Not to quibble the effects of humidity versus cooling (I don't know what they are), but humid air is LESS dense than dry air. The reason is that the partial pressure of water vapor is less than that of dry air. The only question I missed on my parachute riggers exam!

Flinch

 

Looks like that one missed question turned out to be a lifetime remembered lesson! It seems natural to assume that humid air is denser than dry air, even when science has found and proven the opposite to be true.

Mark, do you have an explanation that would help us make better sense of Ford's or your reasoning behind what you stated earlier?

 

OK, I didn't know that. You're right, humid air is less dense than dry air. Who knew?

I assumed that the opposite was true, and look where it got me. I'm wrong. I hate when that happens!

I do know for a fact that the Ford cooling tests always have a maximum humidity that the test may be run at. I just did some internet research and found the reason. It isn't because humid air is denser (it isn't,) it is because humid air has more heat capacity. It can absorb more heat than dry air. Here is an article from a meteorologist at the Argonne National Laboratory that explains this. Humid Air, Heat Capacity, Kinetic Theory

 

Misters. I went to Six Flags one year and they had the fans with misters in front of them along the walkway. It sure helped to keep the cool as we walked.

The evaporation would cool the engine - regardless of density. I never speculated on the density of the air, (which it sounds counterintuitive to me) - but I know all too well how humidity under the right conditions can help or hinder cooling. Anybody who has been in the South or the Midwest on those 85-degree days with 100% humidity knows how miserable that is. I'll take 106 degrees with low humidity every time. That's for people with sweat glands - not for an engine that moves through the air with mechanical cooling devices in the nose.

Water transfers heat 25 times faster than air does, so a moist air will suck the heat out of a radiator, AC condenser, and CAC faster than dry air of the same temperature. That's the heat transfer side - that doesn't account for the cooling effects of evaporation. Once you add the cooling effects of evaporation, humidity it the engine's friend.

Humidity that gets sucked and charged into the engine has an effect on the combustion cycle, but I'm not the guy to explain that one - because it involves conflicting effects, like steam, compression, slowed combustion, etc....

 

As humidity increases, the thermal conductivity of air decreases. Below about 105F, the difference is pretty minimal, though.

The Thermal Conductivity of Moist Air « Electronics Cooling Magazine - Focused on Thermal Management, TIMs, Fans, Heat Sinks, CFD Software, LEDs/Lighting Electronics Cooling Magazine – Focused on Thermal Management, TIMs, Fans, Heat Sinks, CFD

I don't see how humidity could contribute any evaporative cooling effect. The water in humid air is already a vapor, so there's no further state change to absorb any heat energy.

 

That thread is good info, but it doesn't take into account what our trucks do - heat the cooling fins to 200+ degrees F (95 C) and pass cooler moist air over it rapidly. That moisture is going to evaporate.

 

My thinking is that since humidity is already vapor in the air; it can't evaporate beyond that state. Fog or rain, on the other hand would.

 

Humidity can't evaporate. It is already a vapor. Liquid water can evaporate, not gaseous water.

 

Once again, I have been a shining example of why one should not take everything you read on the internet as gospel. In my attempt to suss this out, I was focused on the fact that warmer air can have higher moisture content than cooler air can. That's why cold drinks "sweat", the cooler air near the drink can no longer "hold it's water". We're not talking bout water here, we're talking about water vapor - which the radiators on our trucks can not alter, because we can only increase the temperature.

Nothing to see here, folks... move along. Just a member mooning himself.

 

Dude,

you are thinking and trying and investigating, yes you will make mistakes, but as long as you learn from them it is fine (provided said mistake does not kill you) If you never try, where would you be? that is the question you need to ask yourself everyday, did I make an attempt?


cheers
ken

 

I'm not sure if my truck likes humidity or not,but I hate it!
Central florida is miserable this time of year.

I have a 6.0 cooler, otw cooler, & a BTS trans. I'll see 150-190 pulling nothing on my drive to work. It's different every day & generally my gauge reads 20-ish degrees cooler than AE.

Honestly I wouldn't worry about those low temps your seeing. Your gauge may be fibbing a bit.

 

The assumption being that the lower temp reading are wrong and the higher readings are right?

I too was concerned after I installed my trans temp gauge was reading too low, it would not even leave the peg at 100 degrees. I installed it in the winter time when outside temps were in the 40's.

I don't know how scientific it was but I heated some oil in a pan to 200 degrees and dropped the trans temp sensor in the heated oil. the gauge read 200 degrees.

I now live in a warmer area 97 here today and I prefer that it runs on the cool side.