Non-azeotropic Refrigerant Mixtures Research Articles

Prediction method for evaporation heat transfer of non-azeotropic refrigerant mixtures flowing inside internally grooved tubes

Local heat transfer coefficients were experimentally measured for evaporation of R417A (R125/R134a/R600) flowing inside horizontal smooth and two internally grooved tubes with different geometrical parameters. The experimental results of R417A inside different test tubes were analyzed and compared with existing correlations; several microfin correlations failed to predict heat transfer coefficients of refrigerant mixtures and could not express the local variation of heat transfer coefficients during the evaporation. Based on the experimental data of R417A, an empirical correlation for microfin tubes was developed by introducing the enhancement factors into the modified Kattan model. The comparison of the calculations and the experimental results reveals that the microfin correlation suggested at the present study generally predicts experimental data with a deviation of ±30% for vapor qualities below 80% and also expresses the local variation of heat transfer coefficients for refrigerant mixtures evaporating inside microfin tubes.

Condensation heat transfer coefficients of binary HFC mixtures on low fin and Turbo-C tubes

In this study, external condensation heat transfer coefficients (HTCs) are measured for nonazeotropic refrigerant mixtures (NARMs) of HFC32/HFC134a and HFC134a/HCFC123 on a low fin and Turbo-C tubes. All measurements are taken at the vapor temperature of 39 °C with the wall subcooling of 3–8 °C. Test results showed that condensation HTCs of NARMs on enhanced tubes were severely degraded from the ideal values showing up to 96% decrease. HTCs of the mixtures on Turbo-C tube were degraded more than those on low fin tube such that HTCs of the mixtures at the same composition were similar regardless of the tube. The mixture with larger gliding temperature differences (GTDs), HFC134a/HCFC123, showed a larger heat transfer reduction from the ideal values than the mixture with smaller GTDs, HFC32/HFC134a. Heat transfer enhancement ratios of the enhanced tubes with NARMs were almost 2 times lower than those with pure refrigerants and they decreased more as the GTDs of the mixtures increased.

Condensation heat transfer coefficients of halogenated binary refrigerant mixtures on a smooth tube

In this study, external condensation heat transfer coefficients (HTCs) of nonazeotropic refrigerant mixtures of HFC32/HFC134a and HFC134a/HCFC123 at various compositions were measured on a horizontal smooth tube of a 19 mm outside diameter. All data were taken at the vapor temperature of 39 °C with a wall subcooling of 3–8 °C. Test results showed that HTCs of the tested mixtures were 19.4–85.1% lower than the ideal values calculated by the mole fraction weighting of the HTCs of the pure components. A thermal resistance due to the diffusion vapor film seemed to be partly responsible for the significant reduction of HTCs with these nonazeotropic mixtures.

Condensation heat transfer coefficients of R22, R407C, and R410A on a horizontal plain, low fin, and turbo-C tubes

In this study, condensation heat transfer coefficients (HTCs) were measured on a horizontal plain tube, low fin tube, and Turbo-C tube at the saturated vapor temperature of 39 °C for R22, R407C, and R410A with the wall subcooling of 3–8 °C. R407C, a non-azeotropic refrigerant mixture, exhibited a quite different condensation phenomenon from those of R22 and R410A and its condensation HTCs were up to 50% lower than those of R22. For R407C, as the wall subcooling increased, condensation HTCs decreased on a plain tube while they increased on both low fin and turbo-C tubes. This was due to the lessening effect of the vapor diffusion film with a rapid increase in condensation rate on enhanced tubes. On the other hand, condensation HTCs of R410A, almost an azeotrope, were similar to those of R22. For all refrigerants tested, condensation HTCs of turbo-C tube were the highest among the tubes tested showing a 3–8 times increase as compared to those of a plain tube.

Calculation of NARM’s equilibrium with Peng-Robinson equation of state

The liquid molar volumes of nonazeotropic refrigerant mixtures (NARM), calculated with Peng Robinson (PR) equation, were compared with vapor -liquid equilibrium experimental data in this paper. Provided with co-reaction coefficient kij, the discrepancies of liquid molar volume data for R22+R114 and R22+R142b using PR equation are 7.7% and 8.1%, respectively. When HBT (Hankinson-Brobst-Thomson) equation was joined with PR equation, the deviations are reduced to less than 1.5% for both R22+R114 and R22+R142b.

THERMODYNAMIC PROPERTY VARIATION OF NONAZEOTROPIC REFRIGERANT MIXTURES (NARMs) IN THE TEMPERATURE GLIDING ZONE

The relations among enthalpy, temperature and quality of nonazeotropic refrigerant mixtures (NARMs) in the phase change region (temperature gliding region) are investigated to seek a possibility for linear approximations. Using REFPROP, a refrigerant property calculation package developed by NIST, temperature-enthalpy, temperature-quality, quality-enthalpy relations are investigated for 4 binary and 15 ternary NARMs. Those 19 NARMs tested are the most promising alternative refrigerants for conventional CFC and HCFC refrigerants. A normalized enthalpy. which is a pseudo-quality in a sense, is defined based on the dew and bubble point enthalpies to compare with the conventional quality. The results show that the pseudo-quality and the conventional quality are almost identical independent of system pressure for all the NARMs tested while enthalpy-temperature and quality-temperature relations are diverse and highly pressure dependent depending on mixture combinations. The significance of the near-identical relation between the two qualities is that the easy-to-calculate pseudo-quality can replace quality in convective heat transfer coefficient representations.

Flow Pattern, Heat Transfer and Pressure Drop in Flow Condensation Part II: Zeotropic Refrigerant Mixtures (NARMs)

This paper, which is part II of a study on flow condensation is focused on zeotropic (or non-azeotropic) refrigerant mixtures (NARMs). In the experiments, condensation in a horizontal tube of inner diameter 6 mm and 10 m length were studied with fluids R-404A, R-407C, and three mixtures of R-32 and R-134a. A flow pattern map by Tandon et al. (1982) roughly predicts flow patterns associated with NARMs studied in this work. Most tests recorded are in the annular or semi annular flow region. The Froude number is, however, found to be an additional indicator to identify transition between annular and wavy flows. The transition in the experiments occurs mostly at Fr = 15 to 20 for the fluids tested. For NARMs with a small temperature glide (e.g. R-404A), as observed in the case of pure and azeotropic fluids, the heat transfer coefficient is independent of the mass flux in wavy flow regions, and increases with an increasing mass flux in annular flow regions. For other NARMs tested, the heat transfer coefficient (starting from a lower level) always increases with an increasing mass flux within the tested ranges. The heat transfer data from the tests with R-404A, R-407C, and R-32/R-134a mixtures can be predicted reasonably well by a modified Tandon et al. (1985b, 1995) equation with a correction proposed by Granryd (1989) for NARMs. The classical correlations for the pressure drop do not work well. Instead, the data for local pressure drop are correlated within ±15% by means of the same correlation as for the pure and azeotropic fluids. A simple correlation for the overall pressure drop based on the experimental data for pure and azeotropic fluids is good also for R-404A (with a small glide), but overpre-dicts the pressure drop (by up to 50%) for NARMs with glide, such as R-407C.

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.

Thermodynamic Performance of Nonazeotropic R-134a/R-143a Refrigerant Mixtures

A study of the thermodynamic performance of nonazeotropic refrigerant mixtures (NARMs) involving R-143a/R-134a was completed. The aim of the study was to identify possible replacements for R-12. Two refrigeration cycles were considered, the vapor-compression cycle and the internal heat exchanger cycle. Our results suggest that the nonazeotropic R-143a/R-134a mixtures studied yield comparable performance to R-12 when the internal heat exchanger cycle is used.

Thermostatic valve control using a non-azeotropic refrigerant, isobutane/propane mixture

This article describes the evaluation and comparison of a conventional R12 cross-charged thermostatic valve and an electronic expansion valve using a non-azeotropic refrigerant mixture (NARM); isobutane/propane mixture (CARE30). The superheat temperature setting on an expansion valve needs to compensate for the temperature glide associated with a non-azeotropic refrigerant as these can be of similar magnitude. It is also advisable to increase the superheat setting to make allowance for change in refrigerant composition as a result of preferential refrigerant/oil solubility. The majority of refrigeration systems operate at fixed evaporating temperatures, hence, once superheat setting is trimmed during commissioning, then there should be no further problems associated with evaporation of a non-azeotropic refrigerant provided the system is leak-tight. An R12 expansion valve with a factory superheat setting of 5°C tested over a wide range of evaporating temperatures proved satisfactory in operation with CARE30 after increasing the superheat temperature screw setting equivalent to 5°C.

Determination of optimum working conditions in heat-pumps using nonazeotropic refrigerant mixtures

The objective of this work is to investigate experimentally the effects of mixture concentrations, source temperature, flow rate of condenser cooling water and air flow rate in the cooling tower on the Coefficient of performance (COP) and η ex (exergetic efficiency) values of vapour compression heat pump systems. The experimental apparatuses consist of a vapour compression heat pump conducting according to the liquid to air principle, refrigerant mixture unit, cooling tower, measuring elements and other auxiliary equipment. Refrigerants R11, R12, R22 and six of their binary mixtures which contain about 25%, 50% and 75% mass fractions of R22 were tested. The experiments were performed in the region of source temperatures from 18 to 28°C and flow rates of condenser cooling water from 500 to 1250 kg/h. Four different air flow rates were chosen in those experiments in the cooling tower. To determine the efficiency of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. In this study, it was observed that the COP and η ex increased with the addition of R22 to the system over R11 and R12 pure refrigerants.

Experimental and theoretical study on flow condensation with non-azeotropic refrigerant mixtures of R32/R134a

Experiments on flow condensation have been conducted with both pure R32, R134a and their mixtures inside a tube (10 m long, 6 mm ID), with a mass flux of 131–369 kg m −2s −1 and average condensation temperature of 23–40°C. The experimental heat transfer coefficients are compared with those predicted from correlations. The maximum mean heat transfer coefficient reduction (from a linear interpolation of the single component values) occurs at a concentration of roughly 30% R32 for the same mass flux basis, and is approximately 20% at Gr = 190 kg m −2s −1, 16% at Gr = 300 kg m −2s −1. Non-ideal properties of the mixture have a certain, but relatively small, influence on the degradation. Among others, temperature and concentration gradients, slip, etc. are also causes of heat transfer degradation.

The optimal design of refrigerant mixtures for a two-evaporator refrigeration system

The use of liquid-phase mixtures is common in a number of industrial applications. Mixtures have certain advantages over individual components, and these have been exploited advantageously. For the case of refrigerants, a number of azeotropic mixtures are used in practise. The use of non-azeotropic refrigerant mixtures, however, is not as common. This paper looks at the design of refrigerant mixtures for a refrigeration cycle consisting of two evaporators operating at two different temperatures. Such a cycle has been proposed for use in, for example, a commercial refrigerator having a separate freezer section. Compared to the single evaporator cycle operating at the freezer temperature and circulating the cold air from the freezer to the rest of the refrigerator, the double-evaporator cycle can give higher efficiencies since cooling is not done at a lower temperature than what is required. Also, the use of nonazeotropic mixtures has a number of advantages over single component refrigerants and azeotropic mixtures. A mathematical programming approach developed earlier is applied to the double-evaporator cycle to obtain refrigerant mixtures that maximize cooling.

Experimental study on convective boiling heat transfer for pure refrigerants and refrigerant mixtures in a horizontal tube

Boiling heat transfer coefficients of pure refrigerants (R22, R32, R134a, R125, R290, and R600a) and refrigerant mixtures (R32/Rl34a, R290/ R600a, and R32/R125) are measured experimentally and compared with Chen's correlation. The test section is a seamless stainless steel tube with inner diameter of 7.7mm and uniformly heated by applying electric current directly to the tube. Heat fluxes range from 10 to 30kW. Mass fluxes are set to 424 ~ 742kg/ms for R22, R32, R134a, R32/R134a, and R32/Rl25 ; 265 ~ 583kg/ms for R290, R600a, and R290/R600a. Heat transfer coefficients depend strongly on heat flux at a low quality region and become independent as quality increases. Convective boiling term in the Chen's correlation predicts experimental data of the pure refrigerants fairly well (relative error of 12.1% for the data of quality over 0.2). The correlation for pure substances overpredicts the heat transfer coefficients for nonazeotropic refrigerant mixtures.

Forced convective condensation of nonazeotropic refrigerant mixtures in horizontal annulus with petal shaped fin tubes

In this paper, condensation performance in horizontal annulus was compared with a smooth tube, one Saw-Tooth Finned tube (STF tube), four Petal Shaped Fin tubes (PF tubes), using R113, R11 and their mixtures (vapor molar fractions of R11 at the test section inlet were 0.384, 0.588 and 0.809) as working fluid. The mass flux at the test section ranged from 15–220 kg/m2s. Camera and video camera were used to shoot the flow pattern and condensation phenomena.

Condensation of Nonazeotropic Binary Refrigerant Mixtures Including R22 as a More Volatile Component Inside a Horizontal Tube

Condensation of Nonazeotropic Binary Refrigerant Mixtures Including R22 as a More Volatile Component Inside a Horizontal Tube

95/01912 Forces convective condensation and boiling of ternary non-azeotropic refrigerant mixtures inside water/refrigerant enhanced surface tubing

95/01912 Forces convective condensation and boiling of ternary non-azeotropic refrigerant mixtures inside water/refrigerant enhanced surface tubing

95/00761 Heat exchanger analysis for nonazeotropic refrigerant mixtures

A fundamental method for analyzing heat exchangers using pure refrigerants and nonazeotropic refrigerant mixtures is presented. The method allows for calculation of heat and mass transfer between moist air and nonazeotropic refrigerant mixtures and predicts local parameters of air and mixtures. Both single and two phase refrigerants can be analyzed with this method. Algorithms for the use of this model are presented. Data and calculated thermal performance for two conventional types of air-side geometries are also presented. The algorithms to calculate thermal performance of heat exchangers can be used for either conventional or enhanced geometries. A comparison of crossflow, cross-counterflow, and counterflow heat exchangers is given. The algorithms are sufficient for design and development of equipment using pure and mixed refrigerants.

Numerical prediction of heat pump dynamic behaviour using ternary non-azeotropic refrigerant mixtures

A lumped parameter model presented in this paper, to predict the dynamic behaviour, is an extension of binary modelling of heat pumps with non-azeotropic refrigerant mixtures. The mathematical formulation of this model is based on mass, momentum, and energy balances. Several constitutive relationships are adopted in this model to describe the different phenomena encountered during heat pump operation with special emphasis on newly developed correlations to predict heat and mass transfer. In addition, the proposed model includes the consequent effect of different refrigerant flow regimes and slip between the two phases. Extensive simulations showed that the present model predicts fairly the heat pump dynamic response using ternary non-azeotropic refrigerant mixtures, and compress well with experimental data under various geometries and conditions.

Forced convective condensation and boiling of ternary non-azeotropic refrigerant mixtures inside water/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two-phase flow condensation and boiling of ternary non-azeotropic refrigerant mixtures, on water/refrigerant horizontal enhanced surface tubing, is presented. The enhanced surface tubing data showed a significant enhancement of the heat transfer compared to an equivalent smooth tube depending on the mixture components and their concentrations. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of ternary non-azeotropic refrigerant mixture flow condensation, and 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.