Polymer flow, nonisothermal

Finite Element Modeling of Nonisothermal Polymer Flows... 

Temperature Profile n (1) In extrusion or injection molding, the sequence of barrel temperatmes from feed opening to head, sometimes presented as a plot of temperatme versus longitudinal position, hence profile. (2) The sequence of metal temperatmes across a sheet or film die, or around a large blown-fihn die. (3) The sequence of temperatmes across the width of a slab of newly extruded or cast plastic foam, is indicated by temperatme sensors placed laterally at the same depth in the foam. (4) In analysis of Nonisothermal, laminar flow of very viscous liquids (e.g., polymer melts) within tubes and dies, the sequence of temperatmes from the one sidewall through the center to the opposite sidewall at any point along the axis of flow. Such profiles have also been measured experimentally with traversing thermocouples. 

The modern discipline of Materials Science and Engineering can be described as a search for experimental and theoretical relations between a material s processing, its resulting microstructure, and the properties arising from that microstructure. These relations are often complicated, and it is usually difficult to obtain closed-form solutions for them. For that reason, it is often attractive to supplement experimental work in this area with numerical simulations. During the past several years, we have developed a general finite element computer model which is able to capture the essential aspects of a variety of nonisothermal and reactive polymer processing operations. This "flow code" has been Implemented on a number of computer systems of various sizes, and a PC-compatible version is available on request. This paper is intended to outline the fundamentals which underlie this code, and to present some simple but illustrative examples of its use. 

This review has highlighted the important effects that should be modeled. These include two-phase flow of liquid water and gas in the fuel-cell sandwich, a robust membrane model that accounts for the different membrane transport modes, nonisothermal effects, especially in the directions perpendicular to the sandwich, and multidimensional effects such as changing gas composition along the channel, among others. For any model, a balance must be struck between the complexity required to describe the physical reality and the additional costs of such complexity. In other words, while more complex models more accurately describe the physics of the transport processes, they are more computationally costly and may have so many unknown parameters that their results are not as meaningful. Hopefully, this review has shown and broken down for the reader the vast complexities of transport within polymer-electrolyte fuel cells and the various ways they have been and can be modeled. 

Fig. 10.50 Location of the pressure gauge (P) and the thermocouples (7) at the five axial barrel positions. The three cross sections A-A, B-B and C-C are used for contour plots of the numerical results. [Reprinted by permission from T. Ishikawa, S. Kihara, K. Funatsu, T. Amaiwa, and K. Yano, Numerical Simulation and Experimental Verification of Nonisothermal Flow in Counterrotating Nonintermeshing Continuous Mixers, Polym. Eng. Sci., 40, 365 (2000).]...

T. Ishikawa, S. Kihara, K. Funatsu, T. Amaiwa, and K. Yano, 3-D Numerical Simulations and Nonisothermal Flow in Co-rotating Twin Screw Extruders, Polym. Eng. Sci., 40, 357-364 (2000). 

The equations which govern the nonisothermal flow of a reactive fluid are derived in several texts on transport phenomena and polymer processing (e.g. refs. 1,2). Regarding velocity, temperature, and concentration of unreacted species as the fundamental variables, the governing equations can be written as ... 

This paper has described an analytical tool which can predict velocities, stresses, and temperatures in nonisothermal flow situations of the sort encountered in many polymer melt processing operations. Such a model cannot be expected to replace the experience and intuition which provide the basis for most process design today, but it is hoped that this inexpensive and easily implemented model can provide a means by which the process designer s intuition might be expanded. Properly used, it can be a valuable additional tool at the process designer s disposal. 

Nonisothermal Flows of Molten or Thermally Softened Polymers... 

NONISOTHERMAL FLOWS OF MOLTEN OR THERMALLY SOFTENED POLYMERS... 

Control of the Sample Environment High-vacuum conditions or constant inert gas flow are necessary for studying intrinsic relaxation phenomena in hygroscopic materials. A chemically inert atmosphere is also desirable in studies of polymer solutions, biomacromolecules, and other biological substances, where precise control of the hydration levels is vital. In isothermal scans fluctuations of the sample temperature should be as small as possible (below 0.1 K), such fluctuations are usually controlled by most commercial temperature stabilization/regulation systems (see Section 6.4.1.2). The same recommendation applies for the heating rates typically used in nonisothermal dielectric techniques. 

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