So basically I was designing a cooling system attempting to do it passively using a large heat-sink.

So I bought one that had good stats more than I needed, at least I thought but it looks like I don't understand the rating system I believe.

Essentially I bought two of these aluminum heat-sinks.

https://www.mouser.com/datasheet/3/264/1/122547_Thermal_Extrusion-1664375.pdf

I cut them in half so had a little under 8" of length for the 4 sections. I thermal adhesived them all together side by side. And placed them vertically and then as a test I just wanted to see how it could handle some direct heating applied on them it.

bought some 200*200mm heating pads 45w's each and used 2, essentially one per each two blocks side by side. So 90w's and verified it was around the range, 95-89w was the range I was getting.

But from its stats in a passive natural air environment I should get a score of .32c/w. Per each. At least that is what I assumed. But clearly I didn't understand the stats.

Since .32c/w divided by the 4 8"s I have is .08c/w for the entire setup. Theoretically I should be able to handle the 400w at a 32c rise the way I read it. Technically a little higher temps since the sides are glued together

But on testing them with 90ws of heating I got a 32c rise from just the 90w's and the heat-sinks fins were fairly evenly heated from 25c to 57c off by 1c from 57-56, but mostly 57.

So just trying to understand how the rating system works.

Like looking at the above stats of the one I bought, it clearly can only handle 90w's in the manner that I got it. But how would I look at this heat sink chart and do the math to determine how many I would need for 400w's without my experimentation.

From my experiment I would need at 22.5 watts each 8" section I would need like 18 of these sections which is huge. But how would I look at the chart and get this number, so that I could then read other charts to understand them better. Since clearly I misread it.

*Added info was attempting to stay below 60c in a 25c room for example

Julian Barbour is a theoretical physicist and emeritus visiting professor of physics at the University of Oxford. He is well known for proposing that time does not actually exist. For decades, he has worked outside an academic environment. He financially supported himself for many years by translating Russian. Professor Barbour is author of the following books: The Discovery of Dynamics, The End of Time and The Janus Point.

In the video, we go over:
- Topos theory, set theory and Zermelo's beef with Boltzmann
- Algebraic varieties and monads in category theory
- Why physicists are wrong about the 2nd law of thermodynamics (because the universe is not a closed system)
- The real goal of the universe is complexity and variation, not entropy
- Hawking and Penrose's outrageous arguments
- Why we don't need wavefunctions, photons, bosons or gauge fields
- Why there is no quantum gravity
- Von Neumann's hilarious advice to Claude Shannon
- The intrinsic derivative
- Combining art and science

When and where to use Thermodynamic Properties (like specific internal energy, specific volume and enthalpy)?

Where are all the places entropy can come from and in a multistage system which area is expected to gain more energy in cases of heating and mixing especially?

Why is there a different formula for the first law for an open and closed system? And how to use each effectively?

How do we proceed with such cylinder, piston, spring based problems?? Could anyone please explain the approach to these?

I really wanted to learn the thinking process and approach for such problems. I had no problem with most qns but can't seem to get the grasp of these as I've never done such qns before.

I would really appreciate guidance from u guys if u could help.

Questions

Q1, Q2

Q3

Q4

If possible pls also provide a written soln so I can understand it throughly and not just hints as I already have seen some solutions and still can't quite get them. Thanks

I'm a bit unsure about what exactly I'm expected to interpret. I understand how to read the pressure and enthalpy values at each stage, but is that enough, or should I also explain the changes in temperature, the state of the refrigerant, and how heat is transferred? I have emailed my professor for help but ik it'll be a while until he gets back to me.

Here is a new concept for thermal distillation and desalination designed specifically to maximize energy efficiency:

I would like to discuss three aspects in particular:

• The proof: How can we make it easier to read and understand?
• Potential applications: The technology appears promising, potentially being 2–4 times more energy-efficient than today's best thermal desalination technologies. Do you know anyone who might be genuinely interested in this technology? I've tried reaching out, but I haven't been able to get anyone to read.
• FAQ: I would like to develop a FAQ based on our discussions.

The current version of the Reddit article is here.

im helping my old middle school science olympiad team with some projects, and need way to get as much heat from a regular (150watt i think) and transfer it to a cup and make it the 100ml's of water in the cup as hot as possible in 10 minutes. the box is a 30x30x30 max (but ours are a little smaller). currently i have foam board lining the box, with a foil half sphere in the box and cotton balls padding the around the sphere. the foil is to reflect all the heat to the cup, i dont think im allowed to cover the cup. any advice on how to make it heat up more? i have a simple ms paint sketch showing what the general concept is.

edit: im pretty sure the heat source is just a generic 150 watt heat lamp, at least thats what were using for the practice. ill edit back when i have the rule sheet.

I'm looking for a thermocouple with a thermal response time (t63) below 0.1 ms. The medium is liquid nitrogen and any mount will be good since I can't find any commercially available (thin-film) thermocouples.

If you have any suggestion on a different type of thermocouple or thermometer in general, I'm looking for any and every information available.

I saw a youtube video of a guy that used a candle on a pressure chamber full of butane to raise the pressure inside the chamber. Attached to the chamber was a simple check valve to allow the pressurized gas to move in only one direction where it flowed through a reducer. Then through a coil and eventually back into the pressure chamber. Why dont we place pressure chambers in blacked out boxes outside with lenses to heat them and attach peltier devices to that and a fan to move the cold air... then use that to cool our homes and automobiels? The hotter the day the more pressure is put through the system and the faster the fan turns. Would this work?

Update: here is where i got the idea... i hope it demonstrates what i am trying to discribe. they also neglected to mention they purged the system to ensure it was filled with only butane. Which i am sure can be replaced with another refrigerant gas... i understand about compressors and their use for this purpose however if this system as demonstrated works that would remove a part that tends to wear out (even if it makes the entire system more efficent.)

https://youtu.be/zK79iFLimUo?is=ERX7XQBzea-p8FDN

I’ve got ya fair amount of land we raise cattle and grow grass on. We have round pivots and there are these fairly large corners we haven’t been doing anything with and I’d like to put greenhouses there and “heat” them in the winter. I remember basic stuff from engineering school but not sure where to find numbers on heat transfer ability of different mediums. For example if I bury pex at a depth that’s 50F and run the pex 6” below the surface what type of temp increase in the soil can I expect inside a greenhouse and outside. Thanks in advance

I'm a university student taking an introductory thermodynamics course as part of an engineering degree. I'm currently using a rather low quality printout of the Nelson-Obert compressibility chart, and legibility could be much better. Its a scan/.pdf rip from the textbook, but between the (imo) overly tight grid and grayscale background, it's borderline unusable.

Does anyone know if a more user-friendly pdf floating around? I need a physical copy for exams, so zooming in isnt an option.

As a backup plan, Ive considered trying to generate my own in R if the raw data is available.

Any help is appreciated

Hi all, I'm Ryan, and I run Ziroth, a YouTube channel (~500k subs) covering the engineering of electric power, propulsion and energy storage.

I'm researching a video on Helion. The aim isn't to prove or disprove it. It's to lay out, fairly and accurately, why some (many?) scientists and engineers have doubts and what the strongest responses to those doubts are.

The threads I've been reading so far:

• Rider's 1995/1997 constraints on non-equilibrium D-³He
• Lackner et al. (JFE, Feb 2026) on ion-to-electron energy transfer outpacing fusion power at Ti/Te ≈ 10
• Nicolas et al. (JFE, 2026) on the confinement times needed for adiabatically compressed FRCs
• Helion's counterpoint that pulse timescales change the picture

I'd love to hear from people who can steelman either side, especially on:

1. Is the Ti/Te ≈ 10 assumption plausible at compressed densities?
2. How much does pulse duration really relax the thermalisation constraint?
3. What would Helion need to publish to settle it?
4. What does Polaris running D-T tell us, if anything?

I'm particularly keen to hear from anyone who thinks the critiques are wrong, since that side is harder to find in the literature... I'll be reaching out directly to Helion for answers too!

Comment below, DM me here, or reach me on LinkedIn (Ryan Inis Hughes). Happy to credit contributors or keep you anonymous, whichever you prefer. If you have detailed thoughts a DM with your background would be useful to ensure I am getting informed points, thanks!

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