Laboratory Fume Hood Fans: Basic Parameters and Unit Conversions
To ensure efficient operation of laboratory fume hood systems, it is essential to understand the key parameters and unit conversions for fan performance. Here is an overview of basic parameters and common unit conversions for fume hood fans:
I. Basic Fan Parameters
1. Air Volume (Q)
– Measures the total amount of air that passes through a given cross-section per unit time, indicating airflow volume.
– Units:
– m³/h (cubic meters per hour), abbreviated as CMH
– m³/min (cubic meters per minute), abbreviated as CMM
– m³/s (cubic meters per second), abbreviated as CMS
2. Pressure
– Divided into dynamic pressure and static pressure.
– Dynamic Pressure: The pressure generated by the airflow velocity, always positive and determined by air density and velocity.
– Static Pressure: Internal pressure in a stationary fluid, related to air density and compression level but independent of airflow speed, often equated to system resistance.
– Common units:
– mmAq (millimeters of water column) or **Pa** (Pascals)
3. Rotational Speed
– Measures the speed of fan blade rotation, with units in rotations per minute (rpm).
4. Shaft Power
– The actual power needed for fan operation; when selecting a motor, its power should exceed the shaft power.
5. Balance Grade
– Reflects the residual imbalance during rotation, typically graded for quality. In China:
– G6.3 is considered standard for fan blades.
– G4.0 is premium, while precision level G3.2 offers even better balance, reducing vibration, noise, and extending bearing and fan life.
II. Common Unit Conversions
1. Air Volume (Flow Rate) Conversions
– CMH: Cubic meters per hour
– CMM: Cubic meters per minute
– CFM: Cubic feet per minute
– LM: Liters per minute
– Conversion:
1m³/s = 60m³/ min= 3600m³/ h
– Nm³/h: “N” denotes standard conditions, with 20°C, 0.101 MPa pressure, and 65% relative humidity.
2. Pressure Conversions
– 1 standard atmosphere (atm) = 101.325 kPa
– 1 technical atmosphere (at) ≈ 98.0665 kPa
– 1 bar = 100,000 Pa
– 1 mmHg (millimeter of mercury) = 133.322 Pa
– 1 mmAq (millimeter of water column) = 9.8 Pa
3. Power Conversions
– 1 Hp (horsepower, imperial) = 0.746 kW
– 1 Ps (metric horsepower) = 0.735 kW
