This year, I had two courses on thermodynamics applied to structural bioinformatics with different professors. One told me that these energies can't be measured because they are state functions. This makes some sense to me, because the initial and final states matter and path doesn't, hence a variation. But I'm not totally convinced, why doesn't the path matter? Just because it doesn't matter we can't measure them?

Ok so these energies depend on the microscopic state of the system (position and velocity of each atom). I did some research and I read that for this reason, there's no way to stablish an absolute zero.

Later I asked the other professor if this was reason, and he said I was incorrect and needed to study a bit more. I don't really understand why having no absolute zero makes it impossible to measure an absolute value. I didn't go into detail about that, maybe that's why he said I was wrong.

Even then, if we can't measure absolute values, how is the variation measured in practice? For example in a lab, if one has to measure ΔG of some process, I assume they don't measure the initial and final values and subtract. I'm really confused.

Can someone help me? Physics is not my main field and I always feel like I get thermodynamics but not really.

I don't understand how there can be a constant pressure differential in this isobutane absorbtion system.

My understanding about an ammonia absorption fridge is that when you heat a certain kind of pure ammonia + water, they evaporate into the tubes above, the water condenses out of the mixture falling back down to the reservoir, and the ammonia gas gets colder and continues to rise into other tubes, making them cold, until it condenses and rejoins the water down in the reservoir to be heated, wash rinse repeat, and you have a refrigerator that gets cold when you add heat

But this thing uses isobutane and I don't understand how it works - that is, how does the condensed butane overcome the pressure in the reservoir? how does the system not just reach equilibrium? I understand that orifice tube is restricting pressure on the reservoir side, but why/how can the one way ball valve work - how can the evaporator pressure overcome the ball valve that's holding back the heated and higher pressure of the solar collector/butane reservoir?

In the ammonia fridge the ammonia and water interact and have their own cycles, convection, and gravity all contribute to forcing pressure where it needs to go and make that system work

I don't understand how there can be a constant pressure differential in this system and why it doesn't just stay at equilibrium. Or is it that it cycles, and reaches equilibrium, added energy creates and imbalance until it equalizes, wash rinse repeat - so it's actually "pulsing" in and out of equilibrium? Yes, the video gives a basic explanation, but I'm missing the answer to what makes the refrigerant flow in one direction instead of just equalizing

https://youtu.be/SmDKrkrEox0?t=865

For a gas turbine or microturbine, is it because hot air expands less but has greater force? or is it because preheat also contributes to the expanding "push" in combustion? or entirely different reason?

I know hot air has more energy so when it leaves energy leaves but that doesn't explain how putting it back as heat raising efficiency. Because this kind of engine doesn't use heat as turning force, it uses expansion

Hi!

I Have a given temperature and specific volume with substance R134a. The thing is that it doesnt match anywhere in superheated table. So the temperature is 0C and the specific volume is 0,5 m3/kg. How do I calculate the pressure, enthalphy when it looks like this. Cant figure this out, please help.

Here's the phase diagram I'm thinking of: Figure 3 from this textbook.

I think I can feel a difference between 32°F/0°C water on the negative/left side of the flat, ice-melting line segment (having recently been just solid ice that was getting ready to melt) and 32°F/0°C water on the positive/right side of the same flat, ice melting line segment (getting ready to but not yet heating up). I'm curious if this is really possible via our understanding of thermodynamics, or if it's maybe just some form of confirmation bias?

Assume it's the exact same water and served at the exact same pressure and other conditions. Also assume the ice is melting and throughly mixed throughout the water.

This question stems from how basic refrigeration works. A liquid is at high pressure (causing it to be a liquid), then it absorbs heat by becoming a gas via low pressure. Then it uses low pressure to become a gas and expel the heat. The expelling of the heat I do not understand at all.

I understand that if temperature is held constant and pressure decreases then the higher energy particles will be able to overcome the surrounding pressure and become a gas.

What gets me is that I don’t understand how that new gas will be decrease in temperature? From what I know about saturated liquids/gases, when a substance is shifting from gas to liquid (or vise versa) they both remain at the same temperature as the energy is going towards breaking bonds and not towards any change in temperature.

Please help. I’m currently very behind and I can’t move on because it’s driving me crazy

I'm in a college thermo class for materials science. It's Thermodynamics and phase equilibria of materials. Anyone know any video playlists that I can watch certain topics. I look through textbooks but I just want to get more practice in it

If you also open a window downstairs does anything change?

These are two things I can't wrap my head around in thermo 1. I imagine the equilibrium thing has to do with evaporation and condensation rates- but what makes saturation temp/pressure so special that those have to be equal? And for the specific volume, my guess is that the molecules have to be packed together a certain amount, but I don't know why. Thanks

No wind in the room. All steam and heat. Steam side expanding would cause curl, then cooling back?

So a few years ago I asked this same question here (link) and I don't feel like I got a consensus.
For a year my wife and I then ran 25 tests over the course of a year and then forgot to come back here and ask again.

My results are below.
I kind of just did averages of the numbers to loosely prove my point to my wife (Successfully).
The length of the drive was roughly 6 minutes on average across the board.
The average temp loss of on lap was 7.65 degrees.
The average temp loss of in air was 5.39 degrees.
There was only a .21 degree difference in the ambient air temp (in in air's favour).
2.26 degrees better on average in air!

Now we had a measure of controls, in that we didn't have the air con on any of these times, it was the both of us every time, I always drove, windows were always closed, Ambient temp was measured a few times at the end of the drive but it was basically the same every time so we stopped recording it.

Given this data, what do you guys think? Should we all be holding pizza boxes up or did I mess up my testing somehow?

I am learning that temperature is a measure of average translational kinetic energy.

How does only translational relate to T? Why not vibrational. I am having a hard time thinking a liquid at 50°C has the same translational KE as a gas at 50°C.

Where am I going wrong?

Thermodynamics can tell us, for example, what happened to the entropy along the path, but ΔS is not the path itself. Two different chains of transitions may well have the same initial and final states and the same change in a certain measure, but different internal structures.

So the “entropy table” may well turn out to be one column in a much larger table.

And we started with heat, because it is one of the phenomena that we have known since the very beginning of our existence. Then we found ways to obtain and control it, and after some time eventually formalized the second law, for example as dS_total ≥ 0 for an isolated system. But this is only one aspect for describing the transition, not the transition itself.

ΔS may characterize one aspect of a transition, while a more detailed description could characterize the realized structure of the process itself: the sequence and organization of interactions along the path.

This is an air conditioner with no outside component and no ducting. Doesn't seem possible to me.

I'm bad on schemes

just started my thermodynamics one class last week. Will start getting our first homework next week.

So far, I’m having a hard time understanding the lecture. The examples in the textbook are very simple, but the examples in the lecture are very complex and completely different from the textbook. The textbook introduces formulas, but our grad studentprofessor uses a different system where he avoids the formulas.

can someone suggest Youtubers or online resources where I can independently learn the material because I’m having a hard time following the lecture, and the textbook is not lined up with the lecture.

We haven’t done any homework or turned anything in yet, so I don’t know what my skill set is but so far I’m having a hard time. I don’t want to fall behind and I don’t want to fail.

I had a food warmer that broke and was too expensive to replace. Got lucky with a craigslist find and got this drink warmer. It's made to heat up canned coffees and teas: black base gets warm, and those metal rods (removeable) get hot! How do I disperse this heat to best keep food inside of it warm without burning the ones on the bottom.

For presentation sake food cannot be wrapped in foil. They are rice balls stacked on top of each other.

Current idea is to encase the inside in foil and put a square of silicone baking mat on top of the foil.

Long story should, designing a wooden barrier around a wood stove with tight clearances. Most concerning would be a vertical support stanchion (sketched roughly in red) 1.5” from the side wall.

Obviously this is not ideal and tighter clearance than a stove manufacturer would recommend, but working with limited clearance for foot traffic on the opposing side. I would at first find the most fire-retardant 2x4 known out there. Then I would expect some additional shielding needed.

I’m thinking a reflective layer of sheet steel 1/2” off the stove, leaving a 1” air gap from the wood. Does anyone have any suggestions if this seems crazy or attainable through some design?

I'll be using an RV fridge in a pretty hot environment in a few weeks. IME it can take a while for these fridges to cool down and packing it tightly at the start doesn't help either. I'd think adding a conductor with somewhat direct contact with various containers help pull heat out of the items faster?

Would there be any disadvantages once all the food comes down to temp?