EXPERIMENT NO: 4
IMPACT OF JET
OBJECTIVE:
To determine the coefficient of impact for vanes (flat and curved) and compare with theoretical value.
APPARATUS REQUIRED:
Collecting tank, transparent cylinder, nozzle of diameter 10 mm and vane of different shape (flat and
curved)
THEORY:
Momentum equation is based on Newton’s second law of motion which states that the algebraic sum of
external forces applied to control volume of fluid in any direction is equal to the rate of change of
momentum in that direction. The external forces include the component of the weight of the fluid & of
the forces exerted externally upon the boundary surface of the control volume.
If a vertical water jet moving with velocity is made to strike a target, which is free to move in the
vertical direction then a force will be exerted on the target by the and impact of jet, according to
momentum equation this force (which is also equal to the force required to bring back the target in its
original position) must be equal to the rate of change of momentum of the jet flow in that direction.
Balancing Weight
1. Nozzle
2. Direction of Velocity before impact
3. Direction of Velocity after impact
4. CV- curve vane
Figure1: Impact of jet on curve plate axis vertical
Prepared by: Er./Lr. Saraswati Thapa and Er./ Lr. Tirtha Raj Karki Lecturer, Dept. of Civil Engineering, KEC, Kalimati Page 16
Figure 2: Illustrative figure of impact of jet apparatus
Formula Used:-
F'=ρ Q V (1-cosβ)
F'=ρ QV (1-cosβ) , as v=Q/a
Where F' =force (calculated)
ρ = density of water
β =angle of difference vane
V =velocity of jet angle
Q =discharge
A =area of nozzle (πd2/4)
(i) For flat vane β=90o
F' = ρ QV= ρ Q2/a
(ii) For hemispherical vane β=180o
F' = 2ρ QV= 2 ρ Q2/a
F = Force (due to putting of weight)
For % error = (F- F')/ F'x10
Prepared by: Er./Lr. Saraswati Thapa and Er./ Lr. Tirtha Raj Karki Lecturer, Dept. of Civil Engineering, KEC, Kalimati Page 17
PROCEDURE:
1. Note down the relevant dimension or area of collecting tank, dia of nozzle, and density of water.
2. Install any type of vane i.e. flat or curved.
3. Install any size of nozzle i.e. 10mm or 12mm dia.
4. Note down the position of upper disk, when jet is not running.
5 Note down the reading of height of water in the collecting tank.
6. As the jet strike the vane, position of upper disk is changed, note the reading in the
scale to which vane is raised.
7. Put the weight of various values one by one to bring the vane to its initial position.
8. At this position finds out the discharge also.
9. The procedure is repeated for each value of flow rate by reducing the water supply.
10. This procedure can be repeated for different type of vanes and nozzle.
PRACTICAL RELEVANCE:
It helps to illustrate the momentum principle used to convert the rate of change of momentum into force.
And also help to understand the concept of electricity energy is generation through hydropower.
OBSERVATION AND CALCULATION:
Dia of nozzle = 10mm
Mass density of water ρ = 1000kg/m2
Area of collecting tank =
Area of nozzle =
Horizontal flat vane
When jet is not running, position of upper disk is at =
Discharge measurement Balancing Theoretical Force Error in %
S.N. Initial Final Time Discharge Mass, Force F'= = (F-F')/F'
(cm) (cm) (sec) (cm3/sec) Q W (gm) F (dyne) ρ Q2/a (dyne)
1.
2.
3.
4.
5.
Curved hemispherical vane
When jet is not running, position of upper disk is at =
Discharge measurement Balancing Theoretical Force Error in %
S.N. Initial Final Time Discharge Mass W Force F'= 2ρQ2/a (dyne) = (F-F')/F'
3
(cm) (cm) (sec) (cm /sec) Q (gm) F (dyne)
1.
2.
3.
4.
5.
Prepared by: Er./Lr. Saraswati Thapa and Er./ Lr. Tirtha Raj Karki Lecturer, Dept. of Civil Engineering, KEC, Kalimati Page 18
RESULT:
CONCLUSION AND DISCUSSION:
Prepared by: Er./Lr. Saraswati Thapa and Er./ Lr. Tirtha Raj Karki Lecturer, Dept. of Civil Engineering, KEC, Kalimati Page 19
