a_cute_epic_axis t1_j5rl0d1 wrote

Reply to comment by jermdizzle in Why does hot air cool? by AspGuy25

> like inertial

One method simply measures how long it takes light to go through a coil, and if the coil is rotating it will take slightly longer or shorter than if it isn't. Three coils perpendicular (orthogonal?) to each other and you know how you're moving. Run the long term results through a filter and you can determine your latitude as well.

(Technically it's two beams in each fiber going opposite directions and they compare the phasing).




a_cute_epic_axis t1_j5qoaif wrote

Reply to comment by jawshoeaw in Why does hot air cool? by AspGuy25

> Windchill is a human experience and does not apply to physical objects like a computer.

It does if the computer is on and is exposed to wind. It has nothing to do with being human or alive, and everything to do with having an internal source of heat. Even in things that have no source of heat, wind chill will accelerate cooling until the object reaches the dry bulb temp (assuming there's no evaporation), as you mention... which rather obviously means it is not limited to "human experience".

You can argue that the term windchill refers to something typically used to describe human/animal outdoor comfort, but the concept is in no way limited to that.


a_cute_epic_axis t1_j5qnz9n wrote

Reply to comment by bikerlegs in Why does hot air cool? by AspGuy25

Wind chill can never reduce the temperature of an object below the dry bulb temperature of the air, unless that object is wet. In that case evaporation can occur and will result in cooler-than-dry-bulb temps until the water evaporates or until the air reaches 100% humidity.

The only time wind chill has any other effect is if the item in question is producing heat...e.g. a person or a house with the heat on inside. In this case the object will experience greater heat loss as the windspeed goes up. If the object doesn't have an internal heater, then the wind chill will speed cooling until the object reaches the dry bulb temp, and then have no impact.


a_cute_epic_axis t1_j5qn7mx wrote

Reply to comment by jermdizzle in Why does hot air cool? by AspGuy25

This is how a sling psychrometer works. It has two thermometers, one which has a cloth soaked in distilled water wrapped around the bulb. This produces a "wet bulb" and "dry bulb" temperature, from which you can determine humidity, enthalpy, dew point, etc. The wet bulb will always read the same or lower than the dry bulb. If they read the same, the RH% is 100%. If they are far apart, it's closer to 0%.


a_cute_epic_axis t1_j26lxov wrote

> That's a LOT more work than writing an article that says hope it's clear and look up tonight.

That's true but you said

> It's not something that can fit in a picture.

Which is bullshit because you certainly can. In fact you can take all of them in just three shots with an 18mm kit lens, well within the range of most people who would care to stand on a hill and take a picture. Obtaining a picture isn't hard at all, and you could probably do it in 10 shots zoomed in on the same kit lens, then stitch it with free or low cost software online. It's not going to be the JWST, but "not something that can fit in a picture" and "VERY difficult" are BS.

> I don't see you paying any subscription money.

I'm not sure how you determine that, but that said if I wanted that picture, I'd just go take it. Astro mounts for a camera are relatively cheap.


a_cute_epic_axis t1_j26jhs2 wrote

It really wouldn't be hard at all to obtain if you have one location that can see the entire relevant section of the sky without obstruction, although you would indeed see mostly just dots of light. For illustrative purposes (assuming you don't want to make a literal drawn illustration), you could take a picture with some understandable foreground and then enhance or mark up the photo to point out what it would look like. A drawn illustration or a screenshot from planetarium software would be easier, of course.


a_cute_epic_axis t1_j266oia wrote

I feel like this is the third time this year this rare event happened or one that is almost the damn same.

Like how every year the (insert name here) meteor shower will be the (insert nonsensical and possibly not even true platitude) of our lifetime. My favorite was one where the claim was something like "there are estimated to be more meteors than any other time in the past" and included a diagram of the sky on where to look, but omitted the full moon that almost perfectly coincided with the apparent source of the meteor shower.


a_cute_epic_axis t1_j18r45c wrote

In real world AC applications, if the outside air is colder (or substantially colder), then you run pumps, not compressors, and push the fluid around to move heat energy from inside to the cold outside. You could do this with water or glycol instead, but refrigerant is way more efficient. You could also just push air between the outside and inside, but then you have humidity issues and potentially pollution/contamination issues, which a refrigerant exchange avoids. If the outside air is warmer than the inside air, you switch to compressors and use the phase change to both overcome to inverse heat gradient (which you could not do at all without some amount of compression), and also because the energy exchanged in phase change is super efficient.

While on paper you might be able to keep everything a gas but achieve some comparably insane pressure to get from say below 50F to WAY above 150F on the inside and outside respectively, it's way easier to use a gas/liquid phase change.

You also have other benefits with gas/liquid... you can have an accumulator or a receiver that holds liquid and effectively reduces the refrigerant charge if there is too much refrigerant for the current operating conditions... and you can flood the refrigerant back into the outdoor condenser to effectively reduce its capacity if you are operating in very cold outdoor conditions but still need DX without freezing your inside coil (or don't have the option for pumped refrigerant economizers).


a_cute_epic_axis t1_j18p97i wrote

> But what real life factor means we can't try and use a gas both sides

You can, and some systems do used a pumped refrigerant economizer, where it just pushes the refrigerant around to move heat around without any phase change or any compression at all.

That said, the amount of energy that you use for a phase change is WAY more than you get with simple heating and cooling.