Analysis of Energy Consumption in Drying Process of Biomaterials Using a Combined Unsymmetrical Double-Feed Microwave and Vacuum System (CUMV)—Case Study: Tea Leaves

Abstract

An energy analysis of drying of biomaterials (tea leaves) was conducted on a combined unsymmetrical double-feed microwave and vacuum system (CUMV) to optimize the operating conditions and quality of the products. Tea leaves were dried from an initial moisture content of 172 to 7% (db). An energy consumption model based on the first law of thermodynamics was developed to evaluate energy efficiency. The influences of microwave power, vacuum pressure, and microwave operation modes on energy consumption were investigated in detail. The results showed that energy consumption as well as energy efficiency were strongly dependent on vacuum pressure and microwave power. Energy consumption and color parameters of the tea leaves were compared at different drying conditions. In particular, the experiments were carried out at different microwave powers (800 and 1,600 W) at a frequency of 2,450 MHz and different vacuum pressures (535 and 385 torr) to investigate the effects of these factors on the microwave–vacuum drying.

Keywords:

• Energy efficiency
• Microwave energy
• Specific energy consumption
• Vacuum pressure

ACKNOWLEDGMENTS

The authors gratefully acknowledge the Thailand Research Fund and the National Research University Project of Thailand Office of Higher Education Commission for supporting this research project.