Azeotropic Refrigerant Research Articles

Coefficients d'échange locaux au cours de l'ébullition du R22 et du R407C dans des tubes horizontaux, lisse ou micro-aileté

The purpose of this study is to experimentally investigate forced convective boiling. The heat transfer coefficients of pure refrigerant R22 and non azeotropic refrigerant mixture R407C were measured in both a smooth tube and a microfin tube. The tests have been carried out with a uniform heat flux all along the tube length. The refrigerant mass flux was varied from 100 to 300 kg m −2 s −1 and heat fluxes from 10 to 30 kW m −2. Local heat transfer coefficients depend strongly on heat flux at a low quality and on mass fluxes at a high quality. When compared to smooth tube, the microfin tubes exhibit a significant heat transfer enhancement, up to 180%. In comparison to R22, the R407C heat transfer coefficients of smooth and microfin tubes are 15 to 35% lower, respectively. The best heat transfer enhancement is obtained at low heat flux and mass flow rate.

Boiling characteristics of ternary mixtures inside enhanced surface tubing

Two phase flow characteristics such as coefficient of heat transfer and pressure drop observed during boiling of ternary azeotropic refrigerant mixtures R-404A (R-125/RR--134a/R-143a:44/4/52), R-407B (R-32/R-125/R-134a: 10/70/20), R-407C (R-32/R-125/R-134a:23/25/52) and R-408A (R-22/R-125/R-143a:46/7/47) are presented and analyzed in this paper. Experiments showed that for Reynolds numbers higher than 4.5 E04, R-408A and R-404A appear to have greater heat transfer rates than the other blends under investigation. Furthermore, it is quite evident from this data that at higher Reynolds number R-404A and R-408A have the highest pressure drop while R-407 experiences the lowest pressure drop among the refrigerants under investigation.

Heat transfer of ternary mixtures inside enhanced surface tubing

Two phase flow heat transfer parameters such as coefficient of heat transfer and pressure drop observed during condensation of ternary azeotropic refrigerant mixtures R-404A (R125/Rl34a/R143a:44/4/52), R-407B (R32/R125/R134a:10/70/20), R407C (R32/R125/R 134a:23/25/52) and R408A (R22/R125/R143a:46/7/47) are presented in this paper. Experiments showed that for Reynolds numbers higher than 3.00 E06, R-408A appears to have greater heat transfer rates than the other blends under investigation. Furthermore, it is quite evident from this data that R-407C has the highest pressure drop among the refrigerants under investigation.

Flow Pattern, Heat Transfer and Pressure Drop in Flow Condensation Part I: Pure and Azeotropic Refrigerants

This study concerns the flow pattern, heat transfer, and pressure drop for flow condensation. The experimental results are recorded in tests with a smooth horizontal tube of 6 mm inner diameter and 2 to 10 m long. This manuscript, which is part I of a two part series, focuses on pure and azeotropic fluids. Part II describes results with non-azeotropic refrigerant mixtures. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with pure and azeotropic fluids in this work. However, the Froude number is found to be a good additional indicator to identify transition between annular and wavy flows. The transition occurs mostly at Fr = 15 to 20 for both pure and azeotropic fluids. In the case of pure and azeotropic fluids, the heat transfer coefficient was found to be independent of the mass flux in wavy flow regions, but increased with an increasing mass flux in the annular flow regions. For pure and azeotropic fluids, a modified Tandon et al. correlation agreed best with experimental data from tests with R-12, R-22, R-134a, and R-502. For the local pressure drop it is correlated within ±15% by using the Lockhart-Martinelli parameters. The experimental data for pure and azeotropic refrigerants can be predicted by using a correlation for overall pressure drop.

Performance enhancement of some alternatives to R-502

The results of an experimental study on the behaviour of some new alternatives to R-502 using heated suction accumulator are presented. The experimental set up was composed of a fully instrumented air-source heat pump with a capacity of 12000 BTUH and equipped with a heated suction accumulator. The refrigerant temperatures were varied at the evaporator entrance to simulate various extreme conditions encountered in air-source heat pump applications. The primary parameters observed during the course of this study were mass flux, heat flux, quality evaporator and condenser thermal capacities, power consumed and pressure ratios for the azeotropic refrigerant mixtures under investigation. The test results showed that a heated suction accumulator enhanced the evaporation of more volatile component of ternary azeotropic refrigerant mixtures. Thus, increasing the mixture thermal capacity as well as the COP. Furthermore, experiments have also shown capacity increases of 27 per cent with a heat accumulator over an unheated accumulator at - 15°C outside air temperatures.

Performance enhancement of some alternatives to R‐502

The results of an experimental study on the behaviour of some new alternatives to R-502 using heated suction accumulator are presented. The experimental set up was composed of a fully instrumented air–source heat pump with a capacity of 12000 BTUH and equipped with a heated suction accumulator. The refrigerant temperatures were varied at the evaporator entrance to simulate various extreme conditions encountered in air–source heat pump applications. The primary parameters observed during the course of this study were mass flux, heat flux, quality evaporator and condenser thermal capacities, power consumed and pressure ratios for the azeotropic refrigerant mixtures under investigation. The test results showed that a heated suction accumulator enhanced the evaporation of more volatile component of ternary azeotropic refrigerant mixtures. Thus, increasing the mixture thermal capacity as well as the COP. Furthermore, experiments have also shown capacity increases of 27 per cent with a heat accumulator over an unheated accumulator at −15°C outside air temperatures. Copyright © 2000 John Wiley & Sons, Ltd.

Prediction of convective boiling characteristics of alternatives to R-502 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of alternative azeotropic refrigerant mixtures to R-502 on air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R-502; such as R-507, R-404A, R-407B, and R-408A in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture’s pressure drop is a weak function of the mixture’s composition. It was found that the correlations were applicable to the entire heat and mass flux, investigated in the present study for the proposed blends under question. The deviation between the experimental and predicted values for the heat transfer coefficient and pressure drop were less than ±20% and 35%, respectively, for the majority of data.

Prediction of two-phase condensation characteristics of some alternatives to R-22 inside air/refrigerant enhanced surface tubing

The results of an experimental study on the heat transfer characteristics of two-phase flow condensation of some azeotropic refrigerant mixtures, proposed as alternatives to R-22, on air/refrigerant horizontal enhanced surface tubing are presented. The condensation data indicated that the heat transfer coefficient of the blend R-408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R-507 and R-404A have similar heat transfer rates to that of R-22 when plotted against the refrigerant mass flow rate. It can also be observed that, as the mass flux increases, the heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of alternatives to R-22 such as R-507, R-404A, R-407C and R-408A, as well as R-410A in two-phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two-phase flow heat transfer condensation data. Copyright © 2000 John Wiley & Sons, Ltd.

Prediction of condensation characteristics of alternatives to R-502 inside air–refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow condensation of alternative azeotropic refrigerant mixtures to R-502, on air/refrigerant horizontal enhanced surface tubing, is presented. The condensation data indicated that the heat transfer coefficient on the blend R-408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R-502 and R-407B have similar heat transfer rates when plotted against the refrigerant mass flow rate. It also can be observed that, as the mass flux increases, heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R-502; such as R507, R404A, R407B and R408A in two-phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two-phase flow heat transfer condensation data.

Behaviour of ternary blends in heated suction accumulator

The results of an experimental study on the behaviour of azeotropic ternary refrigerant mixtures in heated suction accumulator are presented. The experiment set up was composed of a fully instrumented air-source heat pump with a capacity of 36 000 BTUH and equipped with a heated suction accumulator. Standard test conditions were used at the condenser inlet; however, the refrigerant temperatures were varied at the evaporator entrance from 2 to −40°C, to simulate various conditions encountered in extreme air-source heat pump applications. The primary parameters observed during the course of this study were mass flux, heat flux, and quality, evaporator and condenser thermal capacities, and power consumed and pressure ratios for the azeotropic refrigerant mixtures under investigation. The test results showed that heated suction accumulators enhance the evaporation of the more volatile component of ternary azeotropic refrigerant mixtures. Thus, increasing the mixture thermal capacity as well as the coefficient of performance (COP). Furthermore, experiments have also shown capacity increases of 27% with heated accumulator over unheated accumulator at −30°C outside air temperatures. Copyright © 1999 John Wiley & Sons, Ltd.

Performance Evaluation of Heat Exchanger using Alternative Refrigerant R407C.

R22 (HCFC22) has been widely used as the refrigerant in refrigerators and air conditioners. According to the Montreal protocol for ozone layer protection, the total amount of HCFCs was capped from the beginning of 1996. Zeotropic refrigerant mixture R407C and azeotropic refrigerant mixture R410A have been selected as the promising alternative refrigerants of R22. This paper examined the passage of R407C refrigerant in heat exchangers through simulation, and obtained the following results. In the heat exchangers used in heat pump type room air conditioners, a counter flow configuration when operating as condenser had high efficiency. In outdoor heat exchangers operating as evaporators, a configuration that restrained temperature glide by partly reducing refrigerant passage had not only high efficiency but also reduced the formation of frost on coils.

Two phase flow heat transfer of binary mixtures inside enhanced surface tubing

The primary heat transfer parameters such as coefficient of heat transfer and pressure drop observed during condensation of binary azeotropic refrigerant mixtures R-410a (R125/R32: 50/50), and R-507 (R125/R143a: 50/50) are presented in this paper. Experiments showed that for Reynolds numbers higher than 4.2 E06, R-410a appears to have greater heat transfer rates more than the other blends under investigation. Furthermore, it is quite evident from this data that R-507 has the highest pressure drop among the refrigerants under investigation.

Results of experimental and theoretical studies of the azeeotropic refrigerant R507

For a blend containing R143a and R125 ( 50 50% by weight), thermodynamic data like vapour pressures, liquid densities, as well as the volumetric behaviour of the gaseous phase, have been experimentally measured and mathematically correlated. This refrigerant blend shows azeotropic behaviour and is known as R507 according to the ASHRAE nomenclature. For use in refrigeration and air-conditioning units in low and medium temperature applications, R507 is a suitable refrigerant. Test results based on measurements from a refrigeration installation have shown that similar operating parameters can be achieved in comparison to R502. The compressor discharge temperatures, pressure ratios and coefficients of performance compare well to the traditionally used azeotropic refrigerant R502. Further, the tests have shown that on average the refrigerating capacities of R507 are approximately 5–6% higher than the capacities of R502.

Heat transfer and pressure drop characteristics of HFC quaternary refrigerant mixtures inside horizontal enhanced surface tubing

Heat transfer characteristics of two-phase flow condensation and boiling of quaternary (four components) refrigerant mixtures, on air/refrigerant horizontal enhanced surface tubing are presented, discussed and compared to other refrigerants proposed as substitutes for CFC-502, such as R-507 and R-407B. Heat transfer characteristics, such as average heat transfer coefficients, as well as pressure drops of ternary azeotropic refrigerant mixtures, flow condensation and boiling inside enhanced surface tubing, were predicted. Experimental data showed that our proposed quaternary blend has a superior boiling heat transfer coefficient and higher pressure drop compared to CFC-502.

Performance Evaluation of Two Azeotropic Refrigerant Mixtures of HFC-134a With R-290 (Propane) and R-600a (Isobutane)

The reduction in chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) production and the scheduled phase-out of these ozone-depleting refrigerants require the development and determination of environmentally safe refrigerants for use in heat pumps, water chillers, air conditioners, and refrigerators. This paper presents a performance evaluation of a generic heat pump with two azeotropic refrigerant mixtures of HFC-134a (1,1,1,2-tetrafluoroethane) with R-290 (propane) and R-600a (isobutane); R-290/134a (45/55 by mass percentage) and R-134a/600a (80/20 by mass percentage). The performance characteristics of the azeotropes were compared with pure CFC-12, HFC-134a, HCFC-22, and R-290 at the high temperature cooling and heating conditions including those using liquid-line/suction-line heat exchange. The coefficient of performance of R-290/134a is lower than that of HCFC-22 and R-290, and R-134a/600a shows higher coefficient of performance than CFC-12 and HFC-134a. The capacity for R-290/134a is higher than that for HCFC-22 and R-290, and R-134a/600a exhibits higher system capacity than CFC-12 and HFC-134a. Experimental results show that the discharge temperatures of the studied azeotropic mixtures are lower than those of the pure refrigerants, CFC-12 and HCFC-22.

Modelled performance of non-chlorinated substitutes for CFC11 and CFC12 in centrifugal chillers

A number of partially fluorinated alkanes and ethers were identified from earlier technical publications and from a joint Electric Power Research Institute/Environmental Protection Agency (EPRI/EPA) project as potential alternatives for chloroflurocarbon (CFC) and hydrogen-containing CFC refrigerants. These larger molecules, by virtue of their more elaborate structure, have larger vapour phase heat capacities ( C ps) and larger molecular weights than currently used refrigerants, which result in decreased volumetric capacities and greater flash gas losses in simple cycle applications. The compounds were fitted to the Lee-Kessler-Plöcker and Carnahan-Starling-DeSantis equations of state, and refrigerant property routines based on these equations were used to simulate their performance in a single-stage centrifugal chiller as pure refrigerants and nearly azeotropic refrigerant mixtures. Consideration was given to the effects of acoustic velocity in the refrigerant, rotational mach numbers, the application of superheat prior to the compressor inlet to avoid ‘wet isentropic compression’, and liquid subcooling before isenthalpic expansion. Results indicate that several chlorine-free compounds give modelled chiller performance comparable to R11 and R123 and better than R12 and R134a. Blends of these refrigerants may be required to mitigate the inflammability of alternatives that show the best performance. Modifications to the basic chiller cycle — such as liquid subcooling and suction gas superheat — may offer unique advantages for more complicated, larger refrigerant molecules. An algorithm based on molecular bond energies and vapour phase C ps was used to estimate the flammability of these alternatives and of blends made from them. Depending on desirable and permissible deviations from the currently used chiller operating conditions and on the acceptability of flammable refrigerant combinations, ideal coefficients of performance comparable to R11 and 5–10% better than R12 are indicated.

Introduction to the development programme of an azeotropic refrigerant mixture of CFC 12 and dimethylether

In 1987 AKZO applied for patents regarding the application of mixtures of dimethylether (DME) and dichlorodifluoromethane (CFC 12) as refrigerants. Mixture ratios range, according to the patent application, between 12 and 35% DME (% by weight). Special emphasis is currently given to the non-flammable mixture of 13% DME and 87% CFC 12. This particular azeotropic refrigerant mixture is proposed by AKZO as a temporary substitute for CFC 12, pending the introduction of suitable alternative refrigerants. It is an attractive temporary substitute, because it can replace CFC 12 in many applications without major retooling and without deterioration of refrigerating performance. Because of its reduced CFC 12 content, substitution of CFC 12 with an azeotropic mixture of CFC 12 and DME gives an immediate reduction of CFC 12 emissions and thus reduces the potential for stratospheric ozone depletion. The present Paper gives an overview of the development programme after its initiation in 1984. The programme addresses the following areas: Refrigerating performance. Experiments comparing CFC 12 and the azeotropic mixture of CFC 12 and DME in domestic, automobile and industrial refrigerating units. Theoretical analysis. Thermodynamics. Theoretical prediction of thermodynamic properties. Experimental determination of azeotropic behaviour. Flammability. Experiments for ranges of mixture ratios. Toxicity. Chemical decomposition studies. Toxicity testing. Endurance and reliability. Oil compatibility. Corrosion and wear testing in domestic refrigerators. Compatibility with synthetic materials. Effusion tests. The progress in these areas is described and further planned activities are discussed.

Estimation and application of thermodynamic properties for a non-azeotropic refrigerant mixture

The use of an azeotropic refrigerant mixture of R 131B1 and R 152a to replace R 22 in an air-to-air heat pump with an accumulator and capillary tube expander is discussed. The Redlick-Kwong-Soave equation of state provides a convenient method for generating thermodynamic data needed for this mixture.