Experiment 3 Hydraulics Lab (1)

8/19/2019 Experiment 3 Hydraulics Lab (1)

1/12

Hydraulics Lab (ECIV Islamic University –

1 Instructrs ! "r# $%alil En# &%ammed #

Experiment (3): Impact of jet

Introduction:

Impact of jets apparatus enables experiments to be carried out on the reaction

force produced on vanes when a jet of water impacts on to the vane. The study of

these reaction forces is an essential step in the subject of mechanics of fluids

which can be applied to hydraulic machinery such as the Pelton wheel and the

impulse turbine.

Purpose:

To investigate the reaction force produced by the impact of a jet of water on to

various target vanes.

Apparatus:

1. Impact of jet apparatus (Figure

1.

!. "ydraulic bench.


2/12

Hydraulics Lab (ECIV Islamic University –

! Instructrs ! "r# $%alil En# &%ammed #

Figure 1: Impact of jet apparatus


3/12

Equipment setup:

#et up the apparatus on top of the hydraulics bench with the left hand support

feet of the impact of jet apparatus located on the two left hand locating pegs

of the hydraulics bench so that the apparatus straddles the weir channel. $onnect

the feed tube from the hydraulics bench to the boss on the rear of the base of the

impact of jet apparatus. Fit the %mm no&&le and the normal 'at target.

Figure 2: Illustratie figure of impact of jet apparatus

!"eor#:

hen a jet of water 'owing with a steady velocity stri)es a solid surface the

water is deflected to 'ow along the surface. If friction is neglected by assuming

an inviscid 'uid and it is also assumed that there are no losses due to shoc)s

then the magnitude of the water velocity is unchanged. The pressure exerted by

the water on the solid surface will everywhere be at right angles to the surface.

$onsider a jet of water which impacts on to a target surface causing the direction


4/12

of the jet to be changed through an angle as shown in figure ! below. In the

absence of friction the magnitude of the velocity across the surface is e*ual to the

incident velocity +i. The impulse force exerted on the target will be e*ual and

opposite to the force which acts on the water to impart the change in direction.


5/12

,pplying -ewtons second law in the direction of the incident jet

This is the resultant force acting on the 'uid in the

direction of motion. This force is made up of three

components/

• Force exerted in the given direction on the 'uid by any solid body touching the

control volume.

• Force exerted in the given direction on the 'uid by body force (e.g. gravity.

• Force exerted in the given direction on the 'uid by fluid pressure outside the control

volume.

0y -ewtons third law the fluid will exert an e*ual and opposite reaction on its

surroundings.

The force exerted by the 'uid on the solid body touching the control volume is

e*ual and opposite to F2 . #o the reaction force 2 is given by/


6/12

Figure 3: Impact of a jet


7/12

Application to impact of jet apparatus

In each case it is assumed that there is no splashing or rebound of the water from

the surface so that the exist angle is parallel to the exit angle of the target.

The jet velocity can be calculated from the measured 'ow rate and the no&&le exit

area.

"owever as the no&&le is below the target the impact velocity will be less than

the no&&le velocity due to interchanges between potential energy and )ineticenergy so that /

where is the height of target above the

no&&le exit.

1$ Impact on normal plane

target For the normal plane

target 3 45° Therefore

!. Impact on conical target

The cone semi6angle 3 7%°

Therefore

8. Impact on semi%sp"erical target

The target exit angle 3 18%°

Therefore


8/12

Figure &: Interc"angea'le target anes

Procedures:

1. Position the weight carrier on the weight platform and add weights until the top of

the target is clear of the stop and the weight platform is 'oating in mid position.

9ove the pointer so that it is aligned with the weight platform. 2ecord the value of

weights on the weight carrier.

!. #tart the pump and establish the water 'ow by steadily opening the benchregulating valve

until it is fully open.

8. The vane will now be de'ected by the impact of the jet. Place additional

weights onto the weight carrier until the weight platform is again 'oating in mid

position. 9easure the 'ow rate and record the result on the test sheet together

with the corresponding value of weight on the tray. :bserve the form of the

de'ected jet and note its shape.

7. 2educe the weight on the weight carrier in steps and maintain balance of the

weight platform by regulating the 'ow rate in about three steps each time

recording the value of the 'ow rate and weights on the weight carrier.

%. $lose the control valve and switch o; the pump. ,llow the apparatus to drain.


9/12

>. 2eplace the normal vane with the 7%? conical vane and repeat the test with both

the %mm and =mm no&&les.

=. 2eplace the 7%? conical vane with the hemispherical vane and repeat the tests withboth the

%mm and =mm no&&les.


10/12

< Instructrs ! "r# $%alil En# &%ammed #

esults:

1. 2ecord the results on a copy of the results sheet provided.

!. $alculate for each result the 'ow rate and the no&&le exit velocity. $orrect the

no&&le velocity for the height of the target above the no&&le to obtain the impact

velocity.

8. $alculate the impact momentum and plot graphs of impact force against impactmomentum

and determine the slope of the graphs for each target. $ompare with

the theoreticalvalues of 1 5.!4!4 and 1.>5>1 for the normal plane target conical target andhemispherical

target respectively.

!arget

anes

(degree

*o++l

e ,ia$

(mm)

-eig"t of

target

a'oe

Additional.eig"ts

olume of

/ater

collected

!ime

(sec)

%

85

85

85

F l a t =

85

85

85

%

!%

!%

!%

o n i c a l =

!%

!%

!%

%

85

85

85

=

85

85


11/12

< Instructrs ! "r# $%alil En# &%ammed #

2 e m i %

s p 85


12/12

> Instructrs ! "r# $%alil En# &%ammed #

!arget

anes

(degree

*o++l

e

,ia$ (m3s)

(ms)

(ms)

(*)

lope

%

1

F l a t =

%

4$2525

n i c a l =

%

1$6461

e m i %

" e r i c a l

=

Documents

Experiment 3 Hydraulics Lab (1)