A study of chaotic behavior of heat transfer in gas-solid fluidized bed

الملخص EN

Fluidized beds are characterized by high heat transfer rates between the bed and internal surfaces and have uniform temperature distribution that can be achieved in fluidized bed systems.

In the same time there is a chaotic behavior of hydrodynamic and heat transfer in gas-solid fluidized bed. Experimental work was carried out in gas-solid (air – sand) fluidized bed to investigate the steady state heat transfer coefficient.

The bed column used was (172) mm in diameter and (1000) mm height, fitted with immersed cylindrical heating element of (25.4) mm in diameter.

The fluidizing medium was air flowing at different velocities from fixed bed to fluidized bed of (0.006-0.078)m/s, and three 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 and Narrow Range Solids). A comparison have been done with values of the minimum fluidizing velocity that calculated analytically, empirical, and which got experimentally.

The results show a chaotic behavior of hydrodynamic gas-solid fluidized bed. The heat transfer coefficient and the bed viodage increase with increasing gas fluidizing velocity and the heat transfer coefficient decreases with an increase in particle diameter. Two empirical correlations are proposed which can calculate wide range solids and narrow range solids based on experimental data.

The Nusselt number presented with some dimensionless groups as follows:- For Wide Range Solids Nu = 0.81Re0.94 Pr0.35 Where the correlation coefficient (R) was equal to (0.92) and the average absolute relative error was (12.62 %). For Narrow Range Solids Nu = 0.45Re0.65 Pr0.33 Where the correlation coefficient (R) was equal to (0.86) and the average absolute relative error was (24.2 %).