Water cooling information

[Shooter]

His volume may have gotten so great that the cooling jacket was no longer filled. Water was only in contact with part of the motor.

[1945dave]

Alex in all my years as an engineer and 6 years of college I never heard of the "sweetspot" term as it applies to thermodynamics. Still the only variable that could enter the discussion when enlarging a cooling jacket has to be the trapped air inside the chamber and yes that could affect the over all efficiency of the heat transfer process. However, to slow the flow would take a restriction, not an increase in pressure. I would be interested in seeing the setup that Dave used to test his cooling jackets. I would like to know if they could trap air or if the exit was placed so that all the air could escape. I suspect that was not the case.

The other Dave

[Alexgar]

perhaps a lexan tube fitted as a water jacket would show us this evidence and using differant size orings would act as the volume increase

[HRC]

1945dave,
You are correct, by increasing the volume to a point where the cooling was less effective, the motor temp. actually increased. Having found the “sweet spot” if you will.

I found the higher end motors had a slight temp. difference from front (shaft end) to back (wire end). The more economical motors had a 8-10 degree split from front to back. The back being the hottest.

The position of the jacket on the motor had little effect. The location of the water in and out fittings however made a difference. The inlet side being on the bottom made about 6-8 degree cooler motor temp. as opposed to both being on top. I did try it having both water fittings in line and was very disappointed. Having them offset must help the circulation.
I just thought I would share my actual test results. Sometimes theory and actuality are different. We all have a tendency including myself to over think things.
Dave

[MassiveOverkill]

So I used to water cool my processors to increase my e-penis and a company called Swiftech at one point made a design that couldn't be beat at the time called the Storm (I still have it collecting dust in my garage) that used jet-impingment, which could support the higher pressure theory:

http://forums.bit-tech.net/showthread.php?t=114866

http://www.ecst.csuchico.edu/srproject/project_files/pdfs/ppt_jet_heat_sink.pdf

http://qats.com/cms/2010/06/09/jet-impingement-cooling-provides-high-heat-transfer-rates-for-thermal-management-of-high-power-electronics/

One problem with this water block, even using deionized water is that the jets would eventually get clogged.

I don't know how relevant this is to our application as we're not using jets, but maybe the higher pressure may have an effect. I would think the sweet spot would be the highest pressure/flow setup, not just the best of one or the other.

[Cooper]

More flow= lower temp .

Example, if you have a hot motor and you drip water over it how long would it take to cool it?

Now if you have a hot motor and throw it into the lake how long would it take to cool? :)

Can't compare to cars/radiators totally different system. In my opinion I prefer to have the restriction at the intake side of things as to not create pressure at my fittings, ever have a hose slide off? And I do not mean to restrict flow, I mean I have the smallest diameter of the whole system at the intake. As far as the air in the system, come on guys, what boat running holds perfectly still to where the air can accumulate in the top "pocket" of a cooling jacket? Just a little movement and that theory goes out. Example shake a caped water bottle and set it down, the air goes to the top right? Now shake the bottle again and keep shaking, the air stays mixed right? It's all just my opinion based on the first rule of thermodynamics fact of heat transfer. Heat is always trying to dissipate. Heat will always dissipate to it's surroundings.

[ManuelW]

For the most efficient water cooling jackets some time ago Hopf Modelltechnic manufacturer probably one of the best cooling jackets I had ever seen. They combine the best solutions of the coil type with a standard water jacket. Its basically a massive tube of aluminium with just a tight gap between OD of the motor and ID of the jacket. Then they used a milling chuck with the shape of a ball to mill a coil into the inner surface. This enables coil type cooling with direct water contact over the full motor surface.

Here a picture of these jackets:


regards,
manuel

[srislash]

Those are some work of art there Manuel.That would carry the water direction guaranteed.

[1945dave]

Those are sure pretty Manuel. Could you show us a photo showing the water inlet and outlet.

thanks Dave

[phil t]

I tend to just put a restriction on the output that way the water stays in the system longer under higher pressure, I assume......

Although in the summer heat, free flow may be better with 90F "cooling" water.

We are cooling the motors, not heating water so get the water flowing fast as possible thru the system.

[1945dave]

Last comments on this thread. I think we have about beat this thing to death. I agree with Phil T. Cooling the motors is the goal. The exit temp of the water is totally a non issue, nobody cares and you don't learn anything knowing what it is. Free flowing as fast as possible is better and the fewer restrictions the better. Pressure is bad and holds no advantage except to create leaks and possibly push the water lines off their fittings.

Good luck, next thread?

Dave

[Shooter]

But Dave.......we need you!!

Under the guise of a bathroom plumbing project (wife on watchful eye this morning..supposed to be tiling), I did this experiment. Flow provided from my airplane electric fuel pump, adjusted voltage to provide similar flow to what I observed in my boat.

Pic #1 (side outlet): Note the large air bubble.
Pic #2 (top outlet): Very small bubble at top since my outlet is still at a slight angle, but for the most part the air bubble is gone.

Point is that it's probably best to put the outlet on top. Both HRC's temp data (outlet top, inlet bottom) and this experiment support it.

SideOutlet.jpgTopOutlet.jpg

[1945dave]

Shooter great job. That is good to see. Now do the same thing while shaking the container and see how long you can keep air in the container.

No question choosing an exit hole at the highest point possible is the best plan. Again good job.

Dave

[Shooter]

The set-up was still out there, so I ran it a few more times while shaking. No doubt, the up and down shaking improves the size of the air bubble (makes it smaller), but it takes some extremely vigorous shaking up and down. Most definitely more than what our boats experience, and I still wasn't able to completely eliminate the bubble.

The wide open tupperware container doesn't quite simulate the water jacket, but it's an easy way to demonstrate the concept. Alex hit the nail on the head with a lexan jacket. Would make a great experiment.

[ReddyWatts]

Heat Transfer


Heat transfer works best with the biggest temp differential: The most efficient transfer happens at the greatest temperature differential, therefore higher flow rates will always help with all other variables remaining the same.
It is the Heat Transfer that we want to maintain as efficiently as possible, and that is best done with a higher flow rate. Rather than thinking that there won't be enough time for heat to move towards the cool water, and therefore compromising heat loss, it is better to think that there is more fresh water moving onto the motor and therefore, there is increased cooling.

The reason higher flow rates work better in boat water cooling is this:
There is more water with a larger temperature differential moving through the motor cooling jacket- this removes more heat.

This is true even though a boat with a lower flow rate will have more time to heat the water in the jacket: since the heat exchange works best with the greatest temperature differential, longer “stay time” is counter-productive.