Numerical and Experimental Study on Bed-to-Wall Heat Transfer in Conical Fluidized Bed Reactor 17 th International Conference on Mechatronics, Electrical and Mechanical Engineering (ICMEME 2015) Chonbuk National University Presented By Eng. Hamada Mohamed Abdelmotalib

Heat transfer & reactive flow Lab. 2 IntroductionIntroduction Fluidized bed combustion technology is known to be the most efficient and environmentally friendly technology for conversion of energy from a wide diversity of solid fuels ranging from coal to agricultural residues to hazardous waste. A conical fluidized bed reactor is the most suitable technique for testing new alternative bed materials because of the several benefits such as a relatively small amount of inert bed material, shorter start-up time of the combustor and lower pressure drop across the fluidized bed. Studying of the heat transfer and hydrodynamic characteristics of conical fluidized bed combustors (FBCs) is very important for their design and operation.

Heat transfer & reactive flow Lab. 3 Aim of Study In this study, the hydrodynamics as well as bed-to-wall heat transfer characteristics of a gas-solid conical FBR were investigated experimentally and computationally at various operating conditions such as different superficial gas velocities, and different drag models.

Heat transfer & reactive flow Lab. 4 * The bed was heated using hot inlet air, which was heated using two electrical tubular heaters of 5 mm diameter and 400 mm length. The inlet air was subjected to a constant heat input of 600 W so its temperature will change according to the inlet air velocity. * The wall and bed temperatures were measured by thermocouples type k connected to a data acquisition system. * The pressure drop across the air sand bed, was measured using two static pressure taps connected to U-tube manometer. Experimental setup Fig. 1. Schematic of the conical fluidized bed reactor.

Heat transfer & reactive flow Lab. 5 The bed-to-wall heat transfer coefficient was estimated from the measured gas and particles temperatures as given below: Experimental setup Where Q, represents the total input heat rate, A b, is the bed surface area. T b and T s are bed and surface temperatures, respectively

Heat transfer & reactive flow Lab. 6 Model setup Parameters used in simulations Numerical Study Flow typeLaminar Gas–solid model Eulerian-Eulerian, with kinetic theory Wall boundaryNo slip condition for gas and solid Time step used s Convergence criteria10 −3 Under relaxation factors 0.5 for pressure, 0.4 for momentum and 0.2 for volume and granular temperature Maximum solid packing volume fraction 0.63 Pressure velocity couplingSIMPLE Discretization schemeSecond-order upwind Outlet conditionAtmospheric pressure Superficial gas velocity(m s -1 )0.65, 0.73, 0.85, 0.95 Fig. 2. Schematic of the conical FBR used in the simulations.

Heat transfer & reactive flow Lab. 7 ResultsResults 1. Grid independency study Fig. 3. The axial sand volume fraction for different grid system.

Heat transfer & reactive flow Lab Drag models Fig. 3 Bed pressure drop for experiments and simulations results.

Heat transfer & reactive flow Lab. 9 Fig. 4 Sand volume contours for Syamlal–O'Brien and Gidaspow drag models at different fluidizing velocity.

Heat transfer & reactive flow Lab. 10

Heat transfer & reactive flow Lab. 11 Fig. 6 Lateral profiles of granular temperature for Syamlal–O'Brien and Gidaspow drag models at N =1.5and N =2. Fig. 5 Axial sand volume fraction for Syamlal–O'Brien and Gidaspow drag models at N= 1.5and N = 2.

Heat transfer & reactive flow Lab. 12 Fig. 7 Heat transfer coefficient for experiments and simulations results.

Heat transfer & reactive flow Lab Friction viscosity

Heat transfer & reactive flow Lab. 14 Fig. 9 The bed pressure drop with and without friction viscosity at various fluidizing number. Fig. 10 Sand volume fraction for simulation considered and not considered friction viscosity.

Heat transfer & reactive flow Lab. 15 Fig. 11 The heat transfer coefficient for experiments and simulation.

Heat transfer & reactive flow Lab. 16 An experimental and numerical investigation on flow characteristic and bed-to-wall heat transfer in a conical fluidized bed reactor was carried out. A two fluid model using kinetic theory of granular flow was used to simulate both flow and bed-to- wall heat transfer in a 2-dimensional conical fluidized bed reactor. Experiments and simulations were performed using sand particles with diameter of 560 µm under different values of fluidizing number and different drag models. Simulations were carried out especially using Gidaspow drag model had a good agreement with experimental results. The friction viscosity had no clear effect on pressure drop and slightly effect on heat transfer coefficient. ConclusionsConclusions

APPENDEXESAPPENDEXES Table 1 Properties and characteristics of air and quartz sand used in the simulations. Sand properties Mean particle size (µm)560 Thermal conductivity (W/m K)0.25 Specific heat (J/kg K)800 Density (kg/m 3 )2665 Minimum fluidizing velocity(m/s)0.42 Volume fraction0.4 Air properties Density (kg/m 3 )1.2 Thermal conductivity (W/m K)0.025 Specific heat (J/kg K)1.005 Viscosity (Ns/m)1.86E-5

APPENDEXESAPPENDEXES Table 2 Governing equations for flow and heat transfer in a conical FBR.

APPENDEXESAPPENDEXES Table 3 Constitutive equations used to close the governing equations for a conical FBR.