquid film thickness. The dimpled tube was found to promote droplet entrainment and disturbance. Both of those effects contributed to improving the HTCs in the two enhanced tubes investigated. The HTCs of R410A were found to be lower than those of R32 because of the smaller specific heat capacity, smaller latent heat of condensation, and relatively poorer thermal conductivity of R410A. Taking the combined effect of heat transfer and pressure drop into account, a performance enhancement factor (PEF) was computed and was found to range from 0.9 to 1.51. Based on the experimental data collected, a new empirical correlation equation has been proposed with a maximum error band of 10%. Flow pattern maps for the tested tubes have also been generated and are presented in the paper. Both of the two enhanced tubes were found to promote the development of annular flow. The HTCs were found to be highest when the flow pattern was of the annular flow type.

Experimental Analysis of Local Condensation Heat Transfer Characteristics of CF3I Inside a Plate Heat Exchanger

Due to its low global warming potential (GWP) and good environmental properties, CF3I can be a suitable component of refrigerant mixtures in the field of refrigeration and air conditioning. In this work, the local condensation heat transfer characteristics of CF3I were experimentally investigated in a plate heat exchanger (PHE). The condensation heat transfer experiments were carried out under conditions of vapor qualities from 1.0 to 0.0, at saturation temperatures of 25–30 °C, mass fluxes of 20–50 kg/m2s, and heat fluxes of 10.4–13.7 kW/m2. Local heat transfer coefficients were found to vary in both the horizontal and vertical directions of the plate heat exchanger showing similar trends in all mass fluxes. In addition, the characteristics of local heat flux and wall temperature distribution as a function of distance from the inlet to the outlet of the refrigerant channel were explored in detail. The comparison of the experimental data of CF3I with that of R1234yf in the same test facility showed that the heat transfer coefficients of CF3I were comparable to R1234yf at a low vapor quality and a mass flux of 20 kg/m2s. However, R1234yf exhibited a transfer coefficient about 1.5 times higher at all vapor qualities and a mass flux of 50 kg/m2s. The newly developed correlation predicts well the experimentally obtained data for both CF3I and R1234yf within ±30%.

Investigation of condensation with non-condensable gas in natural circulation loop for passive safety system

The system-integrated modular advanced reactor 100 (SMART100), an integral-type pressurized water small modular reactor, is based on a novel design concept for containment cooling and radioactive material reduction; it is known as the containment pressure and radioactivity suppression system (CPRSS).There is a passive cooling system using a condensation with non-condensable gas in the SMART CPRSS. When a design basis accident such as a small break loss of coolant accident (SBLOCA) occurs, the pressurized low containment area (LCA) of the SMART CPRSS leads to steam condensation in an in-containment refuelling water storage tank (IRWST). Additionally, the steam and non-condensable gas mixture passes through the CPRSS heat exchanger (CHX) submerged in the emergency cooldown tank (ECT) that can partially remove the residual heat. When the steam and non-condensable gas mixture passes through the CHX, the non-condensable gas can interrupt the condensation heat transfer in the CHX and it degrades CHX performance.In this study, condensation heat transfer experiments of steam and non-condensable gas mixture in the natural circulation loop were conducted. The pressure, temperature, and effects of the non-condensable gas were investigated according to the constant inlet steam flow rate with non-condensable gas injections in the loop.

A novel strategy to improve steam heat utilization and reduce carbon emissions during heavy oil development

In recent years, the green transformation of the traditional energy industry and the reduction of carbon emissions have attracted widespread societal attention. In the thermal recovery process of heavy oil, the low heat utilization rate has always been the bottleneck restricting its production. In addition, the associated flue gas emissions also pose a considerable challenge to environmental protection. In this paper, flue gas and SiO2 aerogel were jointly applied to reduce steam heat loss while achieving exhaust gas sequestration. Condensation heat transfer experiments were carried out to explore the mechanism of the two affecting the heat dissipation process of steam liquefaction. A series of displacement experiments with different injection methods in a one-dimensional sandpack were performed to select combinations of developing heavy oil with high efficiency and low carbon. By detecting the temperature changes of the model and calculating the final storage volume, the effects of promoting steam chamber expansion and flue gas sequestration were evaluated. The results showed that the aerogel adsorption layer could change the wettability of the condensing surface, thereby showing the characteristics of film condensation. Flue gas molecules could be captured by aerogel nanofluids, further exerting a synergistic thermal insulation effect, and the temperature of the deep reservoir increased by 7.7 °C. Simultaneously, the crude oil recovery increased by 8.8% compared with pure steam flooding. Moreover, the numerous nanoparticle-stabilized foams generated via this method were noted as an essential way to sequester carbon in a high water-cut formation, and the final sequestration rate reached 77.4%.

In tube condensation heat transfer and pressure drop for R454B and R32—Potential replacements for R410A

The heating, ventilation and air conditioning (HVAC) industry in the United States seeks near-term alternative refrigerants to replace R-410A in unitary equipment. Two potential replacement refrigerants are R-454B and R-32. It is of interest to investigate the capability and accuracy of existing heat exchanger design methods when applied to these replacement refrigerants. To that end, this work presents empirical condensation quasi-local heat transfer coefficient and pressure drop data for R-454B and R-32. These data were obtained in a 38 in. (9.52 mm) outside diameter (OD) smooth copper tube with a wall thickness of 0.032 in. (0.81 mm). The experimental variables and their ranges included refrigerant absolute pressure (1960≤Pabs≤3196 kPa), condensation temperature (35≤Tcond≤50oC), mass flux (100≤G≤200 kg m-2 s-1), vapor quality (0≤x≤1), and heat flux (32.9≤q″≤62.97 kW m-2). It was found that the heat transfer correlation developed by Cavallini et al. Cavallini et al. (2006) predicted the experimental condensation heat transfer data, for both R-454B and R-32, with the greatest accuracy. Using the Cavallini et al. correlation, it was found that the mean absolute percentage error (MAPE) was 10.5% and 15.1% for R-454B and R-32, respectively. Additionally, the pressure drop correlation developed by Friedel Friedel (1979) predicted the experimentally determined pressure gradient with a MAPE of 7.7% and 5.5% for R-454B and R-32, respectively. These results will assist the practicing thermal engineer to choose the most appropriate design correlation for these near-term replacement refrigerants.

Effect of lubricating oil on condensation characteristics of R600a inside a horizontal U-shaped tube: Experimental study

In this paper, heat transfer characteristics of hydrocarbon refrigerant R600a-oil mixture during condensation inside a horizontal U-shaped tube are investigated. The experiments are performed in three parts: (i) pure refrigerant flow inside a straight tube, (ii) pure refrigerant flow inside a U-shaped tube, and (iii) refrigerant-oil mixture flow with compactness of 1, 1.5, and 2% inside a U-shaped tube. An experimental setup has a copper tube of 8.7 mm inner diameter as a test condenser which is installed into a polyethylene pipe of 6 cm inner diameter to form a tube-in-tube heat exchanger. The experimental tests are carried out in a wide range of operating conditions, including mass flux of 140–280 kg/m2s, vapor quality of 0.04–0.80, and condensation pressure of 510–630 kPa. The results are validated by comparing the experimental condensation heat transfer coefficient of pure refrigerant flow inside straight tube with well-known empirical correlations. Accordingly, they predict most of the experimental data within ±20% error in pure refrigerant part. The results represent that using a U-shaped tube increases the local and the average heat transfer coefficients by a maximum of 34% and 29.7% in comparison to the straight tube, respectively. In addition, in the presence of oil, the local heat transfer coefficient of refrigerant-oil mixtures increases at low vapor qualities, while decreases at middle and high qualities due to the effect of oil on the condensation liquid film.

A visualization experimental study on gas penetration through interlayer to improve SAGD performance

Abstract Low-permeability interlayer is common in reservoir, which can hinder the steam chamber expansion and the gravity drainage in SAGD. It is crucial to find an economical and practicable method to promote the steam chamber to break through the interlayer. In this work, four condensation heat transfer experiments were conducted to investigate the effect of flue gas on steam condensation heat transfer. On this basis, 2D visualization tests, including a SAGD experiment and two flue gas assisted SAGD experiments, were carried out to see if the steam chamber can break through the interlayer under the effect of flue gas. Results show with the increase of gas proportion in the steam-flue gas mixture, the condensation heat transfer coefficient decreased and the condensation pattern was transformed from drop condensation to film condensation gradually. This indicates that flue gas can inhibit the condensation heat transfer, which has great influence on the heat transfer and steam chamber growth in SAGD. Visualization tests show the interlayer could block the steam chamber development. After the interlayer was heated sufficiently, flue gas could penetrate the interlayer and promote steam chamber to break through the interlayer because of its inhibiting effect on condensation heat transfer. Besides, the horizontal sweep efficiency was improved significantly under the synergistic effects of steam, gas, and interlayer. The gas addition can reduce the adverse impact of interlayer on SAGD performance, which provides a potential method to improve SAGD development in the reservoir with interlayer.

Experimental study on condensation of high-pressure steam in a horizontal tube with pool boiling outside

In order to investigate the heat transfer and resistance performance of high-pressure steam in-tube condensation with pool boiling outside the tube, experiments were conducted on a short horizontal tube with a 25mm outer diameter and 3mm wall thickness. The test parameters were in the range of 4–10MPa pressure, 400–1000kg/m2s mass velocity, and 0.1–0.9 steam quality. New measurement methods of wall temperature and heat flux were introduced. It is found that the outer wall temperature distribution is not uniform in the circumferential direction, and the wall temperature and heat flux increase with pressure, mass velocity, and steam quality. The condensation heat transfer coefficient and frictional pressure drop increase with the mass velocity and steam quality, but decrease with pressure. In addition, the pool boiling regimes were captured by a high-speed camera. The experimental condensation heat transfer coefficients were compared with available existing correlations, and the comparison results were found to be unsatisfactory. Finally, a modified condensation correlation from Akers et al. was proposed for high-pressure steam in-tube condensation with pool boiling outside in smooth horizontal tubes.

Use of fundamental condensation heat transfer experiments for the development of a sub-grid liquid jet condensation model

Condensation on liquid jets is an important phenomenon for many different facets of nuclear power plant transients and analyses such as containment spray cooling. An experimental facility constructed at the Pennsylvania State University, the High Pressure Liquid Jet Condensation Heat Transfer facility (HPLJCHT), has been used to perform steady-state condensation heat transfer experiments in which the temperature of the liquid jet is measured at different axial locations allowing the condensation rate to be determined over the jet length. Test data have been obtained in a pure steam environment and with varying concentrations of noncondensable gas. This data extends the available jet condensation data from near atmospheric pressure up to a pressure of 1.7MPa. An empirical correlation for the liquid side condensation heat transfer coefficient has been developed based on the data obtained in pure steam. The data obtained with noncondensable gas were used to develop a correlation for the renewal time as used in the condensation suppression model developed by Young and Bajorek.This paper describes a new sub-grid liquid jet condensation heat transfer model. In the current work, mass and energy balance equations are solved in a marching scheme in each sub-grid node along the path of the jet trajectory. Jet specific condensation heat transfer closure relations are used. The jet sub-grid method has been implemented as a boundary condition in an in-house version of the sub-channel analysis code COBRA-TF (COBRA-IE). COBRA-IE fluid nodes provide the required vapor and noncondensable gas conditions for the heat transfer solution. The sub-grid model solves the liquid side heat transfer and the condensation rates for each volume in the sub-grid solution. These terms are summed along all of the sub-grid cells that pass through each COBRA-IE control volume to provide mass and energy transfer rates for the COBRA-IE solution. Results using the new jet injection boundary condition show an improved ability to simulate jet condensation experimental data.

Condensation of ammonia and high-temperature-glide ammonia/water zeotropic mixtures in minichannels – Part I: Measurements

In this two-part study, a comprehensive investigation of the condensation of pure and zeotropic mixtures of ammonia and ammonia/water is conducted and improved models for condensation are developed. In Part I, condensation heat transfer experiments were conducted on ammonia and ammonia/water mixtures. Data for pure ammonia were obtained for varying tube diameters (0.98<D<2.16mm), mass fluxes (75<G<225kgm−2s−1), and saturation conditions (30<Tsat<60°C). Experiments on zeotropic ammonia/water mixtures were conducted for multiple tube diameters (0.98<D<2.16mm), mass fluxes (50<G<200kgm−2s−1), and bulk ammonia mass fractions (xbulk=0.8, 0.9 and >0.96). For zeotropic mixtures, the apparent heat transfer coefficient showed a different trend from the pure ammonia heat transfer coefficient, with strong degradation observed in quality ranges with large temperature glides. At low quality ranges (i.e., low temperature glides and smaller mixture effects), the pure ammonia heat transfer coefficient and zeotropic mixture apparent heat transfer coefficient were in good agreement. In Part II of this study, a new model for predicting condensation heat transfer for pure ammonia in mini- and microchannels is introduced.

Condensation of ammonia and high-temperature-glide zeotropic ammonia/water mixtures in minichannels – Part II: Heat transfer models

In this two-part study, a comprehensive experimental investigation of the condensation of pure ammonia and zeotropic mixtures of ammonia/water is conducted and improved models for predicting condensation heat transfer are developed. In Part I, condensation heat transfer experiments were conducted with ammonia and ammonia/water mixtures. In Part II, a heat transfer model is developed for condensation of ammonia in mini/microchannels. The model is validated with data and shows a significantly improved predictive capability (AAD=12.8% for all ammonia data) compared to models and correlation developed for different classes of fluids and channel geometries. Using the insights derived from the pure ammonia model, an improved zeotropic condenser design method for high-temperature-glide ammonia/water mixtures in small diameter channels, based on the non-equilibrium film theory, is introduced. The key features of the improved model are the consideration of annular and non-annular flow effects on liquid film transport, including condensate and vapor sensible cooling contributions, and accounting for mini/microchannel effects through the new liquid film correlation.

The investigation on condensation performance of gas/steam mixtures with the fine coal particles in a vertical channel

Theoretical and experimental study is conducted to investigate the condensation heat transfer characteristics of mixed gas with fine coal particles in this paper. The visualization experiments of fine coal particles striking the film and mixed gas condensation heat transfer experiments in a vertical channel are carried out. Mixed gases contain different proportions of N2, steam and fine coal particles. The theoretical model of particles flicking condensate film is established. Results show that fine coal particles can penetrate the condensate film and flow inside the film when the particle diameter and the incidence velocity meet the conditions of penetrating judgment. The Nu number of heat transfer and the mass of the condensation decrease with the increase of the diameter and the concentration of the particles in the mixed gases.

Dropwise steam condensation on various hydrophobic surfaces: Polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), and self-assembled micro/nano silver (SAMS)

Drop-wise condensation (DWC) phenomena are closely related to hydrophobic promoters. In this study, various hydrophobic coatings such as PPS, PTFE, and self-assembled micro/nano silver were fabricated using surface treatments, with plain copper as a reference. Fabricated surfaces were examined by scanning electron microscope, contact angle measurements, and condensation heat transfer experiments. Heat fluxes were measured, and DWC population densities were recorded and compared. Results showed that surface morphologies and wetting behaviors directly affected drop sizes and population densities. When steady-state was reached, superhydrophobic surfaces showed poor condensation heat transfer compared to the self-assembled micro/nano silver deposited surface. It is assumed that contact angle hysteresis induced strong pinning along condensate periphery, which hindered rolling-off motion and droplet renewal rates. Also, durability of performance of the self-assembled layer coating was demonstrated.

20315 凝縮熱伝達に及ぼす各種表面金属薄膜の影響

The present study was intended to examine how the condensation heat transfer, especially the dropwise condensation, was affected by modifying the surface nature. In the present study, condensation heat transfer experiments for steam were performed by using mirror-finished copper surface and some very thin metal-film surfaces by using sputtering on mirror-finished copper block. That is, the effects on pattern of condensation heat transfer, i.e., dropwise or film-wise condensation, of metal-sputtered surfaces were examined experimentally and qualitatively. The present experimental results showed that the condensation on sputtered metal surfaces of Chromium(Cr), became dropwise condensation. The heat transfer coefficients were ten times higher than the Nusselt equation. The condensation on Copper block(Cu-bare), Titanium block(Ti-bare), and sputtered metal surface of Titanium(Ti) became filmwise condensation.

Neural Network Based Analyses for the Determination of Evaporation Heat Transfer Characteristics During Downward Flow of R134a Inside a Vertical Smooth and Corrugated Tube

The heat transfer characteristics of the refrigerant HFC–134a are investigated, such as convective heat transfer coefficient and pressure drop during evaporation inside a vertical smooth and five pieces of corrugated tube, using experimental data with the aim of numerically determining the best artificial intelligence method. The double tube test sections are 0.5 m long with refrigerant flowing in the inner tube and heating water flowing in the annulus. Input of the ANNs are the 14 numbers of dimensional and dimensionless values of test section, such as mass flux, heat flux, temperature difference between the tube wall and saturation temperature, average vapour quality, evaporating temperature, two-phase friction factor, two-phase multiplier, liquid and vapour Reynolds numbers, Bond number, Froude number, Weber number, depth of corrugation and helix angle for the tested corrugated tubes, whereas the outputs of the ANNs are the experimental condensation heat transfer coefficient and measured pressure drop from the analysis. The evaporation heat transfer characteristics of R134a are modelled to decide the best approach, using several ANN methods such as multi layer perceptron (MLP) and radial basis networks (RBFN). The performance of the method of MLP with 10-5-1 architecture and RBFNs with the spread coefficient of 100,000 and a hidden layer neuron number of 200 were found to be in good agreement, predicting the evaporation heat transfer coefficient and pressure drop. Dependency of outputs of the ANNs from input values is investigated and new ANN-based heat transfer coefficient correlations are developed as a result of the analyses.

Experimental study on condensation heat transfer and pressure drop in horizontal smooth tube for R1234ze(E), R32 and R410A

Experimental condensation heat transfer and pressure drop of R1234ze(E), trans-1, 3, 3, 3-tetrafluoropropene (trans-CHFCHCF3) in a horizontal smooth tube are measured and compared with R32 and the nearly azeotropic HFC refrigerant blend R410A. The effects of mass flux and saturation temperature on heat transfer and pressure drop have been conducted and analyzed. The copper tube with inner diameter of 4.35mm and length of 3.6m was used as the test sections. The tests were conducted for mass fluxes varying from 150 to 400kg(m−2s−1) and the saturation temperature ranging between 35 and 45°C over the vapor quality range 0.0–1.0. It was found that the experimental heat transfer performance of R1234ze(E) was about 20–45% lower than R32 but 10–30% higher than R410A for saturation temperature 40°C. The experimental results are compared with some well-known existing prediction methods of condensation of pure refrigerant.

Experimental study on condensation heat transfer in vertical minichannels for new refrigerant R1234ze(E) versus R134a and R236fa

Experimental condensation heat transfer data for the new refrigerant R1234ze(E), trans-1,3,3,3-tetrafluoropropene, are presented and compared with refrigerants R134a and R236fa for a vertically aligned, aluminum multi-port tube. Local condensation heat transfer measurements with such a multi-microchannel test section are very challenging due to the large uncertainties related to the heat flux estimation. Presently, a new experimental test facility was designed with a test section to directly measure the wall temperature along a vertically aligned aluminum multi-port tube with rectangular channels of 1.45 mm hydraulic diameter. Then, a new data reduction process was developed to compute the local condensation heat transfer coefficients accounting for the non-uniform distribution of the local heat flux along the channels. The condensation heat transfer coefficients showed the expected decrease as the vapor quality decreased (1.0–0.0) during the condensation process, as the mass velocity decreased (260–50 kg m −2 s −1) and as the saturation temperature increased (25–70 °C). However, the heat transfer coefficients were not affected by the condensing heat flux (1–62 kW m −2) or by the entrance conditions within the tested range. It was found that the heat transfer performance of R1234ze(E) was about 15–25% lower than for R134a but relatively similar to R236fa. The experimental data were then compared with leading prediction methods from the literature for horizontal channels. In general, the agreement was poor, over-predicting the high Nusselt number data and under-predicting the low Nusselt number data, but capturing the mid-range quite well. A modified correlation was developed and yielded a good agreement with the current database for all three fluids over a wide range of operating conditions.