Fluid Dynamics and Pressure

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Chapter 3: FLUID FLOW

CHAPTER

THREE
FLUID FLOW

3.1 3.2 3.3 3.4 3.5

Fluid Flow Unit Pump Test Unit Hydraulics bench and accessories Flow Curve Determination for Non-Newtonian Fluids Fixed and Fluidized Bed

Facts which at first seem improbable will, even in scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty. GALILEO GALILEI

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3.1. FLUID FLOW UNIT

Keywords: Pressure loss, straight pipe, pipe bend, orifice meter, venturi meter.

3.1.1. Object

The object of this experiment is to investigate the variations in fluid pressure for flow in straight pipes, through pipe bends, fittings, orifice and venturi meters.

3.1.2. Theory

When a fluid flows along a pipe, friction between the fluid and the pipe wall causes a loss of energy. This energy loss shows itself as a progressive fall in pressure along the pipe and varies with the rate of the flow. The head loss due to friction can be calculated by the expression: Lu 2  D

hf  4 f 

(3.1.1)

where

hf : head loss due to friction, m H2O D : diameter of pipe, m f : friction factor g : acceleration due to gravity, m/sec2 L : length of pipe, m u : mean velocity, m/sec  : density of fluid, kg/m3

The change of direction forced on a fluid when it negotiates a bend produces turbulence in the fluid and a consequent loss of energy. The net loss in pressure is greater than that for the same length of straight pipes. Abrupt changes of direction produce greater turbulence and larger energy losses than do smoothly contoured changes.

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Chapter 3: FLUID FLOW

When a fluid flows through an orifice or a venturi meter, a loss of pressure energy occurs due to the turbulence created. A straight line relation exists between the flow rate and the square root of the pressure drop value, and this principle is utilized in the design of the orifice and venturi meters.

The internal construction of many pipe fittings leads to the construction of fluid flowing through them causing turbulence of varying magnitude with a consequent energy loss. This behavior can be clearly shown using gate and globe valves in comparison with one another. A globe valve will cause an energy loss even when fully open. Partially closed position of either of these valves increases appreciably the energy loss across them compared with the fully open position. energy losses across a fitting are observed in the experiment by noting the pressure drops across each of these valves.

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3.1.3. Apparatus The apparatus used in this experiment is shown in Figure 3.1.1. It consists of 14 main parts. 5 5

7

6

8

9

3

10

9

4 11 11

9

9 1 2 12 13 14

Figure 3.1.1. The fluid flow unit.

1. Pump 2. Flexible joint 3. Water pressure gauge 4. Liquid flowmeter 5. Vent valve 6. Cylindrical vessel (50 lt) 7. Venturi-meter 8. Orifice-meter 9. Make-up joint 10. Staright pipe section 11. Various pipe fittings 12. Gate valve 13. Globe valve 14. Drain valve

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Chapter 3: FLUID FLOW

3.1.4. Experimental Procedure

A. Straight pipes, pipe bends, orifice and venturi meters

1.

Select the pipe line on which the experiment will be performed by turning of the isolation valves for all other horizontal pipe runs.

2. 3. 4. 5.

Be sure that water manometers are connected to the pressure tappings read zero. Check that isolating valve on the selected pipe run is fully open. Turn off the flow control valve. Operate the control valve to give successively higher flow rates (9 times) and note manometer readings for each case.

6.

With the same flow rates, repeat the experiment once more to avoid wrong or insufficient data.

B. Pipe fittings

1. 2.

Apply steps 1 through 4 of the procedure (A) and then continue with the following ones. With the valves fully open, operate the control valve to give successively higher flow rates, noting the manometer readings for each case.

3. 4.

Repeat step 2 with the gate...
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