Biomedical subjects

Parag R Gogate

Publications and source records attributed to Parag R Gogate.

14 recordsLinked to original sources

PubMed2007

Mapping the efficacy of new designs for large scale sonochemical reactors.

Sonochemical reactors have a great promise for many physical and chemical processing applications but its applicability at pilot or industrial scale levels is hindered by lack of novel designs which can reproduce the spectacular effects generated at the laboratory scale. The present work evaluates the efficacy of two new designs, operating at a liquid capacity of 7l. Mapping of the cavitational activity has been carried out using measurements of local pressure using hydrophone and cativational intensity using Cavitation Activity Indicator (Model IC-3, N. Deznukov, Belarus State University, Minsk, Belarus). Aim has been to identify the distribution of the cavitational activity in radial and axial directions and possibly characterizing the zones with very high and very low cavitational activity in these reactor configurations. It has been observed that the cavitational activity is substantially uniform in both the reactors unlike the conventional single transducer based reactors. The study clearly indicates the feasibility of these designs for future large scale applications.

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PubMed2006

Intensification of hydroxyl radical production in sonochemical reactors.

The efficacy of sonochemical reactors in chemical processing applications has been well established in the laboratory scale of operation though at a given set of operating parameters and no efforts have been directed in terms of maximizing the free radical production. In the present work, the effect of different operating parameters viz. pH, power dissipation into the system, effect of additives such as air, haloalkanes, titanium dioxide, iron and oxygen on the extent of hydroxyl radical formation in a sonochemical reactor have been investigated using salicylic acid dosimetry. Possible mechanisms for oxidation of salicylic acid in the presence of different additives have also been established. It has been observed that acidic conditions under optimized power dissipation in the presence of iron powder and oxygen result in maximum liberation of hydroxyl radicals as quantified by the kinetic rate constant for production of 2,5- and 2,3-dihydroxybenzoic acid. The study has enabled the optimization of the conditions for maximum efficacy of sonochemical reactors where free radical attack is the controlling mechanism for the chemical processing applications.

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PubMed2006

Selective synthesis of sulfoxides from sulfides using ultrasound.

The present work aims at developing a new process to selectively synthesize sulfoxide from sulfides using ultrasound. Methyl phenyl sulfide (MPS) has been taken as a model reactant. The reaction has been carried out in ultrasonic bath with an operating frequency of 22 kHz and maximum power supply of 120 W with an actual power dissipation of approximately 40 W measured using calorimetric studies. Effect of various parameters such as presence and absence of catalyst, type of catalyst (catalysts used were sodium tungstate and ammonium molybdate), temperature, concentration of hydrogen peroxide, effect of molar ratio of MPS to H(2)O(2) has been investigated with an aim of obtaining the optimum conditions for the synthesis of sulfoxides. It was observed that the presence of catalyst is a must to achieve appreciable conversions. It was also observed that the periodic addition of stoichiometric amount of hydrogen peroxide instead of sudden addition of it (total quantity of hydrogen peroxide remains the same) gave better selectivity for sulfoxide. The maximum conversion achieved in the present work was approximately 88.42% with sulfone formation being only 0.4% indicating a 99.6% selectivity for the desired product i.e. sulfoxides.

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PubMed2006

Destruction of formic acid using high frequency cup horn reactor.

Degradation of formic acid has been studied in a high frequency cup horn type reactor with an aim of understanding the effect of operating parameters on the destruction efficiency. The methodology used in the work serves as a useful guideline for the optimization exercise for the sonochemical reactors to establish a set of operating parameters at large scale operation for achieving maximum efficiency. Firstly energy efficiency of the reactor has been established as a function of the operating volume with an aim of optimization of the capacity of the reactor for maximum extent of degradation. It has been observed that maximum transfer of supplied power is obtained at 300 ml capacity and hence the actual degradation studies have been performed with this operational capacity. The effect of time of irradiation, initial concentration of the pollutant, stirrer speed, presence of sodium sulfite (to scavenge the initial dissolved oxygen) on the extent of degradation has been investigated. Maximum extent of degradation has been observed under the conditions of 500 mg/l initial concentration, 200 rpm stirrer speed and presence of initial dissolved oxygen (no sodium sulfite in the system). Process intensification studies have been carried out using sodium chloride over a range of initial concentration and it has been observed that maximum extent of degradation of formic acid is obtained at 4% NaCl concentration. Comparison has been also made with different sonochemical configurations operating at lower frequency of irradiation (typically in the range of 20-50 kHz) with an aim of comparing the efficacies of the reactor at equivalent power consumption.

Formates↗

PubMed2005

Process intensification using cavitation: optimization of oxidation conditions for synthesis of sulfone.

Cavitation can be effectively used for intensification of chemical reactions due to the production of free radicals and conditions of high temperatures and pressures locally. In the present work, use of cavitation for the intensification of the synthesis of sulfone has been explored. The oxidation of thioether or sulfide to synthesize corresponding sulfone with 30% H(2)O(2) as an oxidant was studied under acoustic cavitation and the results have been compared with the conventional approach based on the use of mechanical agitation. The aim has been also to optimize the different operating conditions viz. molar ratio of reactants to the oxidizing agent, type of the catalyst as well as its concentration, type of the solvent and the reactant concentration, so as to maximize the degree of intensification. It was observed that under the optimized conditions of sonication, the yield of sulfone was about five to six times higher as compared to the conventional approach of using mechanical agitation only.

Catalysis↗

PubMed2005

Ultrasonic atomization: effect of liquid phase properties.

Experiments have been conducted to understand the mechanism by which the ultrasonic vibration at the gas liquid interface causes the atomization of liquid. For this purpose, aqueous solutions having different viscosities and liquids showing Newtonian (aqueous solution of glycerin) and non-Newtonian behavior (aqueous solution of sodium salt of carboxy methyl cellulose) were employed. It has been found that the average droplet size produced by the pseudo-plastic liquid is less than that produced by the viscous Newtonian liquid having viscosity equal to zero-shear rate viscosity of the shear thinning liquid. The droplet size was found to increase initially with an increase in the viscosity up to a certain threshold viscosity after which the droplet size was found to decrease again. Also droplet size distribution is found to be more compact (uniform sizes) with an increasing viscosity of the atomizing liquid. The presence of the cavitation and its effect on the atomization has been semi quantitatively confirmed using energy balance and by the measurement of the droplet ejection velocities and validated on the basis of the decomposition of the aqueous KI solution. A correlation has been proposed for the prediction of droplet size for aqueous Newtonian fluids and fluids showing non-Newtonian behavior based on the dimensionless numbers incorporating the operating parameters of the ultrasonic atomizer and the liquid phase physico-chemical properties.

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PubMed2005

A review and assessment of hydrodynamic cavitation as a technology for the future.

In the present work, the current status of the hydrodynamic cavitation reactors has been reviewed discussing the bubble dynamics analysis, optimum design considerations, design correlations for cavitational intensity (in terms of collapse pressure)/cavitational yield and different successful chemical synthesis applications clearly illustrating the utility of these types of reactors. The theoretical discussion based on the modeling of the bubble dynamics equations aims at understanding the design information related to the dependency of the cavitational intensity on the operating parameters and recommendations have been made for the choice of the optimized conditions of operating parameters. The design information based on the theoretical analysis has also been supported with some experimental illustrations concentrating on the chemical synthesis applications. Assessment of the hydrodynamic cavitation reactors and comparison with the sonochemical reactors has been done by citing the different industrially important reactions (oxidation of toluene, o-xylene, m-xylene, p-xylene, mesitylene, o-nitrotoluene, p-nitrotoluene, m-nitrotoluene, o-chlorotoluene and p-chlorotoulene, and trans-esterification reaction i.e., synthesis of bio-diesel). Some recommendations have also been made for the future work to be carried out as well as the choice of the operating conditions for realizing the dream of industrial scale applications of the cavitational reactors.

Computer Simulation↗

PubMed2005

Investigation of induction of air due to ultrasound source in the sonochemical reactors.

A detailed investigation into the phenomena of induction of air using a novel arrangement of the ultrasonic horn (tip is located just above the liquid surface) has been made with the quantification of the extent of induction in terms of the air entrainment rate and the gas-liquid mass transfer coefficient for the transfer of air into the system. The measurement of air entrainment rate was found to be quite difficult and hence focus was kept on the quantification in terms of the gas-liquid mass transfer coefficient. The effect of ultrasonic power dissipation and type of the liquid medium (water, sodium chloride and sodium laruyl sulphate [surfactant] solution) on the mass transfer coefficient has been studied and correlations have been developed for the prediction of the same. Comparison with the mechanically agitated surface aerators has enabled us to understand the controlling mechanism in the induction and subsequent distribution of the air i.e. turbulence or convective motion. The present work should open an entirely new field of research in the area of design of sonochemical gas-liquid reactors operating possibly as a combination of gas-inducing reactors and cavitational reactors.

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PubMed2005

Dynamics of cavitational bubbles and design of a hydrodynamic cavitational reactor: cluster approach.

In the present work, a cavity cluster of predetermined size has been considered to study the bubble dynamics in the hydrodynamic cavitation reactor. The effect of different operating and system parameters on the cavitational intensity has been numerically investigated. The yield of any cavitationally induced physical/chemical transformations depends not only on the collapse pressure of the cavities but also on the active volume of cavitation within the reactor. Empirical correlations have been developed to predict the collapse pressure and the active volume of cavitation as a function of different operating parameters based on the bubble dynamics studies. Recommendations are made for designing a cavitational reactor on the basis of the proposed empirical correlations. This work is a first step towards the designing and optimization of hydrodynamic cavitational reactor with cluster approach.

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PubMed2004

Sonochemical reactors: scale up aspects.

The present work deals with the discussion on the engineering aspects of the design of large-scale sonochemical reactors using the solutions of the bubble dynamics equations as well as experimentation with different reactor types and reactions. Design correlations for the collapse pressure and its relation to the cavitational yield have also been given which should assist the designers in the choice of the operating parameters for a desired cavitational effect. Some techniques for the intensification of cavitational activity (with the use of additives) with an aim of reducing the cost of operation have also been discussed. The guidelines for the future work to be carried out to remove the lacunae in the design information with an aim of developing industrial scale efficient sonochemical reactors have also been mentioned.

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PubMed2004

Ultrasonic bath with longitudinal vibrations: a novel configuration for efficient wastewater treatment.

Efficacy of a novel configuration for large-scale wastewater treatment applications has been investigated using formic acid degradation as a model reaction. The reactor is first characterized using energy efficiency measurements and the optimum operating volume for maximum transfer of supplied energy and hence maximum cavitational effects has been established. Effect of initial concentration of the pollutant on the rates of degradation has been investigated. Comparison has been also made with the conventional ultrasonic horn in terms of energy efficiency and cavitational yield for the model reaction. With an aim of possible reduction in the total treatment time, some intensification studies have been undertaken considering hydrogen peroxide as an additional source of free radicals.

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PubMed2003

Cavity cluster approach for quantification of cavitational intensity in sonochemical reactors.

The mechanism involved in the spectacular effects from cavitation phenomenon is very complex and there have been several proposed theories to explain the observed results. The experimental as well as the visual observations indicate that a single collapsing cavity is also influenced by the dynamics of the surrounding cavities, which are very near to the collapsing cavity. The observed effects and erosion patterns cannot be explained properly on the basis of a single cavity collapse and hence in this study a cavity cluster (group of cavities) has been considered to understand the mechanism of cavitational effects. The effect of intensity, frequency of ultrasound, initial size of the cluster and the fraction of energy transferred from the collapsing cavities to the surrounding cavities on the cavitational intensity quantified in terms of the pressure pulse generated at the collapse of cavities as well as the active zone of cavitation has been investigated using bubble/cavity dynamics equations, numerically. On the basis of the trends obtained, empirical correlations estimating the collapse pressure and active volume of cavitation, have been developed.

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PubMed2003

Some aspects of the design of sonochemical reactors.

The magnitudes of collapse pressures and temperatures as well as the number of free radicals generated at the end of cavitation events are strongly dependent on the operating parameters of the equipment namely, intensity and frequency of irradiation along with the geometrical arrangement of the transducers and the liquid phase physicochemical properties, which affect the initial size of the nuclei and the nucleation process. In the present work, the effect of these parameters on the collapse pressure generated and the maximum size of the cavity during the cavitation phenomena have been studied using the bubble dynamics equation, which considers the compressibility of the medium and a single bubble in isolation. The different liquid phase properties considered include, liquid vapor pressure, viscosity, bulk liquid temperature, surface tension and nature of dissolved gases (polytropic constant of the gas). The theoretical predictions have been also compared with the experimental results observed in the literature qualitatively and some recommendations have been made for the selection of the operating parameters so as to achieve maximum benefits. The work presented here is novel in sense that no earlier studies have considered the compressibility of the liquid medium and tried to evaluate the effect of all the operating parameters on the cavitational activity.

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PubMed2003

Mapping of an ultrasonic horn: link primary and secondary effects of ultrasound.

The erratic behaviour of cavitational activity exhibited in a sonochemical reactor pose a serious problem in the efficient design and scale-up; thus it becomes important to identify the active and passive zones existing in the reactor so as to enable proper placement of the reaction mixtures for achieving maximum benefits. In the present work mapping of ultrasonic horn has been carried with the help of local pressure measurement using a hydrophone and estimation of amount of liberated iodine using the Weissler reaction and a quantitative relationship has been established. The measured local pressure pulses have been used in the theoretical simulations of the bubble dynamics equations to check the type of cavitation taking place locally and also estimate the possible collapse pressure pulse in terms of maximum bubble size reached during the cavitation phenomena. Relationship has been also established between the observed iodine liberation rates and the maximum bubble size reached. The engineers can easily use these unique relationships in efficient design, as the direct quantification of the secondary effect is possible.

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