Showing papers by "Vasudevan Raghavan published in 2019"

Numerical Modeling of Evaporation and Combustion of Isolated Liquid Fuel Droplets: a Review

Abstract: Understanding the transport processes during evaporation and combustion of isolated liquid fuel droplet is highly important in several applications involving sprays. Comprehensive numerical models assist in carrying out simulations involving interlinked transport processes in liquid and gas phases using proper interface coupling conditions. The predictions from such numerical models reveal flow, temperature and species fields, with which the evaporation, as well as combustion characteristics, can be thoroughly analyzed. In this article, a detailed review of numerical models used to simulate evaporation of isolated droplets under several operating conditions is presented. This includes evaporation in high-pressure conditions, where real gas effects and solubility of ambient gas into the liquid droplet, come into play. Subsequently, a review of droplet combustion models, which are comprehensive enough to reveal the burning characteristics of an isolated droplet, is presented. Importance of liquid phase motion on evaporation and combustion behavior and water absorption in the case of alcohol droplets are reported. This review also includes modeling concepts applied to multi-component droplets.

Numerical investigations on particle separation in dynamic separators

Abstract: Purpose Dynamic separator is an equipment having a rotor and static vanes and is used to separate solids from gas-solids flow based on size. Particle separation in a dynamic separator happens due to complex interchanges between multiple forces exerted in the separation zone. Currently, there is only limited knowledge concerning the working principles of separation. This paper aims to systematically study a dynamic separator using numerical models to get insights into particle separation. Design/methodology/approach The Lagrangian–Eulerian formulation is used to simulate gas-solid flow. Multiple frames of reference using stage interpolation are used to account for rotation. Periodic symmetry in the equipment is exploited to create a simplified numerical model. The predictions from the numerical model are compared against available experimental data. Findings The numerical results indicate that only when particle collision is included, the separation efficiency trend from the experiment is matched by numerical predictions. Further, it is shown that at the same range of rotor speeds where numerical results predict increased separation efficiency, the solid pressure due to particle collision also reaches its maximum value. The gas flow and particle behavior in the separator are explained in detail. Originality/value The importance of particle collision in separation is interesting because traditionally, particle separation is assumed to be influenced by three forces, namely, centrifugal force, drag force and gravity. The numerical results, however, point to the contribution by particle collision, in addition to the above three forces.

Experimental Study of Non-Premixed Flames of Liquefied Petroleum Gas and Air in Cross-Flow and the Effects of Fuel Properties on Flame Stability

Abstract: Stability of flames are affected by fuel properties, geometry of the burner and operating conditions. In this experimental work, first the characteristics of non-premixed flames of Liquefied Petroleum Gas (LPG) and air in cross-flow configuration, where air jet flows perpendicular to the fuel stream, are studied experimentally. Flame transition and stability regimes of non-premixed flames of LPG and air, in a cross-flow burner without and with obstacles, are determined by systematically varying the fuel and air flow rates. Obstacles such as backward facing step and cylindrical bluff bodies are considered. Subsequently, the effects of fuel properties on the stability of flames are analyzed, Flame stability regimes of natural gas (methane) and biogas (methane and carbon-dioxide), measured from a similar burner are available in literature. These have been compared with the stability of LPG flames in terms of power rating of the burner and global equivalence ratio (defined for non-premixed flames).

Experimental and computational investigation of the influence of stoichiometric mixture fraction on structure and extinction of laminar, nonpremixed dimethyl ether flames

Abstract: Experimental and computational investigation is carried out to elucidate the influence of stoichiometric mixture fraction, ξst, on the structure and critical conditions of extinction of nonpremixed...

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.