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Name: Daniel 
Status: educator 
Grade: 7 
Location: CA 


Question:
I am a teacher. Though an environmental lab owner, I am at a loss for an answer for my students. With regard to the conduction of cold, frigorific energies (as opposed to heat/thermal), what are some of the best conductors of said cold, frigorific energies? I ask this knowing that some metals behave oddly when they encounter cold (sub-freezing temps). The conundrum that stumped me is the question: Being that aluminum, for example, is an excellent conductor of heat, therefore, said heat applied to a frozen-cold aluminum plate, would easily drive away cold energies to exchange or replace said cold with heat...in an instant. But what metals best resist heat, yet allow for ready cold conductance and cold transmission?


Replies:
Daniel,

Perhaps we should start by simplifying the conception of energy as suggested in your question. Establishing a "cold energy" concept independent of "heat" would be equivalent to establishing "dark" as having properties independent of "light". The definition of heat is that this is the energy that is transferred from one body to another if the two bodies have different temperatures. Thus, if the temperature of object 1 is higher than that of object 2 than heat will transfer from object 1 to object 2 until the two are equal in temperature. While "cold" is an existing colloquial term suggesting either low temperatures or the transfer of heat away from an object, it has no scientific meaning as a form of energy.

Thermal conductivity is defined as the amount of heat transferred over a particular length of time, through a particular thickness of the material with a certain surface area - due to a temperature difference. As such aluminum with a thermal conductivity of 237 W/m.K is less thermally conductive than water at 0.6 W/m.K.

Since, as we said, "cold" is simply a colloquial term suggesting an absence of heat or a particular temperature, then we can *not* expect to find -as your question suggests- a substance that is a poor thermal conductor (an insulator) but is also able allow heat to pass readily and make something cold (a good thermal conductor).

Greg (Roberto Gregorius)


Hi Daniel,

There is no such thing as "frigorific energies" in the context you are referring to. This simply does not exist. There is also no such thing as the conductance of "cold". Thermal conductivity is the ability of a material to conduct heat. Cold is simply the relative absence of heat energy.

Conduction of "cold" is nothing more than the extraction of heat energy from an object; remove its heat energy and it will get colder. Refrigerators, for example, get cold because their heat pump (the compressor system) extracts heat from the inside of the fridge, and pumps the heat to the outside. Your fridge gets colder inside and the kitchen gets a little warmer.

"Cold" is emphatically not a different kind of energy from heat. The coldest possible temperature is absolute zero, and it is defined by the total absence of any heat energy whatsoever; in other words, it is the temperature at which all molecular motion (i.e. heat energy) stops.

You wanted to know which metals "resist heat" but allow "ready cold transmission". The answer is none! "Heat" and "cold" are simply relatively different degrees of the same thing.... heat energy. There is absolutely no separate form of energy called "cold energy"! For further verification I refer you to any first-year engineering book on basic Thermodynamics.

Regards,
Bob Wilson


Daniel,

Before I try to answer your specific question, I am going to ask you to rethink and reframe how you are viewing this question. Especially since you are an educator, it is important to teach your students using terms and concepts that are consistent with the rest of the world of science. Unfortunately, the terms and concepts to which you refer are somewhat antiquated. I am going to try to re-phrase your question in more modern terms, and then try to provide some suggestions to answer it.

The concept of ‘frigorific’ energy (and calorific energy) was pretty much abandoned many decades ago as we better understood heat and energy. These are not terms that modern scientists would commonly use. There are many forms of energy, one of which is thermal energy, or heat. Heat can be exchanged between objects. An object that is considered ‘cold’ has a low temperature [compared to you, or some other reference], and an object that is ‘hot’ has a high temperature. ‘Hot’ or ‘cold’ (or frigorific or calorific) are relative terms, and not qualitatively different. Heat moves from hot objects to cold objects. A difference in temperature causes this conductive heat exchange. It does not matter how much of a material there is – if it is hotter than another object that it is in thermal contact with, it will transfer heat to the colder object. In terms of thermal properties, it’s more useful to think of energy being transferred via temperature differences, rather than to think of ‘cold/frigorific energy’ as a different form of energy than ‘hot/calorific energy’.

The reason I bring up size is because energy is an extensive property (extensive means it depends on the amount of material) – the more of a material you have, the more energy it has. In contrast, temperature is an intensive property (it does not depend on the amount of material). A uniform object of a given temperature is the same temperature no matter what size it is. A very small, hot object may have less energy than a large, cold object, but it will still transfer heat to the cold object. It is temperature, not energy, that drives heat transfer.

When transferring heat from one object to another, some objects are ‘better’ at transferring heat than others, as you identify in your question. Aluminum is a great conductor of heat, as you note. This property is known as thermal conductivity. Depending on temperature, the thermal conductivity can change. How and the degree to which it changes depends on the material and its specific properties.

With all this in mind, I would like to rephrase your question as follows: what materials exhibit changes in thermal conductivity with respect to temperature such that they would be highly thermally conductive at low temperature, but very low thermal conductivity at high temperature?

I do not know the answer to that, although common materials (metals, polymers, and common ceramics) would not change enough to have the use that you have in mind. Perhaps there is some exotic material (an alloy or rare-earth ceramic) that exhibits the properties, but I do not know. However, there are TONS of reference books other there that list various materials’ thermal properties – a good technical library (an engineering library at a university) would be a place to start.

If you have tried to do research to answer your own question but did not find success, I suspect it may be because of the terms you are using. I *highly* recommend you take a step back and read a book on heat transfer. Perhaps that will help you to frame your questions in a way more consistent with other scientists, which would allow you to find relevant information more easily.

Hope this helps,
Burr Zimmerman


Your concept of heat is seriously flawed. There are not two "kinds" of heat (thermal vs. frigorific). In fact there is no such thing as "frigorific energy". For two or more bodies,or parts of bodies in thermal contact. Heat "flows" from regions of higher temperature to regions of lower temperature. Heat is due to the random motions of atoms and molecules. The higher the temperature, the more the atoms and molecules twist, rotate, and vibrate.

When put into contact with an object having a lower temperature, that is, the atoms and molecules are giggling around less, the collisions of the atoms and molecules in the hotter object transfer some of their motions to the more sluggish atoms and molecules. Eventually enough collisions occur so that the atoms and molecules of the two objects are giggling about the same amount. When that happens, the two objects are at the same temperature.

Vince Calder


Daniel,

I am very glad my response was useful to you and your students.

I am still quite concerned about some of the things you have mentioned in this note, enough that I feel compelled to offer a few more comments. I hope these additional comments are well received and prove useful to you, but in the industrial world, some actually treat cold as if it were an energy

Certain individuals may adopt unusual semantic descriptions that are useful in specific cases, and whole industries may retain antiquated terms through sheer "inertia". For example, when I worked in the pharmaceutical industry, we called sodium hydroxide "caustic" and PowerPoint slides "foils". It is not necessarily wrong/bad, but it could be misleading to someone who does not know what we were talking about. As a primary educator, I would caution you against using nonstandard terms for your students. In fact, I would argue it is quite important for you to learn the standard terminologies and insist your students use them. They will be better off now and in the future if you train them in terms that are compatible with current understanding and standard terminology. A great illustration of this is the problem you had with the term "frigorific". Had you begun with standard terms, you might have been able to find resources much more quickly.

Some scientists, I am discovering, argue that 'thermodynamics is but an ancient 1800's theory employing assumptions.' One student yanked a Van Nostrands definition that also denotes same.

Trying to understand the thermal properties of materials *is* ancient (older than the 1800's for sure), but thermodynamics, entropy, and the like did gain prominence in the 1800's. Thermodynamics *does* rely on numerous assumptions. However, your language implies that making assumptions is somehow bad. Assumptions are fine – it is the *invalid* assumptions that are not fine. Fortunately, the assumptions that underpin thermodynamics are well-defined, thoroughly challenged, and quite valid. In thermodynamics, both experiments and fundamental theory are consistent. I would assert your concerns about the validity of thermodynamics in the context of our discussions are misplaced.


Daniel, you seem to have a positive attitude and a willingness to work hard. I love how you have your students try to gather their own information to answer their questions. I recognize how difficult it is to teach a subject that stretches your own horizons. I commend you for trying. However, there is also a point when more systematic help is required. In the case of heat transfer and thermodynamics, it seems you have reached that point. I have helped you as much as I can (and I hope it has, indeed, been helpful). You might try to find some help beyond just an exchange of emails.

It is good to challenge assumptions, but to an extreme, it can leave one unable to critically assess sources and unable to come to a comprehensive conclusion. The optimum is somewhere between unquestioning belief and extreme skepticism.

Best regards,
Burr Zimmerman


Your response has been the most helpful of all: In some situations, I honestly tell my students that, "I simply do not know." Moreover, when students (who are all studying your letter as a very serious topic of daily discussion), research and drum up, aside from the norm, other scientists 'of the day' arguing vehemently that said 'cold' is an absolute energy as 'it' causes countless reactions in physics and chemistry, I have to consider (or at least attempt to) precisely what they are saying. It turns out that a few of my students are getting feedback from prominent universities (Oxford, MIT, and others) that, though "kinky" compared to what the DOE claims, seems somewhat correct...not that what you say is 'wrong,' but in the industrial world, some actually treat cold as if it were an energy (as witnessed serving as an engineer/operator in an oil refinery). Some scientists, I'm discovering, argue that 'thermodynamics is but an ancient 1800's theory employing assumptions.' One student yanked a Van Nostrands definition that also denotes same. I'm not one to argue that an absence of heat = the colloquialism, 'cold.' Albeit, heat, in essence does not fight an 'absence of something,' as the cold/heat configuration could be turned on its opposite, to say...I mean, that said 'something' is not a nothing, as one MIT gal detailed it.

All in all, what is apparent is that heat (as from stars) is as natural as the state of its absence while the dominating 'agency' or 'quality' would be said 'absence' of heat. And because one 'quality' seems to oppose the other (granted, your gracious and much appreciated explanation), no doubt, what you say makes sense.

Insofar as the metals (hah, and that 'absence of heat' causes many various crystallization reactions in metals), it appears that, a metal being a good conductor of heat, also means it drives out cold (heat, in essence) lickety-split, hence, if extreme cold, liquid oxygen or nitrogen, were applied to a surface of copper, for example, said 'cold' would drive out heat as fast as IT (cold) can be driven out.

Anyhow, we are using your words as a textbook, in fact, it is clearer, say the kids, than textbooks.

Sincerely,
Daniel D.


Daniel,

Before I try to answer your specific question, I am going to ask you to rethink and reframe how you are viewing this question. Especially since you are an educator, it is important to teach your students using terms and concepts that are consistent with the rest of the world of science. Unfortunately, the terms and concepts to which you refer are somewhat antiquated. I am going to try to re-phrase your question in more modern terms, and then try to provide some suggestions to answer it.

The concept of "frigorific" energy (and calorific energy) was pretty much abandoned many decades ago as we better understood heat and energy. These are not terms that modern scientists would commonly use. There are many forms of energy, one of which is thermal energy, or heat. Heat can be exchanged between objects. An object that is considered "cold" has a low a low temperature [compared to you, or some other reference], and an object that is "hot" has a high temperature. true. "Hot" or "cold" (or frigorific or calorific) are relative terms, and not qualitatively different. Heat moves from hot objects to cold objects. A difference in temperature causes this conductive heat exchange. It does not matter how much of a material there is – if it is hotter than another object that it is in thermal contact with, it will transfer heat to the colder object. In terms of thermal properties, it is more useful to think of energy being transferred via temperature differences, rather than to think of "cold/frigorific energy" as a as a different form of energy than "hot/calorific energy".

The reason I bring up size is because energy is an extensive property (extensive means it depends on the amount of material) – the more of a material you have, the more energy it has. In contrast, temperature is an intensive property (it does not depend on the amount of material). A uniform object of a given temperature is the same temperature no matter what size it is. A very small, hot object may have less energy than a large, cold object, but it will still transfer heat to the cold object. It is temperature, not energy, that drives heat transfer.

When transferring heat from one object to another, some objects are "better" at transferring heat than others, as you identify in your question. Aluminum is a great conductor of heat, as you note. This property is known as thermal conductivity. Depending on temperature, the thermal conductivity can change. How and the degree to which it changes depends on the material and its specific properties.

With all this in mind, I would like to rephrase your question as follows: what materials exhibit changes in thermal conductivity with respect to temperature such that they would be highly thermally conductive at low temperature, but very low thermal conductivity at high temperature?

I do not know the answer to that, although common materials (metals, polymers, and common ceramics) would not change enough to have the use that you have in mind. Perhaps there is some exotic material (an alloy or rare-earth ceramic) that exhibits the properties, but I do not know. However, there are TONS of reference books other there that list various materials' thermal properties – a good technical library (an engineering library at a university) would be a place to start.

If you have tried to do research to answer your own question but did not find success, I suspect it may be because of the terms you are using. I *highly* recommend you take a step back and read a book on heat transfer. Perhaps that will help you to frame your questions in a way more consistent with other scientists, which would allow you to find relevant information more easily.

Hope this helps,
Burr Zimmerman



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