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

Abstract

The flow and heat-transfer characteristics over a continuously moving horizontal material with suction or injection are studied very close and far away downstream from the extrusion slit. The finite-volume method is used to map out the solutions in the nonsimilar and similar regions subject to uniform surface velocity and temperature. The effects of Prandtl number (Pr), suction/injection parameter (d) and Reynolds number (Re(x)) on the friction and heat-transfer coefficients are studied. Comparisons with the similarity method solutions downstream at high Re(x) are made. Critical Reynolds numbers to distinguish between the self-similar and nonsimilar regions are obtained. The region very close to the slit is characterized by: (i) a rapid increase in skin-friction coefficient with increasing suction, or with increasing injection above d ~ 0.45; the lowest friction coefficient is attained at an injection parameter d ~ 0.45, and (ii) large heat-transfer coefficient which increases with increasing Prandtl number and suction, and decreases with increasing injection. On the other hand, downstream where the similarity solution is valid both the skin-friction and heat-transfer coefficients reach asymptotic values depending on d and, for the latter, on Pr. (C) 2000 Elsevier Science Inc. All rights reserved. The flow and heat-transfer characteristics over a continuously moving horizontal material with suction or injection are studied very close and far away downstream from the extrusion slit. The finite-volume method is used to map out the solutions in the nonsimilar and similar regions subject to uniform surface velocity and temperature. The effects of Prandtl number (Pr), suction/injection parameter (d) and Reynolds number (Rex) on the friction and heat-transfer coefficients are studied. Comparisons with the similarity method solutions downstream at high Rex are made. Critical Reynolds numbers to distinguish between the self-similar and nonsimilar regions are obtained. The region very close to the slit is characterized by: (i) a rapid increase in skin-friction coefficient with increasing suction, or with increasing injection above d≈0.45; the lowest friction coefficient is attained at an injection parameter d≈0.45, and (ii) large heat-transfer coefficient which increases with increasing Prandtl number and suction, and decreases with increasing injection. On the other hand, downstream where the similarity solution is valid both the skin-friction and heat-transfer coefficients reach asymptotic values depending on d and, for the latter, on Pr.