ASTM D3464-96(2001)
(Test Method)Standard Test Method for Average Velocity in a Duct Using a Thermal Anemometer
Standard Test Method for Average Velocity in a Duct Using a Thermal Anemometer
SCOPE
1.1 This test method describes the measurement of the average velocity with a thermal anemometer for the purpose of determining gas flow in a stack, duct, or flue (1-5). It is limited to those applications where the gas is essentially air at ambient conditions and the temperature, moisture, and contaminant loading are insignificant as sources of error compared to the basic accuracy of the typical field situation.
1.2 The range of the test method is from 1 to 30 m/s (3 to 100 ft/s).
1.3 The values stated in SI units are to be regarded as the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D3464–96 (Reapproved 2001)
Standard Test Method for
Average Velocity in a Duct Using a Thermal Anemometer
This standard is issued under the fixed designation D 3464; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 4. Summary of Test Method
1.1 This test method describes the measurement of the 4.1 This test method describes the operational and calibra-
average velocity with a thermal anemometer for the purpose of tion procedures necessary for the measurement of point veloc-
determininggasflowinastack,duct,orflue(1-5). Itislimited ity and calculation of the average velocity of air or gas flows in
to those applications where the gas is essentially air at ambient flues, ducts, or stacks utilizing a thermal anemometer.
conditions and the temperature, moisture, and contaminant
5. Significance and Use
loading are insignificant as sources of error compared to the
basic accuracy of the typical field situation. 5.1 The method presented is a “short method” that may be
1.2 The range of the test method is from 1 to 30 m/s (3 to used where contamination levels are less than 5000 ppm by
weight or volume, temperatures are between 0°C (32°F) and
100 ft/s).
1.3 The values stated in SI units are to be regarded as the 65°C (150°F), and the humidity is not considered. The gas is
consideredasstandardairandthevelocityisreaddirectlyfrom
standard.
1.4 This standard does not purport to address all of the the instrument.
5.2 This test method is useful for determining air velocities
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- in HVAC ducts, fume hoods, vent stacks of nuclear power
stations, and in performing model studies of pollution control
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. devices.
6. Apparatus
2. Referenced Documents
2.1 ASTM Standards: 6.1 Thermal Anemometer—A commercially available elec-
trically operated hot sensor anemometer with direct readout.A
D 1356 Terminology Relating to Sampling and Analysis of
Atmospheres thermal anemometer senses the cooling effect of a moving gas
stream passing over an electrically heated sensor. This cooling
D 3796 Practice for Calibration of Type S Pitot Tubes
2.2 Other Standards: effectorheattransferrateiscorrelatedtothevelocityofthegas
stream. The instrument is calibrated to display a direct readout
ASME PTC 19.5-72 Application of Fluid Meters, Sixth Ed.
1971 (Interim Supplement 19.5 on Instruments & Appa- in terms of velocity.
6.2 Sensors and Probes—There are a number of different
ratus)
types of sensors available for thermal anemometry including
3. Terminology
the hot-wire sensor, the hot-film sensor, and the quartz-coated
3.1 For definitions of terms used in this test method, refer to sensor. Probes are available in many different shapes depend-
Terminology D 1356. ing upon application.
6.3 Temperature Compensation—If the temperature of the
gas stream changes during velocity measurements, the an-
This test method is under the jurisdiction of ASTM Committee D22 on Air
emometer reading will change accordingly unless a constant-
Quality and is the direct responsibility of Subcommittee D22.03 on Ambient
temperature or “temperature-compensated” anemometer is uti-
Atmospheres and Source Emissions.
Current edition approved Apr. 10, 1996. Published June 1996. Originally lized. This type of instrument shall be specified for most
published as D 3464 – 75. Last previous edition D 3464 – 96.
applications of this measurement standard.
The boldface numbers in parentheses refer to the references listed at the end of
6.3.1 Temperature-Compensated Anemometer—A
this method.
temperature-compensated anemometer has a temperature-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
sensing probe within the instrument sensor that automatically
Standards volume information, refer to the standard’s Document Summary page on
corrects errors caused by changes in temperature in the gas
the ASTM website.
Available from TheAmerican Society of Mechanical Engineers, 345 East 47th
Street, New York, NY 10017.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D3464–96 (2001)
stream. For temperature-compensated anemometers, a change 9.2.1 In rectangular flues, divide the cross-sectional area
in temperature (DT) of 28°C (50°F) typically produces an error intoequalrectangularsubareasasshowninFig.1.Thenumber
of 2 %. of areas to be used depends on the flow pattern and flue size.
6.3.2 Temperature-Uncompensated Anemometer—For a Use Table 1 to find the minimum number of areas when
“constant-current” or uncompensated anemometer a change in sampling at least eight equivalent diameters downstream and
temperature (DT) of 28°C (50°F) typically produces a 25 % two equivalent diameters upstream from the nearest flow
error. For laboratory work where this type of anemometer disturbance, such as a bend, expansion or contraction. The
might be preferred, the output data shall be corrected for equivalent diameter can be determined as follows:
temperature changes in the gas stream.
D 5 2LW/ L 1W! (1)
~
e
6.4 Calibration Apparatus:
where:
6.4.1 Flows above 3 m/s (10 ft/s)—See Section 6, Practice
D = equivalent diameter, m (ft),
D 3796. e
L = duct length, m (ft), and
6.4.2 Flows below 3 m/s (10 ft/s)—See PTC 19.5-72.
W = duct width, m (ft).
If a site less than eight diameters downstream and two
7. Calibration
diameters upstream from a flow disturbance, such as a bend,
7.1 For velocities in excess of 3 m/s (10 ft/s) calibrate the
expansion or contraction is used increase the number of
thermal anemometer with a standard pitot tube, in accordance
sampling points in accordance with 9.2.4.
withPracticeD 3796.Itispreferabletomakethesecalibrations
9.2.2 In circular flues divide the area concentrically as
under laboratory conditions; however, where expediency dic-
showninFig.2.Theminimumnumberareastobeusedandthe
tates, field calibration at the sampling site is permissible.
distance to the test point are shown in Table 2 or calculate as
7.2 For velocities below 3 m/s (10 ft/s) calibrate in the
follows:
laboratory using a calibrated orifice or nozzle in accordance
r 5D ~2n 2 1!/4N (2)
with PTC 19.5-72. =
n s
7.3 Calibrate the thermal anemometer for a minimum of
where:
three velocities covering the range of velocities which are
D = internal diameter of flue, cm (in.),
s
anticipated for a particular test. Calibrate an increased number
r = radial distance from center of flue to nth sampling
n
of points, typically five to seven, for the complete range of the
point, cm (in.),
instrument if the anticipated test velocity range is not known.
n = nth sampling point from center of flue, and
(Warning—If this test method is used for gases other than air,
N = number of sampling points across a diameter.
calibrate using the test gas.)
Conduct traverses across two diameter axes right angles to
each other. Again, if a site less than eight diameters down-
8. Single-Point Velocity Measurement
stream and two diameters upstream from a flow disturbance is
8.1 Velocity—The hot-wire anemometer is effective for used, increase the number of sampling points as indicated in
measuring velocities over a range from 1 m/s (3 ft/s) to 30 m/s
9.2.4.
(100 ft/s). Record measurements at specific points within the 9.2.3 When readings must be taken in an irregular-shaped
flue in accordance with a plan determined by the flue size.
flue, divide the flue into equal areas of any shape, and measure
Place marks on the instrument probe or probe extension to aid the parameters at the centroid of each area.
in locating the sampling points at which the velocity is to be
9.2.4 Increase the number of sampling points when sam-
measured. pling less than eight diameters downstream and two diameters
upstream from any flow disturbance. When only four to six
9. Ave
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