الفهرس 
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Abstract
Abstract The fluidized bed has many applications in several industry fields, especially heat exchangers that use this technique. A 20 x 20 cm square fluidized bed facility has been designed, constructed and assembled with a view to perform bed dynamics and heat transfer studies under cold conditions. After the initial shakedown and calibration tests to commission, the fluidization and heat transfer characteristics around a single horizontal heated circular tube, in line circular tubes arrangement and staggered circular tubes arrangement immersed in a gas fluidized bed are fundamentally studied to clarify the mechanism of heat transfer in a fluidized bed heat exchanger. The experiments were carried out for different bed depth with single circular tube and the plane tube bank for both in line and staggered arrangement consisting of 5 rows and four tubes per row in equal vertical and horizontal pitch arrangement. The dimensionless transverse pitch was , a=Sh/DT=2.27 and dimensionless longitudinal pitch, b=Sv/DT=2.27 .The state of fluidization of particles is observed at a various fluidization velocities. The bed material used is silica sand with different particle size (450,650,950?m) .The fluctuating pressure with different fluidization velocities is measured. Heat transfer to beds of sand particles fluidized by air has been measured from the bed and from the wall of the tested heated tube immersed in fluidized bed. A correlation between the average heat transfer characteristics and the state of flow of particles and gas near the tubes is obtained. For single tube, in line and staggered arrangement the experimental results show that the average Nusselt number against Reynolds number based on tube diameter always is higher than that of the single tube and tube bank in empty bed .The results obtained illustrate that in case of single tube the Nusselt number is higher up to 70 % , and in case of in line arrangement is higher up to 57.8 % while for staggered arrangement up to 75 % than that of empty bed . The comparison between the in line and staggered tube arrangement in the fluidized bed illustrate that the average of heat transfer coefficient in case of staggered tube bank is higher up to 17 % than that in case of the in line tube arrangement.