Science desk
< November 5	<< Oct \| November \| Dec >>	November 7 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 6[edit]

air conditioner refrigerant charge refill[edit]

I recently had had the refrigerant charge within my air conditioner refilled. The procedure was the same as described here[1][2]. But since I live in a high-rise building and my compressor is installed outside, the worker had to put on a safety harness, climb out my window, and carry the heavy steel refrigerant container with him to recharge the compressor unit. Needless to say it looked horrifically unsafe, but the worker told me there was no way to refill the refrigerant charge through the indoor unit. A quick search online would confirm this. I haven't been able to find any split-unit AC that you can refill through the indoor unit.

A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor

My understanding is that the outdoor compressor and the indoor unit make up a sealed loop. How come it's not possible to inject refrigerant using the indoor part of this loop? Mũeller (talk) 04:15, 6 November 2019 (UTC)[reply]

The hot side should be at highest pressure normally, and thus designed to withstand higher pressure. Assuming the refill tank is at a comparable pressure, then injecting it into the low-pressure (cold) side might cause a leak, unless done very slowly while the A/C operates. If nothing else, you would think the manufacturer would provide a valve that leads to the high pressure side from the inside of the building, for service. SinisterLefty (talk) 04:28, 6 November 2019 (UTC)[reply]

According to the instructions, the AC is supposed to be recharged in the powered off state. Wouldn't the pressure be equalized after power has been off for a few minutes? Mũeller (talk) 04:47, 6 November 2019 (UTC)[reply]

That would depend on the design. The compressor probably prevents back-flow, and at the other end there may be a valve that closes, when off, to prevent pressure equalization. That would make it start up faster, more efficiently, and would avoid them having to make the cold side able to withstand high pressures. SinisterLefty (talk) 04:56, 6 November 2019 (UTC)[reply]

I see. That makes a lot of sense. Thank you!Mũeller (talk) 07:57, 6 November 2019 (UTC)[reply]

There are two filling ports: high pressure and low (usually coded red and blue). A refill manifold has a hose to the gas cylinder or vacuum pump (yellow hose) and valves and gauges to the high and low sides.

It's possible to refill low-side if it's only a minor top-up, but any significant refill needs to be done on the high side. For a through-wall unit, they're all in the same box and access is easy. If it's a split unit though, you'll need access to the piping around the condenser, somewhere between the compressor and the expansion valve - all of which is likely to be in the outside box, where the condenser needs to be, where the compressor is to avoid indoor noise, and where the expansion valve is so that the long flexible pipes between the boxes are all in the low-pressure part of the circuit.

They could provide a limited-use high pressure connection from indoors to outdoors, just for filling. I'm sure somewhere will have done this, for some application where access is particularly awkward. But it's not usual, just to avoid long high-pressure pipe runs.

It's also necessary to run the compressor a little, during the filling process, just to circulate the gas and ensure that the whole loop has been filled correctly. Andy Dingley (talk) 15:47, 6 November 2019 (UTC)[reply]

STIs emergence[edit]

How exactly STI pathogens, like bacteria, got onto humans in the first place? This only says that such diseases were known since antiquity, but it seems that the human-to-human transmission chain of all STIs should have its origin somewhere, similar to HIV emergence (something like evolutionary jump or picking up from soil). Thanks. 212.180.235.46 (talk) 12:07, 6 November 2019 (UTC)[reply]

See Coevolution. One likely possibility is that the pathogens may have been infecting species along the human ancestral chain back millions of years, and have evolved along with us. Or someone has some weird kinks... --Jayron 32 12:56, 6 November 2019 (UTC)[reply]

Also, a disease which wasn't solely sexually transmitted could have evolved to specialize in that mode of transmission, perhaps splitting from the original form, perhaps replacing it. Viral hepatitis is a disease which currently has multiple modes of transmission, with only Hep B being primarily sexually transmitted. SinisterLefty (talk) 16:22, 6 November 2019 (UTC)[reply]

Quote, R. D. Laing " Life is an STI with 100% fatality" Thanks Anton 81.131.40.58 (talk) 16:44, 6 November 2019 (UTC)[reply]

Just to avoid confusion, diseases don't really undergo biological evolution. Their agents do. This is an important distinction as illustrated by the example. From a quick look, the Hepatitis viruses: Hepatitis A virus, Hepatitis B virus, Hepatitis C virus, Hepatitis D virus, Hepatitis E virus don't seem particularly related to each other. While viral evolution is complicated and it's particularly difficult to discern the early evolutionary history, it's likely that the fact these cause similar diseases is more a result of convergent evolution and the mammalian host body. In fact, I just notice that Viral hepatitis mentions the unrelated bit. Hepatitis D seems a particularly interesting case, it requires a concurrent hepatitis B infection. See e.g. [3] [4] [5], Nil Einne (talk) 16:54, 6 November 2019 (UTC)[reply]

To clarify an additional point, a number of Sexually transmitted infection aren't exclusively sexually transmitted. This is particularly the case for viral diseases which may simply require blood or some other bodily fluids without even requiring contact with the genital area, HIV is far from an outlier. Bacterial STIs are more complicated, as quite a few of these only really infect the genital area and so at a minimum require contact with those. Still, these don't necessarily require weird kinks, someone contacting some non humans genital area such as when they are eating it (assuming no cooking) or preparing it to be eaten may not be that unlikely, and touching their own genital area not that long later, again maybe not that unlikely. While transmission through this means may be very rare, it may only take one case. That said, I suspect most STIs have simply coevolved as Jayron32 suggested. Nil Einne (talk) 17:16, 6 November 2019 (UTC)[reply]

Our article on History of syphilis may be instructive in showing how difficult it can be to determine the origins of a disease, even ones as sensational and infamous as syphilis. Matt Deres (talk) 20:21, 6 November 2019 (UTC)[reply]

Is there an element, alloy or other substance[edit]

That is less dense than osmium but, if the pressure got high enough, is predicted to compress to a higher density than osmium would at the same pressure? Sagittarian Milky Way (talk) 21:39, 6 November 2019 (UTC)[reply]

neutron, as in neutron star? Gem fr (talk) 22:46, 6 November 2019 (UTC)[reply]

As I understand it, the pressure needed to create neutron-degenerate matter, loosely called neutronium, would inevitably convert osmium and any other substance to neutron-degenerate matter also. The density of a single neutron is calculated here, and shown (at 3.0 x 10²⁶ kg/km³) to be 1.5 x that of a neutron star (which contains more than just neutronium). My back-of the envelope calculation (which may well be wrong – corrections welcome!) indicates this is about 1.3 x 10¹³ times the density of osmium at STP, FWIW. {The poster formerly known as 87.81.230.195} 2.122.179.237 (talk) 00:32, 7 November 2019 (UTC)[reply]

Yes, see https://www.technology.matthey.com/article/58/3/137-141/ which claims that iridium density will overtake that of osmium at 2.98 GPa, because its bulk modulus is much smaller, and thus it squashes down more. Gold is even more compressible, and can reach quite high densities (29 at 200 GPa) see https://www.researchgate.net/profile/Jeffrey_Peterson3/publication/232242654_Tabular_equation_of_state_for_gold/links/00b4951aea3924f39f000000/Tabular-equation-of-state-for-gold.pdf so it very likely overtakes osmium too. Graeme Bartlett (talk) 12:02, 7 November 2019 (UTC)[reply]