Is it possible to drop below ambient temperature

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So

So

Lifer
Jul 2, 2001
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Even with forced air cooling. My gut instinct says no. Given steady state conditions, the object will drop only to ambient and not below. My boss thinks that (infrared) black body radiation would allow it drop below ambient. I don't think so, but even if it could, it surely would be so small as to not be measurable.

All this is assuming roughly 50 Degrees ambient, if it makes a difference.

Also, phase change cooling is not within the realm of this discussion.

The reason this comes up, is that my boss claims that his uncle (intelligent, EE, masters degree, etc...) had a dutch oven filled with water that dropped below ambient when left outside in cool but above freezing temps. I think his uncle is missing something.

What does AT think?
 
dullard

dullard

Elite Member
May 21, 2001
26,105
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With a moving ambient temperature, yes. That is, when the ambient temperature was cold, the oven got cold. But then the ambient temperature rose (warm winds or the sun came out) and the oven had thermal mass that took longer to increase.

However, I don't think that is what your boss was thinking about.
 
S

Savij

Diamond Member
Nov 12, 2001
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0
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Originally posted by: So
Even with forced air cooling. My gut instinct says no. Given steady state conditions, the object will drop only to ambient and not below. My boss thinks that (infrared) black body radiation would allow it drop below ambient. I don't think so, but even if it could, it surely would be so small as to not be measurable.

All this is assuming roughly 50 Degrees ambient, if it makes a difference.

Also, phase change cooling is not within the realm of this discussion.

The reason this comes up, is that my boss claims that his uncle (intelligent, EE, masters degree, etc...) had a dutch oven filled with water that dropped below ambient when left outside in cool but above freezing temps. I think his uncle is missing something.

What does AT think?
Click to expand...

What was the ground temp?
 
So

So

Lifer
Jul 2, 2001
25,923
17
81
Originally posted by: ggnl
caused by evaporation maybe?
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That might be the cause in this example, but assume that no evaporation happens (phase change cooling) for the hypothetical.
 
mrSHEiK124

mrSHEiK124

Lifer
Mar 6, 2004
11,488
2
0
If I'm getting this right, a proper example would be a room at 72F/whateverC, and a CPU that was running at <72F with only a heatsink? Impossible, it can only be as cool as the surrounding air will allow it to be. It'll transfer heat to the environment until it reaches equilibrium, or as close as the thermal properties of both mediums will allow.
 
So

So

Lifer
Jul 2, 2001
25,923
17
81
Originally posted by: dullard
With a moving ambient temperature, yes. That is, when the ambient temperature was cold, the oven got cold. But then the ambient temperature rose (warm winds or the sun came out) and the oven had thermal mass that took longer to increase.

However, I don't think that is what your boss was thinking about.
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Right. That's what I suggested, we agreed that for the point of discussion, assume constant temperature.
 
So

So

Lifer
Jul 2, 2001
25,923
17
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Originally posted by: Nik
Originally posted by: So
Originally posted by: hiromizu
who fin cares?
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People with big enough brains to have interesting intellectual discussions. You might want to get yourself checked.
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Yeah, really. I mean, we have some really highly technical people here who know alot about general hardware.
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I don't think a cast iron skillet is what they had in mind when the created "general hardware."
 
So

So

Lifer
Jul 2, 2001
25,923
17
81
Originally posted by: mrSHEiK124
If I'm getting this right, a proper example would be a room at 72F/whateverC, and a CPU that was running at <72F with only a heatsink? Impossible, it can only be as cool as the surrounding air will allow it to be. It'll transfer heat to the environment until it reaches equilibrium, or as close as the thermal properties of both mediums will allow.
Click to expand...

Basically, but assume that the CPU is off. It starts hot, but no additional power is being input.
 
dullard

dullard

Elite Member
May 21, 2001
26,105
4,751
126
Originally posted by: So
Right. That's what I suggested, we agreed that for the point of discussion, assume constant temperature.
Click to expand...
Ok, now, how did the uncle measure this temperature? I believe that the temperature measurement was in error.

 
Fayd

Fayd

Diamond Member
Jun 28, 2001
7,970
2
76
www.manwhoring.com
it's not possible for a heatsink to go below ambient temp, unless something was conducting heat away from it. (taking the heat into somewhere other than "ambient".)

wrt infared, heat moves like anything else. it tries to find equillibrium, moving to a place of lower concentration than itself. as such, it's not possible to have infared radiation off a heatsink when the temperature of the air around the heatsink is the same as the heatsink.

please correct me if i'm wrong. the most advanced science course i took in college was literally named "physics for business majors".
 
Fayd

Fayd

Diamond Member
Jun 28, 2001
7,970
2
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www.manwhoring.com
Originally posted by: So
Originally posted by: mrSHEiK124
If I'm getting this right, a proper example would be a room at 72F/whateverC, and a CPU that was running at <72F with only a heatsink? Impossible, it can only be as cool as the surrounding air will allow it to be. It'll transfer heat to the environment until it reaches equilibrium, or as close as the thermal properties of both mediums will allow.
Click to expand...

Basically, but assume that the CPU is off. It starts hot, but no additional power is being input.
Click to expand...

that doesnt change the fact that the heatsink cant be cooled below the airs temperature.
 
So

So

Lifer
Jul 2, 2001
25,923
17
81
Originally posted by: dullard
Originally posted by: So
Right. That's what I suggested, we agreed that for the point of discussion, assume constant temperature.
Click to expand...
Ok, now, how did the uncle measure this temperature? I believe that the temperature measurement was in error.
Click to expand...

Yeah, I'm betting on a mistake somewhere in here for a real world explanation, but I'm interested in the hypothetical. Is it at all possible? I say no, he says maybe given IR radiation from a black body (i.e. warm water in a black dutch oven).
 
A

AmberClad

Diamond Member
Jul 23, 2005
4,914
0
0
Originally posted by: Fayd
it's not possible for a heatsink to go below ambient temp, unless something was conducting heat away from it. (taking the heat into somewhere other than "ambient".)
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That's what TEC coolers are for. But OP said passive heatsink, so yeah, not happening.
 
mrSHEiK124

mrSHEiK124

Lifer
Mar 6, 2004
11,488
2
0
Originally posted by: So
Originally posted by: mrSHEiK124
If I'm getting this right, a proper example would be a room at 72F/whateverC, and a CPU that was running at <72F with only a heatsink? Impossible, it can only be as cool as the surrounding air will allow it to be. It'll transfer heat to the environment until it reaches equilibrium, or as close as the thermal properties of both mediums will allow.
Click to expand...

Basically, but assume that the CPU is off. It starts hot, but no additional power is being input.
Click to expand...

Still, I think it would never be able to get below ambient temperature. Ignore our concepts of hot/cold, and just look at the heat we're dealing with. It would somehow have to displace its thermal energy away into the environment, which would require some active process (phase change cooling, compressor, whatever).
 
H

Howard

Lifer
Oct 14, 1999
47,982
11
81
A sink can radiate heat below ambient, but convection will simply warm it back up.
 
D

DisgruntledVirus

Lifer
Dec 26, 2007
11,782
2
76
Originally posted by: mrSHEiK124
Originally posted by: So
Originally posted by: mrSHEiK124
If I'm getting this right, a proper example would be a room at 72F/whateverC, and a CPU that was running at <72F with only a heatsink? Impossible, it can only be as cool as the surrounding air will allow it to be. It'll transfer heat to the environment until it reaches equilibrium, or as close as the thermal properties of both mediums will allow.
Click to expand...

Basically, but assume that the CPU is off. It starts hot, but no additional power is being input.
Click to expand...

Still, I think it would never be able to get below ambient temperature. Ignore our concepts of hot/cold, and just look at the heat we're dealing with. It would somehow have to displace its thermal energy away into the environment, which would require some active process (phase change cooling, compressor, whatever).
Click to expand...

If I take a massive heatsink that is chilled to sub-zero temps, and use that it will temporarily cool the proc below ambient until it warmed over time and reach equilibrium.
 
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