Some Steady-Flow Applications of the Momentum Balance

3 SOME STEADY-FLOW APPLICATIONS OF THE MOMENTUM BALANCE 

If we choose as our system some pipe, duct, or channel with steady flow through it in one direction, e.g., the x direction, then Eq. 7.15 becomes 

The application of this steady-flow one-dimensionai momentum balance will be illustrated by several examples. 

Many applications of Eq. 7,16 involve jets. A jet is a stream of fluid which is not confined within a pipe, duct, or channel examples are the stream of water issuing from a garden hose and the exhaust gas stream from a jet engine. If a jet is flowing at a subsonic velocity, its pressure will be the same as the pressure of the surrounding fluid. If a jet enters or leaves a system or device at subsonic speed, it will enter and leave at the pressure of the surrounding fluid, although its pressure may be different inside the device. 

Example 7.3. The police are using fire hoses to disperse an unruly crowd. The fire hoses deliver. 01 m /s of water at a velocity of 30m/s. One member of the crowd has picked up a garbage can lid and is using it as a shield to deflect the flow. She is holding it vertically, so the jet splits into a series of jets going off in the y and z directions, with no x component of the velocity see Fig. 7.2. What force must she exert to hold the garbage can lid  

---