T Renganathan

Microfluidic paper-based analytical devices (µPADs) have provided a breakthrough in portable and low-cost point-of-care diagnostics. Despite their significant scope, the complexity of fabrication and reliance on expensive and sophisticated tools, have limited their outreach and possibility of commercialization. Herein, we report for the first time, a facile method to fabricate µPADs using a commonly available laser printer which drastically reduces the cost and complexity of fabrication. Toner ink is used to pattern the µPADs by printing, without modifying any factory configuration of the laser printer. Hydrophobic barriers are created by heating the patterned paper which melts the toner ink, facilitating its wicking into the cross-section of the substrate. Further, we demonstrate the utilization of the fabricated device by performing two assays. The proposed technique provides a versatile platform for rapid prototyping of µPADs with significant prospect in both developed and resource constrained region.

In this work, a thermodynamic analysis of a stand alone gasifier is carried out. The analysis uses the nonstoichiometric approach based on the minimization of the Gibbs free energy. The gasification temperature, amount of oxygen required, composition of syngas, and cold gas efficiency are predicted at the carbon boundary point (CBP) using Aspen Plus. The influence of nitrogen when air is used as the gasifying agent is studied. It is found that the presence of nitrogen results in a lower gasification temperature, higher oxygen requirement, lower concentration of CO and H2, higher concentration of CO2 and CH4, and lower cold gas efficiency. The influence of pressure when air is used as the gasifying agent is also studied. It is found that increasing the pressure results in higher gasification temperatures, higher oxygen requirement, lower concentration of CO and H2, higher concentration of CO2 and CH4, and lower cold gas efficiency. Performance charts in the form of contour plots are presented to predict the performance of a high pressure gasifier using air as gasifying agent.

The present study focuses on the hydrodynamic characteristics of a cocurrent liquid-liquid downward system with perforated distributor. Hydrodynamic variables like pressure drop, phase holdup, drop size distribution and flow regimes are experimentally studied using a kerosene-water system. Two major flow regimes-kerosene continuous and kerosene dispersed-are identified. The effect of water and kerosene velocities on pressure drop and phase holdup in these two regimes is studied. Drop size distribution variation with water velocity is also studied. An empirical correlation is proposed for the dispersed phase holdup, which satisfactorily predicts the experimental data.

CO2 is a major anthropogenic gas contributing to global warming. The growing concerns for climate change have encouraged research activities towards developing more-efficient processes for CO2 capture. Some of the excellent adsorbents like zeolites, carbon nanotube-based solid sorbents and carbon molecular sieves have been suggested for adsorption of CO2 in a dry gas stream. However, presence of moisture content creates a deteriorating effect on these sorbents [1]. CO2 can be chemically adsorbed on dry regenerable alkali-metal carbonate-based sorbents (M2CO3, where M = K, Na, Li) by the reaction: (Equation Presented). This shows that this class of sorbents have an inherent advantage as moisture is a necessity for this reaction. It is seen that K2CO3 gives the best performance and has a wide range of carbonation temperature where the sorbent efficiency is almost 100% [2]. In the present work, Activated Carbon (AC) is chosen as a support for potassium carbonate, due to its highly porous structure and high surface area. A 30 wt % of K2CO3 is coated on AC by wet impregnation method [3]. This sorbent is then characterized by XRD, EDX, SEM and BET Surface area. Kinetic studies are done in a fluidized bed column heated in a furnace, using a mixture of air or N2 and CO2, humidified to desired moisture content as the fluidizing medium. The reaction is followed by measuring the concentration of CO2 in the exit gas as a function of time. The effect of various parameters such as flow rate of gas, composition of gas, height of the bed and temperature on the conversion of K2CO3 is studied. The reaction is carried out in the temperature range of 60-90°C. The composition of both CO2 and water vapor is varied between 5-20% with gas velocities ranging from 1-3 times of minimum fluidization velocity.

The present work deals with the experimental and modeling studies of hydrodynamics in a continuous countercurrent liquid-solid system. The hydrodynamic variables considered are the pressure drop, phase holdup and flooding velocities. It is observed that the pressure drop and solid holdup in the system increase with increase in phase velocities and decrease with increase in particle diameter and density. The one-dimensional two-fluid model comprising of continuity and momentum equations for each phase with the most suitable drag law closure is used to predict the axial pressure drop profile and the effect of operating variables and particle characteristics on solid holdup. The model predicts satisfactorily the experimental data of the present study and those reported in the literature over a wide range of fluid and particle characteristics. The model also captures the trends of the hydrodynamic variables with the independent parameters.

Blast furnace slag is a high-value by-product of the iron and steel industry. It leaves the plant at a very high temperature and possesses a large quantity of high-grade energy. One of the promising methods to extract this energy is dry slag granulation. In this study, the effectiveness of dry slag granulation was studied using a mixture of rosin and paraffin wax as an analogue for blast furnace slag. The effects of various parameters such as rotational speed of the disc, diameter of the disc and flow rate of the molten liquid have been studied. Different ranges of operating conditions in terms of non-dimensional numbers for fiber formation and particle formation were determined. This helps us determine the operating conditions under which particle formation is ensured. The study shows that with an increase in the rotational speed or disc diameter the average particle diameter decreases whereas with an increase in the flow rate the average particle diameter increases. The design of a granulation unit for a commercial plant utilizing the data from lab scale experiments is discussed.

There has been a recent interest in integrating external fields with inertial microfluidic devices to tune particle focusing. In this work, we analyse the inertial migration of an electrophoretic particle in a two-dimensional Poiseuille flow with an electric field applied parallel to the walls. For a thin electrical double layer, the particle exhibits a slip-driven electrokinetic motion along the direction of the applied electric field, which causes the particle to lead or lag the flow (depending on its surface charge). The fluid disturbance caused by this slip-driven motion is characterized by a rapidly decaying source-dipole field which alters the inertial lift on the particle. We determine this inertial lift using the reciprocal theorem. Assuming no wall effects, we derive an analytical expression for a 'phoretic lift' which captures the modification to the inertial lift due to electrophoresis. We also take wall effects into account, at the leading order, using the method of reflections. We find that for a leading particle, the phoretic lift acts towards the regions of high shear (i.e. walls), while the reverse is true for a lagging particle. Using an order-of-magnitude analysis, we obtain different components of the inertial force and classify them on the basis of the interactions from which they emerge. We show that the dominant contribution to the phoretic lift originates from the interaction of the source-dipole field (generated by the electrokinetic slip at the particle surface) with the stresslet field (generated due to particle's resistance to strain in the background flow). Furthermore, to contrast the slip-driven phenomenon (electrophoresis) from the force-driven phenomenon (buoyancy) in terms of their influence on the inertial migration, we also study a non-neutrally buoyant particle. We show that the gravitational effects alter the inertial lift primarily through the interaction of the background shear with the buoyancy-induced Stokeslet field.

Mass transfer studies have been carried out in a continuous countercurrent liquid–solid adsorber to remove methylene blue from wastewater using activated carbon under steady-state conditions. Experimental data on axial concentration profile and overall removal efficiency has been obtained using a pilot plant set-up. The overall colour removal efficiency of the adsorber increases with increase in solid velocity, and a decrease in liquid velocity and initial dye concentration. A mathematical model has been developed to predict the axial concentration profiles, which compare with the experimental data satisfactorily. The overall mass transfer coefficient has also been evaluated using this model.

Thermodynamic modeling of gasification process provides a quick estimate of performance of the gasifier. Most of the earlier work on thermodynamic modeling is restricted to a particular feedstock-gasification agent combination and hence the results cannot be generalized. In the present work, the equilibrium modeling based on Gibbs free energy minimization approach is used to analyze the performance of gasification of any fuel using oxygen or steam. The performance is analyzed at the carbon boundary point at which the cold gas efficiency is maximum. The gasification temperature, amount of gasification agent required, composition of syngas, and cold gas efficiency are predicted using Aspen Plus. The results are presented as contour plots on Van Krevelen coordinates (H/C vs O/C) and interpreted based on simplified gasification reactions. The performance for different feedstocks represented in Van Krevelen diagram is also analyzed. Finally, advantage of cogasification of feedstocks is highlighted. © 2011 American Chemical Society.