Thermodynamic Properties Of Refrigerants Research Articles

PRACTICAL SESSION USED FOR A DEEPER UNDERSTANDING OF VAPOUR COMPRESSION SYSTEMS – A PURPOSE OF TEACHING IN CONSTANTA MARITIME UNIVERSITY

In order to increase the knowledge of future marine engineers it is needed to bring closer the practical skills with theoretical gains. In Constanta Maritime University, Marine Refrigerating Plants is a discipline included in the curricula of future marine engineers. Practical learning can be also developed on low cost and effective means – as it will be proven in the paper. By using Coolselector 2, future marine engineers are trained to apply theoretical knowledge such as thermodynamics principles and to better understand the vapour compression cycle analysis, thermodynamic properties of refrigerants or the importance of the main components of a basic vapour compression refrigeration cycle. At the end of the practical session, students will gain important skills specific to theoretical aspects of refrigeration and thermodynamic processes and real situations.

Modelling of pure refrigerant thermodynamic properties and vapor-liquid equilibrium of refrigerant mixtures with the UMR-PRU model

In this work, the UMR-PRU model is extended to refrigerant mixtures. Key properties of pure refrigerants, such as vapor pressure, saturated volume, heat capacity and enthalpy of vaporization are examined with the Peng-Robinson equation of state, to which UMR-PRU reverts for pure components, and appropriate modifications to the attractive and repulsive terms are made. For the extension of UMR-PRU to refrigerant mixtures, four new UNIFAC groups are introduced and binary UNIFAC interaction parameters are fitted to experimental vapor-liquid equilibrium data. The predictive capability of the model is tested in ternary refrigerant mixtures. A comparison is made between UMR-PRU and the REFPROP model, which is currently considered as the state-of-the-art model for refrigerants. The results reveal that UMR-PRU describes the vapor-liquid equilibrium of refrigerant mixtures with similar accuracy as REFPROP. Both models are also employed for performing process simulations of vapor compression refrigeration cycles, yielding very comparable results regarding the COP and mass flowrate of the working fluid.

Thermodynamic properties of refrigerant trans-1,3,3,3-tetrafluoropropene: method for constructing the fundamental equation of state and calculation of thermodynamic tables

A new environmentally friendly fourth-generation refrigerant trans-1,3,3,3-tetrafluoropropene R1234ze(E) is considered as an alternative to R134a refrigerant in chillers and heat pumps, as well as R22 refrigerant in air conditioning systems. A technique has been developed for constructing a unified fundamental equation of state of liquid and gas, implemented for trans-1,3,3,3-tetrafluoropropene. The proposed fundamental equation in the vicinity of the critical point satisfies the requirements of the scale theory for asymmetric systems, and in the region of rarefied gas it is reduced to the virial equation of state. Based on this fundamental equation, tables of standard reference data on pressure, density, enthalpy, isobaric and isochoric heat capacities, entropy, heat of vaporization, and speed of sound, trans-1,3,3,3-tetrafluoropropene in the region of state parameters in the temperature ranges 169–420 K and pressure 0.1–100 MPa were calculated. A number of statistical characteristics have been calculated – absolute mean deviation, systematic deviation, standard deviation, root mean square deviation, which characterize the accuracy of the proposed fundamental equation in describing the experimental values of equilibrium properties obtained in generally recognized international thermophysical centers. It has been established that the values of these statistical characteristics are significantly less than the values of the corresponding characteristics of international fundamental equations given in the literature when describing thermal and caloric experimental data of trans-1,3,3,3-tetrafluoropropene. The estimated expanded uncertainties of the tabulated data obtained based on the proposed fundamental equation were 0.26 % for density, 0.57 % for pressure, 1.7 and 1.2 % for isochoric and isobaric heat capacities, 0.38 % for speed of sound. The results obtained allow us to conclude that the proposed unified fundamental equation of state adequately conveys the thermodynamic characteristics of trans-1,3,3,3-tetrafluoropropene in the specified range of temperatures and pressures.

A fast method for the calculation of refrigerant thermodynamic properties in a refrigeration cycle

Modeling and simulating dynamic and complex energy systems that are composed of a large number of components where every component model is described by mathematical equations can take high computational time. The calculation of the refrigerant thermodynamic properties has a big impact on the computational speed of the model. In an attempt to speed up simulations, two implementation methods for the calculation of refrigerants’ thermodynamic properties were investigated, the Coolprop thermodynamic equations of state and the Implicit fitting method. A complex dynamic cascade refrigeration cycle was developed and simulated using the two fluids implementation methods. The advantages and disadvantages of each method were discussed. The results show that using the implicit fitting method instead of Coolprop for the simulations of complex dynamic systems in Dymola will accelerate the simulation by about 30 times. In addition, the implicit method is accurate and offers more flexibility for modeling complex realistic energy systems.

Thermodynamic Analysis of Vapor Compression Refrigeration System for Aircraft with Refrigerant R134a

The Environmental Control System (ECS) for a typical fighter aircraft is used for cabin cooling and pressurization, demisting operations, and for avionics cooling. Most of the passenger and fighter aircrafts use Bleed-Air Cycle for ECS. In this paper a new ECS called All Electric Environmental Control System (AEECS) is presented which works on Vapor Compression Refrigeration System using ram air as medium. It is called a power optimized system. The sizing of the system is based on the heat load calculations of the cabin and avionics for different flight conditions. A generalized software program is developed for evaluating system performance which includes key results regarding air compressor capacity, thermodynamic properties of refrigerants and Vapor Compression Refrigeration System. The AEECS is found to reduce the power requirement of the system to 80 kW compared to the Bleed Air Cycle ECS which requires a power of 0.8 MW to run the system. The results are presented in the form of graphs.

Validation of and optimization with a vapor compression cycle model accounting for refrigerant thermodynamic and transport properties: With focus on low-GWP refrigerants for air-conditioning

CYCLE_D-HX is a semi-theoretical model that simulates the performance of a vapor-compression cycle with forced-convection heat exchangers for specified temperature profiles of the heat source and heat sink. In this study, we validated CYCLE_D-HX using experimental measurements from a small (< 4 kW capacity) heat pump test apparatus operated in cooling mode. The tested refrigerants included the medium-pressure refrigerant R-134a and candidate replacements with a lower global-warming potential (GWP): R-513A, R-450A, Tern-1 (R-134a/1234yf/1234ze(E) 49.2/33.8/17.0 mass fraction,%), R-515B, and R-1234yf. We also tested high-pressure refrigerant R-410A and candidate replacements with lower-GWP: R-32, R-452B, and R-454B. The model generally agreed with experimental results, with COP and volumetric capacity overpredicted by (0 – 3)% for the basic cycle, and by (0 – 5)% for the cycle with the liquid-line/suction-line heat exchanger (LLSL-HX). We applied the model to evaluate the performance of the refrigerants in a system with optimized refrigerant circuitries in the evaporator and condenser. The simulations showed the lower-GWP medium-pressure refrigerants, including some non-flammable blends, had COP (0.2 – 2.3)% less than R-134a. The lower-GWP high-pressure refrigerants, which all have the ‘2L’ flammability rating, had COP (2.3 – 3.2)% higher than R-410A.

Low GWP Refrigerant R1234yf, R1234ze(z), R13I1 as an Alternative to New Zeotropic Refrigerant

This study will present R13I1 or trifluoroiodomethane as a CFCs refrigerant, the chemical formula is CF3I. R13I1 is a halocarbon agent used in fire extinguishing agents same as R227ea. R13I1 has a GWP of 1, a boiling point of -21.9, a critical temperature of 123.3 °C and a critical pressure of 3950kPa. It can be seen that it is a refrigerant with properties similar to R134a. R1234yf and R1234ze(z) therefore can be mixed with HFCs. The result the national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software as CAN/ANSI/AHRI540 standards of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) show that R13I1 has cooling coefficient of performance of 1.49, 2.43 and 2.79 kJ/kg which are lower than of R13I1 10.33% 8.13% and 9.40% for LT, MT and HT conditions as a result of low evaporator pressure, condenser pressure and refrigerant work .R13I1 which is a refrigerant that is mixed in low-GWP and low-GWP HFCs, as well as providing good energy efficiency zeotropic blends.

The Data Mining Technique Using RapidMiner Software for New Zeotropic Refrigerant

This research presents the development of environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration systems that new azeotropic refrigerant mixture of hydrofluorocarbons and hydrocarbon that can retrofit in the refrigeration system using R404A. The medium back pressure refrigeration testing standard that follow CAN/ANSI/AHRI540 standard air-conditioning, heating, and refrigeration institute (AHRI) and The properties of refrigerants and refrigeration simulation system that used national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software. The methodology uses decision tree function in datamining by rapid minor software that first of KDnuggets annual software poll that showed new azeotropic refrigerant mixture had cooling capacity, refrigerant effect, GWP and boiling point were lower than R404A but work and pressure for medium temperature refrigeration system of azeotropic refrigerant mixture were higher than R404A. The artificial intelligence (AI) by data mining technic can predictive environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration. The result of refrigerant mixed by R134A, R32, R125 and R1270 and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs and HCs which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant.

Excel Add-In Program for Computation of Thermodynamic Properties of R134a and R718 Refrigerants

Excel Add-In Program for Computation of Thermodynamic Properties of R134a and R718 Refrigerants

Investigation and Analysis of R463A as an Alternative Refrigerant to R404A with Lower Global Warming Potential

This research presents the development of R463A refrigerant, a nonflammable refrigerant that was retrofitted to replace R404A. R463A is primarily composed of hydrofluorocarbons/hydrocarbons/carbon dioxide (HFCs/HCs/CO2), and has global-warming potential (GWP) of 1494. It is a nonazeotropic mixture of R32 (36%), R125 (30%), R134a (14%), R1234yf (14%), and R744 (6%). R463A is composed of polyol ester oil (POE), and it is classified as a Class A1 incombustible and nontoxic refrigerant. R463A has a higher cooling capacity (Qe) than that of R404A, as it is composed of hydrofluorocarbons (HFCs) R32 and carbon dioxide (CO2) R744, and has lower GWP than that of R404A due to the use of hydrofluoroolefins (HFOs) from R1234yf. The results of this research showed that R463A can be retrofitted to replace R404A due to its composition of POE, Class A1 incombustibility, and lower toxicity. The properties of R463A and R404A, as analyzed using national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software, are in accordance with the CAN/ANSI/AHRI540 standards of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI). The normal boiling point of R463A was found to be higher than that of R404A by 23%, with a higher cooling capacity and a 63% lower GWP value than that of R404A. The critical pressure and temperature of R463A were found to be higher than those of R404A; it can be used in a high-ambient-temperature environment, has higher refrigerant and heat-rejection effects, and has lower GWP than that of R404A by 52% due to the HFOs from the R1234yf component. The cooling coefficient of performance (COPc) of R463A was found to be higher than that of R404A by 10% under low-temperature applications. R463A is another refrigerant option that is composed of 7% carbon dioxide (CO2), and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs, HFOs, HCs, and natural refrigerants, which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant.

Molecular simulation and experimental investigation for thermodynamic properties of new refrigerant NBY-1 for high temperature heat pump

This paper presents the differences in thermodynamic properties of refrigerants in different spatial conformation, showing the superiority of molecular simulation in predicting thermodynamic properties of fluids. And molecular simulation was modified to improve prediction accuracy of thermodynamic properties of fluids at high temperature and pressure. Meanwhile, a new high temperature heat pump refrigerant mixture named NBY-1 was proposed, and its thermodynamic properties were estimated with the modified molecular simulation. Then the experiment investigation was carried out and showed the good cycle performance of NBY-1 as the refrigerant. The experimental results indicated that high temperature heat pump using NBY-1 could supply high temperature water of 130 °C with the highest coefficient of performance of 2.74 and the condensing pressure of 2.55 MPa, when the temperature lift was 50 °C. Moreover, the experiment also demonstrated the high accuracy with molecular simulation in predicting thermodynamic properties of NBY-1 in the two phase region, and the average relative deviation of condensing pressure between predicted results and experimental results was 2.59% with the highest value of 3.89%.

Modeling and Simulation of a Novel Combined Solar Photovoltaic-Thermal Panel and Heat Pump Hybrid System

A numerical simulation model for a novel concept of a hybrid composed of photovoltaic-thermal solar panels and a heat pump is presented. This concept was developed to assess the performance and energy conversion efficiency of the hybrid system used to produce domestic hot water and electricity. A two-dimensional heat transfer and fluid flow dynamic model was developed to describe the behavior of the hybrid system under different solar irradiance, heat pump boundary conditions and different refrigerants. The model is based on dynamic mass and energy equations coupled with the heat transfer coefficients, and the thermodynamic properties of refrigerants as well as material properties. The model compared fairly to experimental data.

Assessing the exergy performance of heat pump systems without using refrigerant thermodynamic properties

This paper tackles the assessment of the exergy performance of heat pumps. This work is based on a modeling that does not require the evaluation of refrigerant thermodynamic properties and is applied to two commercial (water–water and air–air types) units for various operating conditions (i.e., temperatures at the inlet side of the evaporator and the condenser). The total exergy destruction and the irreversibility distribution into the components are estimated and cover a broad range of values. As well, the nature of the sources of exergy destruction, divided into non-renewable (electrical) and renewable (thermal) energy flows, is also investigated. This distribution, which allows the use of electricity that is really paid by the user to be clearly identified, provides different optimal operating conditions, as compared with the total exergy destruction. Finally, the influence of the exergy reference state temperature (either constant or variable) is examined; in particular, with the air–air heat pump that permits the space heating demand of a building to be achieved. Although the effect on the exergy destruction is relatively low, varying the exergy reference state temperature strongly affects the exergy efficiency, which then appears to appropriately evaluate the use of energy in heat pumps.

A Historical Review on the Tribological Performance of Refrigerants used in Compressors

Refrigerants directly affect the tribological performance of interacting components in a compressor. Since the introduction of artificially formulated refrigerants, the types of refrigerants used in compressors have changed over the years. Apart from evaluating the physical, chemical and thermodynamic properties of refrigerants, the refrigerants have also been studied from a view point of tribology by various researchers worldwide. Changing a refrigerant in a compressor not only has an effect on the thermodynamic cycle but also effects the lubricants viscosity, lubricants pressure-viscosity coefficient, oil film thickness, lubricant/refrigerant miscibility, friction, wear, durability, reliability and overall power consumption. Refrigerants have been studied from a view point of tribology by varying the contact geometries, by using different lubricating oils with and without additives, by altering the environmental pressure/temperature, by changing the phase of the refrigerant, by using different interacting materials and by applying numerous surface treatments. The tribological behavior of refrigerants can be better understood by consolidating the findings in a comprehensive manner. An in-depth review on the tribological behavior of refrigerants is missing from the literature. This article reviews the tribological studies carried out on refrigerants, with focus on refrigerants used in domestic appliances, automobile air-conditioning systems and small scale industrial and commercial applications.

Performance analysis of a new ejector expansion refrigeration cycle (NEERC) for power and cold: Exergy and energy points of view

In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle serving as a harvesting tool of gas cooler wasted heat, is investigated. An attempt has been made to harvest and utilize the low-grade wasted energy, in the gas cooler component of the refrigeration basic cycle, through a transcritical carbon dioxide Rankine cycle. The work produced by the new cycle is used to drive the compressor and the feed pump, hence reducing the consumption work input and, as a result, it will enhance the performance characteristics of the whole system. The system operating and performance characteristics are investigated theoretically by energetic and exergetic methods. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the proposed new refrigeration ejector expansion cycle (NEERC) had higher coefficient of performance and higher system second law efficiency in compare to the basic ejector expansion refrigeration cycle (BEERC). An enhancement of 12% in the COP and exergy efficiency of NEERC was found in comparison with BEERC when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEERC and its efficiency along with the reduction of power consumption make it more practical for the use in residential air conditioning and cooling applications. A techno-economic analysis to compare ORC with Rankine cycle is provided. The results indicated that Rankine cycle for transcritical CO2 refrigeration cycle is more appropriate and has an advantage over the use of ORC. In addition, the small scale Rankine cycle combined with BEERC is economically viable for countries where the electricity price is above 15 c€/kWh.

Optimal fluids for adsorptive cooling and heating

The search for optimal fluid/adsorbent working pairs in adsorption heat transformers is featured by trial and error method. In the last decades this approach has produced relevant progresses especially resulted in new advanced adsorption materials. On the refrigerant fluid side water, ammonia, methanol and ethanol still seem to be the only viable options. This work aims to explain the reason of that and the requirement that a refrigerant fluid must fulfil in order to be considered as promising for adsorptive cooling and heating. A thermodynamic framework is developed that merges the corresponding states principle with the characteristic curve of adsorption. Finally the framework is applied to assess the theoretical coefficient of performance of 258 fluids on 16 adsorption materials belonging to activated carbons, silica gels and zeolites, by avoiding in this way blind search strategy of the optimal working pair. Furthermore, the approach is used also to identify more generally the refrigerant thermodynamic properties for maximum performance. Fluid critical temperature is often the chief property enabling higher performance, although not always all the adsorption materials share the same sensitivity to the same thermodynamic properties.

Thermodynamic analysis of a novel ejector expansion transcritical CO2/N2O cascade refrigeration (NEETCR) system for cooling applications at low temperatures

Natural substances are becoming very promising for long term alternative for refrigeration purposes. In this paper, two natural refrigerants have been proposed and analyzed for a novel ejector expansion transcritical cascade refrigeration (NEETCR) system. Nitrous oxide (N2O) is used in the low temperature circuit (LTC) whereas carbon dioxide (CO2) is used in the high temperature circuit (HTC) of the NEETCR system. The reject of refrigerant vapor heat in the HTC is carried out through the use of transcritical carbon dioxide Rankine cycle. This produces work, which will be used to reduce the consumption work of compressors and feed pump thereby resulting in the improvement of the energy efficiency of the whole system. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the (NEETCR) system had higher coefficient of performance and higher system second law efficiency compared to the EETCR system.An enhancement more than 9% in the COP and exergy efficiency of NEETCR system was found in comparison with EETCR system, when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEETCR system and its efficiency along with the reduction of power consumption make it more practical for the use in cooling applications.

Alternative refrigerants for the heat pump of a ground source heat pump system

It is attempted to define more environment friendly working fluids for the heat pump of ground source heat pump systems (GSHPSs). The examined case is an office building with total cooled area 1000 m2, which is connected with such a system. The energy demands are computed by TRNSYS 16.1 and the ground loop is modeled by GLD2009. Alternative refrigerants are proposed instead of the one that has been extensively used worldwide, for many years, the R-22. The proposed replacements are the binary mixtures R-32/R-134a in compositions 20/80%, 30/70%, 40/60% by mass, and the ternary blends R-407B (10wt% R-32, 70wt% R-125, 20wt% R-134a), R-152a/R-125/R-32 (48wt% R-152a, 18wt% R-125, 34wt% R-32), R-410B (45wt% R-32, 55wt% R-125) and R-507A (50wt% R-125, 50wt% R-143a). A MATLAB code is developed in order to calculate coefficient of performance (COP) values for one stage vapor compression reference cycle with no evaporator superheating and condenser subcooling. The thermodynamic properties of refrigerants are derived from previous works of our laboratory, REFPROP 8.0 and international bibliography. The choice of the most suitable refrigerant depends on the criteria which are set.

Modeling the exergy performance of heat pump systems without using refrigerant thermodynamic properties

This paper presents an exergy modeling approach for heat pumps which does not require the evaluation of refrigerant thermodynamic properties. Exergy balance and exergy destruction are estimated by the product of energy terms and energy quality factors. Therefore, evaluating refrigerant thermodynamic properties is not essential, only energy terms and operating temperatures (those of the refrigerant), are required. This method makes exergy analyses accessible to existing units and undefined processes. Since these temperatures are not necessarily given by the manufacturers, a mathematical method is presented for their calculations. Furthermore, to better understand the behavior of the system, a graphical exergy representation is presented; it allows the exergy destruction to be localized and the reasons of irreversibility to be identified. Based on the proposed exergy model, irreversibility is also analyzed along each energy path. It permits renewable flows from non-renewable ones to be separated and thus, the proper use of energy is emphasized. This method has been applied to existing water–water and air–air heat pump units and the results were compared with those obtained by using the classical thermodynamic cycle approach. The temperatures of the refrigerant are then given for various operating conditions and exergy assessments are discussed in detail.

Modeling of Thermodynamic Properties for Pure Refrigerants and Refrigerant Mixtures by Using the Helmholtz Equation of State and Cubic Spline Curve Fitting Method

When simulating refrigeration systems or equipment, knowledge of refrigerant thermodynamic properties is required. While some of the refrigerants are made of pure fluids, some of these refrigerants are made by mixing of two or more pure refrigerants with the predetermined percentages. Properties of refrigerants are a major part of international trade, therefore, it is a subject of interest of international standards. In this study a computer model was developed based on Helmholtz equation of state and cubic spline curve fitting models developed by using saturation thermophysical properties of the refrigerants and refrigerant mixtures. Java programming language was used to model equation of state. As an example the equations for R1234yf and R410A were presented in this paper. With the new model, thermodynamic properties of R1234yf and R410A were compared with REFPROP 9.0. It shows that the total mean deviations of the new model are less than 0.5%.