Measuring Airflow in Material Handling: Techniques and Importance
Air flows from a high-pressure zone to a low-pressure zone due to the pressure difference. Several variables can cause dust to remain in the material stream, including particle sizes, material cohesiveness, and moisture content. Generally, dust particles have a pickup velocity in the range of 1.0 to 1.25 meters per second (200 to 250 ft/min). This means that air moving over a bed of material at this speed can pick up dust from the surface and carry it away.
The quantity of air flowing through the transfer point each minute can be calculated from measurements. To calculate the volume of moving air, multiply the measured airspeed leaving each open area of the transfer point—including the belt exit, tail box, sides of the belt, dust pickups, and other openings—by the area of each opening. These airflows are then added together to produce a total airflow. These measurements must be taken while the transfer point is in operation. Air velocity measurements can be performed with a relatively inexpensive handheld anemometer, and the area can be measured with a tape measure.
Additional airflow through the transfer-point enclosure can be produced by crushers, vibrating screens, feeders, and other process and handling equipment. Therefore, it is necessary to measure the air velocity while these devices are in operation as well.
This air volume calculation should be compared to the theoretical computations of the air volume. If a major discrepancy exists, the airflow calculated from measured air velocity should ALWAYS be used.