NIST Standard Reference Database 73
REFLEAK:
NIST Leak/Recharge Simulation Program for Refrigerant Mixtures
Version 2.1
Users' Guide
D.A. Didion
M.S. Kim
December 2002
Technology Administration
National Institute of Standards and Technology
Standard Reference Data Group
Gaithersburg, MD 20899
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Certain trade names and company products are mentioned in the text to specify adequately the computer products and equipment needed to use this software. In no case does such identification imply endorsement by the National Institute of Standards and Technology of these computer products and equipment, nor does it imply that the products are necessarily the best available for the purpose.
Microsoft is a registered trademark, and Windows is a trademark of Microsoft® Corporation. All other brand and product names are trademarks or registered trademarks of their respective companies.
ACKNOWLEDGMENTS
The authors wish to express their thanks to Drs. Piotr Domanski and Mark Kedzierski for their many helpful comments. Also a special acknowledgment is given to Drs. Eric Lemmon, Mark McLinden and Marcia Huber for their work with REFPROP upon which this program is based.
MODELING OF LEAK AND RECHARGE PROCESS
Appendix A. SAMPLE RUN FOR LEAK PROCESS
Appendix B. SAMPLE RUN FOR LEAK AND RECHARGE PROCESS
Appendix D. SINGLE-COMPONENT REFRIGERANTS AVAILABLE IN REFLEAK
Appendix E. PREDEFINED REFRIGERANT MIXTURES AVAILABLE IN REFLEAK
As alternative refrigerants to ozone depleting materials, mixtures of two or more refrigerants are being utilized as working fluids in heat pumping, air conditioning, and refrigeration systems. Generally, these mixtures form zeotropes, which show temperature and composition changes during any evaporation, condensation, or flashing process whether it be intended (i.e., through an expansion device) or unintended such as a leak from a refrigerant container or system. For the zeotropic mixtures, it may be important to predict the composition change under any of these leak conditions.
This REFLEAK program simulates leak and recharge processes for refrigerant zeotropic mixtures. This Windows-based program provides an easy-to-use package that allows estimation of composition changes of the zeotropic mixtures in leak and recharge processes for either vapor or liquid leaks under isothermal or adiabatic conditions. Studies related to the leak process of refrigerant mixtures were performed [1, 2]. Leak experiments of refrigerant mixtures have been compared with the simulation results [3, 4].
Thermodynamic properties of refrigerant mixtures are calculated based on the NIST Reference Fluid Thermodynamic and Transport Properties – REFPROP, Version 7.0 [5]
Uncertainties in Calculated PropertiesThe objective in selecting property models for use in REFPROP was to implement the most accurate models currently available. The user should be aware that the uncertainties in these models vary considerably depending on the fluid, property, and thermodynamic state. It is thus impossible to give a simple, global statement of uncertainties. Even for the most-studied fluids with equations of state based on accurate, wide-ranging data, uncertainties are complicated functions of the temperature and pressure. The interested user is referred to REFPROP’s original literature sources for details.
The user is further cautioned that, by the very nature of a calculational database, property data are often displayed with more digits than can be justified based on the accuracy of the property models or the uncertainties in the experimental data to which the models were fitted.
Remarks
Occasionally a convergence problem may occur in calculating thermodynamic properties of some azeotropic or near-azeotropic mixtures. This will result in an error message. Since this will occur only for a narrow band of input conditions, the user may want to change the initial input conditions and try the analysis again. Perhaps the property values obtained on either side of the error zone can be interpolated to satisfaction. It appears that the REFLEAK solution procedure taxes REFPROP property routines in unanticipated ways.
The program provides 'Help' sections to assist users. Several keywords are displayed in the help section, and users can choose a keyword by clicking on it.
NIST regularly updates the REFPROP database [5]. When this occurs, this program will be revised to reflect the new property routines.
System Requirements
Free space
for complete installation: 10.0 MB
PC with Microsoft(R) Windows(TM) 95/98/2000/Me/XP or NT
3.51/4.0
Printer: optional and should be
Windows compatible
Memory required: at least 32 MB
Installation Procedure
In Windows NT 3.51, select File from the Program Manager's Menu Bar followed by Run from the File menu. In the entry box, type the CD-ROM drive letter and SETUP (e.g., D:SETUP) and press <enter>.
In Windows 95/98, NT 4.0, 2000, Me, XP click on the Start button and select Run. In the entry box, type the CD-ROM drive letter and SETUP (e.g., D:SETUP) and press <enter>.
Follow the remainder of the installation instructions.
MODELING OF LEAK AND RECHARGE PROCESS
During a leak process of a refrigerant mixture, fluid in a vapor or liquid phase escapes from the system. In the leak process of a refrigerant mixture, preferential evaporation of one or more components makes the composition in the vapor phase different from that in the liquid phase.
Inherently, the temperature of the fluid in the system decreases because the energy required for the vaporization is taken from the refrigerant remaining in the system and from the system wall.
Two idealized cases are considered in this program: isothermal and adiabatic leaks. An isothermal leak process represents a very slow leak situation in which the temperature of the system is maintained constant because of the heat transfer through the walls from the environment. In the adiabatic leak process, it is assumed that the refrigerant leaks so quickly that no heat is transferred through the walls, and the temperature in the system decreases as the leak progresses. A comparison of experimental data with REFLEAK simulations has shown that slow leaks are well predicted by the isothermal assumption. However, all real system containers have a significant heat capacity, which will release some heat into the expanding vaporization process as the liquid temperature drops. Thus, an actual fast leak process probably falls between the adiabatic and isothermal assumptions.
In order to model these leak situations, the following assumptions are made:
(1) During the leak, only one phase
(vapor or liquid) is escaping from the system.
(2) The refrigerant mixture inside
the system is at a vapor-liquid equilibrium state.
(3) The leak process is either isothermal
or adiabatic.
(4)
The escaping refrigerant has the same composition as the vapor inside the system
during the vapor leak, and as the liquid during the liquid leak.
In the recharging process, a leak of a portion of the system charge is simulated, and then the system is recharged with a refrigerant of the original composition. In modeling the recharge process, the liquid phase refrigerant in the charging cylinder is assumed to be put into the system. The mass of refrigerant recharged is the same as that leaked from the system. After recharging, the temperature in the system is "reset" to the initial temperature before the leak for the adiabatic leak process.
The leak process is simulated in a quasi-steady manner by alternate steps of refrigerant escaping and adjustment of internal refrigerant to thermodynamic equilibrium. The properties of refrigerant mixtures in the simulation are calculated by the property routines included in the NIST Reference Fluid Thermodynamic and Transport Properties – REFPROP, Version 7.0 [5]. As a result, all limitations applicable to REFPROP (e.g., avoiding the critical point region) are equally applicable to REFLEAK.
The leak/recharge simulation program consists of three parts: (1) a pre-processing section to input required data, (2) a main section to simulate the leak/recharge process, and (3) a post-processing section to display calculated results and save data and graphs.
The main section for leak only or leak/recharge simulation is comprised of one procedure, which is initiated by clicking on the 'Analyze' button. At this point, a new window for DOS opens to show intermediate stages of execution. All the data are used for plotting purposes. When the program is run completely, this window disappears.
In the post-processing section, the following functions are provided:
(1) Displaying calculated results
in a graphical format; the graph shows compositions of liquid and vapor phases
as a function of leaked mass fraction. A vertical bar in the graph indicates
specific values corresponding to x-axis value (leaked mass fraction). The data
at this location is displayed in the lower part of the graph to show temperature,
pressure, volumetric quality (void fraction), liquid specific volume, and vapor
specific volume. Leaked mass fraction is displayed in the lower right corner
of the screen. The limits of the y-axis can be changed via the Option button.
(2)
Saving output data in a file; the file name must be provided
(3) Printing output data and/or graph
(4) Redrawing a graph
(5) Closing the display of data and graph
When a simulation for one refrigerant mixture is done, the next simulation can be performed from the main window. A subsequent simulation can be carried out when a user selects conditions and repeats several steps described in this section. If a user selects 'New' from 'File' menu, all the test conditions are set to the default values. In this case, the refrigerants should be selected separately.
[1] M. S. Kim and D. A. Didion, 1995, "Simulation of Isothermal and Adiabatic Leak Processes of Zeotropic Refrigerant Mixtures", Int. Journal of HVAC&R Research, ASHRAE, Atlanta, Georgia, USA, Vol. 1, No. 1, pp. 3-20.
[2] M. S. Kim and D. A. Didion, 1995, "Simulation of a Leak/Recharge Process of Refrigerant Mixtures", Int. Journal of HVAC&R Research, ASHRAE, Atlanta, Georgia, Vol. 1, No. 3, pp. 242-254.
[3] Shiflett, M.B., Yokozeki, A., and Reed, P.R., 1992, "Property and Performance Evaluation of 'SUVA' HP Refrigerants as R-502 Alternatives", Proc. of 1992 International Refrigeration Conference, Purdue Univ., West Lafayette, Indiana, U.S.A., Vol. 1, pp. 15-22.
[4] Kruse, H. and Rinne, F., 1992, "Performance and Leakage Investigations of Refrigeration and Airconditioning Systems Using Refrigerant Mixtures as Working Fluids", Proc. of 1992 International Refrigeration Conference, Purdue Univ., West Lafayette, Indiana, U.S.A., Vol. 2, pp. 621-630.
[5] Eric W. Lemmon, Mark O. McLinden, Marcia L. Huber, 2002, NIST Reference Fluids Thermodynamic Properties, Ver. 7.0, NIST Standard Reference Database 23, National Institute of Standards and Technology, Gaithersburg, Maryland, U.S.A.
SAMPLE RUN FOR LEAK PROCESS
A sample execution of the leak/recharge program to simulate the leak process is briefly described below. In this example, a leak process for a R32/134a mixture with a composition of 30/70 mass percentage is simulated. The leak process is assumed to be isothermal, and the vapor phase is leaking out of a system. Initial temperature is selected as 25°C, and the initial volumetric quality, which is the ratio of the volume of vapor to the total volume, is selected as 0.2.
To start the program, select the icon 'REFLEAK' in the program window, and then double click the REFLEAK icon.
An introductory screen appears; click 'OK' to proceed.
Figure A-1 Introductory screen of the program
The input screen is displayed next (Figure A-2). For this example, click 'Isothermal' in the leak process box and 'Vapor Phase' in the leaking phase box. Then, select an initial temperature (25.00) and initial volumetric quality (0.20) by typing in the numbers or by using the horizontal scroll bars. Click 'Leak Process Only' in the simula-tion box.
Figure A-2 Main window for data entry (leak process simulation)
Next, click on the button labeled 'Refrigerants’ to specify the components. The screen shown in Figure A-3 is displayed. This input screen enables you to specify the mixture components desired.
Figure A-3 Main window to determine refrigerants
Enter the number of components (here 2) in the box indicated and then click on the adjacent button. Next, click on the active ‘Click Me’ button in the left-hand column to select refrigerants. The window in Figure A-4 is then displayed.
An option for many of the mixtures that are commercially available is the predefined mixtures radio button. By clicking on the desired predefined mixture, the composition will appear in the lower right corner.
Figure
A-4 Window for selection of refrigerant
name and composition.
Double-click (!) on the desired mixture component and enter the mass fraction in the upper right-hand box when prompted to do so. In this example, R32 with a mass fraction 0.30 and R134a with a mass fraction 0.70 have been selected. After selecting refrigerants and entering their respective mass fractions, click on the ‘OK’ button in the Refrigerant Selection window (Figure A-3).
If you wish to change units, click on the 'Units' button on the main window for data entry (Figure A-2). You can select any combination of the units individually for temperature, pressure, volume, and mass (Figure A-5). Consistent units can be selected by pressing 'SI' or 'English'.
Figure A-5 Window for unit selection
Press 'Analyze' in the main window to start the simulation. (See Figure A-2).
During the execution, a DOS window appears to display the progress of simulation (Figure A-6). All the calculated data are used for printing or plotting purposes.
Figure
A-6 Window to show a progress of simulation
(leak process)
When the calculations conclude, a graph (Figure A-7) is immediately displayed showing composition change during the leak or recharge process versus mass percentage leaked out of the system. The vertical bar in the graph indicates the corresponding mass fraction of each of the components. Corresponding vapor and liquid compositions are displayed on the screen as numbers. The vertical bar can be moved by dragging it with the mouse, by typing x-axis values, or by scrolling a horizontal bar. At each mass percentage (x variable), vapor and liquid compositions including temperature, pressure, quality, liquid specific volume, and vapor specific volume are displayed.
Figure A-7 Data display in a graph format (leak process)
To change the conditions for data display, click the 'Option' button to bring up the Output Option dialog (Figure A-8).
Figure A-8 Several options for data display
The data can be saved in a file by clicking on the ‘Save’ button. The data can be printed in tabular or graphical format by clicking the 'Print' button. When the 'Redraw' button is clicked, the graph is redrawn on the screen, during which time, the 'Redraw' button is replaced by 'Stop' or 'Continue' to toggle the redrawing process. Clicking on 'Close' returns to the main window.
SAMPLE RUN FOR LEAK AND RECHARGE PROCESS
This section describes an example of a leak and recharge process. The leak and recharge process for a R32/134a mixture is simulated with initial composition of 30/70 percentage by mass. The leak process is assumed to be isothermal and the vapor phase is leaking out of a system. It is also assumed that the system is recharged when 30% of the initial mass is leaked out of the system, and the system is recharged three times with the initial refrigerant composition. The temperature is 25°C, and the initial volumetric quality (void fraction) is 0.2.
Select the icon in the program window, and then double click the REFLEAK icon.
An introductory screen appears (See Figure A-1); click 'OK' to proceed.
In the main window marked 'Leak Process', choose 'Isothermal' in the leak process box and 'Vapor Phase' in the leaking phase box. Select initial temperature (25.00) and initial volumetric quality (0.20) (see Figure A-2). Click 'Leak and Recharge Process' in the simulation box and the Recharge Process is displayed.
You can specify the number of recharge and mass percentage of loss for recharge by typing numbers or by using the scroll bars (see Figure B-1).
Figure B-1 Data entry window for leak and recharge simulation
Selection of a refrigerant mixture and units are the same as in Appendix A. (See Figure A-3, A-4, A-5)
Click on ‘Analyze' to start the simulation.
During the execution, a DOS window appears to show the progress of simulation (See Figure B-2).
Figure B-2 Window to show a progress of simulation
(leak and recharge process)
The final output is displayed in graphical
format (See Figure B-3).
Figure B-3 Data display in graphical format
(leak and recharge process)
ICONS
The icons in the tool bar provide additional flexibility and convenience in using REFLEAK. Individual functions and their equivalent menu options are listed below.
Icon Equivalent File Option Functions and Uses
Open
Open the file saved in a previous process
Save
Save the current process
Print
Print output
Refrigerant
Selection of refrigerants
Output
Display output
Units
Selection of units
SINGLE-COMPONENT REFRIGERANTS AVAILABLE IN REFLEAK
| Short Name | Full Chemical Name | |
| Ammonia | or R717 | ammonia |
| Butane | or R600 | butane |
| carbon dioxide | or R744 | carbon dioxide |
| ethane | or R170 | ethane |
| isobutane | or R600a | 2–methylpropane |
| methane | or R50 | methane |
| propane | or R290 | propane |
| propylene | or R1270 | propene |
| R11 | trichlorofluoromethane | |
| R12 | dichlorodifluoromethane | |
| R13 | chlorotrifluoromethane | |
| R14 | tetrafluoromethane | |
| R22 | chlorodifluoromethane | |
| R23 | trifluoromethane | |
| R32 | difluoromethane | |
| R41 | fluoromethane | |
| R113 | 1,1,2–trichloro–1,2,2–trifluoroethane | |
| R114 | 1,2–dichloro–1,1,2,2–tetrafluoroethane | |
| R115 | chloropentafluoroethane | |
| R116 | hexafluoroethane | |
| R123 | 1,1–dichloro–2,2,2–trifluoroethane | |
| R124 | 1–chloro–1,2,2,2–tetrafluoroethane | |
| R125 | pentafluoroethane | |
| R134a | 1,1,1,2–tetrafluoroethane | |
| R141b | 1,1–dichloro–1–fluoroethane | |
| R142b | 1–chloro–1,1–difluoroethane | |
| R143a | 1,1,1–trifluoroethane | |
| R152a | 1,1-difluoroethane | |
| R218 | octafluoropropane | |
| RC318 | octafluorocyclobutane | |
| R227ea | 1,1,1,2,3,3,3–heptafluoropropane | |
| R236ea | 1,1,1,2,3,3–hexafluoropropane | |
| R236fa | 1,1,1,3,3,3–hexafluoropropane | |
| R245ca | 1,1,2,2,3–pentafluoropropane | |
| R245fa | 1,1,1,3,3–pentafluoropropane |
CONTACTS
If you have comments or questions about the database, the Standard Reference Data Group would like to hear from you. Also, if you should have any problems with the CD-ROM or installation, please let us know by contacting:
If you have questions or problems pertaining to the data or use of the database program, contact:
Dr. Piotr A. Domanski
National Institute of Standards and Technology
Building and Fire Research Laboratory
100 Bureau Drive, Stop 8631
Gaithersburg, MD 20899-8631
(e-mail) piotr.domanski@nist.gov
