Showing papers by "Sateesh Gedupudi published in 2018"

Oscillatory solutothermal convection-driven evaporation kinetics in colloidal nanoparticle-surfactant complex fluid pendant droplets

Abstract: To elucidate the pure physics of evaporation which is free from surface effects, the pendant mode of evaporation is employed in the present study. The present study brings out the evaporation kinetics of a combined surfactant and nanoparticle colloidal system. We also segregate the contributing effects of surfactants alone, particle alone, and the combined effect of surfactant and particles in modulating the evaporation kinetics. It is observed that the rate of evaporation is a strong function of the particle concentration for nanocolloidal suspensions of particle alone and concentration of surfactant molecules up to the micellar concentration and thereafter insensitive to concentration for an aqueous surfactant solution. The combined colloidal system of nanoparticles and surfactant exhibited the maximum evaporation rate, and the rate is a strong function of the concentration of both the particle and surfactant. The theoretical classical diffusion-driven evaporation falls short of the experimentally observed evaporation rate in aqueous surfactant and colloidal solutions. Evidence of convective currents was observed in flow visualization studies in aqueous surfactant solutions, nanocolloidal solution of particle alone, and an oscillatory convective circulation in a combined surfactant-impregnated nanocolloidal solution. Thermal Marangoni and Rayleigh numbers are calculated from the theoretical examination and are found not potent enough to induce strong circulation currents in such systems from a stability map. Scaling analysis of solutal Marangoni is observed to be capable of inducing circulation from a stability map in all the systems and the enhanced thermophoretic drift and Brownian dynamics, and enhancement in the diffusion coefficient of the nanoparticles is also contributing to the enhanced evaporation rate for only nanocolloidal solutions. The oscillatory convective current arising out of two opposing driving potential enhances the evaporation rate of surfactant-impregnated nanocolloids. The present findings could reveal the effect of surfactants in tuning the evaporation rate of colloidal solutions.

Correlating contact line capillarity and dynamic contact angle hysteresis in surfactant-nanoparticle based complex fluids

Abstract: Dynamic wettability and contact angle hysteresis can be correlated to shed insight onto any solid-liquid interaction. Complex fluids are capable of altering the expected hysteresis and dynamic wetting behavior due to interfacial interactions. We report the effect of capillary number on the dynamic advancing and receding contact angles of surfactant-based nanocolloidal solutions on hydrophilic, near hydrophobic, and superhydrophobic surfaces by performing forced wetting and de-wetting experiments by employing the embedded needle method. A segregated study is performed to infer the contributing effects of the constituents and effects of particle morphology. The static contact angle hysteresis is found to be a function of particle and surfactant concentrations and greatly depends on the nature of the morphology of the particles. An order of estimate of line energy and a dynamic flow parameter called spreading factor and the transient variations of these parameters are explored which sheds light on the dynami...

Governing Influence of Thermodynamic and Chemical Equilibria on the Interfacial Properties in Complex Fluids

Abstract: We propose a comprehensive analysis and a quasi-analytical mathematical formalism to predict the surface tension and contact angles of complex surfactant-infused nanocolloids. The model rests on the foundations of the interaction potentials for the interfacial adsorption–desorption dynamics in complex multicomponent colloids. Surfactant-infused nanoparticle-laden interface problems are difficult to deal with because of the many-body interactions and interfaces involved at the meso-nanoscales. The model is based on the governing role of thermodynamic and chemical equilibrium parameters in modulating the interfacial energies. The influence of parameters such as the presence of surfactants, nanoparticles, and surfactant-capped nanoparticles on interfacial dynamics is revealed by the analysis. Solely based on the knowledge of interfacial properties of independent surfactant solutions and nanocolloids, the same can be deduced for complex surfactant-based nanocolloids through the proposed approach. The model ac...

1-D modelling and CFD study of the transient behaviour of a single phase Coupled Natural Circulation Loop

Abstract: A Coupled Natural Circulation Loop (CNCL) consists of two Natural Circulation Loops (NCL) coupled thermally via a common heat exchanger. The transient modelling of such systems that have practical relevance has not been reported in the literature to the best of the author's knowledge. The present work aims to bridge this gap and investigate the dynamic characteristics of a CNCL system using a 1-D mathematical model. The validation of the model is accomplished by comparison of the results obtained via 3-D CFD simulation. Both horizontal and vertical CNCL systems have been considered for this study and behaviour of the system for parallel and counter flow configurations in the heat exchanger section is elaborated. Transient and steady state CFD analysis has been conducted to analyse CNCL system for different heater and cooler orientations and flow initialisation. The behaviour of the CNCL system is then examined by carrying a thorough parametric study employing the validated 1-D single phase CNCL model with liquid sodium as the operating fluid. The CNCL orientation (vertical or horizontal) coupled with the heater and cooler configuration determines the system dynamics and behaviour. The CNCL system also exhibits chaotic flow oscillations at high heat loads.

Numerical and experimental investigation of multi-mode heat transfer in a square cavity with and without triangular fins

Abstract: Numerical and experimental studies on laminar natural convection and radiation in a differentially heated cavity with/without triangular fins are presented. The square cavity is filled with air (Pr = 0.71). The top and bottom walls are adiabatic, while the active (hot) and cold walls are isothermal. Triangular conductive fins made of highly conductive material are placed on the heated and cooled vertical surfaces of a square cavity. The effects of pertinent parameters on fluid flow and heat transfer characteristics are studied. The governing differential equations, assuming laminar flow, are solved using the commercial software FLUENT. Experiments have been carried out for three different configurations viz square cavity without fins, square cavity with two fins on vertical walls and square cavity with continuous fins on vertical walls. Rayleigh number varies from 1.18 × 105 to 2.15 × 105 for the first experiment (square cavity without fins). The other two experiments with fins have been conducted for six different heat inputs. The numerical results have been validated against the experimental results obtained. It is concluded that the triangular fins on isothermal walls enhance the heat transfer in the cavity. Natural convection is influenced by wall surface emissivity. The square cavity with continuous fins is more effective than square cavity with two fins on vertical isothermal walls.