Average Effective Diffusivity Research Articles

Comparative Study on Drying of Selected Marine Products: Bombay Duck (Herpodon nehereus) and Prawn (Penaeus indicus)

A study on drying of two types of fish, viz., Bombay duck and Prawn, using the open sun, a solar cabinet, hot air and freeze drying was carried out. The fish were dried to 5–6% moisture content. The drying rates were calculated and drying data were fitted to the Page model, and on the basis of R2 and RMSE values it was found that the Page model describes satisfactorily the drying behavior of Bombay duck and Prawn. Also, effective moisture diffusivity values were calculated during fish drying by different methods. The values of the average effective moisture diffusivity of Bombay duck and Prawn were in the range of 1.01 × 10-9 to 1.51 × 10-9 m2 s-1and 0.21 × 10-9 to 0.31 × 10-9 m2 s-1, respectively. Freeze drying was found to provide the best quality of dehydrated product, which was as expected. Solar cabinet drying was found to be a low-energy intensive process compared to freeze and hot air drying, resulting in a dehydrated product with acceptable quality.

Mucoadhesive Nanoparticles May Disrupt the Protective Human Mucus Barrier by Altering Its Microstructure

Mucus secretions typically protect exposed surfaces of the eyes and respiratory, gastrointestinal and female reproductive tracts from foreign entities, including pathogens and environmental ultrafine particles. We hypothesized that excess exposure to some foreign particles, however, may cause disruption of the mucus barrier. Many synthetic nanoparticles are likely to be mucoadhesive due to hydrophobic, electrostatic or hydrogen bonding interactions. We therefore sought to determine whether mucoadhesive particles (MAP) could alter the mucus microstructure, thereby allowing other foreign particles to more easily penetrate mucus. We engineered muco-inert probe particles 1 µm in diameter, whose diffusion in mucus is limited only by steric obstruction from the mucus mesh, and used them to measure possible MAP-induced changes to the microstructure of fresh human cervicovaginal mucus. We found that a 0.24% w/v concentration of 200 nm MAP in mucus induced a ∼10-fold increase in the average effective diffusivity of the probe particles, and a 2- to 3-fold increase in the fraction capable of penetrating physiologically thick mucus layers. The same concentration of muco-inert particles, and a low concentration (0.0006% w/v) of MAP, had no detectable effect on probe particle penetration rates. Using an obstruction-scaling model, we determined that the higher MAP dose increased the average mesh spacing (“pore” size) of mucus from 380 nm to 470 nm. The bulk viscoelasticity of mucus was unaffected by MAP exposure, suggesting MAP may not directly impair mucus clearance or its function as a lubricant, both of which depend critically on the bulk rheological properties of mucus. Our findings suggest mucoadhesive nanoparticles can substantially alter the microstructure of mucus, highlighting the potential of mucoadhesive environmental or engineered nanoparticles to disrupt mucus barriers and cause greater exposure to foreign particles, including pathogens and other potentially toxic nanomaterials.

Thin layer drying of tomato slices

The hot air convective drying characteristics of blanched tomato (Lycopersicon esculantum L.) slices have been investigated. Drying experiments were carried out at four different temperatures (50, 60, 65 and 70°C). The effect of drying temperatures on the drying behavior of the tomato slices was evaluated. All drying experiments had only falling rate period. The average effective diffusivity values varied from 0.5453 × 10(-9) to 2.3871 × 10(-9)m(2)/s over the temperature range studied and the activation energy was estimated to be 61.004kJ/mol. In order to select a suitable form of the drying curve, six different thin layer drying models (Henderson-Pabis, Page, Diamante et al., Wang and Singh, Logarithmic and Newton models) were fitted to the experimental data. The goodness of fit tests indicated that the Logarithmic model gave the best fit to experimental results, which was closely followed by the Henderson-Pabis model. The influence of varied drying temperatures on quality attributes of the tomato slices viz. Hunter color parameters, ascorbic acid, lycopene, titratable acidity, total sugars, reducing sugars and sugar/acid ratio of dried slices was also studied. Slices dried at 50 and 60°C had high amount of total sugars, lycopene, sugar/acid ratio, Hunter L- and a-values. Drying of slices at 50°C revealed optimum retention of ascorbic acid, sugar/acid ratio and red hue, whereas, drying at higher temperature (65 and 70°C) resulted in a considerable decrease in nutrients and colour quality of the slices.

Common Gene Therapy Viral Vectors Do Not Efficiently Penetrate Sputum from Cystic Fibrosis Patients

Norwalk virus and human papilloma virus, two viruses that infect humans at mucosal surfaces, have been found capable of rapidly penetrating human mucus secretions. Viral vectors for gene therapy of Cystic Fibrosis (CF) must similarly penetrate purulent lung airway mucus (sputum) to deliver DNA to airway epithelial cells. However, surprisingly little is known about the rates at which gene delivery vehicles penetrate sputum, including viral vectors used in clinical trials for CF gene therapy. We find that sputum spontaneously expectorated by CF patients efficiently traps two viral vectors commonly used in CF gene therapy trials, adenovirus (d∼80 nm) and adeno-associated virus (AAV serotype 5; d∼20 nm), leading to average effective diffusivities that are ∼3,000-fold and 12,000-fold slower than their theoretical speeds in water, respectively. Both viral vectors are slowed by adhesion, as engineered muco-inert nanoparticles with diameters as large as 200 nm penetrate the same sputum samples at rates only ∼40-fold reduced compared to in pure water. A limited fraction of AAV exhibit sufficiently fast mobility to penetrate physiologically thick sputum layers, likely because of the lower viscous drag and smaller surface area for adhesion to sputum constituents. Nevertheless, poor penetration of CF sputum is likely a major contributor to the ineffectiveness of viral vector based gene therapy in the lungs of CF patients observed to date.

Mass Transfer Kinetics during Osmotic Dehydration of Pomegranate Arils

The mass transfer kinetics during osmotic dehydration of pomegranate arils in osmotic solution of sucrose was studied to increase palatability and shelf life of arils. The freezing of the whole pomegranate at -18 °C was carried out prior to osmotic dehydration to increase the permeability of the outer cellular layer of the arils. The osmotic solution concentrations used were 40, 50, 60°Bx, osmotic solution temperatures were 35, 45, 55 °C. The fruit to solution ratio was kept 1:4 (w/w) during all the experiments and the process duration varied from 0 to 240 min. Azuara model and Peleg model were the best fitted as compared to other models for water loss and solute gain of pomegranate arils, respectively. Generalized Exponential Model had an excellent fit for water loss ratio and solute gain ratio of pomegranate arils. Effective moisture diffusivity of water as well as solute was estimated using the analytical solution of Fick's law of diffusion. For above conditions of osmotic dehydration, average effective diffusivity of water loss and solute gain varied from 2.718 × 10(-10) to 5.124 × 10(-10) m(2)/s and 1.471 × 10(-10) to 5.147 × 10(-10) m(2)/s, respectively. The final product was successfully utilized in some nutritional formulations such as ice cream and bakery products.

Convective dehydration kinetics of osmotically pretreated pomegranate arils

The freezing of the whole pomegranate at −18 °C was carried out prior to convective dehydration to increase the permeability of the outer layer of the arils. The arils were osmotically pretreated in 50°B of sucrose solution at 40 °C for 100 min with fruit to solution ratio of 1:4 (w/w). The osmotically dehydrated arils were further dehydrated convectively at different drying air temperatures of 50, 60 and 70 °C up to final moisture content of 9 ± 1% (w.b). Among the models investigated, the Middilli model fitted the experimental data for convective drying of natural and osmosed pomegranate arils. During convective dehydration, the average effective moisture diffusivity of natural samples and osmosed samples at drying air temperatures ranging from 50 to 70 °C varied between 2.60 × 10−10 to 4.89 × 10−10 m2 s−1, between 3.37 × 10−10 to 5.04 × 10−10 m2 s−1, respectively. The activation energy was 66.12 kJ mol−1 for natural samples and 42.06 kJ mol−1 for osmosed samples, respectively.

Mathematical Modeling and Experimental Study on Thin-Layer Vacuum Drying of Ginger (Zingiber Officinale R.) Slices

The vacuum-drying characteristics of ginger (Zingiber officinale R.) slices were investigated. Drying experiments were carried out at a constant chamber pressure of 8 kPa, and at four different drying temperatures (40 °C, 50 °C, 60 °C, and 65 °C).The effects of drying temperature on the drying rate and moisture ratio of the ginger samples were evaluated. Efficient model for describing the vacuum-drying process was chosen by fitting five commonly used drying models and a suggested polynomial was fitted to the experimental data. The effective moisture diffusivity and activation energy were calculated using an infinite series solution of Fick’s diffusion equation. The results showed that increasing drying temperature accelerated the vacuum-drying process. All drying experiments had only falling rate period. The goodness of fit tests indicated that the proposed two-term exponential model gave the best fit to experimental results among the five tested drying models. The average effective diffusivity values varied from 1.859 × 10−8 to 4.777 × 10−8 m2/s over the temperature range. The temperature dependence of the effective moisture diffusivity for the vacuum drying of the ginger samples was satisfactorily described by an Arrhenius-type relationship with activation energy value of 35.675 kJ/mol within 40–65 °C temperature range.

Experimental determination of effective moisture diffusivities of whole- and cut-rosehips in convective drying

Average effective moisture diffusivities for both the whole- and cut-rosehips were obtained during convective drying. The effects of process variables such as air temperature, air velocity and air absolute humidity on effective moisture diffusivity were studied. The average effective moisture diffusivity in rosehip ranged between 1.45 × 10 −10 and 10.3 × 10 −10 m 2/s for whole-rosehip and between 1.44 × 10 −9 and 5.13 × 10 −9 m 2/s for cut-rosehip at the temperatures studied. Activation energies for convective drying were found to be 62 kJ/mol for whole-rosehips and 58 kJ/mol for cut-rosehips.

Drying kinetics of high moisture paddy undergoing vibration-assisted infrared (IR) drying

Both heating and drying of high moisture paddy using vibrating platform coupled with infrared heating source dryer give uniform but quick drying by exposing each and every grain uniformly to the IR source. A laboratory apparatus capable of modulating both frequency and amplitude of vibration had been developed to study vibration aided drying characteristics of high moisture paddy. The effective moisture diffusivity of the grain during drying under this mode has been evaluated. The drying characteristics of high moisture paddy was studied under different vibrating conditions for five levels of radiation intensity (1509, 2520, 3510, 4520 and 5514 W/m 2) and four levels of grain bed depths (single kernel thickness of 3, 6, 12 and 25 mm). The optimum frequency and amplitude of the vibrations were found to be in the range of 20–22 Hz and 8–9 mm for all the three grain bed depths of paddy (25, 12 and 6 mm) for obtaining nearly complete and uniform mixing (mixing index ≅ 1.0) [Das, I., Das, S.K., Bal, S., 2003a. Determination of mixing index of paddy grains under vibrating conditions. Journal of Food Process Engineering 26 (2), 121–133]. Drying occurred almost under falling rate period. The value of the average effective moisture diffusivity ( D eff) avg ranged between the 0.778 × 10 −10 and 3.884 × 10 −10 m 2/s for different drying treatments. Both the radiation intensity and grain bed depth found to have significant effect on the ( D eff) avg value at 1% level of significance.

Release of potassium sorbate from active films of sodium alginate crosslinked with calcium chloride

AbstractThe release of potassium sorbate from alginate films was evaluated considering different active agent concentrations in the film and three levels of alginate crosslinking. The mechanism involved in the diffusional process was investigated using the Power Law Model. The results indicated that potassium sorbate diffusion in alginate films has characteristics of Fickian and non‐Fickian behaviour. Effective diffusion coefficients obtained using the solution in series derived from Fick's Second Law are close to values obtained by the short‐time solution, indicating that the influence of swelling on effective diffusivity, although perceptible, is small, allowing the use of an average effective diffusivity. The values of effective diffusivity found indicate that alginate films have a potential use as systems for release of active substances. Copyright © 2009 John Wiley & Sons, Ltd.

On the modeling of an airlift photobioreactor

A mathematical formulation of a model of an airlift photobioreactor in the cases of interphase mass transfer between gas and liquid in the riser and photobioreaction in the downcomer is presented. The equations allow the calculation of the vertical distribution of the average concentrations of an active gas component (CO2, O2) and a photoactive material (cells), using average velocities and effective diffusivities in the riser and the downcomer. A hierarchical approach for the model parameter identification on the basis of experimental data is proposed.

Drying of a Low Porosity Product (Carrot) as Affected by Power Ultrasound

The main aim of this work was to assess the influence of power ultrasound on mass transfer process during convective drying of a low porosity product submitted to different acoustic energy levels. Drying kinetics of carrot cubes (side 8.5 mm) were carried out at 40 °C and 1 m/s applying different electric power levels to the ultrasonic transducer: 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90 W. Drying kinetics were modelled considering the diffusion theory. From the results, a significant (p<0.05) influence of power ultrasound application on drying kinetics of carrot cubes was found. Drying rate increased as the electric power applied got higher. The influence was only observed above an acoustic energy threshold, which corresponded to an electric power applied to the transducer of 20-30 W. From this threshold, a linear relationship was found between the average effective moisture diffusivity or the mass transfer coefficient and the electric power applied to the transducer.

Influence of dipping on thin-layer drying characteristics of seedless grapes

The drying characteristics of pretreated seedless grapes were studied using a laboratory-scale tray dryer with the air temperature varied from 40 to 70 °C at air velocity of 1 m s −1 . The effective moisture diffusivities were determined using an analytical–numerical solution method considering shrinkage, while variable thermal diffusivity was calculated from experimentally estimated values of thermo-physical properties at a given moisture contents. These parameters were correlated with the corresponding moisture content and temperatures in an empirical model using a non-linear regression method. This shows that the seedless grapes of the same clone vines, as subjected to the hot water (HW) and alkaline emulsion of ethyl oleate (EO) pretreatments, exhibited average effective moisture diffusivities that ranged from 3.34 to 8.46×10 −10 m 2 s −1 at 50 °C. The increase in mass transfer coefficients at a given moisture content at different temperatures for the EO-pretreated samples was two times that for the HW-pretreated samples during the drying. However, the pretreatments had no the significant effect on the thermal diffusivities of the grapes during the drying.

Modeling heat and mass transfer during drying of green coffee beans using prolate spheroidal geometry

A heat and mass transfer model in prolate spheroidal coordinates system was proposed to describe the drying of green coffee beans. The model describes the 3D moisture and temperature profiles inside the bean. The results were integrated over volume in order to obtain a drying kinetic equation for prolate spheroidal geometry. The average effective diffusivity of water as function of temperature and moisture was estimated at 45 and 60 °C by slope method from experimental drying kinetic of green coffee beans. The expression obtained applied to drying kinetic equation reproduced approximately the experimental behavior.

Characteristics of Thin-Layer Infrared Drying of Apple Pomace With and Without Hot Air Pre-drying

Thin-layer infrared drying characteristics of apple pomace, with and without hot air pre-drying, were studied with a laboratory scale infrared dryer. Moreover, ten commonly used mathematical models were used to fit experimental data. Logarithmic model and Page model were most adequate in describing thin-layer drying of fresh and pre-treated apple pomace respectively. The values of average effective diffusivity in drying the pre-treated apple pomace were about 1.3 times of that in the fresh apple pomace with the initial moisture content of 40% (wet basis).The values of activation energy of moisture diffusion were about 30 kJ/mol for the fresh and pre-treated apple pomace respectively. Infrared drying, combined with hot air pre-drying, can save 20% of drying time to remove the same amount of remained moisture as compared to the infrared drying alone. The above findings might be used for operation of drying apple pomace.

On the modeling of an airlift reactor

A model of an airlift reactor in the cases of interphase mass transfer between gas and liquid in the riser and chemical reaction in the liquid phase has been done. The model equations permit to obtain the vertical distribution of the average concentrations of an active gas component in gas and liquid phases and average concentration of the active liquid component, using average velocities and effective diffusivities in the riser and downcomer zones. The proposed model allows scale-up problem solution. An hierarchical approach for model parameter identification on the bases of experimental data has been proposed.

Study the drying kinetics of open sun drying of fish

The drying behavior of prawn and chelwa fish (Indian minor carp) has been studied under open sun drying (OSD). The drying rate curves contained no constant rate period and showed a linear falling rate throughout the drying process. An asymptotic regression precisely represents the open sun drying behavior with the coefficient of determination and mean square of deviation as 0.9996 and 0.33 × 10 −4 for prawn and 0.9993 and 0.58 × 10 −4 for chelwa fish, respectively. Effective moisture diffusivity values were estimated from Fick’s equation. The hourly effective moisture diffusivity has an exponential relation with the hourly mean moisture content of fish. The average effective moisture diffusivities were 11.11 × 10 −11 and 8.708 × 10 −11 m 2 s −1 for prawn and chelwa fish drying, respectively.

Effective Moisture Diffusivity of Onion Slices undergoing Infrared Convective Drying

Drying experiments of onion slices (6 mm thickness) were carried out by using infrared convective drying. Infrared convective drying of onion slices was observed to be a falling rate process. The average effective moisture diffusivity of onion slices ranged between 0·2514×10−10 and 0·3233×10−10 m2 s−1. The values of average effective moisture diffusivity increased for the same values of drying air temperature and air velocity as applied radiation intensity was increased. Average effective moisture diffusivity decreased at all air temperature and applied radiation intensity with increase in air velocity. The activation energy in infrared convective drying between 5·06 and 10·63 kJ mol−1. It has been indicated that decrease in energy of activation caused an increase in drying rate.

Biofilm physical structure, internal diffusivity and tortuosity

The paper proposes tortuosity as a physical concept particularly useful to interpret internal diffusivities in terms of biofilm structure. Results from different authors are presented showing how average effective diffusivities in biofilms (measured with inert tracers) vary with the fluid velocity: in the case of biofilms formed under turbulent flow conditions, an increase in fluid velocity corresponds to a decrease in the diffusivity, although sometimes this decrease is very slight; however, in laminar flow situations, no common trend is found from research group to research group.

In vitro and in vivo evaluation of recombinant silk-elastinlike hydrogels for cancer gene therapy

The objectives of this study were to evaluate: (i) the influences of hydrogel geometry, DNA molecular weight, and DNA conformation on DNA release from a silk-elastinlike protein polymer (SELP) hydrogel, (ii) the bioactivity and transfection efficiency of encapsulated DNA over time in vitro, (iii) the delivery and transfection of a reporter gene in a murine model of human breast cancer in vivo, and (iv) the in vitro release and bioactivity of adenovirus containing the green fluorescent protein (gfp) gene as a marker of gene transfer. Plasmid DNA was released from SELP hydrogels in a size-dependent manner, with the average effective diffusivity ranging from 1.70±0.52×10 −12 cm 2/s for a larger plasmid (11 kbp) to 2.55±0.51×10 −10 cm 2/s for a smaller plasmid (2.6 kbp). Plasmid conformation also influenced the rate of release, with the rank order linear>supercoiled>open-circular. DNA retained bioactivity in vitro, after encapsulation in a SELP hydrogel for up to 28 days. Delivery of pRL-CMV from a SELP hydrogel resulted in increased transfection in a murine model of human breast cancer by 1–3 orders of magnitude, as compared to naked DNA. The release of a bioactive adenoviral vector was related to the concentration of the polymer in the hydrogel. These studies indicate that genetically engineered SELP hydrogels have potential as matrices for controlled nonviral and viral gene delivery.