An Empirical Model for the Estimation of Moisture Ratio During Microwave Drying of Plaster of Paris

The drying characteristics of plaster of Paris (POP) under microwave irradiation were studied for different shapes of materials through various drying parameters like microwave power, initial moisture content, and drying time. An empirical model for the estimation of moisture ratio was developed using the drying kinetic data of POP. Further, the experimental data on moisture ratio of POP for different operating conditions were fitted with the nine basic drying model equations. Based on the observations, the constants and coefficients of the literature models were rewritten in the form of Arrhenius and logarithmic expressions considering microwave power as input variable. Fifty-eight new model expressions were derived by changing the constants and coefficients and tested using the present experimental data. From the analysis of RMSE, χ², and EF parameters for the derived models, a suitable empirical model (Model No. 55, RMSE = 0.0874; χ² = 0.0020; EF = 0.9999) was established to represent the present experimental data on microwave drying of POP.     

Optimization of Microwave-Vacuum Drying Parameters of Saskatoon Berries Using Response Surface Methodology

A combined microwave and vacuum system was used to dry the Saskatoon berries (Amelanchier alnifolia). A central composite rotate design and response surface methodology were used to determine the influence of process variables (microwave power, drying time, and fruit load) and arrive at optimal processing conditions to reduce the moisture content and water activity of the berries to a safe level. It is concluded that the yield of moisture content and water activity can be reduced to 20% and 0.50, respectively, for microwave power 5.7–6 kW, drying time 51.5–55 min, and fruit load 10–9.75 kg.     

Microwave Drying Kinetics of Okra

In this work, the effects of power level and sample mass on moisture content, moisture ratio, drying rate, and drying time of Turkey okra (Hibiscus esculenta L.) were investigated using microwave drying technique. Various microwave power levels ranging from to 180 to 900 W were used for drying of 100 g of okra. To investigate the effect of sample mass on drying, the samples in the range of 25 to 100 g were dried at microwave power level of 360 W. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content. Among of the models proposed, Page's model gave a better fit for all drying conditions used. The activation energy for microwave drying of okra was calculated using an exponential expression based on Arrhenius equation and was found to be 5.54 W/g.     

A Small-Scale Pneumatic Conveying Dryer of Rough Rice

This article studies the possibility of reducing the high initial moisture content of wet rough rice using a small-scale low-cost pneumatic conveying dryer as a first stage dryer. The parameters investigated are final moisture content, surface temperature of rough rice, head rice yield, drying rate, power consumption per unit mass of evaporated water, and physical characteristics of rice. Parametric effects of the following variables are examined: velocity of drying air from 20 to 30 m/s, feed rate of rough rice from 150 to 350 kg/h, initial moisture content from 22 to 26% (wet basis), and drying air temperature from 35 to 70°C. From the experimental results, it is found that this drying method can be used for fresh rough rice with an initial moisture content of over 24% (wet basis). The drying process is able to lead to very rapid drying without any grain quality problems such as cracks in the rice kernel. The moisture content can be reduced to approximately 18% (wet basis) or about 5–6% of the initial moisture content within 3–4 s. The optimal drying air temperature is in the range of 50 to 60°C. A comparison of pneumatic conveying drying data obtained from the present study with fluidized bed drying data reported in the open literature is also discussed.     

THIN-LAYER DRYING CHARACTERISTICS AND MODELING OF CELERY LEAVES UNDERGOING MICROWAVE TREATMENT

The effect of microwave drying on moisture content, moisture ratio, drying rate, drying time, and effective moisture diffusivity of celery leaves (Apium graveolens) was investigated. By increasing the microwave output power from 180 to 900 W the drying time decreased from 34 to 8 min; by increasing the sample amount from 25 to 100 g, the drying time increased from 25 to 49 min. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among the models proposed, the semi-empirical Midilli et al. model gave a better fit for all drying conditions applied. The activation energy was calculated using an exponential expression based on the Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated and gave a linear relationship.     

Effect of Convective Air Attributes with Microwave Drying of Soybean: Model Prediction and Experimental Validation

The heat and mass transfer that occurred during drying of soybeans by a combined process using microwave (MW) and convective hot air was studied. A coupled mathematical model was developed to simulate this phenomenon. The soybean samples were re-wetted to 20% wet basis, the selected level of initial moisture content (IMC), and then dried in a domestic microwave oven under various MW power levels from 300 to 390 W, using inlet air with relative humidity of 35, 55, 75, and 95%. The simulated moisture loss profiles obtained from the coupled model compared well with those obtained in the experiments. Results showed that the drying rate decreased from 6.235 × 10^?5 to 6.192 × 10^?5 kg water/(kg wb s) as the inlet air temperature increased from 30 to 60°C. Furthermore, the drying rate was observed to increase from 6.192 × 10^?5 to 6.211 × 10^?5 kg water/(kg wb s) as the relative humidity (RH) increased from 35 to 95%.     

Dielectric Properties and Optimization of Parameters for Microwave Drying of Petroleum Coke Using Response Surface Methodology

The dielectric properties of petroleum coke at five temperatures between 20 to 100 ^° C, covering different moisture content levels at 2.45 GHz, were measured using an open-ended coaxial probe dielectric measurement system. The effects of drying temperature, duration of drying, and sample mass on the moisture content and dehydration rate of petroleum coke was assessed utilizing the response surface methodology. The dielectric constant, loss factor, and loss tangent were all found to increase nearly linearly with increase in moisture content. Three predictive empirical models were developed to relate the dielectric constant, loss factor, and loss tangent of petroleum coke as a linear function of moisture content from 3–10%. An increase in temperature between 20 to 100 ^° C was found to increase the dielectric properties. The penetration depth was observed to increase linearly with decrease in moisture content in the range of 3 to 10%. A predictive empirical model was developed to calculate penetration depth for petroleum coke. Two mathematical models were established and analyzed using RSM to describe the relationship between the microwave drying conditions and the responses, moisture content, and dehydration rate. Statistical analysis with response surface regression showed that microwave drying temperature, duration of drying, and sample mass were significantly related to moisture content and dehydration rate. Based on the RSM analysis, the optimum process conditions were estimated to be a microwave drying temperature of 75 ^° C, drying duration of 10 sec, and sample mass of 60 g, with the resultant moisture content being 0.34 at a dehydration rate of 2.94 g/min.     

Microwave Drying Kinetics of a Thin-Layer Liquorice Root

Liquorice root (LR) (Glycyrrize glabra) is known as a sweetener and medicine plant. Drying kinetics of LR with initial moisture content of 49.5% (wet basis (w.b)) were experimentally investigated in a microwave drying system. The drying experiments were carried out at different drying temperatures (40, 45, 50, and 55°C) and microwave power levels (250, 500 and 750 W). Several models from literature were selected to fit the experimental data. The fit quality of models was evaluated using the coefficient of determination (R²), sum square error (SSE), and root mean square error (RMSE). A new model has been proposed for LR drying in the microwave drying. This new model best describes the experimental data for LRs. The activation energy was calculated to be 46.807 kJ/mol and effective diffusivity ranged from 2.9 × 10^?9 to 5.41 × 10^?9 m²/s, depending on drying temperatures at constant microwave power level.     

Microwave Finish Drying of Osmotically Dehydrated Cranberries

Abstract

Combined microwave and hot-air drying characteristics was studied for the drying of cranberries that had been previously partially dehydrated by osmosis in a high fructose corn syrup (76°Brix). A 750 W 2450 MHz microwave oven was used to dry cranberry samples from 57% to 15% moisture content using three different power densities (0.75, 1.0, 1.25 W/g of initial cranberries) and two different power cycles (30 s On/30 s Off and 30 s On/60 s Off). All combinations of these variables were tested in triplicate. Quality of the cranberries was measured using a universal testing machine, chromameter, and with the use of a taste test panel. Drying times ranged from 2.2 to 5.0 h. Power times and power cycles affected the drying time and the quality of the dried cranberries. Lower power densities resulted in cranberries with higher quality. High power densities (125 W/g) resulted in the burning of some cranberries.     

Microwave-Assisted Thin Layer Drying of Wheat

Drying characteristics of Canada Western Red Spring (CWRS) wheat were studied using a domestic microwave convective oven. The effects of microwave power level, grain bed thickness, and initial grain moisture on the drying kinetics were investigated. Wheat samples with initial moisture levels of 0.18 to 0.29 kg water/kg of dry matter were dried for different drying periods of 180 to 360 s. The moisture loss data were recorded at regular short intervals. Then moisture loss data were fitted to various models (Page equation, modified drying equation, and Midilli equation) to study the drying kinetics of wheat. The results showed that wheat moisture loss increased with increasing microwave power level. A mathematical model was developed by coupling mass and energy balances, resulting in a system of non-linear equations. The predicted moisture loss data from the developed model were compared by fitting to experimental microwave data that were in good agreement.     

Drying kinetics and effective moisture diffusivity of purslane undergoing microwave heat treatment

The effects of microwave drying on moisture content, moisture ratio, drying time and effective moisture diffusivity of purslane leaves (Portulaca oleracea L.) were investigated. By increasing the microwave output power (180–900W) and the sample amounts (25–100 g), the drying time decreased from 43 to 12.5 minutes and increased from 27 to 54 minutes, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among the models proposed, the semi-empirical Midilli et al. model gave a better fit for all drying conditions applied. By increasing the microwave output power and decreasing the sample amount, the effective moisture diffusivity values ranged from 5.913×10⁻¹¹ to 1.872×10⁻¹⁰ m²/s and from 9.889×10⁻¹¹ to 3.292×10⁻¹¹ m²/s, respectively. The activation energy was calculated using an exponential expression based on the Arrhenius equation.     

Optimization of Microwave Drying Biomass Material of Stem Granules from Waste Tobacco Using Response Surface Methodology

Tobacco stems, an underutilized waste in the tobacco industry, can be transformed into a viable product through the preparation of biomass material of stem granules. Response surface methodology (RSM) was used to optimize microwave drying of stem granules from waste tobacco. The effects of microwave power (35–40 kW), moisture content (25–35%), material thickness (30–50 mm), and drying time (90–150 s) on filling power and yield of stem granules were studied. Gas chromatography–mass spectroscopy (GC-MS) and scanning electron microscopy (SEM) were used to determine volatile components and microstructures of stem granules dried under optimal conditions. The filling power and yield of stem granules could be adequately fitted to a quadratic model (R ² = 0.951) and a two-factor interaction model (R ² = 0.887), respectively. The optimal conditions for microwave drying of stem granules were 35 kW, 30%, 30 mm, and 150 s. When prepared under optimal conditions, the filling power and yield of stem granules were 7.94 cm³/g and 64.06%, respectively, which differed by only 4.53 and 3.50% from model predictions. The quadratic and two-factor interaction models provided a reasonably accurate (<5% error) assessment of optimal conditions for microwave drying of biomass material of stem granules from waste tobacco stems.     

Optimization of Potato Cube Drying in a Microwave-Assisted Pulsed Spouted Bed

The drying homogeneity of the microwave–pulsed spouted bed drying (MPSBD) method was studied via preparing tubers granules by MPSBD under different predefined conditions. The effects of three parameters (microwave power, moisture content transition point, and loading) on the homogeneity of prepared tubers granules were studied. Based on response surface analysis results, it was concluded that the optimum conditions for tuber granules prepared by MPSBD method is 1.10 W/g microwave power, 80% moisture content transition point, and 90 g material loading. It was proven that the experimental result from the predicted optimal condition agreed with the model-predicted results, which evidenced the accuracy of the response surface analysis. Furthermore, the brighter color and higher rehydration capacity of samples prepared by MPSBD indicates that MPSBD is a promising method that can be applied in the food dehydration industry.     

Estimation of Effective Moisture Diffusivity of Okra for Microwave Drying

The effect of microwave output power and sample amount on effective moisture diffusivity were investigated using microwave drying technique on round okra (Hibiscus esculentus L.). The various microwave output powers ranging from 180 to 900 W were used for the determination of effective moisture diffusivity for constant sample amount of 100 g okra. To examine the effect of sample amount on effective moisture diffusivity, the samples in the range of 25–100 g were dried at constant microwave output power of 360 W. By increasing the microwave output powers and decreasing the sample amounts, the effective moisture diffusivity values ranged from 20.52 × 10^?10 to 86.17 × 10^?10 and 34.87 × 10^?10 to 11.91 × 10^?9 m²/s^?1, respectively. The modeling studies were performed to illustrate the relationship between the ratio of the microwave output power to sample amount and effective moisture diffusivity. The relationship between drying constant and effective moisture diffusivity was also estimated.     

Microwave Heat Treatment of Spinach: Drying Kinetics and Effective Moisture Diffusivity

The effect of microwave drying technique on moisture content, moisture ratio, drying rate, drying time, effective moisture diffusivity, and porosity of spinach (Spinacia oleracea L.) were investigated. By increasing the microwave output powers (180–900 W) and the sample amounts (25–100 g), the drying time decreased from 18 to 3.5 min and increased from 7.7 to 25 min, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among of the models proposed, Page's model gave a better fit for all drying conditions applied. The activation energy was calculated using an exponential expression based on Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated and gave a linear relationship.     

Analysis of Energy Consumption in Drying Process of Biomaterials Using a Combined Unsymmetrical Double-Feed Microwave and Vacuum System (CUMV)—Case Study: Tea Leaves

An energy analysis of drying of biomaterials (tea leaves) was conducted on a combined unsymmetrical double-feed microwave and vacuum system (CUMV) to optimize the operating conditions and quality of the products. Tea leaves were dried from an initial moisture content of 172 to 7% (db). An energy consumption model based on the first law of thermodynamics was developed to evaluate energy efficiency. The influences of microwave power, vacuum pressure, and microwave operation modes on energy consumption were investigated in detail. The results showed that energy consumption as well as energy efficiency were strongly dependent on vacuum pressure and microwave power. Energy consumption and color parameters of the tea leaves were compared at different drying conditions. In particular, the experiments were carried out at different microwave powers (800 and 1,600 W) at a frequency of 2,450 MHz and different vacuum pressures (535 and 385 torr) to investigate the effects of these factors on the microwave–vacuum drying.     

Effective Diffusivities and Energy Consumption of Whole Fruit Chinese Jujube (Zizyphus jujuba Miller) in Microwave Drying

Microwave drying of whole fruit Chinese jujube was performed at 45, 90, and 135 W. Ten commonly used mathematical models of thin-layer drying were compared. The Midilli model was best in describing drying time dependency of product moisture ratios. The initial drying rate and drying rate constant are linearly proportional to microwave power level. An effective diffusivity model was presented and validated with the Renka-Cline algorithm. The model has very high predictive precision, suggested by the relative percentage error of 3.734% on average between the model and the Renka-Cline algorithm. The effective diffusivity was proved to be a linear function of microwave power level and a quadratic function of moisture content. Energy consumption in microwave drying of Chinese jujube decreased as microwave power increased from 45 to 135 W, but 90 W was adequate for high-quality products with less energy consumption.     

Combined Application of Experimental Design and Artificial Neural Networks in Modeling and Characterization of Spray Drying Drug: Cyclodextrin Complexes

The aim of this study was to investigate the usefulness of combined application of quality by design tools such as central composite design (CCD), response surface methodology (RSM), and artificial neural networks (ANN) in the characterization, modeling, and optimizaton of spray drying of a poorly soluble drug : cyclodextrin complex. Models were developed by RSM and ANN from different pools of data. The model with best predictability was the ANN multilayer perceptron (MLP)1 model developed from the largest group of data (R ² for response yield 0.854, moisture content 0.886). On the other hand, analysis of equations derived from the application of RSM contributed in better understanding the complex relationships between input and output variables. By application of a desirability function approach, optimal process parameters that resulted in the best process yield (86%) and minimal moisture content in the powder (3.3%) were established (25% feed concentration, 180°C inlet air temperature, 10% pump speed).     

响应曲面法漂白紫胶微波-真空干燥工艺研究

为提高漂白紫胶产品质量及生产效率,采用微波-真空干燥漂白紫胶研究了不同压强、微波功率和干燥时间对漂白紫胶产品颜色指数和含水率的影响,用响应曲面法（RSM）设计试验并建立了该工艺条件的拟合方程。结果表明,拟合方程的拟合度较高,所建立的数学模型可以用于描述漂白紫胶的微波-真空干燥。漂白紫胶微波-真空干燥的最优条件：干燥压强为3.0 kPa,微波功率为795 W,干燥时间为30 min。在优化条件下进行了验证实验,得到了颜色指数为0.9、含水率为0.028 9kg水/kg干料的产品。     

Study on drying kinetics of calcium oxide doped zirconia by microwave-assisted drying

Ca–ZrO₂ is an essential structural and functional material, which is commonly used in refractories, electronic ceramics, and functional ceramics. The properties of Ca–ZrO₂ materials are depending on the quality of Ca–ZrO₂ powders. The main factors affecting the quality of powder are sintering temperature and the drying effect. This paper applied modern microwave drying technology to dry Ca–ZrO₂ powder. The impact of initial mass, microwave heating power, and initial moisture content on the drying of Ca–ZrO₂ were explored. The results showed that the average drying rate increased with the rise of initial mass, microwave heating power, and initial moisture content. Wang and Singh, Page, and Quadratic Model were applied to fit Ca–ZrO₂ with an initial moisture content of 5.6%, mass of 30 g, and microwave output power of 400 W. The results displayed that the Page model had a better fitting effect. It was also applicable to other different initial moisture content, original mass, and microwave heating power. The diffusion coefficient calculated by Fick's second law displayed that with the increase of initial mass, initial moisture content, and microwave heating power of Ca–ZrO₂, the effective diffusion coefficient increased first and then declined. When the Ca–ZrO₂ of microwave heating power was 640 W, mass was 30 g, and the moisture content was 5.65%, the effective diffusion coefficients of zirconia were 1.42533 × 10^?13, 2.91806 × 10^?13, 5.652.2471 × 10^?13 m²/s, respectively. To determine the activation energy of microwave dried zirconia, using the relationship between microwave power and activation energy, the activation energy of microwave dried zirconia was calculated to be ?23.39 g/W. This paper aims to rich experimental data for the industrial application of microwaves to strengthen dried zirconia and propose a theoretical basis.