Wikipedia:Reference desk/Archives/Science/2012 June 5

= June 5 =

What is the difference between Julian and Georigian calendars?
This is related to question I asked on Maths reference desk, but I figure this is more of an astronomy thing. I need to calculate age for bunch of people given their ages on certain dates. The dates are old style. As far as I understand the only difference between Julian and Georgian calendar is that in the former case there is always a leap year at the turn of the century. So I would figure that as long as both dates are old style, I could use online calculator somebody has made for Georgian calendar. However doing so causes descrepency in the results, that makes the estimiation imposible. I tried to do estimiate for different person from one described before living in different pace, in case of which exact date for all reference points was available. I get discrepency exactly on turn of the century - it is possible to do estimiate with data from before and after the fact, but using all data points produces impossible result, which is off by months, not just one day. (Person was 17 on 10.03.1782, 30 on 30.05.1795, 46 on 04.09.1811, 50 on 17.04.1816, 60 on 02.08.1826, thus the earliest he could have been born is august, but the latest - april of the same year) Is all data wrong or am I missing something? Xil (talk) 02:04, 5 June 2012 (UTC)


 * The use of the Julian calendar with its excessive leap years for so long resulted in a calendar drift of about 1 day every 133 years. This means you need to subtract a particular number of days when moving from old style to new style; see Gregorian calendar.  It wouldn't account for a discrepancy of months, though.  From reading the other question, it sounds like a simple case of your data being wonky. :) FiggyBee (talk) 03:43, 5 June 2012 (UTC)
 * I said I expect them to be a little off, because I imagined the date might as well refer to when data colected were written down and submited the authoroty and the first set I tried had exact date missing for one reference. However I did a bit of research - they refer to age on the date of the census, the datees in different settlements are different, and originaly data was double checked, the whole thing was used for tax collection, so I wouldn't expect it to be that much off (in first case the first reference was almost a year off from what consistent data suggested, but seemed more realistic given the age of person given in previous census), rather something is wrong with the method of calculation Xil  (talk) 06:53, 5 June 2012 (UTC)


 * If your dates cross 1752, then there was the problem with the change in the start of the year from March 25th to January 1st. See Old Style and New Style dates for details.  This doesn't account for the error in your example of 1782, unless the recorder was still using old-style dates (common in Quaker records).    D b f i r s   07:15, 5 June 2012 (UTC)
 * The dates are from Russian Empire, which used old style untill 20th century, the date for the new year, though, apparently was changed in 1700 Xil  (talk) 07:57, 5 June 2012 (UTC)


 * Just google "julian to gregorian converter" and "distance between two dates". Sagittarian Milky Way (talk) 17:08, 6 June 2012 (UTC)

Another problem is that the date when the year number changed was not always January 1. For example, in England up to and including 1751 the year number changed on March 25. See Calendar Act of 1750. I don't know if the Russian empire used January 1 as the date to increase the year number during the period you are interested in. Jc3s5h (talk) 17:38, 6 June 2012 (UTC)
 * Yeah, it did, they swiched to January 1 in 1700 and I don't think it would have any influence on age counting - say if you are born on 20th August, you will still have birthday on the same day, if the new year is on a different date (when you swich to Georgian though, your birthday is moved by about two weeks). I am quite at loss what else could be wrong here. I'd expect inconsistencies officials make to be consistent in themselves. Also I find it weird that the problem occurs exactly on turn of the century, which to me suggests the leap year could be the cultprit. I tested the method by seeing if it was possible to work back to my own birthday, which is Georgian calendar date, and it seemed viable as I did come up with six month period during which I indeed was born. I figure the best way to test it would be to find exact birth date in someone's vital records and see if I can calculate that, but unfortunetly many of the vital records also state age, not birth date, so I haven't yet come accross one that will do Xil  (talk) 00:11, 7 June 2012 (UTC)


 * Just a word that it's the Gregorian calendar, named after Pope Gregory XIII. There has never yet been a Pope George.  --  ♬  Jack of Oz  ♬  [your turn]  06:13, 7 June 2012 (UTC)
 * There's been a John-Paul, though, so we're just waiting on George and Ringo... - Nunh-huh 08:53, 7 June 2012 (UTC)
 * I am well aware of that, don't know why I wrote something else :) at any rate I managed to find a julian to gregorian converter, which proved that using Gregorian dates also results in BS, also I think I figured out why (I'll explain on Maths desk), so as far as calendar is concerned - thanks for confirming what is the difference Xil  (talk) 10:00, 7 June 2012 (UTC)

Tubular lights for DIY lamp
There is a computer game (Deus Ex: Human Revolution) which features a candle stick with an electric light. I rather like it and would like to attempt to create something similar myself. I was wondering what would be suitable to best mimic the sticks of light. Neon tubes? EL tape coiled around a cylinder? --2.120.147.92 (talk) 07:13, 5 June 2012 (UTC)
 * Sort of like this? --TammyMoet (talk) 07:44, 5 June 2012 (UTC)
 * Good call, Tammy - I think LEDs are the right way to go with this. Another option (note that this is educated guesswork rather than experience) would be to find some clear polycarbonate rods or cylinders, then either sandblast them or use some other form of abrasive medium to scuff the surface so they'll scatter light when lit from below. I suspect a 2 W or 3 W LED would be more than enough, depending on how bright you want it. There's a website called Hackaday which has a lot of people on it who will have all sorts of ideas about how to do the project, and crafting expertise to go with it. Might be worth paying a visit to their forums. Brammers (talk/c) 10:54, 5 June 2012 (UTC)
 * If you want a tubular light where the whole cylinder has a fairly uniform lighting like in the screenshot (which doesn't look much like a candle to me) compared to edit:instead of something like Tammy showed (which does), you may want to look in to people making light sabers lookalikes. There are plenty of plans and discussions on how to do it online, I think I even mentioned some on the RD before. Your base will obviously be different (edit: and I presume you don't care about things like extend/retract effects, dueling durability or sound effects ), but that's a fairly minor thing to modifyNil Einne (talk)
 * Here you go http://www.instructables.com/id/Flickering-LED-Candle-1/ or http://www.instructables.com/id/YAFLC-Yet-Another-Flickering-LED-Candle/ and there are several others on the site too. --TrogWoolley (talk) 18:21, 5 June 2012 (UTC)
 * Right but that's like what Tammy showed, something that really simulates a candle and not like what's shown in the screen shot the OP provided, for which as I said you can get a lot of help from those who make light sabers. The OP hasn't clarified which one they meant (but you reply is indented under my reply). Nil Einne (talk) 08:19, 6 June 2012 (UTC)
 * Thanks Nil Einne; that's a great idea. I've checked out some of the tutorials and now I've got good guidance. 2.120.147.92 (talk) 10:16, 6 June 2012 (UTC)

Growing computer memory using bacteria - Why use gold?
While reading this article, it struck me... Why use gold?


 * "Next, they imprinted a block of gold with a microscopic chessboard pattern of chemicals. Half the squares contained anchoring points for the protein. The other half were left untreated as controls. They then dipped the gold into a solution containing the protein, allowing it to bind to the treated squares, and dunked the whole lot into a heated solution of iron salts."

Is it because it's not magnetic? It's a good conductor? It lends your project a certain flair? Why? Thanks, Dismas |(talk) 07:56, 5 June 2012 (UTC)


 * The best conductors are silver, copper, and gold, in descending order. Both silver and copper have antibacterial properties, so gold would be the practical choice. Gold is also much more corrosion resistant than the other two, so that's probably a plus in the laboratory setting. Anonymous.translator (talk) 11:09, 5 June 2012 (UTC)
 * Corrosion resistance is pretty important when you're making microscopic metal structures and then dipping them in an aqueous solution. --Srleffler (talk) 17:20, 5 June 2012 (UTC)
 * Thiols bind to gold fairly well, so it's a common trick to use a cysteine residue to anchor a protein to a gold substrate. Not too many other metals have that property without having other chemical effects as well (corroding, excessively reactive with your protein or other chemicals in general, etc.) DMacks (talk) 15:03, 5 June 2012 (UTC)

Mono- and di-glycerides of fatty acids - Trans fats?
According to some questionable sources found via Google, mono- and di-glycerides of fatty acids (E471) are just a sneaky way of not listing trans fats in the ingredients of certain products. My question is, when MAGs/DAGs are produced from vegetable oils, how do the manufacturers know they aren't producing MAGs/DAGs with a trans-fatty acid side chain? --Markr4 (talk) 12:31, 5 June 2012 (UTC)


 * This is more of a legal question than a scientific one, and I haven't yet found where "E471" is defined in a standard. Certainly looking at a wholesaler site, there are different grades .  One says "90% stearate", for example, which means much of it is not trans fat.  Since it is called "distilled monoglycerides", there should be no deliberate partial hydrogenation over a catalyst... I think.  And many have sources like palm oil and tallow which should be nearly saturated to start with.  But I don't know how well its quality would be defined or enforced...  in theory, a monoglyceride is just a one-chain fat, with no specification of whether it's trans or not. Wnt (talk) 20:33, 6 June 2012 (UTC)
 * Thank you for the reply. When I see mono/diglycerides in the list of ingredients of a product, it normally also lists the product as Suitable for Vegetarians, so at least for those products it obviously isn't derived from tallow. Some other sources say that palm oil is expensive, so manufacturers are using MAGs/DAGs derived from cheaper oils which may be less saturated and therefore more prone to being trans fats.
 * I'm surprised by the lack of information about this though, and I wonder if the plethora of epidemiological studies that look at the effects of fats on heart disease have controlled for MAG/DAG intake... --Markr4 (talk) 14:36, 7 June 2012 (UTC)
 * I would expect that the amount of E471 used is far less than the amount of fat in a typical product (it is an emulsifier which has quite different properties from fat). Icek (talk) 19:16, 7 June 2012 (UTC)

Transit of Venus-inspired question
Today's transit of Venus got me wondering what other astronomical phenomenon are coming up in the next few years. Do we happen to have such an article? A Quest For Knowledge (talk) 17:26, 5 June 2012 (UTC)
 * The best I can suggest is to start from Category:Astronomical events of the Solar System, and explore the subcategories. Each subcategory has lists within it, such as Lists of solar eclipses.  There are so many dozens of these "events" that having a master list of everything would get cumbersome.  Between conjunctions, syzygys, eclipses, transits, etc. etc. there's probably something "interesting" monthly.  Sadly, Jack Horkheimer has passed; he had an excellent weekly TV program that aired on PBS that did a great job of highlighting exciting and interesting astronomical events.  The show still exists, but without Jack it has lost much of its excitement (IMHO).  See Star Gazers.  If you don't have access to PBS on your TV, you may be able to find episodes online.  -- Jayron  32  17:38, 5 June 2012 (UTC)
 * Hmmm...List of astronomical phenomenon visible from Earth might not be unwieldy as long as the inclusion criteria includes:
 * Must be visible from Earth with the naked eye.
 * Must be notable on its own. A Quest For Knowledge (talk) 17:48, 5 June 2012 (UTC)


 * The first Google hit on is http://www.seasky.org/astronomy/astronomy-calendar-2013.html. There are pages for all years from 2010 to 2020. PrimeHunter (talk) 17:50, 5 June 2012 (UTC)
 * The Sky at Night is a similar TV programme in the UK. It's monthly and each episode includes a segment on naked eye/binocular astronomy in the next month. --Tango (talk) 18:35, 5 June 2012 (UTC)

Occultation of Regulus by asteroid 163 Erigone on March 20, 2014, visible near New York. Count Iblis (talk) 19:32, 5 June 2012 (UTC)

Supernova explosion of Betelgeuse:

"The explosion will be so bright that even though the star in the Orion constellation is 640 light-years away, it will still turn night into day and appear like there are two suns in the sky for a few weeks."

Count Iblis (talk) 19:42, 5 June 2012 (UTC)
 * Ah but, which will explode first - Betelgeuse or Yellowstone park? Richerman ''   (talk) 20:03, 5 June 2012 (UTC)
 * This slide show was in today's Telegraph: Only goes up to 2014 though. --TammyMoet (talk) 19:54, 5 June 2012 (UTC)


 * I was not aware of this until recently, but while comet orbits are well known after their discovery, whether they will be barely visible or spectacular even during the day is wildly unpredictable. Comet Kohoutek in the 70s was touted as the greatest astronomical spectacle of my parents' generation, but it turned out to be quite a dud; while Comet McNaught (C/2006 P1) caught people quite by surprise and became the brightest comet in 40 years (unfortunately, not visible to those of us in the Northern Hemisphere). So heck, there could be the greatest comet in modern history visible next month for all we know! - Running On Brains (talk) 01:00, 6 June 2012 (UTC)
 * Actually it was if you knew where to look. I saw its braided tail above the southern horizon at twilight in Coventry, UK. Granted it was faint, but I saw it for at least a week before it finally disappeared. A stunning sight. There is a photo of the phenomenon taken from Switzerland in the gallery in the article. --TammyMoet (talk) 09:32, 6 June 2012 (UTC)

Particle in a box
Let's say under Quantum Mechanics you have a particle in a box. Let us say that at some point in time you measure the momentum of the particle to be $$p_0$$. Obviously, the wavefunction has collapsed to this state of definite momentum. Now, let us wait a sufficiently long time until the wavefunction has stabilized such that there are probabilities of measuring other probabilities. Now, let us say we measure a new momentum $$p_1 \ne p_0 $$. Why does this not violate the notions of conservation of energy and/or conservation of momentum? — Trevor K. — 18:30, 5 June 2012 (UTC)  — Preceding unsigned comment added by Yakeyglee (talk • contribs)


 * Momentum, like any other conserved quantity, commutes with the Hamiltonian, so the result doesn't change under time evolution. Count Iblis (talk) 19:28, 5 June 2012 (UTC)


 * Two points, which are really saying the same thing: (1) If you know the particle is in the box then the uncertainty in its position is finite, and so Heisenberg's uncertainty principle says that the uncertainty in its momentum must be non-zero. (2) How do you propose to measure its momentum with exact precision without disturbing it ? Gandalf61 (talk) 11:48, 6 June 2012 (UTC)


 * This is a trickier question than I thought at first. Momentum is not conserved in the particle in a box. The particle's momentum changes when it bounces off the walls and there's no corresponding change in the momentum of anything else. There are no states of definite momentum, either (as Gandalf said, that would violate the uncertainty principle). So there's no way to measure the momentum exactly in the first place, and no reason to expect the same answer when you try again later. -- BenRG (talk) 21:21, 6 June 2012 (UTC)

Why does a power station need cooling?
Whereas a steam locomotive doesn't? (possibly related side question: why isn't the steam coming from a locomotive or power station used to pre-heat the water to preserve charcoal?) Joepnl (talk) 22:27, 5 June 2012 (UTC)
 * To the 1st question, I suppose it's just a factor of power output. If a steam locomotive could generate hundreds of megawatts, I imagine it would also need cooling. To the 2nd question, steam is most certainly used to pre-heat the water in power plants and locomotives using a Feedwater heater. Vespine (talk) 22:52, 5 June 2012 (UTC)


 * A steam locomotive does need constant cooling. That's why there are water towers in each train station back in the day. The water turns into steam and carry the excess heat off, while doing useful work. Anonymous.translator (talk) 22:57, 5 June 2012 (UTC)


 * A steam locomotive doesn't need cooling because it's an open cycle steam engine, and the power increase from passing the exhaust steam through a condenser isn't enough to offset the increased weight and complexity. (There were condensing steam locomotives, but they tended to be used only in unusual conditions).  I'm not aware of any locomotives that pre-heated the feedwater, rather, the steam was sent through a blastpipe to greatly increase the draft (and thus the combustion effectiveness) of the firebox. --Carnildo (talk) 23:31, 5 June 2012 (UTC)


 * Our feedwater heater article discusses its use on locomotives. DMacks (talk) 00:07, 6 June 2012 (UTC)


 * Steam locomotive has lots of detail on the operation of those machines. The water towers along the tracks were for refilling the water tanks on the train, not for cooling as such. Where there was a gap, towns were constructed specifically to provide water for the locomotives, hence the term "tank town" for any small town. ←Baseball Bugs What's up, Doc? carrots→ 23:53, 5 June 2012 (UTC)


 * Well, in a way, they were for cooling, in that cool water was taken in and hot steam was let off while the engine ran. The only way to avoid this cooling effect would be to recondense the steam, which, as previously noted, was rarely done in locomotive steam engines. StuRat (talk) 01:36, 6 June 2012 (UTC)


 * That's possible. In any case, the tank towns' primary purpose was to resupply the locomotives with water. ←Baseball Bugs What's up, Doc? carrots→ 02:38, 6 June 2012 (UTC)


 * Right, but it's really the same thing, in that the reason they needed to resupply water is that the old water got hot and boiled off. StuRat (talk) 03:14, 6 June 2012 (UTC)


 * I recon that the reason is that it is easier to control internal temperature for a steam locomotive that it is for a power station. It is a matter of scaling laws. A larger engine takes more time to change its temprature in reponse to a change in fuel. Plasmic Physics (talk) 03:25, 6 June 2012 (UTC)
 * Similiarly, which melts faster: a one ton ice block, or a ton's worth of ice cubes spread out? Plasmic Physics (talk) 03:27, 6 June 2012 (UTC)


 * When Plasmic Physics and StuRat cook their vegetables in a saucepan or steamer (http://en.wikipedia.org/wiki/Steamer_(appliance)), they must think the water is for cooling the said vegetables, unlike the rest of us. Wickwack120.145.177.252 (talk) 08:11, 6 June 2012 (UTC)


 * What are you retorting about? Plasmic Physics (talk) 09:21, 6 June 2012 (UTC)


 * The water in the pan cools the pan, not the vegetables. The vegetables cool the water (if you put cold potatoes into boiling water, it stops boiling for a while). If you had an empty pan on a hot ring, it would become red-hot like the ring is. The water keeps the (inner surface of) the bottom of the pan down to 100°C (or a bit more if you've added salt) until it boils away. So the water cools the boiler, just like the water in a steam train cools the furnace by turning to steam. TrohannyEoin (talk) 11:46, 6 June 2012 (UTC)


 * So what? That is not why water is used (water is used in cooking vegetables as it conducts the heat to the vegies), and does not imply you need to have a cooling system.  It has nothing to do with the OP's question.  Water is NOT used in a steam engine to cool the furnace - if you want a cool furnace, don't light the coal.  Rather, the purpose of the water is to be heated so it is steam and is thereby a usuable (expandanable and compressible) working fluid.  Wickwack58.164.238.58 (talk) 12:20, 6 June 2012 (UTC)


 * That is exactly what I said, a power station needs a cooling system to actively regulate the temperature. A locomotive doesn't, because of its size it responds much faster to simply changing the amount of fuel consumed. Plasmic Physics (talk) 12:26, 6 June 2012 (UTC)


 * The temperature in the boiler of a power station is regulated by the cooling tower? Sounds rather indirect. I would say that the cooling tower is needed as part of the equipment to help condense the steam for re-use in the boiler. Several components operate as a system to achieve the desired boiler temperature. Steam locomotive boilers and combustion chambers must be rugged and lightweight, and relatively small, and as a result are way less efficient than steam power plants. Steam locomotives often had once through use of the water, necessitating water towers every so many miles.  To avoid stopping at the water tower in a "tank town," railroads in the 1870's introduced the use of a track pan between the tracks and a scoop which could be lowered to force water up into the tender, giving rise to the term "jerkwater town." It's a place where the train doesn't even stop for water. My copy of the OED  states (incorrectly)  that the term "jerkwater" meant the engine would stop and the crew would "jerk" water from a stream with a bucket to fill the tender's water tank.  Edison (talk) 14:55, 6 June 2012 (UTC)


 * The purpose of a power station's cooling tower is to dissipate heat from the condenser; the condenser, in turn, is used to create a vacuum at the exit of the turbine which increases the efficiency of said turbine. A condenser with cooling system is a big, bulky thing (one sized for a steam locomotive is about the size and weight of a train car), so trains didn't use them often, and simply accepted the lower efficiency that resulted.  Regulating the temperature of the boiler in both steam locomotives and power stations is done through the simple fact that unpressurized boiling water cannot be hotter than 100C: so long as the boiler tubes are completely immersed in water, the boiler cannot overheat. --Carnildo (talk) 00:09, 7 June 2012 (UTC)
 * Locomotives even in the 19th century used temperatures above 100C in a pressurized boiler. 100 pounds per square inch, corresponding to 338 degrees F, was typical for early locomotive boilers in the US, and 50 PSI in Britain, corresponding to 298 degrees F . The boiling water and steam in the boiler have tremendous potential energy. It was not just the equivalent of an open kettle of boiling water. High pressure is required for the steam to be useful in pushing the piston and making the engine go. A power plant is likely to operate at 1000 F, not 212F.  Edison (talk) 04:39, 7 June 2012 (UTC)
 * In both the steam locomotive engine and boiling vegetables examples, water cooling is an essential part of the process, just not a part we normally think about. Without it, the engine and pot would get too hot and be damaged (having left a pot on too long, I can attest to the damage that causes). StuRat (talk) 15:09, 6 June 2012 (UTC)


 * Water cooling is not an essential part of the process. Yes, you can damage a pot if you boil it dry, but then the food won't be being cooked at that stage either.  Water is essential to the process of cooking vegies as it is the medium that conducts heat from the pot to the vegies.  You could make a pot out of tunsten (melting point ~3400 C) and use it dry.  The stove heat won't hurt it, but with no water, the food won't cook  either.  Or, you could use a temperature sensor in a feedback system (some modern stoves have this) to prevent the pot from being overheated, even if dry.  But, again, the food won't cook without the water to conduct the heat to it.  Neither is water used in a steam engine to cool it.  It's used because it is a convenient low cost compressible and expandable working fluid when heated.  Wickwack58.164.238.58 (talk) 16:09, 6 June 2012 (UTC)


 * The food would be cooked without water, but it would be cooked entirely too much, into cinders, on the bottom. The water is used to redistribute heat to cook the top of the food more than it would get without water, and to COOL the pan to a temp that won't scorch the bottom.  (This is what redistribution of heat is, cooling some areas and heating up others.) StuRat (talk) 23:03, 6 June 2012 (UTC)


 * Regarding a steam locomotive take a look at Steam engine safety. If the water level in the boiler dropped too low the burner would melt or weaken the boiler and it would explode.  The water in the steam engine's boiler was both the working fluid for the engine and also the coolant.  The energy required to vaporize the fluid prevented the boiler from going above the melting point of the metal.  You could build the pressure vessel and burner out of tungsten, but if your burner temperature exceeded the melting point of tungsten, you would have to have a working fluid to cool it.  Otherwise your boiler would melt.  Of course if your burner temperature is too low to melt or even weaken the tungsten, then your working fluid is only needed to run the engine.  The cooling for a steam train came as the steam was used to work the engine and when the steam was vented into the atmosphere or was re-condensed.Tobyc75 (talk) 23:49, 6 June 2012 (UTC)


 * A nitpick; the danger is not that the boiler melts, but that it expands unevenly to the point that it buckles and ruptures. FiggyBee (talk) 00:33, 7 June 2012 (UTC)
 * The failure mode called "crown sheet failure" happened when the fireman let the water level drop so much that there was not a layer of water on top of the top sheet of the firebox. Then the steam above it would not adequately cool it, and it would soften and be pushed downward by the steam so that it opened, separating from the stay bolts which connected the sheet to the top of the boiler.and the heated boiler contents would flash into steam through the firebox into the cab, scalding the crew to death in a most horrible way. This could also happen in a crash, when mechanical stress caused a boiler failure.  Another cause was an accumulation of scale on top of the crown sheet. Steam locomotives were high maintenance devices, with frequent internal inspections of the boiler recommended.  Edison (talk) 04:55, 7 June 2012 (UTC)


 * I agree with StuRat about boiling food. Boiling is not the only way to cook food: you can steam veggies, or grill them, or sautée them in a pan (eg. onions). A bit of liquid for thermal contact is useful, but a tablespoon of oil in a frying pan is more than sufficient. Boiling is used as a cooking technique when precise temperature control is desired: the boiling water maintains a very accurate 100°C temperature throughout the pot by actively cooling any part of the pot that exceeds the boiling temperature (conversion of water to steam is of course endothermic). This makes it easy to cook the vegetables without burning them, and doesn't require as much attention from the cook as other cooking methods would.--Srleffler (talk) 17:15, 8 June 2012 (UTC)


 * Surface condenser has the answer: In thermal power plants, the primary purpose of a surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water (referred to as steam condensate) so that it may be reused in the steam generator or boiler as boiler feed water. The difference between the heat of steam per unit mass at the inlet to the turbine and the heat of steam per unit mass at the outlet to the turbine represents the heat which is converted to mechanical power. Therefore, the more the conversion of heat per pound or kilogram of steam to mechanical power in the turbine, the better is its efficiency. By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased, which increases the amount of heat available for conversion to mechanical power. Most of the heat liberated due to condensation of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser." When James Watt invented the separate condenser, the main point was that this increased the efficiency of steam engines, and made them more practical. It also reduced the need for water – something that was less of an issue in railway locomotives which could take on water while running. See Steam locomotive and Condensing steam locomotive. dave souza, talk 16:37, 6 June 2012 (UTC)


 * The OP posted under title "Why does a power station need cooling?" and then posted "Whereas a steam locomotive doesn't? and "why isn't the steam coming from a locomotive or power station used to pre-heat the water?" This is 2 questions: 1) why do power stations have cooling (as in cooling towers) and not locomotives? and  2) why don't locomotives use (waste) steam to preheat the water (before boiling it).  Nobody has answered these specific questions.  Carnildo has a clue, and Dave Souza has some good understanding.  Plasmic Physics has no idea - perhaps he's seen a photo of a loco, but he doesn't know how they work.  StuRat has got himself muddled.  Here are some on-target answers:-


 * (1) The reason why power stations have cooling and locos generally don't stems from the fact that power stations stay in one place, and locos move about on rails, which sometimes go round curves. Power stations have coooling systems (condensers), feed water preheating, combustion air preheating, and all manner of extra bits of hardware, each adding little bits of efficiency, and in some cases improving the service life.  It doesn't matter if all this hardware takes up space and has weight - its all sitting on solid foundations in a big parcel of land, and doesn't move.
 * The worth of a railway loco is in pulling carriages or wagons i.e., its drawbar pull. Maximum drawbar pull is a simple function of the driving wheel ratio (ratio of wheel diameter to crank pin offset, which sets the stroke), the piston diameter, the steam pressure, and the number of pistons. To support this drawbar pull, there must be sufficient weight on the driving wheels, otherwise they will spin/slip on the rails.
 * It happens that all the hardware to supply this steam pressure, at an adequate steam flow rate, is generally much greater in weight than the weight required to prevent slip. If you look at a photo of a typical loco, you see a number of small wheels, used to help support the weight, that aren't driving wheels.  A loco is confined to a small frontal area, to fit on the track/raod width, fit under bridges, etc.  You could make it longer, but you can only have no more than 4 or 5 pairs of driving wheels, or it won't go round the bends.  It follows from all this that weight in a railway loco must be kept to a minimum, and its length must not be too long.  It would be nice to add condensers, preheaters and all the other tricks, but they will add weight & take up space.  More weight in the loco (or its tender(s)) and the less weight in carriages or wagons it can pull.  Experience has found that its best to keep it simple.


 * (2) The reason locos generally don't preheat the water is, because of the need to keep it simple and keep weight and length down, the onboard water storage and the boiler vessel is the same unit. To preheat water before it enters the boiler vessel, you need to store the water in a separate tank.  Separate tank locos (called "tank engines") do exist for special requirements (eg working long routes or routes where water is not available) where reduced drawbar pull must be accepted.  There must be a pump to force water from the tank into the boiler vessel, whcih of course must be under the full working presure.  At a power station, all pumps can be driven by electric motors connected to the station auxilary bus, at a net thermodynamic efficiency of ~40%.  On a loco, any pump must be driven from either the driving wheels (thermodymanic efficient around 12% at best), or a separate auxilary steam engine (max efficiency perhaps 20%)
 * Incidentally, to use other efficieny-improving devices like condensers, you need pumps.


 * It should be noted that power stations generally operate 24 hours a day, 7 days a week. This forces the use of continuous feed arrangements - water is continually pumped into the boiler, air continually forced into the furnace, lube oil continually pumped through bearings. So, you've got pumps anyway, might as well use some of them to help with efficiency. Railway locos must be a batch process - stock up with coal and water, replenish bearing cups with oil, and go on the day's trip (a few hours), then some down time.  So, pumps aren't strictly necessary.  Parlicularly in base-load power stations, it doesn't matter if it take the beast part of the day to get all the equipment, condensers, tanks, vessels, up to temperature and pressure - you only start a power station from cold under exceptional circumstances.  But with a locomotive, you do it every day.  It takes a while to get the coal burning properly, raise steam, and warm up the cylinders, as it is.


 * It should also be noted that a railway loco has a crew of only two - the driver (USA term: engineer) and the fireman. Both have plenty to do without being expected to monitor extra equipment.  You don't want more crew.  Apart from their wages, you would have to increase the size of the loco to make room for them. In a power station, more staff to manage all the extra bits of efficiency adding equipment can be justified, and there's heaps of room for them.


 * For a very interesting and well informed layman's view of a multitude of bright, stupid, dumb, and outright bizare ideas that have been tried in railway steam locomotives, see http://douglas-self.com/MUSEUM/LOCOLOCO/locoloco.htm


 * Wickwack120.145.54.86 (talk) 02:24, 7 June 2012 (UTC)


 * Can I just say, on your point two, WHAT THE HELL ARE YOU TALKING ABOUT? Railway locomotives most certainly do not carry all their available water in their boiler;  in fact, they don't "use up" water in the boiler at all; it has to be kept at a fairly constant level for efficient (not too high) and safe (not too low) operation.  Tank engines (which carry additional water in tanks around the boiler) have a much smaller additional water capacity (and hence a much shorter range) than tender engines, which typically drag around thousands of gallons of extra water in a trailer for that purpose.  The transfer of water from these storage tanks to the boiler did indeed require a complex pump in the early days of railways, but from the mid 19th century solid-state injectors were universal.  Additionally, feedwater heaters were quite common on steam locomotives in the 20th century, with the ultimate development being the Franco-Crosti boiler. FiggyBee (talk) 03:10, 7 June 2012 (UTC)
 * As I said, all manner of ideas have been tried at one time or another. But the bulk of locomotives don't use them, again for reasons I gave.  Your argument is like saying all gasolene-powerd motor cars should have superchargers and turbochargers, because a) it has been tried, and b) it can be shown theoretically that their use can give greater efficiency.  But very few gasolene-engine cars have been made with super- and turbochargers, because, like railway locos, its best to keep them simple.  Tank engines were used where special circumstances required it - they were definitely NOT typical.  Obviously, you can't preheat water unless the heater is somewhere between the source of water and the boiler vessel - that means either a tank engine (or the Franco-Crosti type which is a sort of tank engine with a high-presure heated tank) or a condenser engine - neither are typical. Implicit in the OP's question (essentailly why wasn't it done) is why wasn't it commonly done, not can it be done, nor has it been done. Stay focused on answering the question.  As far as I can gather, there have been a handfull of F-C types built, as against thousands upon thousands of conventional type. Wickwack120.145.54.86 (talk) 03:26, 7 June 2012 (UTC)


 * No, the reasons you gave were that locomotives don't carry a seperate feedwater stock, which is flat-out wrong; 100% of every water-boiling steam locomotive ever built carried a seperate feedwater stock. Feedwater heating was usually accomplished by heating the water shortly before it was injected into the boiler.  If you've ever seen a photo of a steam locomotive with a mass of pipework over the top of the firebox or going from the back all the way to the front, that's a feedwater heater.  They were not universal, but they were not uncommon. FiggyBee (talk) 03:34, 7 June 2012 (UTC)


 * In case you're not getting it, look at this photo: File:PRR_K5_5698.jpg. See the thing with "Pennsylvania" written on the side?  That thing is full of water (also, see the bump with the pipe coming out of it behind the chimney at the front?  That is part of the preheater).  The answer to "why wasn't it done" is "it was".  The answer to "why wasn't it always done" is "in some times and places it was cheaper to run less efficient locomotives than to do more maintenance".  The answer to no question is "because locomotives don't carry a feedwater source seperate from the boiler", because that is nonsense. FiggyBee (talk) 03:49, 7 June 2012 (UTC)


 * Nah, I got it all right, as soon as I looked at http://en.wikipedia.org/wiki/Tender_(rail), while you were typing your last post. Yep, I certainly stuffed up answer (2).  Not sure about how common feed water heaters were though.  I have technical drawings of a few 1940's locos and feedwater heaters are not shown.  The WP article on steam locos mentions them but the schematic http://en.wikipedia.org/wiki/File:Steam_locomotive_scheme_new.png does not mention them. Wickwack120.145.54.86 (talk) 04:10, 7 June 2012 (UTC)


 * As for the comments about using tungsten tanks/pots, that might well eliminate the need for cooling, but is, of course, prohibitively expensive. StuRat (talk) 04:48, 7 June 2012 (UTC)


 * And heavy! FiggyBee (talk) 05:03, 7 June 2012 (UTC)


 * And won't eliminate the need for water - because the water is NOT there for cooling - it's there to transfer the heat to the food (cooking) or to be the expansion medium (engines). Wickwack124.178.36.4 (talk) 08:17, 7 June 2012 (UTC)


 * Tank engines merely carry their water on the locomotive chassis (normally in boxlike tanks beside the boiler but sometimes in a 'saddle' tank over the boiler) rather in a towed tender. There is no other distinction.Hayttom (talk) 15:19, 7 June 2012 (UTC)


 * Somehow the work of pumping in water to the boiler to replace that used by steam is far less than the work obtained from the steam as it pushes the piston or drives a turbine. I suppose the small volume of water pumped in against the boiler pressure is less work than the large volume of steam pushing the piston at the same pressure. Early engines might have used steam engine driven from the boiler to pump in water. A pump which operated only when the wheels were turning would have been a disaster (boiler explosion when the water level dropped if the engine sat stationary for a while). Was it ever a human-powered pump? Later 19th century and later locomotives used a steam injector, where a cleverly designed valve managed to get a jet of steam to push water into the boiler without a piston pump or rotary pump. I am probably one of the few here who had the opportunity as a child  to step into the cab of a working steam engine of a major railroad back in the era of steam. The locomotive fireman injected water strategically: it would not do to pump in a large volume of cold water when the locomotive was about to pull a train up a long hill, since it would be hard to maintain steam pressure and speed. Conversely, the fireman would add water when the engine was pulling into a station, since that avoided a possible buildup of steam pressure and the need to release excess pressure through a high pressure relief valve, wasting the coal and the employer's money.  Economy was king in railroad operation, and there was always an awkward  balance between adding complex gadgets to save coal, such as by preheating water and superheating steam and condensing the water, and the new failure modes they introduced, along with more maintenance expense, more training time for engine crews and maintenance employees, more tasks and monitoring for the crew, with increased chance of missing some problem such as low water level, as well as higher initial cost.  I own a couple of small toy steam engines which actually do operate as some above suggested, with the boiler filled half full of water and sealed, then a fire lit below it until steam pressure is enough to blow the whistle and operated the piston and flywheel, and any small load attached to it. Edison (talk) 16:51, 8 June 2012 (UTC)
 * I mentioned driving the water inlet pump from the driving wheels as a possibility - I haven't heard of it being done. Never the less, it would be practical, apart from the extra thermodynamic losses, and boiler explosions definately NOT a problem.  When a steam locomotive is not moving, there is no consumption of steam in the pistons (some steam is still consumed in cylinder heating and may also be used to keep up the firebox draft).  Crews obviously know this and don't put on coal when they are about to stop.  There is nearly always some loss of steam though, as it is impossible to get firing exactly right.  Not only can the driver control pressure by water injection, as you've said, if he doesn't, all that will happen is that the safety valve will open and blow off some steam.  The books I have, especially History of Westrail by Fred Aflick, state that fuel consumption can vary considerably from crew to crew.  There are 2 main reasons for this - (1) apparently it takes some skill and experience to lay out the coal in the firebox for optimum combustion, and (2) fuel consumption depends on the mental planning along the route.  More coal should be put in the firebox before hills, as there is a time lag between more coal and more steam pressure.  Similarly, less coal should be put on before getting to downhill runs or stop points.  Too little heat at the right time and pressure drops, reducing efficiency.  Too much heat at the wrong time, and steam will be vented off and wasted.  Some crews are better at route planning than others, but all crews will vent some steam at one or more points along a route.  Wickwack120.145.9.95 (talk) 14:09, 9 June 2012 (UTC)