ENERGY, WORK, AND HEAT
Thermodynamics
Example:
Determine the kinetic energy of 7 lbm of steam flowing through a pipe at a velocity of
100 ft/sec.
Solution:
Using Equation 1-12.
KE
mv2
2gc
KE
(7 lbm) (100 ft/sec)2
2(32.17 ft lbm/lbf sec2)
KE
(7 lbm) (10,000 ft2/sec2)
(64.34 ft lbm/lbf sec2)
KE
1088 ft lbf
Specific Internal Energy
Potential energy and kinetic energy are macroscopic forms of energy. They can be visualized
in terms of the position and the velocity of objects. In addition to these macroscopic forms of
energy, a substance possesses several microscopic forms of energy. Microscopic forms of energy
include those due to the rotation, vibration, translation, and interactions among the molecules of
a substance. None of these forms of energy can be measured or evaluated directly, but
techniques have been developed to evaluate the change in the total sum of all these microscopic
forms of energy. These microscopic forms of energy are collectively called internal energy,
customarily represented by the symbol U. In engineering applications, the unit of internal energy
is the British thermal unit (Btu), which is also the unit of heat.
The specific internal energy (u) of a substance is its internal energy per unit mass. It equals the
total internal energy (U) divided by the total mass (m).
(1-13)
u
U
m
where:
u
=
specific internal energy (Btu/lbm)
U
=
internal energy (Btu)
m
=
mass (lbm)
HT-01
Page 16
Rev. 0
