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2.7: Thermodynamic Properties Programs
The two programs steam and thermprop were
borrowed from Professor A. J. Chapman in the Mechanical Engineering
Department. Thermprop was revised and combined with
steam to produce programs called tprop2
and tprop3 that facilitate creating
thermodynamic tables. They give you an
alternative to looking up thermodynamic properties of steam and several
refrigerant
fluids in printed tables such as in Appendix 8 of Reklaitis. A Matlab plotting program
called tplot3 uses the files created by the FORTRAN programs to
show you how the thermodynamic functions look. Here is a
demonstration of steam.
wsname% steam This program calculates the thermodynamic properties of steam in either English or SI units. Enter either eng or si : si <-- Usually this is easier. Steam properties are calculated using one of four options: 1: given p,t,x(if necessary) 2: given p,v 3: given p,s 4: given p,h Enter 1, 2, 3, or 4:
The first two symbols in option 1 are obvious: we will need to give
the pressure and temperature. The third symbol, x, is the
"quality" of the steam; i. e. the fraction that is a vapor. The
symbol, v, in option 2 is the specific volume of the steam.
The symbol, s, in option 3 is the specific entropy, and the
symbol h in option 4 is the specific enthalpy.
Let's try the first option and see where it leads if we try to
specify all three quantities.
1 <-- asking for the first option Option 1;Enter: p(MPa),t(C),x -separated by commas <-- Note the "SI" units: MPa is 10^6 Pa or 1000kPa. and temperaure is in C. Let's try 1 atm and 100C with 50% vapor. 0.101,100,.5 Steam; given p,t,x p= 0.10100 MPa s= 7.35695 kJ/kg-K t= 100.000 C h= 2676.05 kJ/kg v= 0.16785e+01 m3/kg u= 2506.52 kJ/kg Superheated vapor <-- Strange! This is not what we wanted! Enter: 1 to run another case for same option & same units 2 to run another case for new option with same units 3 to change option and/or units 4 to terminate program
Steam listed specific volume, specific entropy,
specific enthalpy, and u, the specific internal energy of
steam along with p and t. Notice that the state of
the "steam" is listed also--as superheated vapor--although x was
given as 0.5. On reflection, 101kPa and 100°C is
superheated and therefore we could not have a
saturated vapor-liquid system. Let's try that again and this time
enter a more precise value for one atmosphere.
1 <-- Asking to run another case for same option & same units Option 1;Enter: p(MPa),t(C),x -separated by commas 0.101325,100,.5 Steam; given p,t,x p= 0.10132 MPa s= 4.33116 kJ/kg-K t= 100.000 C h= 1547.54 kJ/kg v= 0.83702e+00 m3/kg u= 1462.73 kJ/kg Wet mixture: x= 0.5000
Now we know a little more about the first option. It is the one that
you will probably use the most. It can also be used to find the
saturation pressure or temperature of a fluid. If you give 0 for the
pressure, the program assumes you want the saturated pressure that
goes with the temperature and quality. Conversely, if you give the
temperature as 0, it will find the temperature of saturation that
goes with the given pressure.
Let's now try the second option.
2 <-- Asking to run another case for new option with same units Steam properties are calculated using one of four options: 1: given p,t,x(if necessary) 2: given p,v 3: given p,s 4: given p,h Enter 1, 2, 3, or 4: 2 <-- and choosing to specify p and v. Option 2;Enter: p(MPa), v(m3/kg) -separated by a comma 0.101325, 1.5 Steam; given p,v p= 0.10132 MPa s= 6.72954 kJ/kg-K t= 100.000 C h= 2442.48 kJ/kg v= 0.15000e+01 m3/kg u= 2290.49 kJ/kg Wet mixture: x= 0.8965
You will find that it is much easier to find properties of "wet
steam" with this option, since you do not have to give a precise
(p,t) pair that are on the saturation line for water.
Since we don't deal with entropy in this course we will not consider
the third option, but option 4 may be handy.
Enter: 1 to run another case for same option & same units 2 to run another case for new option with same units 3 to change option and/or units 4 to terminate program 2 Steam properties are calculated using one of four options: 1: given p,t,x(if necessary) 2: given p,v 3: given p,s 4: given p,h Enter 1, 2, 3, or 4: 4 Option 4;Enter: p(MPa), h(kJ/kg) -separated by a comma 0.101325, 2300 Steam; given p,h p= 0.10132 MPa s= 6.34771 kJ/kg-K t= 100.000 C h= 2300.00 kJ/kg v= 0.13945e+01 m3/kg u= 2158.71 kJ/kg Wet mixture: x= 0.8334
The programs tprop2 and tprop3
allow you to get properties for 12 different fluids, including water,
for a range of temperatures and pressures. Tprop2
allows you to specify up to ten pressures and to specify a range of
up to 50 equally-spaced temperatures. Tprop3 is the
other way around, allowing a range of up to 50 pressures, and up to
ten temperatures. Each one starts by asking if you want to save your
output in a MATLAB .mat-file and then goes on to list the fluids. For
each pressure in tprop2 (each temperature in
tprop3 ) a table is shown containing the same data
given by steamprop for each temperature (each pressure in
tprop3 ). In addition to this, the state for each
temperature and pressure is given, and, if there is a change of state
then data is given for the saturated vapor and saturated liquid
conditions. Here is what a run of tprop2 looks
like:
wsname% tprop2 Give the name of your data variable for a .dat file to be put in your matlab directory or just hit a RETURN if you do not want to store such a file. ammonia You should have started in your home directory. You should also have a matlab directory. To correct either of these, just reply: y to the prompt: Do you want to stop? The file name will be: matlab/ammonia.mat THERMODYNAMIC PROPERTIES OF FLUIDS This routine calculates the thermodynamic properties of the fluids listed below given t, p and x 1: Ammonia 2: Carbon dioxide 3: Butane 4: Ethane 5: Methane 6: Propane 7: Refrigerant-11 8: Refrigerant-12 9: Refrigerant-14 10: Refrigerant-22 11: Refrigerant-114 12: Water Enter the Fluid number, above 1 <--to get properties for ammonia Give the number of pressures, max.= 10 4 Pressures must be between: 8.644and 20000.000 kPa. Give the pressure Number: 1 in kPa 10 Give the pressure Number: 2 in kPa 60 Give the pressure Number: 3 in kPa 101.325 Give the pressure Number: 4 in kPa 250 Give the number of temperatures, max. = 50 6 Temperatures must be between: -73.150and 386.850 C. Give the min. and max. temperatures in C. -50 50 Ammonia pressure = 10.0000kPa Temperature Volume Entropy Enthalpy Int. Energy State C m3/kg kJ/kg-K kJ/kg kJ/kg -50.000 0.10855E+02 6.86007 1377.68 1269.23 Vapor -30.000 0.11842E+02 7.03469 1418.37 1300.06 Vapor -10.000 0.12825E+02 7.19680 1459.39 1331.24 Vapor 10.000 0.13806E+02 7.34850 1500.81 1362.85 Vapor 30.000 0.14786E+02 7.49150 1542.72 1394.96 Vapor 50.000 0.15765E+02 7.62713 1585.18 1427.64 Vapor Press a RETURN to continue. Ammonia pressure = 60.0000kPa Temperature Volume Entropy Enthalpy Int. Energy State C m3/kg kJ/kg-K kJ/kg kJ/kg -50.000 0.14245E-02 -0.19227 -43.88 -43.86 Liquid -43.284 0.14410E-02 -0.06227 -14.43 -14.42 Sat. Liquid -43.284 0.18345E+01 6.01841 1383.31 1273.34 Sat. Vapor -30.000 0.19489E+01 6.13902 1411.83 1294.99 Vapor -10.000 0.21188E+01 6.30787 1454.54 1327.52 Vapor 10.000 0.22863E+01 6.46394 1497.16 1360.08 Vapor 30.000 0.24524E+01 6.60976 1539.89 1392.85 Vapor 50.000 0.26176E+01 6.74721 1582.92 1425.97 Vapor Press a RETURN to continue. Ammonia pressure = 101.3250kPa Temperature Volume Entropy Enthalpy Int. Energy State C m3/kg kJ/kg-K kJ/kg kJ/kg -50.000 0.14245E-02 -0.19227 -43.82 -43.86 Liquid -33.339 0.14667E-02 0.12411 29.40 29.35 Sat. Liquid -33.339 0.11241E+01 5.83444 1398.80 1285.00 Sat. Vapor -30.000 0.11416E+01 5.86530 1406.25 1290.67 Vapor -10.000 0.12453E+01 6.04005 1450.45 1324.38 Vapor 10.000 0.13465E+01 6.19986 1494.09 1357.75 Vapor 30.000 0.14463E+01 6.34809 1537.52 1391.08 Vapor 50.000 0.15451E+01 6.48709 1581.03 1424.58 Vapor Press a RETURN to continue. Ammonia pressure = 250.0000kPa Temperature Volume Entropy Enthalpy Int. Energy State C m3/kg kJ/kg-K kJ/kg kJ/kg -50.000 0.14245E-02 -0.19227 -43.61 -43.86 Liquid -30.000 0.14757E-02 0.18501 44.32 44.05 Liquid -13.666 0.15225E-02 0.47554 117.32 117.04 Sat. Liquid -13.666 0.48213E+00 5.51920 1426.07 1305.64 Sat. Vapor -10.000 0.49051E+00 5.55357 1435.05 1312.53 Vapor 10.000 0.53480E+00 5.72814 1482.70 1349.10 Vapor 30.000 0.57744E+00 5.88552 1528.81 1384.55 Vapor 50.000 0.61904E+00 6.03035 1574.14 1419.49 Vapor Press a RETURN to continue. Session ended. Your data is in your matlab directory under the name:ammonia.mat wsname% cd matlab wsname% more ammonia.mat 10.000 -50.000 0.10855E+02 6.86007 1377.68 1269.23 10.000 -30.000 0.11842E+02 7.03469 1418.37 1300.06 10.000 -10.000 0.12825E+02 7.19680 1459.39 1331.24 10.000 10.000 0.13806E+02 7.34850 1500.81 1362.85 10.000 30.000 0.14786E+02 7.49150 1542.72 1394.96 10.000 50.000 0.15765E+02 7.62713 1585.18 1427.64 60.000 -50.000 0.14245E-02 -0.19227 -43.88 -43.86 60.000 -43.284 0.14410E-02 -0.06227 -14.43 -14.42 (more data at 60 kPa) 60.000 50.000 0.26176E+01 6.74721 1582.92 1425.97 101.325 -50.000 0.14245E-02 -0.19227 -43.82 -43.86 (more data at 101.325 kPa) 101.325 30.000 0.14463E+01 6.34809 1537.52 1391.08 101.325 50.000 0.15451E+01 6.48709 1581.03 1424.58 250.000 -50.000 0.14245E-02 -0.19227 -43.61 -43.86 250.000 -30.000 0.14757E-02 0.18501 44.32 44.05 (more data at 250 kPa) 250.000 50.000 0.61904E+00 6.03035 1574.14 1419.49 wsname%
Tprop3 is similar to tprop2, except
it is more useful when you know the temperature and need to find a
pressure. The file created by the programs is formatted so that the
MATLAB program tplot2
can read them and plot various properties.
This program finds properties for Humid air. You must give its temperature and either its wet bulb temperature or its relative humidity.
The program will then report for a given T, in C or K, and relative humidity the wet bulb temperature, the water vapor pressure, the mass ratio of water to dry air, the enthalpy in the units kJ per kg of dry air, the specific volume in the units m3 per kg of dry air, and the dew point.
If the wet bulb temperature is given, the relative humidity is reported. If the temperature is given in R or F, the units reported will be: Btu per lbm of dry air for the enthalpy and ft3 per lbm of dry air for the specific volume.
The following is a demo of its use:
wsname% humid This program finds properties for Humid air. You must give its temperature and either its wet bulb temperature or its relative humidity. Give the unit for temp. K, C, R, or F C Give the temperature in C 25 You can now specify either the relative humidity or wet bulb. Reply rh for relative humidity or wb for wetbulb. rh Give the relative humidity .75 Temperature Relative Humidity Wet Bulb Temp. C C 25.00 0.75000 21.64 H2O Vapor P. Mass Ratio Enthalpy Specific Volume Dew Point kPa H2O/dry air kJ/kg DA m3/kg DA C 3.182 0.015057 63.42 0.8682 20.24 NOTES: The reference temperature is 0C or 273.15K. The reference state for water is as a liquid. If you want to give another set of conditions, reply: y y Give the unit for temp. K, C, R, or F F Give the temperature in F 95 You can now specify either the relative humidity or wet bulb. Reply rh for relative humidity or wb for wetbulb. wb Give the wet bulb temp. in F 85 Temperature Relative Humidity Wet Bulb Temp. F F 95.00 0.67050 85.00 H2O Vapor P. Mass Ratio Enthalpy Specific Volume Dew Point psia H2O/dry air Btu/lbm DA ft3/lbm DA F 0.817 0.024174 41.78 14.5780 82.27 NOTES: The reference temperature is 32F or 491.67R. The reference state for water is as a liquid. If you want to give another set of conditions, reply: y
As you can see, this is a very useful program that gives you a lot of information at once. Most of this information can also be obtained through the use of the Matlab humidity functions.