Natural Convection in a Saturated Variable-Porosity Medium Due to Microwave Heating

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Watit Pakdee ◽  
Phadungsak Rattanadecho
Keyword(s):  
Porous Medium ◽  
Microwave Heating ◽  
Maxwell’S Equations ◽  
Maxwell's Equations ◽  
Saturated Porous Medium ◽  
Simple Algorithm ◽  
Heating Process ◽  
Variable Porosity ◽  
Dimensional Variation ◽  
Difference Time

Microwave heating of a porous medium with a nonuniform porosity is numerically investigated based on a proposed numerical model. A two-dimensional variation of porosity of the medium is considered. The generalized non-Darcian model developed takes into account the presence of a solid drag and the inertial effect. The transient Maxwell’s equations are solved by using the finite difference time domain method to describe the electromagnetic field in the waveguide and medium. The temperature profile and velocity field within a medium are determined by solution of the momentum, energy, and Maxwell’s equations. The coupled nonlinear set of these equations is solved using the SIMPLE algorithm. In this work, a detailed parametric study is conducted on heat transport inside a rectangular enclosure filled with a saturated porous medium of constant or variable porosity. The numerical results agree well with the experimental data. Variations in porosity significantly affect the microwave heating process as well as the convective flow pattern driven by microwave energy.

Theoretical Analysis of Microwave Heating of Dielectric Materials Filled in a Rectangular Waveguide With Various Resonator Distances

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Phadungsak Rattanadecho ◽  
Waraporn Klinbun
Keyword(s):  
Microwave Heating ◽  
Rectangular Waveguide ◽  
Control Volume ◽  
Saturated Porous Medium ◽  
Simple Algorithm ◽  
Dielectric Materials ◽  
Microwave Cavity ◽  
Heating Process ◽  
Finite Control ◽  
Volume Method

This paper proposes mathematical models of the microwave heating process of dielectric materials filled in a rectangular waveguide with a resonator. A microwave system supplies a monochromatic wave in a fundamental mode (TE10 mode). A convection exchange at the upper surface of the sample is considered. The effects of resonator distance and operating frequency on distributions of electromagnetic fields inside the waveguide, temperature profile, and flow pattern within the sample are investigated. The finite-difference time-domain method is used to determine the electromagnetic field distribution in a microwave cavity by solving the transient Maxwell equations. The finite control volume method based on the SIMPLE algorithm is used to predict the heat transfer and fluid flow model. Two dielectric materials, saturated porous medium and water, are chosen to display microwave heating phenomena. The simulation results agree well with the experimental data. Based on the results obtained, the inserted resonator has a strong effect on the uniformity of temperature distributions, depending on the penetration depth of microwave. The optimum distances of the resonator depend greatly on the operating frequencies.

Forced Convection in a Channel Filled With Porous Medium, Including the Effects of Flow Inertia, Variable Porosity, and Brinkman Friction

1987 ◽  
Vol 109 (4) ◽  
pp. 880-888 ◽  
Author(s):  
D. Poulikakos ◽  
K. Renken
Keyword(s):  
Porous Medium ◽  
Forced Convection ◽  
Flow Model ◽  
Saturated Porous Medium ◽  
Porous Matrix ◽  
Parallel Plates ◽  
Entry Length ◽  
Variable Porosity ◽  
Flow Inertia ◽  
Temperature And Flow Fields

This paper presents a series of numerical simulations which aim to document the problem of forced convection in a channel filled with a fluid-saturated porous medium. In modeling the flow in the channel, the effects of flow inertia, variable porosity and Brinkman friction are taken into account. Two channel configurations are investigated: parallel plates and circular pipe. In both cases, the channel wall is maintained at constant temperature. It is found that the general flow model predicts an overall enhancement in heat transfer between the fluid/porous matrix composite and the walls, compared to the predictions of the widely used Darcy flow model. This enhancement is reflected in the increase of the value of the Nusselt number. Important results documenting the dependence of the temperature and flow fields in the channel as well as the dependence of the thermal entry length on the problem parameters are also reported in the course of the study.

Analyzing photonic space-time crystal with FDTD

2020 ◽  
Vol 34 (06) ◽  
pp. 2050082 ◽  
Author(s):  
Zheng Zhang ◽  
Wenjun Zhang ◽  
Lunwu Zeng
Keyword(s):  
Maxwell’S Equations ◽  
Maxwell's Equations ◽  
Electromagnetic Wave Propagation ◽  
Fdtd Method ◽  
Space Time ◽  
Crystal Forms ◽  
Time Translation ◽  
Permittivity And Permeability ◽  
Translation Symmetry ◽  
Difference Time

When space (time) translation symmetry is spontaneously broken, the space crystal (time crystal) forms; when permittivity and permeability periodically vary with space (time), the photonic space crystal (photonic time crystal) forms. We rewrote Maxwell’s equations in photonic time crystal, and discretized Maxwell’s equations with finite difference time domain (FDTD) method, deduced the discretized electric and magnetic field, and simulated electromagnetic wave propagation in two-dimensional (2D) photonic space-time crystal and photonic space crystal (or photonic crystal), and discussed the effect of parameters on the band gap.

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