Pressure Drop for Flow Disturbances

Equation (11) is the form of the mechanical energy balance that is useful in microfluidics. Note that a Reynolds number multiplies the term representing the change of kinetic energy, which is small in microfluidics. Consider the case when the Reynolds number is extremely small. Then, any flow situation is governed by Stokes equation  

the non-dimensional flow does not depend upon the Reynolds number. This means that both  

A convenient way to correlate data for excess pressure drop when there are contractions, expansions, bends and turns, etc., when the flow is turbulent is to write them as  

to calculate the pressure drop for any given fluid and flow rate, one only needs to know the values of K, a few of which are tabulated in Table 8.1. 

As shown above, for slow how the pressure drop is linear in the velocity rather than quadratic, and a different correlation is preferred  

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