S. Pushpavanam

Bio: S. Pushpavanam is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Reynolds number & Stratified flow. The author has an hindex of 20, co-authored 159 publications receiving 1525 citations. Previous affiliations of S. Pushpavanam include Indian Institute of Technology Kanpur & University of Florida.

CO2 utilization for gasification of carbonaceous feedstocks: A thermodynamic analysis

Abstract: A thermodynamic analysis of gasification of carbonaceous feedstocks using carbon dioxide and a mixture of carbon dioxide with steam or oxygen is carried out using Gibbs minimization approach. Simulations are carried out to study the effect of different operating conditions on the gasifier performance using Aspen Plus. Gasification using CO 2 at ambient conditions is not favorable under adiabatic condition. Complete carbon conversion can be obtained by increasing the operating temperature or flowrate of carbon dioxide. A cold gas efficiency greater than 1 is obtained under certain operating conditions. Maximum carbon dioxide conversion is obtained at the carbon boundary point. Based on the minimum energy requirement for complete carbon conversion, a universal optimal operating temperature of 850 °C has been identified for gasification of any feedstock. Biomass requires less heat input compared to coal. Use of steam or oxygen as a cogasifying agent reduces the carbon dioxide and energy requirement but reduces carbon dioxide conversion. Syngas with a wide ranging ratio of hydrogen/carbon monoxide can be obtained using carbon dioxide gasification. Trends of simulation predictions are qualitatively consistent with experimental observations.

Experimental and Numerical Investigations of Two-Phase (Liquid−Liquid) Flow Behavior in Rectangular Microchannels

Abstract: The interaction between kinetics and mass-transfer effects is determined by the flow regime in liquid−liquid multiphase microreactors. The operating conditions under which the various flow regimes such as slug flow and stratified flow occur in liquid−liquid systems has not been extensively studied and is not well-understood. The effect of operating conditions on slug length for instance is not well-known. The present study focuses on microreactors fabricated in Perspex (poly(methyl methaacrylate) (PMMA)), which are essentially microchannels with a rectangular cross-section. Experiments are carried out for a wide range of flow rates, channel sizes, and fluid systems with varying properties. Two different kinds of flow regimes, slug flow and stratified flow, are experimentally observed, and these are predicted using numerical simulations. We divide the space of operating conditions (the two liquid flow rates) into different regions such that in each region the flow regime is distinct. The dependence of slug...

Synthesis and characterization of chitosan-TiO2:Cu nanocomposite and their enhanced antimicrobial activity with visible light.

Abstract: In the present investigation, novel strategy for the preparation of hybrid nanocomposite containing organic polymer (Chitosan) and inorganic (TiO2:Cu) nanoparticles (NPs) has been developed and demonstrated its biomedical application. The sol-gel and ultra-sonication method assisted for the preparation of uniformly distributed Chitosan-TiO2:Cu (CS-CT) nanocomposite. The structural properties of prepared CS-CT nanocomposite were studied by XRD and FTIR techniques. The XPS was used to estimate elemental composition of the nanocomposite. Thermal properties were studied using TGA. TEM and SEM analysis showed the non-spherical nature of NPs with the average mean diameter 16nm. The optical properties were analyzed with UV-vis diffuse reflectance spectroscopy to confirm optical absorption in the visible region of light. Where CS-CT showed 200% enhanced light mediated photocatalytic antimicrobial activity against microorganism (Escherichia coli and Staphylococcus aureus) as compared with control. The antimicrobial activity of CS-CT nanocomposite in presence of light is found to be enhanced than that of its components, this is due to synergistic effect of organic and inorganic material complimenting each other's activity. The OH radicals release studied by PL spectroscopy on the surface of nanocomposite was used to examine antibacterial activity. Cytotoxicity assessment of CS-CT on human fibroblast cells was performed by MTT assay.

Nonlinear behavior of an ideal reactor separator network with mass recycle

Abstract: In this work the nonlinear behavior of a coupled reactor–separator network is analyzed using singularity and bifurcation theory. The reactor is modeled as a CSTR, which sustains an exothermic first-order reaction. The separator is modeled as a flash process. The effluent from the reactor is fed to the separator. The reactant-rich stream (assumed to be the bottoms) from the separator is recycled back to the reactor. Focus is on pure mass recycle, as the two units are decoupled energetically via heat exchangers. Two different modes of operation are considered. These are compared with each other and with the well-known stand alone reactor with a first-order exothermic reaction. For the first mode of operation, the feed rate is fixed and for the second the recycle rate is fixed. In practice, these different modes of operation can be achieved by a suitable control strategy. It is shown that the behavior crucially depends on the mode of operation. Fixing the feed rate can lead to severe operational problems including monotonic and oscillatory unstable steady states over a wide range of operating conditions. Further, parameter regions are identified, where no steady state exists at all. On the other hand when the recycle rate is fixed the coupled system admits at least one stable steady-state solution for a fixed set of operating conditions.

Comparison of liquid-liquid extraction in batch systems and micro-channels

Abstract: Liquid-liquid extraction is an important mass transfer operation in the chemical, food processing and pharmaceutical industries. Our work focuses on experimentally quantifying mass transfer performance in a well stirred batch vessel and in stratified flow and slug flow in micro-channels. Extraction of propionic acid from toluene to water is chosen as a test system. The distribution of propionic acid in toluene and water at equilibrium was found to be non-linear. The batch experiments were carried out both with a flat interface and as a well-mixed dispersed system. The continuous experiments were carried out in micro-channels with a square cross-section. A lumped parameter model was used to quantify the mass transfer coefficient in batch mode. A lumped (distributed) model was used to describe the extraction in a slug (stratified) flow in a micro-channel. The overall extraction performance is characterized as a function of residence time of the phases and the hydrodynamics. It was found that the micro-channel gives a superior extraction performance in the slug flow regime as compared to the well mixed batch system although both have comparable sizes of the dispersed phase. This is attributed to the strong internal circulations induced by shear in the slug flow regime.

Nonlinear Model Reduction via Discrete Empirical Interpolation

Abstract: A dimension reduction method called discrete empirical interpolation is proposed and shown to dramatically reduce the computational complexity of the popular proper orthogonal decomposition (POD) method for constructing reduced-order models for time dependent and/or parametrized nonlinear partial differential equations (PDEs). In the presence of a general nonlinearity, the standard POD-Galerkin technique reduces dimension in the sense that far fewer variables are present, but the complexity of evaluating the nonlinear term remains that of the original problem. The original empirical interpolation method (EIM) is a modification of POD that reduces the complexity of evaluating the nonlinear term of the reduced model to a cost proportional to the number of reduced variables obtained by POD. We propose a discrete empirical interpolation method (DEIM), a variant that is suitable for reducing the dimension of systems of ordinary differential equations (ODEs) of a certain type. As presented here, it is applicable to ODEs arising from finite difference discretization of time dependent PDEs and/or parametrically dependent steady state problems. However, the approach extends to arbitrary systems of nonlinear ODEs with minor modification. Our contribution is a greatly simplified description of the EIM in a finite-dimensional setting that possesses an error bound on the quality of approximation. An application of DEIM to a finite difference discretization of the one-dimensional FitzHugh-Nagumo equations is shown to reduce the dimension from 1024 to order 5 variables with negligible error over a long-time integration that fully captures nonlinear limit cycle behavior. We also demonstrate applicability in higher spatial dimensions with similar state space dimension reduction and accuracy results.

Journal of Fluid Mechanics创刊50周年

Abstract: 流体力学杂志“Journal of Fluid Mechanics”由剑桥大学教授George Batchelor在1956年5月创办，在国际流体力学界享有很高的学术声望，被公认为是流体力学最著名的学术刊物之一，2005年的影响因子为2．061，雄居同类期刊之首．在它创刊50周年之际，2006年5月JFM出版了第554卷的纪念特刊，其中刊登了现任主编（美国西北大学S．H．Davis教授和英国剑桥大学T．J．Pedley教授）合写的述评：“Editorial：JFM at50”，以JFM为背景，从独特的视角对近50年来流体力学的发展进行了简明的回顾和展望，并归纳了一系列非常有启发性的有趣统计数字．2006年7月21日在剑桥大学应用数学和理论物理研究所（DAMTP）举行了创刊50周年的庆祝会．下午2点，JFM的新老编辑和来宾会聚一堂，Pedley教授致开幕词，其后是5个精彩的报告：The mysterious rattleback and its fluid counterpart（Keith Moffatt），Developments in shear instabilities（Patrick Huerre），Falling clouds（Elisabeth Guazzelli），Ecotectural fluid mechanics（Paul Linden），The success of JFM（Herbert Huppert），最后由Davis教授致闭幕词．

Materials Genome Initiative for Global Competitiveness

Abstract: This Cabinet-level Council is the principal means within the executive branch to coordinate science and technology policy across the diverse entities that make up the federal research and development enterprise. Chaired by the President, the NSTC is made up of the Vice President, the Director of the Office of Science and Technology Policy, Cabinet Secretaries and Agency Heads with significant science and technology responsibilities, and other White House officials. For more information visit www.ostp.gov/nstc. OSTP's responsibilities include advising the President in policy formulation and budget development on all questions in which science and technology are important elements and articulating the President's science and technology policies and programs. For more information visit www.ostp.gov. In much the same way that silicon in the 1970s led to the modern information technology industry, the development of advanced materials will fuel many of the emerging industries that will address challenges in energy, national security, healthcare, and other areas. Yet the time it takes to move a newly discovered advanced material from the laboratory to the commercial market place remains far too long. Accelerating this process could significantly improve U.S. global competitiveness and ensure that the Nation remains at the forefront of the advanced materials marketplace. This Materials Genome Initiative for Global Competitiveness aims to reduce development time by providing the infrastructure and training that American innovators need to discover, develop, manufacture, and deploy advanced materials in a more expeditious and economical way. Prepared by an ad hoc group of the National Science and Technology Council, this initiative proposes a new national infrastructure for data sharing and analysis that will provide a greatly enhanced knowledgebase to scientists and engineers designing new materials. This effort will foster enhanced computational capabilities, data management, and an integrated engineering approach for materials deployment to better leverage and complement existing Federal investments. The success of this initiative will require a sustained effort from the private sector, universities, and the Federal Government. I look forward to working with you to make this vision a reality. A genome is a set of information encoded in the language of DNA that serves as a blueprint for an organism's growth and development. The word genome, when applied in non-biological contexts, connotes a fundamental building block toward a larger purpose. The Materials Genome Initiative is a new, multi-stakeholder effort to develop an infrastructure to accelerate advanced materials discovery and deployment in the United States. Over the …

Nanomaterials for alternative antibacterial therapy

Abstract: Despite an array of cogent antibiotics, bacterial infections, notably those produced by nosocomial pathogens, still remain a leading factor of morbidity and mortality around the globe. They target the severely ill, hospitalized and immunocompromised patients with incapacitated immune system, who are prone to infections. The choice of antimicrobial therapy is largely empirical and not devoid of toxicity, hypersensitivity, teratogenicity and/or mutagenicity. The emergence of multidrug-resistant bacteria further intensifies the clinical predicament as it directly impacts public health due to diminished potency of current antibiotics. In addition, there is an escalating concern with respect to biofilm-associated infections that are refractory to the presently available antimicrobial armory, leaving almost no therapeutic option. Hence, there is a dire need to develop alternate antibacterial agents. The past decade has witnessed a substantial upsurge in the global use of nanomedicines as innovative tools for combating the high rates of antimicrobial resistance. Antibacterial activity of metal and metal oxide nanoparticles (NPs) has been extensively reported. The microbes are eliminated either by microbicidal effects of the NPs, such as release of free metal ions culminating in cell membrane damage, DNA interactions or free radical generation, or by microbiostatic effects coupled with killing potentiated by the host's immune system. This review encompasses the magnitude of multidrug resistance in nosocomial infections, bacterial evasion of the host immune system, mechanisms used by bacteria to develop drug resistance and the use of nanomaterials based on metals to overcome these challenges. The diverse annihilative effects of conventional and biogenic metal NPs for antibacterial activity are also discussed. The use of polymer-based nanomaterials and nanocomposites, alone or functionalized with ligands, antibodies or antibiotics, as alternative antimicrobial agents for treating severe bacterial infections is also discussed. Combinatorial therapy with metallic NPs, as adjunct to the existing antibiotics, may aid to restrain the mounting menace of bacterial resistance and nosocomial threat.