Exp. (3): Impact Jets Purpose Impact Jet Apparatus (Fig. 1...

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Exp. (3): Impact Jets Purpose: To investigate the reaction force produced by the impact of a jet of water on various target vanes. Apparatus: Impact Jet Apparatus (Fig. 1), Targets (Fig. 2). Figure 1: Impact jet apparatus Figure 2: Interchangeable Target Vanes

Transcript of Exp. (3): Impact Jets Purpose Impact Jet Apparatus (Fig. 1...

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Exp. (3): Impact Jets

Purpose: To investigate the reaction force produced by the impact of a jet of water on various target vanes. Apparatus: Impact Jet Apparatus (Fig. 1), Targets (Fig. 2).

Figure 1: Impact jet apparatus

Figure 2: Interchangeable Target Vanes

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Theory:

Figure 3 : Impact of a Jet

θ - ρ Q V

R

i

cos1

AQVn

g hVV ni 2 - 22 Where: R : Impulse force.

iV : incident velocity.

Q : Volumetric flow rate.

nV : jet velocity.

h : height of target above nozzle. Procedure:

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 floating in mid position. Move the pointer so that it is aligned with the weight platform.

2. Start the pump and establish the water flow by steadily opening the bench regulating valve until it is fully open.

3. The vane will now be deflected by the impact of the jet. Place additional weights onto the weight carrier until the weight platform is again floating in mid position. Measure the flow rate (volume collected in certain time) and record the result on the test sheet, together with the corresponding value of additional weight on the tray. Observe the form of the deflected jet and note its shape.

4. Reduce the weight on the weight carrier in steps and maintain balance of the weight platform by regulating the flow rate in about eight or ten even steps (In the lab we made 3 steps only), each time recording the value of the flow rate and weights on the weight carrier.

5. Close the control valve and switch off the pump. Allow the apparatus to drain.

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6. Replace the 5mm nozzle with the 8mm diameter nozzle and repeat the tests. 7. Replace the normal vane with the 45 conical vane and repeat the test with both

the 5mm and 8mm nozzles. 8. Replace the 45 conical vane with the hemispherical vane and repeat the test with

both the 5mm and 8mm nozzles. Data & Results:

1. Record the results on a copy of the result sheet provided. 2. Calculate for each result the flow rate and the nozzle exit velocity. Correct the

nozzle velocity for the height of the target above the nozzle to obtain the impact velocity.

3. Calculate the impact momentum, and plot graphs of the impact force R against impact momentum and determine the slope of the graphs for each target. Compare with the theoretical values.

Target Vanes (degrees)

Nozzle Dia -- d --

(mm)

Additional Weights -- m --

(gm)

Volume of water Collected - V - (Liter)

Time to collect -- t --

(sec)

°

5

90

θ=

Flat

8 320 20 48 250 20 58 160 20 71

°

5

45

θ=

Coni

cal

8 110 20 48 80 20 52 60 20 82

°

5

135

θ=

Sem

i-sp

heric

al

8 450 20 55 300 20 66 150 20 88

Comment: ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………