Energy savings in convective drying of various materials using variable temperature conditions

摘要

Convective drying process is among the most energy-intensive ones; therefore, every kind of its improvement may result in a significant reduction of energy consumption, which contributes to sustainable energy planning. Intermittent drying, often accomplished by periodical temperature lowering and/or stopping the air flow completely, is one of the most popular measures for energy saving. Herein, intermittent regime was carried out only by temperature variation, keeping the heater turned on for 60 min, and then turned off for another 30 min, while the fan was turned on all the time. Temperature lowering in certain periods saves energy, but some extension of total drying time is also expected. The aim of the article was to explore the possibility of energy saving with no significant time extension and the influence of different effective diffusivities in that context. Hence, the drying materials with different properties were chosen—walnuts, chestnuts with and without shell, pumpkin, and potatoes. Drying of walnuts was described in more detail to briefly explain the basic idea of the analysis, whereas other materials were analyzed only in terms of energy saving. The research showed the noticeable effective diffusivity influence on energy saving, and only materials with its high value are suitable for such a treatment