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Adsorption is carried out for the removal of two reactive dyes from an industrial effluent. The specific dyes are reactive red and reactive black, commercially known as Cibacron Red RB and Cibacron Black B, respectively. An adsorbent developed from sawdust is used. Equilibrium and kinetic studies are carried out with the synthetic solutions of the dyes. For the mixture of two dyes, the bisolute Langmuir isotherm modified with an interaction factor is used. A mass transfer model including an external film mass transfer coefficient and an internal effective diffusivity is used to interpret the adsorption kinetic data. These parameters are obtained by fitting the experimental data to the model. An industrial effluent is successfully treated with the same adsorbent. The estimated model parameters are used for the prediction of the concentration profiles of dyes of the industrial effluent.

A series of pretreatment methods to mosambi juice were undertaken and results were compared to pectinase treatment for clarification of the treated juice using ultrafiltration. The pretreatment methods attempted were centrifugation, centrifugation followed by addition of gelatin, centrifugation followed by addition of bentonite, centrifugation followed by fining using both bentonite and gelatin and enzymatic treatment, using pectinase as the enzyme. A systematic study was undertaken to select the operating centrifugation speed and time. The permeate flux and quality of the permeate were comparable to the enzyme-treated juice.

Pattern formation during evaporation of biofluids finds significant applications in the biomedical field for disease identification. Aβ (25–35) is the smallest peptide in the amyloid peptide family that retains the toxicity of a full length peptide responsible for Alzheimer's disease and is chosen here as the model solute. Drying experiments on substrates of varying wettability exhibit unique drying patterns of Aβ (25–35) fibrils visualized through fluorescence microscopy and transmission electron microscopy. The unique pattern formations can be interpreted as manifestations of the changes in the self-pinning mechanism with changes in wettability, which in some cases resembles the well-known coffee ring effect. Additionally, the delicate balance between the drag and capillary forces has been perturbed by initiating controlled rates of evaporation and probing their effects on the fibril patterning.

Neural network models have been used to describe the permeate flux and permeate concentration (total soluble solid) profiles during the ultrafiltration of synthetic fruit juice and mosambi juice dynamically. It aims to predict the permeate flux and total soluble solid of the permeate as a function of transmembrane pressure, sucrose, pectin concentration in the feed and the processing time. A multi-layer feed forward network structure with input, output and hidden layer(s) is used in this study. The back-propagation algorithm is utilized in training of ANN models. Two neural network models are constructed to predict the permeate flux and the total soluble solids in the permeate using the filtration data of the synthetic juice. The modeling results showed that there is an agreement between the experimental data and predicted values, with mean absolute errors less than 1% of the experimental data. Also the trained networks are able to capture accurately the non-linear dynamics of synthetic fruit juice and the actual mosambi juice even for a new condition that has not been used in the training process.

An attempt has been made to remove color from wastewater containing toxic eosin dye (anionic dye) by cloud point extraction (CPE) in batch mode using a nonionic surfactant, Triton X-100 (TX-100). Most of the dye molecules get solubilized in the coacervate phase leaving a color free dilute phase. The effects of the concentration of feed mixture, temperature and salt concentration on the concentration of both dye and surfactant in the coacervate phase and dilute phase have been studied after the complete separation of two phases. Experimental investigations have also been carried out for the recovery of surfactant from dilute phase applying solvent extraction (SE) in batch condition. It has been observed that 87.5-100 percent eosin removal is possible for the feed dye concentration of up to 200 ppm using 0.1(M) of TX-100 and 0.2(M) of salt (NaCl) at 80 degrees C. About 88 percent of TX-100 can be recovered from dilute phase using solvent extraction method. It is concluded that the cloud point extraction techniques for the dye removal may be an alternative to the present dye removal processes.

Effects of suction are included in the mass transfer coefficient in the performance prediction of spiral wound and tubular membrane module. The analysis is valid for the laminar flow regime and osmotic pressure controlled filtration. Sodium chloride and dextran are chosen as the solutes. The design equations are solved numerically and the profiles of the bulk concentration, bulk velocity, feed channel pressure, permeate flux, permeate concentration, etc., are obtained along the length of the membrane module. The results are compared with the standard method of module design using film theory and mass transfer coefficient without suction. The results show that the design method without the inclusion of the effects of suction, leads to gross underprediction (about 2–2.5 times) of the average permeate flux and overprediction of the permeate concentration (about 2–14%) for various operating conditions in ultrafiltration. Use of standard film theory also results in an underprediction of the permeate flux of about 10–15% (over a range of operating conditions) compared to the exact mass transfer coefficient with suction. For reverse osmosis, the effects of suction are insignificant.

Ultrafiltration of enzymatically treated mosambi ( Citrus sinensis [L.] Osbeck) juice was performed in a batch, unstirred membrane cell. Thin film composite polyamide membrane of molecular weight cut-off 50,000 was used. The flux-decline mechanism was identified by the growth of a gel-type layer over the membrane surface. The flux decline, the gel resistance, the gel-layer thickness and various domains of resistances were calculated at a constant pressure difference in the range of 276‐552 kPa. The conventional gel-filtration theory was employed to analyze the flux-decline behavior. The calculated permeate flux and gel-layer resistances were consistent with the experimental results. The calculated gel-layer thickness varied from 4.12 to 74.1 m m for different operating condition (pressure) and time. The time at which the gel resistance becomes equal to the membrane-hydraulic resistance ranged from 13 to 31 s for the pressure range studied herein. Thus, the deposited layer resistance to permeate flow was substantial, throughout the whole operation, except in the first few seconds.

The performance of activated carbon has been investigated for the adsorption of eosin dye dissolved in water. Eosin is anionic in nature and highly toxic. The effects of initial dye concentration, contact time, pH and temperature on adsorption of eosin by a fixed amount of activated carbon (1.0 g/L) have been studied in batch and column mode. The equilibrium data are successfully fitted to the Freundlich adsorption isotherm. The adsorption rate data are successfully explained by a pseudo second-order kinetic model. Breakthrough curves for column adsorption have also been studied. The regeneration of spent carbon by desorbing the dye has been experimentally investigated applying a surfactant enhanced carbon regeneration (SECR) technique using both cationic and anionic surfactants. An empirical kinetic model for dye desorption from the commercial activated carbon (CAC) using different surfactant and desorption techniques, viz. change in pH, has been proposed. The comparison between the model and the experimental results is found to be satisfactory.

A model for fluid flow and heat transfer in a micro heat pipe of any arbitrary (polygonal) shape is presented utilizing a macroscopic approach. The coupled non-linear governing equations for the fluid flow, heat and mass transfer are developed based on first principles and are solved numerically. The performance and the capillary limitations of such a device are analyzed in detail. The profile of the radius of curvature is used to predict the onset of the dry-out point and the propagation of the dry out length. A method is developed to estimate the dry out length as a function of system geometry and process variables, e.g., heat input and inclination. The model predicted results are successfully compared with the experimental results from a previous study. The general nature of the model and the associated parametric study ensure the wide applicability of the model.

An artificial neural network (ANN) model is presented for the prediction of viscosity of fruit juice as a function of concentration and temperature. The fruit juices considered in the present study were orange, peach, pear, malus floribunda and black current. The viscosity data of juices (1.53–3300 mPa s) were obtained from the literature for a wide range of concentration (5–70 °Brix) and temperature (30.7–71.7 °C). Several configurations were evaluated while developing the optimal ANN model. The optimal ANN model consisted of two hidden layers with two neurons in each hidden layer. This model was able to predict viscosity with a mean absolute error of 3.78 mPa s. The performance of the ANN was checked using experimental data. Predicted viscosity using the ANN was proved to be a simple, convenient and accurate method. The model can be incorporated in the heat transfer calculations during fruit processing where concentration and temperature dependent viscosity values are required. This may also be useful in mass transfer calculations during filtration of the juice using membranes for clarification.

Surfactant‐based separation of two oxyanions (Cr2O7 = and MnO4 −) from their mixture is studied to assess the potential of micellar enhanced ultrafiltration (MEUF). Cetyl(hexadecyl) pyridinium chloride (CPC) has been taken as the cationic surfactant. An organic polyamide membrane of a molecular weight cut off of 1000 is used. About 99% retention of the solutes is observed under unstirred batch mode. In order to improve the permeate flux and the retention of the solutes, cross‐flow studies are also conducted. The retention of solutes without using surfactant varies from 6 to 15% only, at a typical feed mixture concentration of 0.05 kg/m3 for each of the two solutes. Under the same operating conditions, the solute retention increases up to 99% using surfactant micelle. The effects of various operating conditions, e.g., concentrations of surfactant and solutes, transmembrane pressure drop and cross‐flow rate (for cross‐flow experiments), etc., on the permeate flux and observed retention are studied ...

A combination of adsorption and nanofiltration (NF) was adopted for the treatment of a textile dyehouse effluent containing a mixture of two reactive dyes. The effluent stream was first treated in a batch adsorption process with sawdust as an adsorbent to reduce the dye concentration of the effluent by about 83% for Dye 1 and 93% for Dye 2. The effluent from the adsorption unit was passed through an NF unit for the removal of the remaining small amount of dyes and to recover the associated chemicals (mainly salt) in the effluent stream. The dyes remaining after this step were less than 1 ppm. The percentage removal of COD was greater than 99%, and the salt recovery was on the order of 90%. Equilibrium studies were carried out with synthetic solutions of the dyes (both single component as well as two-component systems) at room temperature. The adsorption rates were studied in detail using varying amounts of the adsorbent. NF of the effluent was performed in a cross-flow system using a 400 molecular weight cut-off membrane. A detailed study was carried out to observe the effect of the process parameters, namely applied pressure and bulk velocity on the process outputs such as dye rejection, COD removal, permeate flux and salt recovery. Finally, direct NF of the effluent (with the original high concentration) was undertaken, and the performance of the process was compared with the combination method. The permeate flux for the proposed combined method was found to be about twice that for the direct NF method. The dye rejection improved significantly compared to adsorption.

A semi-empirical model has been proposed to predict the permeate flux and permeate concentration during the cross flow nanofiltration of a dye solution. The model includes laminar flow regime as well as flow assisted by the turbulent promoters. Membrane hydraulic resistance, osmotic pressure resistance and the gel type layer resistance are considered in series. The gel type layer resistance is correlated to the operating conditions, namely, the feed concentration, the transmembrane pressure difference and the cross flow velocity for a set of selected experiments. For the rest of the experiments, the permeate flux values are predicted using the developed correlation and are found to be in good agreement with the experimental results. It has been found that the gel type layer resistance decreases up to 68% due to the presence of the turbulent promoters leading to an enhancement of the permeate flux by about 109%.

One-dimensional transient model for fluid flow and heat transfer is presented for a micro-grooved heat pipe of any polygonal shape utilizing a macroscopic approach. The coupled non-linear governing equations for the fluid flow, heat and mass transfer are developed based on first principles and are solved simultaneously. The transient behavior for various parameters, e.g. substrate temperature, radius of curvature, liquid velocity, etc. are studied. The effects of the groove dimensions, heat input and Q-profiles on the studied parameters have been evaluated. The steady state profiles for substrate temperature, radius of curvature, liquid velocity etc. have also been generated. The model predicted steady state substrate temperature profile is successfully compared with the experimental results from the previous study. The general nature of the model and the associated parametric study ensure the wide applicability of the model.

Ultrafiltration (UF) of sucrose and pectin solutions, their mixtures and enzymatically treated mosambi (Citrus sinensis [L.] Osbeck) juice has been performed on a batch unstirred membrane cell. Thin film composite polyamide membrane of molecular weight cut-off 50,000 was used. The sucrose solution's permeate flux declined marginally, but for the pectin solution, it decreased rapidly over time. The sucrose-pectin mixture exhibits a flux decline similar to that of the pectin solution. The gel-type pectin layer over the membrane's surface governs the flux decline of the sucrose-pectin mixture. The nature of the flux decline and the values of the permeated total soluble solids of enzymatically treated mosambi juice show similar behavior as compared with that of the UF of the sucrose-pectin mixture. The permeate of the enzyme-treated mosambi juice contains almost all the soluble solids and acids (in terms of citric acid) with a remarkable improvement in juice clarity.

The removals of single aromatic alcohols, including para nitro phenol (PNP), meta nitro phenol (MNP), phenol (P), catechol (CC), beta napthol (BN) and ortho chloro phenol (OCP) from aqueous solution have been studied using micellar-enhanced ultrafiltration (MEUF). Cetyl (hexadecyl) pyridinium chloride (CPC) has been taken as the cationic surfactant. An organic polyamide membrane of molecular weight cut-off 1000 is used in the MEUF experiments. Experiments are conducted using unstirred batch cell and a continuous cross flow cell. The effects of surfactant-to-solute concentration ratio in the feed, transmembrane pressure drop and cross flow rate on the permeate flux and observed retention of each solute have been studied in detail. The retention of solutes without using surfactant varies from 3 to 15% only at a typical feed solute concentration of 0.09 kg/m 3 . However, under the same operating pressure (345 kPa), retention increases to about 66–98% depending on the nature of solute at the end of 30 min of experiment in the batch cell using surfactant micelles (10 kg/m 3 ). The maximum retention of solute is obtained at surfactant-to-solute concentration ratio of 110. Free surfactant molecules present in the permeate and retentate are then recovered by a two-step chemical treatment process. In the first step, the surfactant is precipitated by potassium iodide and in the second step, the surfactant is recovered from the precipitate by the addition of cupric chloride. Optimum consumptions of potassium iodide and cupric chloride are also obtained experimentally.

Experimental investigations were carried out to adsorb red colored chrysoidine dye from an aqueous medium by using activated charcoal (AC) as an adsorbent. The effects of adsorbent dose, initial dye concentration, contact time, pH, and temperature were studied for the adsorption of chrysoidine under stirred conditions and batch wise. Standard adsorption isotherms were considered to fit the experimental equilibrium data. It was found that the adsorption of chrysoidine on AC follows the Freundlich adsorption isotherm. The rate of adsorption was described by both first‐ and pseudosecond‐order kinetic models. Experimental investigations also were carried out for the regeneration of spent carbon by applying surfactant enhanced carbon regeneration (SECR) technique by using both cationic and anionic surfactant. An empirical kinetic model for regeneration of adsorbent was presented.

The expression of mass transfer coefficient is derived from first principles for the turbulent non-Newtonian fluid flow in the membrane modules. The effects of suction are incorporated in the mass transfer coefficient from a theoretical basis. The analysis is carried out for a power law fluid, the common rheology for fruit juices and other food products. The analysis shows that there is significant effect of suction on mass transfer coefficient. The effects of the operating conditions, e.g., Reynolds number, permeate flux and the rheological nature of the fluid (pseudoplastic or dilatant) on the mass transfer coefficient are also investigated. Both rectangular thin channel and tubular modules are considered.

An attempt has been made to remove color from wastewater containing congo red (a toxic cationic dye) by surfactant mediated cloud point extraction (CPE) in batch mode using Triton X-100 (TX-100) as non-ionic surfactant. Most of the dye molecules get solubilized in the coacervate phase leaving a dye free dilute phase. The effects of the concentration of feed mixture (both dye and surfactant), temperature and salt concentration on the concentration of both dye and surfactant in the coacervate phase and dilute phase have been studied. An optimum set of surfactant concentration, temperature and salt concentration are obtained for removal of dye. Experimental investigations have also been carried out for the recovery of surfactant from dilute phase applying solvent extraction (SE) in batch condition using heptane as extracting medium.

Nanofiltration of dye (crystal violet) is carried out in a rectangular cross-flow cell. The feed concentration of the dye is selected in the range generally encountered in the actual textile plant effluent. Apart from the feed concentration, the effects of other operating conditions, e.g. transmembrane pressure and cross-flow velocity are studied as well. The effects of these operating conditions on the permeate flux and observed retention are evaluated by conducting one complete set of experiments (consisting of 27 experiments) under a laminar flow regime. Thin wires are used as turbulent promoters and the full set of experiments is carried out under the same operating conditions (as in the laminar flow). It is observed that the significant flux enhancement in the range of 40–100% is achieved while the retention of dye remains unchanged.

Mosambi juice was treated with pectinase enzyme at different durations (40–141 min), temperatures (32–49 °C), and at various concentration level of enzyme (0.0004–0.0014 w/v%). The effects of the enzyme treatment conditions on various parameters (e.g., apparent viscosity, clarity and alcohol insoluble solid) were studied. The optimum process condition, were determined employing a second-order central composite rotatable design in combination with response surface methodology. Apparent viscosity and alcohol insoluble solid decreased with temperature and enzyme concentration. Clarity of juice increases with temperature and the enzyme concentration.

Micellar enhanced ultrafiltration (MEUF) is used to remove acid dye from aqueous solution. Cetyl(hexadecyl) pyridinium chloride (CPC) and eosin (molecular weight 691.86) have been taken as cationic surfactant and acid dye, respectively. An organic polyamide membrane of molecular weight cut-off 1000 is used in unstirred batch experiments. The effects of surfactant-to-dye concentration ratio in the feed and the transmembrane pressure drop on permeate flux and observed retention of the dye have been studied as a function of the operating time. The retention of dye without using surfactant is only 10% at a typical feed dye concentration of 10×10−3 kg/m3. Whereas under the same operating pressure (276 kPa), retention increases up to 73.4% using surfactant micelles. The maximum retention of eosin is obtained at a surfactant-to-eosin ratio of 2000. Free surfactants molecules present in the permeate are then recovered by a two-step chemical treatment procedure. In the first step, surfactant is precipitated by potassium iodide and in the second step, the surfactant is recovered from the precipitate by addition of cupric chloride. In the first step, 1:1 molar ratio of potassium iodide to CPC results in about 90% precipitation of the surfactant. In the second step, 5:1 molar ratio of cupric chloride-to-cetyl pyridinium iodide (CPI, precipitated form of CPC) leads to about 90% recovery of the surfactant.

A Constrained Vapor Bubble Loop Thermosyphon, CVBLT, made of quartz was used to study the stability and oscillations of an evaporating curved wetting film of pentane in a corner. The film thickness profile was measured as a function of heat input, time, and axial position using image analyzing interferometry. The curvatures and apparent contact angles for the evaporating film under various operating conditions were obtained from the measured film thickness profiles. Instability (oscillation) of the liquid film was observed at relatively higher values of the heat input. The behavior of the curvature and the apparent contact angle of an oscillating film with changes in heat input was evaluated. Moving velocities of the oscillating film were calculated from the measured values of the liquid-wall wetted lengths and were found to be directly proportional to the difference between the instantaneous force acting on the curved film and the reference force. Using an augmented Young-Laplace pressure jump model, the effect of the excess free energy at the contact line on the oscillations was demonstrated.

A vertical constrained vapor bubble, VCVB, made of fused silica was used to study the stability and oscillations of an evaporating wetting film of HFE- 7000® in a corner. The film thickness profile was measured as a function of time and axial position using an advanced form of image analyzing interferometry. The curvature, apparent contact angle, and pressure profiles for the evaporating film were calculated from the measured film thickness profiles. Oscillation of the liquid film was observed and profiles for both the advancing and receding films were obtained. These are the first such detailed profiles obtained for an oscillating meniscus below a thickness of 0.1 μm. The film thickness profiles demonstrated the spreading of the meniscus during advance as well as the presence of a curvature gradient near the contact line region. The maximum curvature decreased for the advancing menisci and increased with time for the receding menisci. An increase in the adsorbed film thickness was associated with the advancing stage and a decrease with the receding stage. Pressure profiles were measured as a function of position indicating the potential for driving the flow of the fluid toward or away from the contact line. As the film advances or recedes, the pressure gradients change as a function of position fueling the next oscillation cycle.

Unstirred batch and cross flow nanofiltration have been carried out to separate dye from aqueous solution. The effect of different process parameters on separation of dye is studied. Experiments are conducted with aqueous solution of crystal violet (CV, molecular weight 408) using a 400 molecular weight cut-off membrane. An unsteady state mass transfer model is developed to predict the permeate flux and the permeate concentration in a batch cell. Using the experimental results, the model parameters i.e. the diffusivity of the solute (D) and real retention (Rr) of the membrane are evaluated by optimizing the experimental flux and permeate concentration profiles. Using the estimated D and Rr from the batch cell results, the permeate flux and concentrations are predicted for a cross-flow nanofiltration system using film theory.

A study has been performed to quantify the extent of flux decline during micellar enhanced ultrafiltration (MEUF) of an acid dye (eosin red) using hexadecyl (cetyl) pyridinium chloride as the cationic surfactant. Effects of the operating conditions, e.g., transmembrane pressure drop and feed-surfactant-to-dye ratio, on the permeate flux profile and observed retention have been investigated in an unstirred batch ultrafiltration (UF) cell. A simple resistance-in-series model has been used to quantify the flux decline. From the flux decline history, it has been found that the membrane permeability decreases rapidly due to reversible pore blocking and further flux decline is caused by the growth of a gel-type layer over the membrane surface. The different resistances and growth kinetics of the gel layer have been investigated as functions of the operating conditions.

Modeling of separation of two-component dye mixture has been carried out in an unstirred bath cell. Nanofiltration of a two-component industrial dye-house effluent containing reactive black dye (Cibacron Black B, molecular weight 924.5) and reactive red dye (Cibacron Red RB, molecular weight 855.5) has been considered using a 400 molecular weight cut-off (MWCO) membrane. An unsteady state mass transfer model is developed using an integral method to predict the permeate flux and the permeate concentration of each component. The experimental profiles of permeate concentration and permeate flux are optimized with the calculated profiles to estimate the model parameters. The predicted results using these optimized parameters are in good agreement with the experimental results.

A membrane based separation process (nanofiltration, NF) is used to treat the effluent from a textile plant. The dye mixture contains reactive black dye (Cibacron Black B) and reactive red dye (Cibacron Red RB). An organic membrane with molecular weight cut-off of 400 is used for the experiments. The experiments are conducted in an unstirred batch and a rectangular cross flow cell. Separations with retentions up to 94 and 92% of the two dyes are achieved respectively in the cross flow cell where steady state is attained quickly. It is important to note that NF techniques achieve a sharp reduction in chemical oxygen demand (COD), (up to 94% in cross flow cell), as the dyes are removed from the permeate. A parametric study of the separation process is undertaken to characterize the effects of the operating variables, e.g., trans-membrane pressure, dye concentration in the feed and cross flow velocity in case of cross flow NF.

Adsorbent prepared from fly ash obtained from a thermal power plant was successfully used to remove cresol from an aqueous solution in a batch reactor. The adsorbent was characterized, and significant removal of cresol was achieved. The adsorption isotherms were evaluated and the effects of system parameters, e.g., stirrer speed and temperature on the adsorption, were studied. A theoretical model was proposed, and it was solved by using a quasi-steady-state approach. The intraparticle diffusivity was evaluated from one set of experimental data and was subsequently used to predict the change in bulk concentration with time for other experimental conditions. The predicted and the experimental results are in close agreement. The performance of the adsorbent prepared was favorably compared with that of commercially available activated carbon.

A comprehensive predictive model for the osmotic pressure controlled turbulent cross-flow membrane separation process is presented. A thin rectangular channel is selected as the system geometry. The model can handle solutes with wide range of diffusivities (from sodium chloride to dextran) under different modes of membrane separations (RO, UF, etc.). It is not limited to the condition that the mass transfer boundary layer lies within the viscous sublayer of the hydrodynamic boundary layer. The governing equations are solved using an integral method. The performance characteristics of the system in terms of permeate flux and permeate concentration can be predicted simultaneously. The experimental data available in the literature under turbulent conditions [Ind. Eng. Chem. Fundam. 3 (1964) 210; J. Membr. Sci. 22 (1985) 117] are successfully compared with the model predicted results. A parametric study has been carried out to observe the effects of various operating conditions on the permeate flux and permeate concentration (in terms of observed retention).

Modeling and subsequent simulation of electric field enhanced ultrafiltration (UF) under osmotic pressure controlled regime in a rectangular channel under laminar flow conditions is presented herein. Bovine serum albumin (BSA) at pH 7.4 in 0.15 M NaCl solution is considered as the system. The analysis is carried out under the framework of boundary layer theory in conjunction with the electro-kinetic phenomena for a colloidal solution. Important effects due to the interaction between charged macro- and micro-particles with the solvent, e.g. viscoelectric effects, variation of diffusivity and Debye length with concentration, etc. have been incorporated in the model. It has been observed that the external dc electric field has a significant effect on the permeate flux and permeate concentration. A parametric study has been carried out to observe the effects of different operating conditions on the system performance.

Experiments are carried out in a specially designed cell to study the onset and propagation of dryout point on a chemically machined microgrooved silicon surface with pentane as the coolant liquid. The axial temperature distribution is accurately measured as a function of the heat input and inclination of the substrate. The comparison between the dry (without liquid) and wet (with liquid) temperature profiles is used to locate the dryout point. The axial flow of an evaporating thin liquid film through a V-shaped microgroove with an appreciable inclination angle and varying evaporative heat flux is theoretically investigated. The nonlinear governing equations are solved numerically to predict the onset, location and propagation of the dryout point. The predictions from the theoretical analysis are successfully compared with the experimental results.

We report a study on the ion-size dependent electroosmosis of viscoelastic fluids in microfluidic channels with interfacial slip. Here, we derive an analytical solution for the potential distribution in a parallel plate microchannel, where the effects of finite sized ionic species are taken into account by invoking the free energy formalism. Following this, a purely electroosmotic flow of a simplified Phan-Thien-Tanner (sPTT) fluid is considered. For the sPTT model, linear, quadratic, and exponential kernels are chosen for the stress coefficient function describing its viscoelastic nature across various ranges of Deborah number. The theoretical framework presented in our analysis has been successfully compared with experimental results available in the literature. We believe that the implications of the considered effects on the net volumetric throughput will not only provide a deeper theoretical insight to interpret the electrokinetic data in the presence of ionic species but also serve as a fundamental ...

Pathogenesis of amyloid-related diseases is related to nonnative folding of proteins with the formation of insoluble deposits in the extracellular space of various tissues. Having the unique properties of small size, large surface area, biodegradability, and relative nontoxicity, magnetic nanoparticles have drawn a lot of attention in biomedical applications. Herein, we demonstrate the effect of bare and differently functionalized magnetic MnFe2O4 nanoparticles on fibrillation of human serum albumin in vitro. The process has been monitored using Thioflavin T fluorescence, Congo red binding assay, circular dichroism, fluorescence microscopy, and transmission electron microscopy. From our experimental results, amine functionalized MnFe2O4 nanoparticles are found to inhibit formation of fibrils more effectively than bare ones, while carboxylated nanoparticles do not have a significant effect on fibrillation. This study has explored the prospects of using specific magnetic nanoparticles with appropriate modification to control self-assembly of proteins and may act as a precursor in therapeutic applications.

The intricate interaction between the deformability of a substrate and the dynamic spreading of a liquid drop on the same, under the application of an electrical voltage, has remained far from being well understood. Here, we demonstrate that electrospreading dynamics on soft substrates is dictated by the combined interplay of electrocapillarity, the wetting line friction, and the viscoelastic energy dissipation at the contact line. Our results reveal that during such electro-elastocapillarity mediated spreading of a sessile drop, the contact radius evolution exhibits a universal power-law in a substrate elasticity based non-dimensional time, with an electrical voltage dependent spreading exponent. Simultaneously, the macroscopic dynamic contact angle variation follows a general power-law in the contact line velocity, normalized by elasticity dependent characteristic velocity scale. These findings will be beneficial for comprehending droplet spreading dynamics stemming from the combination of electrically modulated spreading and “soft wetting.” Hence, our results are likely to provide the foundation for the development of a plethora of applications involving droplet manipulations by exploiting the interplay between electrically triggered spreading and substrate-compliance over interfacial scales.

A theoretical analysis for predicting the performance of laminar osmotic pressure controlled cross flow ultrafiltration (UF) is presented in this work. Variations of the physical properties e.g., viscosity, diffusivity, etc., with concentration have been incorporated. The analysis is carried out from the first principles. There is no adjustable parameter in this work to account for the effects of property variation in UF. The predictions from the analysis are in excellent agreement with the published experimental data of bovine serum albumin at pH 4.7. The theoretical predictions of Sherwood numbers under different operating conditions agree remarkably well with the results using semi-analytical Sherwood number relationships available in the literature.

Analytical expressions for limiting flux, limiting concentration at the membrane surface, limiting operating pressure are developed for osmotic pressure controlled cross flow ultrafiltration. Modified Sherwood number relationships incorporating the effects of suction and variations of physical properties are used to estimate mass transfer coefficient in a rectangular geometry. The model is solved to predict the limiting flux of bovine serum albumin and dextran data, obtained from the literature. A parametric study of limiting flux with different parameters (e.g., Reynolds number, feed concentration, real retention of the membrane, etc.) is also carried out. Further, the analysis is also carried out for a partially retentive membrane. Explicit quantification of limiting pressure would be of immense help for the design engineers from both operational and economic points of view.

Sherwood number relations for the prediction of the mass transfer coefficient for developing concentration boundary layer have been obtained for turbulent flow regime from first principles. The common flow modules, namely, rectangular channel, tubular and radial cross flow are considered. The relationships developed include the effect of suction through the membrane. Relevant relations for the estimation of mass transfer coefficient for cross flow ultrafiltration are formulated. The proposed Sherwood relations are used in conjunction with the osmotic pressure model to predict the permeate flux in osmotic pressure governed ultrafiltration. The simulated results are compared with the experimental data obtained from the literature. A detailed parametric study has been performed to observe the effects of the operating conditions on the filtration performance in terms of the permeate quantity and quality.

A one-dimensional model of evaporation from V-grooved microchannels is presented herein. The integrated model incorporates the evaporation from the capillary as well as the transition region of the extended meniscus. The amount of evaporation from these two regions are calculated as function of the input heat flux, groove geometry and the liquid-solid combination. The evaporation from the capillary meniscus region is found to be substantially higher than that from the extended thin film region. The effects of the groove geometrical parameters on the performance (e.g., critical heat fluxrpar; of the microchannels have been studied. It has been found that including the specific heat requirement in the model equations has negligible effect on the evaluated parameters.

Isothermal profiles of the extended meniscus in a quartz cuvette were measured in the earth's gravitational field using an image-analyzing interferometer that is based on computer-enhanced video microscopy of the naturally occurring interference fringes. These profiles are a function of the stress field. Experimentally, the augmented Young-Laplace equation is an excellent model for the force field at the solid-liquid-vapor interfaces for heptane and pentane menisci on quartz and tetradecane on SFL6. The effects of refractive indices of the solid and liquid on the measurement techniques were demonstrated. Experimentally obtained values of the disjoining pressure and dispersion constants were compared to those predicted from the Dzyaloshinskii - Lifshitz - Pilaevskii theory for an ideal surface and reasonable agreements were obtained. A parameter introduced gives a quantitative measurement of the closeness of the system to equilibrium. The nonequilibrium behavior of this parameter is also presented

High flux evaporations from a steady meniscus formed in a 2 micron channel is modeled using the augmented Young-Laplace equation. The heat flux is found to be a function of the long range van der Waals dispersion force which represents interfacial conditions between heptane and various substrates. Heat fluxes of (1.3-1.6) x 10(exp 6) W/m(exp 2) based on the width of the channel are obtained for heptane completely wetting the substrate at 100 C. Small channels are used to obtain these large fluxes. Even though the real contact angle is 0 deg, the apparent contact angle is found to vary between 24.8 deg and 25.6 deg. The apparent contact angle, which represents viscous losses near the contact line, has a large effect on the heat flow rate because of its effect on capillary suction and the area of the meniscus. The interfacial heat flux is modeled using kinetic theory for the evaporation rate. The superheated state depends on the temperature and the pressure of the liquid phase. The liquid pressure differs from the pressure of the vapor phase due to capillarity and long range van der Waals dispersion forces which are relevant in the ultra think film formed at the leading edge of the meniscus. Important pressure gradients in the thin film cause a substantial apparent contact angle for a complete wetting system. The temperature of the liquid is related to the evaporation rate and to the substrate temperature through the steady heat conduction equation. Conduction in the liquid phase is calculated using finite element analysis except in the vicinity of the thin film. A lubrication theory solution for the thin film is combined with the finite element analysis by the method of matched asymptotic expansions.

A Kelvin–Clapeyron change-of-phase heat transfer model is used to evaluate experimental data for an evaporating meniscus. The details of the evaporating process near the contact line are obtained. The heat flux and the heat transfer coefficient are a function of the film thickness profile, which is a measure of both the intermolecular stress field in the contact line region and the resistance to conduction. The results indicate that a stationary meniscus with a high evaporative flux is possible. At equilibrium, the augmented Young–Laplace equation accurately predicts the meniscus slope. The interfacial slope is a function of the heat flux.

Aim of the present work is to investigate the reaction–diffusion process of a two species system under laminar flow in a T-shaped microchannel. A zone formed at the interface between the aqueous solutions of these two species is affected by advection and diffusion. Through theoretical analyses and experimental results, the effect of dispersion has been shown to influence this diffusion zone. We have defined a parameter called effective diffusivity, to account for the dispersion effects and observed it to be a function of the channel Peclet number. In the limiting case of low Peclet number, this parameter is constant and turns out to be equal to the molecular diffusivity. We have also related effective diffusivity and the dispersion coefficient through scaling estimates.

Numerical solutions of equilibrium and nonequilibrium models based on the augmented Young-Laplace equation were successfully used to evaluate experimental data for an extended meniscus. The data for the equilibrium and nonequilibrium meniscus profiles were obtained optically using ellipsometry and image processing interferometry. A Taylor series expansion of the fourth-order nonlinear transport model was used to obtain the extremely sensitive initial conditions at the interline. The solid-liquid-vapor Hamaker constants for the systems were obtained from the experimental data. The consistency of the data was demonstrated by using the combining rules to calculate the unknown value of the Hamaker constant for the experimental substrate. The sensitivity of the meniscus profile to small changes in the environment was demonstrated. Both temperature and intermolecular forces need to be included in modeling transport processes in the contact line region because the chemical potential is a function of both temperature and pressure.

The microscopic details of fluid flow and heat transfer near the contact line of an evaporating extended meniscus of heptane formed between a horizontal substrate and a “washer” were studied at low heat fluxes. The film profile in the contact line region was measured using ellipsometry and microcomputer-enhanced video microscopy, which demonstrated the details of the transition between a nonevaporating superheated flat thin film and an evaporating curved film. Using the augmented Young-Laplace equation, the interfacial properties of the system were initially evaluated in situ and then used to describe the transport processes. New analytical procedures demonstrated the importance of two dimensionless parameters. Both fluid flow and evaporation depend on the intermolecular force field, which is a function of the film profile. The thickness and curvature profiles agreed with the predictions based on interfacial transport phenomena models. The heat flux distribution and the pressure field were obtained. Since there are significant resistances to heat transfer in this small system due to interfacial forces, viscous stresses, and thermal conduction, the “ideal constant heat flux” cannot be attained. The description of the pressure field gives the details of the coupling between the disjoining and capillary pressures.

The enhancement of transport rates due to the smaller length scales, transfer areas and high surface to volume ratio in miniature devices are explored along with the evaluation of additional shape-dependent forces at small length scales. The thickness of the adsorbed film, apparent contact angles and the curvature profiles of the evaporating film and the contact line velocities of the oscillating thin liquid film on silicon and high refractive index glass surfaces are accurately measured using image analyzing interferometry. The measurements are consistent with previous models describing fluid flow and heat transfer in thin liquid films based on interfacial concepts. The oscillating velocities of the thin film and the contact angle variations accurately capture the forward and backward motion of the film during oscillation.