The Experts below are selected from a list of 24738 Experts worldwide ranked by ideXlab platform
Michael Melkonian - One of the best experts on this subject based on the ideXlab platform.
-
Optimising biomass and peridinin accumulation in the dinoflagellate Symbiodinium voratum using a twin-layer Porous Substrate bioreactor
Journal of Applied Phycology, 2019Co-Authors: Dorothee Langenbach, Michael MelkonianAbstract:Dinoflagellates are a natural source for unique secondary metabolites and pigments, which have considerable potential for applications in biomedical drug development and cosmetics. However, the technical cultivation of dinoflagellates in commonly used suspension-based closed photobioreactors (PBRs) has been shown to be difficult due to the sensitivity of the cultures to turbulence and shear forces. To overcome these and other constraints of suspension cultivation, immobilised cultivation of the dinoflagellate Symbiodinium voratum has been performed using a twin-layer Porous Substrate bioreactor (TL-PSBR). By optimising biomass growth using printing paper as Substrate, a maximal biomass growth rate of 7.8 g dry weight m^−2 growth area day^−1 was measured over a period of 40 days at the relatively high-light intensity of 600 μmol photons m^−2 s^−1 and 2% ( v / v ) CO_2. Linear growth of the S. voratum biofilm was observed over 40 days, and a maximal biomass standing crop of 305 g m^−2 was gained. Synthesis of the potentially high-value carotenoid pigment peridinin, however, was favoured at low-light conditions (≤ 100 μmol photons m^−2 s^−1). By combining maximal biomass growth at high-light conditions with maximal peridinin accumulation at low-light conditions in a two-phase approach (14 days cultivation at 600 μmol photons m^−2 s^−1 and 2% CO_2 followed by 14 days at 100 μmol photons m^−2 s^−1 and ambient air), a peridinin productivity of 51.4 mg peridinin m^−2 day^−1 was measured (about 30% higher than the values determined at either low- or high-light conditions). Using the two-phase approach, peridinin accumulated to a standing crop of ~ 1 g peridinin m^−2 after 28 days of cultivation in a bench-scale TL-PSBR with a peridinin content in the dry biomass of 1% ( w / w ). Symbiodinium voratum may thus be a suitable source of peridinin for a diverse range of applications when grown in a twin-layer Porous Substrate bioreactor.
-
Microalgal cultivation in Porous Substrate bioreactor for extracellular polysaccharide production
Journal of Applied Phycology, 2017Co-Authors: Alice Ekelhof, Michael MelkonianAbstract:Netrium digitus is a representative of the species-rich class Zygnematophyceae (Streptophyta). Its intensive extracellular polysaccharide (EPS) production makes this alga interesting for biotechnological applications with a focus on cosmetics and food additives. Quantitative data on growth and EPS production in suspension and, for the first time, in immobilized culture using lab-scale Porous Substrate bioreactors, so-called Twin-Layer (TL) systems, is presented. It is shown that the cell as well as the EPS dry weight content is increased at least sixfold in immobilized compared to suspension culture. Due to the high amount of EPS, the biofilms reach a thickness of more than 8 mm after 27 days at 70 μmol photons m^−2 s^−1 and with 1.5% CO_2 supply. Frequent exchange of the growth medium results in a linear cell biomass increase of 2.02 ± 0.09 g m^−2 growth area day^−1 compared to 2.99 ± 0.09 g m^−2 day^−1, when the medium is not exchanged. Under this mode of cultivation, the EPS production is lower and a final concentration of 12.18 ± 1.25 g m^−2 compared to 20.76 ± 0.85 g m^−2, when medium was exchanged, is reached. It is clearly demonstrated that the relatively slow growing, but excessively EPS producing, microalgal species N. digitus can be grown in Porous Substrate bioreactors and that this culturing technique is a promising alternative to suspension culture for the Zygnematophyceae.
-
Porous Substrate Bioreactors: A Paradigm Shift in Microalgal Biotechnology?
Trends in biotechnology, 2016Co-Authors: Björn Podola, Michael MelkonianAbstract:Many of the demands in the production of microalgae at a technical scale cannot presently be met by state-of-the-art cultivation technologies based on suspensions. Immobilized cultivation using Porous Substrate bioreactors (PSBRs) is characterized by a reduction of liquid reaction volumes by several orders of magnitude and has solved several volume-related problems. Recently, PSBRs demonstrated potential for both established and novel applications in microalgal biotechnology, and first insights into biophysical processes have provided an understanding of the benefits of PSBR biofilm cultivation. Further efforts should primarily focus on scale-up and engineering challenges in this emerging field and, additionally, provide experience in the long-term operation of bioreactors. The results may contribute to assessing the technical and economic potential of PSBR cultivation.
R. Usha - One of the best experts on this subject based on the ideXlab platform.
-
Thin film flow down a Porous Substrate in the presence of an insoluble surfactant : Stability analysis
Physics of Fluids, 2013Co-Authors: A. Anjalaiah, R. Usha, Séverine MilletAbstract:The stability of a gravity-driven film flow on a Porous inclined Substrate is considered, when the film is contaminated by an insoluble surfactant, in the frame work of Orr-Sommerfeld analysis. The classical long-wave asymptotic expansion for small wave numbers reveals the occurrence of two modes, the Yih mode and the Marangoni mode for a clean/a contaminated film over a Porous Substrate and this is confirmed by the numerical solution of the Orr-Sommerfeld system using the spectral-Tau collocation method. The results show that the Marangoni mode is always stable and dominates the Yih mode for small Reynolds numbers; as the Reynolds number increases, the growth rate of the Yih mode increases, until, an exchange of stability occurs, and after that the Yih mode dominates. The role of the surfactant is to increase the critical Reynolds number, indicating its stabilizing effect. The growth rate increases with an increase in permeability, in the region where the Yih mode dominates the Marangoni mode. Also, the growth rate is more for a film (both clean and contaminated) over a thicker Porous layer than over a thinner one. From the neutral stability maps, it is observed that the critical Reynolds number decreases with an increase in permeability in the case of a thicker Porous layer, both for a clean and a contaminated film over it. Further, the range of unstable wave number increases with an increase in the thickness of the Porous layer. The film flow system is more unstable for a film over a thicker Porous layer than over a thinner one. However, for small wave numbers, it is possible to find the range of values of the parameters characterizing the Porous medium for which the film flow can be stabilized for both a clean film/a contaminated film as compared to such a film over an impermeable Substrate; further, it is possible to enhance the instability of such a film flow system outside of this stability window, for appropriate choices of the Porous Substrate characteristics.
-
Shear-Thinning Film on a Porous Substrate: Stability Analysis of a One-Sided Model
Chemical Engineering Science, 2011Co-Authors: R. Usha, Séverine Millet, Hamda Ben Hadid, François RoussetAbstract:The temporal stability of a Carreau fluid flowing down an inclined Porous Substrate is considered. A reduced model is derived under the assumption of small permeability which decouples the flow in the liquid layer from the filtration flow in the Porous medium and incorporates the effect of the Porous medium by means of an effective slip condition at the liquid-solid interface. The slip coefficient in the effective slip condition is a function of the structure, permeability of the Porous medium and the rheology of the fluid saturating the Porous medium. The effects of shear-thinning rheology and permeability of the Substrate on the stability of the film flow system are investigated. This problem gives rise to a generalized eigenvalue formulation which is solved through two approaches. The problem is solved analytically for long waves in the limiting cases of weakly and strongly non-Newtonian behaviors (power-law limit). A numerical investigation is carried out in the general case. The results are shown to agree well for the weakly non-Newtonian limit. Further, the power-law model and the Carreau model agree on a wide range of shear-thinning parameter values for a thin film over a rigid Substrate. However, when considering a Porous medium, this trend is not observed. The Carreau model gives valid results for the entire range of shear-thinning parameter values for a film over a rigid/Porous Substrate. The novelty of the present investigation lies in the inclusion of both the effects of bottom permeability and shear-thinning rheology. Both permeability and shear-thinning rheology have a destabilizing effect on the film flow system. The numerical results indicate the correlation between the effects due to shear-thinning properties and permeability. An energy balance analysis performed on the perturbation fields shows that destabilization induced by both shear-thinning and permeability is linked to the viscous shear work rate on the free surface.
-
Stability of a Shear-Thinning Film on a Porous Substrate
ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1 Symposia – Parts A B and C, 2010Co-Authors: R. Usha, Séverine Millet, H. Benhadid, François RoussetAbstract:A significant feature of gravity-driven film flows of Newtonian and rheologically complex fluids down an inclined/vertical Substrate is the instability of the free surface which manifests as surface waves having wavelengths much larger than the film thickness. There are a number of applications which can be modeled as thin film flow systems on Porous Substrates. Pascal [1] investigated the stability of a falling power-law film on an inclined Porous Substrate. This model for the fluid predicts a viscosity that goes to infinity as the shear rate approaches zero. There is a need to employ a more appropriate model to examine the effects of non-Newtonian rheology on the dynamics and stability of thin film free surface flows down inclined or vertical rigid/Porous Substrates. The four-parameter Carreau model predicts a viscosity that remains finite as the shear rate approaches zero and is given by η−η∞η0−η∞ = [1+(δγ)2]n−12. (1) Weinstein [2] and Rousset et al. [3] have considered the Carreau model and have examined the temporal stability of a film flow down an impermeable rigid inclined Substrate. The authors show that a shear-thinning Carreau fluid film on a rigid impermeable Substrate is more unstable than a Newtonian film. This calls for an analysis that includes both the effects of Carreau non-Newtonian rheology and bottom permeability and the present study reports such an investigation of a Carreau non-Newtonian film on a Porous inclined Substrate.Copyright © 2010 by ASME
François Rousset - One of the best experts on this subject based on the ideXlab platform.
-
Shear-Thinning Film on a Porous Substrate: Stability Analysis of a One-Sided Model
Chemical Engineering Science, 2011Co-Authors: R. Usha, Séverine Millet, Hamda Ben Hadid, François RoussetAbstract:The temporal stability of a Carreau fluid flowing down an inclined Porous Substrate is considered. A reduced model is derived under the assumption of small permeability which decouples the flow in the liquid layer from the filtration flow in the Porous medium and incorporates the effect of the Porous medium by means of an effective slip condition at the liquid-solid interface. The slip coefficient in the effective slip condition is a function of the structure, permeability of the Porous medium and the rheology of the fluid saturating the Porous medium. The effects of shear-thinning rheology and permeability of the Substrate on the stability of the film flow system are investigated. This problem gives rise to a generalized eigenvalue formulation which is solved through two approaches. The problem is solved analytically for long waves in the limiting cases of weakly and strongly non-Newtonian behaviors (power-law limit). A numerical investigation is carried out in the general case. The results are shown to agree well for the weakly non-Newtonian limit. Further, the power-law model and the Carreau model agree on a wide range of shear-thinning parameter values for a thin film over a rigid Substrate. However, when considering a Porous medium, this trend is not observed. The Carreau model gives valid results for the entire range of shear-thinning parameter values for a film over a rigid/Porous Substrate. The novelty of the present investigation lies in the inclusion of both the effects of bottom permeability and shear-thinning rheology. Both permeability and shear-thinning rheology have a destabilizing effect on the film flow system. The numerical results indicate the correlation between the effects due to shear-thinning properties and permeability. An energy balance analysis performed on the perturbation fields shows that destabilization induced by both shear-thinning and permeability is linked to the viscous shear work rate on the free surface.
-
Stability of a Shear-Thinning Film on a Porous Substrate
ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1 Symposia – Parts A B and C, 2010Co-Authors: R. Usha, Séverine Millet, H. Benhadid, François RoussetAbstract:A significant feature of gravity-driven film flows of Newtonian and rheologically complex fluids down an inclined/vertical Substrate is the instability of the free surface which manifests as surface waves having wavelengths much larger than the film thickness. There are a number of applications which can be modeled as thin film flow systems on Porous Substrates. Pascal [1] investigated the stability of a falling power-law film on an inclined Porous Substrate. This model for the fluid predicts a viscosity that goes to infinity as the shear rate approaches zero. There is a need to employ a more appropriate model to examine the effects of non-Newtonian rheology on the dynamics and stability of thin film free surface flows down inclined or vertical rigid/Porous Substrates. The four-parameter Carreau model predicts a viscosity that remains finite as the shear rate approaches zero and is given by η−η∞η0−η∞ = [1+(δγ)2]n−12. (1) Weinstein [2] and Rousset et al. [3] have considered the Carreau model and have examined the temporal stability of a film flow down an impermeable rigid inclined Substrate. The authors show that a shear-thinning Carreau fluid film on a rigid impermeable Substrate is more unstable than a Newtonian film. This calls for an analysis that includes both the effects of Carreau non-Newtonian rheology and bottom permeability and the present study reports such an investigation of a Carreau non-Newtonian film on a Porous inclined Substrate.Copyright © 2010 by ASME
Séverine Millet - One of the best experts on this subject based on the ideXlab platform.
-
Thin film flow down a Porous Substrate in the presence of an insoluble surfactant : Stability analysis
Physics of Fluids, 2013Co-Authors: A. Anjalaiah, R. Usha, Séverine MilletAbstract:The stability of a gravity-driven film flow on a Porous inclined Substrate is considered, when the film is contaminated by an insoluble surfactant, in the frame work of Orr-Sommerfeld analysis. The classical long-wave asymptotic expansion for small wave numbers reveals the occurrence of two modes, the Yih mode and the Marangoni mode for a clean/a contaminated film over a Porous Substrate and this is confirmed by the numerical solution of the Orr-Sommerfeld system using the spectral-Tau collocation method. The results show that the Marangoni mode is always stable and dominates the Yih mode for small Reynolds numbers; as the Reynolds number increases, the growth rate of the Yih mode increases, until, an exchange of stability occurs, and after that the Yih mode dominates. The role of the surfactant is to increase the critical Reynolds number, indicating its stabilizing effect. The growth rate increases with an increase in permeability, in the region where the Yih mode dominates the Marangoni mode. Also, the growth rate is more for a film (both clean and contaminated) over a thicker Porous layer than over a thinner one. From the neutral stability maps, it is observed that the critical Reynolds number decreases with an increase in permeability in the case of a thicker Porous layer, both for a clean and a contaminated film over it. Further, the range of unstable wave number increases with an increase in the thickness of the Porous layer. The film flow system is more unstable for a film over a thicker Porous layer than over a thinner one. However, for small wave numbers, it is possible to find the range of values of the parameters characterizing the Porous medium for which the film flow can be stabilized for both a clean film/a contaminated film as compared to such a film over an impermeable Substrate; further, it is possible to enhance the instability of such a film flow system outside of this stability window, for appropriate choices of the Porous Substrate characteristics.
-
Shear-Thinning Film on a Porous Substrate: Stability Analysis of a One-Sided Model
Chemical Engineering Science, 2011Co-Authors: R. Usha, Séverine Millet, Hamda Ben Hadid, François RoussetAbstract:The temporal stability of a Carreau fluid flowing down an inclined Porous Substrate is considered. A reduced model is derived under the assumption of small permeability which decouples the flow in the liquid layer from the filtration flow in the Porous medium and incorporates the effect of the Porous medium by means of an effective slip condition at the liquid-solid interface. The slip coefficient in the effective slip condition is a function of the structure, permeability of the Porous medium and the rheology of the fluid saturating the Porous medium. The effects of shear-thinning rheology and permeability of the Substrate on the stability of the film flow system are investigated. This problem gives rise to a generalized eigenvalue formulation which is solved through two approaches. The problem is solved analytically for long waves in the limiting cases of weakly and strongly non-Newtonian behaviors (power-law limit). A numerical investigation is carried out in the general case. The results are shown to agree well for the weakly non-Newtonian limit. Further, the power-law model and the Carreau model agree on a wide range of shear-thinning parameter values for a thin film over a rigid Substrate. However, when considering a Porous medium, this trend is not observed. The Carreau model gives valid results for the entire range of shear-thinning parameter values for a film over a rigid/Porous Substrate. The novelty of the present investigation lies in the inclusion of both the effects of bottom permeability and shear-thinning rheology. Both permeability and shear-thinning rheology have a destabilizing effect on the film flow system. The numerical results indicate the correlation between the effects due to shear-thinning properties and permeability. An energy balance analysis performed on the perturbation fields shows that destabilization induced by both shear-thinning and permeability is linked to the viscous shear work rate on the free surface.
Victor Starov - One of the best experts on this subject based on the ideXlab platform.
-
Spreading and Imbibition of Vesicle Dispersion Droplets on Porous Substrates
Colloids and Interfaces, 2019Co-Authors: Abhijeet Kumar, Victor Starov, Anna Trybala, Jochen Kleinen, Joachim Venzmer, Tatiana Gambaryan-roismanAbstract:Vesicles have recently found widespread use in applications such as conditioning of textiles, paper and hair, as well as transdermal drug delivery. The mode of treatment in several such cases involves the application of droplets of aqueous dispersions of vesicles onto dry Porous Substrates like paper and textiles. One of the factors which affects the performance of such treatments is the rate at which the droplets spread and imbibe on the Porous Substrate. Depending upon the specific purpose of the treatment either a fast or slow droplet spreading kinetics could be desired. Therefore, it is important to have a good understanding of the droplet spreading process and the factors which influence it. In this work, an experimental investigation of the simultaneous spreading and imbibition of vesicle dispersion droplets on cellulose filter papers is carried out. Two different types of vesicles which are composed of similar lipid molecules but exhibit contrasting lipid bilayer phase behavior are used. Two different grades of filter papers with comparable porosities but different thicknesses are used as Porous Substrate. It is found that the droplet spreading behavior is of the “complete wetting” type on the thicker Porous Substrate, whereas it is of the “partial wetting” type on the thinner Substrate. Furthermore, it is observed that the spreading of droplets containing vesicles with liquid-crystalline phase bilayers occurs faster than that of vesicles with solid-gel phase bilayers. The secondary radial penetration which commences after the initial droplet spreading is complete is also investigated and discussed.
-
Foam drainage placed on a thin Porous layer
Soft matter, 2019Co-Authors: Nektaria Koursari, Omid Arjmandi-tash, Phillip Johnson, Anna Trybala, Victor StarovAbstract:Drainage of foams placed on Porous Substrates has only recently been theoretically investigated (O. Arjmandi-Tash, N. Kovalchuk, A. Trybala, V. Starov, Foam Drainage Placed on a Porous Substrate, Soft Matter, 2015, 11(18), 3643–3652), where an equation describing foam drainage (with non-slip boundary conditions on the liquid–air interfaces) was combined with that of imbibition of liquid into the thick Porous Substrate. Foam-based applications have been used as a method of drug delivery, which is a recent and promising area of research related to application of medicinal products onto the skin or hair, which are both thin Porous layers. A theory of foam drainage (taking into account surface viscosity) placed on a completely wettable thin Porous layer is developed: the rate of foam drainage and imbibition inside the Porous layer and other characteristics of the process are predicted. The “effective slip” caused by the surface viscosity increased a movement of the top boundary of the foam. The theoretical predictions are compared with experimental observations of foam drainage placed on thin Porous layers. The comparison showed a reasonable agreement between the theoretical predictions and experimental observations. One of the phenomena during foam application is the possibility of a build-up of a free liquid layer on the foam/Porous layer interface, which can be very useful for applications. Three different regimes of spreading/imbibition process have been predicted. Conditions and durations of free liquid layer formation have been theoretically predicted and compared with experimental observations.
-
Interaction of liquid foams with Porous Substrates
Current Opinion in Colloid & Interface Science, 2019Co-Authors: Anna Trybala, Omid Arjmandi-tash, Nektaria Koursari, Phillip Johnson, Victor StarovAbstract:Abstract We review the most recent studies of drainage/imbibition of foams placed on Porous Substrates: the latest theoretical models, simulation studies and experimental observations. Foam products are ideal for imbibition and penetration into Porous media, and they have gained substantial interests in both industrial and scientific areas. Foams are suitable products in cosmetics and pharmaceutical industry and have recently been used in drug delivery processes due to the improved wetting behaviour. A description of the features and parameters affecting foam drainage placed on Porous Substrates is presented; complexity and simultaneous actions occurring in the process are discussed. The difference between free foam drainage and the drainage of foam placed on a Porous Substrate is clarified, and a new phenomenon, which is a formation of a free liquid layer at the foam/Porous Substrate interface, was theoretically predicted and experimentally verified. Considering the effect of parameters on the rate of imbibition into thick or thin Porous Substrate revealed the existence of three different regimes of the process. Recent theoretical predictions and simulation of wetted area, foam height and possibility of free liquid layer formation in the course of drainage and imbibition into thin Porous layer showed a good agreement with experimental observations.
-
Foam drainage on thick Porous Substrate
Physicochemical Problems of Mineral Processing, 2017Co-Authors: Toby Armstrong, Omid Arjmandi-tash, Anna Trybala, Hannah Smith, Jennifer Cook, Victor StarovAbstract:The use of foam-based applications as a method of drug delivery represents a recent and promising area of research. The interaction of foam and Porous Substrates have been recently theoretically described using a mathematical model, which combines the equation of foam drainage with that of imbibition of liquid into the Porous Substrate. Below the drainage of foam placed on chalk experimentally investigated to verify the theory prediction. The surfactants sodium dodecyl sulfate (SDS) and Triton X-100 were used to form a foam. The initial liquid volume fractions of the foam were found to be ranging in between 14.12 and 16.46%. The porosity and permeability of the chalk Substrate were experimentally obtained at 59.1% and 3.122.10 -11 m 2 respectively. The height of foam deposited onto the thick Porous Substrate (chalk) was 2.5 cm and 6 cm. The imbibition into the chalk, the height of foam, and the bubble size within the foam were monitored. The latter enabled the kinetics of the drainage/imbibition to be determined and compared with the predictions according to the theoretical model. The rate of decrease in foam height was initially high and decreased over time as predicted by the theoretical model. All the foam displayed an initial rapid imbibition through the Porous Substrate, which is again in the agreement with the theory predictions. It was found that solutions with lower surfactant concentrations could penetrate deeper into the chalk. The imbibition front was observed to be uniform: evenly distributed liquid throughout the cross-section of the Porous Substrate.
-
Foam drainage placed on a Porous Substrate
Soft matter, 2015Co-Authors: Omid Arjmandi-tash, Anna Trybala, Nina Kovalchuk, Victor StarovAbstract:A model for drainage/imbibition of a foam placed on the top of a Porous Substrate is presented. The equation of liquid imbibition into the Porous Substrate is coupled with a foam drainage equation at the foam/Porous Substrate interface. The deduced dimensionless equations are solved using a finite element method. It was found that the kinetics of foam drainage/imbibition depends on three dimensionless numbers and the initial liquid volume fraction. The result shows that there are three different regimes of the process. Each regime starts after initial rapid decrease of a liquid volume fraction at the foam/Porous Substrate interface: (i) rapid imbibition: the liquid volume fraction inside the foam at the foam/Porous Substrate interface remains constant close to a final liquid volume fraction; (ii) intermediate imbibition: the liquid volume fraction at the interface with the Porous Substrate experiences a peak point and imbibition into the Porous Substrate is slower as compared with the drainage; (iii) slow imbibition: the liquid volume fraction at the foam/Porous Substrate interface increases to a maximum limiting value and a free liquid layer is formed between the foam and the Porous Substrate. However, the free liquid layer disappears after some time. The transition points between these three different drainage/imbibition regimes were delineated by introducing two dimensionless numbers.
