
Principle of Conservation of Energy 39
Example 3.7
Write the mass balance equation for the control volume of Figure 3.9.
Solution
The mass balance equation is
or, in terms of density, cross section area, and velocity at every inlet and exhaust
ρρρρ ρAV AV AV AV AV
(
)
+
(
)
=
(
)
+
(
)
+
(
)
2314 5
.
A procedure similar to that used to develop the mass balance equation for a con-
trol volume is used to derive an appropriate form of the energy balance equation for
a control volume. Figure 3.10 shows the same control mass at times t and t + dt. In
FIGURE 3.9 A control volume with multiple inlets and multiple exhausts.