Okay okay thank you again guys, this discussion is getting more and more interesting and multidimensional.
Let me summarise some of the contributions that are directly relevant to this crazy idea:
1. Water (+Methanol…) injection inside the inlet would be the perfect solution, but this be would completely impossible to get signed off.
2. Some of us believe that spraying a fine water mist on the radiators will not result in evaporation due to the fact that the surface is not hot enough. Therefore massively lower cooling effect. I fully understand their point, this must be tested.
Can anyone point me to the boiling temperature of water at FL100 ISA? As I said before, the system will not be used unless the temperature of the fluids is in excess of 100° C, so the question is how much more is that vs the boiling temperature and is the delta enough. Maybe it will be possible to even calculate the amount of water that must not be exceeded.
3. The issue of this water freezing has also been raised. After giving it a hard thought I believe this will only be a potential problem at the nozzle level, and here my reasoning:
- I routinely fly in heavy rain. This is a lot more water throughput then I could possibly spray on the radiators, and none of this causes any icing issues.
furthermore I will be spraying very small amounts (1 liter/min) and only when the engine compartment is hottest, so that whatever water is being expelled will have been thoroughly heated.
And finally, all three radiator outlets flow very far away from lifting/control surfaces.
- As to the nozzle, indeed, there may be a problem related to the cooling effect if vaporising water
if and when this project reaches the point where things will go in the aircraft I will make sure to position the nozzle in an area where ambient air temperature is very high – very easily done in this aircraft! I will also select a pump that will not explode in case the output gets clogged and test for this.
As do the experiment itself I was thinking of starting by heating up the (empty) radiator to simulate the above mentioned Delta with a heat gun (so it would be 105 C or so?) and spraying some water on it using a gardening spray tank to see what happens and filming in slomo …
To me, the biggest problem in cooling the radiator is the amount of heat that can be dissipated this way. Heat is carried to the radiator by the oil, so to dissipate more heat, you may have to increase the oil flow in the first place. Specific heat capacity c of mineral oil is about 1.7 kJ/(kg·K). If you cool this oil by ∆T, then the power dissipated is P = Q · c · ∆T, where Q is the mass flow of oil (kg/s). A quick calculation shows that, for example, in order to dissipate 40 kW with ∆T = 50°C, you need to pump 35 L/min of oil through the radiator. Will the oil pump have a sufficient throughput for your needs?
“The water molecules themselves don’t care if they transition to gas form due to an external heat source or because they pop out of the surface. For them it is the same”
Physics 101 suggests water molecules won’t “jump out of the surface” if their kinetic energy isn’t sufficient to go through the phase change. Molecular kinetic energy is proportional to heat. Heat has to come from somewhere.
T28 wrote:
Physics 101 suggests water molecules won’t “jump out of the surface” if their kinetic energy isn’t sufficient to go through the phase change. Molecular kinetic energy is proportional to heat. Heat has to come from somewhere.
Water molecules don’t all have the same kinetic energy even if the temperature is constant throughout a volume of water. The molecules that “jump out” will have higher kinetic energy. The result, as we all know, is that the volume of water loses energy, i.e. it gets colder.
Flyingfish wrote:
Can anyone point me to the boiling temperature of water at FL100 ISA?
FL100 is approximately the 700 hPa level. The boiling point of water at 700 hPa is 90°C.
Flyingfish wrote:
- I routinely fly in heavy rain. This is a lot more water throughput then I could possibly spray on the radiators, and none of this causes any icing issues.
Well you surely do not routinely fly in rain in sub-zero temps. I believe even if vaporized at the radiator, most of this water will freeze when in contact with sub-zero surfaces. That may or may not be a problem depending on where on t he airframe, but you will likely carry that ice for the rest of the flight through to your descent below freezing levels.
If I understand correctly, the issue is you would like to have more cooling power so you can perform longer and higher climbs at low IAS and high VS, right? This is common to all TN and TC piston aircraft.
Maybe there is a more straightforward way to partially address it. Unlike RSA-5 systems and the like ,our TSIO 520 /550 simple Bendix fuel injections systems are fuel-pressure sensitive, so if you increase fuel pressure you will get more fuel flow. When flying ROP, this is similar if perhaps a bit less effective and more expensive than water-methanol injection. I just use the electric fuel boost pump on low or high and then adjust with mixture to get the required cooling effect, at the expense of increased fuel flow. Could this work for you? At least the system is already installed on the aircraft!
Evaporation vs boiling explain once and for all 
Thank you for making my point LeSving. Minute 1:23. “Some particles will be moving very quickly”. What in your youtube-educated guess makes said particles move “very quickly” and where does it come from?
@Airborne_again I agree with you but in the absence of an outside source of heat (i.e. absolute zero temperature) I believe there wouldn’t be any significant kE delta between the particles.
T28 wrote:
What in your youtube-educated guess makes said particles move “very quickly” and where does it come from?
LeSving is correct. The YouTube video is, too. I know you can’t expect that, but occasionally it happens.
The random movement of molecules in water causes collisions which mean that they will transfer kinetic energy between each other, so there will be a random variation in kinetic energy.
Read all about it in Wikipedia.
