D. Sathiyamoorthy

Preoxidation and hydrogen reduction of ilmenite in a fiuidized bed reactor

Studies on preoxidation and hydrogen reduction of Quilon-grade ilmenite have been carried out in a fluidized bed reactor. During preoxidation, the effect of various parameters such as temperature, gas flow rate, and period of reaction has been studied. Hydrogen reduction studies have been carried out both for raw and preoxidized ilmenite. Results obtained on the conversion rate of iron oxide to metallic iron for the preoxidation as well as the reduction period showed three distinct stages: (1) initial slow induction stage; (2) intermediate acceleratory stage; and (3) final slowing down process. Kinetic data plot on -In (1 -x) vs time for metallization of iron oxide showed a linear trend for preoxidation and hydrogen reduction.

The choice of distributor to bed pressure drop ratio in gas fluidised beds

Abstract The choice of the gas distributor to bed pressure drop ratio for the stable operation of gas fluidised beds is determined by the type of gas distributor and by the characteristics of the bed material. A critical analysis regarding the choice of the ratio has been made and reasons for diverse views expressed in the literature have been offered. An equation to determine UM, the superficial gas velocity at which all the orifices in a distributor become operative in a uniformly fluidised bed has been suggested, i.e. where Umf and Ut are the minimum fluidisation velocity and the terminal velocity respectively. The distributor to bed pressure drop ratio (ΔPd/ΔPb) can be calculated from Umf and UM using the equation where the constant C equals 2.

Synthesis of Carbon Nanotubes on the Surface of Carbon Fiber/fabric by Catalytic Chemical Vapor Deposition and Their Characterization

Carbon nanotubes (CNTs) were grown radially on the surface of carbon fiber/fabric by catalytic chemical vapor deposition through the decomposition of acetylene gas. Nickel was used as a catalyst. The CNTs were synthesized over a range of temperature from 650°C to 800°C. Scanning electron microscopy and transmission electron microscopy studies reveal the presence of CNTs. The density of CNTs on the carbon fiber is high. Thermal analysis study shows that the CNT coated carbon fiber is more stable in air than in oxygen. Considerable improvement in the remnant and saturation magnetization has been found through a vibrating sample magnetometer study. Current versus voltage measurements show a decrease of ∼47% in onset voltage after the growth of CNTs on the surface of carbon fiber. Measurement of Brunauer Emmett and Teller surface area shows a threefold increase in the surface area of the carbon fibers after the growth of CNTs on their surface. A single‐fiber pull out test indicates that the CNT coated carbon fiber improves the interfacial load transfer with respect to the as‐received fiber. Improvement in storage modulus of a CNT coated carbon fiber composite in a polyester matrix is supported by dynamic mechanical analysis.

Potential of carbon nanotubes in water purification: an approach towards the development of an integrated membrane system

The problems of water shortages and lack of access to safe drinking water have been and will continue to grow as major global problems. To alleviate these problems, water purification technologies are being updated. Recent years have witnessed impressive breakthroughs towards practical application of nanostructured materials such as Carbon Nanotubes (CNTs) in the field of water purification owing to their unique thermal, electrical and mechanical properties. These nanoscale structures need to be arranged into well-defined configurations in order to build integrated systems with high efficiency (the nanotubes being reusable, whereas the traditional membranes foul easily and require frequent replacements), high flux (owing to the hydrophobic super smooth inner surface of nanotubes), and with improvements in chemical selectivity (through suitable chemical functionalisation of the CNTs), so that the idea of using CNTs in separation technology can be made realistic and the potential benefits of practical application of these unique materials can be exploited. This paper assesses the CNTs as an emerging technology in water purification system, particularly with respect to its potential for the removal of arsenic, fluoride, heavy metals and toxic organic components.

Preferential Media for Abrasive Flow Machining

The abrasive flow machining (AFM) is used to deburr, radius, polish and remove recast layer of components in a wide range of applications. Material is removed from the workpiece by a flowing semisolid mass across the surface to be finished. In this study a medium for AFM has been developed from the various viscoelastic carriers and has been contrasted through experimental investigation. The viscoelastic media are selected on the basis of existing media through the studies of thermogravimetric analysis and are characterized by mechanical, as well as rheological, properties with the help of a universal testing machine and a rheometer. The performance of the medium is evaluated through the finishing criteria on a two-way AFM setup. The investigation reveals that the styrene butadiene rubber (SBR) medium gives a good improvement in surface finish. The surface improvement through SBR media is 88%. It is also found that the strain, temperature, shear rate, time of applied constant stress, cyclic loading, etc. have an impact on the mechanical and rheological properties of the newly developed medium, which are ultimately governed by the performance of the medium in the target applications.

Heat Transfer Characteristics of Lithium Titanate Particles in Gas-Solid Packed Fluidized Beds

Abstract Lithium titanate (Li2TiO3) is a potential ceramic material for generation of tritium, which is exploited as a fuel in fusion reactor. However, Li2TiO3 has poor thermal conductivity, due to which thermal management of this material during nuclear reaction is a bottleneck. If this material is used in the form of pebble packed in a column or vessel, namely Test Blanket Module (TBM), the effective thermal conductivity is further brought down due to interstitial voids in the packed bed and also due to point to point contact between spherical pebbles. It is therefore essential to develop a suitable technique to enhance heat transfer properties of a packed pebble bed of Li2TiO3. In the present studies, an attempt has been made to develop a packed fluidized bed wherein particulate Li2TiO3 will be allowed to fluidize in the interstitial void of large stationary pebbles, called packing. Experiments have been carried out on heat transfer from wall to bed in a 162.74-mm-diameter column. Stationary pebbles of Li2TiO3 of size 1 mm to 10 mm and fluidized Li2TiO3 particulate solids of size 231 µm to 780 µm in the interstitial voids were used. Bed wall temperature in the range of 200°C to 600°C and operating fluidizing gas velocity corresponding to 1-4 times minimum fluidization velocity of fluidized particulate solids in the voids, were used for 20 to 60 volume percent of fluidized particulate solid of Li2TiO3. It has been found that the effective thermal conductivity of packed fluidized bed increased close to the value of thermal conductivity of pure Li2TiO3 at an optimum fluidization velocity corresponding to 2-3 times minimum fluidization velocity depending on fluidized particle, size, its volume fraction and wall temperature.

AN ENGINEERING SCALE STUDY ON RADIATION GRAFTING OF POLYMERIC ADSORBENTS FOR RECOVERY OF HEAVY METAL IONS FROM SEAWATER

The ocean contains around eighty elements of the periodic table and uranium is also one among them, with a uniform concentration of 3.3 ppb and a relative abundance factor of 23. With a large coastline, India has a large stake in exploiting the 4 billion tonnes of uranium locked in seawater. The development of radiation grafting techniques, which are useful in incorporating the required functional groups, has led to more efficient adsorbent preparations in various geometrical configurations. Separation based on a polymeric adsorbent is becoming an increasingly popular technique for the extraction of trace heavy metals from seawater. Radiation grafting has provided definite advantages over chemical grafting. Studies related to thermally bonded non woven porous polypropylene fiber sheet substrate characterization and parameters to incorporate specific groups such as acrylonitrile (AN) into polymer back bones have been investigated. The grafted polyacrylonitrile chains were chemically modified to convert acrylonitrile group into an amidoxime group, a chelating group responsible for heavy metal uptake from seawater/brine. The present work has been undertaken to concentrate heavy metal ions from lean solutions from constant potential sources only. A scheme was designed and developed for investigation of the recovery of heavy metal ions such as uranium and vanadium from seawater.

Gas distributor in fluidised beds

Abstract Satisfactory performance of fluidised bed reactors in terms of bed characteristics, chemical conversion and power requirement for pumping the fluidising medium is influenced by the design features of gas distributors. In industrial practice multi-orifice types of distributors are frequently used. This paper presents the results of experiments carried out in a 100-mm-diam. glass column using multi-orifice plate distributors. The effect of bed height and bed materials on the number of operating orifices is reported. The number of operating orifices is found to be a function of gas velocity and the ratio of pressure drops across the distributor and the bed.

Characterization of pyrocarbon coated materials using laboratory based x-ray phase contrast imaging technique

In-line x-ray phase contrast is an emerging x-ray imaging technique that promises to improve the contrast in x-ray imaging process. This technique is most suited for x-ray imaging of soft materials, low atomic number elements such as carbon composite fibers, very thin coatings, etc. We have used this new emerging technique for visualization and characterization of the pyrocarbon coated materials using a combination of microfocus x-ray source and x-ray charge coupled device detector. These studies are important for characterization of coating and optimization of various process parameters during deposition. These experiments will help us to exploit the potential of this technique for studies in other areas of material science such as characterization of carbon fibered structures and detection of cracks and flaws in materials. The characterization of the imaging system and optimization of some process parameters for carbon deposition are also described in detail.

Solid circulation in a compartmented gas fluidized bed

Abstract A fluidized bed having two compartments and incorporating a pair of V-valve and riser combination has been used to study the solid circulation across the compartments as a function of various design and operating parameters. Experimental studies show a variety of trends on the variation of solid circulation rate with parameters like aeration rates in the upstream bed, V-valve and riser, solid size and the upstream bed height. A solid circulation model incorporating a pressure balance over the circulation loop has been developed to analyze the experimental findings.