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.

Studies on voidage fluctuations, axial voidage profile and bed expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid-solid inverse fluidized bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the bed except for particles with size distribution. All the literature and present experimental data on bed expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The bed expansion data are also predicted using the drift flux model. © 2005 Elsevier Ltd. All rights reserved.

This paper proves the mathematical equivalence of infinite mixed flow reactors in series and a plug flow reactor, in the time domain using an impulse input. The proof is mathematically less complicated, compared to the previous statements in the literature.

This work proposes a novel detection method for the ultra-sensitive colorimetric determination of lead and copper in complex water matrix. The method integrates signal amplification with analytical sensing, achieved by adsorptive preconcentration and a colorimetric assay. We report for the first time a strategic application of batch adsorption as a preconcentration method and colorimetry performed directly on the adsorbent surface enriched with metal. Commercially available kaolin was used as the adsorbent to preconcentrate the metals. The colorimetric detection of Pb and Cu was achieved using sodium rhodizonate and bathocuproine salt as chromogenic indicators, respectively. This method eliminates the involvement of complex instrumentation and the need for new sensing material preparation. The proposed method possesses high sensitivity for both Pb and Cu under optimized conditions. A linear calibration curve is obtained in two concentration ranges, spanning 1 to 100 µg L−1 with a low detection limit of 0.6 and 1.2 µg L−1 for Pb and Cu, respectively. Further, the method enables visual detection of Pb at concentrations as low as 2.5 µg L−1 by the naked eye. We demonstrate the practical applicability of the method by simultaneous detection of Pb and Cu in six different real-water samples with good apparent recovery % [90–120%]. Detection using hand-held devices indicates the feasibility for on-site analysis. Overall, this platform method offers a high scope for de-centralized monitoring of pollutants at concentrations which are prevailing in the environment. Graphical abstract: Integrating adsorptive preconcentration with colorimetric assay enables quantitative metal detection in environmental water sample matrix. [Figure not available: see fulltext.]

Janus particles propel themselves by generating concentration gradients along their active surface. This induces a flow near the surface, known as the diffusio-osmotic slip, which propels the particle even in the absence of externally applied concentration gradients. In this work, we study the influence of viscoelasticity and shear-thinning (described by the second-order fluid and Carreau model, respectively) on the diffusio-osmotic slip on an active surface. Using matched asymptotic expansions, we provide an analytical expression for the modification of slip induced by the non-Newtonian behaviour. The results reveal that the modification in slip velocity, arising from polymer elasticity, is proportional to the second tangential derivative of the concentration field. Using the reciprocal theorem, we estimate the influence of this modification on the swimming velocity of a Janus sphere: (i)for second-order fluid, the contribution is non-negligible and its sign is dependent on the surface coverage of activity and (ii) for Carreau fluid, the contribution is more pronounced and always enhances the swimming velocity. The current study also has implications on the understanding of the transport of complex fluids in diffusio-osmotic pumps.

A chemical looping gasification process comprising of fuel and air reactors (FR and AR) is thermodynamically analyzed under autothermal conditions. The analysis takes into account the incomplete carbon conversion in the FR. Depending on how the unburnt carbon in the FR is processed, 3 modes of operation are analyzed viz. (1) sending unburnt carbon to the AR, (2) removal of unburnt carbon from the process, and (3) recycle of unburnt carbon to the FR. Autothermal operating conditions are identified for each mode of operation. It has been shown that, for optimal performance, while mode 1 and mode 2 have to be operated with minimum flow of oxygen carrier (OC) and medium air flow, mode 3 has to be operated with maximum OC flow and minimum air flow. Performance results for mode 1 of operation at the optimal operation point are generalized to any solid fuel.

In this work, adsorption of triclosan (TCS) on nylon 66 membrane is explored to develop a preconcentration and sensing platform. Nylon 66 membrane exhibits superior sorption ability even for trace amounts of TCS (10 μg/L). Investigating the surface adsorption chemistry by XPS analysis revealed the formation of a hydrogen bond between the hydroxyl group of TCS and the amide group of nylon 66. In the absence of TCS, the amphiprotic water molecule forms a multilayer OH group on the membrane surface. However, TCS showed preferential adsorption on the membrane-replacing water molecule due to its higher hydrophobic partition coefficient. We validated the effective preconcentration of TCS on the membrane using LC-MS analysis. Performing colorimetry directly on the TCS-enriched membrane surface showed a visible color change for concentrations as low as 10 μg/L. The relative blue intensity was found to vary linearly over a concentration range of 10-100 μg/L, and we achieved a detection limit of 7 μg/L for a 5 mL sample. This method utilizes easy-to-use resources which drastically reduce the cost and complexity of analysis.

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.

Water in diesel emulsions are known to have superior combustion properties. A critical factor that determines their applicability as a fuel is their stability. In this work we propose a novel method for continuous on-board generation of stable water in oil emulsions that is best suited for direct application in internal combustion engines. Here superheated steam is generated and is brought in contact with the oil phase containing surfactant in a helically coiled tube. The steam continuously condenses resulting in micron size droplets in the oil phase. Controlled experiments were done with dodecane as the organic phase containing a surfactant. The droplets size of the dispersed phase is found to be in the range of 1–12 µm. The emulsions obtained were found to be stable for at least 15 days. The mean droplet size is determined as a function of water volume percentage, surfactant concentration and emulsion flow rate. The droplet size features obtained when diesel is used as the continuous phase is found to be similar to that obtained using dodecane.

The stochastic method of Monte Carlo simulation is used to predict the hydrodynamic characteristics of a liquid-solid inverse fluidized bed for various particle sizes and densities. Pressure drop, bed voidage, and minimum fluidization velocity under steady-state conditions are predicted. Unsteady-state bed expansion/contraction for a step change in liquid flow rate is also simulated. To validate the simulation, experiments are conducted to measure the different hydrodynamic variables such as pressure drop, bed voidage, and minimum fluidization velocity under steady-state conditions and unsteady-state bed expansion/contraction. The predicted values of the hydrodynamic variables compare satisfactorily with the experimental data under both steady- and unsteady-state conditions.