A Phase-Shifting Method for Improving the Heating Uniformity of Microwave Processing Materials

Abstract

Microwave processing of materials has been found to deliver enormous advantages over conventional processing methods in terms of mechanical and physical properties of the materials. However, the non-uniform temperature distribution is the key problem of microwave processing, which is related to the structure of the cavity, and the placement and physical parameters of the material. In this paper, a new microwave cavity structure with a sliding short based on phase-shifting heating is creatively proposed to improve the temperature uniformity. An electronic mathematical model based on the Finite Element Method (FEM) is built to predict the temperature distribution. Meanwhile, a new computational approach based on the theory of transformation optics is first provided to solve the problem of the moving boundary in the model simulation. At first, the experiment is carried out to validate the model, and heating results from the experiment show good agreement with the model’s prediction. Based on the verified model, materials selected among a wide range of dielectric constants are treated by stationary heating and phase-shifting heating. The coefficient of variation (COV) of the temperature and temperature difference has been compared in detail between stationary heating and phase-shifting heating. A significant improvement in heating uniformity can be seen from the temperature distribution for most of the materials. Furthermore, three other materials are also treated at high temperature and the heating uniformity is also improved. Briefly, the strategy of phase-shifting heating plays a significant role in solve the problem of non-uniform heating in microwave-based material processing. A 25%–58% increase in uniformity from adapting the phase-shifting method can be observed for the microwave-processed materials.

Dynamic Model for a Uniform Microwave-Assisted Continuous Flow Process of Ethyl Acetate Production

“…Based on the BJ-22 rectangular waveguide, the experiment system of the microwave-assisted continuous flow process is shown in Figure 1 . A circulator is employed to protect the microwave generator with the output power of 700 W at 2450 MHz [ 23 ]. As a real-time monitor, an AV2433 microwave power meter is used to detect the output power of the microwave generator.…”

“…The 2D cross-section diagram of the geometry is shown in Figure 2 . Five of the six faces of the waveguide were set as Perfect Electric Conductors (PEC) except the left-side face as shown in Figure 2 [ 23 ]. Microwaves come into the waveguide from the left-side plane.…”

Energy issues in microwave food processing: A review of developments and the enabling potentials of solid-state power delivery

“…Frequency, phase and power amplitude control as well as multi-source power delivery have all been individually shown to improve heating uniformity in several studies (Bows, 1999;Antonio and Deam, 2005;Gunasekaran and Yang, 2007;Dominguez-Tortajada et al, 2007;Liao et al, 2016;Bae et al, 2017). When combined effectively in solid-state systems, more significant improvements in uniformity are expected.…”

Improved approach using symmetric microstrip sensor for accurate measurement of complex permittivity

“…The response of microwave planar circuits is greatly influenced by the dielectric properties of materials used in the substrate. Therefore, an accurate characterization of materials or detecting a change in the electrical properties of materials is an important task in the field of industrial, scientific, and medical applications pertaining to the microwave region …”

“…Therefore, an accurate characterization of materials or detecting a change in the electrical properties of materials is an important task in the field of industrial, 1-3 scientific, [4][5][6] and medical applications pertaining to the microwave region. [7][8][9] Various microwave characterization techniques are proposed in the literature for the permittivity measurement of materials. These methods can be classified as free-space methods, transmission/reflection methods, and resonant cavity methods.…”