Back leakage flow

The total output is the combination of drag flow, back pressure flow and leakage. So from (4.3), (4.7) and (4.8)... 

So far we have neglected the effect of the flight clearance. As small as the clearance is, polymer melt is being dragged across the clearance by the barrel surface and the pressure drop may pump melt across the flight width. This creates a continuous leakage flow from downstream locations to (one turn back) upstream locations, reducing net flow rate. 

Fig. 20 Maximal back pressure without leakage flow and switching time of a microvalve in dependence on the filling degree VoeiA c of the valve chamber. The valve chamber (800 pm x 800 pm X 200 pm) is filled with dry PNIPAAm MBAAm 4 particles particle size 82.5 5 pm (according to (Richter et al. 2004b)). Toei bulk volume of dry hydrogel particles, Vc valve chamber volume...

The back-up ring influence on the oil film thickness, the leakage flow and the friction forces in the three contact zones is studied. Note that holding constant pressures between the back-up rings and the main seal element,... 

In this work a symmetric piston seal with back-up rings is analysed. Calculations of oil film thickness, leakage flow and friction forces are carried out using the inverse hydro-dynamic theory. Measured pressure distributions, for either the whole seal including the back-up rings, for the soft seal element or for one back-up ring at a time are used as input data. 

Fig. 16.7a,b. Male, 4 years old. Lumbar myelomeningocele, contractile detrusor VCU. a Closed bladder neck during bladder filling, bladder trabeculation, and sacculation, b Uninhibited detrusor contractions, massive back-up flow of contrast infusion contrast filled bulging bladder neck (arrow) up to contracted external sphincter (sphincter detrusor dyssynergia), some leakage around the catheter... 

The simplest section to model can be treated as three sources of flow drag flow due to the relative motion of the screw and barrel pressure back-flow along the channel, as a result of the pressure build up along the channel, often approximated as linear from feed throat to the tip of the screw leakage flow over the flight tips, again as a result of the positive pressure gradient. 

A last test in which a low barrel temperature combined with a low manifold temperature was used showed a maximum removal of mica, 4.8795 cumulative area as shown in Table 3. However, the third and last test took 4 purge shot to reduce the mica concentration below 0.1%. It indicated that the low melt temperature in the barrel gives a more plug like flow mainly due to lower leakage flow of the melt over the screw flights which prevents back mixing in the barrel. It is almost as effective as the low temperature in the manifold and barrel... 

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