__. - - _ _ - __ .__ . _ _ _ _ _ _ - . . _ _ _ _ _ _ ._. __ _ _ _

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NUREG/CR-1418ORNL/ NUREG/TM-387.*

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Experiments with a Vortexunion

cansioE Shedding Flowmeter in Two- i

Phase Air-Water Flow'

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K. G. Turnage

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Prepared for the U.S. Nuclear Regu'atory CommissionOffice of Nuclear Regulatory Research

Under interagency Agreements DOE 40-551-75 and 40-552-75

8 2 04 5 6 o (;,f G

*,i

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Printed in the United States of America. Available fromNational Technical Information Service

U.S. Department of Commerce5285 Port Royal Road, Springfield, Virginia 22161

Available from'GPO Sales Program

Division of Technical Information and Document Control*

U.S. Nuclear Regulatory CommissionWashington, D.C. 20555

This report was prepared as an account of work sponsored by an agency of theUnited States G overnment. Neither the U nited S tates G ovemment nor any agencythereof, not any of their employees, makes any warranty, empress or implied, orassumes any legal liability or roeponsibility for the accuracy, completonoas, orusefulness of any information, apparatua, product, or process disclosed, orrepresents that its use would not infnnge p rivate:y owned rights. Reference hereinto any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise, does not necessarily constitute or imply itsendorsement, recommendaten, or favoring by the United States Govemment orany agency thereof. The views and opinions of authore expressed herein do notnecessarily state or reflect those of the United States Govemment or any agencythereof.

4

.

NUREG/CR-1418ORNL/NUREG/TM-387Dist. Category R2.

.

Contract No. W-7405-eng-26

Engineering Technology Division

EXPERIMENTS WITil A VORTEX SHEDDING FLOWMETERIN TWO-PHASE AIR-WATER FLOW

K. G. Turnage

4

.

Manuscript Completed - May 20, 1980Date Published - June 1980

NOTICE This document contains information of a preliminary nature,it is subject to revision or correction and therefore does not represent afinal report.

Prepared for theU.S. Nuclear Regulatory Commission

Of fice of Nuclear Regulatory Research

| Under Interagency Agreements DOE 40-551-75 and 40-552-75I

NRC FIN No. B0401

'

Prepared by t'leOAK RIDGE NATIONAL LABORATORY

* Oak Ridge, Tennessee 37830operated by

<

| UNION CARBIDE CORPORATIONfor the

DEPARTMENT OF ENERGY

!

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CONTENTS

.

Page.

ABSTRACT 1..........................................................

1. INTRODUCTION '

1..................................................

2. BACKGROUND 3....................................................

2.1 Vortex Shedding 3..........................................

2.2 Vortex Flowmeters 4........................................

2.3 Previous Research 5........................................

3. APPROACH 6......................................................

3.1 Description of Test Meter 6................................

3.2 Description of Facility 9..................................

3.3 Electronics 11..............................................

4. RESULTS 13.......................................................

4.1 Single-Phase Flow 13. ........................................

4.2 Two-Phase Flow 15............................................

5. CONCLUSIONS AND RECOMMENDATIONS 24...............................

REFERENCES 25........................................................

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EXPERIMENTS WITH A VORTEX SHEDDING FLOWMETERIN TWO-PHASE AIR-WATER FLOW

e

K. G. Turnaga.

ABSTRACT

Experiments performed with a strain gage-type vortex shed-ding flowmeter in two phase vertical upflow and downflow in theAir-Water Test Facility at the Oak Ridge National Laboratory aredescribed. Digital signal analysis techniques were used to eval-uate the utility of the test meter for measuring two phase flow.The studies indicate that vortex shedding can be used to produceclear, modulated signals in a generally homogeneous stream withrelatively small quantities of a dispersed phase. At intermedi-ate void fractions, however, the test meter produced meaning-less or intermittent signals except when the flow velocity wasvery high.

0

1. INTRODUCTION.

Correct interpretation of experimental data from studies of hypo-

thetical nuclear reactor loss-of-coolant accidents (LOCAs) demands ac-curate measurement of two phase flow parameters. Several types of flow-

meters have been used in attempts to measure two phase flow velocities,1

but none of those techniques has been totally successful. This report

describes an experiment at the Oak Ridge National Laboratory (ORNL) toexamine the utility of a commercially available vortex shedding flow-

meter for measuring velocity in two phase flow. Vortex flowmeters are

attractive for this application because they are rugged, have no moving

parts exposed to the flow, and are relatively insensitive to long-termvariations in fluid density and viscosity. The question remained, how-

ever, whether suf ficiently strong, coherent vortex trails would be gen-erated under the inhomogeneous flow conditions typical of two phase flow,.

and the study undertook to answer this question..

Literature f rom several suppliers of vortex anemometers was studied,and the meter described below was purchased for testing because it seemedmost promising for this application. The mater was installed and tested

. _ - -

2

in two phase vertical downflow and vertical upflow in the ORNL Air-Water

Test Facility (AWTF). State-of-the-art signal analysis techniques were .

applied to reduction of data from the vortex transducer. Analysis of data'

taken with the meter has led to a general understanding of the two-phase

flow conditions for which useful ineasurements are possible.

.

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3

2. BACKGROUND

,

2.1 Vortex Shedding

.

Oscillating vortex trails in flow streams behind bluf f bodies havebeen observed for hundreds of years. In 1878, Strouhal described the

basic characteristics of the wake (Fig.1), which is also known as the

Karman vortex trail or street. Strouhal found that the frequency of vor-

tex formation f was directly proportional to the fluid speed V and in-versely proportional to the diameter of the bluff. body d, or

f = K(V/d) . (1)

The proportionality constant K is known as the Strouhal number. For

a circular cylinder, the value of the Strouhal number is essentially con-stant at 0.20 over a Reynolds number range of 2,000 to 100,000. When theshedding body is enclosed in a conduit carrying fluid, the size of theconduit has some ef fect on the vortex shedding f requency; . even then, how-

.

i' ever, the Strouhal number is constant for a wide range of flow rates. In

a homogeneous flow stream, fluid density or viscosity has no effect on~

the vortex shedding f requency - hence the attractiveness of vortex shed-ding as a measurement scheme in dispersed two phase flow. (Other commonlyused velocity meters such as turbines or Pitot tubes do exhibit a depen-dence on density or void fraction.) Interestingly, the amplitude of sig-nals produced by passing vortices may be related to fluid density, so themass flow rate may, in theory, be deduced f rom a single flow element.2

t

iORNL-DWG 79-17233 ETD

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Fig. 1. Karman vortex street pattern behind right circular cylinder.

- - -- - - - . .. .- _ . - _ - . _ ._.

4

2.2 Vortex Flowmeters

.

Vortex flowmeters are inherently rugged and dependable for many ap-plications. There are no moving parts exposed to the flow stream, so -

corrosion is no problem. For service in a single phase flow, frequentcalibration is normally not required since, in the proper Reynolds numberrange, vortex shedding frequency is a function of fluid speed and bodygeometry only. Most meters are of relatively small cross section andproduce small pressure drop. Recent innovations have led to construction

of very small meters suitable for free-field applications. Nonetheless,since the meters are intrusive, they will perturb the flow field to some

extent. A meter which works for bidirectional flow could possibly be de-signed, but to our knowledge, none has been built.

Application of the vortex shedding principle to flow metering hasadvanced rapidly in recent years, with the development of improved shapesfor the shedding body and better techniques for sensing and counting the *

vortices. Several configurations for the bluff body are now available in.

commercial meters. Some meters are intended only for measuring pure gasor pure liquid flows, while others are capable of measuring single phaseflows of either medium. Methods of sensing passing vortices may be clas-sified as follows: (1) thermistors or hot wires cooled by the flowingstream, (2) electromechanical transducers for detecting pressure differ-ences, (3) strain gage techniques, and (4) ultrasonic techniques. Thesensors, or transducers, may be mounted on the surface of the bluff body,within it, or on the pipe adjacent to it.

Vortex flowmeters are available that are sensitive to flew rates aslow as 0.1 m/s for liquid or 1 m/s for gas. At low flow rates (and intwo phase flow), the minimum flow rate measurable depends on the signal-

to-noise ratio at low vortex shedding frequencies. In single phase fluid,the meters' ranges typically cover a factor of 200 or more; in gas a fac-tor of 15 is common. The response time of vortex meters depends on the -

shedding frequency and is therefore a function of fluid speed. Rapid.

changes in velocity require time for readjustment of the vortex pattern,so vortex flowmeters generally will not follow rapid transients. (Thischaracteristic also affects the adaptability of vortex flowmeters for use

3

in two phse flow regimes such as slug flow.) Manufacturers of vortex

flowmeters claim accuracies within about 1% of the measured values for,

'

liquids or gases. Repeatability (precision) is some 0.25% of measured

va lu e.

2.3 Previous Research

To the author's knowledge, previous work with vortex shedding intwo phase flow is limited to two studies. In 1972, Burgess 3 tested a

3-in. prototype swirlmeter in wet gases with liquid volume fractions up

to 5%. (The swirlmeter uses the vortices shed from a number of twistedvanes to measure gas flow rate. The vortices are sensed by a thermistor

located downstream of the vanes.) Burgess found that the flow rate in-

dicated by the meter in two phase flow Q2$ was approximately

Q24 = [1 + 0.03 (1 + 100ag)] (Qt + Qg) , (2),

where Qg and Q are flow rates corresponding to the separately metered. g

gas and liquid streams, respectively, and o is the volume fraction ofg

liquid.

In 1978 Loesch4 built vortex flowmeters and tested them in two-phase air-water flow inside a 1.9-cm-ID tube. A water-filled purge line

was used to transmit pressure variations from the surface of the bluf f

body to a pressure-difference transducer. In high-void-fraction mist

flow, the observed pressure oscillations were of much lower f requencythan expected for vortex shedding. This was attributed to oscillation

of water drops that accumulated on the downstream part of the meter anddominated the ef fects of vortex shedding.

.

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- _ _ . . . _ , , -- _ , . - , , _ _ _ , _ _ , = , , . . , , , , - .

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6

3. APPROACH

,

Vortex flowmeters might be expected to succeed in a postulated homo-'geneous, one-dimensional, two phase flow field. However, actual inhomo-

geneities in the flow tend to disperse the vortices shed by the bluff bodyor to redirect them so that they do not interact consistently with thevortex-sensing transducer. A commercially available vortex shedding flow-meter (Fischer and Porter Model 10LV) was tested in two phase flow in theORNL AWTF to study the severity of this problem.

<

3.1 Description of Test Meter

The bluff body in the test meter (Fig. 2) consists of a compoundshape designed to enhance the amplitude of pressure fluctuations causedby the passage of vortices. A single strain gage sensor is embedded in

*the body to sense forces along the vectors AB, in the plane of the paper *

in Fig. 2. Net strain resulting from all forces on the downstream por-,

tion of the body is sensed. Thus the sensor detects the average of flowforces that are normal to the body, rather than localized effects. This

design was judged to have a greater probability of success than designswith a single shedding body and a localized vortex-sensing transducer.Because of recent advances in strain gage technology, meters of this de-sign could probably be adapted for operation at high temperatures typi-cal of some LOCA experiments.

ORNL.OWG 79-17p D

An h;

IBu

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k -

wFig. 2. Vortex street pattern generated by compound bluff body in

vortex flowmeter. Force variations along AB are detected by strain gage.

.

7

The flow element (shedding body) in the test meter is mounted trans-

versely in a flanged flow. tube (Fig. 3) that is inserted into the down-'

stream pipe with the flange ring fitting between the two adjacent piping,

flanges. A signal-conditioning module is mounted on the flanged part ofthe meter. Figure 4 is a photograph of the meter installed for downflowtesting.

ORNL-DWG 79-17235 ETD

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- - _ _ _ __ ____. _ .. . _ . _ _ _ . -_._____- .

_ -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

9

3.2 Description of Facility

*

The test meter was installed in the AWTF in the two posJtions indi-cated in Fig. 5. The AWTF consists primarily of translucent 4-in. nomi-,

nal polyvinyl chloride (PVC) pipe, so that the two phase flow regimesoccurring in the system can be observed. The position for vertical down-

flow testing was 1.4 m (4.5 f t) f rom the elbow leading to the downcomerand 1.1 m (3.5 f t) above the flow separator. For vertical upflow testing

the meter was installed 2.2 m (7.2 f t) above the tee leading to the riserand 1.1 m (3.5 f t) below the tee connecting to the horizontal run of pipeat the top of the loop. Operating instructions supplied by the manufac-turer recommend inclusion of a straight length of piping equivalent to tenpipe diameters (1.0 m long in this case) for optimum meter performance.In the AWTF, critical flow orifices are used for metering air flow, androtameters and magnetic flowmeters are used for water metering. Air flow

; rates ranging f rom 0.6 to 288 g/s (1 to 512 scfm) and water flow rates,

f rom 0.3 to 32 liters /s (5 to 512 gpm) were used for the vortex meter.

testing. Superficial velocities in the test section ranged f rom 0.07 to

40 m/s (0.25 to 128 f t/s) for air and 0.05 to 5 m/s (0.2 to 17 f t/s) forwater. The useful flow range of the meter was 2.5 to 39 liters /s (40 to600 gpm).

The flow rate combinations yielding high or low void f ractions re-ceived primary consideration, since many other possible flow rate combina-tions were found to produce meaningless signals from the test meter. Mix-ing of air and water occurred near a divider plate installed at the teeshown in Fig. 5. Temperatures in the AWTF were ~25'c (~77'F), and pres-sures were less than 360 kPa (51 psia) during two phase operation. Thetwo phase flow regimes attained in the AWTF correspond in general to flowregimes predicted by Oshinowo and Charles 5 for analogous flow rates and

pipe diameters. In particular, steady-state inputs of water and air yieldoscillatory flow behavior (e.g., slug flow) for some flow rates. Tech-,

niques such as mixers and flow-dispersing screens enhance local or radial*

mixing of the phases but do little to eliminate slugging. Apparently,such flow regimes are inherent to the flow and must be accommodated byflow-metering techniques designed for such regimes.

- _ _ _ _ . -

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ORNL-DWG 78-3235C

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AIR METERING- _

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HCV HAND CONTROL VALVEFCV FLOW CONTROL VALVEi

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Fig. 5. Schematic of AWTF showing locations used for testing vortex

flowmeter.

|

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. -

11

3.3 Electronics

The signal-conditioning electronics supplied with the vortex flow--

meter amplify and shape the variable frequency signal, improve the signal-,

to-noise ratio, and convert the frequency to a 4- to 20-mA analog current

proportional to the vortex shedding frequency. Electronic components used

in the AWTF experittents are shown schematically in Fig. 6. For normal

use, leads connecting to the meter are for a 115-V, 60-Hz power supply andfor the analog current output. In these tests, current meters and chart

recorders were used to record the analog output signal from the signalconditioner unit. In addition, output of the strain gage sensor within

the flow element was monitored directly by means of a terminal strip inthe signal-conditioning module. Outputs from the strain gage were AC

coupled and amplified using a Princeton Applied Research Model 113 ampli-fier. Low- and high-frequency rolloff filters were available as part of

.

ORNL-DWG 79-17236 ETO.

ONANALYZER

AMPLIFIER1r

STRAIN SCOPE

GAGE gL

_

SIGNAL _ CURRENT - CHARTCONDITIONER

' METER' RECORDER

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Fig. 6. Block diagram of electronics used for vortex flowmetertesting.

-

_ _

.-. . . _ ~ . . - - - - - - . . - . --- ...- . ..

,

12

4

4 the amplifier. Amplifier output was routed to a storage oscilloscopewhere time traces could be photographed. In some tests, a Hewlett-Packard

.

Model 5420 digital signal analyzer was used to perform on-line analysis of*the strain gage signals. The signal analyzer performs a Fourier transform

on the input signal so that parameters such as the signal power spectrum,

can be displayed in the frequency domain. Long averaging times (e.g.,i

100 s) made possible good statistical averages of the signal behavior..,

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3

13i

f 4. RESULTS

.

Single phase and two phase tests were performed in both upflow and*

downflow. Results f rom the single phase flow experiments'will be pre-- sented first; then two phase flow test results will be treated.,

!1r

i 4.1 Single-Phase Flow

'

The test flowmeter performed satisf actorily in all-water flow in: both orientations. (The meter is marketed specifically for liquid flow

service.) Using Eq. (1), the analog output of the signal conditioner was,

converted to flow rates which agreed with those from the magnetic flow-meter within a few percent. Figure 7 shows the output of the strain gagetransducer vs time. for all-water flow rates of 6.25, 15.6, and 25 liters /s,

j (100, 250, and 400 gpm).

Measuring velocity in single phase air flow was also possible, but.-

the pressure oscillations on the flow element caused by vortex shedding'

,

created signals that were too small to trigger the signal conditioneri

counting circuit. For air flow, well-defined, low-amplitude waves werevisible on the oscilloscope (Fig. 8). These signals were processed with

the signal analyzer, which yielded the plot of power spectrum vs f requencyshown in Fig. 9. The peak f requency corresponded to the air velocity

'

through the meter in the same manner as for liquid flow. For instance,; when the input air rate was 102 g/s (181 liters /s at STP) (Fig. 9), the!

peak frequency was 251.2 Hz. The meter. constant of the vortex meter was1.558 Hz/(liter s). Thus_the implied air flow rate was Q = 251.2/1.558 =,

j 162 liters /s, which was a reasonable result, since the system pressure was'

; slightly above ambient at the meter location. However, with air inputb rates below about 69 g/s (128 scfm) or air velocities below about 10 m/s,

the signals could not be distinguished f rom the background noise. A low-

amplitude (60-Hz) signal was present; and because it approximated the sig--.

nal f requencies of interest, it could not be filtered out. In addition,

{ f requency peaks at 1278 and 200 Hz were observed. The frequency of the; peak at 1270 Hz was much higher than the f requency of any signals of in-1 terest and probably corresponded to the natural f requency of the compound!iI

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ORNL-DWG 79-17238 ETD

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Fig. 8. Output of flowmeter strain gage vs time for single phaseair flow rate of 216 g/s (384 scfm).

shedding body. The f requency spectrum in Fig.10 shows the 1270- and 200-

| Itz peaks and their harmonics. Frequency spectra obtained under other flowconditions were often contaminated with these frequency components.

4.2 Two-Phase Flow

In two phase flow, the vortex flowmeter yielded information about theflow-field velocity at very low and very high void fractions. The range

.

af void fractions for which the meter worked was somewhat wider when the.

velocity in the pipe was high.

The output f rom the signal-conditioning electronics provided with themeter was oscillatory and indicated progressively lower flow rates as more

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16

oRNL-DWG 79-17239 ETD-10

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Fig. 9. Power spectral density of signal from flowmeter with single-phase air flow rate of 216 g/s (384 scfm).

,

ORNL-DWG 79-17240 ETD-50

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-130 , , , , , , ,

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Fig. 10. Power spectral density of signal from flowmeter with waterflow rate of 126 liters /s (200 gpm) and air flow rate of 36 g/s (64 scfm).,

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__ .. _ .. . - - . . . -_ , .- . . .

.. . ._. _ .-

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17

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air was introduced. The meaning of those signals was not interpreted.

Behavior of the output signal f rom the flow element strain gage as void,,

f raction was increased (air was added to an initially all-water stream) is' '

illustrated by the oscillographs in Fig, 11. For all f rames, the water

flow was downward at 19 liters /s (300 gpm). Successive frames show theoutput signal at 1.1, 2.2, 3.3, and 4.5 g /s (2, 4, 6, and 8 scfm). Data

taken at almost the same location in the system using a three-beam gammai

densitometer indicate that the air-volume f raction, or void f raction, for

each flow rate was about 0, 0.033, 0.07, and 0.17, respectively. The flow

regime was bubbly flow. As seen in Fig.11, the signal fluctuations due

ORNL-DWG 79-17241 ETD

1 mV 10 ms 1 mV 10 ms*

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VV V'_v u v --

'V

Q, = |.1 g/sO-0a

, ,,

t t

1 mV 10 ms | 200 pV || | 10 ms j

.

II, Ill | I

V V -

_

l !l|' 0 = 2.2 g/s| jQ, ,= 4.5 g/s | | |3

t t.

Fig. 11. Output of flowmeter strain gage vs time for water flow rateof 19 liters /s (300 gpm) and air flow rate of 0,1.1, 2.2, and 4.5 g/s (0,2, 4, and 8 scfm). Scale units are shown on oscillographs.

- .__ . _ _ __ _ _ _ - - _ _ _ . _ _ .____

_.

4

18

to vortex shedding from the flow element deteriorated with increasing void'

f raction. When the vortex shedding oscillations were occurring, their ,

magnitude was not greatly reduced compared with their magnitudes in,

.

single phase water flow. However, periods when the vortex signal was oc-curring became shorter and less f requent with higher air flow rates.

Signals observed at other times were believed to be flow noise or 60-Hz

noise.

A digital signal analyzer provided information on the frequency con-tent of the signal from the vortex meter under various flow conditions.

Analysis of the signals obtained at a water flow rate of 25 liters /s (400

gpm), with air flow rates of 0,1.1, 2.2, and 4.5 g/s (0, 2, 4, and 8

scfm) led to the power spectrum plots shown in Fig.12. With increasingair flow rate, frequency content of the signals was broadened, and the

total signal power decreased. Observing the peak channel in the power

spectral density provided indications of the approximate velocity under;

.,

two pnase conditions. When that method was used, velocities which were

indicated by the meter in low-void-f raction two phase flow increased with -

increasing air flow (Fig. 12). This is to be expected because with con-

stant volumetric flow rate of water, introduction of air leaves less flow

area to be occupied by water, and thus higher mean velocities will occur.,

Figure 13 shows the power spectrum obtained at a slightly low water flow

rate (22 liters /s or 350 gpm) and an air flow rate of 4.5 g/s (8 scfm);

| the broad peak observed at the higher water flow rate is now completelyt

! gone.

At a void f raction of ~15% at the highest water flow rate tested,6

(there was practically no meaningful peak in the signal. If the analyzer'

could have been triggered intermittently when the vortex shedding was

actually being sensed (Fig. 11), better-defined peaks and reasonable re-

sults could perhaps have been obtained at somewhat higher void fractions.

Similar behavior of the vortex meter was observed when small quantities'

of liquid were introduced to high-speed air flows. Figure 14 shows oscil-

lographs obtained with an air flow rate of 108 g/s (192 scfm) and water .

flow rates of 0 and 0.063 liter /s (0 and 1 gpm). For high-void-fraction

runs, the vortex signals were generally of higher frequency and lower am-

plitude compared with the low-void-fraction data shown previously. Power

.._ _. _ _ - _ _ __ __ _.

. . _ _ _ . .. ._. _ . _ _ .

. . . . . .

ORN L-DWG 79-17242 ETO

-40 _gO, = 1.1 g/s

Q, = 2.2 g/s

'

83 E~

J

O O

w +' w,,%ed \ %-100 -1100 51.6 100 0 53.6 100

f (Hz) f (Hz)

~"O, = 3.3 g/s Q, = 4.5 g/s

E 83 30 o

Y p %%

-110 -1100 56.4 100 0 59.8 100

f (Hz) f (Hz)

Fig. 12. Power spectral density of signal from flowmeter for. waterflow rate of 25 liters /s (400 gpm) and air flow rate of 1.1, 2.2, 3.3, and4.5 g/s (2, 4, 6, and 8 scfm).

_ _ _ _ _ _ _ _ _ _ _ _ _ _

20

ORNL-DWG 79-17243 ETO-40

.

.

.

E'

Eo

%p %d Nh,

-110 , , , , , , , ,,

0 100

f (Hz)

Fig. 13. Power spectral density of signal from flowmeter for waterflow rate of 22 liters /s (350 gpm) and air flow rate of 4.5 g/s (8 scfm).

spectral densities at an air flow rate of 288 g/s (512 scfm) and waterflow rates of 0, 0.3, and 0.6 liter /s (0, 5, and 10 gpm) (Fig.15) dramat-ically illustrate the loss of the vortex signal as liquid content in-creased. The well-defined peak at 450 Hz broadened and virtually disap-peared at 0.6 liter /s.

A number of air-water flow rate atjnations that produced interme-diate void fractions were investystet (e.g., Fig. 10). Flow regimeswere frothy and slug flow. 72 f; 's, no coherent or meaningful vor--

,

tex shedding signals were obta.ned wicu the intermediate void fractions.

There was also little dif ference between the observations made in '

vertical upflow and vertical downflow. Data shown in Fig. 12 were fromvertical downflow runs, while data shown in Fig.16 cover approximately

|

- ______ _ _ _ _ |

21

ORNL-DWG 79-17244 ETD

'

500 pV 10 ms

.

60i

Og=0

500 pV 10 ms

VSG,

Og = 0.06 t/s*

Fig. 14. Output of flowmeter strain gage vs time for air flow rateof 108 g/s (192 scfm) and water flow rate of 0 and 0.06 g/s (0 and I gpm).For both oscillographs, full-scale abscissa is 100 ms, and full-scaleordinate is 5 mV.

the same flow rates from vertical upflow. Because of gravitational ef-

fects, a given flow rate of air and water will produce a higher void

f raction in downflow than in upflow. Figure 16 shows that the vortex

signal f aded completely above ~4% void f raction in upflow. With high

void f raction flows, there was also little dif ference in the meter's

performance between upflow and downflow.

A flow disperser consisting of four stacked layers of 20-mesh /in..

screen was placed upstream of the vortex flowmeter when it was installed'

f or vertical downflow testing. No discernable improvement of the signal

f rom the meter in two phase flow occurred when the flow disperser was

used.

- - _ _ _ . . ..-- . - . .

22

ORNL-DWG 79-17245 ETD --40

Opm O8=0512 scfm D - .

.

E3*

0

i

- W

-130-0 450 Hz 1000

-405 gpm O = 0.3 E/sg

512 scfm Dc

*

_E.0

b-

I -1301600

. -3010 gpm O = 0.6 C/sg

512 scf m D

i

BS0

|!

\ ^-120*

IUf (Hz)

! Fig. 15. Power spectral density of signal from flowmeter for airflow rate of 288 g/s (512 scfm) and water flow rate of 0, 0.3, and 0.6

|liter /s (0, 5, and 10 gpm).

I

!

- - -- , ._ - . _ . , . - .. . --- - . , _ _ - _ _ _ _ _ _ . - - __ - - _

._

. . . . . .

OR NL-DWG 79-17246 ETO

0 30

0 , = 1.1 /9s

g,, 3 ,jh

N,4, lj,1

Yb {< f,./[ \f

mp# % A m ..-60 -70

O 100 0 100f (Hi) , gg,y

,a"

30 -30O, = 2.2 9/s 0, = 3.3 g/s

E E3

.6

Y/ 4 *1

-60 -600 100 0 100

t (Hz) t (Hz)

Fig. 16. Power spectral density of signal from flowmeter with two-phase vertical upflow. Water flow rate was 25 liters /s (400 gpm); airflow rates were 0, 1.1, 2.2, and 3.3 g/s (0, 2, 4, and 6 scfm).

_ _ . ._ - _ _ _ .

1 24

!5. CONCLUSIONS AND RECOMMENDATIONS

,

1.

I

Experiments performed in two phase air-water flow indicate that the'

usefulness of the vortex shedding mechanism is severely limited for two-phase flow application. The meter tested is generally representative of

A all vortex flowmeters. Work at ORNL indicates that vortex shedding can'

be used to produce clear, modulated signals in a generally homogeneousstream with relatively small quantities of a dispersed phase. . The ex-periments were inconclusive as to whether vortex shedding simply did notoccur at intermediate void fractions or vortices were produced but werenot sensed because they were obscured by flow noise (generally randompressure variations in the stream). Further research and development of

' the design of the shedding body, vortex-sensing techniques, and/or signalj conditioning probably would not significantly improve meter performance ,

in the intermediate-void-f raction ranges. Vortex shedding techniques may1

! .

have some utility for two phase flow applications at very low and veryhigh void fractions. However, most single phase flow measurement tech- *

| niques also work fairly well under those conditions. Comparisons of data; f rom the vortex meter with data from other devices such as turbines (in

the geometry being considered for a particular application) might estab-lish superiority of one device. Generally, however, the vortex meter

9

would probably have the disadvantage of producing an intermittent signaland requiring high stream velocities in order to work in two phase flow.

i

|-

, ,

e

i

t

t

r-, - . . , . . , . - . _ _ , . . , - . , . . . . , _._,,..g., , , . , ~ , . _ , , . , , . - , _ _ . _ . _ , _ , , . . _ . . .__.-y-.

- . . .

.

25

REFERENCES

'

1. G. F. Brockett and R. T. Johnson, Single-Phase and Two-Phase FlowMeasurement Techniques for Reactor Safety Studies, EPRI Report NP-195'

(July 1976).

2. Peter J. Herzl, " Vortex-Type Mass Flowmeters," U.S. Patent Number3,766,033 (Dec. 4, 1973).

3. Personal communication from J. G. Kopf to K. G. Turnage, Oak RidgeNational Laboratory, Dec. 21, 1978.

4. S. B. Loesch, "A Feasibility Study of a Vortex Flowmeter for a Two-Phase Flow," B. S. thesis, Massachusetts Institute of Technology(1978).

5. T. Oshinowo and M. E. Charles, Can. 7. Chem. Eng. 53, 25 (1974).

-

4 .

e

!

,

S

!

.

!i

5 +M- - ep p+e-- a w -- r - -- ,

_ _

.,

27

. NUREG/CR-1418,

ORNL/NUREG/TM-3874

Dist. Category R2.

.

Internal Distribution

1. R. L. Anderson 15. R. N. McGill2. M. E. Bagwell 16. F . R. My na t t -3. C. Brashear 17. J. L. Rich4. S. K. Combs 18. M. J. Roberts5. W. B. Cottrell 19. J. A. Stevens

i 6. W. G. Craddick 20. D. G. Thomas7. C. E. Davis 21. H. E. Trammell8. 1. T. Dudley 22-24. K. G. Turnage9. B. C. Eads 25. J. D. White

10. D. K. Felde 26. ORNL Patent Of fice11. J. E. Hardy 27-28. Central Research Library12. M. B. Herskovitz 29. Document Reference Section13. H. W. Hof fman 30-31. Laboratory Records Department14. A. F. Johnson 32. Laboratory Records (RC)

.

External Distribution-.

33-40. Director, Division of Reactor Safety Research, Nuclear RegulatoryCommission, Washington, D.C. 20555

41. Director, Reactor Division, DOE, ORO42. Of fice of Assistant Manager, Energy Research and Development,

DOE, ORO43-47. Director, Reactor Safety Research Coordination Of fice, DOE,

Washington, D.C. 2055548-49. Technical Information Center, DOE

50-409. Given distribution as shown in category R2 (10-NTIS)

,

4

.

.

|

f

e U.S. GOVERNesENT PRINTING OFFICE:1904640 245/123

,. ._ __ _ _.