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.

Effect of temperature on dielectric property and microwave heating behavior of low grade Panzhihua ilmenite ore

The permittivity of low grade Panzhuhua ilmenite ore at 2.45 GHz in the temperatures from 20 ℃ up to 100 ℃ was measured using the technology of open-ended coaxial sensor combined with theoretical computation. The results show that both the real （ε′） and imaginary （ε′） part of complex permittivity （ε′-jε′） of the ilmenite significantly increase with temperature. The loss tangent （tanδ） is a quadratic function of temperature, and the penetration depth of ilmenite decreases with temperature increase from 20 ℃to 100 ℃ The increase of the sample temperature under microwave radiation displays a nonlinear relationship between the temperature （T） and microwave heating time （t）. The positive feedback interaction between complex permittivity and sample temperature amplifies the interaction between ilmenite and the microwave radiation. The optimum dimensions for uniform heat deposition vary from 10 cm to 5 cm （about two power penetration depths） in a sample being irradiated from both sides in a 2.45 GHz microwave field when temperature increases from room temperature to 100 ℃

Nucleation and crystallization of tailing-based glass-ceramics by microwave heating

The effect of microwave radiation on the nucleation and crystallization of tailing-based glass-ceramics was investigated using a 2.45 GHz multimode microwave cavity. Tailing-based glass samples were prepared fi＇om Shandong gold tailings and Guyang iron tailings utilizing a conventional glass melting technique. For comparison, the tailing-based glass samples were crystallized using two different heat-treatment methods： conventional heating and hybrid microwave heating. The nucleation and crystallization temperatures were determined by performing a differential thermal analysis of the quenched tailing-based glass. The prepared glass-ceramic samples were further characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, thermal expansion coefficient measurements, and scanning electron microscopy. The results demonstrated that hybrid microwave heating could be successfully used to crystallize the tailing-based glass, reduce the processing time, and decrease the crystallization temperature. Furthermore, the results indicated that the nucleation and crystallization mechanism of the hybrid microwave heating process slightly differs fi＇om that of the conventional heating process.

Carburization of ferrochromium metals in chromium ore fines containing coal during voluminal reduction by microwave heating

Chromium ore fines containing coal (COFCC) can be rapidly heated by microwave to conduct the voluminal reduction, which lays a foundation of getting sponge ferrochromium powders with a lower content of C. Under the conditions of COFCC with n(O)-n(C) (molar ratio) as 1.00-0.84 and n(SiO2)-n(CaO) as 1.00-0.39, the samples were heated by 10 kW microwave power to reach the given temperatures and held for different times respectively. The results show that the low-C-Cr ferrochromium metal phase in the reduced materials forms before the high-C-Cr ferrochromium metal phase does. With increasing temperature the C content of ferrochromium metals is in a positive correlation with the content of Cr. The C content of ferrochromium metal in reduced materials is 0-10.07% with an average value of 4.68%. With the increase of holding time the Cr content in ferrochromium metals is in a negative correlation with the content of C, while the content of Fe changes in the contrary way. In the microwave field the kinetic conditions of carburization are closely related with the temperature of microwave heating, holding time and carbon fitting ratio.

Rapid growth of ZnO hexagonal tubes by direct microwave heating

Zinc oxide hexagonal tubular crystals were synthesized by direct microwave heating from ZnO powders within 5 min without any metal catalysts or transport agents. ZnO source materials were evaporated from the high-temperature zone in an enclosure, and crystals were grown on the self-source substrate in an appropriate condition. The ZnO vapor formed in the high-temperature zone can deposit and grow on the powders located in the low-temperature zone to form crystals. The scanning electron microscopy （SEM） reveals that these products are hexagonal tube crystals with 80 ~rn in diameter and 250 μm in length, having a well faceted end and side surface. A possible growth mechanism and the influence of reaction temperature on the formation of crystalline ZnO hexagonal tubes were presented. The photoluminescence （PL） exhibits strong ultraviolet emission at room temperature, indicating the potential applications in short-wave light-emitting photonic devices.

Acid-pickling plates and strips speed control system by microwave heating based on self-adaptive fuzzy PID algorithm

Double self-adaptive fuzzy PID algorithm-based control strategy was proposed to construct quasi-cascade control system to control the speed of the acid-pickling process of titanium plates and strips. It is very useful in overcoming non-linear dynamic behavior, uncertain and time-varying parameters, un-modeled dynamics, and couples between the automatic turbulence control (ATC) and the automatic acid temperature control (AATC) with varying parameters during the operation process. The quasi-cascade control system of inner and outer loop self-adaptive fuzzy PID controller was built, which could effectively control the pickling speed of plates and strips. The simulated results and real application indicate that the plates and strips acid pickling speed control system has good performances of adaptively tracking the parameter variations and anti-disturbances, which ensures the match of acid pickling temperature and turbulence of flowing with acid pickling speed, improving the surface quality of plates and strips acid pickling, and energy efficiency.

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.

Investigation on microwave heating for direct leaching of chalcopyrite ores and concentrates

The use of microwave energy in materials processing is a relatively new development presenting numerous ad- vantages because of the rapid heating feature. Microwave technology has great potential to improve the extraction efficiency of metals in terms of both a reduction in required leaching time and an increase in the recovery of valuable metals. This method is especially pertinent in view of the increased demand for environment-friendly processes. In the present study, the influence of microwave heating on the direct leaching of chalcopyrite ores and concentrates were investigated. The results of microwave leaching experiments were compared with those obtained under conventional conditions. During these processes, parameters such as leaching media, temperature, and time have been worked to determine the optimum conditions for proper copper dissolution. Experimental results show that microwave leaching is more efficient than conventional leaching. The optimum leaching conditions for microwave leaching are the solid-to-liquid ratio of 1：100 g/mL, the temperature of 140℃, the solution of 0.5 M H2SOa- 0.05 M Fe：（SOa）a, and the time of I h.

Properties of sodium silicate bonded sand hardened by microwave heating

The sodium silicate bonded sand hardened by microwave heating has many advantages,such as low sodium silicate adding quantity,fast hardening speed,high room temperature strength,good collapsibility and certain surface stability.However,it has big moisture absorbability in the air,which would lead to the compression strength and the surface stability of the sand molds being sharply reduced.In this study,the moisture absorbability of the sodium silicate bonded sand hardened by microwave heating in different humidity conditions and the effect factors were investigated.Meanwhile,the reasons for the big moisture absorbability of the sand were analyzed.Some measures to overcome the problems of high moisture absorbability,bad surface stability and sharply reducing strength in the air were discussed.The results of this study establish the foundation of green and clean foundry technology based on the microwave heating hardening sodium silicate sand process.

Direct reduction of carburized pre-reduced pellets by microwave heating

A new iron-making process using carburized pre-reduced iron ore pellets and microwave heating is investigated. The pre-reduced pellets, with a porous structure, and fine particles are carburized homogeneously at 400-650 ℃ in a CO atmosphere. The carburized carbon not only acts reaction as a reduction agent, but also absorbs microwave in the reduction process. Hence, the carburized pre-reduced pellets can be rapidly reduced by microwave heating. There are three procedures involved in the process, namely, gas-based pre-reduction, low-temperatttre carburization and deep reduction by microwave heating. Carburized pre-reduced iron ore pellets show a rapid temperature rise that is twice as fast as the results for pre-reduced pellets in the laboratory. This not only improves the efficiency of the microwave heating, but also accelerates the reduction of iron oxides. The temperature of the pre-reduced pellets rises to 1050 ℃ in 45 min when the carburization rate is 2.02%, and the metallization rate and compressive strength reach 94.24% and 1725 N/pellet, respectively.

Regeneration of waste activated carbon after extracting gold with steam under microwave heating:Optimization using response surface methodology

The technology that waste activated carbon after extracting gold is regenerated with steam under microwave heating was studied. The influence of the activation temperature, activation duration and steam flow rate on iodine adsorption value and regeneration yield of activated carbon was investigated. The response surface methodology （RSM） technique was utilized to optimize the process conditions. The optimum conditions for the preparation of activated carbon are identified to be activation temperature of 831 ℃, activation duration of 40 min and steam flow rate of 2.67 mL/min. The optimum conditions result in an activated carbon with an iodine number of 1048 mg/g and a yield of 40%, and the BET surface area evaluated using nitrogen adsorption isotherm is 1493 m2/g, with total pore volume of 1.242 cm3/g. And the pore structure of activated carbon regenerated is mainly composed of micropores and a small amount of mesopores.

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 disch...

Application of Microwave Heating Technique to Esterification

Introduction Although the application of microwave technique has been reported as a new type of energy source chemically, it is only in recent years that this technique has been used as the energy source for organic synthesis. In 1986, R. Gedye, et al., published the report of the benzoate synthesis from the respective reactions between benzene carboxylic acid and methanol, propanol or butanol under microwave heating and the catalysis of H;SO;.

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.

Chemical Oxygen Demand of Seawater Determined with a Microwave Heating Method

This paper investigates a microwave heating method for the determination of chemical oxygen demand (COD) in seawater. The influences of microwave-power, heating time and standard substances on the results are studied. Using the proposed method, we analyzed the glucose standard solution, the coefficient of variation being less than 2%. Compared with the traditional electric stove heating method, the results of F-test and T-test showed that there was no significant difference between the two methods, but the microwave method had slightly higher precision and reproducibility than the electric stove method. With the microwave heating method, several seawater samples from Jiaozhou Bay and the South Yellow Sea were also analyzed. The recovery was between 97.5% and 104.3%. This new method has the advantages of shortening the heating time, improving the working efficiency and having simple operation and therefore can be used to analyze the COD in seawater.

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.

Synthesis of Compact NaA Zeolite Membrane by Microwave Heating Method

A continuous and dense NaA zeolite membrane was synthesized by microwave heating method while employing a multi-step seeding LTA zeolite with the average size of 120 nm. The gas H2/N2 mixture separating results indicated that the mixture selectivity increased with increasing of synthesis times. In addition, selectivity of the three-step synthesis was higher than the value(3.74) expected from Kundsen diffusion.

Rapid growth of ZnO hexagonal prism crystals by direct microwave heating

ZnO hexagonal prism crystals were synthesized from ZnO powders by microwave heating in a short time （within 20 min） without any metal catalyst or transport agent. Zinc oxide raw materials were made by evaporating from the high-temperature zone in an enclosure atmosphere and crystals were grown on the self-source substrate. The inherent asymmetry in microwave heating provides the temperature gradient for crystal growth. Substrate and temperature distribution in the oven show significant effects on the growth of the ZnO crystal. The morphologies demonstrate that these samples are pure hexagonal prism crystals with maximum 80 lain in diameter and 600 lure in length, which possess a well faceted end and side surface. X-ray diffraction （XRD） reveals that these samples are pure crystals. The photoluminescence （PL） exhibits strong ultraviolet emission at room temperature, indicating potential applications for short-wave light-emitting photonic devices.

Synthesis of WC powder through microwave heating of WO_3–C mixture

A simple, easy, and low-cost process for the fabrication of tungsten carbide （WC） powder through microwave heating of WO3-C mixtures was developed. Thermodynamic calculations and experimental investigations were carried out for WO3-and W-C systems, and a formation mechanism was proposed. In the results, for the synthesis of WC, the use of over stoichiometric amount of C together with a spe- cially assembled experimental setup （which effectively retains heat in the system） is necessary. The WC powder is successfully obtained by heating WO3：5C mixture for 900 s in a domestic microwave oven.

Research on Microwave Heating-Direct Steelmaking in Electric Furnace

Self-fluxing iron ore concentrates containing coal have good microwave Absorbability. With the voluminal heating property of microwave, the concentrates can be reduced uniformly and swiftly. The metallized semi-product can be directly charged into electric furnace for making clean steel. The total consumed energy of overall route is about 20 98 GJ.