Fluid flow phenomena in materials processing - The 2000 Freeman Scholar Lecture

There has been an explosive growth in the development of new new materials and processing techniques in recent years to meet the challenges posed by n ew applications arising in electronics, telecommunications, aerospace, tran sportation, and other new and traditional areas. Semiconductor and optical materials, composites, ceramics, biomaterials, advanced polymers, and speci alized alloys are some of the materials that have seen intense interest and research activity over the last two decades. New approaches have been deve loped to improve product quality reduce cost, and achieve essentially custo m-made material properties. Current trends indicate continued research effo rt in materials processing as demand for specialized materials continues to increase. Fluid flow that arises in many materials processing applications is critical in the determination of the quality and characteristics of the final product and in the control, operation, and optimization of the syste m. This review is focused on the fluid flow phenomena underlying a wide var iety of materials processing operations such as optical fiber manufacture, crystal growth for semiconductor fabrication, casting, thin film manufactur e, and polymer processing. The review outlines the main aspects that must b e considered in materials processing, the basic considerations that are com mon across fluid flow phenomena involved in different areas, the present st ate of the art in analytical, experimental and numerical techniques that ma y be employed to study the flow, and the effect of fluid flow on the proces s and the product. The main issues that distinguish flow in materials proce ssing from that in other fields, as well as the similar aspects, are outlin ed. The complexities that are inherent in materials processing, such as lar ge material property changes, complicated domains, multiple regions, combin ed mechanisms, find complex boundary conditions are discussed. The governin g equations and boundary conditions for typical processes, along with impor tant parameters, common simplifications and specialized methods employed to study these processes are outlined. The field is vast and it is not possib le to consider all the different techniques employed for materials processi ng. Among the processes discussed in some detail are polymer extrusion, opt ical fiber drawing, casting continuous processing, and chemical vapor depos ition for the fabrication of thin films. Besides indicating the effect of f luid flow on the final product, these results illustrate the nature of the basic problems, solution strategies, and issues involved in the area. The r eview also discusses present trends in materials processing and suggests fu ture research needs. Of particular importance are well-controlled and well- designed experiments that would provide inputs for model validation and for increased understanding of the underlying fluid flow mechanisms. Also, acc urate material property data are very much needed to obtain accurate and re peatable results that can form the basis for design and optimization. There is need for the development of innovative numerical and experimental appro aches to study the complex flows that commonly arise in materials processin g. Materials processing techniques that are in particular need of further d etailed work are listed Finally, it is stessed that it is critical to under stand the basic mechanisms that determine changes in the material, in addit ion to the fluid flow aspects, in order to impact on the overall field of m aterials processing.