There has been a long-standing need for a piezoviscous parameter, αfilm, that together with the ambient viscosity, μ0, will completely quantify the Newtonian rheology so that the film thickness for liquids that do not shear-thin in the inlet may be calculated as h = h0, αfilm, ...) regardless of the details of the pressure-viscosity response. It seems that Blok’s reciprocal asymptotic isoviscous pressure, α*, has certain advantages over the conventional pressure-viscosity coefficient that is poorly suited for this purpose. The first detailed review of piezoviscous models for low pressures is provided. A simulation code that is apparently stable for all realistic pressure-viscosity response was utilized with diverse piezoviscous models and model liquids to develop a satisfactory definition of αfilm that reads  
αfilm=[1exp(3)]/03/α*μ(0)dpμ(p);
 
1/α*=0μ(0)dp/μ(p).
In the case of μ = μ0 exp(αp), αfilm = α and formulas are provided for other models.
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