Modern Engineering Thermodynamics

6.5 Nozzles and Diffusers 177
We are now ready to carry out a thermodynamic analysis ofanopensystem.Webeginwithsimpleexamples
and work toward more difficult ones. The example problems are designed to illustrate the text material that
immediately precedes the example. Therefore, the analysis section of the solution often is abbreviated, with
appropriate reference made to the previous text material wherein the analysis has already been carried out. Do
not be misguided by this.
Homework and examination problems usually do not simply mimic textbook examples. The purpose of these
examples is not to give you a set of ready-made formulae into which you can plug numbers to solve specific
problems. Their function is to teach you analysis techniques so that you have the ability and self-confidence to
solve any thermodynamics problem whatsoever, whether you have seen one similar to it or not.
EXAMPLE 6.2
The nozzle on a lawn or garden hose has a 1.00 inch inlet inside diameter and an inlet pressure of 80.0 psig at 60.0°F. The
mass flow rate of water through the nozzle is 0.800 lbm/s. Assuming the water flows through the nozzle isothermally,
determine
a. The outlet velocity from the nozzle, ðV out Þ a .
b. The height to which the stream of water rises above the nozzle outlet when the nozzle is pointed straight up, ðZ out Þ b
.
Solution
First, draw a sketch of the system (Figure 6.4).
(Z out ) b
(V in ) b = (V out ) a
System b
System a
p = 80.0 psig
T = 60.0°F
1.00 in diameter
FIGURE 6.4
Example 6.2.
m = 0.800 lbm/s
This is an open system, and the unknowns are ðV out Þ a
and ðZ out Þ b
(see Figure 6.4). The material is liquid water. We assume
from our experience with garden hose nozzles that the system is a steady state, steady flow, single-inlet, single-outlet open
system.
(Continued )