You were made for this (thermo cycles)

There was a moment during class tonight that felt exhilarating.

I don't mean that hyperbolically.

I mean that I was overcome with wonder and that dovetailed into a teaching moment.

A student asked me to distinguish between a refrigeration and a heat pump cycle--they are very similar processes.  In fact, the only difference is in how you use them.

I didn't have a very clear or concise explanation the first time--to be perfectly honest, I realized in that moment that my understanding was incomplete--and I was supposed to explain this to the class.  At that point, you can either think really fast on your feet, or acknowledge that you don't know.

Normally I would tell them I'd get back to them.

This time was different.

Refrigeration cycles are an interesting concept because they use materials that boil at very low temperatures.  I understand how refrigeration cycles work very well.  It's fundamental to much of my work.

In that moment I decided to try and work out the explanation of a heat pump to myself while I did it for them.  Kind of risky, but since I knew how the 'opposite' cycle worked, I should be able to convince myself.

And in that moment, I had it!  For some reason, the heat pump cycle had previously seemed to have a kind of magical quality to it.  For years I never really felt like I understood it.

Now I had the key!  And I was able to jump right in and explain it with a metaphor/picture that, while absurd*, made sense.

Normally when these little realizations about how the world works come, I'm not with my 'right' people.  That is to say, ChE's.  This time however, I had a captive audience of budding engineers, and they weren't allowed to leave.

That's why it was exhilarating: an epiphany in the presence of a captive audience that has the background to appreciate and learn from it.

Most times I would keep something like that to myself and enjoy the moment amidst my lawyer, biologist, accountant, public administration, social worker friends.  This time though, I got to share my realization (had to really), and in the process looked like I had my s*** together.  I feel like I was made for this.

*a heat pump cycle is basically functioning like a refrigerator for the earth (when the source is geothermal).  You are taking 'heat' in the ground (thereby cooling it) that is at a lower temperature than the object to be heated, a house for example, and boiling a (low T, low P) liquid refrigerant.  The power input comes in compressing the (low T, low P) refrigerant vapor into a (high T, high P) vapor.  That vapor runs through a condenser and gives up its latent heat of vaporization to heat the house.  You then throttle the (high T, high P) liquid through a valve back to a (low T, low P) liquid and boil it with low grade heat from the ground to start the cycle again!  You're making the ground refrigerated and using that heat in your house!  It's the opposite of a refrigerator because our system of interest in a refrigerator is the insulated box--the heat gets expelled to your kitchen (the surroundings).  Now, the system is your home, and you're adding heat to it by taking it from the low temperature ground (surroundings)!!!  The beauty is that you can reverse the process and have air conditioning--now you're just putting that heat in the ground!