No abstract

The present work aims to study the fluidization and heat transfer characteristics around a single horizontal heated tube, in-line tubes arrangement and staggered tubes arrangement immersed in a gas fluidized bed. The experiments were carried out on a square test section column (16 cm x 16 cm x 95 cm) from a steel sheet of 3 mm thickness. Each arrangement of the tubes is installed in a separate test section. The plane tube bank for both in-line and staggered tubes arrangement consists of 5 rows and four tubes per row in equal vertical and horizontal pitch arrangement. The experimental setup has a transition channel with the same square section and 30 cm height. The other side of the transition channel has one hole of 5 mm inside diameter and 30 mm long to measure the pressure before the distributor plate. The bed material used is sand particles of different sizes (1400 µm, 1600 µm, and 1850 µm). For the tested arrangements, the results show that the average heat transfer coefficient increases with the increase of the fluidizing velocity and with the decrease in particle diameter. Also, the comparison between the in-line and staggered tube arrangement showed that, the average heat transfer coefficient in case of staggered is higher than that of the in-line tube arrangement. Moreover, empirical correlations for the average Nusselt number of the tested arrangements using the experimental data are presented.

No abstract

This paper provides heat transfer enhancement and flow friction data for swirl flows enter tangentially to an annulus roughened with helical-ribs. The effects of the roughness intensity, tangential to total momentum flux ratio and Reynolds number were studied. The tested annulus has a radius ratio of 0.25 with the inner surface insulated and the outer one was heated with a uniform heat flux. The inner surface of the outer tube was roughened with helically coiled wires which act as turbulence promoters breaking up the viscous sublayer formed in the fluid region nearest to the wall. Roughness was made by using helical-wires at two different diameter to pitch ratios (d/p) of 0.025 and 0.050 within a range of Reynolds number from 5x103 to 25x103, and at values of the tangential to total momentum flux ratios of 1.73, 2.94, 3.46 and 5.88. It was found that there is a significant enhancement in the heat transfer due to inlet injection swirl compared with that gained by helical roughness. Also, the efficiency index is critically dependent on the roughness Reynolds number, momentum flux ratio and the roughness intensity and it is almost less than that for the rough plain annulus. New correlations for Nusselt number enhancement ratio and the Fanning friction factor ratio were obtained as functions of Reynolds number, momentum flux and d/p ratios. Also, a maximum Nusselt number enhancement ratio of about 2.0 was found corresponding to 8.7 fold increase in the flow friction factor for a single entry injector with Mt/MT of 5.88 at relatively dense roughness with d/p of 0.05.

No abstract