The instrument preferred in the measurement of highly fluctuating velocities in air flow is: Hot wire anemometer

Explanation:

A hot wire anemometer is the preferred instrument for measuring highly fluctuating velocities in air flow. This instrument is based on the principle of convective heat transfer.

Principle:
The hot wire anemometer consists of a thin wire that is heated electrically. As air flows over the wire, it cools the wire and causes a change in its resistance. By measuring this change in resistance, the velocity of the air flow can be determined.

Advantages:
1. High sensitivity: Hot wire anemometers are highly sensitive and can accurately measure small fluctuations in air flow velocities.
2. Wide measurement range: These instruments can measure a wide range of air velocities, from very low to very high speeds.
3. Fast response time: Hot wire anemometers have a fast response time, allowing them to capture rapid changes in air flow velocities.
4. Non-intrusive measurement: This instrument does not require any physical obstruction in the air flow path, making it non-intrusive and suitable for measuring highly fluctuating velocities.

Applications:
Hot wire anemometers are commonly used in various applications where accurate measurement of highly fluctuating air flow velocities is required. Some of the applications include:
- HVAC systems: Hot wire anemometers are used to measure air velocities in heating, ventilation, and air conditioning systems to ensure efficient and optimal performance.
- Wind tunnel testing: These instruments are used in wind tunnel testing to measure the velocity of air flowing over models or prototypes.
- Environmental monitoring: Hot wire anemometers are used in environmental monitoring to measure air flow velocities in order to study pollutant dispersion and air quality.
- Aerodynamics research: These instruments are widely used in aerodynamics research to measure air flow velocities around aircraft, automobiles, and other aerodynamic structures.

Conclusion:
In conclusion, the hot wire anemometer is the preferred instrument for measuring highly fluctuating velocities in air flow. Its high sensitivity, wide measurement range, fast response time, and non-intrusive nature make it suitable for a variety of applications in mechanical engineering and environmental monitoring.