HM15013E

Equipment for Engineering Education

,QVWUXFWLRQV0DQXDO HM150.13

Methods of Flow

Measurement

G.U.N.T. Gerätebau GmbH P.O. Box 1125 D-22881 Barsbüttel • Germany Phone (040) 670854-0 Fax (040) 670854-42

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HM150.13 Flowmeter Demonstration Apparatus

Instruction Manual

Publication No.: 917.00013A15012

12/95

HM150.13 Flowmeter Demonstration Apparatus

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Table of Contents 1

Technical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2

Pressure measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1

6-tube manometer panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2

Measuring differential pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.3

Measuring absolute pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.4

Connecting and operating the manometer . . . . . . . . . . . . . . . . . . . . 6

3

4

Flow measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1

Variable-area flowmeter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2

Nozzle and Orifice plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3

Venturi meter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Technical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1

HM150.13 Flowmeter Demonstration Apparatus

1

Technical Description The apparatus is designed to demonstrate three basic types of flow meter. The apparatus enables the following instruction capabilities:

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1

-

Comparision of different flow meter types

-

Study of flow and pressure measurement methods

-

Determining the meter coefficient

-

Calibration of flow meters

9

1 Panal with stand 2 Multi-tube manometer

5

3 Venturi meter 4 Orifice plate 5 Variable area meter 6 Flow control

2

6

7 Water inlet 8 Water drain

3

9 Pressure tapping

4

8

7

The test section consists of a Venturi meter (3), an orifice plate (4) and a variable area meter (5). A flow control valve (6) permits variation of the flow rate. Pressure tappings enable measurement of the head losses of each flow meter. The tappings are

1 Technical Description

2

HM150.13 Flowmeter Demonstration Apparatus

connected via hoses to a multi-tube manometer bank (2). The manometer panel incorporates a manifold with an air bleed valve. Flow can be measured by using the volumetric measuring tank of the Hydraulics Bench HM150. For visible function the Venturi meter and the orifice device are made of perspex. All components of the unit are assembled on an instrumentation panel (1) with stand.

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The unit is suited to be placed on the top of the HM 150 Hydraulics Bench in order to make use of the water supply and volumetric measurement facilities of the bench.

1 Technical Description

3

HM150.13 Flowmeter Demonstration Apparatus

2

Pressure measurement

2.1

6-tube manometer panel Vent valve

The 6-tube manometer panel consists of 6 glass level tubes with a mm scale behind them. -

The measuring range is 300 mm of water

-

All level tubes are connected to one another at the top and have a common vent valve.

-

Differential pressure is measured with the vent valve closed, and absolute pressure with the vent valve open.

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level tubes

Drain valve

2.2

Connection for measurement lines

Measuring differential pressure For this purpose, the vent valve is closed. A cushion of air with pressure pL is created above the two columns of water. This produces the following equation for the pressures to be measured, p1 and p2

Air cushion pL

p1 = pL + h1 ρ g , p2 = pL + h2 ρ g .

∆h h1

The differential pressure is then h2

p1

p2

∆p = p1 − p2 = pL + h1 ρ g − pL − h2 ρ g. The pressure pL is extracted, producing

∆p = ∆h ρ g

2 Pressure measurement

with

∆h = h1 − h2 .

4

HM150.13 Flowmeter Demonstration Apparatus

The zero point for differential pressure measurement can be set via the pressure pL. For a maximum measuring span, it is expedient to position the zero point or mid-point centre of the measuring scale

h1 + h2 2

at the

hmax 2

h1 + h2 hmax p1 − pL + p2 − pL = 2 = . 2 2ρg

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This produces the following equation for the pressure of the air cushion pL =

p1 + p2 − hmax ρ g . 2

The pressure is set via the vent valve.

2.3

Measuring absolute pressure

Air pressure p0

h

For measuring absolute pressure, the vent valve is kept open and the pressure pL refers to the atmospheric air pressure p0. In this case, it is also necessary to consider the height hm between the measuring point and the zero point of the manometer pabs = p0 + ( h + hm ) ρ g .

hm pabs

2 Pressure measurement

5

HM150.13 Flowmeter Demonstration Apparatus

Connecting and operating the manometer

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2.4

2 Pressure measurement

-

Connect measurement lines

-

Open all valves at pipe section and 6-tube manometer, let the water flow for 1 minute

-

Close flow control valve

-

Close drain valve of the 6-tube manometer to vent the measurement lines

-

Close vent valve of the 6-tube manometer

-

Close water inlet

-

Disconnect measuremet lines

-

Open vent and drain valve to discharge level tubes of the 6-tube manometer

-

Close vent and drain valves

-

Open flow control valve slowly

-

Connect measurement lines again

-

Open water inlet slowly

-

Adjust the heights of the water in the manometer tubes with the help of flow control valve until water becomes visible

-

Set the flow rate and the measuring scale with the inlet and outlet control valves

6

HM150.13 Flowmeter Demonstration Apparatus

3

Flow measurement

3.1

Variable-area flowmeter A variable-area flowmeter with the following characteristics is used to measure flow rate.

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h

Read here

Float

3.2

-

Plastic measuring tube

-

Interchangeable stainless steel float

-

Interchangeable percentual scale

-

Max. flow rate 1600 l/h

The flow rate can be read from the upper edge of the conical attachment. Air bubbles or dirt particles on the float may affect measurement precision. To flush them out, operate the test stand at maximum flow rate first. To do so, open all cocks fully.

Nozzle and Orifice plate

Nozzle

The orifice plate housing is made of transparent plastic allowing visible functioning of the orifice plate. The flow causes a pressure loss between inlet and outlet. Two tappings allow measurement of inlet and outlet pressurs.This differential pressure ∆p is proportional to the flow. . 2 ∆p V = α ε Ad √  =k√  ∆p ρ

∆p

litre for Nozzle h√  mbar litre k = 293 for Orifice h√  mbar

with the constant k = 231 and

3 Flow measurement

7

HM150.13 Flowmeter Demonstration Apparatus

3.3

Venturi meter The Venturi housing is made of transparent plastic allowing visible functioning of the Venturi. The pressure in the Venturi is inversly proportional to the velocity in the Venturi according to Bernoulli’s Law.

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∆p

Two tappings allow measurement of the inlet pressure and the pressure at the smallest area.This differential pressure ∆p is proportional to the flow. . 2 ∆p V = α ε Ad √  =k√  ∆p ρ with k = 240

4

litre .  mbar h√

Technical Data Water multi-tube manometer, 6-fold:

300

mm H2O

Venturi meter: nom. diameter: min. diameter:

28.4 14.0

mm mm

Nozzle and Orifice meter: nom. diameter: 28.4 Nozzle diameter: 18.5 Orifice diameter: 14.0

mm mm mm

Variable area meter:

1600

ltr/h

1100 x 640 x 870 40

mm kg

Overall dimension (L x W x H): Weight:

4 Technical Data

8