Cooling fan structure design principle(4)

Euler's equation is based on the theorem of the moment of momentum of a particle system, that is, the resultant torque of the external force acting on the particle system to the same fixed point or fixed rotation axis.

M=qmcu2r2-qmcu1r1

You multiply it by w

Mw=qm (cu2r2-cu1r1)

For axial-flow Fans, the above formula is simplified since Mw=pthqv=qmgHth, rw=u, gHth=hth

gHth=hth=u(cu2-cu1)

(1) The theoretical head H obtained by the fluid is only related to the velocity of the fluid at the inlet and outlet of the blade, and has nothing to do with the flow process of the fluid inside the impeller.

(2) The theoretical head H obtained by the fluid is independent of the type of fluid being transported. No matter what kind of fluid is transported, as long as the inlet and outlet velocity triangles are the same, the same liquid column or gas column height can be obtained

The Bernhard equation is a form of the law of energy conservation and conversion, which is essentially a gas entering and leaving the pipeline, and the blade changes the energy of the gas by doing work on the gas, including internal energy and macroscopic kinetic energy and potential energy. And I'm going to use the formula for that

hth =h2-h1+(c2²-c1²)/2+g(z2-z1)

ws - The work done by the blade on the gas

h---- internal energy

c² /2 - kinetic energy

gz - Potential energy

In an Axial Fan, the potential energy of the gas is negligible because it is very small. The above formula is simplified as

hth =h2-h1+(c2²-c1²)/2

In the design of fan blade, pressure is an important parameter, so the pressure value is introduced according to h=p/ρ, the above equation becomes

hth =p2/ρ2-p1/ρ1 +(c2²-c1²)/2

At the inlet and outlet of the fan, because the pressure changes little, it can be used as an incompressible fluid, that is, ρ1 =ρ 2 =ρ, and the above formula becomes

hth =(p2-p1)/ρ +(c2²-c1²)/2

Axial fan application: Power supply, Case, UPS, CPU Cooler, audio and other home appliances

Centrifugal fan application: Blower, NoteBook

Oblique fan application: VGA, CPU Cooler