Energetic Analysis of Drying Biological Materials with High Moisture Content by Using Microwave Energy

Abstract

One of the most important parameters in the drying process is the efficiency of energy transfer. Although it is well known that the absorbed component of the referred energy in the dehydration process under microwave conditions is theoretically lower—especially during the falling rate period of drying—by an order of magnitude than that of convective drying, the real efficiency of energy transfer in the microwave field depends on numerous—partly unknown—factors. In this study, the most significant relations between the energy transfer efficiency and the drying parameters were investigated. During the experiments, two power levels were used to study the effects of domain variables in apple, potato, and onion dehydration processes. The results showed that variations in microwave power level played an important role in overall drying kinetics.

Based on the recorded data, we determined the typical energy efficiency factors for microwave drying of apple, potato, and onion. The specific energy consumption was calculated to compare the energy efficiency of a single measurement series. It was evident that by applying higher power levels, the energy utilization was more efficient. Furthermore, we theoretically proved and experimentally showed the nonthermal effects of the microwave energy.

Keywords:

• Apple
• Nonthermal effect
• Onion
• Potato microwave drying

Acknowledgments

This article was part of the 17th International Drying Symposium (IDS2010), held October 3–6, 2010 in Magdeburg, Germany. Other articles from IDS2010 were published in special issues of Drying Technology, 29(13) and 29(16).