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Old 08-21-2013, 03:43 PM   #19531
GrahamD
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Originally Posted by Tim View Post
Nope attending the Ténére 30th party in Switzerland
Cool, but don't do <--- Too often will you?
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Old 08-21-2013, 04:15 PM   #19532
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Originally Posted by Wreckchecker View Post
The point was simply that humidity does make a difference in the efficiency of getting rid of engine heat.
The question is whether the efficiency of a liquid-to-air heat exchanger (a radiator) or an solid-to-air heat exchanger (cooling fins on an air-cooled bike) is affected by moisture in the air. I doubt it does, but really don't know for sure. (There is probably some small effect because the specific-heat of water vapor is different than air, but given the small amount of water vapor by mass in a parcel of even saturated air, it shouldn't be much.) Heat pumps are an entirely different deal which work on completely different thermodynamic principles, so sorry, but I don't think they're relevant to the discussion.

- Mark

markjenn screwed with this post 08-21-2013 at 04:20 PM
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Old 08-21-2013, 05:10 PM   #19533
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***Edit: These were bad numbers for a evap system not a closed loop***********

Reddog* screwed with this post 08-21-2013 at 07:06 PM Reason: Sorry markjenn
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Old 08-21-2013, 05:12 PM   #19534
markjenn
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Well seeing how a cooling tower is just a giant stationary radiator, we can use the design of those to prove yes cooling is affected by relative humidity.
Sorry, but again, mostly irrelevant. Cooling towers work by evaporative cooling. A vehicle radiator does not. Totally different thermo principles.

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Old 08-21-2013, 06:01 PM   #19535
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See post #19540

Reddog* screwed with this post 08-21-2013 at 07:04 PM Reason: fixed from more studying
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Old 08-21-2013, 06:28 PM   #19536
GrahamD
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Originally Posted by markjenn View Post
Sorry, but again, mostly irrelevant. Cooling towers work by evaporative cooling. A vehicle radiator does not. Totally different thermo principles.

- Mark
Just my suspicion, but I would have thought that air at a certain temperature with a higher humidity may be able to capture MORE heat than dry air at the the same temp in NON evaporative applications.

Yep found it. but it's a negligible difference.

Quote:
Air has a specific heat capacity of slightly more than 1kJ/kgk at room temperature
So it takes a 1kW heater 1 second to heat 1kg (roughly 1 m^3) of air 1 deg C

Fairly humid air (say 60% RH at 20C) will contain around 10g/m^3 of water vapour with a specific heat capacity of 1.8 kJ/kgk - so it takes almost twice as much energy (per unit mass) to heat the water in the air than the dry air itself.

But, only 10g in every 1kg of air is water vapour ( ie 1%) so you only have to do twice as much work to that 1%.

In other words - no you won't see any measurable difference.
Well in a lab you would see measurable differences it depends on your equipment doesn't it.

Glad to see all the professors out and about doing peer reviewed science.
Another thousand posts and we should have the the subject nailed.

Anyway, my take at this point is..

Ride More, Use good oil, Keep the cooling system in top nick, Worry less
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GrahamD screwed with this post 08-21-2013 at 06:39 PM
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Old 08-21-2013, 06:46 PM   #19537
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Forecast tomorrow is 95F 90% humidity. 50% rain.

Now here is my question.
Will my bike be operating at a higher temp if I get lucky and miss the rain? (90% humidity) Or if I get soaked. (100% humidity?)

Just messin with ya.
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Old 08-21-2013, 07:03 PM   #19538
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Originally Posted by markjenn View Post
Sorry, but again, mostly irrelevant. Cooling towers work by evaporative cooling. A vehicle radiator does not. Totally different thermo principles.

- Mark
That was suppose to be dry towers/closed loop. To much fine print and I buggered the numbers reading charts.

At a given temp that we can live in say up to 100F, 0% to 99% humidity changes the rate by less than 2%.

So it would not be noticed in any thing less than a lab as Graham pointed out.
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Old 08-21-2013, 08:23 PM   #19539
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At a given temp that we can live in say up to 100F, 0% to 99% humidity changes the rate by less than 2%.
Sounds about right. Interesting discussion.

- Mark
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Old 08-22-2013, 08:35 AM   #19540
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Originally Posted by Dallara View Post
Well, that would be true if it weren't for one minor detail...

On almost all liquid-cooled engines there is always some method to allow a certain amount of "bypass" to occur somewhere in the area of the water pump. On many cars it is as simple as a bypass hose, but on most motorcycle engines it is some sort of small casting divot or a simple hole across the intake and exhaust side of the pump. On some bikes it is even done at the thermostat housing, but one or the other, it's there (except for some race bikes that have no thermostat).

Why, you may ask?

When an engine starts cold, before the thermostat begins to open, if the engine were designed as you describe, coolant would sit stagnant and would not move at all. We know that we want the coolant to stay in the engine block so it will warm up quickly, but some coolant must circulate. If it didn't circulate, and remained completely stagnant, localized areas around the cylinder head would literally boil coolant and create steam pockets, quickly superheating the area and causing metal fatigue and component failure. Incorporating a simple bypass arrangement that allows just a small amount of circulation of coolant within the block before the thermostat opens and allows circulation through the remainder of the system.

Further, if there was not some sort of bypass the pump would suck the coolant return hose shut, so the bypass acts as a bit of a negative pressure "bleed" to avoid this.

Don't believe me? Look it up.

Hope this helps!

Dallara

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Old 08-22-2013, 08:42 AM   #19541
true grip
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Pluric to the rescue!

This thread had turned into science weekly. Just kidding guys
My wife would say that is just one more way to kill yourself more fun than a fork or spoon
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Old 08-22-2013, 08:54 AM   #19542
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Pluric to the rescue!

This thread had turned into science weekly. Just kidding guys
My wife would say that is just one more way to kill yourself more fun than a fork or spoon
I don't know about the rest of you, but this is how I picture Dallara.....



Not that that's a bad thing he does seem to know his shit.
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Old 08-22-2013, 10:16 AM   #19543
TH
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Not that that's a bad thing he does seem to know his shit.
Isn't that a proctologist?
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Old 08-22-2013, 10:24 AM   #19544
pluric
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Isn't that a proctologist?
Not to get technical and start three pages of responses, but I think you mean Scatology.

The study of ones bypass. Normally it comes from a closed system that is controlled
by the bodies thermostat. If you have a faulty system it circulates prematurely and
causes your ride to end faster than you had planned. Beware of the air bubbles in the
system as they cannot be trusted to only vent excess system gas.
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Old 08-22-2013, 10:27 AM   #19545
Dallara
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Laugh It's a tough job, but somebody has to do it...

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Isn't that a proctologist?


Well, somebody has to take care of all you a**holes...







Dallara


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