Which of the following pneumotachometers is influenced by gas viscosity and thermal conductivity?
A. differential pressure
B. hot wire
C. ultrasonic
D. Fleisch
?ANS: B
A. Incorrect response: Pneumotachometers that use differential pressure to determine flow from pressure drop across a known resistance.
B. Correct response: Hot wire pneumotachometers operate on the principle that cooling of a heated wire is proportional to the gas flow past it. The rate of cooling depends on the gas viscosity and the thermal conductivity.
C. Incorrect response: Ultrasonic pneumotachometers use an ultrasonic transmitter-receiver and function on the principle that ultrasonic transit times are proportional to gas flow.
D. Incorrect response: Fleisch is another name for the pneumotachometer described in explanation A.
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