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Title
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On the Interpretation of the Output of Hot-Film Anemometers and a Scheme of Dynamic Compensation for Water Temperature Variation
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Creator
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Tan-atichat, J.
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Nagib, H. M.
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Pluister, J. W.
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Corporate Author
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Mechanics and Mechanical and Aersopace Engineering Department, Illinois Institute of Technology
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Laboratory
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Air Force Office of Scientific Research
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Corporate Report Number
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IIT Fluids & Heat Transfer Report R73-7
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Date
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1973
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Date Issued
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1973-08
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Date Modified
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Scanned and posted 2023-11-28
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Extent
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55
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Contract
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Grant AFOSR 73-2509
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NTRL Accession Number
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AD784912
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Identifier
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AD0784912
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Format
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1 online resource
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Abstract
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Using a special calibration tunnel developed during the course of this study, the
static and dynamic response of several kinds of commercially available hot-film probes
with single and multiple sensors of the cylindrical-fiber type are examined. The effects
of different parameters, including those of the anemometer bridge, on the output
and performance of the probes are evaluated. In particular, the consequences of variations
in water temperature on the hot-film anemometer output are determined. The low
turbulence level (less than 0.1%) calibration tunnel is equipped with a heater capable
of raising the water temperature to any desired value up to 120°F and controlling it
within 0.2°F over a range of calibrated mean velocities from 0.01 to 1.4 ft/sec (better
than .±_0.2% accuracy except for U < 0.1 ft/sec where the accuracy is approximately
+O. 5%). The results reveal a large effect of the water temperature on the calibration
curves (in an extreme case a change in temperature of only 5.5°F can result in a 100%
error in the mean velocity reading). A scheme which utilizes a temperature sensing
probe immersed in the working fluid is used to compensate for the water temperature
variation . Several possible circuit configurations for this scheme, including an
optimum circuit design, are investigated and the results from some of them are presented
and discussed. The circuit has a frequency response to temperature variations which
depends on the thermal time constant of the temperature probe (up to several cycles per
second can be obtained using commercially available probes) and can be used to compensate
for temperature variations of more than 20°F with an accuracy better than +0.2%.
By using an effective value (much smaller than E0 ) instead of the zero velocity bridge
voltage (Eo) in exponential-type linearizers, a constant exponent is found useful in
linearizing the anemometer output over a wider range of velocities.
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Description
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Using a special calibration tunnel developed during the course of this study, the
static and dynamic response of several kinds of commercially available hot-film probes
with single and multiple sensors of the cylindrical-fiber type are examined. The effects
of different parameters, including those of the anemometer bridge, on the output
and performance of the probes are evaluated. In particular, the consequences of variations
in water temperature on the hot-film anemometer output are determined. The low
turbulence level (less than 0.1%) calibration tunnel is equipped with a heater capable
of raising the water temperature to any desired value up to 120°F and controlling it
within 0.2°F over a range of calibrated mean velocities from 0.01 to 1.4 ft/sec (better
than .±_0.2% accuracy except for U < 0.1 ft/sec where the accuracy is approximately
+O. 5%). The results reveal a large effect of the water temperature on the calibration
curves (in an extreme case a change in temperature of only 5.5°F can result in a 100%
error in the mean velocity reading). A scheme which utilizes a temperature sensing
probe immersed in the working fluid is used to compensate for the water temperature
variation . Several possible circuit configurations for this scheme, including an
optimum circuit design, are investigated and the results from some of them are presented
and discussed. The circuit has a frequency response to temperature variations which
depends on the thermal time constant of the temperature probe (up to several cycles per
second can be obtained using commercially available probes) and can be used to compensate
for temperature variations of more than 20°F with an accuracy better than +0.2%.
By using an effective value (much smaller than E0 ) instead of the zero velocity bridge
voltage (Eo) in exponential-type linearizers, a constant exponent is found useful in
linearizing the anemometer output over a wider range of velocities.
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Distribution Classification
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1
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Distribution Conflict
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No
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DTIC Record Exists
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Yes
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Illinois Tech Related
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Yes
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Photo Quality
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Complete
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Report Availability
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Full text available
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Type
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report
AD0784912