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The present study investigated the Interval Starting Accessibility Drying (ISAD) process with the main objective to optimize the main processing parameters, i.e. the active time (toN) and the tempering time (toFF)> which ranged between 5 to 30 s and 1 to 3 min, respectively. ISAD performances were compared with continuous airflow drying for several quality parameters and energy consumption. The modulation of the time related operating conditions allowed rewetting the surface after each tempering time in a total way with toN= 5s-and toFF=2 or 3min. ISAD significantly affected (p<0.05) the effective drying time and the energy saving which reached as much as 87.26% compared to continuous drying when toN= 5s and toFF =3 min. The processes did not significantly impact the shrinkage, rehydration capacity or total color change. However, drying processes notably influenced the content of polyphenols and carotenoids. The optimal conditions of combined optimized responses were toN = 5 s of toFF = 2.52 min with a desirability D= 0.924. [ABSTRACT FROM AUTHOR]

As a section on improving the energy efficiency and thermal efficiency of convection dryers, a different airflow distribution system in the convection dryer was established. The grape drying experiment was investigated by applying three types of distribution air inside a convection hot-air dryer. The vertical system (VS) in which hot air passes vertically through the tray of samples. However, the air was delivered parallel to the sample tray in two horizontal systems (HS) Types (I, II). The investigations were approved with the different air-drying temperatures of 40, 50, and 60 °C at different velocity 1.0, 1.5, and 2.0 m/s. The drying time in the horizontal dryer compared to the vertical system was significantly less. The data analysis showed that horizontal energy consumption with a type (II) dryer was low while the energy consumption was high under the vertical dryer. Moreover, applying the horizontal Type (II) for grapes drying had numerous improvements above the conventional vertical system, such as shorter processing times, less overall energy utilisation, and higher dryer thermal efficiency. According to the results, after fitting the experimental data with eleven drying kinetics models and comparing the results in terms of the root mean square error (RMSE), the reduced chi-square (χ2), and the correlation coefficient (R2), it was obtained that logarithmic model can give practically accurate evaluations of the drying curve for grapes drying in different convection dryers. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD) drying relies on the generation of a corona wind that is created with a high electric potential between an emitter and a ground electrode. The impinging corona wind enhances convective heat and mass transport close to the sample, which is positioned on the ground electrode. Although EHD drying is reported to have large potential for milder and energy efficient drying, most studies have only evaluated its potential at the lab scale and for specific applications. This review focusses on discussing the underlying physical phenomena that may be expected to influence the performance of EHD drying processes. Specifically, we discuss how corona wind changes due to discharge behaviour as it is influenced by moisture release during drying, how the microstructural properties of the product could influence electromigration in the drying material and how EHD drying could be efficiently and safely scaled up for biobased & food products. We conclude with an outlook to the research that still is required to concretize the potential of EHD drying in practice. In EHD drying, electrical discharge induces airflow which enhances external convective drying. Studies coupling physical phenomena are still lacking, although some possible couplings are mentioned in chapter 2. Internal mass transfer is enhanced due to presence of an electrical potential over the product, which can cause several electrically-driven transport phenomena a s discussed in chapter 3. Several drying setups have been explored in industry, of which the characteristics are summarized in chapter 4. • In EHD drying, moisture transport is enhanced using electrical phenomena. • Phenomena occurring in the air domain and interactions between them are summarized. • Suggestions are made for electrically driven internal moisture transport phenomena. • Current EHD setups and the (dis)advantages of their characteristics are discussed. [ABSTRACT FROM AUTHOR]

Convective thermal drying is usually used in sludge dryers, and the air supply forms significantly affect the sludge drying efficiency. In this work, the drying process of multi-layered sludge is numerically simulated using a coupled computational fluid dynamics-discrete element method (CFD-DEM) approach. Better than our previous work, the current CFD-DEM model further considers the dynamic process of humidity within the flow field. Firstly, the CFD-DEM model is validated based on the mechanistic experimental data. Then, extensive numerical simulations are carried out to investigate the two-layered sludge drying process in the dryer, and the effects of two conventional air supply forms (Top-to-Bottom and Bottom-to-Top) as well as a novel air supply form (Side-assist) on the two-phase flow system are discussed. The simulation results provide in detail the dynamic processes of momentum, heat and mass (moisture) in the convective drying system under different working conditions. Following recommendations are presented to facilitate the operation of the dryer: Bottom-to-Top is better for sludge drying and tends to utilize less heat from the heat source compared to the Top-to-Bottom. The drying efficiency can be further improved by supplying the Side-assist with an optimal flow ratio of side-wind to bottom-wind. Numerical results show that the optimal flow ratio is related to the total air volume, the deflection angle and the side-wind temperature. The present study reveals in depth the impact mechanism of the air supply form on the convective thermal drying process of sludge, which contributes to the design and optimization of high-efficiency dryers. [Display omitted] • A CFD-DEM model describing the sludge drying process is further developed. • The convective drying of multi-layered sludge is numerically investigated. • Two conventional air supply forms for the dryer are analyzed. • A novel air supply form and its optimal solution are proposed. [ABSTRACT FROM AUTHOR]

The influence of drying process on the properties of ceramic filter elements for industrial high-temperature gases purification was studied. Filter elements were based on aluminosilicate fiber manufactured via vacuum filtration with the following molding and machining of the workpiece, it's treatment with a colloidal silicon oxide sol binder, and drying with the employment of various processes. Convective drying (CD), microwave drying (MWD) and filter element freezing followed by convective drying (FCD) processes were employed to study the related binder migration and its effect on filter properties. Diffusional redistribution of the binder through the thickness of the filter element's wall decreases in the series CD→FCD→MWD with the accordingly observed improvement of the structural uniformity and mechanical strength of the filters. The tensile strength of samples dehydrated via convective drying, freezing followed by convective drying and microwave drying, all of which then heat-treated at 1000 °C (the assumed maximum operating temperature), is 0.35 MPa, 0.57 MPa and 0.48 MPa, respectively. The pressure drop measured at the specific air flow of 100 m3/m2 is respectively 700Pa, 490Pa and 410Pa. [ABSTRACT FROM AUTHOR]

This work considers robust moisture content and activity control in a continuous convective drying for particulate bio-materials. The major process uncertainty is in the kinetics of the second (falling-rate) drying period. Robust feedback controllers in the multi-variable and de-central case are designed to guarantee desired product specifications. The advantages of the robust controllers are discussed in comparison with a conventional PI controller. The case study presented is the drying of baker's yeast in a fluidized bed dryer. The results show constant performances concerning the uncertainty of the drying kinetics and disturbance rejection at different operating points. • Robust multivariable controller design for convective drying. • Constant controller performance concerning various process uncertainties and operating points. • Baker's yeast in fluidized bed dryer as case study. [ABSTRACT FROM AUTHOR]

• Ultrasound-assisted drying (UAD) could intensify the moisture separation in pulp drying process. • The drying time was shortened by 26 %∼42 % as a result of UAD intensification. • Drying at 55 °C and 60 W led to the minimized energy consumption with UAD. • The Page model was found to be the best for predicting the pulp drying kinetics. • No significant differences in drying rates were observed when the moisture ratio was below 0.43. Traditional pulp convective drying (CD) is time-consuming and energy-intensive. This study aimed to assess the drying performance of pulp using ultrasound-assisted drying (UAD) and compared it with CD to intensify moisture separation. UAD was found to be fast and efficient with high effective moisture diffusivity of 2.77 × 10–10 ∼ 3.20 × 10–10 m2/s, low activation energy of 20.2 kJ/mol, and short drying time of 21.0 ∼ 16.5 min. It demonstrated that applying ultrasound could promote moisture separation with 26 %∼42 % reductions in drying time and 42 %∼22 % savings in energy consumption. The constant rate period was not presented and no significant differences in drying rates were observed when the moisture ratio was below 0.43 under the investigated conditions. The kinetics modeling results indicated that the Page model was the best to predict the pulp drying kinetics for both methods. It may lead to an alternative efficient approach for decarbonizing the drying process in pulp and paper production. [ABSTRACT FROM AUTHOR]

• Drying characteristics and mechanisms of hydrogel with a constant temperature stage are clarified and revealed. • A maximum duration (3 h) of constant temperature stage with an evaporation heat flux 268.7 W/m2 is observed in the hydrogel drying. • The maximum reduction in duration of stage II is 100 % when initial Biot number (Bi 0) increases from 0.39 to 0.47. • Under the same drying temperature, a critical Bi 0 (Bi 0,c) exists for the same hydrogel below the Bi c the drying rate increases with Bi 0 significantly. In this study, the convective drying characteristics of hydrogel with a constant temperature stage at different drying temperatures and initial Biot numbers (Bi 0) are experimentally presented. Additionally, a numerical model coupling the mass, energy conservation equations and solid momentum balance equation is developed and validated to reveal the drying mechanisms. The results show that there are three drying stages, i.e., the temperature rise (stage I), constant temperature (stage II), and second temperature rise (stage III). Numerical results demonstrate that the duration of stage II is related to the internal moisture transport resistance which increases rapidly and leads to the end of stage II. A maximum duration of 3 h for stage II with evaporation heat flux of 268.7 W/m2 is observed at drying temperature of 35 ℃. The three drying stages persist as the drying temperature increases, but the duration of stage II decreases rapidly. In particularly, under the same drying temperatures, there is a critical Bi 0 (Bi 0,c) below which the drying rate increases with Bi 0 significantly, but above it, the drying rate increases slightly for the same hydrogels. The duration and temperature of stage II decrease with increasing Bi 0. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcium diffuses through papaya tissue until equilibrium is reached. • Calcium ions restructure papaya tissue forming branched calcic microstructures. • The microstructure modified by the calcium effect changed the texture parameters. • Calcium pretreatment increases the effective diffusivity of moisture during drying. The microstructural changes in papaya tissue during calcium diffusion, the effect on drying kinetics and texture parameters were investigated. Calcium pretreatment was applied to papaya samples for 3 h, at a solution concentration of 1.5 g Ca(OH) 2 /100 mL H 2 O, and a solution temperature of 25 °C; subsequently, the samples were convectively dried at 70 °C, air flow of 1.5 m/s, and a relative humidity of 5 ± 2%. Calcium content was determined using the Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) technique, the microstructure of the samples was analyzed by High-Resolution Scanning Electron Microscopy (HR-SEM), and the elementary analysis was performed by Energy-Dispersive X-ray Spectroscopy (EDS). Effective diffusivity of calcium (D efCa) and moisture (D efw) were calculated during pretreatment and drying, respectively and texture parameters were determined by double compression using a texturometer. The transport mechanism determined during calcium pretreatment was diffusion with a D efCa = 3.10 × 10−10 m2/s. Also, branched calcium microstructures in the cell walls of tissue were observed due to the calcium effect, it was supported by elemental analysis, which showed an increase of calcium in section restructured compared to non-restructured. During drying, D efw = 1.86 × 10−9 m2/s was higher in pretreated compared to non-pretreated samples with D efw = 1.17 × 10−9 m2/s, indicating a higher drying rate and moisture loss. The texture values changed significantly (α ≤ 0.05) due to calcium pretreatment and drying; the calcium microstructures caused higher cohesiveness, springiness, gumminess, and chewiness. Calcium modifies the microstructure and composition of papaya tissue; therefore, drying kinetics and texture parameters depend on this modification. [ABSTRACT FROM AUTHOR]

Desiccated coconut was dried using a novel hybrid dryer that was developed to work in both single and hybrid mode. Single mode consisted of convective (CD) and infrared (IR) drying while hybrid mode involved combined (IRCD) and sequential (IR-IRCD) drying. The effect of two different drying modes, four drying methods with constant temperature process (50, 60, 70 °C) on the drying time, specific energy consumption (SEC), effective moisture diffusivity, color change (ΔE), whiteness index (WI), oil content, free fatty acid (FFA), peroxide value (PV) and microstructure of desiccated coconut were investigated and analysed. The results showed that the drying time was reduced by the increase in drying temperature, where sequential IR-IRCD had the shortest drying time followed by IR, IRCD and CD. In contrast, effective moisture diffusivity was increased by the increase in drying temperature. IR drying had the lowest SEC followed IR-IRCD, IRCD and CD. Hybrid mode IR-IRCD proved to be the best in retaining the color of desiccated coconut with the lowest ΔE and highest WI. Desiccated coconut from all drying methods had acceptable value of oil content, free fatty acid and peroxide value. IR-IRCD at 70 °C was chosen to be the most suitable for drying desiccated coconut based on the combined effect of drying time (28 min), SEC (28.15 kWh/kg), effective moisture diffusivity (3.780 × 10−9 ± 0.19 × 10−9 m2/s), ΔE (1.67 ± 0.04), WI (73.89 ± 0.26), oil content (61.33 ± 0.15 g/100 g), FFA (0.076 ± 0.003 g/100 g) and PV (1.66 ± 0.15 mEq/kg). • Hybrid drying improves whiteness index of desiccated coconut compared to single mode drying. • Hybrid drying increases the drying rate hence desiccated coconut's cell structure become porous. • Sequential drying significantly reduces drying time and energy compared to convective drying. • Sequential hybrid drying produces high quality desiccated coconut with acceptable oil properties. [ABSTRACT FROM AUTHOR]

An experimental setup is designed and developed for characterization of convective drying of food products under various operating conditions. The experiments are performed with cylindrical shaped potato samples at varying air velocity and temperature. From the experimental data, variation of transient moisture content, drying rate, effective moisture diffusivity and activation energy are determined. Air flow velocity and temperature have significant effect on the drying time of the potato sample. Around 30% drying time is reduced when air velocity is increased from 2 to 6 m/s and around 36% drying time is saved when air temperature is raised from 40 to 60 °C. The performance of the test dryer is evaluated based on its energy consumption and specific energy consumption (SEC). It is observed that the energy consumption and SEC increases with air velocity and temperature. Further, the effective moisture diffusivity is increased with an increase in air velocity and temperature and its value lies in the range of 3.78 × 10−10 – 1.45 × 10−9 m2/s. Correlations for energy consumption and effective moisture diffusivity are proposed. The statistical model for energy consumption and effective moisture diffusivity are also developed by correlating air velocity and temperature. The adequacy of the model and analysis of experimental data are done using analysis of variance. Image 1 • Experimental data of convective drying for cylindrical shaped potato sample. • Performance evaluation of the drier based on energy consumption. • Correlations developed for effective moisture diffusivity and energy consumption. • Statistical analyses for energy consumption and moisture diffusivity. [ABSTRACT FROM AUTHOR]

Highlights • US were used to incorporate microencapsulated nutrients into two food products. • Hydrophilic (iron) and lipophilic (carotenoid) microcapsules were incorporated. • Enriched foods were convectively dried after microcapsules incorporation. • Ultrasound allowed more homogeneous iron incorporation. • Ultrasound allowed higher carotenoid content and less degradation during drying. Abstract The present work proposes using the ultrasound technology to incorporate microencapsulated nutrients during pre-treatments for drying of food products. Both hydrophilic and lipophilic nutrients were evaluated: incorporation of microcapsules of iron (obtained by spray drying using maltodextrin as wall material) and carotenoids (obtained by hot emulsification and solidification using hydrogenated palm oil as wall material). The ultrasound pre-treatment was applied in water and ethanol, where the microcapsules were dispersed, and food samples were immersed. Pumpkin and apple were selected as suitable food material to perform the iron and carotenoid incorporation, respectively. Ultrasound allowed more homogeneous iron incorporation in pumpkin. The iron content increased more than 1000% in pre-treated samples compared to control. In the same manner, carotenoid content increased in about 430% when ultrasound was applied. After drying, the carotenoid content decreased by 65% in control samples. However, better carotenoid retention was obtained after drying in ultrasound processed samples. The results show that pre-treatment with ultrasound can be used to incorporate nutrients into the food matrix, increasing not only the incorporated quantity but also promoting their preservation. Nevertheless, future studies must be performed to determine the nutrient bioavailability and bioaccessibility. [ABSTRACT FROM AUTHOR]

Highlights • The impact of ultrasonic intervention on paddy drying in deep bed was studied. • Dying time, ER, broken kernel, niacin, TPC and energy of grain were analyzed. • Ultrasound application during paddy air-drying improved drying kinetics. • Advances were found in grain quality in ultrasound assisted air drying domain. Abstract This study investigates the feasibility of achieving a modified rough rice air-drying with ultrasound intervention (US) set at 21 kHz frequency. The process was carried out using an ultrasound assisted convective dryer and analyzed in terms of drying time, energy consumption (EC), evaporation rate (ER), broken kernel (BK), water activity (a w), vitamin B 3 (niacin), and total phenolic content (TPC). The lab-scale dryer was set to transmit energy at power levels of 30, 60, 90, 120, and 150 W in the air temperatures of 35, 40, 45, 50, and 55 °C and velocities of 0.2, 0.5, 0.8, 1.1, and 1.4 m/s for a thickness of 20 cm. The results showed that in-range drying parameters played a major role in response analysis, suggesting that ultrasound efficiency during convective drying heavily depends on the power, air temperature, and velocity levels. Ultrasound assistance significantly increased bed evaporation rate up to 38.93%. Subsequently, it caused a reasonable reduction in total drying time, EC, and BK percentage up to 27.92%, 25.98%, and 34.22%, respectively in the case of 35 °C, v = 0.8 m/s, and P = 90 W. Remarkable advances were attained in the ultrasound assisted drying domain in grain quality via acceptable decrease in niacin and TPC losses within shorter drying time. There was a significant linear trend in BK, niacin, and TPC values across the bed thickness, which all was increased by the ultrasound application. The highest nutrient retention and physical quality preservation belonged to the top layer, which was influenced by the ultrasound radiation by the highest degree. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Drying is an important unit operation in the manufacturing of polymer strip films as it affects various film quality attributes. Optimal design and control of convective drying process require models that capture the impact of critical process parameters such as air temperature and velocity on the temporal evolution of film thickness and moisture. Here, a detailed transport model was presented to capture moisture diffusion, heat transfer and moving boundary in convective drying of polymer strip films loaded with griseofulvin (GF), a poorly water-soluble drug. It incorporates a solvent diffusivity model based on free-volume theory. Experimentally, film precursor suspensions were prepared by mixing silica-coated and micronized GF powder with an aqueous solution of hydroxypropyl methylcellulose (HPMC)–glycerin. Films were cast and moisture–time variation during drying was measured. The transport model, whose diffusivity parameters were estimated using drying data at a reference condition, was validated at different drying conditions and wet film thicknesses. It delineates underlying mechanisms of drying kinetics and demarcates a smooth transition from constant-rate to falling-rate period. Overall, our results suggest that the transport model is capable of predicting the temporal evolution of moisture and final film thickness at different drying air velocities and temperatures with reasonable accuracy. [ABSTRACT FROM AUTHOR]

Abstract This study concerns a purely convective drying of parallelepiped un-blanched potato slices. A numerical model for heat and mass transfer has been developed in Lagrangian referential to overcome the structural changes. The thermo-physical properties of the slices vary with the temperature and moisture content. The finite volume method combined with a typically implicit time pattern was used to solve the model equations. The evaporated mass flux was calculated using the transfer surface area by which the water evaporates, and heat transfer coefficient was estimated using Nusselt number; The inverse method was used in this computation. The experiments were carried out under several thermo-aeraulics conditions in order to determine the most influent operating variable on the drying kinetic. A good agreement between experimental and simulated results was obtained with a moisture content determination coefficient (R 2 ) higher than 0.9980; Whereas, the surface and center temperatures are higher than 0.9328 and 0.9305 respectively. The results have shown that the air temperature is the most important parameter that controls the drying kinetic. Highlights • Transport of heat and mass transfer inside the product. • The effect of aerodynamic conditions on hydro-thermal transfer on the product. • Water activity rate and the effective diffusion coefficient. • Transfer surface area estimation and Nusselt number using inverse method. • A confrontation between experiments and simulation of drying process. [ABSTRACT FROM AUTHOR]

Highlights • The apple is dried utilizing convective drying method. • The experiments are studied via RSM and utilizing desirability function. • The drying time, energy consumption, and shrinkage are optimized. • The optimal conditions are designated by maximum desirability function (D = 0.781). Abstract In this work, response surface methodology (RSM) is applied to state an optimized system for convective drying of apple slices using desirability function. The interaction of the independent parameters including air temperature (T = 70–90 °C), air velocity (V = 4–5 m/s), and apple slice geometry (G = circle, square, and triangle) with the dependent variables consist of drying time, energy consumption, and shrinkage is determined. Minimum drying time, energy consumption and shrinkage is regarded as the optimizing drying conditions of apple slices. Experimental results are adapted by a second-order polynomial model where analysis of variance is utilized to define model compatibility and optimal drying conditions. The optimal conditions of combined optimized responses were 90 °C inlet temperature, 5 m/s inlet velocity, and square geometry which designated by maximum desirability function (D = 0.781). The air temperature had a notable influence on total responses, but the effect of air velocity and apple slice geometry were important in shrinkage. Generally, the results marked that a greater desirability value could be obtained in the higher air temperature and higher air velocity with the square geometry. [ABSTRACT FROM AUTHOR]

This work discusses the effect of pulsed electric field (PEF) parameters on the convective drying process of fresh onions. First, the PEF treatment parameters and their influence on the cell disruption were investigated by applying various PEF settings ( W  = 0.2–20.0 kJ/kg, E  = 0.36–1.07 kV/cm). The diffusion coefficient D e was calculated and mathematic modeling was conducted. PEF was found to enhance the internal diffusion, but not necessarily to result in an increased drying rate. The shortest drying time at a drying temperature of 60 °C was achieved for onion samples treated at 4 kJ/kg and 1.07 kV/cm. Subsequent drying trials were performed at the pre-determined PEF settings and different drying temperatures resulting in a PEF related drying time reduction of 30.3%, 21.4% and 6.4% at 45 °C, 60 °C and 75 °C to reach a residual moisture ( M r ) of 7%, respectively. [ABSTRACT FROM AUTHOR]

Recently, the effectiveness of combined use of non-thermal technologies to improve hot air dryers' performance from both the energy and quality point of views has been proven. However, no study has been reported on thermodynamic analysis of such hybrid systems. The present work dealt the influence of ultrasonic power combination with convective hot air dryer on exergetic performance of the system. Potato cubes were dried at different drying air temperatures (45–65 °C) and velocities (0.5–1.5 m/s) and ultrasonic powers (0–0.08 kW). Based on the findings obtained through the experiments, the exergy loss varied averagely from 240.58 to 600.83 kJ, and was decreased continuously with increasing the power level. The average exergy destruction ranged from 169.61 to 1554.23 kJ, and was decreased at the higher air temperatures and velocities. Combination of ultrasonic power with hot air intensified the exergy destruction. The average exergy efficiency varied from 24.19 to 91.42% and from 11.67 to 38.27% for the drying chamber and process, respectively. • A hybrid ultrabasic/hot air dryer was thermodynamically investigated. • The average exergy loss was decreased with increasing the power level • The average destructions enhanced with the ultrasonic power. • Utilization of ultrasonic power is not environmentally appropriate. [ABSTRACT FROM AUTHOR]

A self-designed hot-air convective dryer coupled with contacting ultrasound system was used for the dehydration of garlic slices. Contacting ultrasound significantly accelerated the drying process. Compared with non-ultrasound treated samples, the drying time of garlic samples sonicated at 1513.5 W/m 2 was shortened by 35.0% at 50 °C, 48.5% at 60 °C and 50.0% at 70 °C. According to water transport simulation using a diffusion model considering sample shrinkage, both water effective diffusivity and external mass transfer coefficient were enhanced when garlic samples contacted ultrasound directly during drying. In the meantime, internal water diffusion was more affected by contacting ultrasound. Furthermore, contacting ultrasound had a positive effect on the preservation of organosulfur compounds in garlic slices during drying. The browning problem of garlic products during hot-air drying was also alleviated if contacting ultrasound treatment was performed properly. Besides, no over-heating problem was observed during contacting ultrasound enhanced drying within the studied experimental range. [ABSTRACT FROM AUTHOR]

Highlights • Continuous convective drying of particulate materials is considered. • Parametric uncertainties in the second drying period are addressed. • Feedback controller providing robust stability and performance are designed. • Application is exemplified for drying of baker's yeast pellets in fluidised beds. • Very good performance in view of kinetic uncertainty and operating point. Abstract This work considers robust control of continuous convective drying of particulate solids where the major process uncertainty lies in the kinetics of the second (falling-rate) drying period. Using the concept of normalised drying curve, for arbitrary shape of the curve, the steady state particle moisture content is derived. Applying appropriate uncertainty models, a robust feedback controller is designed to guarantee desired product moisture. Advantages of this approach are discussed in comparison to convential PI and LQ-optimal control. The approach is exemplified for the case of fluidised bed drying of baker's yeast particles. Results show very good performance with respect to parametric uncertainty and disturbance rejection even at non-nominal steady-states. [ABSTRACT FROM AUTHOR]

The convective drying of fruits is the most implemented drying technique to stabilize fruits and to increase their shelf life. The mathematical modelling of drying is a useful tool in process optimization and dryer design. The modelling involves the solution of complex partial differential equations of coupled heat, mass and momentum transfer, which can be solved by several numerical and analytical methods. The aim of this review is to present and analyse the main published researches on the modelling of the convective drying of fruits focused on theoretical models. The main parameters involved in the numerical modelling of fruit drying are presented, such as the main mathematical models in the conjugated or non-conjugated approach, the applications on different geometries and dimensions, the scale approach, the thermophysical and transport properties determination, the alternatives of numerical solutions, the main methods to determine convective transfer coefficients, and other modelling considerations such as the shrinkage inclusion and quality deterioration are presented and analysed in this review based on the studies reported in the literature in the past decade. Through their comparison and analysis, future perspectives and challenges in fruit drying modelling are discussed. The computational tools increase the accuracy in predicted values and the possibility to extrapolate the characteristics from a micro-scale level to a macro-scale level. The challenges for convective drying of fruit lead to overcoming the dependence on empirical models for drying parameters determination, the lack of shrinkage inclusion and 3D modelling by means of advanced procedures such as multi-scale and conjugated modelling. The definition of the application of the model is important. Simple models present an effective use in some cases of engineering applications. More complex models are closer to reality and useful to engineering and research purposes. [ABSTRACT FROM AUTHOR]

This study reports the formation of 2-furomethyl-amino acids (2-FM-AA) as indicators of Maillard reaction (MR) in black garlic elaboration, followed by the determination of furosine by ion-pair RP-HPLC-UV. The method was assessed for accuracy, repeatability and detection and quantitation limits indicating its adequacy. Traditional procedure of black garlic obtainment and the inclusion of convective drying (CDP) and ohmic heating (OHP) were assayed. For comparison purposes, three commercial black garlic samples were used. Together with furosine (2-FM-lysine), 2-furoylmethyl-γ-aminobutyric acid and 2-FM-arginine were detected. Levels of furosine were higher in CDP (46.6–110.1 mg/100 g protein) than in OHP (13.7–42.0 mg/100 g protein) samples, probably due to the most severe processing conditions used in the former. These results highlight the suitability of 2-FM-AA as chemical indicators to monitor the process of black garlic elaboration in order to obtain high quality products. [ABSTRACT FROM AUTHOR]

Convective drying is one of the most important forms of moisture removal in macroporous materials exposed to environmental loads. In this study, the influence of airflow on the convective removal of water vapor (passive scalar) from porous asphalt (PA), a macroporous material, is investigated for different wind speeds and levels of liquid water height within the material, using computational fluid dynamics (CFD). The PA domain for the CFD simulations is reconstructed from three-dimensional X-ray micro-computed tomography images. Steady Reynolds-averaged Navier-Stokes (RANS) k- ε model with low Reynolds number modeling for the near-wall region is used for the turbulence modeling. Simulations are carried out for three wind speeds, 0.1, 1.5 and 10 m/s, and three depths of the scalar (vapor) source, 0.13, 15 and 29 mm, within the specimen. Only the highest wind speed has a clear influence on the total vapor flux measured at the interface. Additionally, at the highest wind speed, air entrainment in pores near the air-material interface plays an important role in vapor removal. At lower wind speeds, diffusion within the material is the dominant vapor transport mechanism. At a wind speed of 10 m/s, strong vortices are observed which inhibit vapor removal in cavity-type pores by recirculating vapor within the pore. However, at the same wind speed, vapor transport in a non-cavity-type pore system is found to be very strong due to strong air convection. [ABSTRACT FROM AUTHOR]

Granulated cork is a by-product of natural cork stoppers manufacturing which is incorporated into highly valued products such as agglomerated cork stoppers and expanded cork insulation. Prior to this, the cork granules must be dried. This work presents an experimental study for the characterization of wet granulated cork drying kinetics with different morphologies: a powder and granules with different sizes (2–2.8, 2.8–4 and 4–5.6 mm). A drying process with hot air stream flowing tangentially to the solid was used for a systematic analysis of the influence of air stream conditions (temperature and flowrate) on drying kinetics. Under these conditions, the influence of the stream temperature was much more relevant than its velocity with the drying time almost halving when the temperature rose from 35.0 °C to 56.5 °C. The drained humid solid with higher granulometry was dried entirely during a falling drying rate period. All others products presented a constant drying rate period before the falling drying rate period. The results revealed that the falling drying rate period is conditioned by water migration through the solid and presents a similar shape for all products. Thus, the behavior can be described by a single characteristic drying curve, allowing predicting drying rate as a function of the solid normalized humidity, despite the cork granules dimensions. This normalized curve is a useful tool for dryer equipment dimensioning in the cork manufacturing industry. To predict the time of drying for defined air drying conditions, a simple procedure was proposed using the characteristic drying rate obtained. [ABSTRACT FROM AUTHOR]

The shrinkage of biological materials (agri-food), is a common phenomenon developed during a drying operation that directly affects the product quality. In this work a dimensionless mathematical model including the reduction at the interface of a high moisture content food (tuber) in 1D geometry was developed. The mass and heat conservation equations coupled to the Leibniz-Reynolds Transport Theorem (LRTT) at the interface of a high moisture content food were solved. The system of nonlinear unsteady state equations was solved by using a multi-frontal massively parallel sparse direct Solver. In order to validate this model, tuberous crop slices were dried at three temperatures: 40, 50 and 60 °C, relative humidity of 25% and a constant airflow of 1.5 m/s. Drying kinetics and the evolution of temperature within the product were logged. The model is able to simulate the moisture loss and predict the highest thickness change. The simulations show a good agreement with the experimental drying kinetics, as well as for the evolution of temperature. Simulations show 1-D shrinkage is not linear and the model improves its prediction when the drying temperature is higher (intensive mass flux). [ABSTRACT FROM AUTHOR]

The application of airborne ultrasound is a promising technology in the drying of foods, particularly to fruits and vegetables. In this paper, designs of dryers using ultrasound to combine the convective drying process are described. The main factors affecting the drying kinetics with the ultrasound application are discussed. The results show that the ultrasound application accelerated the drying kinetics. Ultrasound application during the convective drying of fruits and vegetables shorten the drying time. Ultrasound application can produce an increase of the effective moisture diffusivity and the mass transfer coefficient. The influence of ultrasound on physical and chemical parameters evaluating the product quality is reviewed. Ultrasound application can decrease the total color change, reveal a low water activity and reduce the loss of some nutrient elements. Meanwhile, ultrasound application can also better preserve the microstructure of fruits and vegetables in comparison to convective drying. [ABSTRACT FROM AUTHOR]

“ Mollar de Elche ” is the most popular Spanish pomegranate cultivar (intense sweetness and easy-to-chew arils); however, arils have pale pink colour and flat sensory profile. “ Mollar the Elche ” arils first underwent an osmotic dehydration pre-treatment (OD) with concentrated juices: (i) chokeberry, (ii) apple, and/or (iii) pomegranate cultivar “ Wonderful ”, to improve their antioxidant capacity, colour, and sensory profile complexity, and later the arils were dried by a combined method (convective pre-drying + vacuum microwave finish drying). The use of OD provided dried arils with characteristic sweetness, and improved colour and aromatic complexity. The recommended OD methods were those using (i) pomegranate, and (ii) pomegranate with chokeberry juices; they improved the total anthocyanin content (mean of 368 mg kg −1 ), red colour ( a ∗ coordinate 15.6), and antioxidant capacity (e.g. ABTS mean of 5.7 mmol Trolox 100 g −1 ). However, further research is still needed because freeze-dried arils had the highest anthocyanin content. [ABSTRACT FROM AUTHOR]

A pore network (PN) model is developed to explore drying of a thin hydrophobic porous medium bounded with a gas purge channel. The PN is composed of cubic pore bodies connected by cylindrical pore throats. At the interface between a pore throat and body, a sudden geometrical expansion exists. When a meniscus advances to this interface, it will be pinned first until the pressure across the meniscus increases to a critical value. This phenomenon is called the capillary valve effect. Because of this effect, two types of invasion into pore bodies are discerned, i.e. bursting and merging invasion. The developed PN model with the capillary valve effect is validated against the experimental results. For the drying case of dominant merging invasion, a drying front of finite width is stably receded. But when bursting invasion dominates, gas invasion is a random process; the drying process can be characterized by three regimes: a surface evaporation period, a constant rate period, and a falling rate period. The total liquid saturation for transition from the constant to falling rate period is close to that at which the total area for vapor transport is maximal between the partially filled pores and their neighboring empty pores. [ABSTRACT FROM AUTHOR]

Ultrasound application represents an alternative means of improving heat and mass transfer. This study explored the combined application of ultrasound (US) during both the osmotic dehydration (OD) pretreatment and the convective drying of pineapple. For that purpose, fresh and pretreated samples (20 or 40 min, with (55.5 kW/m 3 , 40 kHz) and without ultrasound application) in an osmotic solution of sucrose (40% w /w) were dried (40 °C and 70 °C) with (21.8 kHz, 31 kW/m 3 ) and without ultrasound application. A diffusion model permitted to quantify the influence of the factors studied (time of pretreatment, ultrasound application during pretreatment, drying temperature and ultrasound application during drying) in drying kinetics. The increase in drying temperature and the application of ultrasound during drying significantly accelerated the drying process by reducing both the internal and the external mass transport resistance. On the contrary, the osmotic pretreatments reduced the drying rate by increasing the external resistance. [ABSTRACT FROM AUTHOR]

In this work, energy and quality attributes for deep bed drying of paddy were studied. Drying experiments of freshly harvested paddy were conducted at different levels of drying air parameters including temperature (T=40, 50, 60, 70 and 80 °C), velocity (V=0.5, 0.8 and 1.1 m s −1 ) and relative humidity (RH=40%, 50%, 60% and 70%). It was observed that increasing temperature and velocity increased drying rate and higher levels of relative humidity led to longer drying durations. Total energy consumption ranged from 0.37 kW h to 1.85 kW h where the minimum and maximum values belonged to the experiments carried out at T=80 °C, V=0.5 m s −1 and RH=40%, and T=40 °C, V=1.1 m s −1 and RH=70%, respectively. The results of energy analysis showed that the energy efficiency was improved at higher temperatures, and lower levels of velocity and relative humidity for drying air. Furthermore, it was found that the number of fissured kernels was directly related to drying rate where damaged kernels increased with increasing drying rate. [ABSTRACT FROM AUTHOR]

The present work aimed to describe the mechanisms involved in the enhancement of the drying and rehydration process of carrot slices caused by the pre-treatment using the ultrasound technology. For that, carrot slices of 4 mm of thickness were pre-treated for 30 and 60 min using an ultrasonic bath (41 W/L; 25 kHz). The convective drying process was performed at 40 and 60 °C with 2.0 m/s of air velocity, while the rehydration process was performed at 25 °C. The Henderson & Pabis model was used to describe the drying kinetics and the Peleg model to describe the rehydration process of the carrots slices. As a result, the drying and rehydration kinetics were described, at the different conditions of process, correlating the results with the main effects that the ultrasound cause as a pre-treatment (cell bloating and micro-channels) and the air-drying temperature. Depending on the length of the pre-treatment, the effects caused by the ultrasound in the following processes were different. In addition, it was corroborated that when the drying temperature is increased, less evidenced is the ultrasound effect. The ultrasound, when is applied for long times, enhanced the drying and further rehydration rate at low temperatures, due to the tissue damage. Moreover, vacuum-packed samples were pre-treated with ultrasound in order to exclude the water gain and to evaluate only the micro-channels formation effect. It was concluded that the ultrasound pre-treatment enhances the drying and rehydration processes; however, future optimization studies are recommended. [ABSTRACT FROM AUTHOR]

A one-dimensional unsteady state mathematical model of coupled heat and mass transfer equations is accomplished to simulate the convective drying of cylindrical quince slices with axis parallel to the hot air flow. The semi-analytical proposed solution method considers fundamentals of the convective drying process and takes internal resistances to temperature and moisture content into account. Green's function method (GFM) is used due to existence of time dependent boundary conditions. In the present study, unlike classic problems, evaporation term initiate a strong coupling between heat and mass transfer equations and therefore in the present study the basic idea of numerical solutions which is repetition and correction, is used to present a novel analytical solution and correct it. In addition the effects of Biot number and relative humidity on drying kinetics are investigated. The agreement between published experimental results and model predictions is remarkable. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the effect of different dying methods, such as convective drying (CD: 50, 60, 70 °C), vacuum-microwave drying (VMD: 120, 480, 480–120 W), a combination of convective pre-drying and vacuum-microwave finish drying [(CPD (60 °C)-VMFD (480–120 W)], and freeze-drying (FD) on key quality parameters of dried jujube fruits (cv. “ GAL ”, “ MSI ”, and “ PSI ”). The parameters studied included bioactive compounds (flavan-3-ols and flavonols, identified by LC-PDA-MS, and vitamin C), antioxidant capacity (ABTS and FRAP), and sensory attributes (e.g. hardness, jujube-ID, and sweetness). The best quality of the dried product (high contents of bioactive compounds and high intensity of key sensory attributes) was found in fruits treated by FD and VMD 480–120 W. The best cultivars were “ PSI ” and “ GAL ” from the point of view of bioactive content and sensory quality, respectively. [ABSTRACT FROM AUTHOR]

Physicochemical quality parameters of plum powders obtained by applying conventional drying methods and their combination devised to process plums were evaluated. The effect of freeze-drying (FD), vacuum drying (VD), convective drying (CD), microwave-vacuum drying (MVD) and combination of convective pre-drying and microwave finish-drying (CPD-MVFD) affected physical (bulk density, porosity, colour, solubility) and chemical (polyphenolic compounds determined by UPLC and antioxidant capacity by TEAC ABTS and FRAP methods) properties of plum powders. The MVD at 1.2 W g −1 and a novel combination for plum powders production – CPD-MVFD at 70 °C/1.2 W g −1 allowed the best preservation of phenolic compounds and increased the efficiency of production. Results obtained support the use of MVD and its combination for better quality of dried plum products. The study proved that the determination of the browning index and HMF level (formed via Maillard reaction) might be good tool for monitoring the thermal processing of plum powders. [ABSTRACT FROM AUTHOR]

Convective drying of a moving moist object is investigated numerically solving the conservation equations of mass, momentum, energy and air moisture concentration based on a k – ∊ turbulence model in the external region of the object as well as the conservation equations of energy and object moisture concentration in the internal region. The external and internal conservation equations are coupled to the heat and mass transfer conditions on the object surface including the effects of evaporation and water activity. The numerical results show that the analogy between heat and mass transfer for the convective drying is valid only when the object temperature is close to the equilibrium temperature. The simple analytical formulations developed for the total drying rate are found to compare well with the numerical results. The effects of object velocity and thickness and the wall heat flux on the drying rate are quantified. [ABSTRACT FROM AUTHOR]

The effect of ultrasound pretreatment prior to convective drying on drying kinetics and selected quality properties of mulberry leaves was investigated in this study. Ultrasound pretreatment was carried out at 25.2–117.6 W/L for 5–15 min in a continuous mode. After sonication, mulberry leaves were dried in a hot-air convective dryer at 60 °C. The results revealed that ultrasound pretreatment not only affected the weight of mulberry leaves, it also enhanced the convective drying kinetics and reduced total energy consumption. The drying kinetics was modeled using a diffusion model considering external resistance and effective diffusion coefficient D e and mass transfer coefficient h m were identified. Both D e and h m during convective drying increased with the increase of acoustic energy density (AED) and ultrasound duration. However, D e and h m increased slowly at high AED levels. Furthermore, ultrasound pretreatment had a more profound influence on internal mass transfer resistance than on external mass transfer resistance during drying according to Sherwood numbers. Regarding the quality properties, the color, antioxidant activity and contents of several bioactive compounds of dried mulberry leaves pretreated by ultrasound at 63.0 W/L for 10 min were similar to that of mulberry leaves without any pretreatments. Overall, ultrasound pretreatment is effective to shorten the subsequent drying time of mulberry leaves without damaging the quality of final product. [ABSTRACT FROM AUTHOR]

A computational model capable of simulating heat and mass transfer in conjugate fluid-porous domains is utilized to simulate forced convective drying. The material to be dried is considered as the porous region, which is coupled through interfaces to the surrounding pure fluid region. The computational model solves transport equations for mass and momentum, energy, and moisture in all regions simultaneously. The model includes non-equilibrium heat and moisture transport in the porous region such that the fluid and solid constituents, and the exchanges between them, are captured. The interfacial moisture transfer condition between phases in the porous region, and between the porous and pure fluid regions, is developed to show the level of detail required for modeling. The study considers the drying of apple flesh to validate the developed drying model against available experimental data. The results show accurate prediction of moisture content as a function of drying time for different airflow velocities, and correctly capture the influences of temperature, relative humidity and initial moisture content on the drying rate. Thus, the model is considered viable for taking steps towards implicit dynamic coupling of the constituents in the porous region. [ABSTRACT FROM AUTHOR]

In convective drying of fruits and vegetables the maximum temperature develops at the product surface. Furthermore, heat sensitive products can be subjected to high air temperatures in the first stage of drying where the difference between air temperature and wet bulb temperature of the product is still very high. Automatic control of the surface temperature, avoiding exceeding of the maximum allowable temperature, can guarantee for the best drying results in terms of product quality. In the study presented, a lumped parameter model, based on experimental results, for both the drying process of apple slices as well as the automatic control functionality is proposed. The simulation model shows close correlation with experimental data and can be used to determine optimum control and process parameters for convective drying of apples slices. Application of this strategy leads to a significant decrease of drying time and, potentially, increase of process efficiency and product quality. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of temperature and ultrasound application on drying kinetics and antioxidant potential of passion fruit peel. To this end, drying experiments (1 ms −1 ) were carried out at 40, 50, 60 and 70 °C without and with ultrasound application (21,7 kHz, 30.8 kW/m 3 ). Two diffusion models based on Fick's second law were used to mathematically describe the drying kinetics considering or not the external moisture transport resistance. The antioxidant capacity and the total phenolic content of dried passion fruit peels were assessed. The increase in temperature and the application of ultrasound significantly reduced the drying time. Modeling showed that the application of ultrasound increased both the effective diffusivity and the mass transfer coefficient, particularly at the mildest temperatures tested, 40 and 50 °C. Under these conditions, ultrasound application also reduced the loss of total phenolic content and maintained the antioxidant activity of dried passion fruit peel. [ABSTRACT FROM AUTHOR]

In this study, EHD was applied for apple slices drying through a multiple needle-to-plate electrode with a fixed 25 mm gap, using different combinations of voltage and air velocity at room temperature. Effects of EHD on drying kinetics, color degradation, and energy consumption were studied. High voltage significantly increased drying rate by 1.5–4 times at high (5 m/s) and low (1 m/s) air velocity, respectively. Combined EHD-convective drying was more efficient for moisture removal than sole EHD drying. The most significant effect of EHD on drying rate was observed at the highest voltage and low air velocity. Effect of EHD on color was insignificant at voltages below 10 kV, but higher voltage intensified progressively color degradation. Energy, used in EHD drying, was negligibly small (1–2%) as compared to the total energy consumption of AC/DC converter. [ABSTRACT FROM AUTHOR]

• The idea of jet impingement convective drying utilizing micro-encapsulated PCM is introduced for the first time in the literature. • MEPCM particles dispersed in moisture content of porous material and is exposed to a compressible air jet. • PCM commences its role as a heat sink then becomes a heat source for the rest of drying process. • 70.2% improvement in heat transfer enhancement corresponding to 50% PCM volume fraction. The concept of convective drying of a moist porous material in the presence of micro-encapsulated phase change material is introduced in this study and then its favorable impact on drying efficiency is numerically investigated. In this regard, encapsulated PCM particles are dispersed inside the void part of porous medium while the moist sample is exposed to a compressible impinging slot jet. The transient evaporation process from a moist porous material exposed to a compressible air jet while PCM particles dispersing in water content of a porous sample is mathematically modeled and solved afterwards employing Finite Element Methods. A mathematical optimization technique is performed on the melting temperature of PCM to select a PCM appropriate to the thermal drying process. The numerical experiment in this work indicates that PCM facilitates the moisture removal process and dramatically reduces the water content in a typical convective drying. Investigating the transport mechanism, results show that PCM acts as a heat sink at the early stages of drying and then alternates to a heat source, releasing previously stored energy and internally heating the moist sample. According to the results, a 70.2% improvement in heat transfer enhancement is reported corresponding to 50% PCM volume fraction. The effects of PCM volume fraction, exit Reynolds number, and jet outlet temperature on PCM-equipped convective drying is considered. [Display omitted]. [ABSTRACT FROM AUTHOR]

Convective drying of waste water sludge and sawdust-sludge mixtures in a pilot-scale fixed bed was studied. Drying was performed in a cross-flow convective dryer using 500 g of wet material extruded through a disk with circular dies 12 mm in diameter. The structure of the bed mainly shows volume shrinkage and crack formation during drying. Several characterization techniques were used over a wide range of scales from nm up to mm. The overall bed structure was imaged with X-ray macrotomography, at a resolution of 0.36 mm per pixel. Single extrudates were scanned with X-ray microtomography, at a resolution of 41 μm per pixel. Pore structure of the dried samples were characterized by mercury porosimetry (7.5 nm < d p < 150 μm). Results show significant structural changes on all scales with increasing amounts of sawdust: shrinkage decreases, crack formation increases, and the pores become larger. This confirms the benefits of sawdust addition for sludge drying applications. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD) drying is an innovative drying method. For this investigation, a combined convective-EHD drying system with two variables of voltage (at four levels of 0, 20, 25 and 30 kV) and velocity (at two levels of 0.4 and 2.2 m/s) on drying kinetics, remaining moisture content, porosity, shrinkage, rehydration ratio, shear strength, color, and microstructure of mushroom slices was envisaged. The eight drying treatments (30 kV–0.4 m/s, 25 kV–0.4 m/s, 20 kV–0.4 m/s, 0 kV–0.4 m/s, 30 kV–2.2 m/s, 25 kV–2.2 m/s, 20 kV–2.2 m/s and, 0 kV–2.2 m/s) were carried out at 45 °C for a period of 5 h. ANOVA showed that these eight drying treatments had a significant effect with p ≤ 0.01 on porosity and with p ≤ 0.001 on moisture content, shrinkage, rehydration ratio, and shear strength, but no significant difference was observed in the color of the dried mushroom slices. The advantages of the mushroom slices dried at a higher voltage or air flow velocity included a higher drying rate, porosity and rehydration ratio and a lower remaining moisture content. However, the higher voltage or air velocity caused the development of a wrinkled and broken structure, leading into more shrinkage and shear strength. [ABSTRACT FROM AUTHOR]

The purpose of this work is to analyze the impact of airborne ultrasound on the drying efficiency of biological materials ( Lobo apples). Experimental kinetics curves for drying apples were obtained from tests done in a hybrid dryer equipped with a new plate-transducer in an ultrasonic power generator. These curves were used to validate the numerical kinetic curves determined on the basis of a drying model that was developed by the authors. The intensification of heat and mass transfer by drying due to ultrasound provoked “heating effect” and “vibration effect” are analyzed. The obtained results allow to state that ultrasounds make the drying processes more effective and enhance the drying efficiency of biological products without significantly raising their temperature. [ABSTRACT FROM AUTHOR]

Thermodynamic study of incubated eggs is an important component in the optimisation of incubation processes. However, research on the interaction of heat and moisture transfer mechanisms in eggs is rather limited and does not focus on the hatching stage of incubation. During hatch, both the recently hatched chick and the broken eggshell add extra heat and moisture contents to the hatcher environment. In this study, we have proposed a novel way to estimate thermodynamically the amount of water evaporated from a broken eggshell during hatch. The hypothesis of this study considers that previously reported drops in eggshell temperature during hatching of chicks is the result remaining water content evaporating from the eggshell, released on the inner membrane by the recently hatched wet chick, just before hatch. To reproduce this process, water was sprayed on eggshells to mimic the water-fluid from the wet body of a chick. For each sample of eggshell, the shell geometry and weight, surface area and eggshell temperature were measured. Water evaporation losses and convection coefficient were calculated using a novel model approach considering the simultaneous heat and mass transfer profiles in an eggshell. The calculated average convective coefficient was 23.9±7.5 W/m 2 °C, similar to previously reported coefficients in literature as a function of 0.5–1 m/s air speed range. Comparison between measured and calculated values for the water evaporation showed 68% probability accuracy, associated to the use of an experimentally derived single heat transfer coefficient. The results support our proposed modelling approach of heat and mass transfer mechanisms. Furthermore, by estimating the amount of evaporated water in an eggshell post-hatch, air humidity levels inside the hatcher can be optimised to ensure wet chicks dry properly while not dehydrating early hatching chicks. [ABSTRACT FROM AUTHOR]

Foaming pretreatment has long been recognized to promote drying materials with sticky and viscous behaviors. A novel approach, CaO addition followed by appropriate mechanical whipping, was employed for the foaming of dewatered sludge at a moisture content of 80–85%. In the convective drying, the foamed sludge at 0.70 g/mL had the best drying performance at any given temperature, which saved 35–41% drying time for reaching 20% moisture content compared with the non-foamed sludge. Considering the maximum foaming efficiency, the optimal CaO addition was found at 2.0 wt%. For a better understanding of the foaming mechanisms, the foamability of sludge processed with other pretreatment methods, including NaOH addition (0–3.0 wt%) and heating application (60–120 °C), were investigated while continuously whipping. Their recovered supernatant phases were characterized by pH, surface tension, soluble chemical oxygen demand (sCOD), protein concentration, polysaccharide concentration and spectra of excitation-emission matrices (EEM). These comparative studies indicated that the sludge foaming was mainly derived from the decreased surface tension by the surfactants and the promoted foam persistence by the protein derived compounds. Further, a comprehensive analysis of the sludge drying characteristics was performed including the surface moisture evaporation, the effective moisture diffusivity and the micromorphology of dried sludge. The results indicated that the drying advantages of foamed sludge were mainly attributed to the larger evaporation surface in a limited drying area and the more active moisture capillary movement through the liquid films, which resulted in longer constant evaporation rate periods and better effective moisture diffusivity, respectively. [ABSTRACT FROM AUTHOR]

Fruits and vegetables are porous in nature and undergo pronounced shrinkage during convective drying process. Therefore, shrinkage and porosity should be taken into consideration while predicting heat and mass transfer. This work was conducted to study shrinkage and porosity changes along with simultaneous heat and mass transport during the process. Potato slices were subjected to drying for 7 h at 62 °C. It was observed that shrinkage varies linearly with respect to moisture content and reduction in radial dimension of potato slices was around 35%. Porosity undergoes rapid increase after attaining certain moisture content in final stages of drying. The work was extended to study the influence of shrinkage and porosity on heat and mass transfer. Simulated results were validated with experimental values. This model can be employed to predict temperature, moisture, density profiles and to study shrinkage and porosity of various fruits and vegetables. [ABSTRACT FROM AUTHOR]

Based on the drying theory developed earlier by the authors, this paper presents some results of computerized simulation of convective drying of a solid material, leading to optimal drying conditions; thus, offering minimum energy consumption and high product quality obtained at a maximum yet permissible drying rate. The thermo-hydro-mechanical model of drying is used to describe the kinetics of drying and to analyze drying-induced stresses which are responsible for damage of dried products. The effective stress defined on the basis of the energetic criterion is related to the admissible stress; thus, constituting the strength criterion for a given material. Three different numerical examples of effective drying are presented based on a sample of finite dimensions of a kaolin-clay cylinder subjected to convective drying. [ABSTRACT FROM AUTHOR]

A mathematical model is developed to simulate the response of a kaolin clay sample when subjected to convective, convective–microwave and convective–infrared mode. This model is proposed to describe heat, mass, and momentum transfers applied to a viscoelastic medium described by a Maxwell model with two branches. The combined drying methods were investigated to examine whether these types of drying may minimize cracking that can be generated in the product and to know whether the best enhancement is developed by the use of infra-red or microwave radiation. The numerical code allowed us to determine, and thus, compare the effect of the drying mode on drying rate, temperature, moisture content and mechanical stress evolutions during drying. The numerical results show that the combined drying decrease the intensity of stresses developed during drying and that convective–microwave drying is the best method that gives a good quality of dried product. [ABSTRACT FROM AUTHOR]