Vasudevan Raghavan

Bio: Vasudevan Raghavan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Combustion & Laminar flow. The author has an hindex of 17, co-authored 130 publications receiving 1051 citations. Previous affiliations of Vasudevan Raghavan include University of Nebraska–Lincoln & Indian Institutes of Technology.

Mathematical Modelling of Coal Gasification Processes

Abstract: Coal is by far the most commonly employed fuel for electrical power generation around the world. While combustion could be the route for coal utilization for high grade coals, gasification becomes the preferred process for low grade coals having higher composition of volatiles or ash. Indian coals suffer from high ash content-nearly 50% by weight in some cases. Instead of transporting such high ash coals, it is more energy efficient to gasify the coal and transport the product syngas. Integrated Gasification Combined Cycle (IGCC) plants and Underground Gasification of coal have become attractive technologies for the best utilization of high ash coals. Gasification could be achieved in fixed beds, fluidized beds and entrained beds; faster rates of gasification are possible in fluidized beds and entrained flow systems, because of the small particle sizes and higher gas velocities. The media employed for gasification could involve air/oxygen and steam. Use of oxygen will yield relatively higher calorific value syngas because of the absence of nitrogen. Sequestration of the carbon dioxide after the combustion of the syngas is also easier, if oxygen is used for gasification. Addition of steam can increase hydrogen yield in the syngas and thereby increase the calorific value also. Gasification in the presence of suitable catalysts can increase the composition of methane in the product gas. Several competing heterogenous and homogenous reactions occur during coal major heterogenous reaction pathways, while interactions between carbon monoxide, oxygen, hydrogen, water vapour, methane and carbon dioxide result in several simultaneous gas-phase (homogenous) reactions. The overall product composition of the coal gasification process depends on the input reactant composition, particle size and type of gasifier, and pressure and temperature of the gasifier. The use of catalysts can also selectively change the product composition. At IIT Madras, over the last one decade, both experimental and modelling work has been undertaken to investigate the gasification characteristics of high ash Indian coals and compare the yield with those of high grade Australian and Japanese coals. A 20 kW capacity entrained flow gasifier has been constructed and the gasification characteristics have been studied for Indian coals for different particle sizes, system pressures and air flow rates. The theoretical model incorporates the effects of Knudsen diffusion, devolatilization and various heterogenous and homogenous kinetic steps as well as two-phase flow interactions involving the gaseous and particle phases. Output parameters such as carbon conversion, cold gas efficiency and syngas composition have been compared for different grades of coals under a wide range of operating conditions. The model developed for the entrained flow gasifier predicts the gasification characteristics of both Indian and foreign coals well. Apart from the entrained flow gasifier, a bubbling bed gasifier of 100 kW capacity has also been studied. A pilot plant for the gasification of Indian coals has been set up for this capacity and its performance has been investigated experimentally as well as theoretically at different air and steam flow rates. Carbon conversion efficiency of more than 80% has been achieved.

CFD analysis of thermal control in a vortex tube based polymerase chain reaction chamber

Abstract: In this paper, numerical analys is to investigate the thermal control of an innovative vortex tube based polymerase chain reaction thermocycler (VT -PCR) is described. VT PCR is capable of rapid DNA amplification and real -time optical detection. The device rapidly cycles six 20 µL 96 bp �-DNA samples between the PCR stages (denaturation, annealing and elongation) in approximately 6 mi nutes. Two -dimensional numerical simulations have been carried out using CFD software FLUENT v.6.2.16. Heat transfer rate (primarily dictated by the temperature differences between the samples and the external air heating or cooling them) governs the tempe rature distribution between and within the samples. Temperature variation between and within the samples during the denaturation stage has been quite uniform (maximum variation around ±0.5 uC and 1.6uC, respectively). During cooling, by adjusting the cold r elease valves in the VT -PCR during some stage of cooling, the heat transfer rate has been controlled. Improved thermal control, which increases the efficiency of the PCR process, has been obtained by slightly decreasing the rate of cooling. Thus, almost un iform temperature distribution between and within the samples (within 1 uC) has been attained for the annealing stage as well.

Choice of model parameters in turbulent gas-solid flow simulations of particle classifiers

Abstract: Comprehensive numerical simulations of particle laden gas flows are complex in general and its complexity increases dramatically when real world equipment are modelled. In this study, several model parameters required to simulate such a flow are tested. Initially, single-phase numerical results from a static classifier are validated against published experimental data. The Reynolds Stress Turbulence Model is demonstrated to be capable of accurate predictions for classifier airflow. The model is further extended by the addition of a particle Lagrangian phase. Several particle parameters are investigated and compared with published experimental data. It is found that the particle separation accuracy is improved with the inclusion of turbulence dispersion. Particle rough wall model and wall restitution coefficients influence the flow of coarse particles alone. The model is extended to simulate gas flow in a dynamic classifier with rotor. Physics involved in the flow inside a dynamic separator are explained.

A User’s Guide

Abstract: OUTPU T 29 OUTPU T 30 OUTPU T 31 OUTPU T 32 OUTPU T 25 OUTPU T 26 OUTPU T 27 OUTPU T 28 OUTPU T 21 OUTPU T 22 OUTPU T 23 OUTPU T 24 OUTPU T 17 OUTPU T 18 OUTPU T 19 OUTPU T 20 OUTPU T 13 OUTPU T 14 OUTPU T 15 OUTPU T 16 OUTPU T 9 OUTPU T 10 OUTPU T 11 OUTPU T 12 OUTPU T 5 OUTPU T 6 OUTPU T 7 OUTPU T 8 OUTPU T 1 OUTPU T 2 OUTPU T 3 OUTPU T 4 29 30 31 32 25 26 27 28 21 22 23 24 17 18 19 20 13 14 15 16 9

A review of biodiesel production from Jatropha curcas L. oil

Abstract: The demand for petroleum has risen rapidly due to increasing industrialization and modernization of the world. This economic development has led to a huge demand for energy, where the major part of that energy is derived from fossil sources such as petroleum, coal and natural gas. However, the limited reserve of fossil fuel has drawn the attention of many researchers to look for alternative fuels which can be produced from renewable feedstock. Biodiesel has become more attractive because of its environmental benefits and it is obtained from renewable resources. There are four primary methods to make biodiesel: blending, microemulsion, pyrolysis and transesterification. The most commonly used method is the transesterification of triglycerides (vegetable oil and animal fats) with alcohol in the presence of a catalyst. There is a growing interest in using Jatropha curcas L. oil as the feedstock for biodiesel production because it is non-edible and thus does not compromise the edible oils, which are mainly used for food consumption. Non-edible oils are not suitable for human consumption because of the presence of toxic components. Further, J. curcas L. seed has a high content of oil and the biodiesel produced has similar properties to that of petroleum-based diesel. In this paper, an attempt has been made to review the different approaches and techniques used to generate biodiesel from Jatropha curcas oil. The main factors affecting the biodiesel yield, for example the molar ratio of alcohol to oil, catalyst concentration, reaction temperature and reaction time are discussed. Lastly, the environmental considerations and economic aspects of biodiesel are also addressed.

Wide range modeling study of dimethyl ether oxidation

Abstract: A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of conditions. Experimental results obtained in a jet-stirred reactor (JSR) at I and 10 atm, 0.2 < 0 < 2.5, and 800 < T < 1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, 0 = 1.0 and 650 :5 T :5 1300 K. The JSR results are particularly valuable as they include concentration profiles of reactants, intermediates and products pertinent to the oxidation of DME. These data test the Idnetic model severely, as it must be able to predict the correct distribution and concentrations of intermediate and final products formed in the oxidation process. Additionally, the shock tube results are very useful, as they were taken at low temperatures and at high pressures, and thus undergo negative temperature dependence (NTC) behavior. This behavior is characteristic of the oxidation of saturated hydrocarbon fuels, (e.g. the primary reference fuels, n-heptane and iso- octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions. The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM.