Geometry, Boundary Conditions, and Physical Properties in Melting

2 GEOMETRY, BOUNDARY CONDITIONS, AND PHYSICAL PROPERTIES IN MELTING 

To solve a heat transfer problem in polymer processing, the geometrical boundaries over which heat transfer takes place must be defined, boundary conditions selected, and the nature of the physical properties of the polymer specified. 

The most important boundary condition in heat transfer problems encountered in polymer processing is the constant surface temperature. This can be generalized to a prescribed surface temperature condition, that is, the surface temperature may be an arbitrary function of time T 0, t). Such a boundary condition can be obtained by direct contact with an external temperature-controlled surface, or with a fluid having a large heat transfer coefficient. The former occurs frequently in the heating or melting step in most 

A prescribed surface convection condition mathematically is stated as 

Yet another boundary condition encountered in polymer processing is prescribed heat flux. Surface-heat generation via solid-solid friction, as in frictional welding and conveying of solids in screw extmders, is an example. Moreover, certain types of intensive radiation or convective heating that are weak functions of surface temperature can also be treated as a prescribed surface heat-flux boundary condition. Finally, we occasionally encounter the highly nonlinear boundary condition of prescribed surface radiation. The exposure of the surface of an opaque substance to a radiation source at temperature 7 ,-leads to the following heat flux  

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Geometry, Boundary Conditions, and Physical Properties in Melting, 184... 

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