lobe pump shear rate

[jmonn]

Among different pump types, how does the shear rate of a lobe type rotary pump compare? Is it true that the shear experienced by a liquid in such a pump is extremely low? It has been said to me by the manufacturer that the shear in such a pump is comparable to that of a liquid moved by compressed air, but I am skeptical. I am unable to find any specs.

Also, how does one mathematically apply the concept of shear rate? I have been unable to find any references on the topic.

 

[btrueblood]

Jmonn,

Seems to me there is always some shear in moving fluids. There's at least as much shear in a rotary lobe pump as in a piston or plunger pump of similar (volume per stroke ) and (volume per rotor turn). A plunger pump, however, has a fairly tight seal; a rotary lobe pump has to have some gap between the lobes; there will always be some "slip" of fluid "backwards" through this gap, thus some degree of parasitic shear that doesn't necessarily occur with other types of pumps.

My $.02