Sunando DasGupta

Nanofiltration of textile plant effluent for color removal and reduction in COD

Abstract 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.

Investigation of an Evaporating Extended Meniscus Based on the Augmented Young–Laplace Equation

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.

Use of the Kelvin-Clapeyron equation to model an evaporating curved microfilm

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

Removal of dyes and their mixtures from aqueous solution using liquid emulsion membrane.

Extraction of dyes from aqueous solution was studied using liquid emulsion membrane. Study was carried out using two dyes, namely, crystal violet (CV) and methylene blue (MB). Extraction of single component system of each dye and their binary mixture were investigated. Liquid emulsion membrane was formed using n-heptane as membrane phase, sodium hydroxide solution as the internal phase and dye solution as the external phase. Surfactant span 80 was used as the emulsion stabilizer. Effects of concentration of span 80, concentration of NaOH, stirring speed, composition of feed solution and the volume ratio of the oil phase to the aqueous phase (O/A) were studied in detail both for single and binary system. Maximum extraction of MB was found to be 99% and that for CV was about 95% in single component system. In binary mixture, these values were 97% and 90%, respectively.

An augmented Young-Laplace model of an evaporating meniscus in a microchannel with high heat flux☆

Abstract High flux evaporation from a steady meniscus formed in a 2-μm 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 that represents interfacial conditions between heptane and various substrates. Heat fluxes of (1.3–1.6) × 10 6 W/m 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°, the apparent contact angle is found to vary between 24.8° and 25.6°. 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 ultrathin film formed at the leading edge of the meniscus. Important pressure gradients in the thin film cause a substantial apparent contact angle for a completely 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.

Adsorption Behavior of Chrysoidine Dye on Activated Charcoal and Its Regeneration Characteristics by Using Different Surfactants

Abstract 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.

Prediction of mass transfer coefficient with suction for turbulent flow in cross flow ultrafiltration

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.

Experimental and theoretical study of axial dryout point for evaporation from V-shaped microgrooves

Abstract 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.

Experimental Determination of the Effect of Disjoining Pressure on Shear in the Contact Line Region of a Moving Evaporating Thin Film

The thickness and curvature profiles in the contact line region of a moving evaporating thin liquid film of pentane on a quartz substrate were measured for the thickness region, δ<2.5 μm. The critical region, δ<0.1 μm, was emphasized. The profiles were obtained using image-analyzing interferometry and an improved data analysis procedure. The precursor adsorbed film, the thickness, the curvature, and interfacial slope (variation of the local apparent contact angle) profiles were consistent with previous models based on interfacial concepts. Isothermal equilibrium conditions were used to verify the accuracy of the procedures and to evaluate the retarded dispersion constant in situ. The profiles give fundamental insight into the phenomena of phase change, pressure gradient, fluid flow, spreading, shear stress, and the physics of interfacial phenomena in the contact line region

Inferred pressure gradient and fluid flow in a condensing sessile droplet based on the measured thickness profile

The thickness and curvature profiles of partially wetting condensing drops of 2-propanol on a quartz surface were measured using image analyzing interferometry and a new data analysis procedure. The profiles give fundamental insight into the phenomena of phase change, pressure gradient, fluid flow and spreading in a condensing drop, and the physics of interfacial phenomena in the contact line region of a polar fluid. The precursor adsorbed film and interfacial slope (a measure of the contact angle) and curvature profiles are consistent with previous concepts based on interfacial models. The curvature profiles, which were obtained using a new data reduction procedure, clearly demonstrate the convex nature of the drop near the thicker part (negative value of curvature), whereas, in the thinner region, the drop is concave (positive curvature) where the partially wetting liquid merges with a flat adsorbed film. The pressure profiles inside the drop are calculated from the augmented Young–Laplace equation show...