Located in Salina, KS, the Kansas State University Bulk Solids Innovation Center opened in 2015 to research bulk solids material handling. The center is the first of its kind in America. Johnselvakumar (John) Lawrence, the Center’s research director, is leading a session at this year’s International Powder & Bulk Solids Conference & Exhibition in Rosemont, IL, April 24-26, entitled, “Effect of Temperature and Relative Humidity on Bulk Solids Handling.”
Temperature and relative humidity (RH) play an important role in bulk solids handling. The flowability of the material is affected by change in temperature and relative humidity. Flowability refers to unconfined yield strength of the material with respect to normal force. This strength is lower for easy flow and higher for difficult flow. For example, some materials flow well at low temperature and not so well at high temperature. These materials will have loading and unloading problems when transporting from a cooler region to a warmer region and vice versa. When transported through a pneumatic conveying system, these materials get hot due to heat of compression by the blower and cause problems in flow through a hopper or filter receiver.
Another important aspect is the moisture sorption characteristics of the material. Depending on the material, it will absorb or desorb moisture based on the temperature and the surrounding RH (aka critical relative humidity). This information is useful for materials that are hygroscopic in nature. By maintaining proper temperature and RH in the factory, these hygroscopic materials can be handled effectively, both in terms of maintaining quality and flowability.
Caking is another flowability problem. It depends on the adhesive forces such as van der Waals’ force, capillary force (liquid bridging), electrical force, and electrostatic (Coulomb) force. Moisture plays an important role in these.
Case studies involving sugar and detergent flowability with respect to temperature and humidity will be discussed.