In many cooling problems the phrase "dissipated heat which should be removed" appears. Isn't that misleading since heat is a process quantity and dissipation usually means the conversion of mechanical to internal energy (for example)? I may guess what people mean by it - it is nevertheless not a phrase that should be used any more - do you agree?
There is not "dissipated heat" . There is "dissipated energy" only.
A Google search shows that the term is used mostly with reference to cooling in electronic devices. The use of "dissipation" as a synonym for "removal" is unfortunate, especially since "dissipation" has a special meaning in thermodynamics.
The phrase "dissipated heat which should be removed" as used frequently in relation to electronic devices is certainly not correct, when taken literally. What is meant is that the "heat resulting from a dissipative process should be removed".
But this brings us to the question whether heat *can* be dissipated. Heat is a form of energy and heat is always at the end of an energy-transformation chain. In this sense, heat is energy of low "value" since it cannot be transferred back into other forms of energy like mechanical energy. But here we must be more careful: In this generality, the sentence is certainly not correct: any thermal power plant transfers heat into electrical energy. What is meant is: Heat from a single source (single reservoir, same Temperature, pressure etc.) cannot be transformed into other forms of energy (unless additional external work is supplied).
Now it is obvious: Heat (=thermal energy) can be dissipated, but only if is provided from more than one reservoir, corresponding, e.g. to different temperatures. This is obvious, when we look to the following procedure: a thermal power plant produces electrical energy from heat (of two sources). This electrical energy is then dissipated in a light bulb. Thus, we dissipated heat into heat.
The process can be shortened by mixing two glasses of water (hot and cold). Obviously, when hot an cold water is separated, we could produce other forms of energy from the heat energy. After mixing when the water assumed a unique temperature, we cannot, unless we make use of a further source of energy (e.g. a third glass of water of temperature different from the mixture).
Thus, obviously, heat can be dissipated, but only of it comes from more than one reservoir of, e.g. different temperature.
One can and should be precise:
Taking "heat =thermal energy" is the problem: From the thermodynamics point of view heat is a process quantity while thermal energy is a state quantity and that means that they cannot be "equal".
"dissipation of heat" is even worse: Dissipation is the conversion of mechanical or electrical energy to thermal energy. Obviously it is meant that "by dissipation of electrical energy thermal (internal) energy emerges which can be removed by a heat flux (energy transport in form of heat)" - and this should not be named "dissipation of heat" !!!
H.H.
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