Fluidized bed dryers are widely used in several fields of industry. Sufficiently accurate thermal models provide an opportunity to increase the effectiveness of dryers. The required size of a fluidized bed dryer can be defined with the application of mathematical model. This work is aimed at developing mathematical model to investigate the influence of operating parameters in a fluidized bed dryer using volumetric heat transfer coefficient. After the defining the input parameters of the differential equations, the required entry length of the dryer which effective heat and mass transfer between gas and particles takes place can be estimated. The correct estimation of the entry length is useful in optimal design of a fluidized bed dryer. Using the model the impact of the drying parameters can be determined to the required length.
The special active agent content makes suitable herbals for healing and health preservation. The key element in herbs and spices processing is drying. The required low moisture content of medicinal plants to storage can be achieved only by applying drying equipment at Hungarian climatic conditions. The extent of the dryer capacity defines the processing capacity of the factory. During the daily operation can easily occur bottleneck, when large amount of herbs are transported to the factory, which is above the drying capacity — various plants unexpected simultaneous flowering, weather emergency, extraordinary collecting, etc. The aim of the manuscript is to determinate operational data at herbs pre-drying with low temperature air by measurements. This work defines the drying rate, the volume decrease and the drying air velocity for various medicinal plants at drying with ambient air.