Heat transfer in microwave heating

Abstract

Heat transfer is considered as one of the most critical issues for plan and implement of large-scale microwave heating systems, in which improvement of the microwave concentration of materials and suppression of mismatched temperature distribution are the two main objectives. The present knead focuses on the analysis of heat transfer in microwave heating system for achieving highly efficient microwave assisted steelmaking through the investigations on the follow aspects : ( 1 ) portrayal of microwave profligacy using the derive equations, ( 2 ) quantification of charismatic passing, ( 3 ) decision of microwave preoccupation properties of materials, ( 4 ) model of microwave propagation, ( 5 ) simulation of hotness transfer, and ( 6 ) improvement of microwave absorption and heat uniformity.

Microwave heat is attributed to the heat generation in materials, which depends on the microwave waste. To theoretically characterize microwave heating, simplified equations for determining the cross electromagnetic mode ( TEM ) power penetration depth, microwave field attenuation length, and half-power depth of microwaves in materials having both magnetic and insulator responses were derived. It was followed by developing a simplify equation for quantifying magnetic loss in materials under microwave irradiation to demonstrate the importance of magnetic personnel casualty in microwave heat. The permittivity and permeability measurements of respective materials, namely, hematite, magnetite boil down, wüstite, and ember were performed. Microwave loss calculations for these materials were carried out. It is suggested that charismatic passing can play a major role in the inflame of magnetic dielectrics .
Microwave propagation in diverse media was predicted using the finite-difference time-domain method acting. For lossy magnetic dielectrics, the waste of microwaves in the average is ascribed to the decay of both electric and magnetic fields. The heat transfer process in microwave heating of magnetite, which is a typical magnetic insulator, was simulated by using an explicit finite-difference approach. It is demonstrated that the heat generation due to microwave beam dominates the initial temperature rise in the inflame and the hotness radiation sickness heavily affects the temperature distribution, giving rise to a hot spot in the bode temperature profile. Microwave heat at 915 MHz exhibits better heating homogeneity than that at 2450 MHz due to larger microwave penetration astuteness. To minimize/avoid temperature nonuniformity during microwave heating the optimization of object dimension should be considered.

The account mirror image loss over the temperature crop of inflame is found to be useful for obtaining a rapid optimization of absorber dimension, which increases microwave absorption and achieves relatively uniform heating. To further improve the heating effectiveness, a function for evaluating absorber electric resistance match in microwave heat was proposed. It is found that the maximum preoccupation is associated with arrant electric resistance match, which can be achieved by either selecting a fair sample proportion or modifying the microwave parameters of the sample.