CE 321 INTRODUCTION TO FLUID MECHANICS SPRING 2009

LABORATORY -4: LINEAR MOMENTUM

PURPOSE

To investigate the interaction between reactive forces and directional changes in momentum flux

OBJECTIVE

To determine the forces exerted by a vertical rising liquid jet impacting on targets of various shapes.

EQUIPMENT REQUIRED

Hydraulic Bench, Impact Jet Apparatus, Stopwatch, Targets, Weights

In using the momentum equation applied to deflectors we assume the following:

·  Constant external pressure on the fluid jet so that the pressure in the fluid remains constant as it moves over a deflector

·  Negligible frictional resistance due to the fluid-deflector interaction so that the relative speed between the deflector surface and the jet stream remains unchanged, a result of Bernoulli’s equation

·  Negligible lateral spreading of the plane jet

·  Negligible weight of the control volume (body force)

The linear momentum equation for a rising jet impacting on a target plate is:

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Where,

F is the reactive vertical force on the target (F)

Q is the discharge from the jet (L3/T)

A is the cross sectional area of the jet (L2)

 is the angle of the exiting jet (degrees)

is the fluid Density (M/L3)

Figure1:Representation of the vertical rising jet Impacting on a

target plate. All important parameters are seen in the picture

PROCEDURE

A. PREPARING THE APPARATUS

1. Remove the top plate from the transparent casing of the apparatus.

2. Place the flat target (90°) on the rod attached to the weight pan and

3. Place the top plate back on to the casing.

4. Connect the inlet pipe to the bench and place the apparatus on the open channel.

5. Level the base of the apparatus.

6. Adjust the level gage to suit the datum on the weight pan. Figure 2 : Picture of a Jet Impact Apparatus used in the

experiment. The jet can be seen striking a 1800 target

B. RUNNING THE EXPERIMENT

a) Allow water to flow through the apparatus.

1. Place a mass on the weight pan.

2. Turn on the hydraulic bench.

3. Adjust the flow of the bench by turning the flow valve until the weight pan is in line with the level gage.

4. Oscillate the weight pan to minimize the effect of friction when testing for the level.

b) Take readings of volume and time

1. Measure the time required to fill a known volume and enter the data in the sheet.

2. Record the mass on the weight pan and enter in the data collection sheet

c) Continue the experiment by adding an additional mass to the weight pan and repeat the time and volume measurements.

d) Repeat the above steps using the other targets. (30° and 120°)

C. CLEANING UP

When you have finished collecting data, drain the tank and replace the weights and stop watch back into their appropriate place

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