Showing papers by "Vasudevan Raghavan published in 2014"

Mathematical modeling of gasification of high‐ash Indian coals in moving bed gasification system

Abstract: SUMMARY Simulation of gasification of high-ash Indian coal in an updraft moving bed gasification system is presented in this paper. A steady one-dimensional numerical model, which takes into account of drying, devolatilization, combustion and gasification processes, is used to solve the mass and energy balances in the gasification system. The results from the model have been validated against the experimental data available in literature for various types of coals. The predicted product gas composition, its calorific value and the exit temperature are in agreement with the reported results. The validated model is used to study the effect of input parameters such as oxygen content in air stream, steam flow rates and the pressure of the gasification system. Results indicate that the value of oxygen mole fraction around 0.42 in the oxidizer stream can provide optimum performance in oxygen-based gasification systems. There is a range of steam-to-coal ratio that is dependent on the oxygen content in oxidizer stream. For air-based systems, this value is around 0.4 and for oxygen-based systems it is 1.5. The gasification performance improves with operating pressure significantly. An operating pressure of around 8 bar and higher, based on the application, can be used for achieving the required performance with high-ash coals. The model is useful for predicting the performance of high-ash Indian coals in a moving bed gasification system under different operating parameters. Copyright © 2013 John Wiley & Sons, Ltd.

Numerical investigation of laminar cross-flow non-premixed flames in the presence of a bluff-body

Abstract: A knowledge of flame stability regimes in the presence of cylindrical bluff-bodies of various dimensions is essential to design non-premixed burners. The reacting flow field in such cases is reported to be three-dimensional and unsteady. In the literature, only a few experimental investigations with limited measurements are available. Therefore, in this work, a detailed numerical study of laminar cross-flow non-premixed methane–air flames in the presence of a square cylinder is presented. The flow, temperature, species and reaction fields have been predicted using a comprehensive transient three-dimensional reacting flow model with detailed chemical kinetics and variable thermo-physical properties, in order to get a good insight into the flame stabilisation phenomena. Further, analyses of quantities such as local equivalence ratio, cell Damkohler number, species velocity, net consumption rate of methane, which are not easily obtained through experiments even with detailed diagnostics, have been carried ou...

Experimental study of effect of angular orientation on flame spread over thin solid fuels

Abstract: Understanding the spread rate of a combustible surface is vital in estimating the fire hazards involved while handling that material. The spread rate is a function of several physical parameters, one of which is the inclination of the surface with respect to the gravity vector. Further, flame spread direction plays a significant role. For instance, upward flame spread is gravity assisted since the flame spread direction is same as the buoyancy induced flow direction and it takes place at a much faster rate when compared to the downward flame spread where gravity induced flow opposes the flame spread. Hence, there is a need to study the effect of inclination of the fuel surface with respect to gravity vector in both upward (concurrent) and downward (opposed) flame spread situations. This paper is an attempt to experimentally study the effect of angular orientation of a thin paper surface on flame spread rates. Spread rate of diffusion flame established over a thin paper having dimensions 20 mm by 300 mm, has been measured by orienting the fuel surface at various angles from -90o to 90o measured with respect to the horizontal, (0o corresponds to horizontal orientation).

Steady laminar flame characteristics over methanol surface with air co-flow

Abstract: A numerical investigation of the flame characteristics and mass burning rates of steady laminar diffusion flames established over methanol surface under co-flow configuration is presented. A numerical model that solves the transient, two-dimensional gas-phase governing conservation equations using global single-step reaction kinetics for methanol-air oxidation is employed for the present investigations. The effect of liquid-phase transport is neglected for the present quasi-steady burning process by assuming that the fuel pool is thin and its level is maintained constant by supplying fuel at a rate at which it is being consumed. Since the gas-phase combustion occurs following evaporation from the liquid fuel surface, appropriate interfacial boundary conditions are specified. The model is validated using experimental and numerical temperature profile data across a methanol flame for a particular co-flow configuration reported in literature. Thereafter, parametric investigations are carried out by varying the co-flow air velocity in the range of 0.05–0.75 m/s, keeping the fuel pool length as 20 mm. A detailed discussion of the effect of co-flow air velocity on the thermal and flow fields, as well as on the local and average mass burning rates, is presented. It is observed that as the co-flow air velocity is increased, the mass burning rate attains a minima at an intermediate velocity of around 0.4 m/s for the present configuration. The thermal and flow fields, variation of fuel vapor mass fraction normal to the interface and the diffusion of oxidizer into the flame zone are investigated at various co-flow velocities to explore and explain the flame characteristics.