ME 313-Experiment #3
Hydrodynamic Force Exerted by a Free Jet
Purpose: To verify the linear momentum principle by measuring the force exerted by a vertical
liquid jet on an axi-symmetric flow-deflection vane.
Apparatus:
Armfield Hydraulic Bench and Hydrodynamic Force Demonstration unit.
Sketch a labeled schematic diagram showing the internal functions of the hydraulic bench and
the hydrodynamic force measurement unit.
Theory: (Ref. Munson/Young/Okiishi A Brief Introduction to Fluid Mechanics, p.148-164)
Review the linear momentum equation, and consider the special case of axi-symmetric deflection
of a vertical jet. Sketch a control volume diagram, neglect friction and the weight of the jet
itself, and show that the vertical reaction force to balance the jet is (in terms of liquid density ,
jet velocity V, deflection angle , and cross section area A of nozzle):
F
  Q V   1  cos   
  A  1  cos    V 2
Procedure:
1. Install the 900-deflection vane at the lower end of the shaft of the platform.
2. The weight of the platform plus vane is now balanced by the spring. Adjust the height of the
pointer so that it is aligned with the level marking on the platform.
3. Place a 62.75 g-mass on the platform. The spring is compressed and the platform is lowered.
4. Turn on the water pump and adjust the flow control valve so that the free jet pushes the
platform back to its original level, i.e. aligned with the pointer.
5. Close the drain valve at the bottom of the collection tank of the hydraulic bench. Record the
time required to accumulate a known volume of water in the tank.
6. Open the valve to drain the tank. At the same time add another 62.75 g-mass onto the
platform and repeat steps 4 and 5.
7. Repeat until the control valve is fully open.
8. Turn off the pump, install the 1350-deflection vane and repeat steps 2 through 7.
9. Repeat the experiment with the 1800-deflection vane.
Results:
For each deflection angle, calculate the flow rate, jet velocity and the reaction force. Plot this
theoretical reaction force for each jet velocity. On the same graph, also plot the actual balancing
weight for each jet velocity.
Conclusion:
Compare the theoretical curve with the experimental data, and conclude if the momentum
principle is verified with this experiment. Provide an explanation if the data deviate from the
theoretical prediction.
Date: _____________
Name __________________
ME313-Expt 3 Data
Hydrodynamic Force Exerted by a Free Jet
Water density,  = 998 kg/m3.
Diameter of nozzle, D = 0.8 cm.
Deflection
Angle:
Balancing
Mass (g)
 = 900
Volume (l)
collected
Time to
collect (s)
 = 1350
Volume (l)
collected
Time to
collect (s)
 = 1800
Volume (l)
collected
Time to
collect (s)