Non-azeotropic Refrigerant Mixtures Research Articles

Condensation heat transfer of binary and ternary mixtures inside multiport tubes

This study investigated the condensation heat transfer of pure refrigerants and binary and ternary mixtures inside horizontal multiport tubes with multiple square minichannels. The effects of mass flux, vapor quality, heat flux, channel size, and channel shape were evaluated using pure refrigerants R32 and R1234yf; binary mixtures R32/R1234yf, R32/R1123, R32/R13I1, and R410A; and ternary mixtures R1123/R32/R1234yf and CO2/R32/R1234yf. For pure refrigerants, the heat transfer coefficient in the annular and churn flow regimes decreased monotonically with decreasing vapor quality. By contrast, the heat transfer coefficient in the plug flow regime was higher over a wide vapor quality range because of the thin condensate film formed by surface tension. Smaller channels exhibited higher heat transfer coefficients. The square minichannels exhibited higher heat transfer coefficients than the circular minichannels, except in the region with high mass flux and high vapor quality. For binary and ternary mixtures, the heat transfer coefficients significantly decreased with decreasing mass flux and vapor quality and were strongly deteriorated at lower mass fluxes. Compared with the annular and churn flow regimes, in the plug and slug-annular flow regimes, where heat transfer through the thin liquid film was dominant, the effect of mass diffusion resistance in deteriorating heat transfer was the most pronounced. A new heat transfer model for pure refrigerants inside multiport tubes with multiple rectangular minichannels was developed considering the contributions of vapor shear stress and surface tension. The proposed model was verified using a dataset of pure refrigerants, and a mean absolute percentage error (MAPE) of 11.5% was achieved. Furthermore, a new heat transfer model that considers the heat transfer deterioration of non-azeotropic refrigerant mixtures was proposed, which could predict 508 datapoints with an MAPE of 13.3%.

Numerical simulation on shell-side flow pattern transition and heat transfer of non-azeotropic refrigerant mixture

The non-azeotropic hydrocarbon refrigerant mixture flowing across shell-side of spiral wound heat exchanger is widely used in liquefied natural gas production industry. However, the phase-change heat transfer mechanism is still lack of thorough understanding. A numerical model is presented for simulating evaporation heat transfer of non-azeotropic hydrocarbon refrigerant mixture, CH4/C2H6, across multiple spiral wound tubes. Volume of Fluid model (VOF) was used to obtain liquid–vapor interface. The heat and mass transfer rates for each component were given as source terms. Thermophysical properties of the mixture were given using mixing laws in the literature. A flow pattern map was developed based on simulation results. The flow pattern transition and heat transfer were analyzed for the mixture with several component mixing ratios. With increasing vapor quality, pure ethane and methane-ethane mixture appear different flow patterns. The pure ethane has smoother liquid film on the tube wall than the methane-ethane mixture. The increasing of methane promotes the flow pattern transition. With vapor quality of 0.2–0.3, falling film flow transfers to shear flow. Shear flow transfers to spray flow for vapor quality of 0.7–0.8, where the heat transfer coefficient starts to decrease for methane-ethane mixture. For falling film flow, the heat transfer coefficient of pure ethane is higher than the methane-ethane mixture. The outcomes may help spiral wound heat exchanger design and evaluation for liquefied natural gas production.

Тепловые диаграммы для расчета циклов холодильных машин, работающих на смесевом хладагенте

The article represents the advantages and disadvantages of refrigeration machines operating on non-azeotropic refrigerant mixtures. There has been illustrated their specific feature in comparison with pure substances: they are non-isothermal during phase transitions. It can be effective when cooling or heating flows that significantly change the temperature, and ineffective when working with volumes, where it is necessary to maintain a constant temperature. In the first case there takes place a decrease in the internal irreversibility of heat transfer processes in evaporators and condensers; in the second case - an increase. When using mixed refrigerants, it is possible to simultaneously obtain several temperature levels in a single-stage machine at the same pressure in the evaporators, they can obtain low boiling points of the refrigerant without vacuum in the evaporator and regulate the refrigeration capacity of the machine by changing the composition of the mixture. The prospects of using mixtures of working bodies of refrigerating machines have been proved. The diagrams T-S, T-ξ, i-ξ are presented allowing to calculate the cycle of the machine, to determine its operating parameters and to calculate the technical and energy characteristics. The developed thermal diagrams make it possible to accurately examine the dynamics of the boiling and condensation processes of a binary mixture, show the change in the concentration of the mixture in the vapor and liquid phases and make it possible to construct and calculate the cycle of a refrigeration machine operating on a mixed refrigerant. Examples of constructing cycles of two schemes of refrigeration machines operating on a mixed refrigerant are considered: with separation of the working substance flow and without separation. Methods for calculating the cycle are provided

An experimental study of flow condensation with non-azeotropic refrigerant mixtures of R32/R134a in microchannels

This paper aims at experimental study of heat transfer during flow condensation of a binary mixture of refrigerants R32 and R134a in a microchannel heat exchanger. The experiments were performed in a horizontal microchannel condenser with one-sided cooling. The condenser was based on 20 × 40 mm copper plate containing 21 rectangular microchannels with a section of 335 × 930 μm. The non-azeotropic mixture of R32/R134a refrigerants at molar concentrations of the initial mixture of 35% / 65% and 65% / 35% was used as a working fluid. The experiments were carried out in the mass flow range from 100 to 300 kg/m2 s and with a vapor quality from 0.05 to 1.0 at an absolute pressure in the system of up to 14 bar. The data obtained are compared with the prediction according to Silver – Bell & Ghaly method.

Numerical assessment of critical properties of nanofluids: Applications to nanorefrigerants and nanolubricants

In recent years, researchers have proposed the use of nanoparticles suspended in the working fluid (nanorefrigerants) of vapour compression refrigeration cycles so as to increase the efficiency of the system. It takes a number of variables, notably, operational parameters and thermophysical properties to make such a system to work with an advantageous performance. In this regard, near-critical properties of nanorefrigerants are of particular importance, yet they are scarce in the literature. The aim of this study is to investigate models that predict the critical temperature and density of nanorefrigerants, based on the isomorphism (corresponding states) principle. These variables were estimated using two correlations available in the literature and a third one, proposed here. As there are no experimental data to validate the model, its robustness was assessed by means of its ability to recover the properties of the base fluid (F) from critical properties of the nanofluid (N). This path is defined as N-F method, which is carried out after assessing the impact of the nanoparticles on these two parameters by isomorphism of the base fluid behaviour, named F-N method. Thermophysical properties of the base fluids were calculated using REFPROP (NIST Reference Fluid Thermodynamic and Transport Properties Database) and model calculations were performed with computing platform Matlab. The best of the three models was defined after studying data from R717, R744 and R600a mixed with seven different nanoparticle materials in the range of 1 to 5% in volume basis. Then, refrigerants R744, R410A, R134a, and R1234ze were mixed with CNT, diamond and zinc oxide nanoparticles with concentrations ranging from 1 to 5% in volume basis to study the sensitivity of the model to the saturation lines (liquid or vapour and bubble or dew points lines for nonazeotropic refrigerant mixtures) and nanoparticles' content. Results have shown that data from the liquid lines should be used, since the use of the vapour saturation line results in overestimated values of the critical parameters. Such behaviour was intensified with the nanoparticle density. A maximum concentration around 2% of nanoparticles is also suggested to guaranty the highest robustness of the model. The proposed method showed the departure of the critical parameters as a function of the quantity of carbon for linear alkanes. The shift of the critical parameters seems to have a linear relation for both the number of carbons and concentration of the considered nanoparticle. The presence of heteroelements for derivatives of propane showed a small impact of oxygen and unsaturation degree of the compound and a significant influence of fluorine.

Prediction of heat transfer coefficients for forced convective boiling of N2-hydrocarbon mixtures at cryogenic conditions using artificial neural networks

A key problem faced in the design of heat exchangers, especially for cryogenic applications, is the determination of convective heat transfer coefficients in two-phase flow such as condensation and boiling of non-azeotropic refrigerant mixtures. This paper proposes and evaluates three models for estimating the convective coefficient during boiling. These models are developed using computational intelligence techniques. The performance of the proposed models is evaluated using the mean relative error (mre), and compared to two existing models: the modified Granryd’s correlation and the Silver-Bell-Ghaly method. The three proposed models are distinguished by their architecture. The first is based on directly measured parameters (DMP-ANN), the second is based on equivalent Reynolds and Prandtl numbers (eq-ANN), and the third on effective Reynolds and Prandtl numbers (eff-ANN).The results demonstrate that the proposed artificial neural network (ANN)-based approaches greatly outperform available methodologies. While Granryd's correlation predicts experimental data within a mean relative error mre = 44% and the S-B-G method produces mre = 42%, DMP-ANN has mre = 7.4% and eff-ANN has mre = 3.9%. Considering that eff-ANN has the lowest mean relative error (one tenth of previously available methodologies) and the broadest range of applicability, it is recommended for future calculations. Implementation is straightforward within a variety of platforms and the matrices with the ANN weights are given in the appendix for efficient programming.

Error estimation of single phase effectiveness and LMTD methodologies when applied to heat exchangers with phase change

Single phase formulas based on logarithmic mean temperature difference (LMTD) or Effectiveness (ɛ-NTU) are widely and wrongly used for the thermal analysis of evaporators and condensers. Those formulas do not take into account that temperature variation during phase change is due to pressure variation and/or concentration changes when using nonazeotropic refrigerant mixtures. This paper first presents the correct evaluation of the mean temperature difference and effectiveness, for parallel and counter flow arrangements, under the hypothesis of linear temperature variation, for both evaporator and condenser cases. Then, the analytical solution is employed to evaluate the error of applying the single phase formulas of LMTD and Effectiveness to the phase change part of evaporators and condensers.

열전달 촉진관에서 HFC32/HFC152a 혼합냉매의 외부 응축열전달계수

In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC152a at various compositions were measured on both 26 fpi low-fin and Turbo-C enhanced tubes, of 19.0 mm outside diameter. All data were taken at the vapor temperature of 39℃, with a wall subcooling of 3∼8 K. Test results showed that the HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by mass fraction weighting of the pure component HTCs. Also, the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased, as the wall subcooling increased, which was due to the sudden break-up of the vapor diffusion film with an increase in wall subcooling. Finally, the heat transfer enhancement ratios for mixtures were found to be much lower, than those of pure fluids.

Flow boiling heat transfer coefficients at cryogenic temperatures for multi-component refrigerant mixtures of nitrogen–hydrocarbons

The recuperative heat exchanger governs the overall performance of the mixed refrigerant Joule–Thomson cryocooler. In these heat exchangers, the non-azeotropic refrigerant mixture of nitrogen–hydrocarbons undergoes boiling and condensation simultaneously at cryogenic temperature. Hence, the design of such heat exchanger is crucial. However, due to lack of empirical correlations to predict two-phase heat transfer coefficients of multi-component mixtures at low temperature, the design of such heat exchanger is difficult.The present study aims to assess the existing methods for prediction of flow boiling heat transfer coefficients. Many correlations are evaluated against available experimental data of flow boiling of refrigerant mixtures. Silver-Bell-Ghaly correlation and Granryd correlation are found to be more suitable to estimate local heat transfer coefficients. A modified Granryd correlation is recommended for further use.

평판 표면에서 HFC32/HFC152a 혼합냉매의 풀 비등 열전달계수

Nucleate pool boiling heat transfer coefficients (HTCs) are measured with HFC32/HFC152a mixture at several compositions. All data are taken at the liquid pool temperature of 7°C, on a horizontal plain square surface of 9.53×9.53mm, with heat fluxes of 10 kW/㎡ to 100 kW/㎡ with an interval of 10 kW/㎡, in the increasing order of heat flux. Test results show that the HTCs of these mixtures are up to 45% lower than those of the ideal HTCs calculated by a linear mixing rule with pure fluids’ HTCs, due to the mass transfer resistance associated with non-azeotropic refrigerant mixtures. Pool boiling data show the deduction in HTCs with an increase in GTD of the mixture. The present mixture data agree well with five well known correlations, within 20% deviation.

非共沸混合冷媒 HFC-32/HFC-125/HFC-134aおよびHFC-32/HFC-134aの水平蒸発管内熱伝達と圧力損失

非共沸混合冷媒 HFC-32/HFC-125/HFC-134aおよびHFC-32/HFC-134aの水平蒸発管内熱伝達と圧力損失

Efficiency of vapor compression heat pumps based on non-azeotropic refrigerant mixtures

The work presents the results of cycle computation for vapor compression pumps based on ozone-safe mixed refrigerants. Non-azeotropic binary refrugerants R32/R152a (30/70) and R32/R134a (30/70) were considere as working substances. Properties of non-azeotropic refrigerants were calculated according to the additivity method of thermodynamic functions and method of Lemmon and Jacobsen. Deviations in the values of thermophysical properties obtained with two methods have been determined. It is shown that at the use of nonazeotropic mixture R32/R152a (30/70), energy conversion ratio increases by 2.2–3.6 % compared with the results for R32/R134a (30/70) at temperature difference between the processes of boiling and condensation from 28 to 53 °C.

Experimental Investigation on Flow Boiling in Micro-Channel with R32/R134a

Mechanism of flow boiling heat transfer in micro-channel and mini-channel with non-azeotropic refrigerant mixture R32/R134a is studied in this paper. Experimental research is carried out at different mass flow rate, heat flux and quality. The difference of heat transfer in two single tubes is analyzed.

Experimental investigation of moderately high temperature water source heat pump with non-azeotropic refrigerant mixtures

Experimental investigations were carried out on non-azeotropic refrigerant mixtures, named M1A (mass fraction of 20%R152a and 80%R245fa), M1B (mass fraction of 37% R152a and 63%R245fa) and M1C (mass fraction of 50%R152a and 50%R245fa), based on a water-to-water heat pump system in the condensing temperature range of 70–90 °C with a cycle temperature lift of 45 °C. Performance of R245fa was tested for comparison. Unfair factors in experimental comparative evaluation research with the same apparatus were identified and corrected. Experimental cycle performance of the mixtures were tested and compared with improved experimental assessment methodology. The results show that all of the mixtures deliver higher discharge temperature, higher heating capacity, higher COP and higher εh,c than R245fa. M1B presents the most excellent cycle performance and is recommended as working fluid for moderate/high temperature heat pump.

Post-CHF heat transfer during two-phase upflow boiling of R-407C in a vertical pipe

Abstract This paper reports a study of heat transfer in the post-critical heat flux (post-CHF) regime under forced convective upflow conditions in a uniformly heated vertical tube of 12.7 mm internal diameter and 3 m length. Experiments were conducted with non-azeotropic ternary refrigerant mixture R-407C for reduced pressures ranging from 0.37 to 0.75, mass flux values from 1200 to 2000 kg/m 2 s and heat flux from 50 to 80 kW/m 2 . Data shows a considerable effect of system pressure on the post-CHF heat transfer coefficient for specified mass and heat fluxes. The post-CHF heat transfer coefficients for R-407C are compared with three existing correlations which are found to over predict the current data. A modified correlation to represent the experimental data for R-407C is presented.

Theoretical study on an innovative ejector enhanced Joule-Thomson cycle

This paper describes an innovative ejector enhanced Joule-Thomson cycle for low-temperature refrigerators. Since an ejector is introduced into the cycle, the cycle performance is profoundly affected by the pressure lift ratio and entrainment ratio of the ejector. As a case study, the performance characteristic of the novel cycle refrigerator using the non-azeotropic refrigerant mixture R14/R23 with the molar fraction of 0.6/0.4 is theoretically investigated in detail. The theoretical results show that in a typical refrigeration temperature range from −65°C to −95°C, the novel cycle refrigerator has 24.4%–41.5% improvement in coefficient of performance and 60%–220% enhancement in refrigeration capacity when compared to a basic Joule-Thomson cycle low-temperature refrigerator. This achieves a significant advantage as the use of the novel cycle is applied to low-temperature refrigerators for the medical and commercial applications. Copyright © 2009 John Wiley & Sons, Ltd.

Boiling heat transfer correlations for refrigerant mixtures flowing inside micro-fin tubes

Based on experimental results of ternary non-azeotropic refrigerant mixture R417A flowing and boiling in one smooth and two internally grooved horizontal tubes with different geometrical parameters, a boiling heat transfer correlations was developed for refrigerant mixtures flowing inside micro-fin tubes by applying the enhancement factor in the present modified-Kattan model which was modified by the experimental data of R417A in a smooth tube. The comparison between the calculation and the experimental results indicates that the prediction by the present correlations is in good agreement with the experiment of refrigerant mixtures inside different microfin tubes with a standard deviation of ±30% for vapor qualities below 80%.

Experimental study of forced convective boiling for non-azeotropic refrigerant mixtures R-22/R-124 in horizontal smooth tube

In this article, the experiment is carried out with four stages of test section and new experimental data of non-azeotropic refrigerant mixtures R-22/R-124 are presented. Existing correlations are analysed and new ones are proposed for pure refrigerants. The nucleate boiling correlation of the refrigerant mixtures is modified so as to obtain the evaporation heat transfer coefficient of the refrigerant mixtures in a smooth tube. The result shows that the majority of the predictions fall within ±30% of the experiments.

Heat transfer correlations for evaporation of refrigerant mixtures flowing inside horizontal microfin tubes

Based on the experimental results of R417A flowing inside horizontal microfin tubes, the present work deals with the development of prediction methods for evaporation heat transfer of refrigerant mixtures in microfin tube. The microfin model by Thome et al. is modified by adjusting the convective heat transfer term, and the other microfin model is developed by introducing the enhancement factor into the modified-Kattan model. The comparison of the calculations by several microfin models and the experimental results reveals that the new microfin models developed at the present study are in much better agreement with the experimental results with the reducing average deviation by 30–50% than the models by Thome et al. and Cavallini et al., and are recommended for the prediction of evaporation heat transfer coefficients for non-azeotropic refrigerant mixtures inside microfin tubes.

Performance of a new refrigeration cycle using refrigerant mixture R32/R134a for residential air-conditioner applications

In this paper, a new refrigeration cycle (NRC) using the binary non-azeotropic refrigerant mixture R32/R134a is presented, which can be an alternative refrigeration cycle applied in residential air-conditioner. In the NRC, refrigerant circuit of the evaporator is separated into two branches. Because the non-azeotropic mixture has the characteristic of temperature glide, an important benefit of such configuration is that the Lorentz cycle can be realized. Compared with that of conventional cycle configuration, the new cycle efficiency can be improved. The calculating results show that, in the conventional refrigeration cycle (CRC), the mixture R32/R134a has a close performance to that is obtainable with pure refrigerant R22. However, the mixture R32/R134a in the NRC will result in a better performance. The maximal COP can be improved in a range of 8–9% over that of the CRC, and the volumetric refrigerating capacity can be approximately increased by 9.5%.