Page 4, Turbulence & Rheology, Dr. D. Penney
As stated earlier, the Poiseuille equation only applies when there is laminar flow. When this is the case, flow rate increases directly with the perfusion pressure, assuming in addition, the existence of rigid conduits and Newtonian fluids. With increased perfusion pressure and/or flow rate, turbulent flow develops. Flow rate (Figure 6.01) increases thereafter in a less than directly proportional manner, because some of the driving energy is dissipated as heat and sound.
Turbulent flow is very noisy. The sound can be heard through a stethoscope or other electronic listening device. All the free energy eventually ends up as heat. Thus, instead of a relationship where change in Q is proportional to change in P, with turbulent flow, change in Q is proportional to the square root of change in P.
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