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Date: Fri, 18 Mar 2005 17:47:06 -0700
From: Bob White <bob@bob-white.com>
To: FlyRotary <flyrotary@lancaironline.net>
Subject: Water Pump Viscosity Test
Message-Id: <20050318174706.286880b6.bob@bob-white.com>
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I completed the viscosity test this afternoon.  Bottom line is that
viscosity is not a major factor in determining the flow from a
centrifugal pump in our operating range. 

Here are the facts:

Temperatue of the fluid varied between 49 and 55 F.
Fluid #1 is 50/50 EG/W with a viscosity at 50 F of about 5.3 cp
Fluid #2 is water with a viscosity at 50 F of 1.3 cp

The viscosity of the EG/W is 1.3 at around 130 F, so the water at 50 F
has the viscosity of EG/W at 130 F.  The temperature variations will
change the numbers somewhat, but not enough to invalidate the test.
There is still a significant difference in viscosity.

(viscosity data was obtained from the Engineerng Tool Box,
http://www.engineeringtoolbox.com/ )

If the viscosity theory is correct, I should see a significantly higher
flow with the water as compared to the EG/W.

I set the pump up so that I was pumping water out of a container, thru
the flow meter, and back into the container.  With the system filled
with EG/W, I restricted the flow to 6 GPM which is about what I was
getting with the pump working thru my engine and evap core.  I then
filled the system with water and compared the flow rate.  Keeping in
mind that the flow meter scale is very compressed in this region, the
water flow reading was between 5.5 and 6 GPM.  It was definitely lower
than the EG/W reading.

I also did a flow measurement of both fluids with no extra
restriction.  The EG/W measured 11 GPM and the water 10.8 GPM.  Again,
the water reading was lower.

We still need to apply  the specific gravity correction factor.  The
specific gravity of the EG/W at 50 F is 1.08 and the correction factor
is the square root of (1/1.08) = 0.96. Multiplying the EG/W reading of
11 by 0.96 = 10.56 which, within the measurement error, is the same as
the water measurement.  The best I could say is that lowering the
viscosity a factor of 3 to 4 increased the flow rate by a factor of
10.8/10.56 = 1.02 or 2 percent. Effectively there is no difference in
flow with a change in viscosity in the regime we are working in.

I'll put all of the data and some photos of the test setup on the Wiki
this evening after I get them off the camera.

Bob W.

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