Microwave Drying Process Research Articles

Comparison of the performance of a modified temperature-controlled microwave dryer to improve heat-mass transfer, increase energy efficiency and preserve quality characteristics of shad (Alosa fallax nilotica)

In this study, shad (Alosa fallax nilotica) was dried in microwave (360, 720 W), developed heat controlled microwave (50, 70 °C), hybrid microwave (350 W + 50 °C, 350 W + 70 °C) dryers. Drying time, drying rate-rate, effective diffusion, color, hardness, energy consumption (SMER, SEC), exergy energy, energy efficiency, heat-mass transfer value of the drying processes were investigated. The shortest drying process was determined as 450 seconds at 720 W power, while the longest was 414minutes at 50 °C. Effective diffusion values calculated for microwave, temperature controlled microwave and hybrid drying processes are 1.32–9.43 × 10−8 m2/s, 2.43 × 10−8-2.41 × 10−7 m2/s and 8.52 × 10−7-2.76 × 10−6 m2/s, respectively. Has changed between It has been determined that the most suitable drying method in terms of total energy consumption and energy efficiency values is the drying process performed in a temperature-controlled microwave dryer. Exin and Exout values of the temperature-controlled microwave drying process were calculated to vary between 2.20 and 5.16 J/s and 1.82–4.68 J/s, respectively. Exin and Exout values of the hybrid drying process were calculated to vary between 1.94 and 4.84 J/s and 1.70–4.68 J/s, respectively. The heat transfer values calculated for the temperature-controlled drying process varied between 0.104 and 0.00269 W/m2K and the heat transfer values calculated for the hybrid drying process ranged between 0.100 and 0.00270 W/m2K. It was determined that the most suitable drying processes for color characteristics were 360 W and 350 W + 50 °C. For the hardness value, it was determined that the 350 W + 70 °C drying process was statistically more appropriate (P < 0.05).

Microwave drying process and mechanism analysis of viscous germanium-containing residue

Tannin germanium residue (TGR), which has high viscosity and water content, is one of the most important germanium-containing enrichments in the germanium extraction process. In this study, the microwave drying process of a TGR was studied using a high-temperature dielectric testing device, combined with a thermal drying analysis method and response surface methodology (RSM). The experimental results indicated that the water in TGR consisted of free water, crystalline water, and structural water. Owing to the excellent dielectric properties of water in TGR, microwave drying can save 91.7% of the drying time compared to the conventional method. Under the optimal microwave drying conditions, the dehydration rate of TGR was 40.3%. Microwave drying is advantageous in increasing the specific surface area of the TGR particles by 50.75% and pore volume by 160.42%.

Estimating the Moisture Ratio Model of Cantaloupe Slices by Maximum Likelihood Principle-Based Algorithms.

As an agricultural plant, the cantaloupe contains rich nutrition and high moisture content. In this paper, the estimation problem of the moisture ratio model during a cantaloupe microwave drying process was considered. First of all, an image processing-based cantaloupe drying system was designed and the expression of the moisture ratio with regard to the shrinkage was built. Secondly, a maximum likelihood principle-based iterative evolution (MLP-IE) algorithm was put forward to estimate the moisture ratio model. After that, aiming at enhancing the model fitting ability of the MLP-IE algorithm, a maximum likelihood principle-based improved iterative evolution (MLP-I-IE) algorithm was proposed by designing the improved mutation strategy, the improved scaling factor, and the improved crossover rate. Finally, the MLP-IE algorithm and MLP-I-IE algorithm were applied for estimating the moisture ratio model of cantaloupe slices. The results showed that both the MLP-IE algorithm and MLP-I-IE algorithm were effective and that the MLP-I-IE algorithm performed better than the MLP-IE algorithm in model estimation and validation.

Microwave Drying Kinetics of Chromium-Rich Electroplating Sludge

Chromium-rich electroplating sludge (CRES) is a hazardous solid waste with a high content of moisture requiring efficient drying before subsequent treatment. In this study, the microwave drying kinetics of CRES were examined. The results showed that CRES had good microwave absorptivity, contributing to a much shorter drying time and better drying performance compared with conventional drying. In comparison with conventional drying at 105 °C, the time of microwave drying at 600 W for total moisture removal was reduced by 98.5%. Compared to load mass and particle size, microwave power played a more important role in microwave drying. Based on the kinetics analysis, the microwave drying process of CRES could be divided into three successive stages, in which the drying rates were limited by external diffusion (before 110 s), both external diffusion and chemical reaction (between 110 s and 160 s), and chemical reaction (after 160 s), respectively. The Danish model was found to have the best fit with the microwave drying process of CRES.

Analysis of heat and moisture transfer in the microwave drying of potatoes

In order to gain a deeper knowledge of the heat and mass transfer processes in the case of starchy fruits and vegetables during microwave drying, we have conducted an experimental study based on a developed microwave apparatus for drying potato. The changes in the temperature, drying rate, moisture content, thermal parameters, moisture state and distribution of the potatoes samples during the microwave drying process were obtained. The results show that, according to the temperature changes of the samples dried at different microwave powers (600 W, 800 W, 1000 W), the microwave drying process can be divided into three stages: heating stage, constant temperature stage, and cooling stage. The moisture content reduction of the samples in the constant temperature stage accounted for more than 90% of the total reduction. Meanwhile, as the microwave drying process goes by, the thermal conductivity and thermal diffusivity of the samples both decrease first and then increase, while the volumetric heat capacity presents an opposite trend. Moreover, the range and amplitude of transverse relaxation time of the samples reduce over the drying time, which confirms the existence of massive, outward moisture-migration in the dried samples. The loss of the weakly bound water in the moisture-migration, which is closely related to the starch, has a significant effect on the heat and mass transfer in the dried samples.

Changes and relationships of viscoelastic and physical properties of Chinese yam during a novel multiphase microwave drying process

Changes in viscoelastic properties and physical qualities including rehydration ratio (RR), volume ratio (Vr), porosity and texture of Chinese yams during multiphase microwave drying (MMD) were studied and the intrinsic relationship between them was analyzed. Results showed that RR, Vr and porosity rose and then fell with drying time during MMD, with the endpoint of sublimation drying being the turning point. Scheme III with the highest microwave power (0.2 W/g) in sublimation drying resulted in the lowest RR, Vr and porosity but the highest hardness. The Maxwell model was well fitted to describe the viscoelastic behaviors of yams (R2 > 0.99). Enhanced stress relaxation behavior during sublimation drying was observed. In contrast, a decrease in stress decay but an increase in residual elasticity were found when MMD switched from sublimation drying to evaporation drying. Pearson's correlation analysis showed that relaxation modulus was significantly negatively correlated with RR (r = −0.981, p < 0.01) and porosity (r = −0.961), while positively correlated with hardness (r = 0.94, p < 0.05) and the brittleness (r = 0.96, p < 0.01). Principal component regression models between the viscoelastic indexes and physical features with high R2 (>0.9) values could explain their relationships well. These findings have implications for the production of high-quality products through controlling drying processes.

Determination of the Effect of Different Drying Methods on the Physicochemical Properties of Potato Powder Using Multivariate Analysis

In this study, powder was obtained from yellow and purple-fleshed potatoes by microwave and hot air drying and the effects of drying methods on the total phenolic compounds, total monomeric anthocyanin, color, antioxidant activity, starch ratio and vitamin C on were determined. It was observed that the microwave drying process caused an increase in bioactive components in purple-colored powder samples, and no significant differences were determined in terms of drying methods in bioactive components in yellow-colored powder samples. When the starch ratio of the samples was examined, it was determined that hot air drying caused a significant increase. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used as multivariate analysis to reveal the effects of different drying techniques and potato varieties on the physicochemical properties of potato powders. As a result, it was found that the physicochemical properties of potato powders differentiated depending on the methods and varieties.

Understanding the heating characteristics in microwave heating moving and deforming foods by a hybrid double-layer ALE/implicit algorithm

Multiphysics modeling is an essential tool to understand the heating characteristics of microwave processing food products. However, when the heated sample is moving and deforming during the heating process (e.g. the long-term microwave drying process), the huge mesh distortions caused by the sample's motion and deformation will make the simulation impossible. To solve this problem, a hybrid double-layer Arbitrary-Lagrange-Eulerian (ALE)/implicit algorithm is proposed in this paper, where the sample's motion and deformation is tracked by a double-layer ALE framework and convert to time-varying implicit variables. By doing so, the influence of the sample motion and deformation on the electromagnetic field distribution will be characterized by the evolution of time-varying implicit variables, rather than by explicit modeling, which reduces the mesh distortion and makes the calculation possible. A two-dimensional and a three-dimensional model of microwave cavities containing a rotating and deforming food are given to describe the algorithm in detail. Experiments for the three-dimensional model are also conducted to validate the proposed method. Results show that the shrinkage of the food may have a negative impact on the heating performance (especially energy efficiency) and corresponding remedies need to be performed for long-term microwave heating processes.

Convective and microwave drying kinetics and modeling of tomato slices, energy consumption, and efficiency

AbstractThis investigation presented presents the drying characteristics, and aimed to predict the drying kinetics of tomato slices (Lycopersicon esculentum MILL.) using convection and microwave methods. Hot air drying was carried out in a ventilated oven at 50, 60, 80, and 100°C temperatures and microwave drying was performed in domestic microwave using 300, 500, 800, and 900 W powers. Twenty‐two mathematical models were undertaken to predict the drying kinetics and the best model was chosen based on the highest R2 values and the lowest root mean square error (RMSE) and χ2 values. Drying kinetics, drying rate variation, diffusivity and energy consumption of both methods were evaluated. Fernando and Amarasinghe model and Sledz model were the best models for convective and microwave drying processes, respectively. Effective moisture diffusivity varied from 0.28 × 10−9 to 2.81 × 10−9 and from 1.32 × 10−9 to 21.52 × 10−9, while the activation energy was 27.64 kJ/mol and 5.71 W/g for convective and microwave drying processes, respectively. The energy consumption increases with increasing temperature or power, the reverse was observed for energy efficiency. Microwave drying process has the advantage of drying time reduction, low‐energy consumption, and high‐drying efficiency at a moderate high‐power level (900 W). Hence, it is recommended to apply this innovative process for drying tomato slices.

Drying characteristics of ammonium polyvanadate under microwave heating based on a thin-layer drying kinetics fitting model

The dried ammonium polyvanadate (APV) can be used to produce high-purity Vanadium pentoxide (V2O5) by calcination. Therefore, drying is a necessary process. The advantages of microwave drying are uniform heating, selective heating, high heating efficiency and the operation process is clean and hygienic. This study uses a microwave to dry APV and discusses the effect of the initial mass, microwave power, initial moisture content on the drying efficiency of APV. The results display that the average drying rate is positively correlated with the microwave output power. When the initial mass is 35 g, the average rate is shown as 0.000263%/s. As the initial moisture content and power of APV increases to 25% and 560W, the average drying rate increases to 0.00036231%/s and 0.003125%/s, respectively. At the same time, through the analysis of APV drying kinetics and the fitting of experimental data, it is found that the APV microwave drying process can be precisely described by the Modified Page model. The microwave heating process saves energy and time, directly penetrates the product, and has certain advantages in green metallurgy.

Tomography-assisted control for the microwave drying process of polymer foams

This paper presents the integration of electrical capacitance tomography (ECT) with a moisture controller for the microwave drying of polymer foam. The proportional–integral (PI) control and the linear quadratic Gaussian (LQG) control are employed in designing the controller. The control objective in this process is that the moisture of polymer foam after the drying process reaches the desired set point. The permittivity distribution of polymer foam after the drying process is estimated in real-time using a designed ECT sensor and transferred as feedback to the controller. Since the permittivity and the moisture are strongly correlated, the material moisture can be controlled by controlling the permittivity. A state-space model is derived for the microwave drying process based on a system identification approach using the experimental data from the process. The derived model is employed in designing the LQG controller and adjusting the parameters of the PI controller. The designed controllers are implemented on a testbed microwave oven, and the experimental results show that the designed controllers are able to follow the desired set point moisture. The performance of the system with both controllers is compared, and their advantages and disadvantages are discussed. Moreover, the benefits of having a moisture controller for the microwave drying process are shown in simulation studies compared to an uncontrolled system.

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.

Mechanism of the foaming agent‐assisted microwave drying process on the construction of natural raw rubber network and cross‐linking network

AbstractThe drying process of natural rubber latex significantly affects the structure of the raw rubber network and vulcanizate crosslinking network, resulting in various anti‐aging performances. In the present study, a microwave generator was used as an efficient source of clean energy; potassium oleate was introduced as a foaming agent to increase the porosity and water loss channel of the latex system. Aiming at dehydrating and drying natural rubber latex efficiently, an aging resistant rubber composite was prepared. Meanwhile, the mechanism of the foaming agent‐assisted microwave drying process on the raw rubber network and the cross‐linking network was studied. The experimental results show that the prepared rubber using by this process has higher plastic retention and fluidity. Moreover, it contains more non‐rubber components (e.g. protein and acetone extract) and better network structure of raw rubber and vulcanized rubber. It is found that applying this process increases the tensile product by 13.5% and the retention rate of the tensile product after aging by 15.3 times. This process is important for the development of the rubber industry in the direction of green environmental protection, energy conservation, and high efficiency.

An experimental study probing moisture kinetics and indices of microwave dried fecal sludge with an insight on real world applications

ABSTRACT The ever-increasing population rate, followed by resource deficiency, has made innovations crucial in sanitation. The deteriorating hygiene, particularly in the population’s low strata, is of great concern in most developing countries. As the current fecal sludge management system is linear, it needs to be transformed into a closed-loop circular system like any other waste management system. This study examines the potential of using microwaves to dry feces before transporting and reduce the spread of disease. The microwave output power; sample load; feces-urine composition, were adjusted between 100 and 300 W; 20 and 40 g; and 10% and 90% respectively. Drying kinetics were determined using empirical drying data modeling and the standard error analysis was used to select the best model. Under a range of experimental conditions, the effective moisture diffusivity of drying was determined to be on the order of 10−9, and the effect of process parameters on the effective moisture diffusivity was investigated. Furthermore, thorough tests were performed to determine the microwave drying process’ efficiency and energy consumption (6.782 MJ.kg−1 to 29.268 MJ.kg−1), determining its feasibility for large-scale deployment as a fecal sludge pretreatment method. This study provides a solution for modern sanitation by successfully closing the nutrient loop.

Effect of temperature on the microwave drying process and the viability of amaranth seeds

In this work, the microwave drying of amaranth seeds at different temperatures has been studied. The main objective of this study is to evaluate the effect of temperature on three key variables of the drying process and viability of amaranth seeds (drying time, energy consumption, and germination rate) after drying with microwave energy. The tests were performed in a domestic microwave oven, modified for research use, at six drying temperatures (between 35 and 60 °C). For comparative purposes, the amaranth seeds were dried by forced convection of hot air in an electric oven. It was observed that an increase in the drying temperature causes a simultaneous decrease in drying time (from 378 to 126 min) and in the energy consumption (from 9.07 to 2.61 Wh g −1 , and from 412.6 to 111.7 MJ kg −1 [H 2 O]) and cost (from $0.065 to 0.019 USD) required to dry the seeds. However, there is also an unacceptable decrease (from ∼85% up to 23%) in the germination rate of the seeds with the drying temperature. In order to ensure the amaranth seeds’ viability after the drying process, it is necessary to employ lower drying temperatures-i.e., between 35 and 40 °C. Moreover, drying of amaranth seeds with microwave energy at 40 °C proved to be a faster and more effective method than convective drying by reducing drying time by 22% (from 336 min to 261 min) and energy consumption by 74% (from 928.4 to 274.0 MJ kg −1 [H 2 O]) without significantly affecting their viability. • Microwave drying of amaranth seeds at different temperatures has been studied. • Temperature exerts a significant influence on the process and seeds' viability. • Higher temperatures favor the drying process but significantly impair the viability. • Microwave drying is a faster and more efficient method than convective drying. • Microwave drying, at controlled temperature, could be a viable alternative.

Influence of blanching-freezing pre-treatment on moisture removal characteristics of microwave-dried potatoes

The aim of present work was mainly to study the influence of blanching-freezing pre-treatment on moisture removal characteristics of potato during microwave drying process. The influence of microwave power and the samples thickness was also assessed. For this purpose, microwave powers of 100, 350 and 550 W were practiced to dry discoid shape samples of fresh and blanched-frozen potatoes with a constant diameter of 20 mm and different thicknesses of 5, 10 and 15 mm. The obtained results revealed that time required to dehydrate treated potatoes was significantly (P < 0.05) shorter than the fresh ones. The moisture diffusivity of the fresh and blanched-frozen potatoes was determined to be in the range of 9.13 × 10−9‒7.93 × 10−8 and 9.89 × 10−9‒9.36 × 10−8 m2 s−1, respectively where enhanced with the both increasing power level and samples thickness. The average energy required to instigate water diffusion inside the treated samples with 5, 10 and 15 mm thickness was obtained to be 0.463, 0.379 and 0.331 W g−1, respectively while the values for fresh samples were 0.505, 0.466 and 0.413 W g−1, respectively.

Fuzzy logic control of relative humidity in microwave drying of hawthorn

Previous studies showed that a saturated moisture could protect food materials from quality degradation during drying processes. To further interpret this phenomenon, a microwave drying system with online relative humidity measurement and intelligent control was built. With this system, the impact of relative humidity on the drying speed and product quality in microwave drying was investigated in this study. Constant temperature drying at 50 °C, 60 °C, 70 °C without relative humidity control were first tested and 60 °C was selected as the best drying temperature. Based on this temperature, four fixed relative humidity (5%, 30%, 50%, 70%) were attempted in four different drying processes, respectively. It was found that the middle relative humidity of 30% and 50% resulted in a better product quality. In contrast, a lower and a higher relative humidity degraded the product quality or slowed down the drying speed. A fuzzy logic controller was further designed to automatically adjust the relative humidity in microwave drying process in order to improve the drying effects. By carefully constructing the fuzzy rules and algorithms, an optimal product quality was achieved, while drying speed was also accelerated. Finally, a linear control method was designed to simulate the fuzzy logic control for convenient industrial application. The vitamin C content, hardness, water activity, rehydration rate, color difference, and sensory assessment were analyzed and compared for the final products. The developed methodology has the potential to be extended to other drying methods and various food materials, with readjustment of the fuzzy logic control parameters.

System Identification of Conveyor Belt Microwave Drying Process of Polymer Foams Using Electrical Capacitance Tomography.

The microwave drying process has a wide application in industry, including drying polymer foams after the impregnation process for sealings in the construction industry. The objective of the drying process is to reach a certain moisture in the foam by adjusting the power levels of the microwave sources. A moisture controller can be designed to achieve this goal; however, a process model is required to design model-based controllers. Since complex physics governs the microwave drying process, system identification tools are employed in this paper to exploit the process input and output information and find a simplified yet accurate model of the process. The moisture content of the foam that is the process output is measured using a designed electrical capacitance tomography (ECT) sensor. The ECT sensor estimates the 2D permittivity distribution of moving foams, which correlates with the foam moisture. Experiments are conducted to collect the ECT measurements while giving different inputs to the microwave sources. A state-space model is estimated using one of the collected datasets and is validated using the other datasets. The comparison between the model response and the actual measurements shows that the model is accurate enough to design a controller for the microwave drying process.

System Identification of Conveyor Belt Microwave Drying Process of Polymer Foams Using Electrical Capacitance Tomography

System Identification of Conveyor Belt Microwave Drying Process of Polymer Foams Using Electrical Capacitance Tomography

Quality formation of germination brown rice under microwave drying: from GABA content to color value

In order to improve the final quality of germination brown rice (GBR), the changes of GBR in Gamma-aminobutyric acid (GABA) and color are investigated under microwave drying conditions. Results indicate that Microwave drying process may improve GABA in GBR due to microwave volumetric heating inducing the glutamic acid decarboxylase (GAD) activity; and the dried GBR with golden appearance under the microwave intensity of 2.75 W/g and the apparent velocity of 2.50 m/s considering the drying efficiency and quality of dried GBR. In this study, microwave drying conditions not only improve the drying efficiency of GBR, but also improve the appearance and color of GBR after drying, reduce GABA degradation and control the generation of burst rate.