Download Unit 1: February 11 - College of Engineering and Computer Science

College of Engineering and Computer Science
Mechanical Engineering Department
Mechanical Engineering 370
Thermodynamics
Spring 2003 Ticket: 57010 Instructor: Larry Caretto
Solution to Quiz One – Properties of Pure Substances
Instructions: Work all problems in the space provided. Remember that more credit is given for
showing your basic approach to the problem and developing a method for obtaining the answer
than is given for completing the final details of algebra or arithmetic. Where appropriate you
should state all your assumptions and show all your reasoning in solving a problem.
1. A volume of 2 m3 contains neon at temperature of 200 K and a pressure of 2 MPa. Use
the attached tables to find the mass of neon in the container.
From the attached tables we can find the specific volume at the initial state, v(2 MPa, 200 K )
= 0.04264 m3/kg. With this specific volume and the container volume, V = 2 m 3, we can find
the mass as follows.
m
V

v
2 m3
m3
0.04164
kg
= 48.03 kg
2. What would your answer to first question be if the neon behaved as an ideal gas with
an engineering gas constant, R = 0.4119344 kJ/(kg∙K)?
Applying the ideal gas law to the input data gives the following result for the mass.
1000 kJ
PV
MPa  m 3 = 48.55 kg
m

0.4119344 kJ
RT
( 200 K )
kg  K
( 2 MPa )( 2 m 3 )
3. If the neon at the initial state in question 1 were cooled to a final temperature of 30 K
holding the volume constant what would its pressure be? If the final state is in the
mixed region compute the quality.
The final state would have the same specific volume, 0.04146 m 3/kg, as the initial state and
the given temperature of 30 K. At this temperature, the specific volume is between the
saturated liquid and saturated vapor specific volumes, vf = 0.000869 m3/kg and vg =
0.05016 m3/kg, respectively. This means that the final state is in the mixed region so the
pressure is the saturation pressure. We find this pressure from the saturation tables at a
temperature of 30 K.
P = 0.2238 MPa
The quality is found as follows.
x
v  vf
vg  v f
Engineering Building Room 1333
E-mail: [email protected]

0.04164 m
3
0.05016 m
3
kg
kg
 0.00869 m
3
 0.00869 m
3
Mail Code
8348
kg
 0.7946
kg
Phone: 818.677.6448
Fax: 818.677.7062