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68 / January 2020 powderbulk.com Powder handling is more than just putting components together. custom. sanitary. solutions. unloading & storage - pneumatic & mechanical conveying - batching & Blending - sifting & size reduction - dust control - filling & packaging let pps handle your next powder processing project. contact the experts. www.powder-solutions.com 877-933-2556 food dairy nutritional a slow-moving bed of granular material flows down the hopper in mass flow against a countercurrent upward flow of heated drying air. A microwave transmitter is installed on one vertical wall of the dryer, and a receiver is installed on the oppo- site wall. The transmitter projects a microwave beam across the moving bed of solids, and the loss of micro- wave energy detected by the receiver results directly from the amount of moisture contained in the solids in the beam's path. PBE Reference 1. This refers to residence time distri- bution for the plug-flow approach, when all particles in one zone move at the same velocity (in plug flow) and experience the identical expo- sure time to drying temperature and humidity conditions. For further reading Find more information on this topic in articles listed under "Drying" in Powder and Bulk Engineering's arti- cle index in the December 2019 issue or the article archive on PBE's web- site, www.powderbulk.com. John J. Walsh, PE, (651-263-3697, jjwalshpe@ameridrycon.com) has a BE in chemical engineering from CCNY and has worked in the field of solids thermal processing for more than 40 years. He holds several pro- cess and equipment patents and has written numerous technical articles. He has been an instructor on industrial drying at the Center for Professional Advancement, New Brunswick, NJ, and Amster- dam, the Netherlands. American Drying Consultants St. Paul, MN www.ameridrycon.com