ABSTRACT
The present work deals with the effect of turbulent air-sand suspension flow on
heat transfer and pressure drop in a horizontal tube heated with a uniform heat flux at
different entrance angles. Four different inlet bend-angles (=30, 60, 80 and 90 deg.) in
addition to the case of plain tube (=0 deg.) were studied at different Reynolds
numbers (from 10000 up to 65000), sand particles of two different average-sizes (120
and 200 microns) and different solids-loading ratios (up to 0.40).
It was obtained for the plain tube flow that the presence of the solid particles in
the turbulent flow enhances the heat transfer coefficient giving an enhancement ratio of
the Nusselt number of 1.5 at M=0.4 and Re=35000 for suspended particles with 120
microns average-size. Moreover, at higher Reynolds numbers (over 64000) slightly
enhancement in the heat transfer coefficient was observed. For the flow with different
entrance angles, the heat transfer coefficient enhances in the upstream portion of the
test tube. The results of clean-air flow show that about 1.18 fold increase in average
Nusselt number was corresponding to about 1.5 fold increase in the pressure drop
along the test-section. Also, for air-solids flow the presence of the solid particles in the
flowing air enhances the heat transfer coefficient up to mass-loading ratio of M=0.15
and further addition of solids affects slightly the heat transfer coefficient.
New correlations for the Nusselt number and its enhancement ratio were
obtained for both cases of plain tube and for the tube with different entrance angles. |
