ME 309 Fall 2008
Section 2 (Merkle)
Homework # 3
Due Wed. 3 September 2008
Problem 31.
Air is trapped in a cylinder having a diameter,
D
, of 40
mm
and height,
h
, of
30
mm
.
Given that the temperature,
T
= 1050 K, and the pressure ,
p
= 300
kPa
are essentially
uniform throughout the cylinder.
(a) Express the pressure as a gage pressure (in
kPa
) (Note gage pressure is the absolute
pressure minus atmospheric pressure.)
(b) Express the temperature in degrees Celsius, degrees Rankine and degrees Farenheit
(c) Find the mass of air in the cylinder in
kg
; and
(d) Use a units conversion table to express the mass in
lbm
.
(e)
The cylinder is compressed to a final height of 15 mm.
Determine the final
density of the air.
Does the density depend upon the final temperature?
For part (c), assume that the air can be treated as a perfect gas: The equation of state for a perfect
gas is given by:
M
RT
p
/
ρ
=
, where
p
= absolute pressure,
Pa
or
2
/
m
N
.
T = Absolute temperature,
K
ρ
= Density,
3
/
m
kg
(Note density is the mass divided by the volume it occupies)
M =
Molecular weight of fluid (for air,
M
= 28.97 kg/kgMol
R
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 Spring '08
 MERKLE
 Thermodynamics, Mass

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