Viscosity Change Calculation

[CUBOID88]

Hi.
We have an axial piston variable starter motor in that we normally get sent out for test but are looking into testing ourselves on our own rig. The manual calls for a calibration fluid of a particular operating viscosity (16-36mm2/s) when carrying out the test. The problem is, our rig uses Aeroshell Calibration fluid 2 with a viscosity of 10 mm2/s @ 40degC.
The test basically consists of applying a constant flow of 80litres/min to the unit at constant temperature (~38deg C) and varying the pressure from 160bar to 400bar and back down while recording the output speed of the drive shaft (dependent on the displacement of the pistons).

What Im wondering, and cant figure out is how the different calibration fluid will affect the test? Im thinking of using Poiseuille's Eq, and adjusting the flow rate as per the change in viscosity, keeping the pressure drop, length and radius constant as they will not change, essentially being left with

Q1.v1 = Q2.v2

where Q1 = flow rate as per manual
v1 = viscosity as per manual
Q2 = new flow rate
v2 = Aeroshell viscosity
So in my (probably wrong) thinking, solving for Q2 will give the flow rate required to carry out an equivalent test...

Any ideas?

 

[ione]

Do you have to keep pressure drop constant as the viscosity is changed?

If so I think you should first evaluate pressure drop in your test rig considering the flow rate and the fluid specifications reported in your manual.
When computing pressure drop consider:
1) pressure drop due to friction along pipe length (you can go with Darcy-Weisbach equation)
2) minor losses in fittings (you can go with 2-K method or 3-K method)
3) difference in height

Then, when you know the value of pressure drop, go back and solve for new flow rate with new fluid specifications (those of Aeroshell Calibration fluid 2).

 

[hydtools]

Reduce the test temperature to increase your fluid viscosity to the viscosity range specified in the manual. Use the same flows and pressures.

Ted