Abstract
Microwave heating is rapidly emerging as an effective and efficient tool in various technological and scientific fields. A comprehensive understanding of the fundamentals of microwave–matter interactions is the precondition for better utilization of microwave technology. However, microwave heating is usually only known as dielectric heating, and the contribution of the magnetic field component of microwaves is often ignored, which, in fact, contributes greatly to microwave heating of some aqueous electrolyte solutions, magnetic dielectric materials and certain conductive powder materials, etc. This paper focuses on this point and presents a careful review of microwave heating mechanisms in a comprehensive manner. Moreover, in addition to the acknowledged conventional microwave heating mechanisms, the special interaction mechanisms between microwave and metal-based materials are attracting increasing interest for a variety of metallurgical, plasma and discharge applications, and therefore are reviewed particularly regarding the aspects of the reflection, heating and discharge effects. Finally, several distinct strategies to improve microwave energy utilization efficiencies are proposed and discussed with the aim of tackling the energy-efficiency-related issues arising from the application of microwave heating. This work can present a strategic guideline for the developed understanding and utilization of the microwave heating technology.
Highlights
Microwaves are part of the electromagnetic spectrum that move at the speed of light with a wavelength ranging from 1 m to 1 mm, which corresponds to a frequency range of 300 MHz to300 GHz
In our previous research on microwave-induced pyrolysis of electronic waste, we found that microwave-metal discharges occurred immediately at the onset of microwave irradiation, leading to several local hot spots and a great promotion of the pyrolysis processes
Microwave heating is commonly known as dielectric heating and its application is usually limited to microwave electronic field heating
Summary
Microwaves are part of the electromagnetic spectrum that move at the speed of light with a wavelength ranging from 1 m to 1 mm, which corresponds to a frequency range of 300 MHz to. (3) non-contact heating; (4) quick start-up and stopping; (5) the ability to treat waste in-situ; (6) and portability of equipment and processes [12,13] Based on these distinguished advantages, microwaves have been used in various technological and scientific fields, for example: food processing; different drying processes; as a remedial tool used in the area of sludge processing, medical waste treatment, Materials 2016, 9, 231; doi:10.3390/ma9040231 www.mdpi.com/journal/materials. In addition to the acknowledged conventional microwave heating mechanisms, as a special type of material, the interaction mechanisms become more complicated when metals and their alloys are subjected to a microwave field. Directions for further research and potential applications are suggested
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