Vidéo: Hot-Wire Anemometer; Flow Velocity Based on Heat Dissipation

S'identifier

Hot Wire Anemometry

Vue d'ensemble

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI

Hot-wire anemometers have a very short time-response, which makes them ideal to measure rapidly fluctuating phenomena such as turbulent flows. The purpose of this experiment is to demonstrate the use of hot-wire anemometry.

Procédure

Measure the width of the slit, W, and record this value in table 1.
Verify that the data acquisition system follows the schematic in Figure 2.
Connect the positive port of the pressure transducer (see Figure 2 for reference) to the plenum pressure tap ().
Leave the negative port of the pressure transducer open to the atmosphere. Hence, the reading of this transducer will be directly
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Résultats

The experimental measurements are listed in Table 2 and shown in Figure 5. A linear regression of these data produced the following result for equation (6):

(9)

Which can be used to determine the velocity as a function of the voltage:

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Applications et Résumé

Given that turbulence exhibits high frequency velocity fluctuations, hot-wire anemometers are suitable instruments for its characterization due to their high time-resolution. In the present experiment, we demonstrated the process of calibrating a hot-wire anemometer. To this end, we compared the voltage signal of the anemometer with known values of velocity at the vena contracta of a well-characterized jet. These measurements were used to determine the calibration constants for the linear response of the anemome

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References

Chapra, S.C. and R.P. Canale. Numerical methods for engineers. Vol. 2. New York: McGraw-Hill, 1998.
King, L.V. On the convection of heat from small cylinders in a stream of fluid: determination of the convection constants of small platinum wires with applications to hot-wire anemometry. Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character 214 (1914): 373-432.
White, F. M. Fluid Mechanics, 7th ed., McGraw-Hill, 2009.
Munson, B.R., D.F. Young, T.H. Okiishi. Fundamentals of Fluid Mechanics. 5^th ed., Wiley, 2006.
Buckingham, E. Note on contraction coefficients of jets of gas. Journal of Research, 6:765-775, 1931.

Tags

Hot Wire Anemometry Fluid Velocity Measurement Flow Tests Turbulent Flows Hot Wire Anemometers Diagnostic Tool Constant Temperature Configuration Calibration Resistive Wire Convective Cooling Electrical Power Flow Velocity

Measure the width of the slit, W, and record this value in table 1.
Verify that the data acquisition system follows the schematic in Figure 2.
Connect the positive port of the pressure transducer (see Figure 2 for reference) to the plenum pressure tap ().
Leave the negative port of the pressure transducer open to the atmosphere. Hence, the reading of this transducer will be directly; as required by equation (7).
Start the program for hot-wire calibration. Set the sample rate at 100 Hz for a total of 1000 samples (i.e. 10s of data).
Make sure that channel 0 in the data acquisition system corresponds to the voltage of the hot-wire anemometer.
In the field corresponding to channel 0, select the value of the constant to 0.45.
Set the hot-wire anemometer at the position of the vena contracta (on the centerline, at x = 1.5 W).
Make sure that channel 1 in the data acquisition system corresponds to the signal of the pressure transducer.
Enter the values of local air density (typically 1.2 kg/m³ for average local conditions) and conversion constant from volts to pressure (76.75 Pa/V) in the fields corresponding to the pressure transducer. Record these values in table 1. With this, the data acquisition system will report the data directly in velocity in m/s according to equation (7).
Cover the stack completely to establish the condition for maximum velocity at the jet.
Turn on the flow facility.
Acquire a dataset.
Change the stack plate for one with a lower restriction (larger diameter)
Acquire a dataset.
Repeat steps 1.15 and 1.16 for a total of at least four times. Make sure that the last repetition is carried out with the stack fully unrestricted (lowest jet velocity).
The data acquisition program will carry out the least-squares calculation and report the calibration constants automatically. Record these values on table 1.

Table 1. Basic parameters for experimental study.

Parameter	Value
Slit width (W)	19.05 (mm)
Air density (r)	1.2 (kg/m³)
Transducer calibration constant (m_p)	76.75 (Pa/V)
Calibration constant A	5.40369 (V²)
Calibration constant B	2.30234 (V² s^0.65m^-0.65)

Figure 3. Hot-wire anemometer circuitry. (A): Wheatstone bridge circuit to ensure constant temperature in the hot-wire. (B): detail of the structure of a hot-wire. Please click here to view a larger version of this figure.

Figure 4. Flow control in the flow system. The stack on top of the plenum serves the purpose of diverting flow from the jet slit allowing to control the jet's exit velocity. Please click here to view a larger version of this figure.

Passer à...

0:07

Overview

1:07

Principles of Hot Wire Anemometry

4:18

Preparing the Flow Chamber

6:45

Analysis and Results

7:26

Applications

8:56

Summary

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