Heat

From Galactic Library
Jump to navigation Jump to search
Pageconstructionillustration.png
Notice:
Please bear with us. Your ride's still a work in progress.


Intuitively, we have an inkling of what heat is. It's whatever goes into a cuppa coffee that makes it hot. It's what an ice cube lacks. It's the "stuff" that leaks out of the cuppa to cool it off, and into the ice cube to make it melt.

We have all probably also learned that heat has "energy", that not-exactly-substance quantity that can't be generated ex nihilo nor gotten rid of, but can be moved around and is both useful and necessary for getting stuff done.

So what separates heat and its energy from other stuff that has energy, like electricity or light or compressed springs?

Technically, in the science of thermodynamics, heat is defined as a flow of entropy along with its associated energy. In this sense, the coffee in the cup doesn't have heat as such – it has energy and entropy. But it can transfer that energy and entropy via a flow of heat to its environment.

Like energy, entropy can't be gotten rid of but it can be moved somewhere else. Unlike energy, you can make more entropy. In fact, this tends to happen spontaneously whenever you try do do things. So you end up with this stuff – entropy – building up in your system. If too much builds up, your system will break, so you need to get rid of it. In order to get rid of it, you need to move it as heat. And heat unavoidably also involves taking with it some of that energy that you would prefer to use for doing other things. For many applications, you want to figure out how to move as much entropy away as you can while giving up as little energy as possible.

For other systems, some of that entropy might actually be desired – melting steel or driving chemical reactions, for example. And then the job of a thermal management engineer might be figuring out how to manage the flow of energy and entropy into the system.

In this page, we will be exploring heat, how to move heat around, and how to manage energy and entropy flows.

The nitty gritty of it

Energy, entropy, and temperature

-> Thermal equilibrium

-> spontaneous heat flow from different temperatures

-> energy-entropy relationship for heat flow at constant temperature

-> heat and work

-> microscopic description

Conduction

Convection

Radiation thermal equilibrium

-> black bodies and stuff

Latent heat

Phases and heat capacity

Waste heat

Heat transfer

Heat management

Heat exchangers

Heat pumps

Heat sinks

In atmosphere

Fans

Evaporative cooling

Thermoelectric cooling

In space

Radiators

Open cycle cooling

Additional reading

Additional references

Credit