C. Muraleedharan

Numerical Investigation of Deviation of Phase Change Characteristics of Horizontal and Vertical Flat Heat Pipe Configurations

The flow characteristics in the porous wick of a flat heat pipe subjected to boiling and condensation are analysed here using two-phase mixture model. Steady laminar boundary layer flow in the capillary wick structure is considered for both vertical and horizontal orientations. The governing boundary layer partial differential equations are simplified using similarity transformation. The transformed equations are then solved numerically by using shooting iterative technique. Investigation was carried out for the effects of the involved parameters such as saturation and temperature across the boundary layer. The behaviour of non-dimensional numbers due to the orientation of the heat pipe is also discussed. The study confirms that orientation plays a significant role in flow and temperature field.

CFD Modelling of Biomass Gasification in Fluidized-Bed Reactor Using the Eulerian-Eulerian Approach

A comprehensive two dimensional numerical model has been developed to simulate the biomass gasification in a fluidised bed reactor. Gas-solid flows as well as the chemical reactions are considered. Euler-Euler model is adopted to describe the multiphase flow regime inside the reactor. The standard k-є model is used to model the turbulence for each phase. The particle motion inside the reactor is modelled using various drag laws derived from Kinetic Theory of Granular Flow. Biomass fuel after pyrolysis is fed as char and volatile matter. The reaction rates of homogeneous reactions and heterogeneous reactions are determined by Eddy dissipation reaction rate and Arrhenius-Diffusion reaction rate, respectively. Gas velocities, flow patterns, composition of gas product and distribution of reaction rates are obtained. Results are compared with experimental data and found to be in agreement.

Design of fluidized bed reactor for conversion of biomass energy in to concentrated gaseous fuel

Gasification can be employed to convert dilute biomass energy source in to gaseous products holding concentrated form of energy. A practical design of a pilot scale fluidized bed gasifier was developed in order to exploit the energy values of rice husk. The chemical composition, heating value, mean particle diameter, solid and bulk densities were obtained in characterization tests. These data along with the theoretical information available in literature were used for designing the gasifier. Out of the four feedstocks considered rice husk was selected as fuel. The gasifier has a reaction chamber of diameter 0.15 meter and an overall height of 1.45 meter, which is intended to produce a power of 7.5 kilowatt.

Energy and exergy analysis of thermo-chemical gasification of sawdust using thermodynamic equilibrium model

Biomass, the largely available renewable energy source, will be a future viable solution for worlds energy crisis. A stoichiometric thermodynamic equilibrium model of air-steam gasification of saw dust in fluidized bed is developed in the present work. The model considers both char conversion and tar formation and predicts the product gas composition, and energy and exergy efficiencies at different operating conditions using MATLAB software. For a steam to biomass ratio of unity, maximum mole fraction of hydrogen is found to be 34.68% at a temperature of 1500 K and equivalence ratio of 0.15, with an exergy efficiency of 75.44%.

Simulation of generation of bio-fuels from biomass through gasification

Attainment of a sustainable and self-replenishing source of energy is one of the primary aims of mankind. In this light a lot of researches are being performed on various energy sources. The objective of this work is to simulate a fluidized bed air-steam gasification using thermodynamic equilibrium model with rubber seed shell as the feedstock. A thermodynamic equilibrium model considering char conversion and tar formation is developed using MATLAB software to predict the composition and heating value of product gas. The prediction capability of the model is enhanced by multiplying the equilibrium constants with suitable coefficients. The optimum values for equivalence ratio, steam to biomass ratio, and temperature for maximum hydrogen generation of 33.15% and maximum efficiency of 55.97% are found to be 0.15, 4, 1500 K and 0.15, 0, 1200 K, respectively.

Numerical Analysis on the Dynamic Behaviour of Fluidized Bed Reactor

A gas-solid multiphase flow is simulated using CFD to investigate the fluid dynamics of a fluidized bed reactor. The simulation is based on Euler-Euler two fluid model where Kinetic Theory of Granular Flow is used for predicting the solid phase transport properties. The simulation procedure is validated by reproducing and comparing hydrodynamic parameters with those available in the literature. The effect of different turbulence models on bed fluid dynamics is analyzed and k-ε RNG per-phase model is found to have better prediction accuracy compared to other models. The minimum fluidization velocity, granular temperature, bed expansion, particle velocity and volume fraction are determined by the model.

Comparison of Boiling and Condensation Characteristics in the Porous Wick of a Flat Heat Pipe in Vertical and Horizontal Orientation

The two-phase flow through porous media is an important topic which spans a broad spectrum of engineering disciplines especially in porous heat pipes. Heat pipe is a thermodynamic device that transports heat energy from one location to another with a negligible temperature drop. The aim of the present work is to investigate the phase change mechanisms, namely boiling and condensation, in the flat heat pipe system with different orientation. Governing equations used for the formulation are continuity, mixture momentum, liquid conservation and energy equations. These equations are converted into three ordinary differential equations using similarity transformation and two-phase similarity solutions are obtained for both boiling and condensing flows. In each case, a two phase zone where the liquid and vapour can coexist appears adjacent to the wall. As the heat transfer at the wall gradually enhances, the liquid saturation at the wall approaches to the limiting value, zero, for boiling and unity for condensation. The present work is an attempt to predict numerically the liquid wall saturation, non-dimensional temperature, non-dimensional temperature gradient and effect of Sherwood number during the phase change of water-steam system in the heat pipe for horizontal and vertical cases. Nomenclature