where L is the length, g is the gap between fluid walls, w is
the width of the flow channel between the fixed poles, Q is
the volumetric flow rate, η is the viscosity with no applied
field, y is the yield stress developed in response to an
applied field H. The parameter c is a function of the flow
velocity profile and has a value ranging from 2 (for
P / P less than ~1) to a maximum value of 3 (for
P / P less than ~100) [8].
Behavior of controllable fluids is often represented
as a Bingham plastic having variable yield strength [7]:
, (1)