Microwave Conduction Research Articles

Microwave heating and conduction heating pork belly: Influence of heat transfer modes on volatile compounds and aroma attributes

This work was conducted to compare the differences in odor attributes and the formation causes of pork belly cooked by different heating modes and the feasibility of achieving convenient and delicious cooking of stir-fried pork cuisines by modifying the heat transfer mode of the microwave. The effects of traditional pan-heating (TH), microwave heating (MH), and microwave combined with conduction heating (MH + CH) on sensory aroma attributes, aroma profile, free fatty acids, and volatile compounds of pork belly were investigated. The results showed that the pork belly heated by TH had the lowest total amount of stable volatile compounds (1695.41 μg/kg) and contents of free fatty acids (751.44 mg/100g), but the balanced distribution and the rich contents of volatile compounds derived from thermal processing resulted in the better aroma quality of pork belly. In contrast, although the pork belly cooked by MH had higher free fatty acids contents (1215.32 mg/100g) and the highest volatile compounds (5410.56 μg/kg), due to the cell destruction effect and the molecular movement acceleration of microwave, the contents of volatile compounds derived from spices were too high, leading to the disharmony of aroma characteristics. However, the pork belly cooked with MH + CH not only promoted the production of free fatty acids (1434.23 mg/100g), but also increased the generation and retention of pork characteristic aroma by changing the heating modes. Compared with MH, it enhanced the uniformity of aroma distribution and improved the overall aroma similarity to TH.

Study of 400MHz microwave conduction loss effect for a hydrolysis reaction by thermostable β-Glucosidase HT1.

Microwave irradiation at different frequencies gave molecular selective effects, namely higher frequency microwave effects for waters while lower frequency effects for ions. We already reported that 2.45GHz and 5.80GHz microwave irradiation gave different results for a hydrolysis reaction by thermostable β-Glucosidase HT1. Here, we designed and made a reactor, employed 400MHz microwave irradiation, and studied the effectiveness of 400MHz microwave for HT1 reaction, then 400MHz and 2.45GHz had the ability to accelerate HT1 reaction. In consideration of the general mechanism of enzymatic glycoside hydrolysis, our results would be reasonable if ions are key reaction species because 400MHz microwave activated ions selectively. In addition, the phenomenon that 400MHz microwave would not affect water molecules by dielectric heating might contribute the enzyme stability. This report should support that microwave is not only a tool to heat reactions efficiently but also can bring unique effects for reactions.

Microwave heating and conduction heating pork belly: Non-volatile compounds and their correlation with taste characteristics, heat transfer modes, and matrix microstructure

This study investigated the difference in the taste characteristics of pork belly cooked by traditional pan-heating (TH), microwave heating (MH), and microwave combined with conduction heating (MH + CH). The results showed that MH destroyed the microstructure integrity and made the cooking loss (50.33%) and sodium ion concentration (10.8 mg/g) about 1.6 times that of MH + CH, thereby enhancing the saltiness. In addition, compared with TH, microwave heating could accelerate the hydrolysis of proteins and the thermal degradation of ribonucleotides, resulting in higher contents of free amino acids (880.71 and 714.85 mg/100 g) and nucleotides (181.41 and 145.52 mg/100 g) in MH and MH + CH. Combined with the results of non-volatile compounds and sensory evaluation, the MH + CH not only promoted the accumulation but also improved the dissolution uniformity of taste compounds, which enhanced the sensory umami. The inconsistency between non-volatile compounds, electronic tongue, and sensory evaluation indicated that the matrix effects caused by cooking also had significant influences on the taste quality of solid samples.

Local exergy cost analysis of cullet glass heating by microwaves

In this paper, the analysis of the local exergy costs of a cullet glass heated by microwaves in a cubical cavity activated by a susceptor is presented. The analysis is based on a previously validated 3-D electromagnetic model, but goes further by applying the concepts of local exergy efficiency and local unit exergy consumption, what enables a local analysis (in time and space) of the process efficiency. Furthermore, local exergy cost quantifies in detail the path of the exergy cost formation during microwave heating, which is determined by the local irreversibilities taking place in this transient process.Four different susceptor positions have been also compared, in order to find out not only which one is the most efficient but also to justify in detail this result by the time and space evolution of efficiency, unit exergy consumption (both external microwave power and conduction contributions) and unit exergy cost. The best conclusion of the paper is that the local exergy cost approach can contribute to the design of more efficient energy conversion systems, as it could be noted in its application to a complex process like this 3-D example of microwave cullet heating.

Floquet theory of microwave absorption by an impurity in the two-dimensional electron gas

We investigate the dynamics of a two-dimensional electron gas (2DEG) under circular polarized microwave radiation in the presence of dilute localized impurities. Inspired by recent developments on Floquet topological insulators we obtain the Floquet wave functions of this system which allow us to predict the microwave absorption and charge density responses of the electron gas; we demonstrate how these properties can be understood from the underlying semiclassical dynamics even for impurities with a size of around a magnetic length. The charge density response takes the form of a rotating charge density vortex around the impurity that can lead to a significant renormalization of the external microwave field which becomes strongly inhomogeneous on the scale of a cyclotron radius around the impurity. We show that this inhomogeneity can suppress the circular polarization dependence which is theoretically expected for microwave induced resistance oscillations but which was not observed in experiments on semiconducting 2DEGs. Our explanation for this so far unexplained polarization independence has close similarities with the Azbel'-Kaner effect in metals where the interaction length between the microwave field and conduction electrons is much smaller than the cyclotron radius due to skin effect generating harmonics of the cyclotron resonance.

Is Selective Heating of the Sulfonic Acid Catalyst AC-SO3H by Microwave Radiation Crucial in the Acid Hydrolysis of Cellulose to Glucose in Aqueous Media?

Selective heating of microwave-absorbing solid catalysts in a heterogeneous medium may affect a chemical reaction; such selectivity cannot be achieved by conventional oil-bath or steam heating methods. Moreover, microwave methods are often misunderstood with respect to equipment and temperature measurements, so that additional experimentation is necessary. In this regard, the present study intended to clarify the effect of microwave selective heating on acid hydrolytic processes using a sulfonated activated carbon catalyst (AC-SO3H). The model reaction chosen was the acid hydrolysis of cellulose carried out in a Pyrex glass microwave reactor, with the process being monitored by examining the quantity of total sugar, reducing sugar, and glucose produced. Heat transfer from the catalyst to the aqueous solution through absorption of microwaves by the catalyst occurred as predicted from a simulation of heat transfer processes. The resulting experimental consequences are compared with those from the more uniform microwave conduction heating method by also performing the reaction in a SiC microwave reactor wherein microwaves are absorbed by SiC. Some inferences of the influence of microwave selective heating of carbon-based catalyst particles are reported. Under selective heating conditions (Pyrex glass reactor), the yield of glucose from the acid hydrolysis of cellulose was 56% upon microwave heating at 200 °C, nearly identical with the yield (55%) when the hydrolytic process was performed under mainly conventional heating conditions in the SiC reactor. Although the beneficial effect of catalyst selective heating was not reflected in the reaction efficiency, there were substantial changes in the state of adsorption of cellulose on the catalyst surface.

Numerical study of cullet glass subjected to microwave heating and SiC susceptor effects. Part I: Combined electric and thermal model

A numerical study of energy conversion during microwave heating of cullet glass is presented by means of a combined electric and thermal model. Ceramic materials, such as glass, poorly absorb microwave radiation at temperatures below 300°C. Thus, in order to obtain the simulation of microwave heating from room temperatures, the effects of a SiC susceptor were studied. Four different positions of the susceptor were simulated to improve that heating process. The numerical simulation of cullet glass and susceptor behavior under an electromagnetic field was analyzed by applying transient Maxwell’s equations, which were solved by the finite difference time domain (FDTD) method. Once the electromagnetic field in the waveguide and microwave cavity was computed, temperature inside of the applicator was determined by solving the heat transfer equations including microwave absorption, conduction and internal radiation terms. Parametric simulations showed that the susceptor position changed the electromagnetic and heat transfer patterns, and then the temperature field inside of the cullet glass. Therefore, energy consumption of heated cullet glass was also affected.

Structural variation of rice starch in response to temperature during microwave heating before gelatinisation

Although it is well known that structural variations occur in starch during gelatinisation, little is known about how the structure of starch changes at subgelatinisation levels. The objective of this study was to investigate structural variations of rice starch ascribed to the temperature during microwave heating. Rapid conduction heating was used to imitate the high microwave heating rate through oil bath, which was then compared with traditional conduction heating. Structural changes due to temperature increases were investigated using thermogravimetry and differential scanning calorimetry while the distinct lamellar organisation of starch was obtained through small-angle X-ray scattering. The results showed that the structure of starch responds non-monotonically to temperature rising before gelatinisation, which was also affected by heating rates. The samples treated by microwave and rapid conduction heating essentially underwent the same thermal property changes and the molecular vibration of the microwaves did influence the submicroscopic lamellar structure.

Influence of Humidity and of the Electric and Magnetic Microwave Radiation Fields on the Remediation of TCE-contaminated Natural Sandy Soils

The influence of moisture content (15% w/w) on the remediation (vaporization) of trichloroethylene (TCE) present in natural sands, chosen as a TCE-polluted model system for soils, was investigated with regard to applied microwave power levels, the depth of the sand sample, and the dielectric factors. The heating process occurring in the sand samples arises through the microwave conduction loss heating and dielectric loss heating mechanisms. The characteristic relevance of the electric and magnetic microwave radiation fields to the heating mechanisms was also examined. Heating by the magnetic microwave radiation field was considerable when magnetite was added to the dry and wet sand samples as the microwave absorber. Optimal microwave conditions are reported for a single-mode microwave applicator. Near-quantitative elimination of the TCE contaminant was achieved for sandy soils within a very short time.

Effect of wet‐chemical substrate pretreatment on electronic interface properties and recombination losses of a ‐Si:H/c ‐Si and a ‐SiNx:H/c ‐Si hetero‐interfaces

AbstractSurface charge, surface state density and interface recombination behavior on polished float zone (FZ) solar cell substrates were investigated after various wet‐chemical pre‐cleaning procedures and deposition of amorphous silicon (a‐Si:H) or silicon nitride (a‐SiNx:H). Applying surface photo voltage (SPV), microwave detected photo conductance decay (µW‐PCD) and transient microwave conduction (TRMC) measurements, electronic interface properties were monitored repeatedly during the preparation processes. As shown for an inverted a‐Si:H/c‐Si hetero‐junction structure, with front side passivation by a‐SiNx:H and a p‐type a‐Si:H emitter on the rear side, the effect of optimised wet‐chemical pre‐treatment can be preserved during the subsequent soft plasma enhanced chemical vapour deposition of a‐Si:H or a‐SiNx:H. This leads to hetero‐interfaces with low interface recombination velocities. These results were compared to previously reported findings, obtained on textured Czochralski (CZ) single crystalline substrates. a‐SiNx:H is known to result in a field effect passivation. Nevertheless a strong influence of wet‐chemical treatments on surface charge and recombination losses was observed on both flat and textured a‐SiNx:H/c‐Si interfaces. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Wheat starch gelatinization under microwave irradiation and conduction heating

Wheat starch–water dispersions at excess water conditions were heated under mixing to different temperatures by either microwave energy at 2000 W or by conduction heating in order to compare both heating methods. The effects of microwaves and conduction heating on starch gelatinization were evaluated using different techniques; It was possible to obtain the same viscosity for both heating methods but the required time was much shorter for microwaves heated starch dispersions. No unique structures due to the heating method were observed under the microscope. At the beginning of the heating process an increase in the mobility of the starch protons occurred, slightly higher for microwaves heated samples. Likewise, DSC experiments revealed an increase in the enthalpy for short times microwave heated samples. The heating method caused no differences in the mechanism of gelatinization; nevertheless the crystallinity disappeared at a higher rate when heated with microwaves.

Study of hydration of OPC/PFA blend with various activators using microwave technique

The early hydration of ordinary Portland cement (OPC) pulverized fly ash (PFA) blends with various PFA proportions was investigated using microwave technique and conduction calorimeter. It is found that PFA acts as almost inert filler in the OPC/PFA blends during the first 40 h of hydration, thus it retards the early hydration of the blends. To accelerate the pozzolanic hydration of the PFA, three different additives were studied. It is found that both Ca(OH)2 and Na2SO4 can accelerate the early hydration of the OPC/PFA blends, but Na2SO4 is more effective than Ca(OH)2, whereas NaOH is not suitable for the acceleration of the early hydration of the OPC/PFA blend. © 1998 Kluwer Academic Publishers

Variation of the microwave dielectric permeability of the acrylamide-calcium nitrate system during its spontaneous polymerization

The kinetics of the variation of the complex dielectric permeability at microwave frequencies of 1.1, 1.7, 2.7, and 10 GHz during spontaneous polymerization of acrylamide in the presence of the hydrate of calcium nitrate was studied. The microwave conduction of this system has an ionic nature. It was assumed that some of the water liberated during the polymerization is both transformed into a bound state and forms microinclusions of an electrolyte solution in the bulk of the polymer.

Kinetics of subthreshold luminescence and microwave conductivity of glasses under laser heating conditions

An experimental investigation was made of the luminescence and microwave conductivity of K8 and ZhS 11 optical glasses under conditions of subthreshold irradiation by a quasi-cw neodymium laser. For ZhS 11 glass it was established that the luminescence depended on temperature and the influence of photostimulation was observed at the 1.06 μ wavelength. The activation energies of the microwave conduction and subthreshold luminescence processes were determined for ZhS 11 glass.

Microwave conduction in n-type germanium under hot electron conditions

Microwave conduction in n-type germanium in the presence of a high steady electric field is studied The carrier concentration is assumed to be high enough to ensure that intercarrier collisions enforce a Maxwellian distribution on the carriers and the momentum loss by the carriers occurs mainly through scattering due to lattice vibrations. The effect of anisotropic effective mass on the microwave conduction characteristics is discussed, and the anisotropy is found to be small at room temperature Numerical values of microwave conductivity and the change in dielectric constant are found to agree with the experimental results of a 4 68 Ω cm n-type germanium sample, and the best fit with the experimental characteristics is obtained for a value of the optical deformation potential constant D0 between 0 7 to 0 8 × 109 ev cm-1.