water cooling efficiency

[Jeepers]

A friend of mine ran a SV27 motor without water cooling after 2 min, it was over 200 degrees F, let the motor cool. ran again for another 2min with water cooling motor temps were under130.

[Simon.O.]

I have read this thread up and down and see the usual argument/discussion about the flow rate etc but the aeration of the water from a prop wash pickup has got me thinking again.
My big cat gets a bit warm when I run the 642 for nuts out runs and as it is a 9XL on 5S then that may have to be accepted.
I may give a hull mounted water pickup a try
Maybe one for the can and one for the esc. I'm not sure yet.
More reading required, again.

My riggers and Canard have to have prop wash pickups obviously and I can accept that.

[ReddyWatts]

As Jay has said: Place the water exit on the cooling jacket at the highest point of the motor, so air can easily escape.

[Jeff Wohlt]

There is no better cooling than a closed loop system with cold ice water in a small container or small nitro tank and mini pump.

Tests have been done and can be found on this forum.

[BHChieftain]

This is another common misconception that leads to compromised results. The water has to stay in contact with the hot components for longer than a fraction of a second or the heat transfer will be poor. Water has a high specific heat, it takes time to absorb it. A short 2" to 3" exit stream is probably cooling a lot better than a 12-15" stream. Regardless of what you think you know, physics trumps "common sense".



.

Hi Fluid,

I'd like to see references for the science you are referring to. From the science I'm familar with, what matters the most is the temp difference between the surfaces, and, that the faster the flow rate the more efficient the cooling becomes (the greater the flow - and thus the greater the cooler mass- the lower the actual temperature differental needs to be in order to move the same amount of heat energy to that mass). I suppose there is some theoretical upper flow rate limit where the internal friction of the water movement affects the heat transfer, but I highly doubt we are anywhere near that limit with our water pickups.

Here's one reference I have that supports my claim-- it is talking about water cooling computer components, but it is the closest analogy I could find.

http://wiki.procooling.com/index.php/Water_cooling:_heat_transfer_basics

Please prove me wrong so I can learn something (unsupported claims don't convince me much).

Either some references, or an experiment you ran would be nice ( it would be a nifty experiment to run a data logger on a boat with 2 diffferent water flow settings, but I don't have one of those).

-Chief

[m4a1usr]

My riggers and Canard have to have prop wash pickups obviously and I can accept that.

I have the same philosophy about some of my riggers/hydros as well. They are over powered anyways. Not like any additional drag would knock off any mph.

On the issue of heat transfer the common denominator or bottom line is neither media (air/water) does enough to cool the components. Does it add run time Vs no cooling to minimize heat damage? Yes it does if your setup is under sized or over powered. The real answer is size your components as to not incur heat damage due to improper application or running excessive amps. Neither media has enough heat removal ability to keep up with the heat buildup. The btu's generated are much greater then the cooling system can remove.

When using the ability of an automobile's cooling system effectiveness as a practical application you must remember that a cars cooling system is sized to run continously. Its sized correctly. The cooling cans on our motors, the aluminum plates on our speedos are not. The delta is not great enough.

There is an old saying in the refer business. The innsie's have to equal the goes outsie's. If you havent heard it or worked the biz it means the cooling rate must be at least equal to the heat being generated. That applies to our applications as well if your going to debate which cooling media is most effective.

John

[ReddyWatts]

That is why I like to use both fan and water cooling on high power setups.

[ReddyWatts]

Automotive water cooling myth

Quote: The myth of velocity originated among those unschooled in physics or
thermodynamics, I suppose, because a common racer "solution" is to
press a fixed restriction into the thermostat housing neck when no
thermostat is desired. The conventional (but wrong) wisdom is that
the restriction "slows the water".
In reality, all it does is provide some more dynamic pressure in the
block by restricting the flow. The exact same result could be
accomplished (assuming the water pump doesn't surge or cavitate)
with a higher static pressure (cap pressure), assuming the system
could withstand it.

http://yarchive.net/car/engine_water_restrict.html

Quote: The most common myth is: I have to slow the water down to help it cool. If this is the case; some is good more is better. Just stop the water. As silly as this sounds there people that suggest you do exactly that. Remember what you are cooling. You are not cooling the water you are cooling the engine. A running engine develops a lot of heat. The exhaust temperatures on well tuned race engine can be at 1300 degrees. On the other side of that exhaust port is a water jacket. If the water was to move too slow or be stopped, it would take no time at all for the heat to be transferred to the water. The best coolant and the best pressurized system will still have a boiling point below 300 degrees.
The higher the water flow the better for cooling. Remember a water pump's job is to move the hot water out of the block to the radiator.

http://www.nhraunleashed.com/profiles/blogs/drag-racing-cooling-systems

[rearwheelin]

I once thought about making a small air scrubber tank for my 34'' sprint cat with a inline rudder to help with cooling ifficiancy.I would conect the line or lines from my water pickups to the upper side and water would fall down and air goes to the top and out threw a small hole and water with no air out the bottom. The can would have to be like a lopsided rectangle.Aluminum braising would be a good way to make.