China
Africa
Explore chapters and articles related to this topic
Sample Preparation Techniques to Isolate and Recover Organics and Inorganics
Published in Paul R. Loconto, Trace Environmental Quantitative Analysis, 2020
Figure 3.12 outlines the essential features of a microwave oven designed for MAE. The sealed vessel is placed in the cavity. The magnetron generates microwave radiation that is propagated down the waveguide into the cavity. The mode stirrer distributes the energy in various directions, and the cavity serves to contain the energy until it is absorbed by the sample. The isolator protects the magnetron from radiation that would reflect back into the magnetron. The isolator acts as a one-way mirror. Microwave radiation generated by the magnetron goes to the cavity and is prevented from returning. A turntable is used to rotate the sample vessels within the cavity to evenly distribute the energy.34Figure 3.12 also shows important engineered safety features, such as an airflow switch, solvent vapor detector, and vent. A safe microwave oven for MAE should be designed to:Eliminate possible ignition sourcesDetect solvent leaksRemove solvent vapors.
Microwaves in Nonoxidative Conversion of Natural Gas to Value-Added Products
Published in Jianli Hu, Dushyant Shekhawat, Direct Natural Gas Conversion to Value-Added Chemicals, 2020
Xinwei Bai, Brandon Robinson, Dushyant Shekhawat, Victor Abdelsayed, Jianli Hu
A waveguide cavity is used to guide the electromagnetic wave (microwave in this case) propagates at a designated direction. The electromagnetic field pattern of the electromagnetic radiation inside a waveguide is called mode. The modes can be classified as transverse electromagnetic (TEM) modes, transverse electric (TE) modes, transverse magnetic (TM) modes and hybrid modes. TEM modes suggest neither electric nor magnetic field in the direction of wave propagation; TE modes mean only the magnetic field exist in the direction of wave propagation; TM modes mean only the electric field exist in the direction of wave propagation. Rectangular waveguide is one of the most common waveguide shapes for microwave reactor and it only supports TE and TM modes. It is important to identify the mode number (TEmn or TMmn) for finite-element simulation of the microwave system (m, n are the numbers of half-wave patterns across the longer and the shorter transverse of the waveguide, respectively), and the mode number is depended on the size of the waveguide and supported frequency range. Figure 2.7 shows the electric and magnetic field distribution of a TE10 waveguide which is the waveguide type of the microwave reactor showing in Figure 2.6. As shown in Figure 2.7, the E-field direction in TE10 mode is perpendicular with the direction of wave propagation (−x direction); has only one lobe in the longer transverse direction (z direction); and has 0 lobes in the shorter transverse direction (y direction).
Propagating Electromagnetic Fields
Published in Bogdan M. Wilamowski, J. David Irwin, Fundamentals of Industrial Electronics, 2018
Michael E. Baginski, Sadasiva M. Rao, Tyler N. Killian
Some of the most common types of waveguides include the hollow conducting cylinders, dielectric waveguides, and optical fibers. The analysis of waveguides begins by formulating the problem in terms of Maxwell’s equations and applying the appropriate boundary conditions.
Mode-matching analysis of flexural trifurcated waveguide with porosity effects
Published in Waves in Random and Complex Media, 2022
Haleem Afsar, Mohammad Mahtab Alam
Noise reduction in mechanical industrial processes is a complicated topic for physicists, applied mathematicians, and engineers to solve problems. Many mechanical devices such as internal combustion engines, modified mufflers, or fans are usually responsible for generating noise that travels to the outside world through a network of ducts or channels. Scientists, mathematicians, and engineers have been trying to solve such problems related to scattering waves in ducts or channels. All waves, like water waves, electromagnetic waves or sound waves can be directed by means of some structures called ‘waveguide’, for example, ducts and/or pipes used in buildings, exhausts of power stations and silencers of automobiles. The use of such ducts is clearly beneficial, but in many cases is a source of unwanted noise. As noise has become a hazard to environment in our industrialized society, therefore it results as an object of interest for acousticians. To minimize the noise, silencers are commonly used. These silencers contain absorbent materials, porous linings, or novel geometrical designs to attenuate the propagating noise waves. As we are discussing sound propagation in a compressible fluid (air), so the governing laws for our problem will be same as for fluids.
Preparation of synthetic rutile from high titanium slag using microwave heating
Published in Phase Transitions, 2018
Xiaoying Zheng, Guo Chen, Jin Chen, Jinhui Peng, C. Srinivasakannan, Rongsheng Ruan
The microwave roasting experiments were carried out in a microwave roasting device. The schematic and photograph of the microwave assisted reactor is shown in Figure 2. The microwave roasting device consists of a magnetron to produce the microwaves, a waveguide to transport the microwaves, a resonance cavity to manipulate microwaves for a specific purpose and a control system to regulate the temperature and microwave power. Microwave roasting device has a single-mode cavity, with a continuous controllable power capacity. The microwave power supply for the microwave reactor is made of two magnetrons, which was cooled by water circulation, at 2450 MHz frequency and 1.5 kW power. The inner dimensions of the single-mode microwave resonance cavity were 260 mm in height, 420 mm in length and 260 mm in width. The temperature was measured using a Type K thermocouple, placed at the closest proximity to the sample. The thermocouple provides feedback information to control panel that controls the power to magnetron, controlling the temperature of sample during microwave-assisted pretreatment process in order to prevent the sample from overheating.
Synthesis of dielectric-loaded waveguide filters as an inverse problem
Published in Applied Mathematics in Science and Engineering, 2022
Waveguides are popular microwave devices in satellite communication, military applications, etc., due to their high-power handling capacity, high-quality factor, and low-loss features [1]. Microwave passive devices utilizing waveguide structures are first designed by corrugating the cross-sectional shape [2,3] or inserting metal discontinuities in the waveguide [4]. Since waveguides are mainly preferred for high-frequency applications, minor faults in the fabrication process may drastically affect the operation properties of the device. One another reason for operating waveguides in microwave systems is their high-power handling ability. Therefore, the breakdown voltage of hollow waveguides may cause problems in some high-power applications. Besides, waveguide devices with a corrugated shape or metallic inserts have a bulky and heavy geometry. A possible solution to overcome drawbacks of the corrugated or metal inserted hollow waveguide structures is to fill the apparatus with dielectric materials, which provide reduced size devices with a high breakdown voltage [5,6]. However, difficulties due to the fabrication process of the metallic parts remain in this design solution. Because of the aforementioned facts, uniform waveguides with dielectric loading may propose a possible and efficient solution to the design of waveguide-based microwave devices. Yet, there is rare literature on practically realizable microwave devices built by dielectric-loaded uniform waveguides (DLW). DLW structures can be classified in terms of modal interaction and dielectric discontinuity [7]. Longitudinally inhomogeneous waveguides (LIW) and widthwise and longitudinally inhomogeneous waveguides (WLIW) are two possible DLW configurations in terms of modal interaction, for which the electrical discontinuity exists only in the longitudinal direction and both in widthwise and longitudinal directions, respectively.