Optimization of Intermittent Variable Power Microwave Heating Process for Blueberry Pulp

To improve heating uniformity and anthocyanin content of the blueberry pulp under microwave heating,the intermittent variable power microwave heating technology was introduced in the study.The effects of technology parameters in terms of high microwave intensity heating time,intermittent time,low microwave intensity and low microwave intensity heating time on the blueberry pulp quality parameters(heating uniformity,average moisture content,the highest temperature and anthocyanin content)were investigated by using the response surface method.The results showed that the longer heating time under different microwave intensities resulted in the poorer heating uniformity.The intermittent stage promoted heat and mass transfer within the pulp and reduced the temperature difference and moisture gradient within the pulp,which enhanced desired uniformity of temperature and moisture distribution before entering the low microwave intensity heating stage.Therefore,the longer the intermittent time,the greater the heating uniformity.The optimal parameters were developed as high microwave intensity of 4 W·g^(-1),high microwave intensity heating time of 9.86 min,intermittent time of 10 min,low microwave intensity of 2.2 W·g^(-1)and low microwave intensity heating time of 6 min.This research might provide guidance for microwave heating berry fruits.

Preparation of Phosphors MAl_2O_4∶Eu^(2+)(M=Ca,Sr,Ba) by Microwave Heating Technique and Their Phosphorescence

The phosphors of the alkaline earth aluminates coactivated with europium and other rare earths were successfully obtained by microwave radiation heating technique.These phosphors have bright phosphorescence and maintain their afterglow for a fairly long duration.

Electrochemical performance of C-La^(3+) codoped LiFePO_4 synthesized by microwave heating

La3+ was selected to elevate the lattice electronic conductivity of LiFePO4,and LiFePO4/(C+La3+) cathode powders were synthesized by microwave heating using a domestic microwave oven for 35 min. The microstructures and morphologies of the synthesized materials were investigated by XRD and SEM. The electrochemical performances were evaluated by galvanostatic charge-discharge. The electrochemical performance of LiFePO4 with different La3+ contents was studied. Results indicated that the initial specific discharge capacity of LiFePO4/(C+La3+) composites with 2% La3+ (116.3 mAh/g) was better than that of LiFePO4/C (105.4 mAh/g). The addition of La3+ further improved the electrochemical properties. So the codoping is an effective method to improve the electrochemical performance.

Carbothermal reduction characteristics of oxidized Mn ore through conventional heating and microwave heating

For the purpose of exploring a potential process to produce FeMn,the effects of microwave heating on the carbothermal reduction characteristics of oxidized Mn ore was investigated.The microwave heating curve of the mixture of oxidized Mn ore and coke was analyzed in association with the characterization of dielectric properties.The comparative experiments were conducted on the carbothermal reductions through conventional and microwave heatings at temperatures ranging from 973 to 1373 K.The thermogravimetric analysis showed that carbothermal reactions under microwave heating proceeded to a greater extent and at a faster pace compared with those under conventional heating.The metal phases were observed in the microstructures only under microwave heating.The carbothermal reduction process under microwave heating was discussed.The electric and magnetic susceptibility differences were introduced into the thermodynamics analysis for the formation of metal Mn.The developed thermodynamics considered that microwave heating could make the reduction of MnO to Mn more accessible and increase the reduction extent.

Temperature field simulation of polyolefin-absorber mixture by FDTD-FDM model during microwave heating

This work has performed a numerical simulation of the temperature field during microwave heating of polyolefin-absorber mixture by means of a combined electric and thermal model.A finite difference time domain was used to model the electric field distribution within the cavity,while the finite difference method was used to calculate the temperature field distribution in different reactors.This study has focused only on the process from room temperature to 500 K for reducing heating time and energy consumption.This temperature range is a process with high energy consumption,difficult to control and great influence on the follow-up reaction.Temperature dependence of dielectric properties and thermal properties of heated materials are fully considered and simulated through an iterative process.The simulation results show that input power,the size and location of the heated materials,the position of the waveguide,and the kinds of microwave absorbers are important factors affecting the heating process.As a result,the uniform temperature distribution(the temperature difference Tdb10 K)can be achieved by choosing the appropriate input power(500–2000 W),the appropriate proportion of microwave absorber(the volume ratio of Si C to HDPE is 30:70),and combining with the moving and rotating of the heated materials.The uniform temperature field obtained without mechanical stirring is very important for reducing energy consumption and subsequent reactions.

Step Sintering of Microwave Heating and MicrowavePlasma Heating for Alumina Ceramics

The invention of microwave induced plasma during microwave heating makes it possible to confine plasma inside a crucible, in the pressure range of 1.33 Pa to 0.5 MPa, and above 900℃.In this study, the step sintering of microwave heating and microwave plasma heating (SSMP)was proposed. In this process, microwave heating and plasma heating was ingeniously combined in one chamber, and vacuum was unnecessary for microwave induced plasma. In the first step, the microwave energy directly heated alumina ceramics to a given temperature. above which microwave will mainly ionize the gas and sustain a plasma. Then the plasma further heated alumina ceramics to the final temperature to finish sintering. Maintaining the advantages of microwave heating and plasma heating, this step sintering approach will overcome the limitation of both processes for processing ceramics. and it will be suitable for sintering all kinds of ceramics in

Crystallization Behavior of Polymer Derived Silicon Carbide Sintered Through Microwave Heating Technique

A self-crosslinkable liquid highly branched polycarbosilane(LHBPCS) with 5.07% vinyl group and a C/Si ratio of 1.33 was used as the precursor to prepare Si C ceramic material. Microwave heating technique and conventional heating method were applied for the heating treatment process. It was found that, compared with conventional heating method, microwave heating technique could enhance the crystallinity of Si C ceramic material with small grain size at much lower curing temperature and within shorter time. In addition, the SiO_2 additive could lead to less α-Si C and excess carbon, but worsen the crystallinity of β-Si C in the final samples.

Effect of Encapsulation Combined with Microwave Heating on Self-Healing Performance of Asphalt Mixture

As an innovative maintenance technology of asphalt pavement,encapsulated rejuvenator used to improve its self-healing performance has been widely investigated by researchers in recent years.In this work,the selfhealing properties of asphalt mixture with and without encapsulations were comparatively studied considering these parameters:Healing time,healing cycles and microwave heating.Three-point bending strength recovery test and fatigue loading cycles recovery test were conducted for two kinds of encapsulations containing the healing agents present inside the asphalt mixture,namely compartmented Ca-alginate/SiO_(2) fiber and compartmented Ca-alginate/graphene oxide fiber.The results showed that the optimum healing time was three days.After the 30 s of microwave heating,the recovery of fatigue loading cycles of asphalt mixture with compartmented Ca-alginate/graphene oxide fiber was four times larger than that of control asphalt mixture.Compared with the single effect related to the encapsulated healing agent or temperature,the synergistic effect of temperature and encapsulation could further significantly improve the self-healing properties of asphalt mixture.The compartmented Ca-alginate/graphene oxide fiber not only could soften asphalt through the encapsulated healing agent to improve self-healing properties of asphalt,but also could repeatedly and quickly heal cracks thanks to microwave action.The synthesis of the fiber breaks the current boundary between the two technologies(capsules healing method and induction healing method)and opens up a new horizon for the asphalt self-healing technology.

Microwave heating as a universal method to transform confined molecules into armchair graphene nanoribbons

Armchair graphene nanoribbons(AGNRs)with sub-nanometer width are potential materials for the fabrication of novel nanodevices thanks to their moderate direct band gaps.AGNRs are usually synthesized by polymerizing precursor molecules on substrate surface.However,it is time-consuming and not suitable for large-scale production.AGNRs can also be grown by transforming precursor molecules inside single-walled carbon nanotubes(SWCNTs)via furnace annealing,but the obtained AGNRs are normally twisted.In this work,microwave heating is applied for transforming precursor molecules into AGNRs.The fast heating process allows synthesizing the AGNRs in seconds.Several different molecules were successfully transformed into AGNRs,suggesting that it is a universal method.More importantly,as demonstrated by Raman spectroscopy,aberrationcorrected high-resolution transmission electron microscopy and theoretical calculations,less twisted AGNRs are synthesized by the microwave heating than the furnace annealing.Our results reveal a route for rapid production of AGNRs in large scale,which would benefit future applications in novel AGNRs-based semiconductor devices.

HEATING RATE OF MINERALS AND COMPOUNDS IN MICROWAVE FIELD

More than 40 kinds of selected minerals and compounds were individually irradiated by microwaves under an inert atmosphere,and the temperatures of samples were measured with a metal-sheathed thermocouple inserted into the samples directiy.The results indicated that most sulphide and some oxide minerals and compounds could be heated to high temperatures in a short timet whereas the common gangue minerals,some oxide and oxy-salt minerals or compounds could not.The sulphide minerals had faster heating rate than the oxide minerals containing the same cations.The impurities of minerals had significant effect on the heating rate.The selective heating characteristics of microwaves on different minerals and compounds could be attributed to the differences between their conductivities or dielectric loss factors and bonding properties.

LiFePO_(4)/C cathode materials synthesized by co-precipitation and microwave heating

LiFePO_(4)/C cathode materials were synthesized by a combination of co-precipitation and microwave heat-ing using polyethylene glycol(PEG)as a carbon resource and the influence of microwave heating time on the struc-ture and electrochemical performance of the materials was also discussed.The samples were characterized by X-ray diffraction(XRD),TEM,particle-size analysis and con-stant current charge-discharge experiment.The results show that the LiFePO_(4)/C heated for 9 min has a pure olive-type phase and excellent electrochemical perform-ance.The initial discharge capacities of this sample are 154.3,139.7,123.9 mAh/g at the rates 0.1C,0.2C,1C at room temperature,respectively,and after 20 cycles remain 152.3,134.3,118.5 mAh/g,respectively.

Determination of dielectric properties of titanium carbide fabricated by microwave synthesis with Ti-bearing blast furnace slag

The preparation of functional material titanium carbide by the carbothermal reduction of Ti-bearing blast furnace slag with microwave heating is an effective method for valuable metals recovery;it can alleviate the environmental pressure caused by slag stocking.The dynamic dielectric parameters of Ti-bearing blast furnace slag/pulverized coal mixture under high-temperature heating are measured by the cylindrical resonant cavity perturbation method.Combining the transient dipole and large π bond delocalization polarization phenomena, the interaction mechanism of the microwave macroscopic non-thermal effect on the titanium carbide synthesis reaction was revealed.The material thickness range during microwave heating was optimized by the joint analysis of penetration depth and reflection loss, which is of great significance to the design of the microwave reactor for the carbothermal reduction of Ti-bearing blast furnace slag.

Influence of wet activation of used inorganic binder on cyclically refreshed water glass moulding sands hardened by microwaves

The paper presents the research results of using an innovative method to reclaim the waste moulding sands containing water glass. Two of the examined processes are connected with "dry" or "wet" activation of inorganic binder in waste moulding sand mixtures physically hardened by microwave radiation. The sand mixtures consisting of high-silica sand and water-glass with average molar module 2.5, were subjected to the following cyclical process: mixing the components, compacting, microwave heating, cooling-down, thermally loading the mould to 800 °C, cooling-down to ambient temperature, and knocking-out. After being knocked-out, the waste moulding sands were subjected to either dry or wet activation of the binder. To activate thermally treated inorganic binder, each of the examined processes employed the surface phenomenon usually associated to mechanical reclamation. The study also covered possible use of some elements of wet reclamation to rehydrate waste binder. To evaluate the effectiveness of the two proposed methods of waste binder activation, selected strength and technological parameters were measured. After each subsequent processing cycle, the permeability, tensile strength and bending strength were determined. In addition, the surface of activated sand grains was examined with a scanning electron microscope. Analysis of the results indicates that it is possible to re-activate the used binder such as sodium silicate, and to stabilize the strength parameters in both activation processes. Permeability of the refreshed moulding sands strongly depends on the surface condition of high-silica grains. The wet activation process by wetting and buffering knocked-out moulding sands in closed humid environment makes it possible to reduce the content of refreshing additive in water-glass. The moulding sands cyclically prepared in both processes do not require the addition of fresh high-silica sand. The relatively high quality achieved in the refreshed moulding sands allows them to be reused for manufacture of next moulds. Thus, the two proposed methods for cyclically processing used moulding sands containing sodium silicate, subject to microwave hardening, are suitable for economic and ecological circulation moulding mixtures.

Microwave Irradiated Palladium-Catalyzed Cascade Type Cross Coupling of Phenols and Halides for the Synthesis of Polyphenolic Ethers

A mild, cascade type methodology was developed for the synthesis of polyphenolic ethers by the palladium-catalyzed cross coupling of phenols and halo compounds under microwave heating. In most cases, reactions run in neat conditions and in some cases, IPA/water mixture, and 1,4-dioxane were employed as solvents to furnish the products. By applying this new method, we were able to synthesize and purify a good number of polyether compounds with complete spectral data.

Preparation of lithium carbonate by microwave assisted pyrolysis

Investigations were conducted to purify crude Li_(2)CO_(3)via direct carbonation with CO_(2)at atmospheric pressure and pyrolysis with both water bath heating method and microwave heating method.The reaction kinetics of LiHCO_(3)pyrolysis was studied and the effect of different operating conditions including initial concentration of LiHCO_(3)solution,pyrolysis temperature and stirring speed on the purity of Li_(2)CO_(3)was investigated to obtain the optimal operating conditions.Results showed that the effect law is similar in the two pyrolysis processes.The purity of the Li_(2)CO_(3)increases firstly and then decreases with the increase of the initial concentration of LiHCO_(3)solution and the stirring speed,while the purity of Li_(2)CO_(3)first decreases and then increases with the increase of pyrolysis temperature.The product yield increases with the increase of initial concentration of LiHCO_(3)solution and pyrolysis temperature and is essentially unaffected by the stirring speed.Under the optimal operating conditions,the purity of Li_(2)CO_(3)can reach up to 99.86%and 99.81%in water bath heating and microwave heating process,respectively.In addition,the pyrolysis rate of microwave assisted pyrolysis is 6 times that of water bath heating process,indicating that the microwave heating technology can significantly improve pyrolysis efficiency and reduce energy consumption.

Ultrafast synthetic strategies under extreme heating conditions toward single-atom catalysts

Dispersing atomic metals on substrates provides an ideal method to maximize metal utilization efficiency, which is important for the production of cost-effective catalysts and the atomic-level control of the electronic structure. However, due to the high surface energy, individual single atoms tend to migrate and aggregate into nanoparticles during preparation and catalytic operation. In the past few years, various synthetic strategies based on ultrafast thermal activation toward the effective preparation of single-atom catalysts(SACs) have emerged, which could effectively solve the aggregation issue. Here, we highlight and summarize the latest developments in various ultrafast synthetic strategy with rapid energy input by heating shockwave and instant quenching for the synthesis of SACs, including Joule heating, microwave heating, solid-phase laser irradiation, flame-assisted method, arc-discharge method and so on,with special emphasis on how to achieve the uniform dispersion of single metal atoms at high metal loadings as well as the suitability for scalable production. Finally, we point out the advantages and disadvantages of the ultrafast heating strategies as well as the trends and challenges of future developments.

Novel heating technologies to improve fermentation efficiency and quality in wheat products:A short review

Identifying novel processing methods is an important research direction in the field of food engineering.Fermented flour products have been popular all over the world for a long time because of their unique flavor and texture.Whether for yeast or sourdough,the accurate temperature control is essential for the fermentation process.Some novel heating methods have shown potential in the processing of fermented flour products.Microwave heating(MWH),radiofrequency heating(RFH),and ohmic heating(OH)are undoubtedly the most promising heating methods.MWH affects the fermentation time of the dough by affecting the water molecules in the dough,and may also improve the fermentation quality of wholewheat flour products.RFH contributes to the control of harmful substances in the fermentation process and has shown potential for the production of sourdough bread.OH has superiority in accurately controlling the temperature,enzymes,microorganisms,etc.in the fermentation process,and it is beneficial to shortening the fermentation time.Researchers have applied these heating methods with different properties to different uses.This article summarized the application and potential of these three novel heating methods in the production of fermented flour products.The application scenarios and parameter settings of novel heating technologies in dough fermentation process need further research.It is reasonable to believe that novel heating methods can become an important tool to improve the efficiency of dough fermentation and the quality of fermented dough in the future.

Influence of Radial Dimension and Electric Field on a Microwave-Assisted Esterification

Enzymatic synthesis of ethyl hexanoate from hexanoic acid and ethanol in a solvent-free system, carried out at optimum conditions, has been modeled. The process follows a Ping-Pong Bi-Bi reaction rate and it is endothermic, so microwave heating is provided to prevent its shutdown. The mathematical model has been numerically solved with the FEM method. Results show that microwave heating can be successfully used to carry out this kind of reaction.

炼钢渣和炭的混合物用于微波辅助甲烷干气重整反应(英文)

The use of steel-making slag as catalysts for microwave-assisted dry reforming of CH4 was studied. Two carbon materials (an activated carbon and a metallurgical coke), mixtures of the carbon materials and Fe-rich slag, and mixtures of the carbon materials and Ni/Al2O3 were tested as catalysts. The mixtures of slag with carbons gave rise to higher and steadier conversions than those achieved over the carbon materials alone. In addition, the use of the metallurgical coke mixed with metal-rich catalysts gave rise to remarkable results. Thus, no CH4 and CO2 conversions were achieved when coke was used alone, whereas high conversions were obtained when it was mixed with the metal-rich catalysts.

Comparison of microwave and conventional heating on physicochemical properties and phenolic profiles of purple sweetpotato and wheat flours

The hydrothermal treatment assisted with microwaves on physicochemical properties and phenolic profiles of purple sweetpotato flour and wheat flour was studied and compared with those of conventional heat treatment.Both treatments significantly decreased the enthalpy change,pasting viscosity and gelling capacity of flours,while increasing particle size,gelatinization temperatures and content of resistant starch.Microwaves induced more severe damages on the starch granule morphology and crystallinity than conventional heat treatment,which could be attributed to the intensive friction and collision produced by electromagnetic waves.The total concentrations of hydroxycinnamic acid derivatives and anthocyanins in purple sweetpotato flour extracted using microwaves at 100℃ were 36%and 68%higher than those in the samples after conventional heat treatment at 100℃,respectively.Electromagnetic waves caused a higher extent of cell damage due to sudden temperature rise during microwave treatment.Overall,microwave treatment has potential to produce novel functionalities and nutritional values of flours and can be applied as an effective approach for other starch-based food products.