explain xkcd - User contributions [en]

3035: Trimix

2025-01-10T06:24:25Z

172.71.99.67: /* Explanation */ maybe it's just me, but I'ts easier to read if the order of gasses is consistent

{{comic
| number = 3035
| date = January 8, 2025
| title = Trimix
| image = trimix_2x.png
| imagesize = 436x259px
| noexpand = true
| titletext = You don't want the nitrogen percentage to be too high or you run the risk of eutrophication.
}}

==Explanation==
{{incomplete|Created by a FLOATING TRIMIX SCUBA DIVER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
{{w|Trimix (breathing gas)|Trimix}} is a gas used in {{w|scuba set|scuba}} tanks that consists of {{w|oxygen}}, {{w|helium}}, and {{w|nitrogen}}. Trimix comes in some standard ratios between the component gases, depending on the required diving depth, for example 21/35/44 (percentage oxygen/helium/nitrogen), 18/45/37 and 15/55/30 for increasing depth. Helium safely substitutes a portion of the nitrogen to minimize nitrogen's narcotic effects at greater depths, and to ease the effort required for breathing, as merely reducing the nitrogen ratio in an oxygen/nitrogen mix will increase oxygen to levels that, at the pressures that exist at depth, {{w|Oxygen toxicity|creates other dangers}} (hence why the Trimix ratios also provide slightly lower proportions of oxygen). This comic suggests that, if the ratio of helium to nitrogen/oxygen is too high, a diver will float away before reaching the water to start a dive, as their tank of air starts behaving just like a sufficiently buoyant helium balloon. Divers rarely mix their own blends, so this would be the fault of the supplier who filled the tank from which the cylinder is filled. It would also be impossible to disproportionately breathe more of the non-helium, changing the ratio, although the way the comic depicts the tank only just starting to float ''might'' suggest that it is somehow being adjusted to the 'wrong' ratio as we watch.

The reason a helium balloon [[585: Outreach|creates lift]] is that it can inflate. The balloon has a thin and expandable layer, weighing almost nothing, that allows the intrinsically less dense gas to take up space at not much more than atmospheric pressure. The total weight of the filled balloon is less than the total weight of the air it displaces, thus creating {{w|buoyancy}}. A scuba tank is made of metal, is heavy and cannot inflate in anything like normal circumstances.{{cn}} Even with a {{w|vacuum balloon|perfect vacuum inside it}} (if that were possible) it would still weigh more than the equivalent volume of air. You would simply increase that weight if you pumped helium, or ''any'' kind of gas, into it. An inflating helium balloon also gets heavier, but this is more than compensated for by the greater increase in volume. The more you pumped into a rigid metal tank, the denser and heavier it would get, and it will never be able to create any degree of additional lift. The comic falsely implies that adding more helium to the system decreases its net relative weight, without taking into account the need to displace a greater volume of air.

The real reason scuba divers need to be careful with the amount of helium is to not get too little (or too much) oxygen for the intended depth and pressure, as well as reducing the troublesome nitrogen.

The title text asserts that a trimix diver whose gas mix contains an excess of nitrogen runs "the risk of eutrophication". The term {{w|Eutrophication|eutrophication}} describes the process by which nutrients ("fertilizers") accumulate in an environment, typically a body of water, leading to consequences that are often unfortunate for inhabitants or users of that environment. The human body is an ecosystem, but one that is not typically subject to eutrophication, due to its manner of acquiring and jettisoning nutrients. Moreover, the nitrogen in trimix is diatomic elemental nitrogen, not the {{w|Nitrogen_fixation|"fixed"}} nitrogen that serves as a component of eutrophication. The diver would not breathe "fixed" nitrogen unless nitrogen-fixing bacteria were somehow incorporated into the scuba gear, a complex feature of dubious utility.
Eutrophication can also be understood as the diver dying of nitrogen exposure thus adding nutrients (the dead body) to the body of water.

[[Randall]] addressed the question "how much helium is needed to lift a human body" in a [https://what-if.xkcd.com/62/ What if?] article. Helium has also featured in comics [[2766: Helium Reserve]] and [[2972: Helium Synthesis]].

==Transcript==
:[In a single frame five images of Cueball are shown as a kind of a cartoon event sequence, from left to right, with each image a later time in the process. The first image shows Cueball standing by the shore of a body of water. He is wearing scuba gear, goggles, breathing tubes, scuba tanks with a small H logo on it on his back, and swimming flippers, which almost touch the water.]

:[In the next four images he has the same equipment on, but with changes. He is presumably still at the edge of the water, but the water is not drawn in the next four images.]

:[In the second image, Cueball's scuba tank is beginning to float upwards, so the end that is not teetered to Cueball moves out and up, as shown with three small lines beneath the tank.]

:[In the third image the scuba tank is now floating above Cueball's head and the strings pull his arms a bit upwards. Cueball has turned his head looking up at the tank floating above and behind his head. Again three small lines beneath the tank indicates it is moving upwards.]

:[In the fourth image Cueball is now being lifted up, so his feet are now off the ground and he is tilting forward. The tank is now pointing its bottom almost straight up and Cueball is looking down with his arms out to each side as the tank pulls him up. Two lines on either side of the tank indicate that it now wobbles above him as it lifts him up.]

:[In the fifth and last image the scuba tank is now pulling a dangling Cueball with his legs splayed high above the ground, above his head's height in the first image. The tank is now turned so it points its bottom to the left with lines on either side indicating wobbling motion. Cueball is floating in a roughly horizontal position as the tank's straps pull him upwards. At this point he yells:]
:Cueball: ''Help!''

:[Caption below the panel:]
:Trimix scuba divers need to be careful not to let the helium percentage get too high.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Chemistry]]
[[Category:Sport]]

Talk:3016: Cold Air

2024-11-27T08:19:15Z

172.71.99.67: refrigeration vs. expansion cooling

Back In The Day, one of the idiot youngsters in a first-year chemistry lab, before leaving at the end of the afternoon, connected a water faucet to a natural-gas line (used for Bunsen burners) with a rubber hose, and opened both taps. By the next morning, much of the natural-gas network in the heart of the city was flooded. It took a while to get everything working again, and the cleanup wasn't cheap. [[User:BunsenH|BunsenH]] ([[User talk:BunsenH|talk]]) 22:50, 25 November 2024 (UTC)
:You have the right username to mention this! ;)
:Also, the 'big trick', back in my day, was to be at the (correct end of) the science-lab bench and briefly blow into a pipe (temporarily unplugged from the burner) just as you turn your tap on. Then watch as the rest of the row (downstream of your connection to the supply) have their active flames go out. ...but I leave it to your imagination the ''three'' main problems (and various other less major ones) with trying that, with the benefit of hindsight. [[Special:Contributions/172.69.195.201|172.69.195.201]] 00:02, 26 November 2024 (UTC)

Anyone understand the physics here? It seems clear that adding tanks of cool, dry air will make storms (and particularly tornados) far worse, not better, as the incoming hot, wet air will react with any released air to make even worse/dramatic weather patterns. But is there more to it? If the tanks are sealed, then effect could be muted by simply not releasing the stored air once the problem is realized, but this would be countered by at least two factors: First, the title text indicates that an additonal error was made resulting in it beingg impossible to seal the stored air completely (it escapes through the water system). But also, any time weather got bad enough to open leaks in the system, I think this would produce a catastrophic result as the storm mixed with all the cold dry air at once? [[User:Mneme|Mneme]] ([[User talk:Mneme|talk]]) 23:01, 25 November 2024 (UTC)
:My understanding is generally that explosive failure of a container with sufficient "anti-tornado" air inside is going to be non-trivial (and you face this threat constantly, in the settlement that has an "air tower", whereas tornados are relatively infrequent and mostly cross countryside). ''post-edit: And the editor who set up the current explanation seems to have had much the same idea... gratifying to know I'm on the same wavelength as at least one person!''
:And the water-connection would be bad due to (first) extremely pressurised water and (immediately afterwards) almost as pressurised air pushing through the areas plumbing systems, with unknown secondary effects such as effectively blowing empty any water-heaters that ''really'' shouldn't be left to be 'boiled dry' (after enough air bubbles in, the remaining water will soak up the burner heat and evaporate beyond design limitations, adding to the gas pressure ''and'' no longer moderating the effects on the boiler body itself; not sure exactly what will go wrong, but it may not be pretty). [[Special:Contributions/172.69.195.201|172.69.195.201]] 00:02, 26 November 2024 (UTC)

Without knowing which 'city' the diagram might be of (or, indeed, how figurative Cueball's illustrative figure might be), I checked the first "tornado alley" city I could think of and came up with {{w|One Kansas City Place}} as how tall the taller buildings might be. In that case, just shy of 200m (with spire on top) and 40-odd floors. The dimensions of the 3000psi tank (external, but ignoring support infrastructure) is somewhere around 400m in height, perhaps 600m side to side, presumably oblate spheroidal, so approaching (less thickness of container walls) 75 ''million'' m³ of compressed air. Which is compressed, and would otherwise be around 15,000 million m³ (15 km³!) of atmosphere if ever released. As a very vague upper limit. Notwithstanding the apparent use of an existing (ex-)water-tower in the titletext. But obviously there's possibly abstract and definitely reinterpretable alternative interpretations of the quantities that might be involved. [[Special:Contributions/172.69.195.225|172.69.195.225]] 00:48, 26 November 2024 (UTC)

It seems that the wiki math package <pre><math> </math></pre> Does not work properly, and returns an error Failed to parse <pre>(Missing <code>texvc</code> executable. Please see math/README to configure.):</pre> when I attempted to add the math describing the speed of the air using LaTeX [[Special:Contributions/172.68.22.92|172.68.22.92]] 01:06, 26 November 2024 (UTC)
:This is a long-standing error (at some point, one bit of update invalidated the rendering process, and nobody is currently able to update the other component/configuration).
:There are plenty of alternate ways to format a newly needed formula, without TeX, and anything that's the same as when it was pre-rendered will continue to show as the inline "formula image" (which I think is potentially worse, anyway, when it comes to accessibility issues). It's really not too hard to do it without the math-tag extension working properly, though. e.g. <table style="display: inline-table; line-height: 0.6em; text-align: center; vertical-align: middle; font-size:10pt; font-style: italic; text-size-adjust: none;"><tr><td style="border-bottom: 1px solid black;">p1•v1</td><td rowspan="2">=</td><td style="border-bottom: 1px solid black;">p2•v2</td></tr><tr><td>t1</td><td>t2</td></tr></table> ...as quick example with just a little bit of fine tuning applied. [[Special:Contributions/172.70.160.134|172.70.160.134]] 01:44, 26 November 2024 (UTC)

The statement that 3000PSI is 6x higher than known high pressure systems is false. Scuba tanks contain air at this pressure (240bar/3000psi) and the systems used to fill scuba tanks are twice that. {{unsigned ip|172.71.26.101|09:28, 26 November 2024}}
:Perform the wiki magic and add that source!--[[User:FrankHightower|FrankHightower]] ([[User talk:FrankHightower|talk]]) 15:04, 26 November 2024 (UTC)

[https://www.google.com/search?q=40+Bar+to+psi My calculator (Google)] says 400MPH is 644 KPH (not 500). Also 40 Bar seems to be well on the high side of 500psi (580psi).

''"winds of about 40-400 mph [1] (about 50-500 kph)" "about 40 bar [2] (about 500 psi)."''

--[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 01:11, 26 November 2024 (UTC)
:The source says tornadoes go up to 318 mph (512 kph) but the [https://en.wikipedia.org/wiki/1999_Bridge_Creek%E2%80%93Moore_tornado strongest tornado on record] exceeded that. I couldn't confirm when I wrote whether that was ''actually'' the strongest, and since the only purpose of the number is to say "Cueball's windspeeds are way, way worse", I decided an upper bound of 400 covered it.--[[User:FrankHightower|FrankHightower]] ([[User talk:FrankHightower|talk]]) 15:04, 26 November 2024 (UTC)

"I decided an upper bound of 400 covered it." Somebody edited my words and omitted the key point: ARITHMETIC. English to Metric is NOT 4:5. --[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 23:32, 26 November 2024 (UTC)
:Hmmm... "English to Metric". Strange phrase, for ''various'' reasons. ;) [[Special:Contributions/172.69.195.200|172.69.195.200]] 00:13, 27 November 2024 (UTC)

So my brief wikihole dive has me doubting again; but is the part about requiring refrigeration accurate? By my understanding, pressurising the air in the first place would raise its temperature. It then goes back to equilibrium with the environment while it's stored at pressure, and temperature drops when it's released.