Cheng، Po-Jen نويسنده , , Chen، Chao-Kuang نويسنده , , Lai، Hsin-Yi نويسنده ,
There has been an explosive growth in the development of new materials and processing techniques in recent years to meet the challenges posed by new applications arising in electronics, telecommunications, aerospace, transportation, and other new and traditional areas. Semiconductor and optical materials, composites, ceramics, biomaterials, advanced polymers, and specialized alloys are some of the materials that have seen intense interest and research activity over the last two decades. New approaches have been developed to improve product quality, reduce cost. and achieve essentially custommade material properties. Current trends indicate continued research effort 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 system. This review is focused on the ftuid flow plienomena underlying a wide variety of materials processing operations such as optical fther manufacture, crystal growill for semiconductor fahrication, casting, thin film manufacture, and polymer processing. The review outlines tile main aspects tliat must he considered in materials processing, the basic considerations that are common across fluid flow phenomena involved in different areas, the present state ofthe art in analytical, experimental and numerical techniques that may be employed to study the flow. and the effect of fluid flow on the process and the product. Tlie main issues that distinguish flow in materials processing from that in other fields, as well as the similar aspects, are outlined. Tlie complexities that are inherent in materials processing, such as large material property changes. complicated domains, multiple regions, combined mechanisms, and complex boundary conditions are discussed. The governing equations and boundary conditions for typical processes, along with important parameters, common simplifications and specialized methods employed to study these processes are outlined. The field is vast and it is not possible to consider all the different techniques employed for materials processing. Among the processes discussed in some detail are polymer extrusion, optical fiber drawing, casting, continuous processing, and chemical vapor deposition for the fahrication of thin films. Besides indicating the effect of fluid flow on the final product, these results illustrate the nature of the basic problems, solution strategies, and issues involved in the area. The review also discusses present trends in materials processing and suggests future research needs. Of particular importance are well-controlled and well-designed experiments that would provide inputs for model validation and for increased understanding ofthe underlying fluid flow mechanisms. Also. accurate material property data are very much needed to obtain accurate and repeatable results that can form the basis for design and optimization. There is need for the development of innovative numerical and experimental approaches to study the complex flows that commonly arise in materials processing. Materials processing tecliniques tliat are in particular need of further detailed work are listed. Finally, if is stessed that it is critical to understand tlie hasic mechanisms that determine clianges in the material, in addition to tlie fluid flow aspects, in order to impact on the overall field of materials processing.
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