Wikipedia:Reference desk/Archives/Science/2021 October 1

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October 1

Spark in a flame.

My gas operated refrigerator (in my caravan) has a battery-powered igniter, and the sparking tip of it is about 6mm above where the gas and air mixture comes out of the mixing tube. To light the gas I switch on the igniter, and it sparks away until the gas mixture ignites, then it stops sparking even though the switch is still turned on. There is no heat-detecting mechanism to turn it off, so why does it stop? I am assuming that when there is a flame surrounding the igniter tip it acts as an insulator, but I have no idea why this would be so. Can someone explain what is happening please??49.197.133.215 (talk) 04:55, 1 October 2021 (UTC)

The flame is actually probably (very slightly) more conductive than the cold gas. I therefore suspect that the terminal of the spark plug contains an inbuilt heat detector. A voltmeter should be able to tell if the igniter has been disengaged, but may be hard to apply near the flame. Is it possible to keep the igniter turned on after the gas is turned off? If so, does it begin to spark again very quickly, or only after a considerable delay?  --Lambiam 05:33, 1 October 2021 (UTC)

(OP) It starts to spark again as soon as the gas flow ceases.49.197.133.215 (talk) 07:40, 2 October 2021 (UTC)

• It depends which flame and where in the flame exactly, but a flame is a plasma, meaning a soup of ions and electrons, meaning it is very conductive (much more than air). See for instance this article about the conductivity of an oxyfuel cutting torch.

OP’s gas igniter probably a spark generator circuit. It generates a high voltage to charge a capacitor in parallel with the air gap; when the capacitor starts charging the air gap is an insulator, but when you reach the breakdown voltage of the air gap then you have a (conductive) spark that discharges the capacitor; once the capacitor is discharged, the air becomes an insulator again and the cycle starts anew. See [1] for an electrical scheme (although I am not sure a transformer is used in small sparkers). When the air gap is flooded with a conductive flame, the capacitor cannot charge because the gap is conductive. Tigraan^{Click here for my talk page ("private" contact)} 15:30, 1 October 2021 (UTC)

Strictly speaking, only the fire zone of the flame, a thin boundary where the chemical reaction takes place, is plasma. The reaction product is not hot enough to remain a plasma for more than a fleering instant, and you would not be able to use the flame as a welding torch.  --Lambiam 21:55, 3 October 2021 (UTC)

(OP) Thanks, that sounds like the likely explanation. Wouldn't that mean it is still using up the battery power all the time the fridge is on? There is no mention in the operating instructions to turn the igniter off until you turn the gas off!!49.197.133.215 (talk) 07:40, 2 October 2021 (UTC)

It probably uses some electricity, but not much. I searched for actual numbers, but I did not find them, either by using "electric lighter" or "spark plug" as keywords (in addition to "voltage", "intensity", etc.).

I tried guessing, but it did not really work out: from the oxyfuel study linked above (fig 15) the flame resistance is at least R=20kΩ, and from Paschen's_law#Long_gaps and reasonable guesses on the design (about 1mm gap, voltage not much higher than needed to spark) we can guess the sparker voltage is about 4kV, but this gives a power across the gap of P=U^2/R=800W. That is about as much as a microwave, so, unrealistically high. Most likely, the circuit upstream of the gap produces 4kV voltage only when no current goes through, and it drops sharply as soon as some a few mA go through, so that taking 4kV as a steady-state value for conduction through the flame is incorrect. Tigraan^{Click here for my talk page ("private" contact)} 16:10, 3 October 2021 (UTC)

(OP) Thanks Tigraan 49.197.60.127 (talk) 00:49, 6 October 2021 (UTC)

Skybridge apartments

Has anyone built a tall building where some (more than a few) or all apartments are cantilever bridges? Sagittarian Milky Way (talk) 14:47, 1 October 2021 (UTC)

How would that work? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:02, 1 October 2021 (UTC)

What do you mean? You could have 2 or more towers (which could be anything from a typical residential tower to an apartmentless vertical concrete bunker probably hidden with thin shells (i.e. fake tinted glass wall, marble over concrete in the elevator area)) with a c. 1 room-wide apartment connecting them on every other floor. Engineeringly I think it could be done, don't know about economically. Might take some weird local things like zoning based on floor:land ratio but not height and high need for wind resistance. Sagittarian Milky Way (talk) 16:29, 1 October 2021 (UTC)

How about The Interlace? --Amble (talk) 20:22, 1 October 2021 (UTC)

Not the way I was thinking but a very aesthetic way to do it nonetheless. At ~200x300 yards it couldn't fit on 2 Manhattan blocks glued together! Sagittarian Milky Way (talk) 03:47, 2 October 2021 (UTC)

Maybe OMA was inspired by the "stacks"^[2] of Ready Player One. :)  --Lambiam 08:39, 2 October 2021 (UTC)

Why do Step up transformer used in transmission lines if it decreases the current ?

I just discover Step-Up transformer has more windings in secondary coil than primary coil.

I also discovered that this transformer will decrease current output. If it decrease the output, then why do we use this transformer in transmission lines? Rizosome (talk) 15:27, 1 October 2021 (UTC)

It is all explained at Electric power transmission. Basically, transmitting at high voltages reduces resistive losses. Mike Turnbull (talk) 15:34, 1 October 2021 (UTC)

What did you "discover" when you used a step down transformer? What happened to the current then? --OuroborosCobra (talk) 17:34, 1 October 2021 (UTC)

"Current output" is irrelevant. What counts is power, which is given by the product of current and voltage.  --Lambiam 20:19, 1 October 2021 (UTC)

Sugar in textured vegetable protein

A cup of soybeans contains 300 kilocalories, 31 g protein, 15 g fat, and 5 g sugar. A cup of textured vegetable protein (usually made from soy) contains 300 kilocalories, 48 g protein, 1 g fat and 16 g sugar. I understand that TVP is made from defatted soy flour, which explains the reduction in fat. But what explains the higher sugar content in TVP? Where does it come from? Lantzy : Lantzy 21:17, 1 October 2021 (UTC)

Most processed foods use added sugar in the form of high-fructose corn syrup. I haven't found a specific reference to that use for TVP but if you look at the list of the ingredients on the packet in the supermarket you should see it: possibly called HFCS 42. The idea is that the consumer still needs energy from their food, not just protein, so the carbohydrate provides that. Mike Turnbull (talk) 10:51, 2 October 2021 (UTC)

If you remove a composite part out of something, then, for any measured amount of what remains, the surviving parts should form a greater percentage of the whole than previously. I doubt that manufacturers ever add sugar to provide energy (except in energy drinks etc.) - usually it's added to make something more palatable and/or cheaper to manufacture. Our article on TVP doesn't indicate if there are any ingredients other than de-fatted soya, but it can be surprising what goes into the manufacture of processed foods such as this (for instance, jackfruit, which apparently has a meat-like texture, is used to make a vegan imitation of pulled pork - as described in this BBC article). PaleCloudedWhite (talk) 13:30, 2 October 2021 (UTC)

I think there may be an alternative explanation that partly or completely accounts for the difference. I don't know where the OP's figures come from but we have "Soybean, mature seeds, raw" and "Textured vegetable protein, dry" in our articles per 100g and from the USDA as is the norm with our figures. They are a little different, but maybe not so different.

Raw soybeans have 19.9g fat, 36.5g protein, 8.5g water and 30.2g carbohydrate made up 7.3g sugars and 9.3g dietary fibre. The TVP is 1.2g fat, 51.5g protein, 7.3g water and 33.9g carbohydrate made up of 16.4g sugars and 17.5g dietary fibre. Some obvious things stick out here. The relative proportion of protein has increased more (around 41% increase) than carbohydrate (around 12% increase). However dietary fibre and sugars have increased even more than protein, 88% for the dietary fibre and 125% for the sugars. They now represent basically the entirety of the carbohydrate content, unlike before where there was about 13.6g of other carbohydrates a greater proportion that anything else. According to Soybean#Carbohydrates:

The principal soluble carbohydrates of mature soybeans are the disaccharide sucrose (range 2.5–8.2%), the trisaccharide raffinose (0.1–1.0%) composed of one sucrose molecule connected to one molecule of galactose, and the tetrasaccharide stachyose (1.4 to 4.1%) composed of one sucrose connected to two molecules of galactose.[citation needed] While the oligosaccharides raffinose and stachyose protect the viability of the soybean seed from desiccation (see above section on physical characteristics) they are not digestible sugars, so contribute to flatulence and abdominal discomfort in humans and other monogastric animals, comparable to the disaccharide trehalose. Undigested oligosaccharides are broken down in the intestine by native microbes, producing gases such as carbon dioxide, hydrogen, and methane.
Since soluble soy carbohydrates are found in the whey and are broken down during fermentation, soy concentrate, soy protein isolates, tofu, soy sauce, and sprouted soybeans are without flatus activity. On the other hand, there may be some beneficial effects to ingesting oligosaccharides such as raffinose and stachyose, namely, encouraging indigenous bifidobacteria in the colon against putrefactive bacteria.

I couldn't find the definition of sugars used by the USDA, but I'm guessing it excludes undigestible oligosaccharides which is also supported by the unspecified type of carbohydrate in the sugars. Going by our article, it seems unlikely much of it is starch or similar. (To avoid confusion, the remaining unspecified content in the soybean is mostly "ash" [3], see the USDA data [4].)

Despite the possible advantages of consumption, the negative effects of the oligosaccharides are likely too undesirable. So even if the processing of the defatting process doesn't hydrolise them to at most disaccharides and probably monosaccharides, I'm not surprised it's an additional step. Whatever starch is present is I guess also hydrolised.

The reason for the higher dietary fibre yet lower relative proportion of carbohydrate, that I'm less sure of. It might be a combination of what is lost and kept during processing, the source of TVP not being the same as soybean, mature seeds, raw; and especially the intersection of that with variation between samples.

Nil Einne (talk) 07:51, 3 October 2021 (UTC)

I found [5] which supports my earlier hypothesis based on what our article said that the amount of starch is low in soybeans at the stage they are commercially harvest for oil. Nil Einne (talk) 11:37, 3 October 2021 (UTC)