Temperature and Heat
Temperature and Heat
(OP)
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!





RE: Temperature and Heat
RE: Temperature and Heat
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 ...
http://www.engineering-4e.com
RE: Temperature and Heat
- Steve
RE: Temperature and Heat
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
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RE: Temperature and Heat
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.
RE: Temperature and Heat
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."
RE: Temperature and Heat
RE: Temperature and Heat
Inadequate measurement perhaps. Temperature has no directionality.
- Steve
RE: Temperature and Heat
While temperature has no directionality, heat transfer always goes from hotter to cooler.
David
RE: Temperature and Heat
RE: Temperature and Heat
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.
RE: Temperature and Heat
- Steve
RE: Temperature and Heat
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
RE: Temperature and Heat
RE: Temperature and Heat
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.
RE: Temperature and Heat
Perhaps you are thinking of the wind-up that can occur in a drive shaft, which is energy storage in elastic deformation.
RE: Temperature and Heat
RE: Temperature and Heat
Read up on the 2nd law of thermodynamics.
RE: Temperature and Heat
- Steve
RE: Temperature and Heat
As for the "momentum" question, that's a complete misunderstanding of what the initial conditions are, and where the heat is stored within the system. Consider the simple case of a solid object with a constant T1 on one side, and natural convection on the other, resulting in a surface temperature of T2. There is a thermal gradient, which causes heat to flow from the T1 surface to the T2 surface. Remove the heat source on the T1 side and insulate both sides. The T2 side will increase in temperature, while the T1 side will decrease. over time, the temperature will equilibrate to (T1+T2)/2, the average temperature. Pure conservation of energy, and pure Fick's law (gradient drives flow).
In many supposed thermal momentum allegations, it's simply because people cannot observe all the state variables, and see only T2 increasing, and assume there's a "momentum" involved.
TTFN
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RE: Temperature and Heat
No, what I was thinking - but verbalizing poorly - with the flywheel is that, at the instant the accelerating load is removed, I conceptualize that the rotational speed will nonetheless increase to a maximum (with "acceleration" declining) before decreasing, and this is the "lag" to which I was referring. In other words, I would expect that the transition in angular speed is continuous and cuspless. Put another way, I suspect the speed versus time curve is smooth after the cessation of the applied force, and the duration in this region depends on whatever inertia and damping are present.
But I could be wrong.
Regards,
SNORGY.
RE: Temperature and Heat
Back to the heat analogy. That's wrong too. Heat has no equivalent of moving mass to give it an equivalent of momentum.
- Steve
RE: Temperature and Heat
So, a material when heated (properties willing) can reach the same temperature of the heat source and can never exceed the temperature of the higher temperature heat source?
This assumes the higher temperature source has an infinite supply of energy to remain constant.
( I understand that when two bodies at different temperatures come in contact, the heat will flow from the higher temperature body to the lower temperature body until they come to an equal temperature.)
Thanks!
RE: Temperature and Heat
"This assumes the higher temperature source has an infinite supply of energy to remain constant" is not required in real problems, and cannot be achieved in the real world. Constant temperature merely requires that net heat flow be ZERO. If net heat flow is zero, then be definition, the temperature is constant.
TTFN
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RE: Temperature and Heat
Information noted and confirmed.
Thanks.
RE: Temperature and Heat
My apologies for being wrong. (It happens.)
No worries...you were quite polite about it.
Regards,
SNORGY.
RE: Temperature and Heat
Perhaps I just don't understand jerks (like me) as well as I ought to.
(Poor attempt at humour there.)
Regards,
SNORGY.
RE: Temperature and Heat
RE: Temperature and Heat
rmw
RE: Temperature and Heat
Tobalcane
"If you avoid failure, you also avoid success."
RE: Temperature and Heat
RE: Temperature and Heat
RE: Temperature and Heat
If there is heat flow there must be a temperature difference. You cannot have heat flow at constant temperature.
RE: Temperature and Heat
Tobalcane
"If you avoid failure, you also avoid success."
RE: Temperature and Heat
TTFN
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RE: Temperature and Heat
To all, even though the temperature is rising for the cooler material and is still less then T high. I am sure there is a conduction within the object at T low absorbing heat within itself (its not at uniform temperature from the surface to the inner core) and therefore may absorb more heat but temperature at the surface will not increase if T high is removed. Besides (thermal expansion and other factors) change that energy into something equal but not increase the heat.
RE: Temperature and Heat
TTFN
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RE: Temperature and Heat
Thanks!