1
lesson 2
I. Concepts and Definitions
F. Properties of a system (we use them to calculate changes in energy)
1. A property is a characteristic of a system that can be given a
numerical value without considering the history of the system.
Examples include T, P,
ρ
, velocity, E, U, volume (we can only
measure T, P, velocity, mass, volume)
2. Examples and definitions
a. pressure, P
b. density,
ρ
2
5
()
1
1
1
101325
1.01325
14.696
11
0
force exerted by fluid
P
unit area
N
P
pascal
Pa
m
atm
Pa
bar
psia
bar
Pa
=
==
=
=
=
3
m
kg
,
V
m
volume
mass
=
=
ρ
(14)
lesson 2
I. Concepts and Definitions
c.
atmospheric pressure (absolute) = P
atm
d.
gage pressure
= P
gage
= P
abs
P
atm
(115)
e.
absolute pressure
= P
abs
= P
atm
+ P
gage
f.
vacuum pressure = P
vac
= P
atm
abs
(116)
g.
specific volume = v = 1/
ρ
= Vol/mass, m
3
/kg
h.
intensive
properties are independent of the
size of the system:
T, e, P,
ρ
, specific volume
(v), u.
The units on e are kJ/kg
.
i.
extensive
properties depend on the size of the
system:
actual volume (V), E, m, U.
The units
on E are kJ
.
Example
.
The pressure gage attached to the air storage tank
of a compressor reads 100 psi.
If the atmospheric
pressure of the surroundings is 14.7 psi, what is the
absolute pressure in the tank? (Answer:
114.7 psia)
p
Stiff
metal tube
Bourdon tube
gage gives P
gage.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document2
lesson 2
I.
Concepts and Definitions
Example
. You are designing a snorkel that will allow you to remain
submerged in water at a depth of 1 m.
Discuss any problems you might
experience in using this device.
This is the end of the preview. Sign up
to
access the rest of the document.
 Summer '08
 thermo

Click to edit the document details