Microwave Energy Supply Research Articles

Development of general types of mathematical models for drying food products with microwave energy supply based on the laws of chemical kinetics of heterogeneous processes

Development of general types of mathematical models for drying food products with microwave energy supply based on the laws of chemical kinetics of heterogeneous processes

Волноводный СВЧ-плазмотрон атмосферного давления с суммированием мощности в зоне формирования плазмы

The design of an atmospheric pressure plasmatron on a rectangular waveguide with a two-sided microwave energy supply to the interaction domain is considered. It is shown that the use of two magnetron sources makes it possible to obtain a stable discharge in the plasmatron, providing a continuous input of power into the gas flow. The results of studies of the operating modes of the microwave plasmatron, which prove its advantages over analogs, are presented.

Time-Resolved Optical Emission Spectroscopy Reveals Nonequilibrium Conditions for CO2 Splitting in Atmospheric Plasma Sustained with Ultrafast Microwave Pulsation

Among the pool of Power-to-X technologies, plasmas show high potential for the efficient use of intermittent renewable energies. High efficiencies of CO$_{2}$ conversion have been reported while using microwave plasmas at vacuum conditions which are, however, not suitable for CO$_{2}$ mitigation at industrial scales. Here we show that ultrafast pulsation of microwaves allow significant improvements of energy efficiencies during CO$_{2}$ splitting at atmospheric pressure as compared to continuous wave operation of the microwave source. Moreover, by the interrogation of the plasma with time-resolved optical emission spectroscopy we can, for the first time, observe the evolution of the vibrational and rotational temperatures and define a time window where nonequilibrium can be expected at the beginning of the pulse of an atmospheric CO$_{2}$ microwave plasma. In spite of the evidence of nonequilibrium in our system, thermal mechanism appears to dominate the CO$_{2}$ dissociation. It is shown that a fine control of the energy deposition in the plasma is possible with ultrafast pulsation of the microwave energy supply.

Modelling the drying process in case of combined energy supply

In many chemical, food, biochemical and other industries, drying is the prime process that is characterized by high energy consumption and determines the quality of the finished product. In this regard, the development of mathematical models that allow of optimization and reliable control of the drying process is relevant. A large set of physical and physicochemical phenomena accompanying drying, as well as their mutual influence on each other, gives rise to numerous uncertainties in the mathematical description of this process. The modeling process becomes more complicated under conditions of combined energy supply, for example, convective and microwave energy supply. In this article, based on the laws of chemical kinetics, the authors propose the original approach to modeling the drying process, which, together with experimental studies, allows obtaining a reliable mathematical model that can be used as the basis for optimizing and controlling this process. During the mathematical modeling of drying, it was proposed to apply new process parameters: the degree of drying (the share of removed moisture) and the degree of absorbed energy (the ratio of the amount of energy absorbed by the product at a given moment to the amount of energy absorbed by the product during the entire process). The expediency of characterizing the kinetics of drying by the dependence of the degree of drying on the degree of absorbed energy is demonstrated. The scientific hypothesis was substantiated and confirmed: the generalized characteristic, the kinetics of drying - the dependence of the degree of drying on the degree of energy absorbed by the product, does not depend on the parameters characterizing the drying mode. The proposed model makes it possible to determine the ratio of the components of convective and microwave energy flows when moisture is removed from the material, which can be used as the basis for optimization and reliable control of the process.

RESEARCH OF WHEAT DRYING IN A MICROWAVE AND COMBINED FILTER-MICROWAVE DRYER

The aim of the conducted study is to determine kinetics of the complex effect of microwave energy supply and filter drying of the process of water release from the wheat layer. There is offered a combination of MW and filter drying. A special feature of this combination must be its more effectiveness and high speed of water elimination from surface layers of wet seeds and, as a result, the productivity increase of the drying way, decrease of specific energy consumption. There was determined the influence of the specific load of the material, radiator power on processes of microwave and filter-microwave drying of wheat seeds. There were compared microwave, filter-microwave and convective drying of seeds by parameters of specific energy consumption, drying speed. The specific energy consumption at microwave drying of seeds was 4 MJ/kg, at filter-microwave drying 3.8 MJ/kg that is lower than existent convective dryers. The speed of microwave drying changes from 0,5 to 3 %/min, filter-microwave – from 0.3 to 0.7 %/min. The speed is at the level of standard convective dryers. The conducted studies allow to recommend a new combined way of FMW drying of seeds with low energy consumption. Revealed features of heating and drying are possible to be used at developing industrial dryers. The base of experimental data is possible to be used for optimizing and determining effective conditions of MW and FMW drying.

Simulation and control of continuous glass melting by microwave heating in a single-mode cavity with energy efficiency optimization

Calculations of continuous glass melting in a single-mode 2.45 GHz microwave oven are reported. The aim of this work is to optimize the microwave heating of the glass raw material to have a controlled and highly efficient oven. The two-way coupling process between electromagnetic and thermal fields is solved using COMSOL software in a 3D transient simulation that includes phase change and surface-to-surface thermal radiation. A methodology was developed and coded to automatically control the microwave energy supply and to maximize the material's microwave absorption during the 3D transient simulation. The developed methodology to achieve high Key Performance Indicators (KPI) was applied to the continuous melting of a glass raw material powder, the results show promising energy consumption reduction and improved task efficiency.

The mathematical description of the process of drying the grain of millet in the device with active hydromechanical mode

The basis for the creation of new designs dryers laid the mathematical description of the test process, taking into account the method of loading and handling of the product in the machine, how to supply coolant or other type of energy supply, the theoretical performance, and structural (geometric) component of the apparatus. To simulate the process of our work was considered of cylindrical dryers with active hydrodynamic regime and microwave energy supply, one feature of which is the loading of the product in a stream tangential coolant flow. The object of the study was chosen millet grain, because of the high biological value and high prevalence in the southern regions of the Russian Federation. On the basis of theoretical analysis, it was decided to divide the mathematical model into two conditional components: the study of heat and mass transfer study of aerodynamic component of the drying process. In this paper, we have been disclosed in detail is the second part of the process. The basis of this model were the equations of motion of millet grains by Newton's second law. The coolant in the framework of the proposed model is considered to be a continuous medium, highly compressible and has an internal viscosity, described by the Navier-Stokes equations. The initial conditions of the mathematical model were the following assumptions: the speed of the mechanical motion elements are equal to zero, the initial density of the air environment in all nodes is the equilibrium density of the air, the initial velocity of the air quality in all nodes is zero. The boundary conditions can be described as the constancy of the flow temperature and humidity, and its displacement is directly design constraints of the drying chamber. This model will be useful for professionals engaged in the problems of calculation and design of drying equipment.

Study thermal characteristics of millet grain, dried in the machine with the swirling flow of the coolant and the microwave energy supply

The article discusses the problems of determining the thermal characteristics of millet. The choice of the research object. The paper presents the principle of operation of the plant and the parameters of the standard, organic glass for measurements. Method was to study millet grains and organic glass, which are brought into contact on a common plane. The heater is brought into contact with the product and passed the constant heat flow, which passed through a layer of millet grain at different speeds. As a result, the temperature in the contact plane of the changed and recorded on the chart of the potentiometer in the form of the curve, by which you can determine the time and temperature change. The thermal diffusivity and thermal conductivity determined by empirical formulas obtained by solving a system of differential equations, made up for the system of two bodies, one of which includes the unknown thermal characteristics. Test two bodies in contact on a common plane, resulting in mathematical physics principles constitute two differential equations with uniform initial and boundary conditions of the first kind, due to the parameters of ongoing experience. It is a plot of thermal performance of the temperature and humidity. Revealed linear dependence of the physical thermal characteristics, showing that with increasing temperature the thermal diffusivity value decreases, and the thermal conductivity and specific heat capacity are increasing character. Revealed the equations describing the thermal characteristics of millet grain with a humidity in the range of 13.6–35.1% and the temperature range 293–373 K.

The mathematical description of the process of drying the grain of millet in the device with active hydromechanical mode

The basis for the creation of new designs dryers laid the mathematical description of the test process, taking into account the method of loading and handling of the product in the machine, how to supply coolant or other type of energy supply, the theoretical performance, and structural (geometric) component of the apparatus. To simulate the process of our work was considered of cylindrical dryers with active hydrodynamic regime and microwave energy supply, one feature of which is the loading of the product in a stream tangential coolant flow. The object of the study was chosen millet grain, because of the high biological value and high prevalence in the southern regions of the Russian Federation. On the basis of theoretical analysis, it was decided to divide the mathematical model into two conditional components: the study of heat and mass transfer study of aerodynamic component of the drying process. In this paper, we have been disclosed in detail is the second part of the process. The basis of this model were the equations of motion of millet grains by Newton's second law. The coolant in the framework of the proposed model is considered to be a continuous medium, highly compressible and has an internal viscosity, described by the Navier-Stokes equations. The initial conditions of the mathematical model were the following assumptions: the speed of the mechanical motion elements are equal to zero, the initial density of the air environment in all nodes is the equilibrium density of the air, the initial velocity of the air quality in all nodes is zero. The boundary conditions can be described as the constancy of the flow temperature and humidity, and its displacement is directly design constraints of the drying chamber. This model will be useful for professionals engaged in the problems of calculation and design of drying equipment.

Drying of Silica Gel in a Microwave Electromagnetic Field

This article presents results of an experimental study of the drying kinetics of silica gel in a microwave electromagnetic field. The influence exerted by various process parameters on the drying kinetics under a microwave energy supply is ascertained on the basis of the experimental data. The substantial impact of the initial moisture content of the silica gel and the power supplied on the time required for moisture desorption is demonstrated. Use of a proposed energy criterion has made it possible to generalize experimental results obtained for different regime parameters.

Investigation of the process of regeneration of silica gel by drying it in the super high-frequency electromagnetic field

There were made experimental studies of the drying kinetics of porous silica gel with different initial humidity, and investigated the change in temperature of the material during this process. On the basis of experimental data the parameters of drying process with microwave energy supply, drying time to the equilibrium moisture (≤ 0,5 %), the time limit for processing without disrupting properties of silica gel, as well as temperature adsorbent at the end of the drying process were revealed.

Field study of in situ remediation of petroleum hydrocarbon contaminated soil on site using microwave energy

Many laboratory-scale studies strongly suggested that remediation of petroleum hydrocarbon contaminated soil by microwave heating is very effective; however, little definitive field data existed to support the laboratory-scale observations. This study aimed to evaluate the performance of a field-scale microwave heating system to remediate petroleum hydrocarbon contaminated soil. A constant microwave power of 2 kW was installed directly in the contaminated area that applied in the decontamination process for 3.5 h without water input. The C10–C40 hydrocarbons were destroyed, desorbed or co-evaporated with moisture from soil by microwave heating. The moisture may play an important role in the absorption of microwave and in the distribution of heat. The success of this study paved the way for the second and much larger field test in the remediation of petroleum hydrocarbon contaminated soil by microwave heating in place. Implemented in its full configuration for the first time at a real site, the microwave heating has demonstrated its robustness and cost-effectiveness in cleaning up petroleum hydrocarbon contaminated soil in place. Economically, the concept of the microwave energy supply to the soil would be a network of independent antennas which powered by an individual low power microwave generator. A microwave heating system with low power generators shows very flexible, low cost and imposes no restrictions on the number and arrangement of the antennas.

Investigating Energetic and Impedance Relations of Microwave Transmission Line Filled with Dielectric Material

During microwave treatment, microwave energy is transferred to a material sample placed in an applicator of given geometric parameters. As a result of the energy transfer, the sample absorbs energy from the microwave fleld depending on its dielectric properties. The degree of energy absorption is directly proportional to the dielectric loss and proportional to the square root of the dielectric constant. The temperature of the sample continuously increases due to the energy transfer and the dielectric properties of the sample also change with the rising temperature. Although the microwave energy supply is constant, time and temperature dependent energy impedance and dielectric relations are developed. A part of them is measurable, but the other part of them can not be directly measured, they can only be computed from the previously measured ones. In a closed model which contains the parameters of the sample and the waveguide, the continuously changing parameters can be determined in relation of the temperature. These parameters are as follows: Attenuation of the transmission line, temporal change of the sample temperature, dielectric properties of the sample, loss factor of the sample, penetration depth, impedance of the transmission line, standing wave ratio re∞ection factor. The above parameters can be modeled as a function of the sample's temperature or as a function of time.

Active Regeneration of Diesel Particulate Filter Employing Microwave Heating

Wall-flow diesel particulate filters (DPFs) are considered the most effective devices for the control of diesel particulate emissions. A requirement for the reliable operation of the DPFs, however, is the periodic and/or continuous regeneration of the filters. While microwave heating has been considered a potential active regeneration method for the DPFs, past studies on the technology have identified several technical problems leading to filter failure. The problems are mainly associated with the use of inappropriate filter materials for the microwave system and the generation of local hotspots due to uneven microwave heating, resulting in the physical damage to the filters. The objective of this study was to develop and demonstrate the technology employing a microwave-absorbing filter material coupled with an effective waveguide design for the reliable regeneration of DPFs. In this study, a well-equipped diesel emission control laboratory was established to conduct the experiments. The experimental facilities included a 6-kWe diesel generator, an exhaust flow control system, a diesel particulate filter system, a microwave energy supply system, a soot sampling system, a differential-pressure measurement system, and a temperature measurement system. The DPF was a silicone carbide wall-flow monolith filter enclosed in a quartz filter holder. A commercial 1.4-kWe microwave oven was modified to accommodate the quartz holder and a waveguide was engineered to evenly supply the microwave energy to the enclosed filter to achieve filter regeneration. In the experiments, the diesel engine exhaust was lined up to flow through the filter with a fixed flow rate. The microwave regeneration was triggered after a specific amount of soot loading was reached based on the differential pressure drop reading. The results have indicated that the designed system has been able to achieve uniform temperature profiles both in the radial and the vertical DPF positions. The off-line regeneration of DPF by microwave energy has been observed to be highly efficient in terms of energy consumption and regeneration efficiency. The DPM filtration efficiency has remained comparably high after 150 cycles of filtration/regeneration with no apparent physical damage to the DPF being observed. The on-line microwave regeneration of the DPF, however, is not as efficient as the off-line regeneration due to the insufficient oxygen concentration in the engine exhaust stream.

Full-wave analysis and design of microstrip antenna in-pipe for rectenna using FDTD method

The circular polarized microstrip antenna in the stainless pipe is analyzed by the finite-difference time-domain (FDTD) method with PML absorbing boundary condition. The microstrip antenna is used as a microwave energy supply element for the in-pipe micromachine inspecting. The numerical results agree well with the measured ones.