Initial Stage Of Drying Research Articles

Attempts of B-site doped LaFeO3 oxygen carriers in high-moisture content biomass chemical looping gasification

With the rapid development of anaerobic digestion engineering, the disposal and utilization of digestate are urgently required. Chemical looping gasification (CLG) technology provides potential for eliminate digestate and convert it into high-quality syngas. However, the application of conventional CLG is hindered by the high-moisture content of digestate. In order to decrease the energy consumption of dehydration, this work aims to optimize the CLG process by developing new oxygen carrier (OC) to enhance the transition of self-moisture of digestate. LaFeO3 was employed as the basic OC and Cr, Co, Cu were further doped on the B-site to form LaB0.5Fe0.5O3 (B = Cr, Co, Cu). H2O-TPD, OH/FTIR, NH3-Drifts, Raman, and XPS were employed to analyze the adsorption and dissociation of H2O by different OCs. Results indicated that LaFeO3 and LaB0.5Fe0.5O3 exhibited a synergistic effect with H2O, enabling adsorption of H2O at low temperatures and dissociation at high temperatures. In this case, it allows OC to capture H2O in the initial drying stage, then release H2O and OH at higher temperatures to participate in subsequent reactions, thus significantly increase the gasification performance. Fixed-bed CLG experiments were conducted to corroborate the characterization results. LaCu0.5Fe0.5O3 showcased the best gasification effect, achieving 81.83 % efficiency at a digestate moisture content of 40 %, surpassing LaFeO3 CLG by 5 %. Moreover, LaCu0.5Fe0.5O3 exhibited a noticeable catalytic effect and lowered the activation energy (E). Kinetic analysis revealed a 16 % reduction in E for LaCu0.5Fe0.5O3 CLG in comparison to LaFeO3 CLG.

Upcycling Romaine lettuce outer leaves by infrared blanching and hot air drying.

Romaine lettuce outer leaves, as opposed to the more commonly marketed heart, are typically discarded and present an opportunity for upcycling as dried powders. Duquesne Romaine lettuce was evaluated to quantify and compare quality attributes of fresh outer and heart leaves, dried powders following hot air drying, and dried powders following an infrared (IR) blanching pretreatment before drying. Attributes measured for fresh leaves included moisture, water activity (Aw), color, total soluble phenolics (TSP), and antioxidant capacity (AC). Drying kinetics and time/energy saving through IR blanching were evaluated. Attributes measured for dried powders included moisture, Aw, color, true density, water vapor isotherms, TSP, AC, cadmium (Cd) content, and pesticide residues. TSP, AC, Cd, and pesticide residues were higher, whereas moisture content and Aw were lower in fresh outer versus heart leaves. Hot air drying reduced TSP and AC to 63.6% and 35.2% of fresh values, respectively, whereas IR blanching further reduced TSP and AC to 37.3% and 25.4% in outer leave powders. On the other hand, TSP and AC increased 237% and 151%, respectively, for unblanched heart powders. Higher increase of TSP than AC in heart leaf powder may indicate synthesis of phenolic compounds activated by abiotic stresses such as cutting and high temperatures at the initial drying stage. IR blanching resulted in significant time/energy savings for drying of outer leaves. Microbial loads were substantially reduced during drying, although microbial population on outer leaves were more resistant. Safe to eat outer leaf Romaine lettuce powders can be produced, assuming appropriate agricultural practices.

Effect of ultrasound-assisted osmotic dehydration on the drying kinetics, water state, and physicochemical properties of microwave vacuum-dried potato slices

The effects of pre-treatments on the drying characteristics, water state, thermal properties, and bulk shrinkage of potato slices during microwave vacuum drying (MVD) were investigated. The pre-treatment included ultrasound in distilled water (USOD-0%), and ultrasound-assisted osmotic dehydration in a 60% sucrose solution (USOD-60%). Results showed that the drying time of potato slices was reduced and the drying rate was increased when USOD-0% was used as a pretreatment, whereas USOD-60% had a negative effect on the drying rate of the samples. The Weibull model was effective in predicting the water changes in potato slices during the drying process. NMR analysis revealed that the relative content of immovable water (M22) increased initially, then decreased for drying, while the transverse relaxation time (T2) and the relative content of free water (M23) decreased consistently. The DSC results indicated that the glass transition temperature (Tg) had an inverse relationship with the water content of the samples, yet had virtually no influence on the volume shrinkage. The sample volumes decreased linearly with the decrease in water content during the initial drying stages. USOD pre-treatment lessened the volume shrinkage of MVD potato slices. Static gravimetry was used to determine the moisture sorption isotherms of MVD potato slices at 30 °C within the aw range of 0.113–0.923. The GAB model accurately fitted the experimental sorption data, which showed sigmoid shape curves for the MVD samples. When aw values exceeded 0.7, the USOD-60% treatment significantly reduce the water sorption capacity of MVD potato slices, while USOD-0% treatment was observed to increase the hygroscopic properties of MVD samples. Compared with the control, USOD-0% pretreatment significantly increased the monolayer water content (X0), sorption surface area (S0), the thickness of sorbed water multilayer (tm), and density of sorbed water (Ds) values of MVD potato slices, while USOD-60% decreased these values.

Hydromechanical behavior of wood during drying studied by NIR spectroscopy and image analysis

Abstract The physical properties of wood are important parameters to qualify the material. However, as it is a heterogeneous material, moisture content and wood contractions may vary within the sample. Thus, the objective was to monitor the hydromechanical behavior of wood during drying using near infrared (NIR) spectroscopy and image analysis. Equidistant points were marked on the radial surface of a wooden board and NIR spectra were recorded at each marking during drying of the piece. After spectral acquisition in each drying step, images were obtained and the markings were referenced to monitor contractions during drying. Moisture content (MC) estimates via NIR spectra showed strong correlation with reference values (R2cv = 0.92, RMSEcv = 9.82 %). From the estimates it was possible to generate graphic images to visualize and quantify the spatial variation of MC and shrinkage during wood drying. In the initial stages of drying, the ends of the material showed high moisture in relation to the center of the sample. However, MC loss was 11 % greater at the ends of the wood board when compared to its interior while the shrinkage in external zones was 3 times greater than the internal part. The use of NIR technique associated with image analysis can be a promising tool for estimating moisture contents and contractions in wood.

Effect of blanching and ultrasound pretreatment on moisture migration, uniformity, and quality attributes of dried cantaloupe.

To overcome problems of browning and crusting during the pretreatment process and provide theoretical guidance for cantaloupe convection drying at 80°C, the effects of blanching (BL) and ultrasonic (US) treatments were examined. The effects of various BL (5, 10, and 15 s) and US (10, 20, 30, and 40 min) durations on convection drying were tested. The moisture ratio, drying rate, moisture effective diffusivity, color, browning, nuclear magnetic resonance characteristics, and texture were assessed. Compared with the control group, the maximal decreases in the drying time of BL and US pretreatment groups were 40% and 33.3%, respectively. BL and US pretreatments significantly increased the effective diffusion coefficient and shortened the drying time because of the destruction of the cell structure. Low-field nuclear magnetic resonance analysis showed that free water is mainly lost during the initial drying stage, while solidified water is mainly lost during middle and late stages. According to the results of magnetic resonance imaging, the moisture distribution shows that cavitation from US acts on internal tissue, while BL disrupts the structure of external tissue. Texture data define the area enclosed by SC-D as uniform. After BL and US pretreatment, the hardness of dried cantaloupe decreased and the uniformity increased significantly. The best pretreatment process for cantaloupe at 80°C was 10 min of US. These findings provide a reference for testing in the industrial production of dried cantaloupe and are deeply relevant for practice.

Drying characteristics of a Japanese dry-cured ham model: Effect of temperature and humidity

The drying characteristics of a Japanese dry-cured ham model containing uniformly distributed brine were investigated. A higher effective moisture diffusivity was obtained at a lower relative humidity (RH) level. The activation energy of effective moisture diffusivity at 40 and 70% RH increased with decreasing moisture content, and was almost constant in the late stage of drying. Therefore, the moisture likely diffused without a large difference in the moisture distribution in the sample. In contrast, under low (10%) RH, the activation energy drastically increased with decreasing moisture content in the initial stage of drying. From the results of magnetic resonance imaging, the moisture content on the surface was drastically decreased; the surface was dried and hardened temporarily (i.e., case hardening) by the fast transfer of moisture. In the middle to late stages of drying, the activation energy gradually decreased to the similar values as at 40 and 70% RH in the late stage of drying. From the results of magnetic resonance imaging analysis after drying, the moisture distribution near the surface no longer exhibited a sharp difference in moisture concentration. The partly dried state of the surface could be alleviated by the transfer of moisture from the inside of the sample. Comparing the energy consumption for drying up to 175% dry basis, the drying condition of 35°C and 40% RH was the most efficient.

Effect of microwave freeze drying on moisture migration and gel characteristics of egg white protein

This article mainly explored the influence of microwave freeze drying (MFD) power on water migration and gel characteristics of egg white. Fourier transform infrared spectroscopy (FT-IR), Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and scanning electron microscopy (SEM) were used to determine the water migration law and gel characteristics of egg white under different microwave power drying conditions. The results showed that the free water of egg white was removed first, and the water content decreased exponentially at the initial stage of drying. The weakly bound water and bound water accounted for a large proportion, thus, the drying rate decreased in the later stage. SEM showed that the gel strength of egg white protein enhanced with the drying time and reached a maximum of 399.11 g at 5 h. The gel network structure was also denser and smoother than the initial drying stage. FT-IR analysis implied that in the early stage of drying, protein molecules were unfolded under the influence of drying conditions, the hydrogen bonds maintaining the α-helix were broken, and hydrogen bonds content continually decreased. SDS-PAGE showed that the drying treatment had no effect on the peptide chain structure of the protein, and several protein molecules gathered at 6 h. This study provides a reference for MFD of egg white powder.

Drying quality and energy consumption efficient improvements in hot air drying of papaya slices by step-down relative humidity based on heat and mass transfer characteristics and 3D simulation

Convective hot air drying technology is widely used for fruits and vegetables drying process due to its simplicity in usage, small investment, and convenience in operation. However, it is generally considered energy-intensive process with lower drying efficiency and quality because of unprecise control of drying process. In order to solve these problems, step-down relative humidity (RH) hot air drying technology was applied for papaya drying to improve drying efficiency and quality and reduce energy consumption. The effect of constant RH (20%, 30%, 40%, and 50%) and step-down RH of 50% with different holding times (10, 30, 60, and 90 min) and then decrease to 20% on heat and mass transfer process, drying quality, and energy consumption was examined. Results showed that decreasing RH contributed to improvement in the drying rate (DR). Compared to constant RH of 20%, the drying time under initial RH of 50% for 30 min followed by 20% RH shortened by 21.4%. Additionally, under this RH control strategy, the rehydration ratio (RR) and energy consumption achieved their maximum (7.71 ± 0.06) and minimum value (0.015 ± 0.001 kJ/g), respectively. During initial drying stage, high RH improved convective heat transfer coefficient (ht ) values and material temperature increased quickly. Furthermore, high RH contributed to maintaining pore structure formation, which benefited moisture diffusion. When RH was reduced, low RH enhanced convective mass transfer coefficient (hm ) significantly, resulting in rapid diffusion of internal moisture at high temperature, as well as rapid moisture evaporation from the surface. Therefore, step-down RH hot air drying was verified to improve drying of papaya slices, making it energy efficient process. The findings in current work indicate step-down relative humidity strategy is a promising technique to enhance hot air drying process, quality, and energy efficiency of papaya slices.

Interaction between large deformation and moisture transport during dehydration of vegetables

In this work, we present a multiphysics model describing heat and mass transport during drying of broccoli stalks, which is coupled to mechanical deformation. The model predicts collapse of pores due to compressive stresses during the initial stage of drying, which is later followed by reopening of pores if the liquid pressure gets under tension. This behaviour is qualitative in line with the experimental MRI observations during drying of broccoli stalk. The MRI observations show an apparent increase of moisture content in the centre of the sample during the initial stage of drying, which is consistent with the collapse of pores. In the later stages of drying, the MRI signal is prone to susceptibility effects, which can be explained by the reopened pores in the outer regions of the stalk. The purpose of this study is to show how mechanical deformation can be incorporated in a multiphysics model of drying of vegetables in a thermodynamic consistent manner. • A multiphysics model coupled with mechanical deformation was built. • The elastomeric skin can lead surprising increased moisture content. • The stress gradient can result in moisture transport against the moisture gradient.

Study on the mass and heat transfer characteristics of the drying process of spent nuclear fuel cladding with nitrogen assisted

The spent nuclear fuel cladding needs to be cooled in water for a long time before being compressed. The water attached to the solid must be dried before compressing the spent nuclear fuel cladding. In this paper, based on the heat and mass transfer process inside the porous medium, a coupled heat and mass transfer model for the nitrogen-assisted drying of the waste cladding porous medium is established. The influence of nitrogen flow rate, temperature and inlet position on the heat and mass transfer characteristics of the porous medium in the nitrogen-assisted drying of waste cladding is analyzed. The results show that the calculated results of the model are in good agreement with the experimental results. According to the temperature change on the surface of the waste cladding, the gas-assisted drying process can be divided into three stages: the initial stage of drying, the accelerated drying stage and the latter stage of drying. In addition, the nitrogen flow rate has the greatest impact on the accelerated drying stage in the drying process, and the change of the nitrogen flow rate only changes the heat transfer rate between the liquid and solid phases. Nitrogen temperature affects the drying time by changing the heat transfer coefficient between the gas and liquid phases during the drying process. The inlet position of nitrogen affects the drying time by changing the convection effect between the gas and liquid phases in the drying process. The above research provides reference for the study of the heat and mass transfer characteristics and the mechanism of the drying process in the process of nuclear fuel solid waste treatment. It can also provide an important reference for the application research of key equipment in the reprocessing of spent fuel in nuclear power plants.

JUSTIFICATION OF A RATIONAL METHOD AND EQUIPMENT FOR DRYING HIGH-MOISTURE SEEDS OF MELONS

The main reason holding back the wide distribution of pumpkin, like some other crops, is the lack of quality seeds. The receipt and storage of seed is largely dependent on the methods and means of drying. When choosing a technology and means for drying pumpkin seeds, one must take into account their adhesion properties, that is, the tendency to form conglomerates under certain conditions, sticking to working bodies, etc. Drying equipment should ensure uniform drying throughout the entire volume of products with different moisture content, as well as a change in the main process parameters – temperature and drying agent feed rate, which will allow the use of differential drying modes. But in drying installations used for grain processing, it is practically impossible to organize a high-quality process due to the impossibility of using differentiated modes of drying seeds, as well as increased cohesive-adhesive properties of the pumpkin seed layer. A much greater effect is achieved by devices with active hydrodynamic modes, in particular, in a fluidized bed with its modifications: an aerial boiling, vibroboiling and aerovibroboiling bed. In order to improve the flowability of a layer of materials prone to sticking, sticking, the formation of channels in the material layer, agglomeration, at the initial stage of drying, along with vibration and aeration mixing, it is advisable to use additional mechanical mixing devices. The article proposes a fundamentally new concept of energy-saving drying of high-moisture seed materials, in particular pumpkin seeds, the drying process of which through specific morphological, thermophysical, increased cohesive-adhesive properties, the presence of residues of the surface film and fruit in the seed layer is the most energy-intensive. At the first stage in the process of filtration drying, in which the heated drying agent under the influence of pressure drops moves through the cellular structure of the gas-permeable material, the drying of the material also occurs due to a change in the state of aggregation of the available, mainly surface, moisture. At the second stage, when the seeds acquire discrete properties, drying occurs in the aerovibroboiling layer due to the developed phase contact and an increase in the convective diffusion rate, which contributes to an increase in the drying rate in general and allows the process to be carried out at the maximum permissible values of seed heating. To carry out research to determine the rational technological parameters of the process, a structural and technological scheme of a vibration unit has been developed and a prototype has been created, which sequentially implements the filtration and convective stages of drying pumpkin seeds.

Microwave freeze‐drying of button mushroom (Agaricus bisporus) based on non‐volatile taste components by controlling microwave power density

SummaryThe present study was carried out to establish a dynamic microwave loading strategy for efficient production of high‐quality microwave freeze‐dried button mushroom based on non‐volatile taste components. The change behaviour of non‐volatile taste components of mushroom, including free amino acids and 5′‐nucleotides, was evaluated during microwave freeze‐drying with fixed microwave power. Then, the dynamic microwave loading strategy was established according to the change behaviour of the non‐volatile taste components. Drying and quality characteristics of mushroom were evaluated in terms of drying time, whiteness index, shrinkage ratio, rehydration ratio and vitamin C content. Results showed that high microwave power led to higher contents of free amino acids and 5′‐nucleotides at the initial stage of drying, but more degradation of these non‐volatile taste components was observed during the last period of drying. Moreover, it takes longer for 5′‐nucleotides to reach the highest content than total free amino acids. According to the evolution of non‐volatile taste components, a step‐down dynamic microwave power loading program (0–1.5 h: 4 W g−1; 1.5–4.5 h: 3 W g−1 and 4.5–10.5 h: 2 W g−1) was established to reduce the drying time, keeping a relatively high product quality.

Effects of model boundary conditions on simulated drying kinetics and inversely determined liquid water permeability for cement-based materials

The accurate simulation of moisture transport in cement-based materials is an important step to predict many durability processes of concrete structures. This paper studied the effects of boundary conditions on modeling moisture transport, in particular for simulating drying kinetics and the inverse determination of liquid water permeability. Three boundary conditions were investigated, namely, the Dirichlet (imposed) condition, the flux boundary condition, and the boundary supplied by moisture movement in the ambient environment (coupling with a convection-diffusion moisture transport model). By comparing with the measured drying mass loss curves (without airflow) for ordinary Portland cement pastes, we found that the Dirichlet boundary condition provides slightly better simulated drying kinetics than the flux boundary condition, while results of the coupling model are less promising. As for inversely determined liquid permeability, the studied boundary conditions lead to the max. 36% difference. If considering the airflow in the environment, both the flux boundary condition and the coupling model with computational fluid dynamics (CFD) show that the airflow does not have an effect on moisture evaporation for the studied cement-based materials, because of their low permeability, resulting in a very short initial stage of drying. Moisture evaporation for these materials is mainly controlled by the internal moisture transport. However, for materials with high permeability, the drying kinetics increase with the airflow velocity because the initial stage of drying becomes much longer than the low permeable materials. The implication is that some laboratory methods for drying cement-based materials (specimens stored in a sealed chamber without airflow) may need to be reevaluated because the relative humidity at the material surface is different from the controlled relative humidity.

Computer model of drying behaviour of ceramic green bodies with particular reference to moisture content dependent properties

A numerical model was developed to predict the drying behavior of ceramic green bodies. Resolution of the simultaneous heat and mass transfer equations involved finite elements and the Backward Euler method. Based on experimental data, the model uses equivalent moisture diffusivity, water activity, thermal conductivity and heat capacity as input parameters which depend on moisture content. In particular, the equivalent moisture diffusivity is a key parameter controlling water transport from the body interior to the surface. A simple method was used to estimate the effect of shrinkage on drying rate during the initial drying stage. Predictions of the internal moisture distribution, drying rate and surface temperature as a function of time gave good agreement to experiment for green bodies of alumina paste. External conditions of convection coefficient and relative humidity are shown to sensitively control drying rate and surface temperature evolution during the constant rate period.

The influence mechanism and control strategy of relative humidity on hot air drying of fruits and vegetables: a review

Drying temperature, air velocity, material thickness during hot air drying usually have a significant influence on drying kinetics and quality attributes of fruits and vegetables. However, under constant drying temperature, the influence of relative humidity (RH) of hot air on heat and mass transfer is often ignored in drying practice. On the other hand, the current literature about the influence of relative humidity of drying medium on drying kinetics and quality of fruits and vegetables are inconsistent or even contradictory. Usually, the relative humidity is roughly controlled based on experience. Therefore, it is necessary to summarize and reveal the influence mechanism of relative humidity of drying medium on drying kinetics and quality of fruits and vegetables. The RH effect mechanism on drying kinetics is analyzed in two aspects including heat transfer and mass transfer. Increasing RH intensifies heat transfer process while decreasing RH intensifies mass transfer process. Applied high RH in the initial drying stage and then decreasing RH can improve drying efficiency compared to the continuous dehumidification RH drying method. Additionally, step-down RH drying strategy method helps to mitigate the formation of casehardening on product surface and promote pore network, which is benefit for moisture transfer and diffusion. High RH during hot air has the potential to improve the pore network of materials, which is helpful for rehydration ratio. Additionally, low RH increases drying rate so that material surface generates a rigid crust or shell that fixes the volume. Low temperature but high RH drying medium can preheat the sample as soon as possible so as the energy which was used to heat the drying air can be saved. The applicable of step-down RH drying strategy is suitable for those food materials drying, whose β value is more than 1 in Weibull distribution model and Bi value in Bi-Di model is more than 0.1. In other circumstances, continuous dehumidification drying is suitable for food material drying. The auto RH control adjustment drying strategy has been investigated based on material temperature. Such RH control drying strategy provides theoretical foundation for enhancing drying efficiency and quality of fruits and vegetable materials.

Analysis of Drying Process of Water-Based Architectural Paints

Due to its low toxicity and because they are environmentally friendly, water-based paints are the most employed in the world, mainly to coat buildings. In these systems, the water evaporation process is important to determine the final paint quality and should be carefully evaluated. This work evaluated the suitability of Crank’s model, solution of the Fick’s second law, to experimental drying data of water-based architectural paints to better understand this process. Therefore, the data were adjusted to the linearized and original model and the number of terms used in its approximation was varied. For each model, the diffusion coefficient of the water in the coating material and the coefficient of determination were calculated. The results showed that the use of the linearized model is not adequate to determine the diffusion coefficient, but the nonlinear adjustment of the original model can adjust the data for some paints. These results also suggest the addition of terms to the sum of the model to improve its quality in the initial stages of drying. DOI: http://dx.doi.org/10.17807/orbital.v13i1.1508

Moisturizing strategy for enhanced convective drying of mushroom slices

Moisturizing strategy that controls the water evaporation rate of the wet material and thus the relative humidity in the drying chamber was proposed for hot air drying of mushroom slices for the first time. To assess the effectiveness of moisturizing strategy, drying kinetics, moisture diffusivities, mass transfer coefficients, surface color and rehydration capacity of dried products, energy and exergy efficiencies were evaluated. Mushroom slices were dried at constant drying temperature of 60 °C and air velocity of 3 m/s. The strategies of moisturizing for 0, 15, 30, and 45 min were applied in the initial drying stage. Compared to the continuous dehumidifying strategy (moisturizing time is 0 min), the strategies of moisturizing for 15 and 30 min reduced drying time by 5% and 15%, respectively. The proper moisturizing time (30 min) enhanced the heat transfer by increasing the enthalpy of the drying air, improved surface color, and increased rehydration capacity of dried mushroom slices by reducing cell shrinkage. The energy utilization and energy utilization ratio of drying process varied from 0.16 to 3.48 kJ/s and 0.065 to 0.572, respectively, while the exergy efficiency varied from 8.04% to 84.66%. The strategy of moisturizing for 30 min reduced 23.4% total energy utilization compared to continuous dehumidifying strategy. Both the highest average energy utilization ratio, i.e. 0.156 and average exergy efficiency, i.e. 70.19% were obtained for moisturizing time of 30 min. The increase of moisturizing time from 30 to 45 min showed an adverse impact on drying time, energy utilization ratio, exergy loss, and exergy efficiency due to the inhibition of water evaporation. This study shows that moisturizing strategy can be considered as a promising method to enhance energy and exergy efficiency of hot air dryer with the improvement of products quality and sustainability of drying systems.

Pulsed vacuum drying enhances drying of blueberry by altering micro-, ultrastructure and water status and distribution

Effect of pulsed vacuum drying (PVD) on the drying kinetics, microstructure, ultrastructure, water distribution, and bioactive compounds of blueberries were investigated in the current work. Experiments showed that compared to hot air drying (HAD), the drying time of blueberries under PVD was shortened by 32.14% at the same drying temperature of 65 °C. Scanning electron microscopy (SEM) observations showed that several microcracks were formed on the surface of pulsed vacuum dried blueberries. The transmission electron microscopy (TEM) observations indicated that PVD resulted in the presence of abnormal cells of irregular shape and caused more serious damage to the cell walls of blueberries than HAD. Low field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) analyses showed that the successive changes between atmospheric pressure and vacuum resulted in the enlargement and interconnection of pores that are beneficial to the moisture transfer in the initial stage of drying. Compared to HAD, PVD had also a positive effect on maintaining higher contents of total phenolics (TP) and total monomeric anthocyanins (TMA). These findings clarified the mechanism that PVD enhances the drying efficiency and quality of dried blueberries.

Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas.

Conventional kiln drying of wood operates by the evaporation of water at elevated temperature. In the initial stage of drying, mobile water in the wood cell lumen evaporates. More slowly, water bound in the wood cell walls evaporates, requiring the breaking of hydrogen bonds between water molecules and cellulose and hemicellulose polymers in the cell wall. An alternative for wood kiln drying is a patented process for green wood dewatering through the molecular interaction of supercritical carbon dioxide with water of wood cell sap. When the system pressure is reduced to below the critical point, phase change from supercritical fluid to gas occurs with a consequent large change in CO2 volume. This results in the efficient, rapid, mechanical expulsion of liquid sap from wood. The end-point of this cyclical phase-change process is wood dewatered to the cell wall fibre saturation point. This paper describes dewatering over a range of green wood specimen sizes, from laboratory physical chemistry studies to pilot-plant trials. Magnetic resonance imaging and nuclear magnetic resonance spectroscopy were applied to study the fundamental mechanisms of the process, which were contrasted with similar studies of conventional thermal wood drying. In conclusion, opportunities and impediments towards the commercialisation of the green wood dewatering process are discussed.

Research of the influence of ultrasonic oscillation on the drying of textile materials

The article presents the results of experimental studies of the process of convective drying of textile materials under the influence of ultrasonic oscillation. Research is carried out in a drum type dryer (based on LG household dryer) at different drying air temperatures. Were subjected to drying: cotton fabric, polyester and synthetic fluff. The drying process was carried out without ultrasonic exposure and with ultrasonic exposure at a sound pressure level of about 150 dB. The efficiency of ultrasonic exposure on textile materials at the initial stage of drying is shown. It has been found that ultrasonic exposure provides: for cotton fabric, increasing the drying rate to 12–14 % / min at the initial stage of drying; for polyester, increasing the drying rate by 65 % / min at a moisture content of 0.9–1.0; for synthetic fluff, the drying time is reduced by 33–37 %, with increasing the drying rate up to 30 % / min at the initial stage of drying. Thus, it been shown that it is advisable to apply ultrasonic exposure to increase the efficiency of drying textile materials, especially synthetic ones.