Characteristics of Microwave Vacuum Baking and Drying of Oolong and Its Kinetic Model

Rongchuan Lin,Qingjiao Lin,Hetong Lin

doi:10.19026/ajfst.5.3360

Abstract

This paper studies the characteristics of microwave vacuum baking and drying of oolong and analyzes the influence of microwave power and vacuum degree in the drying process on the moisture in the tea. According to the variation law of moisture, it explores the relationship between time and wet base moisture contents under different microwave powers and vacuum degrees, as well as the kinetic mathematical model of vacuum drying for oolong using the microwave. Based on the energy balance between the sensible heat, latent heat and the absorptive microwave energy, this model builds verification test by a large number of experimental data and the results indicate that within certain range of radiation power and thickness, the temperature and moisture content of oolong are uniformly distributed, even more uniform especially in the drying period; generally, the temperature distribution within the oolong fails to show integrity. The free water and water vapor may flow as permeate stream in the internal part of oolong under the action of pressure gradient. The migration intensity mainly depends on the intensity of microwave radiation and initial moisture content; the mathematical model established on this basis could better simulate the microwave vacuum drying process of oolong. Due to its high simulation accuracy, it can be used to describe the variation of moisture content with the drying time and power. The test results provide a technical basis for the controllable industrial production of oolong baking.

Highlights

Microwave vacuum drying is a combination of microwave and vacuum drying, which means to conduct microwave drying in a vacuum environment
It is still difficult to achieve online test for the moisture content in the dry production process, so researches on the drying characteristics and kinetic model is of great significance for the optimization and control of the drying process (Giri and Suresh, 2005)
The mathematical calculation results show that the square of the correlation coefficient of the measured and simulated values of oolong moisture is 0.99 and the square of the correlation coefficient between the temperature measurement and simulated values is up to 0.98, suggesting that the model is with high precision in simulating the microwave vacuum drying process of oolong below the critical moisture

Summary

Introduction

Microwave vacuum drying is a combination of microwave and vacuum drying, which means to conduct microwave drying in a vacuum environment It can increase the drying rate and reduce the temperature, thereby keeping the original nutrients in the food and other raw materials and improving the drying quality of the product (Li, 2005). The microwave vacuum drying technology is a new combination with the development of microwave drying technology It could dry materials at low temperature, which better maintains their nutritional content as well as the drying quality and overcomes the disadvantage of low conventional heat conduction rate in the vacuum state, greatly shortening the drying time and improving the production efficiency. It is still difficult to achieve online test for the moisture content in the dry production process, so researches on the drying characteristics and kinetic model is of great significance for the optimization and control of the drying process (Giri and Suresh, 2005). Wu et al (2010) have a study on the temperature correlation of ultrasonic attenuation coefficient in microwave hyperthermia

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Results

Conclusion