Flow in high surface energy dies

These feature essentially metal walls (stainless steel, tungsten carbide). The results reported may also apply to dies made of Plexiglas [14] or sihca [11]. 

For each of the fluids tested, variations in pressure loss during flow were represented as a function of flow rate. The general run of the flow curves obtained [14,15, 27] is shown in Fig. 1. 

With low flow rates, the flow is stable and takes place without any slip occurring 

On the flow curves, this slip is accompanied by a discontinuity in the instantaneous flow values (Fig. 1). Its occurrence differs depending on whether or not the installation involves any storage of elastic energy connected with the compressibihty of the polymer upstream of the die. 

In the case of controlled-pressure flow, once a critical pressure value AP is exceeded, it was shown that slip was seen on the flow curves in the form of a jump in flow rate, reaching a factor of as much as 100 (portion (BC) of the flow curve) 

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