A Study of Chaotic Behavior of Heat Transfer In Gas-Solid Fluidized Bed


Fluidized beds are characterized by high heat transfer rates between thebed and internal surfaces and have uniform temperature distribution that can beachieved in fluidized bed systems. In the same time there is a chaotic behavior ofhydrodynamic and heat transfer in gas-solid fluidized bed.Experimental work was carried out in gas-solid (air – sand) fluidized bed toinvestigate the steady state heat transfer coefficient. The bed column used was(172) mm in diameter and (1000) mm height, fitted with immersed cylindricalheating element of (25.4) mm in diameter. The fluidizing medium was air flowingat different velocities from fixed bed to fluidized bed of (0.006-0.078)m/s, andthree different sizes of fine sand particles were used (i.e. 63, 112, and 145 μm),these average particles diameters were estimated by two methods (Wide andNarrow Range Solids).A comparison have been done with values of the minimum fluidizing velocity thatcalculated analytically, empirical, and which got experimentally. The results showa chaotic behavior of hydrodynamic gas-solid fluidized bed.The heat transfer coefficient and the bed viodage increase with increasing gasfluidizing velocity and the heat transfer coefficient decreases with an increase inparticle diameter.Two empirical correlations are proposed which can calculate wide range solids andnarrow range solids based on experimental data. The Nusselt number presentedwith some dimensionless groups as follows:-For Wide Range Solids Nu = 0.81Re0.94 Pr0.35Where the correlation coefficient (R) was equal to (0.92) and the average absoluterelative error was (12.62 %).For Narrow Range Solids Nu = 0.45Re0.65 Pr0.33Where the correlation coefficient (R) was equal to (0.86) and the average absoluterelative error was (24.2 %).