Another thermodynamics question...



16 replies to this topic
  • MN_Kevin

Posted March 31, 2001 - 12:03 PM

#1

Here you go.
Two identical ice cubes.

One is in an environment of 70F, with 10% humidity.

The other is at 70F, with 90% humidity.

Which will melt first?

First off, the lower humidity will cause the "laminar boundary layer" of (liquid) water to evaporate quicker, thereby exposing the iced layer quicker... (so will evaporation have any effect?)

The second ice cube will have the 70F heat transferred more rapidly due to the higher humidity levels and more efficient transferance of heat, BUT the water will evaporate at a slower rate and expose the "fresh" ice slower...

I have asked this to a lot of people. I get one of three answers, the first cube, the second cube or same melting rate.

I really have no idea.

Any takers?

[This message has been edited by NH Kevin (edited 03-31-2001).]

  • bhunt

Posted March 31, 2001 - 12:28 PM

#2

Originally posted by NH Kevin:
Here you go.
Two identical ice cubes.

One is in an environment of 70F, with 10% humidity.

The other is at 70F, with 90% humidity.

Which will melt first?

First off, the lower humidity will cause the "laminar boundary layer" of (liquid) water to evaporate quicker, thereby exposing the iced layer quicker... (so will evaporation have any effect?)

The second ice cube will have the 70F heat transferred more rapidly due to the higher humidity levels and more efficient transferance of heat, BUT the water will evaporate at a slower rate and expose the "fresh" ice slower...

I have asked this to a lot of people. I get one of three answers, the first cube, the second cube or same melting rate.

I really have no idea.

Any takers?

[This message has been edited by NH Kevin (edited 03-31-2001).]


Yes the Wr426F will go faster. :)

  • Guest_Guest_*

Posted March 31, 2001 - 01:27 PM

#3

I thought this was a dirt bike site...but I'll bite. I would think they would melt at the same rate..But the water left behind will evaporate quicker at 10% RH than at 90% RH [only If you have the same cfm in air changes].A btu is a btu.

  • mikeolichney

Posted March 31, 2001 - 01:32 PM

#4

Did I get on a thermo forum by accident? My guess is that there is not enough info, it might depend on if the melted water is allowed to run off or not. This is probably a fairly complicated problem. Laminar boundary layer is the fluid region next to a moving object before there has been sufficient distance for the transition to turbulence (low Re #s). Ussually this refers to the air adjacent to a projectile or airplane wing, I don't think that is relevant here. The melting water moving over the ice will not be anywhere near turbulent. If I had to guess? My vote is that the more humid air will let the ice melt slower.

  • Bill

Posted March 31, 2001 - 02:37 PM

#5

Man, you can tell New Hampshire has gotten to much snow this year. Or Kevins been using contact cleaner with the garage door closed again :)

Hey, Buddy :D

Bill :D

------------------
97 KDX220, 86 TTR225, 99 WR400f, WR timing, throttle stop trimmed, air box lid removed, White Bros head pipe, silencer and air filter. De-octopussed. Works frame guards and Thumper Rad Guards, Scotts steering damper. Odometer and headlight removed. Moose hand and mud guards. YZ stock tank, IMS seat and number plate. Renthal Jimmy Button "highs" and Renthal Soft half waffle grips. AMA, SETRA, Happy Ramblers MXC.

  • MN_Kevin

Posted March 31, 2001 - 03:19 PM

#6

Mike,
I used the term laminar boundary layer loosely to allow the reader to get a better understanding of the formed layer of water that would cover the top of the ice cube. In a hydraullic system, the layer is that which resides against the (internal) walls of the pipe. The higher velocity liquid would be passing through the center of the pipe. That's all.

Bill is right. I have too much time on my hands! We were dumped on by at least 15" more of snow at my house. I think we had something like 40 - 50" already! Just when it seems the snow is going away, another Nor'easter hits us!

Good news though, I got a friend's kid's TTR225 running. After all the work I did, it turned out he dumped crappy, old gas into the tank. He had put new fuel into the tank, but didn't drain the carb. I had checked for fuel flow (opening up the carb drain) but hadn't drained enough to get rid of the yellowed gas that was in there.

The thing has a real, goofy carb. It has no fuel screw, no air screw and a NON adjustable needle. Talk about screwed up! At least two of the ports on the inside of the carb have been sealed by the factory. I suppose for EPA reasons...

[This message has been edited by NH Kevin (edited 03-31-2001).]

  • Bill

Posted March 31, 2001 - 04:05 PM

#7

Kev,

I feel your TTR blues. I have one, an 86, I used to teach Wiiliam to ride on. That dang thing would run with the choke on or off. You couldn't rev the motor for about 10 minutes when you first started it.

The thing is a fuel atomization mystery. Oh well. it's been parked for the KDX. Now we just need some weather to ride in.

Mikes coming down next weekend and we're going to check out the riding areas for June. Stay tuned!

Bill

  • Guest_Guest_*

Posted March 31, 2001 - 08:10 PM

#8

UPON APPLYING THE PRINCIPALS OF THERMODYNAMIC CHEMISTRY TO THE PROBLEM OF THE LAMINAR LAYER EFFECTING THE BTU RELEASE RATE OF TWO ICE CUBES IN A DIFFERENT ATMOSPHERIC ENVIRONMENT I QUICKLY CAME TO A STARTLING CONCLUSION, I HAVE NO FRICKING IDEA WHICH ONE WOULD MELT FASTER!!!

I DO KNOW THAT I'M GOING RIDING TOMORROW, AND I'LL FEEL REALLY BAD FOR YOU KEVIN.

OH BY THE WAY, SINCE YOU HAVE SOME NUCLEAR KNOWLEDGE, IS THE BEST PREVENTITIVE FOR THE INTERNAL BOMBARDMENT OF RADIOACTIVE PARTICLES, THROUGH THEIR CONTAINMENT BY A HYDROCARBIN???

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • joecallan

Posted March 31, 2001 - 09:35 PM

#9

I would go with 70deg. 90% humidity and I'm almost positive. Moist heat transfers much more efficiently than dry heat. Think about running water (100% humidity) over ice! :)

  • MN_Kevin

Posted April 01, 2001 - 02:57 AM

#10

the best shielding against all forms of radiation would be to live in a submarine. Since that is not really possible for everyone:

lead (pb) against gamma;
water/polyethulene against neutron;
throw some steel in for good measure against beta;
and wear clothes against alpha.

Here you go:
You have beta, alpha, gamma, neutron.
One you can eat, one you throw away, one you put in your pocket and one you hold in your hand. Which action for each?
The key to this riddle is the penetrating power of each.

  • Mike_in_Silicon_valley

Posted April 01, 2001 - 10:02 AM

#11

Kevin
It's time to cancel the subscription to popular mechanics! Either that or switch to a low VOC brake cleaner....... :)


Mike

  • MN_Kevin

Posted April 01, 2001 - 10:58 AM

#12

Mike,
I HAVE been using epoxy paint at work, as well as when I painted my MX helmet back in 1991. I was BREATHING that stuff in a paint booth. This paint has been proven to affect the nervous system, as well as causing PERMANENT brain damage.

Now, we all know what my real problem is!

And that is, The Rest of the Story!

  • JAFChE

Posted April 01, 2001 - 04:13 PM

#13

Kevin,

Suffice it to say, "Both ice cubes WILL melt!" :) and so will all the snow!

Good to see your sense of humor has not been diminished by all of the snow. Hang in there, the snow will melt and you will get to ride soon!

Jeff

------------------
No Brain, No Pain!
01' KTM 400EXC
01' Yamaha TTR-125L
01' Yamaha TTR-90
00' Honda XR50R

  • darbsitton

Posted April 01, 2001 - 07:40 PM

#14

Check this site out. It will not answer this question, but it will answer several others.
http://www.howstuffworks.com/

  • Harry_in_Oz

Posted April 01, 2001 - 10:04 PM

#15

The block with the higher humidity will melt faster.
The evaporation of the water in the dryer environ will cool the surface of the mixture slowing down the melting even if we assume that the overall temperature of the system remains constant i.e. has a heat source. The water will not insulate the ice sufficiently to counter this effect since the cold air is a better insulator. Harry

  • MN_Kevin

Posted April 01, 2001 - 11:32 PM

#16

Sounds that this could be the winner, Harry!
Hmmm...!

  • mikeolichney

Posted April 02, 2001 - 11:40 AM

#17

Originally posted by joecallan:
I would go with 70deg. 90% humidity and I'm almost positive. Moist heat transfers much more efficiently than dry heat. Think about running water (100% humidity) over ice! :)


100% humidity is not liquid water, not even close. 100% humidity is air that is saturated with water at the paticular temp and pressure. It is still almost all air by volume.




 
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