Best water pick-up ever!

[H&MWill]

This thread is great everyday i read more and become more confused! Nah just jokin but it is interesting.

[properchopper]

Part of the conflict between the "slower flow/faster flow" controversy here is the possible confusion in considering and differentiating between flow rate and latency in the cooling/heat exchange environment. While it's possible to vary the flow rate by controlling the variables of inlet/ outlet size, tubing size (diameter) and length, the input pressure ( which ties to the final flow rate when combined with these variables) should be viewed as a constant, given , let's say a WOT run. [ Yes, I'm aware that heat generation is moderated by throttle position, but to keep things simple, I'm leaving WOT as a constant in this example]. Hence, the only way to control flow rate is to play with these variables. I stand by my statement that the longer the cooling medium (water in the cooling jacket or SC tubes) stays in contact with the device to be cooled ( motor/SC), the more transfer of heat, e.g. cooling) will take place. Since my "finger on the motor" and "walking on hot coals" example failed to convince some on this, let's go to the good ole' french fry out the window experiment. Simply stated, a french fry held out the window for ten seconds will be cooled more than one held out for only one second. It cooled better when it was in the cooling medium/environment LONGER. Since, in the case of r/c boats we can only vary the heat exchange TIME by controlling the flow RATE, I have concluded that a slower rate allows for better cooling.

I have a simple experiment in mind to gather actual empirical data to support this using my leak tester apparatus, which connects to my kitchen sink faucet. Problem is that in five days I'll be racing five boats in five classes in AZ and my plate is currently full with final testing/tuning and the butterflies are starting to do the Macarena in my stomach so it'll have to wait

[egneg]

Your french fry example is a bit off. The air going past it is not warmer do to restricted flow. For example if you hold one out the window and one near the window where there is less air flow it will take longer to cool than the one out the window.

[properchopper]

Your french fry example is a bit off. The air going past it is not warmer do to restricted flow. For example if you hold one out the window and one near the window where there is less air flow it will take longer to cool than the one out the window.

The speed of the airflow near the window in your example is slower than the speed of the airflow out the window. If the speed of the flow is held constant
{ as it is in a boat setup once installed}, the TIME in the flow is the critical factor, at least as I see it.

[keithbradley]

Since, in the case of r/c boats we can only vary the heat exchange TIME by controlling the flow RATE

This makes no sense, nor does the example about holding a french fry out the window longer...Regardless of flow rate, the time that the cooling media is exposed to the heat source is the same: A-L-L ---- T-H-E ----T-I-M-E. Slowing the flow rate does not do anything but raise the temperature of the cooling media.
The equivelant to stopping exposure of the french fry to cool air would be STOPPING the flow rate, not raising it.

I have to beleive at this point that this is just a matter of looking at things with a confirmation bias. I don't know how its not crystal clear, unless some people just want to hold on to their belief so much they refuse to look at this objectively.

[egneg]

But the speed of the water flow isn't a constant. It is being slowed down by the size of the tubing or whatever. The constant is the volume of the water jacket or ESC tubes. The time it takes for a complete exchange of water takes longer with smaller tubing ergo higher outlet temps. The more times this volume can be exchanged in a given time period the more efficient the cooling will be.

[properchopper]

In response to " Slowing the flow rate does not do anything but raise the temperature of the cooling media" : Maximally raising the temperature of the cooling media is what is desirable in this model. Where does the heat in the cooling media come from ? From the object to be cooled. The hotter the cooling media becomes from extracting heat from the object to be cooled, the cooler the object to be cooled becomes from this transfer and the more efficient the system is. Of course a closed loop system in a car doesn't hold to this, so closed loop systems won't be a good comparison, and of course the boat system is a total-loss configuration.

[keithbradley]

Ok, here we go...

There is an elementary equation from basic thermodynamics that states that the rate of heat transfer (Q) equals the mass flow rate (M) times a Constant (the specific heat of water) times the Delta T (fluid temp out minus fluid temp in):


Q = M x C x Delta T

In other words, the rate of heat transfer is directly proportional to mass flow rate. If you increase the flow rate, you will then increase the rate of heat transfer. Since you cannot mess with mother nature, it is very naive to think it works any other way.

Assume the object being cooled inserts a constant rate of energy (Q) into the cooling system. Then, from the relationship above, increasing the mass flow rate must result in a smaller delta T because Q remains constant. This smaller Delta T (fluid out – fluid in) also means that the average fluid temperature coming out is somewhat lower even though the rate of heat transfer has not changed.

Now let’s look at the heat transfer from the source to the water:

The rate of heat transfer between two points is proportional to the temperature difference between those points.

In our case, this Delta T (not to be confused with the one above) is the temperature of the heat source minus the average water temperature coming out of the heat source. Lowering the average water temperature, as we did above by increasing the flow rate, means we have a little better heat transfer from the heat source to the now somewhat cooler water. The result is that the heat source becomes cooler.

This all says that if you increase the flow rate and everything else remains constant, you will decrease the heat source temperature.

NAIL ---------> COFFIN

[properchopper]

OK, sounds convincing. Bottom line, I'm heading to the lake for some test/tune
H2O therapy. Have a good one !

Ok, here we go...

There is an elementary equation from basic thermodynamics that states that the rate of heat transfer (Q) equals the mass flow rate (M) times a Constant (the specific heat of water) times the Delta T (fluid temp out minus fluid temp in):


Q = M x C x Delta T

In other words, the rate of heat transfer is directly proportional to mass flow rate. If you increase the flow rate, you will then increase the rate of heat transfer. Since you cannot mess with mother nature, it is very naive to think it works any other way.

Assume the object being cooled inserts a constant rate of energy (Q) into the cooling system. Then, from the relationship above, increasing the mass flow rate must result in a smaller delta T because Q remains constant. This smaller Delta T (fluid out – fluid in) also means that the average fluid temperature coming out is somewhat lower even though the rate of heat transfer has not changed.

Now let’s look at the heat transfer from the source to the water:

The rate of heat transfer between two points is proportional to the temperature difference between those points.

In our case, this Delta T (not to be confused with the one above) is the temperature of the heat source minus the average water temperature coming out of the heat source. Lowering the average water temperature, as we did above by increasing the flow rate, means we have a little better heat transfer from the heat source to the now somewhat cooler water. The result is that the heat source becomes cooler.

This all says that if you increase the flow rate and everything else remains constant, you will decrease the heat source temperature.

NAIL ---------> COFFIN

[hyrulejedi86]

I understand both points of view and in the end a combination of both theories is what's working here. But from what I see if Q rate of heat transfer then wouln't allowing the water to sit on the motor longer (resulting in hotter water leaving the system) increase Delta T resulting in a higher Q? The question is how much higher compated to increasing M instead.

[keithbradley]

wouln't allowing the water to sit on the motor longer (resulting in hotter water leaving the system) increase Delta T resulting in a higher Q?

Simple answer, no.

Delta T in the equation will increase at a rate relative to decreased flow rate. The slower the flow rate, the LOWER the delta T will be between the heat source and inlet water, which lowers the cooling efficiency. What I'm saying is by raising the delta T in the equation, "M" will always be lowered at a greater rate, resulting in a Lower Q. It wont work to a greater degree becuase the delta T between the heat source and inlet water temps is less. Its not physically possible.

[keithbradley]

OK, sounds convincing. Bottom line, I'm heading to the lake for some test/tune
H2O therapy. Have a good one !

Im jealous! Our "cooling system" is too efficient here in Michigan. Our water will be hard for another month or two.
Enjoy the california weather!

[Joeyhatch11]

Is it worth going through the trouble of adding an extra cooling system that'll be directed to just the motor or ESC rather than having one system that flows through everything? I have a stock SV27 on the way that only has the rudder pick up and was going to add this system. Was even thinking of using the pick up as an outlet too, as mentioned in the top post. Thanks guys, Joe

[forescott]

Is it worth going through the trouble of adding an extra cooling system that'll be directed to just the motor or ESC rather than having one system that flows through everything? I have a stock SV27 on the way that only has the rudder pick up and was going to add this system. Was even thinking of using the pick up as an outlet too, as mentioned in the top post. Thanks guys, Joe

I added the transom mount water pickup from the supervee nitro version to my sv a long time ago. The stock rudder pickup would lose pressure when turning the opposite direction of the rudder pickup hole, and flow was minimal. After I added the nitro pickup, the flow inreased dramatically and was drastically improved. Especially at low speeds!

[Joeyhatch11]

If I go with the transom or under hall mount system, what diameter hose do I need? Thanks, Joe