Helpline give Process Heating's readers a chance to solve problems that crop up in their heat processing applications.

I need to dry large quantities of different medicinal herbs used in native medicine. At present, they are dried under the sun, over several days. The requirement is to reduce moisture in fresh leaves, which have moisture at various levels from about 60 to 75%, to preferably about 2 to 3 %. Hot air drying at temperatures exceeding about 220°F (104°C) is ruled out. The dryer capacity required is on the order of 500 to about 1,500 lb/hr.

It has been suggested that either a radio frequency or microwave dryer might fit the bill. What do you suggest? - C.J.

Contact California State University at Fresno. They have a new process using microwave and vacuum that keeps the temperature down. - Jeff Smith, Lane Mfg., (530) 622-4663.