I received this question form a colleague through Linked-In last week…
How do I calculate the flow rate of the polymer from the known gate cross-section area?
The formula for the appearant shear rate through a rectangular gate is as follows:
Appearant Shear Rate = (6 x Q) / (W x H x H)
Q = polymer flow rate
W = gate width
H = gate thickness
As long as the flow rate and gate dimensions are in the same units (mm, cm, or in) they will cancel out and you will receive a a resultant in the units of reciprocal seconds which will represent the rate of shear.