Hot wirehot film anemometer

1
Hot wire/hot film anemometer
Hot film for liquids
Hot wire for gases
2
Uses are found anywhere fluids flow

• Aerodynamics lift, drag
• Combustion IC, gas turbine engines
• Meteorology
• Fires and fire safety
• Ocean currents
• How bugs fly and how fish swim
• Turbulence (Richard Feynman, "the most important
  unsolved problem of classical physics." )
• Ordinary measurement tools, i.e. HVAC probes

3
Use of hot wire in turbulence
4
The stove
Heat flow out
Power in
hA
T (K)
5
Constant power device
P
A
Response time dictated by the response of the
system.
6
Constant T device
Constant power mode needs to wait for steady
state to correlate T to h
Constant T mode always at steady state -
instantly correlate P to h
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Proportional Control
kp
Power input
dT/dt
T
hA(T-Tair)
h
T-Tair
Physical system
8
Proportional control
Kp1
Kp0.1
Kp0.01
9
kp
Why cant p-gain be set to be very large?
10
Time delay can cause instability
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What is happening?

• Cant make P-gain too high, time delay can cause
  instability.
• If P-gain is too low there is high offset.

12
PI Control
0.1
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Result with Integral Control
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Results from changes..
T (K)