Hot-wire anemometer: primary application area In instrumentation practice, a hot-wire (or hot-film) anemometer is primarily used to measure which of the following?

Introduction / Context:
Hot-wire anemometers operate on convective heat transfer from a heated sensor to a flowing fluid. Changes in the cooling rate alter sensor resistance, which is related to velocity via calibration laws (e.g., King’s law). They are invaluable in measuring low velocities and turbulence, especially in gases.

Given Data / Assumptions:

• The device uses a thin wire or film heated electrically.
• Fluid flow cools the element; electronics maintain constant temperature or constant current.
• Output correlates with fluid velocity (hence volumetric flow rate with area known).

Concept / Approach:
The fundamental measurand is velocity of a fluid (air, gas, and sometimes liquid with hot-film probes). While the principle relates to heat transfer (and thus to properties like thermal conductivity), the instrumentation purpose is velocity measurement. Hot-wire sensors are not suitable for granular solids (abrasion, poor thermal coupling) and are not direct high-temperature thermometers.

Step-by-Step Solution:

Verification / Alternative check:
Texts and datasheets categorize hot-wire anemometers under velocity measurement devices for gases, including turbulence and boundary-layer studies.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing the underlying heat-transfer principle with the target measurand; the device is designed and calibrated for velocity.

Final Answer:
flow rates (or velocities) of fluids