HM 150.29 Losses in Bends and Fittingscste.sut.ac.th/miscste/company/manual/HM150_29e.pdf · 2017-02-03 · 1 Unit Description The HM 150.29 unit is used to investigate pressure losses

Experiment Instructions

HM 150.29 Losses in Bendsand Fittings

Instructions Manual

Publication-No.: 06/98

Please read and follow the instructions before the first installation!

917.000 29 A 150 12

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Table of Contents

1 Unit Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Performing the Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 6-fold pressure gauge panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Differential pressure measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.3 Absolut pressure measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.4 Connecting and handling manometers . . . . . . . . . . . . . . . . . . . . . . . 6

2.4.1 Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.4.2 Setting the zero position . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 Calibration Curve Using Area Reduction . . . . . . . . . . . . . . . . . . . . . . 8

3.2 Exercise Stand Characteristic Curve . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3 Pipe flow with friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.3.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.4 Resistance coefficients of special pipeline elements. . . . . . . . . . . . 14

3.4.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.4.2 Pipe bend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.4.3 Performing the Experiment . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.5 Changes in Cross-Sectional Area . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.5.1 Performing the Experiment . . . . . . . . . . . . . . . . . . . . . . . . . 19

4 Technical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1 Primary Dimensions of the Exercise Unit . . . . . . . . . . . . . . . . . . . . 20

4.2 Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.3 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.4 Tables and Diagrams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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1 Unit Description

The HM 150.29 unit is used to investigate pressurelosses in elbows and fittings, as well as in valvesand reductions and enlargements in the cross-sec-tional area.

The measuring circuit comprises a pipe systemwith various fittings, a spherical valve, an areaenlarger and a reducer. The flow rate can be variedusing the spherical valve.The unit has a 6 channel manometer and a spring-tube manometer for measuring individual relativepressures. Circular measuring chambers are builtinto the pipework such that the pressure differenceacross all relevant objects can be measured.

Water is supplied either from the HM 150 BasicHydraulics Bench or from the laboratory mains.

Using the HM 150 Basic Hydraulics Bench aclosed water circuit can be constructed.

Experiments that can be performed:

- Investigation of the pressure loss in elbows andfittings

- Comparison of different elbows and fittings

- Influence of the radius of fittings

- Valve characteristics

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1 Unit Description 1

1.1 Unit Construction:

6

13

7

2

9

14

8

3

11 12 5

10 4 1

1 Base Frame with Rear Wall

2 Hose Connection, Water Inlet

3 Hose Connection, Water Outlet

4 Pipe Elbow

5 Rounded Pipe Elbow

6 Tight Radius Pipe Bend

7 Large Radius Pipe Bend

8 Reducer

9 Enlarger

10 Spherical Valve

11 6 Channel Manometer

12 Spring-Tube Manometer

13 Circular Chamber with Measuring Gland

14 PVC Hose with Plug-In Connector

Fig. 1.1 Unit Construction

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1 Unit Description 2

2 Performing the Experiments

The following descriptions of the performance ofexperiments and the experiments in Section 3 arebased on the HM 150 Basic Hydraulics Bench.

- Place the test set up on the HM 150 FluidMechanics Basic Module.

- Make the hose connections between the HM 150and the unit, feed and return.

- Close all spherical valves, basic module andexperimental set up.

- Connect the manometer to the required points.

- Switch on the pump on the basic module andslowly open the spherical valve on the HM 150.

- Slowly open the spherical valve on the HM 150.29and bleed the manometer, see Section 2.4.

- By simultaneously adjusting the bleed anddrain valves on the 6 channel manometer, re-gulate the water level such the columns ofwater are within the measuring range.

- Determine the flow rate. To do this measure thetime t that is required to fill the volumetric tankon the HM 150 from 10 to 20 or 30 litres. Forthis purpose close the drain underneath thetank.

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2 Performing the Experiments 3

2.1 6-fold pressure gauge panel

The 6-fold pressure gauge panel is a 6-level tubemade of glass with a millimeter scale behind.

- The measuring range is 300 mm H2O.

- All levels tubes are connected to each other atthe top end and have a joint vent valve.

- When the vent valve is closed, the differentialpressure is measured with the vent valve of theoverpressure open.

- The measuring points are connected to thebottom end of the level tubes with quick-relea-se hose couplings.

- the first level tube has a drainage valve at thebottom end.

2.2 Differential pressure measurement

The vent valve is closed in this case. An air cushionwith the pressure pL forms via the two water co-lumns. For the measured pressures p1 and p2, thisresults in

p1 = pL + h1 ρ g

p2 = pL + h2 ρ g .

The differential pressure is then

∆p = p1 − p2 = pL + h1 ρ g − pL − h2 ρ g.

The pressure pL stands out and the following isobtained

∆p = ∆h ρ g mit ∆h = h1 − h2 .

Connection tomeasuring lines

vent valve

Level tubes

drain valve

Fig. 2.1 6-fold manometer

∆h

air cushionpL

p2p1

h1

h2

Fig. 2.2 Differential pressuremeasurement

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The zero point for the differential pressure meas-urement can be adjusted via the pressure pL.

For a maximum measuring span, it is advantageous

to place the zero point and the mean value h1 + h22 on

the center of the measuring scale hmax.2 .

h1 + h22 =

hmax.

2 = p1 − pL + p2 − pL

2 ρ g .

This results in, for the pressure of the air cushion

pL = p1 + p2 − hmax ρ g

2 .

The pressure is adjusted via the vent valve, alsosee section 2.4.2

2.3 Absolut pressure measurement

To measure the absolute pressure, the vent valveis open and the overpressure is measured. Thepressure pL corresponds to the atmospheric airpressure p0.

Here, it is also necessary to take into accountthe level hm between the measuring point andthe zero point of the pressure gauge.

pabs = p0 + ( h + hm ) ρ g .

Air pressure p0

h

hm

pabs

Fig. 2.3 Absolut pressure measurement

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2.4 Connecting and handling manometers

Handling the 6-fold manometer requires some ex-periences with the HM 150.29. Please take care toconnect only measuring objects with the samemeasuring range to the manometer.

2.4.1 Ventilation

Since air bubbles in the connecting hoses causeincorrect measurements due to the low air density,these must be bled.

- Connect manometer with hoses to the fittingsbe measured

- Open the drainage valve at the bottom

- Slowly open the ball valve in the HM 150 inflowsection

The pipe section and the connecting hoses arebled by the strong water current.

When there are no more air bubbles in the connec-ting hoses, then:

- Close the pipe section drain

- Close drainage valve at the bottom

- Close ball valve of the HM 150

- Switch off the pump

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2.4.2 Setting the zero position

In order to guarantee the greatest possible mea-suring span, the zero position of the pressuregauge should be in the center of the scale.

- Close the pipe section drain. The flow rate isequal to zero.

- Slowly open the ball valve in the inflow section ofthe HM 150

- Adjust the maximum span with the valves andcocks of the HM 150.29

- Close vent valve and ball valves.

- Switch pump on and start measuring by care-fully opening the ball valves

IMPORTANT: The level can only be adjusted up-wards with the vent valve. If the level is too high,the pipe network must be emptied. Renewed ven-tilation is then necessary before a lower zero po-sition can be set.

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3 Experiments

In the following sections some experiments thatcan be performed using this unit are described asexamples. The experiments selected are not inten-ded to form a complete list of those possible, butare instead intended to be a stimulant for your ownseries of experiments.

The descriptions of the experiments are divided intoa principles section with the most important formulaeand the actual performance of the experimentwith the recording of measured values and analy-sis.

The measured results provided are not to be seenas reference or calibration values applicable in allcircumstances. Depending on the design of the indi-vidual components and the way in the which theexperiment is performed, large variations may,to a greater or lesser extent, occur in your expe-riment.

3.1 Calibration Curve Using Area Reduction

Since the severe reduction in area at the reducerhas the effect of a metering orifice, a calibrationcurve can be generated using this fitting.

To generate the calibration curve, the pressure

loss ∆ p in mmWs is plotted against the flow rateV. in l/min.

However, the volumetric flow rate must be deter-mined via the volumetric tank on the HM 150 forthe once-only measurement of the flow rate.

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3 Experiments 8

The volumetric flow rate is reduced in steps usingthe spherical valve on the HM 150.29 Exercise Unitand the associated pressure loss read off, bothvalues are noted.

Example Measurement Result:

Calibration Curve: Reducer

Pressure Loss ∆ p in

mmWs

Volumetric Flow Rate V.

inl / min

265 9.81

215 8.33

185 7.34

150 6.35

90 4.84

80 4.44

70 4.19

65 4

45 3.33

25 2.61

0

50

100

150

200

250

300

0 2 4 6 8 10 12

Volumenstrom l/min

Dru

ckve

rlust

mm

Ws

Volume flowin l/min

pres

sure

loss

es in

mm

WC

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3 Experiments 9

3.2 Exercise Stand Characteristic Curve

A characteristic curve for the exercise stand canbe recorded using the spring-tube manometer. Ifpressure is plotted against position along the piperun to form the characteristic curve, then the pres-sure losses for the individual objects can be readoff.


Characteristic Curve V. =10.3 l/min

MeasurementPoint

MeasurementObject

Pressure p in bar

1 Pipe Elbow 0.5

2 0.49

3 Reducer 0.49

4 0.44Enlarger

5 0.44Rounded Elbow90°6 0.425

7 Bend 90° tight 0.425

8 0.42

9 Bend 90° large 0.42

10 0.415Spherical Valve

11 0

0,4

0,41

0,42

0,43

0,44

0,45

0,46

0,47

0,48

0,49

0,5

1 2 3 4 5 6 7 8 9 10 11

Meßstelle

Dru

ck in

bar

Red

ucer B

end

90°

tight

Enl

arge

r

Pip

e E

lbow Rou

nded

Elb

ow 9

0°

Sph

eric

al V

alve

Ben

d 90

° la

rge

measuring point

pressure in bar

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3 Experiments 10

3.3 Pipe flow with friction

3.3.1 Fundamentals

The following experiments are intended to deter-mine the pressure loss pv and the loss level hv

under conditions of pipe flow with friction.

In the case of turbulant pipe flow, which is saidto exist at a Reynolds’ number of Re>2320, thepressure loss is proportional to the

- length l of the pipe

- pipe friction coefficient λ

- density ρ of the flow medium

- square of the flow velocity v.

The pressure loss also increases as the pipe dia-

meter decreases. It is calculated as follows

pv = λ l2 d ρ v 2 .

The associated loss level hv is calculated as follows

hv = λ ld

v 2

2 g .

In the case of turbulent pipe flow ( Re>2320) ,

the pipe friction coefficientλ depends on the piperoughness k and the Reynolds’ number Re. Thepipe roughness k states the height of the wall ele-vations in mm. The roughness of the test pipes islisted in a table in the appendix. The relationship

between Re λ and k is shown in the diagram accor-ding to Colebrook and Nikuradse. Here, the wallroughness k is referred to the pipe diameter d.

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3 Experiments 11

The Reynolds’number Re is calculated fromthe pipe diameter d, the flow velocity v and the

kinematic viscosity ν.

Re = v dν

.

The kinematic viscosity can be found in Table 6.3for water as a function of temperature.

The flow velocity v is calculated from the volume-tric flow V

. and the pipe cross section

v = 4 V

.

π d 2 .

Coefficient of pipe friction λ according to Colebrook and (dotted) according to Nikuradse (from Dubbel: Ta-

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3 Experiments 12

For hydraulically smooth pipes(Re < 65 d/k) anda Reynolds’ number in the range of 2320< Re <105 , the pipe friction coefficient is calculated inaccordance with the formula of Blasius

λ = 0.3164

4√ Re .

For pipes in the transitional range to roughpipes ( 65 d/k < Re < 1300 d/k, range in thediagram below the limit curve), the pipe frictioncoefficient is calculated according to Colebrook

λ = 2 lg

2.51Re √λ

+ 0.27

d⁄k

−2

.

It is an implicit formula which must be solved

iteratively. First, estimate λ, apply the formula andcalculate an initial approximation. This approxima-tion is again added again to the equation and thesecond approximation is calculated.

If the estimated value is taken from the Colebrookand Nikuradse diagram, the first approximationgenerally already is sufficiently accurate and thevalues differ only in the third decimal.

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3 Experiments 13

3.4 Resistance coefficients of special pipeline elements

3.4.1 Fundamentals

Special pipeline elements and fittings such as pipebends or curves, pipe branches, cross sectionchanges or also valves and flaps cause pressurelosses in addition to the wall friction losses.

In the case of cross section changes and there-fore associated velocity changes, componentsfrom the Bernoulli pressure loss(dynamic pressure)must be taken into account in the overall pressure-loss. The Bernoulli equation with loss element is

ρ v1 2

2 + p1 + ρ g z1 = ρ v2

2

2 + p2 + ρ g z2 +∆pv .

This results in, assuming the same levels z1 andz2 of the measurable total pressure loss

∆pges = p1 − p2 = ρ 2 (v2

2−v1 2) +∆pv .

The following is obtained accordingly for the losslevel

hvges = 1

2 g (v2 2−v1

2) +hv .

Apart from a few special cases, the additional flowresistances cannot be calculated closed, in con-trast to the wall friction losses investigated inthe previous section.

Here, empirically determined resistance coeffi-

cients ζ are stated in the literature for the variouselements. These enable the additional pressurelosses to be calculated easily

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3 Experiments 14

pvz = ζ ρ v 2

2

or for the loss level

hvz = ζ v 2

2 g .

This enables the following to be written for the totalloss level

hvges = 1

2 g (v2 2−v1

2) + λ1 l 12 g

v1 2

d1+

λ2 l 22 g

v2 2

d2 + ζ

v2 2

2 g

The pipe friction resistances must be determinedseparately for the part before and after the crosssection change. The resistance coefficient on theother hand is only referred to the velocity v2 afterthe cross section change.

Of course, if the speeds are equal, the dynamicpressure component drops out and a commonpipe friction component is used.

The resistance coefficient ζ can be determinedfrom the measured total loss level and the knownpipe friction

ζ = 2 hvges g

v2 2 −

1 −

d2

d1

4

−

λ1

l1

d1

d2

d1

4

+ λ2 l2

d2.

Without a cross section change ( d1/d2 = 1), theexpression is simplified

ζ = 2 hvges g

v 2 − λ ld .

3.4.2Pipe bend

For the pipe bend, there exists a dependence on

the resistance coefficient ζ on the deflection angleof the flow and on the ratio of the bend radius tothe pipe diameter. The resistance coefficient is

Pipe bend Pipe angle Pipe knee

R<d

R>d

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3 Experiments 15

also influenced by the shape of the bend. Thefollowing diagram applies to smooth and rough

pipes for the special pipe bend case which existshere with 90°deflection.

Approximately the resistance coefficient of kneepieces applies to pipe angles, i.e. bend radii of lessthan the pipe diameter (R/d<1). For example, with

a smooth pipe a ζ of 1.3 applies to a 90° knee and

a ζ of 1.27 applies to rough pipes.

0.2

0.4

0.6

0

rough

smooth

0 2 4 6 8 10

Ratio of bend radius to pipe diameter R/d

ζ 90°

Res

ista

nce

coef

ficie

nt

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3 Experiments 16

3.4.3 Performing the Experiment

In the following experiment the pipe elbows in themeasurement circuit are investigated. The heightof the loss hv in mm across one element is alwaysmeasured.

The manometer is connected and the measure-ments performed as given in Section 2.

The maximum volumetric flow rate was set forthe following measured values.


Pipe Fitting Volumetric Flow Rate V.

in l/minLoss Height hv

in mm

Pipe Elbow 90°,PVC, d = 17mm

18.75 245

Rounded Elbow 90°,PVC , d = 17mm

18.75 175

Bend 90°, R = 40mm PVC , d = 17mm

18.75 135

Bend 90°, R = 100mm PVC , d = 17mm

18.75 130

Based on the pressure loss or height of the losshv, the dependence of the resistance on deflectionangle and the relationship of the radius of curvatu-re to the pipe diameter described in the theory canbe clearly seen. The greatest resistance is shownby the pipe elbow with its sharp edged change indirection. Also clearly visible is that the resistancereduces, the larger the ratio R/d becomes.

.

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3 Experiments 17

3.5 Changes in Cross-Sectional Area

The change in cross-sectionalarea on the ExerciseUnit is a discontinuous enlargement or reduction.The coefficient of resistance for a discontinuouschange in cross-sectional area can be derived fromthe Bernoulli equation and the principle of linearmomentum.

For the enlargement the following applies

ζ =

A2A1

− 1

2

=

d2 2

d1 2 − 1

2

.

For the reduction the following applies

ζ =

A1A0

− 1

2

=

d1 2

d0 2 − 1

2

.

Here A0 and d0 represent the constricted cross-sectional area. Since this is generally unknown,the coefficient of resistance for reductions is takenfrom the following diagram.

In the case of continuous changes in cross-sectio-nal area, the coefficients of resistance can betaken from special diagrams (Appendix 4.4 ).

d2d1

d1 d0

Constriction of the Cross-Sectional Area of

0.6

0.4

0.2

0

ζ

0 0.4 0.8

Area Ratio A2/A1

0.6 1.00.2

Coefficient of Resistance for Discontinuous AreaReduction

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3 Experiments 18

3.5.1 Performing the Experiment

In the following experiment the area enlarger andreducer in the measurement circuit are investiga-ted. The height of the loss hv in mm across oneelement is always read off.

The manometer is connected and the measure-ments performed as given in Section 2.

A constant volumetric flow rate was set for thefollowing measured values.


Pipe Fitting Volumetric Flow Rate V.

in l/minLoss Height hv

in mm

Reducer,PVC, d = 17mm to d = 9.6mm

8 255

Enlarger,PVC, d = 9.6mm to d = 17mm

8 5

It is interesting that scarcely any pressure lossoccurred on the area enlarger. It is even possiblefor a pressure gain to occur here, if the increase inpressure from the loss in speed exceeds the pres-sure loss due to pipe friction.

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3 Experiments 19

4 Technical Data

4.1 Primary Dimensions of the Exercise Unit

Length 875mmWidth 640mmHeight 900mmWeight 25kg

4.2 Components

- 6 Channel Manometer for Differential PressureMeasurementMeasuring Range:0 to 0.03 bar / 0 to 300 mmWs

- Spring-Tube ManometerMeasuring Range:0 to 1.6 bar / 0 to 16000 mm Ws

- 11 Circular Chambers with Measuring Glands

- Discontinuous Area Reduction Fitting PVC, d = 17mm to d = 9.6mm

- Discontinuous Area Enlargement Fitting PVC, d = 9.6mm to d = 17mm

- Pipe Elbow 90°, d = 17mm

- Rounded Elbow 90°, d = 17mm

- Bend 90°, d = 17mm, R = 40mm

- Bend 90°, d = 17mm, R = 100mm

- Spherical Valve, d = 17mm

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4 Technical Data 20

4.3 Bibliography

Prof. Dipl.-Ing. Wolfgang Kalide,Einführung in die technische Strömungslehre,Carl Hanser Verlag,6th, revised edition, Munich Vienna 1984

DubbelTaschenbuch für den MaschinenbauSpringer Verlag,16th Edition

4.4 Tables and Diagrams

Wall Roughness

Kinematic Viscosity of Water

Wall Roughness

Material Surface Wall Roughness kin mm

Copper Pipe, Cu technicallysmooth

0.001

PVC pipe technicallysmooth

0.001

Kinematic Viscosity of Water as aFunction of Temperature (after Kalide:Technische Strömungslehre )Temperature in °C

Kinem. Viscosity νin 10 -6 m2/s

15 1.13416 1.10617 1.07918 1.05519 1.02820 1.00421 0.98022 0.95723 0.93524 0.91425 0.89426 0.87527 0.856

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4 Technical Data 21

Pipe Coefficient of Friction λ after Colebrook and (dotted) after Nikuradse (from Dubbel: Ta-schenbuch für den Maschinenbau)

0.2

0.4

0.6

0

rough

smooth

0 2 4 6 8 10Relationship Bend Radius to Pipe Diameter R/d

ζ 90°

0.8

Coefficient of Resistance ζ for 90° Pipe Elbows

0.6

0.4

0.2

0

ζ

0 0.4 0.8Area Ratio A2/A1

0.6 1.00.2

Coefficient of Resistance ζ for Discontinuous Area Re-duction

06/9

8


All

Rig

hts

Res

erve

d G

.U.N

.T. G

erät

ebau

Gm

bH,

Bar

sbüt

tel

4 Technical Data 22

Diameter Ratio d1/d2

α

Wall Friction Factor α for Continuous Area Reduction(Nozzle)

as a Function of the Reduction Angle δ

ζ = α λ1 + λ2

2(from Kalide: Einführung in die technische Strömungslehre)

Diameter Ratio d2/d1

ζ

Resistance Factors for Continuous Area Enlar-gement

(Diffuser) as a Function of the Diffuser Angle δ(from Kalide: Einführung in die technische Strömungslehre)

06/9

8


All

Rig

hts

Res

erve

d G

.U.N

.T. G

erät

ebau

Gm

bH,

Bar

sbüt

tel

4 Technical Data 23

Documents

HM 150.29 Losses in Bends and Fittingscste.sut.ac.th/miscste/company/manual/HM150_29e.pdf · 2017-02-03 · 1 Unit Description The HM 150.29 unit is used to investigate pressure losses