Anomalous dielectric relaxation with linear reaction dynamics in space-dependent force fields

Power Dissipation of Uniaxial Anisotropic/Interacting Polar Molecules with Linear Reaction Dynamics in an Alternating Electric Field

The influence of anisotropic potential energy and interaction between polar molecules on power absorption in chemical reactions with linear reaction dynamics in a weak alternating electric field is studied theoretically according to the reaction-diffusion equation. The expression for transient power loss is derived using two methods, electrodynamic method and equivalent circuit method, based on the electric energy conservation equation. Numerical calculations are carried out, and the results show that both the anisotropic potential energy and the interaction between polar molecules have a strong impact on energy dissipation and storage. For the anisotropic potential energy, when the applied dimensionless anisotropy is equal to 1, the power loss density increases about 32% at a low reaction rate and 27% at a high reaction rate compared to the case without anisotropic potential energy. When the dimensionless anisotropy is equal to -1, the power loss is suppressed and is reduced about 27% and 24% at low and high reaction rates, respectively. On the other hand, for the interaction between polar molecules, the power loss density decreases about 10% and 30% with low and high interaction potential energies, respectively. In addition, if the reaction rate is relatively high, the power loss will quickly decrease due to the end of the reaction process.

Impact of Filled Materials on the Heating Uniformity and Safety of Microwave Heating Solid Stack Materials

Microwave heating of solid stack materials is common but bothered by problems of uneven heating and electric discharge phenomena. In this paper, a method introducing fluid materials with different relative permittivity is proposed to improve the heating uniformity and safety of solid stack materials. Simulations have been computed based on the finite element method (FEM) and validated by experiments. Simulation results show that the introducing of fluid materials with proper relative permittivity does improve the heating uniformity and safety. Fluid materials with the larger real part of relative permittivity could obviously lower the maximum modulus value of the electric field for about 23 times, and will lower the coefficient of variation (COV) in general, although in small ranges that it has fluctuated. Fluid materials with the larger imaginary part of relative permittivity, in a range from 0 to 0.3, can make a more efficient heating and it could lower the maximum modulus value of the electric field by 34 to 55% on the whole studied range. However, the larger imaginary part of relative permittivity will cause worse heating uniformity as the COV rises by 246.9% in the same process. The computed results are discussed and methods to reach uniform and safe heating through introducing fluid materials with proper relative permittivity are proposed.

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

The aim of this work is to present a model of a reaction tube with cross structures in order to improve ethyl acetate production and microwave heating uniformity. A commercial finite element software, COMSOL Multiphysics 4.3a (Newton, MA, USA), is used to build the proposed model for a BJ-22 rectangular waveguide system. Maxwell’s equations, the heat conduction equation, reaction kinetics equation and Navier-Stokes equation are combined to describe the continuous flow process. The electric field intensity, the temperature, the concentration of water, the coefficient of variation (COV) and the mean temperature at different initial velocities are compared to obtain the best flow rate. Four different initial velocities are employed to discuss the effect of flow velocity on the heating uniformity and heating efficiency. The point temperatures are measured by optical fibers to verify the simulated results. The results show the electric field intensity distributions at different initial velocities have little difference, which means the initial velocity will have the decisive influence on the heating process. At lower velocity, the COV will be smaller, which means better heating uniformity. Meanwhile, the distance between each cross structure has great influence on the heating uniformity and heating efficiency, while the angle has little. The proposed model can be applied to large-scale production of microwave-assisted ethyl acetate production.