Experimental investigation of pre-drying data for some medicinal herbs in forced convection

Abstract

The special active agent content of herbs makes them suitable for healing and health preservation. The key element in the processing of herbs and spices is drying. Before drying, the medicinal plants should be stored under appropriate conditions to avoid deterioration of quality where one of the possible methods is pre-drying with ambient air. This work defines the determination of main operational parameters at forced convection drying with ambient air like drying rate, volume decrease, maximum drying air velocity, and porosity for various medicinal plants (common yarrow ? Achillea collina, giant goldenrod ? Solidago gigantea, wormwood ? Artemisia, walnut leaf ? Juglandis folium, wild carrot ? Daucus carota). To determine the drying rate, a convective dryer was used where the average drying rate of common yarrow and wild carrot were the highest followed by giant goldenrod, walnut leaf and wormwood. Measurements were made on a pilot plant fluidized bed dryer to determine the volume decrease and the maximum drying air velocity. The volume decrease was determined as a function of time and moisture content. It was found that the maximum drying air velocity for each medicinal plant was between 1.8 and 2.2 m/s. In addition, for each herb the porosity was measured by an air pycnometer.