The demand for efficient and compact heating for dynamic dielectric liquid has grown significantly. Compared with traditional heating, microwave heating has the advantages of being fast and ...efficient. Moreover, the demand for outdoor portable heating and industrial compact heating is increasing. To address this limitation, this study proposes a compact heating system based on a metamaterial-based circular waveguide. First, asymmetric propagation theory is introduced, and an asymmetric propagation circular waveguide is designed in detail according to the discretisation of the relative permittivity. Then, a multi-physics model using a circular waveguide and a mug for high heating efficiency is developed by coupling Maxwell's equations and the heat transfer equation. Furthermore, heating experiments are performed for liquids with different relative permittivity and the experimental results consistently validated an efficiency rate of over 88 %, which agrees with the simulation results. Finally, the effects of the dielectric properties of the material and mug on the heating efficiency are discussed to highlight the robustness of the proposed heating system, with heating efficiency consistently maintained at 75 % or higher. In summary, the proposed design features a compact structure that is suitable for practical microwave heating applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This paper proposed a method based on transformation optics, implicit function, and level set methods to solve the challenge of multi-physics simulation of a microwave heating cavity with two ...different motion modes. A 3D computation model with a rotating turntable, a lifting support rod, and a sample is proposed as a detailed demonstration. Based on the theory of transformation optics, the rotating turntable is surrounded by two circles with a time-varying, inhomogeneous and anisotropy medium, and the electric field in the moving region is rotated by controlling the two mediums. The implicit function and level set methods compute the lifting motion by setting the properties of the lifting region as a function of space and time. The correctness of the proposed method is verified by comparing the proposed method’s results with the discrete position’s results, and then its accuracy is further verified by experiment. Subsequently, compared with the implicit function and level set methods only, the proposed method is more accurate. Finally, the effects of lifting motion, rotating motion and lifting motion (i.e., spiral motion) on microwave heating uniformity and heating efficiency were analyzed, respectively.
A real-time temperature control system is designed for microwave heating of a continuous-flow substance. In this system, a magnetron is used as the microwave source, and its output power can be ...continuously adjusted though circuit design. A programmable logic controller (PLC) is used to procedure the temperature and power data as well as lead the whole control decision. The sample temperature can be controlled by regulating the output power of the magnetron though the control signal from the PLC during the heating process. The complete system is finally assembled into a user-friendly device, where the users can operate and monitor the heating process conveniently though a touch screen. A temperature-dependent material (Phosphoric acid) is used in system tests. The results show that the designed system can successfully achieve the desired temperature with an acceptable accuracy and stability.
Global warming poses one of the most critical challenges of the 21st century, leading to significant environmental damage. The extraction and combustion of fossil fuels release substantial amounts of ...greenhouse gases, thereby contributing to climate change. In response to this pressing issue, plasma-based conversion of carbon dioxide has emerged as a prominent and widely explored solution. Among the various plasma technologies, microwave plasma setups have garnered considerable attention due to their exceptional ability to decompose carbon dioxide, facilitate the dry reforming of methane and reverse water gas shift. These setups are renowned for their high degree of ionization and generation of non-equilibrium plasma, making them a clean and highly efficient method for treating greenhouse gases. However, researchers often face challenges in selecting the appropriate microwave plasma reactors. Thus, the primary objective of this paper is to provide guidance on microwave plasma setups. It is achieved by illustrating experimental configurations based on the microwave operating mechanism and presenting a classification of microwave plasma sources according to their operating principles. Moreover, specific experimental operations are discussed within the scope of our analysis, offering valuable insights to researchers in this field.
•Novel greenhouse gas treatments: Microwave plasma methods•Performance of different setups of microwave plasma•Coupling of microwave plasma and placement of catalysts•Cooling and treatment of waste heat•The necessity of quenching
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The ternary transitional metal oxide NiCo
2
O
4
is a promising anode material for sodium ion batteries due to its high theoretical capacity and superior electrical conductivity. However, its sodium ...storage capability is severely limited by the sluggish sodiation/desodiation reaction kinetics. Herein, NiCo
2
O
4
double-shelled hollow spheres were synthesized via a microwave-assisted, fast solvothermal synthetic procedure in a mixture of isopropanol and glycerol, followed by annealing. Isopropanol played a vital role in the precipitation of nickel and cobalt, and the shrinkage of the glycerol quasi-emulsion under heat treatment was responsible for the formation of the double-shelled nanostructure. The as-synthesized product was tested as an anode material in a sodium ion battery, was found to exhibit a high reversible specific capacity of 511 mAh g
−1
at 100 mA g
−1
, and deliver high capacity retention after 100 cycles.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This paper aims to propose an online relative complex permittivity measurement system at high temperature based on microwave interferometer. A ridge waveguide with a TE
mode was used in which the ...sample was heated and measured simultaneously at a frequency of 2450 MHz, and the microwave interferometer is used to collect the amplitude and phase difference of the incident signal. The Extreme Gradient Boosting (XGBoost) algorithm trained by the corresponding simulation data is used to construct the inversion model to calculate the complex dielectric coefficient of the tested material. Besides, this paper uses linear regression algorithm (LR) to calibrate the measurement system in order to improve the measurement accuracy. The entire system was tested using different materials at room temperature, and the maximum error of the measurement accuracy is less than 8% compared to the theoretical data. The robustness of the entire system was also tested by measuring Macor materials up to 800 °C. This proposed method provides an effective way to understand the mechanism between microwaves and matter at high temperatures.
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Microwave continuous-flow liquid food sterilisation, in which the liquid is mainly heated by microwaves, has the advantages of fast sterilisation speed, energy saving, comprehensive elimination, and ...less nutrient loss. Circular pipes are commonly used in microwave continuous-flow liquid heating processing. However, with circular pipes, which are widely used in the industry, the heating is uneven owing to the phenomenon of tube focusing when adopting external radiation. In this study, a novel microwave continuous-flow milk sterilisation system based on a coaxial slot radiator is proposed. First, the coaxial slot radiator was designed to realise efficient radiation through the establishment of multi-physics model. The structure of the system was then optimised by comparing the heating efficiency and uniformity of simulation results. The effect of microwave coaxial slot radiator rotation on heating uniformity was simulated and the results show that the heating uniformity is improved obviously. Experimental equipment was set up to verify the results of the simulation. The experimental results are consistent with the simulation results. Finally, the sensitivity analysis of the system is performed to confirm that, when the dielectric properties and types of liquid food change, the heating of the proposed microwave continuous-flow system remains efficient and uniform.
Microwaves have been widely used in the treatment of materials, such as heating, drying, and sterilization. However, the heating in the commonly used microwave applicators is usually uneven. In this ...paper, a novel multi-material turntable structure is creatively proposed to improve the temperature uniformity in microwave ovens. Three customized turntables consisting of polyethylene (PE) and alumina, PE and aluminum, and alumina and aluminum are, respectively, utilized in a domestic microwave oven in simulation. During the heating process, the processed material is placed on a fixed Teflon bracket which covers the constantly rotating turntable. Experiments are conducted to measure the surface and point temperatures using an infrared thermal imaging camera and optical fibers. Simulated results are compared qualitatively with the measured ones, which verifies the simulated models. Compared with the turntables consisting of a single material, a 26%-47% increase in temperature uniformity from adapting the multi-material turntable can be observed for the microwave-processed materials.
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Currently, microwave energy is utilized for many diverse industrial applications because of its various advantages including its eco-friendliness. Low-cost, high-efficiency, and high-power industrial ...microwave sources are in urgent demand. In this paper, we propose a low-cost quasi-coherent power-combining system based on a combination of two magnetrons. We have analyzed and built a low-loss waveguide-based applicator combined with specific phase. This system utilizes the coupling of the combiner to quasi-lock the slave magnetron. A waveguide phase shifter lies in the slave magnetron branch to adjust the phase difference between the master and slave magnetrons' signals to achieve high resultant efficiency. Based on theory, the phase difference between the master and the injected slave magnetrons has been numerically calculated and analyzed. The phase difference changes periodically when the slave magnetron is quasi-locked to the master magnetron and the periodicity increases with the injection ratio. Experimental results show the resultant efficiency of the proposed system can reach as high as 92% when using several suitable waveguide components. The investigation also provides guidelines for further microwave power combination systems with multiple sources.
Microwave heating is well known for its efficiency and instantaneity. However, the non-uniformity results of the microwave heating have limited the development of its large-scale industrial ...application. In order to solve this problem, a metal patch placed on a rotating turntable is proposed as a mode stirrer in this paper. A commercial finite element software, COMSOL Multiphysics, is used to build the proposed model based on a BJ-22 rectangular waveguide and a microwave oven. Maxwell's equations, heat conduction equation, implicit function and level set methods, which are used to realize the rotation of metal patch, are coupled to describe the microwave heating process. The electric field intensity, the temperature, the coefficient of variation and the mean temperature rise in different cases are compared to optimize the parameters of mode stirrer. The point temperatures are measured by optical fibre to verify the simulated results. The results show that the rotation of metal patch has a huge influence on improving the heating uniformity and heating efficiency, but the rotating speed has little influence if the heating time is larger than a rotating period.
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