Abstract. Using a miniature gold plated copper disk as target, quenching experiments were performed with water sprays to correlate heat flux q" to surface-tofluid temperature difference A T, and the local values for the spray hydrodynamic parameters of volumetric flux Q", mean drop velocity Um and Sauter mean drop diameter d32 over a wide range of operating conditions (Q" = 0.58 • 10-3-9.96• 10 -3 m 3 sec-a/m 2, U m = 10.1-29.9 m/sec, d32 = 0.137-1.350 mm), and surface temperatures up to 520 ~ C. Drop diameter was found to have a weak effect on heat transfer in film boiling for all the conditions tested. Two distinct spray cooling regimes were identified, allowing the classification of sprays with respect to volumetric flux, low flux sprays for Q" < 3.5 • 10 -3 m 3 sec-1/m 2, and high flux sprays for Q" > 3.5 • 10 -3 m 3 sec-1/m z. While Q" had a significant influence on film boiling in both regimes, drop velocity was important only for the high flux sprays. A spray quenching test bed was also constructed to simulate, under controlled laboratory conditions, spray quenching of alloys in an industrial environment. The test bed was used to generate temperature-time records for a rectangular aluminum plate during spray quenching. Using the software package ANSYS, the measured temperature response was successfully simulated by utilizing the newly developed boiling correlations in defining boundary conditions for the quenched surface after accounting for spatial variations in the hydrodynamic parameters within the spray field. The effectiveness of this numerical technique for the tested configuration is proof that it may be possible to predict the temperature-time history for quenched parts with complicated shapes provided the spatial distributions of the hydrodynamic parameters are well mapped or predetermined. Nomenclature

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The present study constitutes a step toward the understanding, and eventual optimization, of the spray quenching process for aluminum extrusions. A spray quenching test bed was constructed to simulate an industrial spray quench. This experimental facility allowed for the testing of irregular shapes using up to eight water sprays. Quenching experiments were conducted using flat water sprays in two different configurations with an L-shape testpiece constructed from commercially pure aluminum AI 1100-O. Section thickness and spray configuration were found to have a significant effect on the cooling rate and cooling uniformity. The commercially pure aluminum A11100-O L-shape and a similar L-shape constructed from aluminum alloy 2024-T6 were simulated with a two-dimensional finite-element code and spray correlations available from previous studies. Using the quench factor technique, the numerical simulation enabled the assessment of merits of different spray configurations with respect to the magnitude and uniformity of hardness of the 2024-T6 L-shape.

In this paper, a multidimensional numerical simulation has been used to investigate the creation of fine fiber by the melt-blown process. The problem involves highly complex fluid flow and convective heat transfer processes. The fine fiber is created by the use of high-velocity, obliquely impinging air jets whose high shear forces stretch a polymer extrudate in the partially fluid state. High-temperature air is used to maintain the fluidity of the polymeric material as it exits the die. The model which was developed and implemented for the simulation closely reflects the physical situation employed in the actual production of fine fibers. The actual configuration of fine fiber production is a linear array of orifices from which the partially fluid polymer emerges. The array contains inherent symmetries which enable the problem to be tractable. Notwithstanding this, the numerical simulation still required multimillions of control volumes to achieve results of practical relevance. The results of the simulation indicate that, contrary to physical intuition, the shear exerted by the airflow is relatively uniform around the circumference of a given fiber. Although the interfiber spacing is small, it does not promote unfavorable fiber-to-fiber interactions.

In this article, a synergistic approach encompassing numerical simulation and laboratory experimentation is used to identify the optimal geometry for the creation of fine fiber by the melt-blown process. The problem involves highly complex fluid flow and convective heat transfer. The fine fiber is created by the use of high-velocity, obliquely impinging air jets that stretch a polymer extrudate in the partially fluid state. High-temperature air is used to maintain the fluidity of the polymeric material as it exits the die. Four different geometrical configurations were investigated with regard to their capability of producing high fluid shear and high temperatures in the critical region just downstream of the emergence of the polymer extrudate from the tip of a die. The results of the numerical simulations provided a definitive conclusion about the relative efficacies of the four investigated geometrical configurations. The velocity and temperature profiles of the oblique jets were carefully documented to identify their decay with increasing downstream distance from the die tip. Velocity profile measurements were in excellent agreement with the numerical predictions, thereby validating the simulation model. Another major parameter of the study, in addition to the geometric-configuration issue, was the pressure difference responsible for setting the magnitude of the jet velocity. The accuracy of the results was established by a mesh independence study and by varying the size of the solution domain.