Increasing Microwave Power Research Articles

Increasing the essential oil yield from Shorea roxburghii inflorescences using an eco-friendly solvent-free microwave extraction method for fragrance applications

The short bloom period of Shorea roxburghii G.Don is a technical challenge in the development of a fast and efficient process for recovering essential oils. This study aimed to optimize the conditions for the isolation of essential oil and the determination of the resulting oil's possible bioactivities for fragrance applications. Solvent-free microwave extraction (SFME) coupled with response surface methodology (RSM) was applied to study essential oil from fresh inflorescences. The microwave power and irradiation time were chosen as crucial independent variables, while essential oil yield was the response variable. The physicochemical, antioxidant, olfactory, cytotoxic, and irritant properties of the resulting oil were evaluated. SFME yielded essential oil with a unique and pleasant scent, similar to that of fresh flowers. Increased microwave power and irradiation time increased the oil yield. The proportions of oxygenated compounds with high antioxidant properties were notably higher after SFME than after hydrodistillation. The optimal conditions for maximizing the oil yield were 800 W and 35 min. Among 51 volatile substances, germacrene B, kaur-16-ene, β-caryophyllene, and (E)-linalool oxide (furanoid) were the oil's main components. Low toxicity to primary human dermal fibroblast cells was defined at an oil concentration < 50 μg/mL. Moreover, the application of the extracted volatile oil to hen’s egg-chorioallantoic membrane resulted in a low degree of irritation. This research establishes optimal extraction conditions for the isolation of essential oil with potential for fragrance applications.

Kinetic Study on Chlorophyll and Antioxidant Activity from Polyscias fruticosa (L.) Harms Leaves via Microwave-Assisted Extraction.

Polyscias fruticosa (L.) leaves contain significant bioactive compounds with high antioxidant activity such as chlorophylls, total polyphenols, etc. but these have still been underutilized. In this study, the kinetics of chlorophyll and antioxidant activity extraction from P. fruticosa leaves by microwave-assisted extraction (MAE) were investigated. Microwave power was 300, 450, or 600 (W); the ratio of material/solvent varied from 1:40 to 1:80 (g/mL). In this study, the second-order kinetic model successfully predicted the change of chlorophyll and antioxidant activity during MAE. The increase of microwave power or/and the solvent amount increased saturated extraction efficiency and the extraction rate constant. However, the saturated concentration of chlorophyll and antioxidant activity increased with the increment of microwave power and the decrease in solvent amount.

Optimisation of microwave-rotary drying process and quality parameters of terebinth

Different aspects of terebinth drying in a microwave-rotary dryer were investigated including energy and exergy analysis, quality, and bioactive compounds. Experiments were performed using different parameters of microwave power (270, 450, and 630 W) and chamber rotation speed (5, 10, and 15 rpm). Drying time and effective moisture diffusivity were ranging from 43 to 137 min and 6.25 × 10 −9 to 9.28 × 10 −8 m 2 s −1 , respectively. Energy and energy efficiency increase with increasing microwave power and rotation speed. Exergy loss and improvement potential decreased with increasing microwave power and rotation speed. The physical parameters (shrinkage and total colour difference) increased with increasing microwave and rotation speed, while for the rehydration rate, an inverse relationship was observed. Also for bioactive compounds like total phenolics, total flavonoid content, and antiradical activity, a higher reduction was noticed with used higher microwave power and with higher rotation speed. Thus, the best parameters to obtain the highest content of bioactive compounds were microwave power of 270 W and rotation speed of 5 rpm. Comparison of different algorithms revealed that the grey wolf optimisation (GWO) algorithm had greater accuracy than the whale (WO) optimisation algorithm to predict all parameters of dried terebinth. • Efficiency of the drying process was calculated. • Shrinkage and colour change increased with increasing microwave & rotational speed. • Rehydration rate decreased with increasing microwave and rotational speed. • Bioactive compounds increased with lower microwave power and rotational speed.

Influence of three stage ultrasound—intermittent microwave—hot air drying of carrot on physical properties and energy consumption

Innovative drying technologies are frequently introduced to minimize various disadvantages of hot air dryers such as high energy consumption and low quality dried products. The aim of this study was to investigate the influence of ultrasound (40 kHz for 10, 20, and 30 min) and intermittent microwave (360, 600 and 900 W at pulse ratios of 1, 2, 3 and 4) on physical properties of carrot during low temperature hot air drying at 40˚C. Drying time decreased during continuous microwave drying (pulse ratio of 1) due to higher internal temperature and water vapor pressure of the samples. The lowest bulk density was observed when ultrasound was applied for 30 min at 900 W microwave power with pulse ratio of 1. This result was attributed to a higher number of micro-channels created in the samples, which led to generate a higher porosity. Shrinkage of the samples decreased by increasing microwave power due to a shorter application time of microwave at higher powers. By extending ultrasound application time, rehydration increased by 17.8% as a result of enhanced cell permeability and higher capacity for water absorption. In addition, specific energy consumption decreased by 38.1% by increasing microwave power owing to lower drying time. Overall, the combined drying method improved physical properties of dried carrots and decreased energy consumption, suggesting a suitable alternative for industrial applications.

Effect of microwave heating on fracture behavior of granite: An experimental investigation

Hard rock breaking is a great challenge for deep drilling and mining engineering, and the microwave-assisted rock breaking technique offers a promising solution. However, the lack of knowledge of the effects of microwave irradiation on hard rocks limits the further development of this technology. Laboratory tests have been conducted to investigate the variations of fracture properties of granite subjected to microwave heating. The semi-circular bend (SCB) specimens were prepared, and mode I fracture tests were conducted on the microwave treated granite specimens. The acoustic emission (AE) events was recorded and the strain field was calculated by the digital image correlation (DIC) technique. The test results demonstrated that the temperature of the sample surface increased linearly as the increasing heating time, and increasing microwave power contributes to enhancing the heating rate. According to the results of scanning electron microscope (SEM), intergranular cracks were the main form of cracks, and the transgranular cracks usually appeared in samples with high microwave power or longer heating time. The generation of micro-cracks can be attributed to the high temperature and the thermal shock. With the increasing heating time, the fracture toughness decreased exponentially, the AE active period prolonged, and the fractal dimension of the fracture surfaces (FSD) continuous increased. Compared to an untreated sample, the maximum principal strain and fracture process zone (FPZ) size of the microwave heated sample were larger at the same loading level, which indicated the enhancement of ductility. According to the experimental results, the relationships between FPZ size, fracture toughness and FSD were empirically regressed. Understanding the effects of microwave heating on the fracture properties is of significant to improve hard rock breaking efficiency.

Effect of microwave radiation on the magnetic properties of ludwigite and iron-boron separation

To effectively separate and recover the valuable elements iron and boron from ludwigite, this study investigated the magnetic properties and the magnetic separation efficiency. And the reactivity of boron component in the B-bearing tailing was studied. The results indicated that the saturation magnetization of ore samples was increased with the increase of microwave power and heating time. Under condition of 40 s with 4 kW, the saturation magnetization of ore samples increased from 12.73 emu/g for the raw ore to 24.70 emu/g for the treated ore, an increased of 94.03%. After magnetic separation, the grade and recovery rate of iron in the iron concentrate and the boron grade in the tailing for the treated sample with 4 kW for 40 s were increased by 19.74%, 31.46% and 86.46% in comparison with those of the untreated ore. The sample was heated to 600 °C at 4 kW and held for 20 min, the reactivity of boron component in the B-bearing tailing reached 86.68 wt%, which increased by 34.01% compared with that of the raw ore and 4.43% compared with that of the optimal traditional roasting value at 700 °C for 2 h, indicating that the roasting temperature and time were obviously decreased and the reactivity was significantly improved by the microwave radiation.

Impact of the Microwave Power on the Structural and Optical Properties of Nanocrystalline Nickel Oxide Thin Films

Nanocrystalline nickel oxide thin films were prepared by combined techniques of direct current sputtering (DC sputtering) and microwave plasma chemical vapor deposition to perform high-quality films. The prepared films were subjected to three different microwave powers at 400, 800, and 1200 W. The structural and morphological properties of the prepared films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The prepared films have a trigonal structure. The crystallite size was calculated from Scherer’s formula and uniform dimensional model (UDM). The calculated size increased from 213 to 241 A as the microwave power increases from 400 to 1200 W, respectively. The lattice strain was also calculated from UDM model, and it had a lower value of 1.8 × 10–3 at 800 W. The optical properties such as transmittance, reflectance, absorption coefficient, extinction coefficient, and the dispersion were investigated. The optical transition of such films was direct transition, and the optical band gap values were observed to decrease from 3.950 to 3.367 eV as the microwave power increase from 400 to 1200 W, respectively. The refractive index and the dispersion energy parameters were studied in detail, and the static and lattice dielectric constant were deduced.

Microwave Drying of Banana (Musa acuminata) Stalk Biomass before Conversion to Value-added Products

Banana stalk biomass can pose disposal, environmental and health challenges. Fortunately, this biomass can be converted to value-added products including biofuels, bioenergy, biosorbents, fibers and animal feeds. However, it is necessary to remove moisture from the fresh biomass by drying before storage and conversion processes. Conventional drying in open sun is slow and weather dependent, but higher heating rates and faster drying rates can be achieved in a microwave dryer. Hence, the microwave drying characteristic of banana stalk biomass was investigated. Banana stalks were sliced into 5 mm thick pieces and dried in a microwave oven at power levels of 400 – 1000 W, the stalk slices were weighed at interval until the mass remained constant. The effective moisture diffusivity, activation energy and energy required for drying were determined. The microwave drying data were also fitted to twelve thin layer drying mathematical models to describe the kinetics of the drying process. The drying time of banana stalk slices decreased with increasing microwave power. The drying occurred mainly in the falling rate period. The effective moisture diffusivities were 4.14 × 10-9 – 2.00 × 10-8 m2 s-1 at 400 – 1000 W. The activation energy was 122 W g-1 while the total and specific energies required for the microwave drying were 0.25 – 0.37 kWh and 34.8 – 51 kWh/kg, respectively. The Weibull model suitably described the microwave drying kinetics of banana stalk slices. The moisture present in fresh banana stalk waste biomass can be effectively and rapidly removed by microwave drying before conversion processes.

Eksperimentalno istraživanje svojstava oštećenja na spoju armature i betona nakon mikrovalnog zagrijavanja

With an increase in urban construction waste, and in order to find an effective method of microwave-assisted mechanical RC regeneration, thermal damage characteristics of the interfacial bond between steel rebar and concrete after different microwave irradiations are analysed in this paper. The results show that, with an increase in microwave power, the overall failure mode of the specimen changes from splitting failure to pull-out failure. Bond slip curves and the corresponding fitting equations were obtained at various levels of microwave irradiation. By analysing characteristic points of the curve, 3500W was determined as a reasonable irradiation power.

Improvement of Structural, Electrical, and Optical Properties of Sol–Gel-Derived Indium–Tin-Oxide Films by High Efficiency Microwave Irradiation

Herein, indium-tin-oxide (ITO) thin films are prepared by a solution-based spin-coating process followed by a heat-treatment process with microwave irradiation (MWI). The structural, electrical and optical properties of the films are investigated. The properties of the microwave-irradiated sol-gel ITO films are compared with those of as-spun ITO films and sol-gel ITO films subjected to conventional furnace annealing (CFA) or a rapid thermal process (RTP). After microwave irradiation, the sol-gel ITO thin films are found to have crystallized, and they indicate enhanced conductivity and transparency. Furthermore, the resistances of the ITO films are decreased considerably at increased microwave power levels, and the resistivity of the films almost saturate even at a low microwave power of 500 W. The improved physical properties of the MW-irradiated samples are mainly due to the increase in the electron concentration of the ITO films and the increase in the carrier mobility after MWI.

Measurement of the density and rotational temperature of OH in a saturated water vapor slot-excited microwave plasma

OH density and rotational temperature were measured in a saturated water vapor slot-excited microwave plasma using spatio-temporally resolved laser-induced fluorescence. The microwave power was 20–100 W under continuous wave mode, whereas 40–200 W peak under pulse-modulated mode (30% duty cycle, 100 Hz). The water vapor pressure was 2.3 kPa. An approximately 2 mm thick flat-shaped plasma was generated on the surface of a slot antenna. The OH density and rotational temperature in the plasma ranged from 1 × 1014 cm−3 to 1 × 1015 cm−3 and from 1100 K to 3000 K, respectively. OH was produced via various routes originating from electron collisions (e + H2O) and was primarily lost through recombination (OH+OH → H2O+O) and diffusion. The production rate (k p ) of OH per H2O molecule, which was calculated based on a simplified reaction model using the measured OH density and temperature, showed a relation of , where P represents the microwave power. This relationship implies a two-step production process of OH via the vibrational excitation of H2O. Although the OH density increased with increasing microwave power, the density became saturated at high power values.

Texture properties of microwave post-processed 3D printed potato snack with different ingredients and infill structure

3D printing has the advantage to modify food texture by regulating internal structure. In this study, 3D printing was used to design the infill structure and microwave vacuum drying (MVD) was used to post-process the potato-based snack. Results indicated that MVD was a promising post-processing method with a high drying efficiency and good maintenance of structure information of 3D printed samples. Increased microwave power reduced the drying time, but increased the heating non-uniformity. NaCl addition increased the dielectric loss factor (ε′′), reduced the drying time and hardness of MVD products. Sucrose addition did not affect the dying time, but increased the hardness of products. Infill percentage and infill pattern closely related to the hardness of samples. Increased infill percentage increased the hardness of samples. Cast-made samples and 100% infill 3D printed samples were not suitable for MVD post-processing. Finally, product with various texture within one sample was produced by adjusting the infill structure of each part. This study provides a new aspect to modify food texture by changing infill structure, with MVD as a post-processing method.

An investigation on improving the homogeneity of plasma generated by linear microwave plasma source with a length of 1550 mm

To develop a larger in-line plasma enhanced chemical vapor deposition (PECVD) device, the length of the linear microwave plasma source needs to be increased to 1550 mm. This paper proposes a solution to the problem of plasma inhomogeneity caused by increasing device length. Based on the COMSOL Multiphysics, a multi-physics field coupling model for in-line PECVD device is developed and validated. The effects of microwave power, chamber pressure, and magnetic flux density on the plasma distribution are investigated, respectively, and their corresponding optimized values are obtained. This paper also presents a new strategy to optimize the wafer position to achieve the balance between deposition rate and film quality. Numerical results have indicated that increasing microwave power and magnetic flux density or decreasing chamber pressure all play positive roles in improving plasma homogeneity, and among them, the microwave power is the most decisive influencing factor. It is found that the plasma homogeneity is optimal under the condition of microwave power at 2000 W, chamber pressure at 15 Pa, and magnetic field strength at 45 mT. The relative deviation is within −3.7% to 3.9%, which fully satisfies the process requirements of the equipment. The best position for the wafer is 88 mm from the copper antenna. The results are very valuable for improving the quality of the in-line PECVD device.

Optimization of microwave assisted multilayer drying of bittergourd

Bittergourd rings were dried to a moisture level of 0.1 g water/g dry matter using a multilayer-cummicrowave drying technique. Response surface methodology was used to optimize the drying conditions based on specific energy consumption and quality of dried bittergourd viz. change in color, rehydration ratio, shrinkage ratio, ascorbic acid content and hardness of texture. A second-order polynomial model fitted well to all responses and high R2 values (>0.8) were observed in all cases. The change in color of the dried bittergourd was found higher at high microwave power and exposure time combination, whereas 80% retention of ascorbic acid and maximum rehydration ratio was observed at 504W. The specific energy consumption decreased with an increase in microwave power due to reduced drying time. The optimum operating conditions for drying bittergourd were PL: 504W and ET:24s, resulting in dried product with maximum rehydration ratio, ascorbic acid retention, overall acceptability, minimum shrinkage ratio, hardness and color change. The overall desirability was 0.725. Use of microwave application in the last stage of drying saved 39% energy. Therefore, microwave-assisted drying should be considered for improved heat and mass transfer and produce dried bittergourd with better quality.

Nanoindentation characterization of polymer nanocomposites for elastic and viscoelastic properties: Experimental and mathematical approach

This work aims to determine the elastic and viscoelastic properties of microwave processed nanocomposites. Three different power rating has been used in microwave processing of polymer nanocomposite, i.e., 180 W, 360 W, and 540 W. Nanomechanical elastic properties of nanocomposites have been determined using the conventional nanoindentation method. Viscoelastic properties of nanocomposites have been determined by observing the increase in depth at maximum load (10 mN) during a small holding period (2 s). Polypropylene nanocomposites (PNT), high-density polyethylene nanocomposites (HNT), and low-density polyethylene nanocomposites (LNT) have shown an increase in modulus, hardness, and viscosity term with an increase in microwave power. The plasticity index has been obtained using the area under the loading and unloading curves. HNT and PNT samples have shown a plasticity index of 0.71 ± 0.02 and 0.62 ± 0.05, respectively. However, LNT samples have shown the same plasticity index 0.61 at all three-power ratings.

Ultrason önişlemi uygulanmış mikrodalgada kurutulan zeytin dilimlerinin peleg modeli kullanılarak kuruma ve rehidrasyon kinetikleri

The objective of present research was to determine the ultrasound and microwave mechanisms involved in the improvement of the drying and rehydration of black and green olive slices. Aydın Kaba variety of olive slices in 5 mm diameter were pretreated for 15 min sonication using an ultrasonic bath (32±5 kHz, 420 W). The microwave drying was conducted at 3 different power level for each sample (180, 450 and 800 W). The Peleg model was used to investigate the drying and rehydration kinetics of olive slice samples. The color properties (L*, a*, b*, C and H°) of olive slices were also evaluated in microwave dried samples. The L values of olives increased from 45.36 to 50.05 and from 38.69 to 39.80 for green olive slices and black olive slices, respectively after microwave drying at 180 W and 800 W. An increase was observed for a* and b* values from 0.71 to 0.99 and from 4.37 to 5.11 in black olive slices. While the K1 constant decreased with the increase in microwave power in both type olives in drying process, the K2 constants in the drying of black olive slices and green olive slices increased from 0.56855 to 0.84379 and from 0.68680 to 0.77682, respectively. It was concluded that ultrasound pretreatment improves the both rehydration process and quality parameters of olive slices.

Monitoring the oxidation state evolution of unsaturated fatty acids in four microwave-treated edible oils by low-field nuclear magnetic resonance and 1H nuclear magnetic resonance

Edible oils oxidize during microwave heating, which may affect their nutritional value and safety. Exploring the oxidation mechanisms of unsaturated fatty acids in edible oils to determine which are suitable for microwave heating is therefore important. We used GC-MS, low-field NMR, and 1H NMR techniques to study functional-group oxidation, the unsaturated fatty acid change law, and the distribution and migration of protons in various functional groups of four common vegetable cooking oils during microwave treatment. We show that the acid values of sunflower, soybean, peanut, and corn oil increased by 14%, 31%, 36%, and 101%, respectively, while the concentrations of malondialdehyde increased by 115%, 664%, 158%, and 333%, respectively, and the peroxide value fluctuated with increasing microwave power. The C16:0 concentrations of all four edible oils increased by more than 50%, and the concentration of polyunsaturated fatty acids decreased by more than 30% during microwave treatment; hence sunflower oil is the most suitable of the above-mentioned oils for daily microwave heating. In addition, we recommend the use of three characteristic functional groups to monitor the oxidative changes undergone by oils: olefinic H (CH = CH), diallyl CH2 (CH = CH–CH2–CH = CH), and allyl CH2 (CH = CH–CH2).

Microwave intermittent drying characteristics of camellia oleifera seeds

AbstractThis paper reports on an experimental investigation of the drying characteristics and kinetics of camellia oleifera seeds under microwave intermittent drying conditions. The effects of key parameters such as microwave power, heating time, and the length of the intermittent time are discussed in detail. The energy consumption in the drying process along with the main quality parameters of camellia oil, namely the peroxide and acid values, have also been determined and compared with hot‐air drying. Results show that the microwave drying curve consists of an acceleration rate period, a constant rate period and a falling rate period. As the microwave power and heating time increase, the drying time decreases. While as the length of the intermittent time increases, the drying time increases. The hot‐air drying time was found to be much longer than microwave drying time, and the energy consumed during hot‐air drying was also several hundred times higher than that used during microwave intermittent drying. The acid and peroxide values of camellia oil after hot‐air and microwave drying were both within the allowable range in the National Standard of China. The Midilli and Kucuk model was the best model to describe the kinetics of the drying process.Practical applicationsDrying is the first step in the processing of camellia oleifera seeds, which not only affects the storage of camellia oleifera seeds, but also affects the quality of camellia oil, and has thus become a research hotspot in recent years. However, several disadvantages of hot‐air drying have been identified like the slowness of the drying process and the relatively large energy consumption. Therefore, finding a drying method that is more suitable is necessary. Microwave intermittent drying is a type of discontinuous drying. The moisture and temperature inside the material can be evenly redistributed during the intermittent time, so that the material is not overheated. This feature of preserving the quality of the products to be dried has made microwave intermittent drying attractive and has been successfully applied to agricultural, forestry, and food products.

Decomposition reaction of phosphate rock under the action of microwave plasma* *Project supported by the National Natural Science Foundation of China (Grant No. 21076131).

The decomposition reaction of phosphate rock under the action of microwave plasma was investigated. Phosphate rock and its decomposition products were characterized by x-ray diffraction (XRD), energy disperse spectroscopy (EDS), and chemical analysis. The measurements of electron temperature (T e) and electron density (N e) of plasma plume under atmospheric pressure were carried out using optical emission spectroscopy(OES). The electron temperature (T e) was determined based on the calculation of the relative intensity of the O II (301.91 nm) and O II (347.49 nm) spectral lines. Correspondingly, electron densities were obtained using the Saha ionization equation which was based on the C I (247.86 nm) line and the C II (296.62 nm) line under the assumption of local thermodynamic equilibrium (LTE). The relationship between the relative intensity of the active components and the gas output was studied by the spectrometer. Finally the reaction mechanism of the decomposition of the phosphate rock under the action of the atmospheric pressure microwave plasma was proposed. The results showed that with the increase of CO flow and microwave power, the electron temperature and electron density in the plasma show a decreasing and increasing trend. The CO is dissociated into gaseous carbon ions under the action of microwave plasma, and the presence of gaseous carbon ions promotes the decomposition of the phosphate rock.

Functional group changes and chemical bond-dependent dielectric properties of lotus seed flour with microwave vacuum drying.

Microwave vacuum drying (MVD) was applied to dehydrate lotus (Nelumbo nucifera Gaertn.) seeds. This paper evaluated the changes of molecular, crystalline, and morphological structural properties of lotus seeds after MVD. The results showed the frequency of δ(CH) bending, β(CH), ν(OH), and carbon-oxygen double bonds (C = O) increased with increasing microwave power density. Moreover, as microwave power density increased, the transition enthalpy of crystallinity gradually increased, which was related to the formation of crystalline starch, re-crystallization, and complexes of starch-lipid structure depending on the hydrogen bonds formed. The MVD process resulted molecular polarity of lotus seeds, whereas the dielectric properties also changed. The dielectric properties interacted with the changes of molecules and crystalline structure. The morphology of lotus seed flour changed because the shape of starch granules was disrupted and the granules became aggregated with nonstarch components as the microwave power density increased. All these results explain the interactions among polymer molecules in lotus seeds dried by MVD.