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Articles by K.S. Rajan
Total Records ( 10 ) for K.S. Rajan
  K.S. Suganthi and K.S. Rajan
  Nanofluids are solid-liquid dispersions containing nanoparticles of size 1-100 nm in a liquid. Nanofluids that have enhanced thermal conductivity are best known for their application as coolants in food storage, transportation, refrigeration and air-conditioning industries. Considerable energy savings can be realized through the use of nanofluids as coolants. Viscosity is one of the major transport properties that determine the heat removal capability of nanofluids. The present study reports the effect of calcination temperature on the primary particle size, aggregate size of the ZnO nanoparticles and on the transport properties of the ZnO-water nanofluid. ZnO nanoparticles have been synthesized using Zinc nitrate hexahydrate as precursor. The primary particle size of the ZnO nanoparticles calcined at different temperatures ranging from 100-500°C was found to be in the range of 40-60 nm. The effect of calcination temperature on hydrodynamic size distribution of the ZnO nanoparticles has been investigated using dynamic light scattering technique. The viscosity of ZnO-water nanofluids, using ZnO powders prepared at different calcination temperatures have also been studied, along with their colloidal stability.
  S. Manikandan , N. Karthikeyan , K.S. Suganthi and K.S. Rajan
  Experiments were carried out with Fe2O3-water nanofluids to study possible enhancement in volumetric mass transfer coefficient for transfer of oxygen from air bubble to nanofluid, in an agitated, aerated bioreactor. The nanoparticles concentration was varied in the range of 0.022 to 0.065 wt.%, while the reactor was operated at three operating conditions viz. 200 rpm and 1.5 L min-1 of air flow, 100 rpm and 1.5 L min-1 of air flow and 200 rpm and 0.75 L min-1 of air flow. Nanoparticles were found to contribute to enhance oxygen transfer through ‘grazing effect’. An enhancement of 63% was observed for 0.065 wt.% Fe2O3-water operated at 200 rpm and 0.75 L min-1 air flow.
  N. Iswarya , M.G. Kumar , K.S. Rajan and R.J.B. Balaguru
  Metal Organic Frameworks (MOF) are three dimensional organic-inorganic hybrid crystalline materials where a metal containing inorganic cluster is coordinated to a polydentate organic ligand. MOF-5 consists of Zn4O inorganic moiety, that acts as secondary building unit, coordinating to benzene 1,4-dicarboxylate, a bidentate ligand that acts as spacers, to form a three dimensional structure. We report the synthesis of MOF-5 using zinc nitrate and terephthalic acid as precursors dissolved in dimethyl formamide. The synthesized MOF-5 has been characterized using Fourier Transform Infrared Spectroscopy, X-ray diffractometry, Thermal analysis, Scanning Electron Microscopy and Transmission Electron Microscopy. Surface morphology reveals well-ordered structures with large number of pores in meso-scale. Adsorption capability towards vapours and gases has been studied using ethanol and CO2 as the model vapours using a chemi-resistive approach. Present results indicate that MOF-5 is a promising candidate for CO2 sequestration and gas storage.
  Naresh Yandrapalli and K.S. Rajan
  Nanoparticles have attracted lot of attention for their exceptional properties which are different from those of materials in bulks. Metal oxides have shown application in many domains of science. Especially, manganese oxide has proven applications in energy storage, sensors, imaging technologies and even biomedicine. But, synthesis of ultrafine monodisperse nanoparticles that can be dispersed easily in polar or non-polar solvent is of prime importance for applications involving composites, phase change energy material, thermal management etc. We report the synthesis of ultrafine monodisperse MnO nanoparticles from manganese acetate tetrahydrate by a solvothermal method. Surfactants, oleic acid and 1-octadecene were used in suitable concentrations to yield oleic acid stabilized manganese oxide nanoparticles. The formation of manganese-oleate complex in the first step was confirmed using FTIR. X-ray diffraction spectra confirmed the formation of manganese oxide. Scanning and Transmission Electron Micrographs established the size of nanoparticles to be in the range of 15-20 nm. Crystalline nature of the nanoparticles was confirmed using selected area electron diffraction. Aging time has been found to influence the size of the nanoparticles, with layer particle sizes obtained for higher aging periods. These nanoparticles are suitable for dispersion in non-polar solvents and in thermic fluids like Therminol® 55 resulting in nanofluids.
  Dhivyaa Anandan and K.S. Rajan
  One of the bottle-necks in efficient energy recovery is attributed to the low thermal conductivity of common coolants. When the thermal conductivity of coolant is improved, the flow rate of coolant required and hence, energy required for pumping can be reduced. Nanofluids are novel class of fluids, prepared by dispersing nanoparticles in liquids like water, ethylene glycol-water mixture, oil etc. aimed at increasing the thermal conductivity of such coolants. In order to maximize the advantages of nanofluids, the particles chosen for dispersion must possess high thermal conductivity and maintain excellent colloidal stability. Cupric oxide has very high thermal conductivity (78 W mK-1) compared to that of water (0.6 W mK-1) and hence dispersion of cupric oxide in water will serve to conserve energy. We have developed cupric oxide-water nanofluids using a two-step method. Cupric oxide nanoparticles were synthesized by reduction of cupric acetate. Scanning electron micrographs revealed the presence of needle-shaped particles of 60 nm wide and 252 nm long. These particles were dispersed using ultrasonication and by the use of Cetyl Trimethyl Ammonium Bromide (CTAB) as dispersant. Stability was ascertained by visual observation of nanofluids stored undisturbed. The zeta potential was measured to be -30 mV. Electrostatic repulsion and steric repulsion are expected to be responsible for colloidal stability of CuO-water nanofluids. Particles with aspect ratio >1 provide higher enhancement in thermal conductivity as evident from Hamilton and Crosser model. Hence dispersion of these nanostructures in water will improve the thermal conductivity appreciably.
  Anju K. Radhakrishnan , V. Aishwarya , K.S. Suganthi and K.S. Rajan
  Experimental studies on heat transfer in a jacketed vessel were carried out to test the performance of two nanofluid coolants, viz. Mn0.47Fe2.53O4-propylene glycol (2 vol%) and CuO-propylene glycol (1 vol%) nanofluids, against pure propylene glycol. The flow rate of process fluid (Therminol-55®) flowing through the jacket was varied between 60-500 mL min-1. In general, these nanofluids were able to reduce the outlet temperature of process fluid to values lower than that achieved using pure propylene glycol. These nanofluids are more effective at higher flow rates of process fluid due to their improved transport properties.
  V. Gayadhthri , K.S. Suganthi , S. Manikandan and K.S. Rajan
  Rod-shaped iron oxide nanoparticles were prepared by chemical co-precipitation route using ferric chloridehexahydrate (FeCl3•6H2O) and ferrous chloridetetrahydrate (FeCl2•4H2O) as precursors. Iron oxide nanofluids were prepared by dispersing rod shaped α-Fe2O3 nanoparticles in water. Experiments were carried out to study the influence of surfactants on the colloidal stability, particle size distribution of nanofluids. Nanofluid with Sodium Do-decyl Benzene Sulfonate (SDBS) as surfactant showed increase in thermal conductivity of about 14% when dispersed in water.
  Anju K. Radhakrishnan and K.S. Rajan
  The present work reports on the scale up of synthesis of CuO nanoparticles from two different precursors: Copper (II) nitrate and copper (II) acetate. This is in realization of the importance of scale-up procedures for synthesis of nanoparticles with an ultimate aim to extend the application of nanoparticles for large-scale industrial applications. Our results show that the reaction batch volume can be scaled up to 5000 mL at a yield of 42 g per batch, without loss of morphological and crystallographic features. While using copper (II) acetate as precursor, higher yield and control of particle size can be achieved through re-use of spent precursor solution.
  L. Brinda , K.S. Rajan and John Bosco Balaguru Rayappan
  Metal Organic Frameworks (MOFs) are frameworks of 1-3D formed by the interaction between organic molecules and metal ions/clusters. The high specific surface area (~1000-5000 m2 g-1) and large pore volume (~0.7-2.5 cc g-1) of these molecules render them as ideal candidates for catalysis, gas absorption, separation of gases and sensing applications. The pore size and surface area can be tailored by modifying the synthetic conditions. In this paper, we report the synthesis and characterization of MOF-199 for potential application in enzyme-based sensing. MOF-199 was synthesized under room temperature using benzenetricarboxylic acid and a 1:1:1 mixture of DMF/ethanol/copper (II) acetate. Further, triethylamine (0.5 mL) was added to the reaction mixture and the resultant mixture was stirred for 23 h followed by drying to obtain a bluish crystalline material of MOF-199. The crystalline material was characterized using various analytical and microscopic techniques.
  N. Iswarya , M. Ganesh Kumar , K.S. Rajan and John Bosco Balaguru Rayappan
  Metal Organic Framework-5 (MOF-5) can be used for sensing of Volatile Organic Compounds (VOCs). VOCs are emitted from biological sources, paints, coatings, etc. and they pollute the environment thus posing serious health and environmental hazards. MOF-5 is a three dimensional crystalline coordination compound made up of Zn4O inorganic group as the vertex and benzene decarboxylate organic group as the spacer in the unit cell of the crystal. This study reported the synthesis and characterization of MOF-5 and its capability towards sensing of VOCs like ethanol, formaldehyde and acetone. Transmission Electron Micrograph reveals that the synthesized sample is highly crystalline and porous. BET surface area obtained was found to be 230 m2 g-1. MOF-5 was made into pellets of thickness around 3 mm for sensing purposes. The material was found to be sensitive towards ethanol even at concentrations as low as 5 ppm, towards formaldehyde at higher concentrations and towards acetone at concentrations as low as 10 ppm. The order of increase in sensitivity is ethanol>formaldehyde>acetone.
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