16th International Conference
on Microwave and High Frequency Heating

18-21 September 2017, Delft, The Netherlands
14:30   Dielectric properties measurement (3)
Chair: Jose-Manuel Catala-Civera
14:30
15 mins
TEMPERATURE-DEPENDENT COMPLEX PERMITTIVITY OF SEVERAL ELECTROMAGNETIC SUSCEPTORS AT 2.45 GHZ
José Fayos-Fernández, Itahisa Pérez-Conesa, Juan Monzó-Cabrera, Soledad del Pino-de-León, Juan Carlos Albaladejo-González
Abstract: Electromagnetic susceptors, understood as transductors of energy, from radiative to thermal, are of high interest when combined with materials that are non-efficient by themselves in a heating process using microwave technology. Susceptors can be either embedded into the material (as filaments, powders, etc.) or attached to them as a supplementary layer added on their interfaces. The loss factor modelled as the imaginary part of the complex permittivity of a material can predict the result of the pyroelectric effects that underlies during its microwave heating process. Such mechanisms have a dependence with temperature, and the heating process rate may evolve with time as the temperature varies. Furthermore, the heat transfer coefficient can also vary with the temperature. Both, the loss factor and the heat transfer coefficient are involved in the heat transfer equation, and their dependence with the temperature can justify largely the thermal runaway effects. Such effects are noticeable when the heat generation and transfer rates overcome the period of time required by any artifacts introduced inside a microwave exposure chamber for leveling the volumetric heating uniformity. This study focuses in determining the complex permittivity of several susceptors at the frequency of 2.45 GHz in the temperature range [30, 70] °C.
14:45
15 mins
EXTRACTION OF WIDEBAND COMPLEX PERMITTIVITY IN HIGH LOSS MATERIAL FROM A COAXIAL CELL BY MULTIMODAL VARIATIONAL APPROACH
Jingyi Wang, Junwu Tao, Tan-Hoa Vuong
Abstract: Accurate characterization of dielectric properties in microwave range depends on the use of suitable measurement cell and rigorous electromagnetic simulation method for inverse modeling. Integral equation based method using multimode description may be an alternative for finite element (FEM) based commercial software. A multimodal variation approach is applied to discontinuity between an empty oversized coaxial line and the same coaxial line partially filled with ring form material sample. The mode basis of partially filled coaxial line has been determined in a large frequency range, depending on trial value of sample's complex permittivity. The use of multimodal variational approach leads to the determination of scattering parameter of the cascaded empty coaxial line-sample loaded coaxial line-empty coaxial line double discontinuity. The accuracy of the numerical results is guaranteed by the variational nature of this formulation. The extraction of complex permittivity of sample material will be taken by using an optimization procedure whose objective function is the least square of difference between simulated and measured scattering parameters. Both reflection and transmission coefficients are used in this formulation with different weight function in order to guaranty good convergence.
15:00
15 mins
DIELECTRIC PROPERTIES OF SPENT HYDRODESULFURIZATION MoNi/Al CATALYST
Wenwen Qu, Jialin Zhang, Shengming Xu, Lu Wang, Libo Zhang, Jinhui Peng
Abstract: Microwave heating is a very useful technique for the extraction of rare metals from spent petroleum refining catalysts. The fundamental understanding of dielectric properties of the spent catalysts is very important in the microwave design and simulation for any process. In the present work, the dielectric properties of the spent hydrodesulphurization MoNi/Al catalyst were measured by using the resonance cavity perturbation technique in temperature range from room temperature to 750 °C at both 915 and 2450 MHz. The process was conducted to study the microwave-absorption properties of spent catalyst and the feasibility of microwave roasting spent catalyst to recovering the rare metal of Mo and Ni. The variations of dielectric constant, the dielectric loss factor, the dielectric loss tangent and the penetration depth with the temperature have been investigated. The results indicated that the temperature has a pivotal effect on the dielectric properties, and the spent catalyst is high loss material from 450 to 700 °C. The significant improvement of the microwave absorption capacity of the spent catalyst can be attribute to the conversion of molybdenum and nickel sulfides to oxides, which provide a good explanation of the high recovery of the rare metals in this temperature range.
15:15
15 mins
TEMPERATURE-DEPENDENT DIELECTRIC PROPERTIES OF FOODS DURING FREEZING AND THAWING
Sven Isaksson, Mathieu Sadot, Anderson Da Silva, Sébastien Curet, Olivier Rouaud, Alain Lebail, Michel Havet, Epameinondas Xanthakis
Abstract: Dielectric properties of a variety of foodstuffs were measured during freezing and thawing conditions, and are presented here as functions of temperature. Measurements were done with the Agilent 85070 high temperature dielectric probe. The differences in characteristics of the graphs resulting from cooling and thawing are discussed. A specific model accommodating the amount of frozen water in the food sample as function of temperature is used and compared to experimental results. The mass fraction of each component is coupled to the dielectric properties of each fraction to evaluate the effective dielectric properties based on a two phases Maxwell model considering ice as a dispersed fraction and food as a continuous fraction. An adjusting coefficient is used to optimize the fitting between experimental data and calculated data.