Ahmed Essam Mansour
Section: "1", Monday 2-5 pm
Impact of a Jet
October 9, 2006
• Study the relation between the force produced and the change of momentum when a jet strikes a vane.
• Compare between force exerted by a jet on a flat plate and on a hemispherical surface.
In order to calculate the force caused by impact of a jet into a flat plate or curved vane, the change in momentum principle is applied;
Force = Rate of change in momentum
F = ρ Q ΔV
F = ρ Q (Vin – Vout)
F: the force exerted by the jet on the plate.
ρ: the mass density of water (= 1000 kg/m3).
Q: volumetric rate of flow (m3/s).
ΔV: the change in velocity just after and before impact.
The volumetric flow rate in the equation 'Q' is calculated in the experiment by taking an amount of volume in a known period of time and then use;
Vin is calculated in the experiment by first knowing
the velocity at the nozzle and then using the
Vnozzel is measured by know the diameter of the
nozzle (dia = 10mm) and the volumetric flow rate
'Q' calculated previously,
Vnozzel = Q/ A
Then Vin is calculated by;
Vin2 = Vnozzel 2 – 2 g S
g: the gravitational acceleration (9.81 m/s2).
S: the distance between the jet and the plates (35mm)
Vout generally equals Vin cos θ, where θ represents the change in direction of the jet.
For the flat plat θ = 90◦, so that Vout = 0.0 .
For the Hemispherical cup θ = 180◦, so that Vout = -Vin
So the following relations are used for calculating the Predicted values of the force;
For the Flat plate:
F = ρ Q Vin
For the Hemi spherical cup:
F =2 ρ Q Vin
The measured force from the experiment is calculated by using the equilibrium of moment equation.
And the final relation for calculating the measured force is; F = 4 * 9.81 * d
Where 'd' is the ruler reading for the jockey weight.
This apparatus is designed primarily for use on the TQ H1 or H1D Hydraulics Bench. By directly measuring the force exerted on the plates by the water jet, it allows the student to experimentally study the theoretical momentum laws used to solve jet impact problems. An upper weigh beam is pivoted on precision
bearings at one end and carries along its length the
fixed test plate. The beam jockey and a scale are
used to measure the jet force. An adjustable spring
supports the lever and is used for setting the initial
zero level of the beam. A hanging tally weight on
the end of the beam is used to return the beam to
horizontal each time a reading is required.
A high velocity jet is produced by the vertical
tapered nozzle. For clear observation, both nozzle
and test plate are contained in a transparent
The apparatus is leveled for test using the plastic
screwed ball feet provided on the base legs.
A drain tube, in the base of the cylinder vessel, is used to direct the water to the weigh tank of the H1 or H1D Bench where the flow can be accurately measured.
1. The lever was set to is balanced position with the jockey weight is at its zero position.
2. The water valve was opened to it max, and the jockey was
repositioned so that the lever is back to its balanced position.
3. The water tank was emptied of water and the refilled to take reading of time versus volume which was used to calculate the volumetric rate of flow.
4. A series of reading for the similar procedures was taken for the flat plate with reducing the rate of flow in each reading by using the valve.
5. The same steps were then repeated by using the hemispherical cup instead of the flat plate.
(m /s) * 10