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

[T.S.Davis]

Yeah, it's a fun discussion but there are many ways to reduce heat. A simple prop mod or a 1/2 degree of strut can have more impact on heat then the speed that your water is traveling through the system.

[Shooter]

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.

Hi Peter! It might be a matter of where you were measuring temps. Was your thermal couple measuring the water temp coming out of the motor? If the flow was slower, the water would be hotter for sure (coffee maker).

[Doug Smock]

A simple prop mod or a 1/2 degree of strut can have more impact on heat then the speed that your water is traveling through the system.

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[domwilson]

[ATTACH=CONFIG]135056[/ATTACH]

That's funny. Sometimes we just have to step back and wonder...Am I putting too much thought into this?

[Doby]

That's funny. Sometimes we just have to step back and wonder...Am I putting too much thought into this?

Yes...

[Peter A]

Hi Peter! It might be a matter of where you were measuring temps. Was your thermal couple measuring the water temp coming out of the motor? If the flow was slower, the water would be hotter for sure (coffee maker).

Yes we measured both the water coming out and the 'motor' temp.

[lt130th]

Yes we measured both the water coming out and the 'motor' temp.

Nata2run pretty much said it all in his last post. There's no blanket rule for all systems. Any system can be modeled mathematically with equations for heat transfer & fluid mechanics. The outcome of your science experiment has many variables that must be considered because heat transfer does seem like magic, sometimes yeilding counterintuitive results...jst like the cooling for spindles & tooling in CNC mills & lathes as he stated. I was wondering (just personal curiosity), how many points in the system were being measured, and where. I assume there was a pump in the circuit. Were temps measured before & after the pump at different outputs? Also, I was wondering about the volume of the cavity inside the jacket. Reports published in ASME, IEEE, AIAA journals, etc are overly detailed for a reason. Typically your goal is to present your process such that another engineer can recreate your experiment and acheive the same results. Of course we aren't going for that here, but without more details there are a lot of questions (not doubt, just questions). We can make this as complicated as we want & throw boundary layer analysis into the mix, but in the end, none of us really care to go through all that for an RC boat. I don't, haha, and this kind of thing is what I spent five years of my life in college for. I'd rather shoot water through the ESC & motor jacket as fast as the pickups can scoop it up because it's not a couple million dollar CNC or rocket nozzle.

[Peter A]

Nata2run pretty much said it all in his last post. There's no blanket rule for all systems. Any system can be modeled mathematically with equations for heat transfer & fluid mechanics. The outcome of your science experiment has many variables that must be considered because heat transfer does seem like magic, sometimes yeilding counterintuitive results...jst like the cooling for spindles & tooling in CNC mills & lathes as he stated. I was wondering (just personal curiosity), how many points in the system were being measured, and where. I assume there was a pump in the circuit. Were temps measured before & after the pump at different outputs? Also, I was wondering about the volume of the cavity inside the jacket. Reports published in ASME, IEEE, AIAA journals, etc are overly detailed for a reason. Typically your goal is to present your process such that another engineer can recreate your experiment and acheive the same results. Of course we aren't going for that here, but without more details there are a lot of questions (not doubt, just questions). We can make this as complicated as we want & throw boundary layer analysis into the mix, but in the end, none of us really care to go through all that for an RC boat. I don't, haha, and this kind of thing is what I spent five years of my life in college for. I'd rather shoot water through the ESC & motor jacket as fast as the pickups can scoop it up because it's not a couple million dollar CNC or rocket nozzle.

Ok so it was a year 8 science experiment. Yes we measured the water temp in, (tap water by the way), measured the water temp out after 1 minute into a bucket. Measured the amount of water to calculate the flow. All really simple and not University degree level, but it gave some basic results that anyone can try and I would think that you will get similar results without a lot of juju mumbo jumbo. I guess if there are those who really need to prove it this way or that, then set up a (scientific as you want) experiment and settle the discussion for everyone. Theory is only theory until proven one way or another. Always the proof is in the pudding, and real on water testing and tuning is what will get optimum temps, as has already been said.

[lt130th]

Ok so it was a year 8 science experiment. Yes we measured the water temp in, (tap water by the way), measured the water temp out after 1 minute into a bucket. Measured the amount of water to calculate the flow. All really simple and not University degree level, but it gave some basic results that anyone can try and I would think that you will get similar results without a lot of juju mumbo jumbo. I guess if there are those who really need to prove it this way or that, then set up a (scientific as you want) experiment and settle the discussion for everyone. Theory is only theory until proven one way or another. Always the proof is in the pudding, and real on water testing and tuning is what will get optimum temps, as has already been said.

Here's why I asked for more details. If you're measuring the water temperature before & after the jacket, & the exit temps increase, that means more heat has transferred to the fluid. Assuming the glow plugs heating the pseudo motor were given time to reach steady state before the water was introduced, then the heat output of the motor was the same at all rates of fluid flow in the experiment. Therefore, if exiting water was warmer at a higher rate of flow, then your motor was being cooled better than at the lower rate if flow.

[Peter A]

The water was warmer at lower flow rates, and the 'motor' cooler. The 'motor' was heated to temp before water was flowed through it. Hence the results being that lower flow rates cooled better.

[nata2run]

Lol I think I will still stick with my very simple motto, if you can easily blow, then go! Having very little resistance in the cooling line will help the system to circulate a bit easier. Most times hulls enter and leaves the water randomly anyways, so there is no constant or measurable amount of water pushed through, (like testing with a pump) it's basically hope it stays cool, and not exceeding the rated current draw. "Too much"

[lt130th]

The water was warmer at lower flow rates, and the 'motor' cooler. The 'motor' was heated to temp before water was flowed through it. Hence the results being that lower flow rates cooled better.

Gotcha! Thanks.

[Nikolas Andriop]

At my cat I use this brushless pump with remote control at 5S almost a year now and keep going just fine
Since I use it I have any issue with temperature
The weight of the pump is only 40 grams

http://pages.ebay.com/link/?nav=item.view&alt=web&id=201154196791&globalID=EBAY-US

[SD Eracer]

Wow Nikolas, that is cool! Does it allow water to flow should the pump break down?

I was thinking about a pumping system as well, mainly because I see just how much a little bit of fresh water can quickly cool down everything.

Since I run exclusively in saltwater, after checking temps after each run, I pump fresh water through my cooling system using a portable pump sprayer (which I use to also wash down the boat from time to time), and I am amazed how quickly the temps drop.

After a full 6S SAW run, my motor & ESC temps will go from 120F to 90F in about 15 seconds! I can imagine how beneficial it would be to have water constantly moving through the system no matter what the boat is doing.