Will an object that is heated ever get to a higher temperature then the heat input temperature itself. For example, if I heat a piece of metal with a heat source at 150F, will the temperature of the metal ever exceed 150F if the heat source input remains constant for a long period of time? Thanks!
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Temperature and Heat
- Thread starter XELR8
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This is a tricky question -- it needs to be defined in a better way ...
For example, take a thermometer. If it is exposed to the sun, its temperature will keep going up ... If it is kept in a shade, it will show a fixed temperature value after a certain period of time ...
I agree with DVD's answer, however, I would ask for some additional clarification ...
For example, take a thermometer. If it is exposed to the sun, its temperature will keep going up ... If it is kept in a shade, it will show a fixed temperature value after a certain period of time ...
I agree with DVD's answer, however, I would ask for some additional clarification ...
SomptingGuy
Automotive
Zeroth law, the one they forgot when naming the first law.
- Steve
- Steve
Actually, Newton's law of cooling addresses that reasonably well: Q = k(T1-T2)
A positive temperature difference is required for a positive temperature change. If you want something to get hotter, it needs to be exposed to something that is hotter.
TTFN
FAQ731-376
A positive temperature difference is required for a positive temperature change. If you want something to get hotter, it needs to be exposed to something that is hotter.
TTFN
FAQ731-376
- Thread starter
- #6
Hi Folks,
Thanks for your help and quick response.
No tricks, you answered my question. I thought the answer would be no, you can never exceed the temperature of the source but, I could not document any physical or scientific equation with the theory.
Feel free to add any further comments.
Thanks for your help and quick response.
No tricks, you answered my question. I thought the answer would be no, you can never exceed the temperature of the source but, I could not document any physical or scientific equation with the theory.
Feel free to add any further comments.
Twoballcane
Mechanical
Wow, if we can find a way to heat something up and it actually got hotter than the heat source, we can solve our energy crises.
There is a something called thermal momentum, where you heat up mass and then when you suddenly turn off the heat source, the temp of the mass will still keep going a few degrees before peaking and then come down.
Tobalcane
"If you avoid failure, you also avoid success."
There is a something called thermal momentum, where you heat up mass and then when you suddenly turn off the heat source, the temp of the mass will still keep going a few degrees before peaking and then come down.
Tobalcane
"If you avoid failure, you also avoid success."
ginsoakedboy
Mechanical
Thermal momentum will still need a driving force. You cannot observe this phenomenon starting from steady state. In other words, the temperature of the applied source would have to be higher to cause this temperature peak.
SomptingGuy
Automotive
"There is a something called thermal momentum"
Inadequate measurement perhaps. Temperature has no directionality.
- Steve
Inadequate measurement perhaps. Temperature has no directionality.
- Steve
No it is different heat transfer coefficients of different materials. Take the example of a pot on the stove: The pot absorbs heat from the burner and passes it to the contents, The outside of the pot will be measurably hotter than the inside. After you turn the burner off, the temperature gradient across the pot bottom will equilibrate (raising the temperature of the contents). This happens even if the process was in apparent thermal equilibrium (e.g., a pot of water at its boiling point does not change temperature until the liquid water is gone or the heat input is stopped). That is "thermal momentum".
While temperature has no directionality, heat transfer always goes from hotter to cooler.
David
While temperature has no directionality, heat transfer always goes from hotter to cooler.
David
Compositepro
Chemical
I've got to call this one! There is no such thing as thermal momentum. That is a flawed analogy to describe an observed phenomenon that is caused by heat capacity and thermal conductivity. It might be used as a shorthand term for the effect but shouldn't be used to to explain anything because it isn't real.
On an entirely different situation, one may encounter thermal runaway exothermic chemical reactions...
Thermal runaway can occur because, as the temperature increases, the rate at which heat is absorbed and removed increases, say, linearly but the rate at which heat is produced increases exponentially.
When control of the reaction is lost, temperature can rise rapidly leaving little time for correction. The elevated temperatures may initiate secondary, more hazardous runaways or decompositions.
SomptingGuy
Automotive
Now THAT takes me back to my childhood days of weed-killer and sugar fires.
- Steve
- Steve
SomptingGuy
Automotive
David,
I think you are describing time constants, not momentum. A failure of English language to describe engineering processes. Like those TV journos who can "feel the power" of a car.
- Steve
I think you are describing time constants, not momentum. A failure of English language to describe engineering processes. Like those TV journos who can "feel the power" of a car.
- Steve
ginsoakedboy
Mechanical
You should see some of the arguments between me and the mrs. The hot object gets hotter without any heat source.
Thermal momentum...?
I liken this effect to the analogous situation of energy stored in a capacitor - or a flywheel, for that matter. Maybe the flywheel is a better example; in my mind, while you continue to add energy, the flywheel continues to accelerate, and the instantaneous cessation of energy input will result in the flywheel rotational speed to nonetheless rise to some maximum because of this inertia-driven acceleration (followed by deceleration). That does not mean that energy continues to be added at this stage; all of the energy has already been provided by the source prior to cut-out. What is observed afterwards is not a "momentum" effect so much as a "time lag" effect.
Regards,
SNORGY.
I liken this effect to the analogous situation of energy stored in a capacitor - or a flywheel, for that matter. Maybe the flywheel is a better example; in my mind, while you continue to add energy, the flywheel continues to accelerate, and the instantaneous cessation of energy input will result in the flywheel rotational speed to nonetheless rise to some maximum because of this inertia-driven acceleration (followed by deceleration). That does not mean that energy continues to be added at this stage; all of the energy has already been provided by the source prior to cut-out. What is observed afterwards is not a "momentum" effect so much as a "time lag" effect.
Regards,
SNORGY.
Compositepro
Chemical
A flywheel will accelerate as long as energy is added to it by applying an external force. The instant that force is removed no more energy is added to the flywheel and acceleration instantly stops. Momentum is what resists acceleration.
Perhaps you are thinking of the wind-up that can occur in a drive shaft, which is energy storage in elastic deformation.
Perhaps you are thinking of the wind-up that can occur in a drive shaft, which is energy storage in elastic deformation.
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- #18
I really enjoy the answers and related views. So let me ask this, why can rubbing two sticks together at a lower temperature create a flame at a higher temperature. Please, note, I understand combustion but it does flaw some earlier answers. Thanks!
The sticks are not at the lower temperature at the point where they rub. Friction and the corresponding input of energy makes it locally hotter adjacent to the area where the sticks rub. Wood is a decent insulator so the sticks don't become uniformly warmer.
Read up on the 2nd law of thermodynamics.
Read up on the 2nd law of thermodynamics.
SomptingGuy
Automotive
If you suddenly reverse a pressure gradient, gas will flow against it for a period. The same isn't true with temperature and heat flow.
- Steve
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