Water cooling information

[ray schrauwen]

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.

[ray schrauwen]

Using a small like this http://www.offshoreelectrics.com/pro...prod=ose-80010 that has been put into a sealed container with the input and output outside the container.

Fill container with water and put a lid on it. Freeze this so as to use it to cool the incoming water on those where the ambient water temp is high. You could avoid freezing with water and just add some dry ice pellets.

Never know it may work. Seeing as the flow is not as fast as I first thought.

If you add salt to your ice water mixture you can double the cooling ability compared to plain water.

[srislash]

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.

This is what I have done as well successfully.I run 1/8thI/D right thru from rudder and neck it down to 7/64 where it exits the hull.I have a vid of the stream to show the pressure.

Here is the vid http://www.youtube.com/watch?v=6XksK68P00g&feature=plcp The first little bit shows the stream coming out from under the cowls.This is at 65mph with a dual pick up gasser rudder so there is no question about flow capabilties.

[1945dave]

Sorry guys. I disagree with those that believe restricting the speed of flow of water cooling improves heat transfer. One of the first items covered in basic Thermodynamics is the study of BTU's and heat transfer. In engineering labs we found no matter how rapid the flow of a fluid (even air over cooling colls in AC systems) higher thermal transfer occurred at faster flow rates. This is not just theory it is fact. We can debate the qualifying terms of use such as laminar flow, turbulant flow, air dilution (foam) but faster flow is better period.

REducing the pressure build up in the system is an important consideration as well. It is nice and reassuring to see those strong visible streams of water exiting from the cooling system. Yet some of the fastest most demanding record holders in the Nitro world do other things not discussed here. Like relocating all the water exits for the heads of Nitro engines to the very top of the motor. Factory locations are typically straight out the side but no question the preferred location is at the highest point of the cooling chamber. This reduces trapped air in the chamber. The same logic used when automobiles went to the external plastic water reservor to remove as much air from the radiator and cooling sustem as possible. Another detail not mentioned here is many high performance Nitro boaters may only have one entrance from the water pickup but offen times had multible exits to reduce any restrictions and lower pressures in the system (water lines, and water fittings). My best boat had the water exit dribbling the exit water over the outside of the engine and out the auto-bailer. Note: water inside the cockpit was not something to worry about, we covered the carb intake but worry about a little water inside the boat? heck no!

Dave

[LOVE6S]

I say the more water you can flow the better, I am gona run some larger dia inlet, hose, and outlet.

[ManuelW]

@ 1945Dave

After a few semesters of Thermodynamics and heat transfer at University I just can 100% agree on your post.

Reducers/Restrictors in cars have a use, but NOT to decrease the flow speed of water for better cooling. This is to increase pressure within the system, otherwise water would start to boil at 100°C and this would dramatically decrease cooling ability.

regards,
Manuel

[HRC]

Well guys I can only share what I have found a few years back when I started making cooling jackets.
Using a test stand with a few different motors (36 mm and 39 mm O. D. for example ) and mounting airplane props to put them under a max. rated amps load on each motor.
With temp. Thermometers on the water intake and exit to check the water temp. in and out as well as temp. sensors at each end of the motors this is what I found.

Each step involved boring out the I. D. of the jacket in .020 increments to find the sweet spot. I eventually reached an I. D. size where the jacket was no longer effective. Exit water temp dropped and motor temp. started rising. This testing told me one can have to much flow. All of the jackets we make have undergone this test.
Just saying.
Dave

[1945dave]

Let me see if I understand you correctly? Are you saying you increased the volumetric dimension of the inside of the cooling jacket and once you enlarged this volumn past the "sweet spot" the motor got warmer and the exit temp of the water got cooler? Is that correct?

A different Dave

[MassiveOverkill]

I could see how in a water jacket how you could get stale pockes of water vs using a coil cooler where water is always forced down a certain path. I wonder if the test was redone with a coil cooler if you'd have different results.

[HRC]

Yes Sir, indicating to me water was not removing as much heat with a larger volume of flow. A constant regulated supply pressure of 30 PSI being used for all test.
Dave

Let me see if I understand you correctly? Are you saying you increased the volumetric dimension of the inside of the cooling jacket and once you enlarged this volumn past the "sweet spot" the motor got warmer and the exit temp of the water got cooler? Is that correct?

A different Dave

[HRC]

Sorry I have not done any testing on coil cooling.

I could see how in a water jacket how you could get stale pockes of water vs using a coil cooler where water is always forced down a certain path. I wonder if the test was redone with a coil cooler if you'd have different results.

[1945dave]

Dave are we confusing flow with volumn? I don't care if your cooling jacket holds 2 quarts or 2 onces if it is a closed system what ever flows in has to equal exactly the same flow out. Also cooler water out is good while a warmer motor is bad. I applaud your efforts and testing but something is missing in your evaluation. You said "I eventually reached an I. D. size where the jacket was no longer effective." I think you meant to say once the interior volumn was large enough any further increase did not result in a cooler motor. That probably would be a correct evaluation. But it has nothing to do with flow just volumn of the cavity. Flow is dependant of the inlet size and exit size only.

Now with your testing you are the right guy to answer this question. How much temp. difference did you detect measuring each end of a motor? Is there a big difference or is it pretty similiar? How would you recommend aligning the cooling jacket? Centered between both ends or closer to the collet end of the power lead end?

1945Dave

[1945dave]

I could see how in a water jacket how you could get stale pockes of water vs using a coil cooler where water is always forced down a certain path. I wonder if the test was redone with a coil cooler if you'd have different results.

Massive, your question follows the thought process of several well known designs in water cooling chambers. The problem with true cooling coil water jackets for our small electric motors is the coils are always very cool but they do not remove the heat from the motor very well due to the tiny contact area actually touching the motor can.

Dave

[Shooter]

Finally, some people making sense.....

Higher flow = cooler water around the motor = higher delta T which is the driving force of heat transfer.

If you have HOT water coming out of your outlet, you need to increase the flow.....unless you want to make coffee. Not trying to heat a little amount of water here, we are trying to cool the motor.

I am very interested in Dave's analysis with the diameters, but am confused as well with the last statement regarding the outlet temp being too cool. This should be a good thing.

[Alexgar]

I wonder if by increasing the volume past the sweetspot the pressure was affect thus slowing down the water and slowing the flow just a thought and basing this on my knowledge of neumatics, as i dont know all that much about the thermal characteristics of water