Intermittent Drying Research Articles

Convective-intermittent drying of cherries preceded by ultrasonic assisted osmotic dehydration

This paper presents the results of experimental studies on convective drying of cherries (Prunus cerasus L.) in stationary and intermittent conditions, previously pretreated with ultrasonic assisted osmotic dehydration. The effect of a stepwise changing air temperature and osmotic pretreatment on drying kinetics and the biomaterial quality were investigated. The main aim of the studies was to find the possibly best drying conditions, by which the drying time was shortened and the product quality degradation was minimized. Except drying kinetics and total color and water activity changes, the effect of osmotic pretreatment expressed by such parameters as the Solid Gain and the Water Loss were examined. It was proved that intermittent drying of cherries preceded by ultrasonic assisted osmotic dehydration contributes to shorter drying time, better color preservation and smaller water activity.

The Study on Cell Collapse and Recovery of Eucalyptus urophylla during Drying

To explore the collapse of eucalyptus wood cells during the drying process, continuous and intermittent drying were carried out on Eucalyptus urophylla. The shrinkage throughout the intermittent drying process was less than that of continuous drying. According to observations of cells made using scanning electron microscopy (SEM), there was a large difference in the degree of cell collapse between continuous and intermittent drying. Severe cell collapse was observed after freeze-drying at high moisture content, even after an intermittent drying process. It is clear that collapse recovery via intermittent drying was more extensive than in continuous drying. In particular, ray parenchyma and axial parenchyma recovered from collapse more than did wood fibers.

Energy efficiency investigation of intermittent paddy rice dryer: Modeling and experimental study

In this study, energy consumption of intermittent drying of paddy rice is considered. Firstly, a mathematical model consists of two parts is established to describe the moisture distribution within a grain for both drying and tempering stages. The model, which is solved analytically, is proposed based on Fick's second law of diffusion within a sphere. Effects of different parameters namely air temperature and velocity are experimentally investigated utilizing a lab-scale fluidized bed dryer. Thereafter, moisture diffusivity is estimated in Arrhenius form using experimental results. Finally, the model is utilized in an optimization problem to minimize the total energy consumption. Based on experimental results, impact of air velocity on drying characteristics is found to be negligible. The optimization results shows that employing the tempering stages substantially reduces the energy consumption. Not only that, it dictates a process beginning with longer drying stages and lower temperatures while the subsequent stages are shorter with higher temperatures.

Intermittent Drying of Nopal (Opuntia Ficus Indica) in a Fluidized Bed Pilot Dryer Adapted with Revolving Chambers

AbstractIntermittent drying is a novel method for improving the food drying kinetics, enhancing product quality and reducing energy consumption per unit of moisture removed at the lab scale. However, the drying protocol itself makes it difficult to implement it at the pilot plant scale without important energy loses. Taking this into account, an accessory for a fluidized bed pilot dryer was developed using an arrangement of revolving chambers that could increase the efficiency of the drying process; nopal (Opuntia ficus indica) was employed as a food material. Several drying experiments were conducted at the laboratory scale in order to establish the most appropriate drying condition to be further tested at the pilot plant scale. No statistical difference was observed between the drying curves obtained in the laboratory and pilot plant dryers under conventional and intermittent drying conditions, which means that the arrangement of chambers guarantees equal and consistent treatment of the solid. Interestingly, the results indicate that a drying protocol of nopal size “E” using the adapted fluidized bed dryer with tempering cycles at pilot plant scale can be regarded as an excellent and cost‐effective methodology for processing vegetables without chemical quality losses.Practical ApplicationsIn this work, the performance of a novel fluidized bed dryer, adapted with an arrangement of revolving chambers specially designed to increase the efficiency of intermittent drying at the pilot plant scale, was evaluated. Cubes of nopal (Opuntia ficus indica) was chosen to take advantage of a biomaterial with high nutrimental characteristics. It was concluded that the arrangement of the equipment was able to maintain an equal and consistent treatment of the solid that in consequence, lead to a high chemical quality of the final dried product, comparable to that obtained at the laboratory scale. Additionally, the results indicate that the scaling of the process in the dryer prototype was highly efficient as it allowed to increase 300% the amount of biomaterial to be processed in one single drying operation. It was proposed that the use of the dryer adaptor has a great potential to increase the efficiency of drying processes of other biomaterials.

Mathematical Modeling and Effect of Various Hot-Air Drying on Mushroom (Lentinus edodes)

An experimental study was performed to determine the characteristics and drying process of mushroom (Lentinus edodes) by 6 different hot-air drying methods namely isothermal drying, uniform raise drying, non-uniform raise drying, uniform intermittent drying, non-uniform intermittent drying and combined drying. The chemical composition (dry matter, ash, crude protein, crude fat, total sugars, dietary fiber, and energy), color parameters (L, a*, b*, c*, and h0) and rehydration capacities were determined. Among all the experiments, non-uniform intermittent drying reached a better comprehensive results due to the higher chemical composition, better color quality associated with high bright (26.381±5.842), high color tone (73.670±2.975), low chroma (13.349±3.456) as well as the highest rehydration (453.76% weigh of dried body). Nine kinds of classical mathematical model were used to obtained moisture data and the Midili-kucuk model can be described by the drying process with the coefficient (R2 ranged from 0.99790 to 0.99967), chi-square (χ2 ranged from 0.00003 to 0.00019) and root mean square error (RMSE ranged from 0.000486 to 0.0012367).

Visualization of a protein-protein interaction at a single-molecule level by atomic force microscopy

Atomic force microscopy is unmatched in terms of high-resolution imaging under ambient conditions. Over the years, substantial progress has been made using this technique to improve our understanding of biological systems on the nanometer scale, such as visualization of single biomolecules. For monitoring also the interaction between biomolecules, in situ high-speed imaging is making enormous progress. Here, we describe an alternative ex situ imaging method where identical molecules are recorded before and after reaction with a binding partner. Relocation of the identical molecules on the mica surface was thereby achieved by using a nanoscale scratch as marker. The method was successfully applied to study the complex formation between von Willebrand factor (VWF) and factor VIII (FVIII), two essential haemostatic components of human blood. FVIII binding was discernible by an appearance of globular domains appended to the N-terminal large globular domains of VWF. The specificity of the approach could be demonstrated by incubating VWF with FVIII in the presence of a high salt buffer which inhibits the interaction between these two proteins. The results obtained indicate that proteins can maintain their reactivity for subsequent interactions with other molecules when gently immobilized on a solid substrate and subjected to intermittent drying steps. The technique described opens up a new analytical perspective for studying protein-protein interactions as it circumvents some of the obstacles encountered by in situ imaging and other ex situ techniques.

Modeling of water vapor sorption process by employing the reaction engineering approach (REA)

For dehumidification process, sorption process is commonly applied. Mathematical modeling can be implemented in order to assist in minimization of energy consumption and better process design. In this study, the reaction engineering approach (REA), which has been proven to model various challenging drying process successfully, is developed and implemented for the first time to model completely reverse process of drying. The equilibrium activation energy (ΔEv,b) is evaluated according to the environmental temperature and humidity and combined with the relative activation energy to describe the wetting process. Interestingly, the relative activation energy generated from one accurate drying/desorption run can be used to describe accurately the water vapor sorption/wetting process. The REA implemented as the mass balance is combined with the heat balance incorporating the heat of sorption. A good agreement between the predicted and experimental data is shown. The REA is able to model accurately the wetting process. The applicability of the REA could be because of the flexibility of the relative activation energy to capture the environmental conditions and reflect this in the change of internal behavior, similar to the relative activation energy used for intermittent drying process. This indicates that the relative activation energy can be used as fingerprint of both drying and water vapor sorption process.

Effect of Different Drying Processes on the Protein Degradation and Sensory Quality of Layú: A Chinese Dry-Curing Grass Carp

Five different drying methods, sun drying, intermittent drying, low-temperature drying at 5°C, low-temperature drying at 15°C, and hot-air drying at 45°C, were comparatively evaluated based on physicochemical properties and sensory properties of dry-cured Layú. Sun drying and intermittent drying Layú showed superior sensory qualities compared with other dried samples. Based on the comprehensive comparison of sensory qualities and safety concerns, intermittent drying Layú was more acceptable compared to other dry-cured Layú and thus was recommended for dry-curing fish products as it could shorten the drying time with relative constant drying rate, increased flavor amino acid content, and fewer safety concerns.

DRUPELET GERMINATION IN FICUS RELIGIOSA L.

Germination of drupelets of Ficus religiosa L. was studied from the ecological standpoint in an effort to explain the sporadic distribution in Israel of the epiphytic plants of this species, which escape cultivation and grow on the trunk's of various ornamental trees. Drupelets of F. religiosa germinate readily in closed petri dishes and covered pots, when placed on various substrates (like sterile filter paper, light and heavy soil, leaf litter, decaying fruit or fresh fruit pieces) at 25°C, in the light. No germination takes place in total darkness. Constant humidity has been found essential for germination, whereas frequent drying of the substrate hinders germination. These findings explain why germination of drupelets occurs only in constantly wet niches, and not underneath the crown of F. religiosa trees subjected to intermittent watering and drying.

Multiphase modeling of intermittent drying using the spatial reaction engineering approach (S-REA)

Several schemes of energy minimization of drying process including intermittent drying have been attempted. Intermittent drying is conducted by applying different heat inputs in each drying period. An effective and physically meaningful drying model is useful for process design and product technology. The lumped reaction engineering approach (L-REA) has been shown previously to be accurate to model the intermittent drying In L-REA, the REA (reaction engineering approach) is used to describe the global drying rate. In this study, the REA is used to model the local evaporation/condensation rate and combined with the mechanistic drying models to yield the spatial reaction engineering approach (S-REA), a non-equilibrium multiphase drying model. The accuracy of the S-REA to model the intermittent drying under time-varying drying air temperature is evaluated here. In order to incorporate the effect of time-varying drying air temperature, the equilibrium activation energy and boundary condition of heat balance implement the corresponding drying settings in each drying period. The results of modeling using the S-REA match well with the experimental data. The S-REA can yield the spatial profiles of moisture content, concentration of water vapor, temperature and local evaporation/condensation rate so that better understanding of transport phenomena of intermittent drying can be obtained. It is argued here that the REA can describe the local evaporation rate under time-varying external conditions well. The S-REA is an effective non-equilibrium multiphase approach for modeling of intermittent drying process.

A comparative study on intermittent heat pump drying process of Chinese cabbage (Brassica campestris L.ssp) seeds

The aim of this paper was to make a comparative simulation study on different intermittent heat pump dryings with respect to moisture diffusion, energy consumption and drying time on Chinese cabbage seeds. Various intermittent ratios in describing different intermittent drying characteristic were investigated. Experimental parameters for drying initial moisture content 30% (d.b.), temperature 40°C, relative humidity 40%, airflow velocity 1.0m/s, and drying time in a range from 0 to1200s in a cycle. On the basis of unsteady state drying dynamics model, drying rate was analyzed, parameters of control equation in seeds drying process was proved. Advantages of energy consumption and moisture diffusion uniformity were discussed by using simulation of moisture diffusion process in intermittent drying. Results indicated that model of equilibrium moisture content and drying environment could be expressed by Nellist equation as xc=0.41821−0.05448 ln(1−ϕ)−0.0692 ln T. The best intermittent ratio was 1/3 during intermittent drying process, which drying technology was continuous ventilation drying air 400s, then stop 800s in a cycle at 40°C. In this drying process, percent energy saving over continuous drying was 48.1%. So there was an obvious advantage of intermittent drying over continuous drying as regards energy efficiency.

Optimization of Heat Pump–Assisted Intermittent Drying

In the present study, heat pump–assisted drying of salak fruit was optimized by dividing the dehydration process into three distinct phases, namely, the initial, intermittent, and final stages. Drying variables considered for the optimization were the intermittent duration (X 1), intermittent ratio (X 2), and intermittent cycle (X 3); the response variables studied were the total drying time (Y 1), total heating time during intermittent drying (Y 2), total heating time after intermittent drying (Y 3), total color change (Y 4), ascorbic acid content (Y 5), and total phenolic content (Y 6). Response surface methodology was used to determine the best combination of the drying variables that could provide the shortest drying period and premium product quality. Experimental results showed that all of the response variables were improved under the optimized intermittent drying conditions compared to the conventional method using constant drying conditions. The optimized heat pump–assisted intermittent drying reduced the drying time by 36% and improved phytochemicals retention with ascorbic acid and total phenolic content recorded at 18.4 ± 1.8 mg ascorbic acid/100 g dw and 43.3 ± 2.2 mg gallic acid equivalent (GAE)/g dw, respectively. The color change of the final product was minimum with a ΔE* value of 7.26 ± 2.03.

Experimental and Theoretical Investigation of Moisture Dynamics in Intermittent Drying of Rough Rice

Intermittent drying is a satisfactory technique for drying of heat sensitive grains especially rough rice. This method consists of two separate stages applied intermittently: drying and tempering. In this work, intermittent drying of rough rice is investigated both theoretically and experimentally. In order to characterize this process; a multi-scale model consisting of macroscopic and microscopic submodels has been developed. Macroscopic model calculates the moisture changes of the rough rice bed assuming a lumped model for grains, while the microscopic submodel determines the rate of moisture gradient removal during the resting period. In latter submodel, moisture is assumed to diffuse through the grains governing by Fick’s law. Further, a set of experiments were designed and carried out in a lab-scale fluidized bed dryer to estimate the model parameters as well as to evaluate the effects of different parameters such as temperature, air velocity, and tempering time on the drying rate. The model estimates show good agreement with experimental data. Model's results reveal that thermal equilibrium is rapidly obtained within the first two minutes of grain-hot air exposure. Air velocity shows to have no significant effect on drying rate when fluidized condition is prevailed. In addition, a significant kink occurs in drying rate diagrams which implies that drying rate is improved as a result of moisture gradient removal by applying tempering period.

Modeling Intermittent Drying of Wood under Rapidly Varying Temperature and Humidity Conditions with the Lumped Reaction Engineering Approach (L-REA)

For improving product quality and minimizing energy consumption during drying, intermittent drying is often recommended. The mathematical models that are used to describe intermittent drying are usually transport phenomena based, complex models. In this study, the lumped reaction engineering approach (L-REA) is implemented to model wood drying under rapid periodically changed drying air temperature and humidity with high number of cycles of intermittency. The equilibrium activation energy (ΔE v,b ), an important parameter for REA approach, is evaluated according to the corresponding drying air temperature and humidity in each drying section. The results of modeling suggest the L-REA works well with the experimental data. The simplicity of the L-REA is obvious and is hoped to be used in an industrial setting more readily. The L-REA can be used for sustainable processing in industries to assist in energy audit and management.

Modelos matemáticos para a secagem intermitente de arroz em casca

Propôs-se, com este trabalho, ajustar modelos matemáticos aos valores experimentais em função do teor de água e estudar os efeitos das relações de intermitência na secagem de grãos de arroz na eficiência da operação. Utilizaram-se grãos de arroz com casca produzidos na Região Sul do Rio Grande do Sul. As amostras com teor de água próximo a 20% b.u. foram secadas sob três condições de relação de intermitência: 1:1, 1:2 e 1:4; em todas as condições foram utilizados os mesmos manejos térmicos em temperaturas graduais crescentes do ar: 70, 90, 110 ± 5 °C, respectivamente, na 1ª e na 2ª e a partir da 3ª hora. Para os ajustes dos modelos matemáticos foi realizada análise de regressão não-linear pelo método Simplex e Quasi-Newton, cujos valores são os parâmetros dos modelos estimados em função da temperatura do ar de secagem. Comparando-se os coeficientes de determinação ajustados (R2ajustado), o erro médio relativo (P) e estimado (SE) e a distribuição de resíduos, os resultados obtidos permitem concluir que: a relação de intermitência altera o tempo de operação e a taxa horária de secagem dos grãos de arroz e, ainda, o modelo de Midilli foi o que melhor representou a secagem intermitente do arroz em casca.

Continuous and Intermittent Drying (Tempering) of Oblate Spheroidal Bodies: Modeling and Simulation

Abstract In this work, modeling of continuous and intermittent drying of oblate spheroidal bodies is presented. The model considers the liquid diffusion as the only process of mass transfer inside the body, constant diffusion coefficient and equilibrium conditions at the surface of the solid. The diffusion equation is described in the oblate spheroidal coordinates system and it was discretized using the finite-volume method. Formulation was applied to predict drying of lentil grains. Several cases of intermittent drying for lentils were simulated: using a same time of tempering (time of rest), beginning in different drying time and for two or more drying passes (time steps) along the process. For a same useful time of the dryer, it was observed that the intermittent drying always increases the efficiency of the process. Another outstanding result is the improvement of the final quality of the product due to the absence of large moisture content gradients inside of the product during the drying process after tempering.

Abstract 2883: Enhanced anti-tumor activity and bioavailability of chemopreventives by coated polymeric implants

Abstract Poor oral bioavailability limits the use of many chemopreventives in the prevention and treatment of cancer. We previously reported a novel concept in which polycaprolactone (PCL) implants embedded with test agents provide sustained delivery for long duration (months to >1year), reduce effective dose substantially and increase bioavailability. While tested successfully for various agents, this formulation results in an initial burst release and does not apply to heat-labile compounds. Furthermore, it takes 2 or more years for the polymeric implant to biodegrade. To overcome these limitations, we hypothesized that formulation of low mol wt polymeric implants will provide more sustained and higher release compared with higher mol. wt polymers; the low mol. wt polymers are also expected to biodegrade in weeks to months. To test part of this hypothesis, we used three different mol wt PCL polymers and two co-polymers, poly(D, L-lactide-co-glycolide) (PLGA). The method involves i) preparation of blank PCL implants (1.4 mm dia), and ii) coating of 30-40 layers by dipping blank implants, with intermittent drying, in 10-20% of different mol wt PCL solutions in dichloromethane containing 10% curcumin in tetrahydrofuran. The curcumin implants when tested for in vitro release showed that i) the burst release effect and the amount released varied with mol wt of the polymer. Implants prepared with PCL of 3,600 mol wt (PCL-3.6K) did not show any burst release phenomenon. Instead, these implants took nearly 7 days to render maximum daily release and thereafter the rate of release declined gradually over a period of two weeks. Implants prepared from higher mol wt polymers (PCL-31K and PCL-112K) were accompanied with some initial burst release and the rate of release declined gradually. Cumulative release measured over two weeks was found to be inversely proportional to the mol wt of PCL: PCL-3.6K (30%) > PCL-31K (24%) > PCL-112K (21%). On the other hand, the co-polymers, PLGA (50:50) and PLGA (75:25) showed only 1% and 0.5% total release, respectively. To determine if the implant delivery reduced the effective dose in a tumor model, nude mice were inoculated with human lung cancer (A549) cells and then treated with coated implants of withaferin A, a potent triterpenoid isolated from the traditional Ayurvedic herb “Ashwagandha”. Withaferin A given via the coated implants significantly inhibited (>50%) human lung cancer (A549) xenograft, while it was ineffective when the same dose was administered i.p. Together, our data suggest that coated implants of low mol wt PCL can accommodate heat-labile compounds, enhance bioavailability, furnish more sustained and higher cumulative release, and elicits anti-tumor activity. Our ultimate goal is to use low mol polymeric implants that will biodegrade in few months and provide continuous release of the drug. (Supported from CA-118114, KLCRP and Duggan Endowment). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2883. doi:1538-7445.AM2012-2883

The Design and Test for the Intermittent Work-Style Drying System

In order to improve the quality of microwave drying, we propose the microwave drying temperature control system which consists of microcontroller (AT89S52), temperature sensors (DS18b20) and other electronic components. The system can monitor the real-time temperature of the drying chamber and can control the drying process automatically , let the temperature cannot out of the permitted range(control the extent permitted automatically), these processes ensure the quality of the dried crop. The results shows that crops using the system are better than those that not used（using）. These tests proved (prove) that the microwave temperature control system can achieve its designed function.

Experimental study and numerical modelling of drying characteristics of apple slices

The purpose of this work is to quantify the energetic interest of convective and intermittent drying process of natural products. This drying mode has been achieved within a climatic tunnel blower. This laboratory device permitted us to achieve several tests for different conditions of the apple slices drying. In the intermittent case, a variation of the air temperature and air velocity values permitted us to find the most economic velocities for the drying of the apple thin slices. The numerical simulations in the intermittent tests, give us more information on what really happens to the product during periods of interruption. The drying kinetics at the resumption increases with the air temperature. Then, we gain in energy and in overall drying time. These studies show the considerable advantages of the intermittent drying of agricultural products and confirm the preservation of their qualities and the reduction of the drying time.

Intermittent Microwave Drying of Litchi: Drying Kinetics and Quality Formation in Color Difference

In order to reveal the characteristics of thermal transmission and drying quality on the litchi’s multilayer structure, the peel and flesh that separated from fresh fruit were dried with the whole fruit by microwave radiation in three kinds of tempering intermittent HT0101, HT0505 and HT1010. Their characteristics of dehydration and the changes of color difference in drying process were compared. The results showed that microwave drying had influences on the capability of dehydration and the quality of color difference in different interval. The influence of HT0505 was more significant, while the other two conditions, in which there were only a small amplitude of cross and fluctuation, were approximate. In the same conditions of microwave drying, the capability of dehydration of peel and flesh separated was better than that of whole fruit, and the dehydration speed of peel was the fastest. As to color difference, the changes of peel and whole fruit were smaller and much easily to tend to stable. The change of the color difference on the flesh was obvious and finally tended to stable. The further research still needed the further study on biochemical effect during the transformation of quality.