THERMODYNAMICS LAB
Properties of Pure Substances
ENTC - 370
ENTC 370
PROF. ALVARADO
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Pure
Substances
Substances
with fixed
chemical
composition
Homogenous
mixture of
various
components
Examples:
Water,
Hydrogen,
Nitrogen
Examples: Air
(combination of
oxygen,
nitrogen etc.)
Pure Substances
• It can exist in three different phases- solid,
liquid, gas
• Under certain conditions, two phases can
co-exist
• Ex: liquid and gas co-existing in the
evaporator and condenser of a refrigerator
Property of a substance is independent of
the path travelled
Properties of Pure
substances
Intensive:
Independent of the
mass of the
substance
Ex: Pressure,
Temperature
Extensive:
Dependent on the
mass of the
substance
Ex: Volume, Total
Energy, Quality
• An Extensive property can be converted to an Intensive property by
specifying the property per unit mass, such as specific properties.
Pure Substances
• A state of a substances can be specified by
two independent properties
• In single phase, pressure and temperature
are the two common independent properties
• In two phase, pressure and temperature are
no longer independent. In this case we have
to use another independent property (mostly
“quality”) along with pressure or temperature
to determine the state of the substance.
Quality
• The quality of a fluid is the percentage of
mass that is vapor
– Saturated vapor has a "quality" of 100%
– Saturated liquid has a "quality" of 0%
x
mg
mtotal
• X = 1, Saturated Vapor
X = 0, Saturated Liquid
0 < X < 1, Mixture
Example
• Suppose that we want to complete the following table of
properties for R-134a (‘Refrigerant found in air
conditioning systems’):
T [°C]
P [kPa]
-8
320
V [m3/kg]
180
Phase
Description
Saturated vapor
(x = 1.0)
Note: Remember that in order to specify a
thermodynamic state, you just need two independent
properties.
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Thermodynamics Properties in EES
• EES provides thermophysical property data on a wide variety of
fluids that are found in engineering applications
• To access this option, in the menu Options, select Function info and
The following window will appear
• Select the fluid and the property of interest, and paste it to the equations window
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Properties
• Remember EES uses the following representations for
the most common properties:
– T= temperature
– P= Pressure
– x= Quality
– u= Internal Energy
– h= Enthalpy
– v= Specific Volume
– s= Entropy
• Use EES Property Calculator instead of the EES function
to fill out the previous table
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Example
• In order to find the missing properties of the first row, we just input
the equations, press F2 and get the solutions
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Example
• The second line of the table gives us the pressure and tell us that
the refrigerant is in the form of saturated vapor (quality=1).
• If we paste the temperature function in the equations window; we
will see that the default properties used to calculate the temperature
are Pressure and enthalpy
– TEMPERATURE(R134a,h=h1,P=P1)
• It is possible to change the enthalpy for quality and obtain the
temperature
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Example
• The completed table looks like this:
T [°C]
P [kPa]
V [m3/kg]
Phase
Description
-8
320
7.569 * 10-4
Compressed
Liquid
-12.73
180
0.1104
Saturated
vapor
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Problem 1
H2O
P=600kPa
• A piston-cylinder device contains 0.3 m3 of liquid water and
0.7 m3 of water vapor in equilibrium at 600 kPa. Heat is
transferred at constant pressure until the temperature reaches
400 °C.
– What is the initial temperature of the water?
– Determine the total mass of the water.
– Calculate the final volume
– Let the final temperature vary from 180 to 1080 °C.
Determine the impact on final volume in the tank. Plot the
final volume vs. final temperature. Discuss results.
– Let the pressure vary from 150 to 1050 kPa. Determine the
impact on the final volume of water. Plot the total
volume of water vs. Pressure. Discuss results.
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Lab Report – Problem 1 only
• Discussion: State the problem with your own
words
• Equation: Summary of the equations used in the
experiment with explanation.
• Findings: Summary of the experimental data,
you could use tables, figures, graphs.
• Conclusions: Interpretation of the findings.
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