Air conditioning, heating, and fresh air intake during winter conditions and dry summer months cause electrostatic discharge (ESD) in cleanroom environments. ESD can result in costly damage to the equipment and products manufactured, as well as delays or downtime. Here are some of the forms of ESD control:
De-correlation air atomizing: A de-correlation type system provides a humidification which generates equal sized micron droplets with equal spacing that do not attract to each other but oxidize into the air. It is completely non-wetting and forces the humidity into the air evenly and completely.
Air and water atomizing: Air atomizing humidifiers use compressed air to break down the water droplets in the nozzle. It provides uneven droplets between 7 to 20 microns.
High pressure: High pressure water pumps push water through miniature holes which are sprayed into the air. The miniature holes can clog and require maintenance of the nozzle and water pump, and duct installation requires droplet filters and drainage.
Ultrasonic: Ultrasonic type humidifiers use a submerged vibrating disk to create a high-frequency oscillation, dispersing small water droplets that travel a short distance into the air.
Centrifugal: Centrifugal humidifiers deliver supply water to a fast-spinning disk that fractures water into large uneven droplets, which requires a fan, warm air, and high ceilings to distribute the humidity and evaporate the water. This type of humidifier is not recommended for cleanroom use.
Wet Media: Wet media humidifiers use a water absorbing mesh placed inside a duct or AHU airstream. It can be difficult to achieve a non-fluctuating relative humidity control. A wet media type humidifier is not recommended for cleanroom use.
This cleanroom tip was taken from “ESD Control Using Adiabatic Humidification” by Ido Goldstein. The article originally appeared in the July/August 2013 issue of Controlled Environments.
