The effect of extrusion slit on the flow and heat-transfer characteristicsfrom a continuously moving material with suction or injection

The flow and heat-transfer characteristics over a continuously moving horiz ontal material with suction or injection are studied very close and far awa y downstream from the extrusion slit. The finite-volume method is used to m ap out the solutions in the nonsimilar and similar regions subject to unifo rm surface velocity and temperature. The effects of Prandtl number (Pr), su ction/ injection parameter (d) and Reynolds number (Re-x) on the friction a nd heat-transfer coefficients are studied. Comparisons with the similarity method solutions downstream at high Re-x are made. Critical Reynolds number s to distinguish between the self-similar and nonsimilar regions are obtain ed. The region very close to the slit is characterized by: (i) a rapid incr ease in skin-friction coefficient with increasing suction, or with increasi ng injection above d approximate to 0.45; the lowest friction coefficient i s attained at an injection parameter d approximate to 0.45, and (ii) large heat-transfer coefficient which increases with increasing Prandtl number an d suction, and decreases with increasing injection. On the other hand, down stream where the similarity solution is valid both the skin-friction and he at-transfer coefficients reach asymptotic values depending on d and, for th e latter, on Pr. (C) 2000 Elsevier Science Inc. All rights reserved.