Microwave Drying Characteristics Research Articles

The Research on Microwave Drying Characteristics of Polyethylene Terephthalate Materials Based on Frequency and Power Tuning Technology

Polyethylene Terephthalate (PET), renowned for its exceptional physical and chemical properties, finds widespread use in our daily lives. However, conventional PET drying methods are time consuming and energy intensive. Leveraging microwave heating effects, we investigated drying characteristics concerning both microwave parameters and PET permittivity. The PET permittivity variation during heating is related to the microwave reflection at the incident port. Our innovative approach involves frequency and power tuning based on reflection. This method not only significantly improved heating uniformity and reduced temperature covariance (COVT) but also led to a more uniformly distributed temperature profile and a drastic reduction in energy consumption. Integrating precise and rapid frequency tuning, we compared our method’s efficiency with traditional approaches, revealing an impressive time savings of 2 h and an energy consumption limited to approximately less than 3 kWh/kg. Notably, our laboratory system’s logistic models of the Moisture Ratio (MR) related to rotary rates, masses, and powers whose averages of R-square are 0.9972, 0.9982, and 0.9977, respectively, which provide intriguing insights for industrial production forecasts during variable frequency PET drying.

Experimental Study on Microwave Drying Characteristics of Granite Slabs

Granite slabs are a significant building material, which is widely used in the construction field. An important process in granite slab processing is drying treatment. Currently traditional drying methods such as natural drying and hot air drying have inherent drawbacks such as high energy consumption and low efficiency, which pose higher requirements for drying processes. Herein, a kinetic model of microwave drying for characterizing the variation rule of moisture content in the drying process of granite sheets is established. The effects of microwave power and plate thickness on the drying characteristics of granite slabs are studied through a large number of comparative experiments. On this basis, the variation rule of granite slab moisture ratio during the drying process is further obtained. Experimental results show that microwave drying of granite mainly includes accelerated drying and reduced drying stages, which are consistent with the predicted results of the model. These excellent results prove the effectiveness of the proposed model in this article.

Experimental studies for thin layer model validation and microwave drying characteristics of beetroot considering energy optimization

The drying kinetics of Beetroot was studied experimentally, followed by mathematical modeling. This work reveals the effect of input electrical power at 300, 600, and 800 W on the drying kinetics of Beetroot. The thin layer drying behavior of beetroot specimens was studied by employing seven distinct mathematical models. The models studied were contrasted between experimental and simulated moisture ratios based on their correlation coefficient and root mean square error values. The results indicate the page model as the best-suited model with values of correlation coefficient from 0.9881 to 0.9944 and root mean square error values from 0.0213 to 0.043 to define the thin layer beetroot drying behavior. The drying time was significantly reduced by about 400 s by raising the microwave output power by 500 W, i.e., from 300 W to 800 W. The drying process was noted to occur mainly during the falling rate period. The average moisture diffusivity varied between 1.78 × 10−8 and 4.38 × 10−7 m2/sec, whereas the values of activation energies determined were 69.99, 90.87, and 50.82 W/g for the cube, slab, and disc samples, respectively. The energy consumption and specific energies decreased with an increase in microwave power during drying. It was estimated that their values were in the range of 108–324 kJ and 16.57–49.54 MJ/kg water, respectively. Further, moisture diffusivities decreased with decreasing microwave power.

Microwave drying characteristics and quality of Ananas comosus peel, core and pulp

Microwave drying characteristics and quality of Ananas comosus peel, core and pulp

Modeling of process and analysis of drying characteristics for natural TiO2 under microwave heating

In this paper, factors affecting the microwave drying characteristics of rutile TiO2 were discussed, and the data were fitted with nine common thin layers drying kinetic models. The results demonstrate that the drying efficiency of rutile TiO2 shows a positive relationship with microwave power. With a microwave power increase from 320W to 640W, the drying time is shortened by 35.7%. The microwave drying efficiency presents a positive relationship with initial moisture content. With a moisture content increase from 2% to 12%, the average drying rate increased from 0.009%·s−1 to 0.054%·s−1. Additionally, the microwave drying efficiency is positively correlated with the initial mass when the initial mass is below 45 g. Otherwise, the microwave drying efficiency is negatively correlated with the initial mass. Besides, kinetic models were used to understand the microwave drying process of nature rutile TiO2. The results show that the Modified Page model agrees well with the experimental data, and the fitting parameters are consistent with the law of matching degree. The demonstration of microwave drying techniques can be applied effectively and efficiently to the treatment processing of drying of the raw materials of metallurgy and chemical industry with the theoretical and scientific basis.

Intermittent Microwave Drying Characteristics and Quality Changes of Xilin Fire Ginger Slices

Intermittent Microwave Drying Characteristics and Quality Changes of Xilin Fire Ginger Slices

Microwave Drying Characteristics and Drying Quality Analysis of Corn in China

To identify the microwave drying characteristics of corn, microwave drying tests were conducted on corn. By taking the moisture content, drying rate, and drying temperature as indices, this research revealed the effects of different microwave powers and loads on the microwave drying characteristics of corn. Moreover, energy consumption and quality of dried corn were analysed under different drying conditions. The results demonstrate that microwave drying has significant energy-saving effects. The energy consumption by microwave drying is less than 0.3 times that used by electrothermal drying under the same load. Both microwave power and load exert significant influences on drying characteristics. Higher microwave power results in a greater average drying rate, wherein shorter periods of time are required to reach the maximum drying rate and higher temperatures of the corn. However, the load shows the opposite tendency. The smaller the load, the higher the temperature of the corn in the early stage of drying. However, as drying continues, the temperature curve changes significantly, and the temperature rises with the increase in load in the later stage of drying. In consideration of energy consumption and dried quality, the load of corn should be increased as appropriate, and the microwave intensity should be limited to no higher than 0.7 W/g in the experiment.

Microwave upgradation of Yunnan lignite: dielectric properties, drying pattern and kinetics

The work attempts to investigate the dielectric properties and microwave drying characteristics of Yunnan lignite, so as to upgrade it. The effect of drying temperature, moisture content and microwave heating frequency on dielectric properties was measured using resonant cavity method. Results indicate that both the values of ε′ and ε″ presented two stage at the investigated temperatures. Bulk water was found to be the main factor contributing to an increase in the ε′ and ε″. Microwave drying kinetics of lignite were carried out. The Page model was the best model reflecting the drying kinetics, and the effective diffusion coefficient and active energy at different drying stages were obtained. In addition, the microwave drying mechanism has been proposed based on the study of dielectric and drying properties of lignite. The SEM images indicated that microchannels were formed within the lignite particle by the microwave pumping effect. FT-IR spectra showed that the oxygen-containing functional groups and hydrogen bonds between them were break by microwave drying. Based on the achieved results, the microwave treatment at 150 °C is helpful to upgrade the lignite.

Mathematical Modeling and Drying Characteristics Investigation of Black Mulberry Dried by Microwave Method

ABSTRACT In this study, microwave drying characteristics of black mulberry were studied at microwave power levels of 90, 180 and 360 W. Obtained experimental drying results were applied to seven mathematical models of Aghbashlo et al., Henderson and Pabis, Jena and Das, Logaritmic, Midilli and Kucuk, Page and Weibull. The best model was selected as Midilli and Kucuk based on the highest coefficient of determination (R2) (0.994861–90 W, 0.999824–180 W, 0.998747–360 W) and the lowest χ2 (0.000575–90 W, 0.000027–180 W, 0.000255–360 W) and Root Mean Square Error (RMSE) (0.022427–90 W, 0.004275–180 W, 0.011899–360 W) values compared to other models. According to drying times, the best drying condition was seen on 360 W power. The effective moisture diffusivity (Deff ) values were calculated using the Fick’s second law’s spherical coordinate approximation and were found between 4.79 × 10−8 and 2.60 × 10−7 m2/s. The activation energy (Ea ) was calculated using modified form of Arrhenius equation and found as 13.15 kW/kg.

Modeling and kinetics study of microwave heat drying of low grade manganese ore

During the industrial-scale smelting process of manganese ore, blast may occur due to the high moisture content of the ore, and drying pretreatment of the manganese ore is needed in the aspects of safety. In the present paper, microwave drying experiments were conducted under different particle size distributions and different microwave power conditions to explore the basic theory of microwave drying characteristics and kinetics of manganese ore, and the experimental data were fitted and analyzed by using thin-layer drying dynamics model. Results indicated that with the increase of the particle size and the microwave power of the manganese ore, the microwave drying rate increased, and accompanied with a promoting on the drying efficiency. For describing the microwave drying process of manganese ore, diffusion approach model was adopted among the commonly used thin-layer drying kinetic models. Based on Fick's second law, it can be seen that the surface diffusion coefficient increased from 4.27 × 10−13 m2/s to 8.24 × 10−8 m2/s with the increase of particle size from a particle size range of 0.012–0.095 mm to a particle size range of 4.2–5.0 mm. Clearly, the particle size has a significant influence on microwave drying efficiency.

Convective air, microwave, and combined drying of potato pre-treated by pulsed electric fields

The effects of pulsed electric field (PEF) treatment on drying of potato have been investigated. The convective air (CA) (T = 50 °C), microwave (MW), and combined (CA + MW or MW + CA) drying was applied. The drying curves, progression of temperature inside samples, microstructure, and capillary imbibition capacity of untreated (U) and PEF treated samples were compared. The PEF treatment noticeably affected the CA and MW drying characteristics and structure of dried samples. It reflected impact of electroporation on the heat and mass transfer processes during the different drying periods. The different progressions of temperatures inside U and PEF samples for the MW mode of drying were revealed. The highest and smallest rehydrations were observed for the U samples for individual CA and MW modes of drying, respectively. The observed behavior was explained accounting for the absence of starch gelatinization for the CA mode of drying and presence of it for the MW mode of drying.

Convective and microwave drying characteristics, energy requirement and color retention of dehydrated nettle leaves (Urtica diocia L.)

In this research, convective and microwave drying characteristics, energy requirement and color changes of nettle leaves (Urtica diocia L.) were reported. Samples of freshly harvested nettle leaves were dehydrated under three air temperatures of 50 °C, 60 °C and 70 °C and at three microwave power levels of PL-1, PL-2 and PL-3. Selected drying air velocity was 0.30 m/s for all temperatures. This is coming from the fact that it was understood from the preliminary studies that the temperature less than 50 °C and the air speed more than 0.30 ms-1 increase the drying time and energy requirement, extremely for these products. Nettle leaves were dehydrated from the initial moisture content of 320 (percentage dry basis) to a final moisture content of 7 % to 9 %. During convective drying experiments, product were weighted automatically by the balance per (5 to10) min. Data were transferred to the computer and processed by a software. During microwave drying, the product were weighted and data recorded manually per (15 to 60) min. The influence of drying method, drying air temperature and microwave power level have also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference (DE) on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for nettle leaves. The minimum specific energy requirement were determined as 6.95 kWhkg-1 and 23.63 kWhkg-1 for 70 °C and PL-2 respectively. 70 °C drying air temperature and PL-3 was found to yield better quality product in terms of color retention of Hunter L, a, b and DE. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.

Vacuum-assisted microwave drying characteristics of green bell pepper

Chopped green bell pepper pieces were blanched (95 °C, 5 min) and chemically pretreated (1% potassium metabisulphite solution, 25 min at room temperature) before drying in hot air dryer (HAD) at various temperature ranges (60 – 80 °C). Three vacuum levels (200, 400, 600 mm Hg) and microwave power levels (100, 200, 300 W) were also used to dry green bell pepper samples in a vacuum assisted microwave (VAM) (2.45 GHz, 0.8 kW) dryer. VAM drying methods offered a maximum reduction by four to five times in drying time as compared to that in HAD. The logarithmic model was found to have the best fit based on high R 2 and small values of reduced χ 2 and RMSE. VAM method has higher values for effective moisture diffusivity (D eff ) and lower values for activation energy (E a ), in comparison to the HAD method.

Vacuum-assisted microwave drying characteristics of green bell pepper

Chopped green bell pepper pieces were blanched (95 °C, 5 min) and chemically pretreated (1% potassium metabisulphite solution, 25 min at room temperature) before drying in hot air dryer (HAD) at various temperature ranges (60 – 80 °C). Three vacuum levels (200, 400, 600 mm Hg) and microwave power levels (100, 200, 300 W) were also used to dry green bell pepper samples in a vacuum assisted microwave (VAM) (2.45 GHz, 0.8 kW) dryer. VAM drying methods offered a maximum reduction by four to five times in drying time as compared to that in HAD. The logarithmic model was found to have the best fit based on high R2 and small values of reduced χ2 and RMSE. VAM method has higher values for effective moisture diffusivity (Deff) and lower values for activation energy (Ea), in comparison to the HAD method.

Microwave Drying Characteristics of Soybeans in Single and Variable Microwave Power Density

Abstract Drying characteristics of soybeans under different microwave (MW) processing schemes were studied in regard to energy aspects. For drying in a single microwave power density, the experiments were carried out at a constant MW output power throughout the process. It was found that the drying rate is enhanced together with reduced energy consumption at higher single power density, but the soybean cracking ratio is increased gradually from 2 % to 40 % when the power density was changed from 0.2 W/g to 0.8 W/g. Efforts were made to reach a compromise between the drying rate and dried soybean quality by varying the MW power density in several steps overall the drying process, but soybean cracking occurred at a higher ratio due to the fluctuation of drying rate. Microwave drying of soybeans under the power density less than 0.2 W/g with slow and stable drying rate can achieve the soybean cracking ratio controlled within 5 % and lower energy consumption.

Evaluation of microwave drying characteristics ofFicus deltoidealeaves by using thin layer drying models

Evaluation of microwave drying characteristics of<i>Ficus deltoidea</i>leaves by using thin layer drying models

Microwave drying characteristics of microalgae (Chlorella vulgaris) for biofuel production

Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of the bottlenecks in the conversion of microalgae to biofuels is the drying process. A moisture content of at most 10 % is desired for algal biomass prior to oil extraction to maximise biofuel yield. Conventional means of drying results to longer drying time and uneven drying of algal biomass. This study investigated the drying characteristics of microwave for microalgae (Chlorella vulgaris). Three microwave intensity levels (300, 600, and 900 W) were considered to dry 10, 20, and 30 of algal mass. Page model gave a better fit on the moisture ratio with time of microwave drying than the exponential model. Furthermore, the specific energy requirement was computed, and a relationship was found between moisture ratio with power and mass. Fourier transform infrared spectroscopy results showed significant reduction of infrared signal intensities of the functional groups present in the algae after drying at higher microwave power level. It was concluded that the 20 W/g microwave drying setting gave a lower specific energy requirement with good quality of remaining high lipid content qualitatively. Furthermore, it was recommended to use gas chromatography mass spectroscopy to further quantify the algal lipids and other functional groups.

Microwave drying kinetics and quality characteristics of corn

In recent years, microwave (MW) drying has gained popularity as an alternative drying method for a wide variety of food and agricultural products because of increasing concerns over product quality and production costs. However, the determination of drying kinetics that accurately describes microwave drying characteristics is crucial for the optimization of operating parameters, performance improvement of the drying system and product quality. The objective of this study was to investigate the drying kinetics and the quality characteristics of corn kernels, especially the effects of different initial moisture contents (18.3%, 26.3%, 34.3% and 42.3% db), MW power levels (70, 175 and 245 W) and exposure time (80 s and 120 s) on the drying kinetics, drying rate and various key quality parameters. The results indicated that the increased drying rate at higher power levels (P3, 245 W) reduced the drying time considerably but increased stress crack index and reduced germination. In addition, it reduced bulk density, true density and thousand grain weight (TGW). The germination rate of corn was the highest at MW power level P1 (70 W), with the lowest drying rate and observed to decrease with increase in initial moisture content. The reduction in exposure time decreased stress crack index and increased germination rate, bulk density and true density. The correlation analysis among drying rate, germination, stress-crack index (SCI), bulk density, true density and TGW showed that increasing drying rate could lead to an increase in SCI and decrease in germination, bulk density and true density.

Study on parameters of freezing combined with microwave drying characteristics of polygonum cuspidatum

Polygonum cuspidatum slices were freezing dried transferred to microwave dried.The transfer point of the two drying methods were studied and validated based on the microstructure.In addition,drying rate and quality of samples with different parameters was studied. Sample quality was compared in terms of medicinal ingredients( polydatin,emodin,physcion,resveratrol),color,volume retention rate,rehydrated ratio. The result showed that quality of samples for 5 mm dried with 40 Pa,heating plate for 40 ℃ and transferred at the moisture content of 25%to microwave at 60 ℃ would be closed to samples dried with freezing drying.In addition,it costs half of drying time as freezing drying.

Convective and Microwave Drying Characteristics of Sorbus Fruits (Sorbus domestica L.)

In this research, convective and microwave drying characteristics, energy requirement and color changes of sorbus fruits (Sorbus domestica L.) were reported. Sorbus fruits were dehydrated in a computer connected parallel air flow type dryer and in a microwave oven dryer. Samples of freshly harvested sorbus fruits were dehydrated under two air temperatures of 50° and 70°C and at three microwave power levels of PL-1, PL-2 and PL-3. Selected drying air velocity was 0.30 m/s for both temperatures. Sorbus fruits were dehydrated from the initial moisture content of 300 (percentage dry basis) to a final moisture content of 8...10%. During convective drying experiments, product were weighted automatically by the balance per 5...10minutes. Data were transferred to the computer and processed by a software. During microwave drying, the product were weighted and data recorded manually per 15...60minutes. The influence of drying method, drying air temperature and microwave power level have also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference (ΔE) on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for sorbus fruits. The minimum specific energy requirement were determined as 0.69 kWh/kg and 37.07 kWh/kg for 70°C and PL-3 respectively. 50° C drying air temperature and PL-1 was found to yield better quality product in terms of color retention of Hunter L, a, b and ΔE. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.