Watercooling and flow: is there such a thing as too much flow??

[Shooter]

Pete, you have to balance the two legs to get the same flow at each.

I agree. Everything you said makes absolute sense to me, but what I was trying to understand is the case of an infinite source (constant pressure delta).

If we had an infinite source, adding an additional 100 sprinklers to leg 1 would not affect leg 2 because it is still seeing the same pressure delta at the Y. Am I right? (Example: A 1000’ diameter pipe feeding two legs of 1/32” pipe).

I guess the whole point is moot because we don’t have an infinite source. The inlet at the rudder is too small. Therefore, to get more flow to the restricted motor circuit, you would have to add an orifice to the ESC circuit to balance it out. I think you and lt130th have it figured out. Great discussion!

[lt130th]

...adding an additional 100 sprinklers to leg 1 would not affect leg 2 because it is still seeing the same pressure delta at the Y. Am I right?

With each additional sprinkler, the exit area is growing on that leg of the y-junction, so in order to maintain a constant velocity of fluid flow out of each branch/leg, the exit area of the one-sprinkler exit would have to change.

I'll see if I can type this without subscripts in a way that's still easy to follow. Continuity eqaution states flow rate (Q) is equal at inlet & outlet by conservation of mass. Q=V/t or the volume per unit time (cubic meters per second, in SI units for example), which can also be expressed as the product of area & velocity (A*v)...proof by dimensional analysis: (m^3)(s^-1)=(m^2)(m)(s^-1). We assume our fluid to be incompressible, therefore density is constant. So Q_in=Q_out or (A*v)_in=(A*v)_out. With the case of a Y-junction, you can say (A*v)_in=[(A*v)_left out]+[(A*v)_right out]. Now if you want the fluid to exit each leg with the same velocity, then (A*v)_in=[(A_left out)+(A_right out)]v_out. Now you can see that if you change either outlet area, the other outlet area must change to maintain constant flow velocity. We are making many other assumptions about steady, streamline, irrotational, inviscid flow, & ignoring the affects of sudden changes in pipe ID that affect velocity & pressure...also friction, turbulence & eddies due to curvature in the pipes & treating the water jacket like a straight pipe. So this is a super simplified view of the system, but it should allow some insight.

[T.S.Davis]

.....HAHA Nerd alert! Guilty.

It would be very difficult to prove mathematically that two flows would come out equal in our boats. The curve a tube makes to attach to barb x,y,z would be almost impossible to factor. A change in direction increases friction. Then there is a coefficient of friction between the water and the walls of the tube could be different from tube to tube. Then there's friction loss in the jacket, the speedo, the barbs into and out of the jacket. Some jacket inlets are angled so more friction there. Then there are the bulkhead fittings where the water exits.

I had two pickups that I spliced together once they made it inside the boat. I made sure the distance and routing of each were as similar as possible. So I had twice the supply pressure of single pickup. I doubt it did jack to make it better but I had a dual pick up so I used it.

We do something similar with sprinklers too. A gridded system uses multiple routes to transfer water throughout the building with less pressure losses. It's a mathematical PIA.

[T.S.Davis]

Don't confuse velocity with volume either.

Velocity is feet per second for instance. A measure of speed.

Volume is different.

If we run water through a 1" tube at "X" feet per second it will produce a certain volume. (GPM)
To get the same "volume" through a smaller tube your velocity will need to be higher.

[zooma]

I posed the question involving the "Y" inside the boat. What I am getting from the recent discussion is that I could probably increase the flow through the jacket by restricting the flow through the ESC. But, since some water is dribbling out of the jacket's through-hull, won't that be sufficient? I don't want to jeopardize the ESC cooling either. In truth, I have only performed this test with a squeegee bulb feeding into the hose that would be connected to the rudder nipple. When running in the water, I can only see the stream.

[lt130th]

Maybe try a garden hose with a high velocity nozzle spraying a jet at your rudder pick up. 40mph water moving towards your static rudder is the same as your boat moving 40mph through static water. If you're still only getting a dribble out of the motor, then you might go through the motor leg (between Y & outlet), take everything apart & find the blockage. Was that a freshwater boat before you got it? Brackish water will seriously clog your cooling paths...or could just be something lodged inside the Y, jacket ports or outlet...?

[zooma]

It's a pond boat. I'm the third owner. When I got it I had to swap motors and reinstall the water jacket. Went from a TP Power non-functioning 4070 to a good 4050. Maybe I'll just pull the jacket off and look for obstructions. Have to have it ready for a club race on Saturday.

[keithbradley]

There's always the option of daisy-chaining your components. This is an under-utilized but effective method to cool components.

[Peter A]

ok so I'm going to chime in on this. A year or three back my son had to do a science fair thing. what we did was to do an experiment to prove whether more water flow would result in better cooling, I thought it would. I made a 'dummy' motor with billet aluminium and used spare hilux glowplugs to provide the heat source and made a water jacket around it, so the whole thing was somewhat similar to our motors. The results were that the more the flow the higher the unit's temp, and with slower flow the temps were lower. This supported the theory of heat transfer into slower moving water flow. end result, I learned a new thing, and more is not necessarily better in this case.

[nata2run]

ok so I'm going to chime in on this. A year or three back my son had to do a science fair thing. what we did was to do an experiment to prove whether more water flow would result in better cooling, I thought it would. I made a 'dummy' motor with billet aluminium and used spare hilux glowplugs to provide the heat source and made a water jacket around it, so the whole thing was somewhat similar to our motors. The results were that the more the flow the higher the unit's temp, and with slower flow the temps were lower. This supported the theory of heat transfer into slower moving water flow. end result, I learned a new thing, and more is not necessarily better in this case.

I Agree!! 100% But this whole issue can be discussed on the forum 1 mill times with 10 mill different ideas. Heat transfer plays a big role in ANY COOLING. Example, my water cooled 12kw spindle on my work CNC will overheat if water flow is beyond 7 liters per min "THAT'S A FACT" (1. something gal) 3-5 liters keeps it at the best temps. Transistors/IC's that require heat sinks in electronic devices will over heat if the heat sink is too big and the transfer can't take place (I use to build class A AMP's they run hot). Our boats do the same.!! I don't think there is a flow formula for all the boats here on the forum. But rather make sure there is a flow, and the pressure don't exceed bursting point at silly mph. If too hot, step down. if ice cold, step up.

[tlandauer]

Are we talking about the volume of flow or are we in fact talking the time it needs for the coolant to absorb the heat and transfering it out. I have a hard time comprehending the less flow (volume) translates to better heat dissipation. Because the simplicity of our cooling loop, there is no realistic way to increase the time the coolant travels inside the loop, which is essential for heat dissipation. So it seems the only way is to reduce the flow.

Or may be I am missing the point.

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[Peter A]

Yep, so there is probably no magic formula. It, like much of our setups will come down to testing. In general, running through the esc, motor and out works. Two pick ups on a single setup will allow separate lines to motor and esc. Hull ride attitude, props, run times etc, etc will all have an effect on temps. No new stuff here and it has been discussed plenty in the past. the best thing to do is set up how you think it should be, test, check and change if needed to get the lowest running temps possible as electrical components like motors and esc's don't like excessesive heat.

[gearhd48]

Hey if you blow a line and water gets in...is this what they mean by.....Running wet??? LOL

[tlandauer]

Hey if you blow a line and water gets in...is this what they mean by.....Running wet??? LOL

Also gives new meaning to water cooled batteries. lol......

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[dmitry100]

Keith: Would daisy chaining be something like this?

Style #2 (As seen at times on T180 ESC setups):
(Inlet 1) --> ESC 1 --> ESC 2 --> Motor 1
(Inlet 2) --> ESC 1 --> ESC 2 --> Motor 2

or like this...

Style #3 (Benefits of each ESC having both inlets equally):
(Inlet 1) --> ESC 1 --> ESC 2 --> Motor 1
(Inlet 2) --> ESC 2 --> ESC 1 --> Motor 2