Film Drainage Rate Reynolds Model and Further Modifications

2 Film Drainage Rate Reynold s Model and Further Modifications 

Thin film drainage has been investigated in detail both theoretically and experimentally [22, 28-30, 35]. An extensively applied physical model of a draining thin film is the one of Reynold s, a form of which is shown in Equation 1  

The dependencies of drainage (flow) rate on the variables of film thickness, area and bulk viscosity are quantified in Equation 1. For example, with decreasing film thickness k, the drainage rate decreases in proportion with k furthermore the drainage rate decreases with increasing viscosity. 

Previous discussions [34] of PU film drainage rate (and ultimately foam stability and cell opening) focused on the dependence of rate on bulk viscosity. Per Reynold s model, factors which increased the bulk viscosity, such as catalyst concentration and polyol reactivity, presumably decreased film drainage rate and yielded a more stable, less porous foam. 

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