ZF Fake Trans Cooler Hookup

[Lynn Larsen]

I had tried to avoid this to argue with Cliff that anytime a fluid is passed through a tube (or even an open channel for that matter) there are going to be line losses caused by friction and normally expressed a h sub L (head loss). (Ref the Darcy-Weisbach equation, or the Fanning equation for the chemical engineers here.) Because of the difficulty in doing equations in this editor, I will omit the "sub L".

For a circular pipe (smooth or rough) of L length and D diameter flowing full of a liquid at a velocity of V

h = f(L/D * V²/2g)​

where:

h = head loss in feet of the liquid in the pipe
f= the friction number which is proportional to the Reynolds number R
R = LVp/µ where p is the density and µ is the dynamic viscosity
g = acceleration of gravity - 32.2 f/s²
​

So, losses are proportional to both length of the pipe L and viscosity and inversely proportional to the diameter. However when a ratio of two line losses is done, the viscosities (being the same in each path) will cancel (as will the densities and g) and be determined only on L, D and V.

Lynn

Ref: Chp. 8 Steady Incompressible Flow in Pressure Conduits, Fluid Mechanics with Engineering Appliccations; Daugherty, Franzini & Finnemore. © 1985 McGraw-Hill ISBN 0-07-015441-4

 

[Andy Besic]

Couldn't you just put in a temperature triggered switch to turn on the electric pump?

 

[Lynn Larsen]

Andy,

You are correct, sir: a temp switch to turn the pump on (just have to make sure it's getting a good reading e.g. can't be in the line leading to the pump), which to me is better than a thermostat. With the thermostat, will the pump be on all of the time? I hope not! So, you'd have to add a switch to only have the pump come on when the thermostat opens. Seems redundant to me.

Of course all of the above assumes an exernal pump. If there is an internal pump that runs all of the time anyway and just bypasses when the external flow is closed, then a thermostat alone would work.

Lynn

 

[Andy Besic]

I was thinking stupid simple....oil out the drain to the pump with the temp switch right there, when the oil gets hot it turns on the pump which then pumps through the cooler and to the sprayer or return line. Only concern I see is that the cooler is plumbed in a way that it won't drain all of it's oil back into the trans when the pump is not circulating causing a high oil level.

 

[Randy V]

I was thinking stupid simple....oil out the drain to the pump with the temp switch right there, when the oil gets hot it turns on the pump which then pumps through the cooler and to the sprayer or return line. Only concern I see is that the cooler is plumbed in a way that it won't drain all of it's oil back into the trans when the pump is not circulating causing a high oil level.

Andy - You could put a check valve on the output side of the oil cooler but for what little additional capacity that cooling system would have, I don't think you'd be in any danger in having too high of an oil level in the gearbox.
This is the way I will be plumbing mine for a G50 box.

 

[John Fitzpatrick]

5.000 revs constant. Gearfox GFX oil in the gearbox.
Total flow at 10°C - 6.8 L/min but only 3.2 L/min are passing through the cooler ( Setrab ).
Total flow at 80°C -15.4 L/min but 11.8 are going through the cooler.
Wanni

If your total flow changes from 6.8 L/min at 0 degrees C to 15.4 L/Min at 80 you aren't using a positive displacement pump, and depending on how many 2mm tubes in your cooler, you may not be maintaining laminat flow-it depends on the fluid velocity and how the tube ends are configured.
Be that as it may, you're only getting 76% flow through the cooler, best case. Is the elimination of a thermostat worth that big a loss in efficiency?

 

[wanni]

I do not understand the meaning of the positive displacement pump.
I am using a concentric pump driven by the primary shaft.
If we assume that the oil viscosity is changing in function of the temperature, immediatly we MUST understand that this is happening in a system which is not changing the size of the channels.
Take a piece of butter, warm it up until it gets liquid.
Put it in a previously made cone with an hole about 5 mm
After few seconds, in function of the temperature dropping down, the butter will not get out through the hole anymore. His viscosity has increased until the lamination factor does not permit anymore the flow.
Now do not say that the butter is naturally solid, because also the oil becomes solid when it reaches 50°C below the zero. It is just a simple way to explaine why the flow difference is there between cold and warm.
Ciao
Wanni