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C01 is poisonous C02 is not

OK, we'll put you in a room with 'normal' air apart from 20% CO2/60% Nitrogen instead of the normal 80%Nitrogen. Let us know (from beyond the grave) how you did.
http://www.engineeringtoolbox.com/co2-comfort-level-d_1024.html

"It's a pain in the fucking ass. Now we've got AWG and metric cable types. I'm supposed to be able to find a substitute for a discontinued cable, specs in AWG, but replacements in metric, and every. single. fucking. time. I have to work out the characteristics because the sizes aren't exactly the same."

http://www.engineeringtoolbox.com/awg-wire-gauge-d_731.html

yeah, that was hard. How would you measure even what cable you have (assuming its not labeled) without measuring the diametre in mm?

Surely you can handle two decimal points with a micrometer. I am having a hard time understanding how this small conversion of known values could cause you that much grief. Perhaps it depends on your application, but still. How do you think people every figure out what gauge of wire they have? measure it!!!!

Just another BS trollpost. Heat capacity has EVERYTHING to do with global warming! The atmosphere is a blanket, and blankets are blankets because of their heat capacity. This is the most fundamental kindergarden level of global warming theory, and the fact that you fail to understand even that shows that you are totally ignorant on the subject, and instead are operating solely as an uninformed, ignorant zealot with exactly zero critical thinking skills.

I was going to respond in kind to the accusations of trolling, but it appears you genuinely are that ignorant. You're just repeating your ignorant claims and dismissing criticism as trolling with your veil of ignorance. Blankets are not blankets because of their heat capacity. Kindergarten analogies are not always relevant or accurate. The heat capacity of the atmosphere indeed does have an effect on climate. But since human emissions don't appreciably change the heat capacity of the atmosphere, it is irrelevant to the current debate on global warming and it certainly doesn't make nitrogen or oxygen greenhouse gases.

Nice handwaving dismissal. Why don't you tell me what absorption and re-emission of photons in Raman spectra mean if not absorption and re emission of photons, and maybe post a spectrum showing that nitrogen doesn't do that somehow, and perhaps you can wave your magic wand while you are at it and tell us why physics is wrong and you are right.

You do realise that since Raman scattering has a fourth-power frequency dependence, it's effectively non-existent at mid-infrared wavelengths? There's marginal collision-induced absorption, but it's extremely weak despite nitrogen/oxygen/argon being much more abundant than CO2, and irrelevant because the atmospheric composition of those gases is not changing (except for a very small drop in oxygen from combustion of fossil fuels).

The fact is that it IS a WEAK greenhouse gas. If a planet had a nitrogen atmosphere, it would be blazing hot during the day, and freezing cold at night, but significantly less so than a planet with no atmosphere. The gas particles have a temperature and a heat capacity. Yes they are LOW, but they are non-zero. http://www.engineeringtoolbox.com/spesific-heat-capacity-gases-d_159.html

You really think you're going to get somewhere continually asserting that nitrogen is a greenhouse gas because it has a heat capacity? That is just not what greenhouse gases are, and if you think otherwise, you miss the point entirely.

Just another BS trollpost. Heat capacity has EVERYTHING to do with global warming! The atmosphere is a blanket, and blankets are blankets because of their heat capacity. This is the most fundamental kindergarden level of global warming theory, and the fact that you fail to understand even that shows that you are totally ignorant on the subject, and instead are operating solely as an uninformed, ignorant zealot with exactly zero critical thinking skills.

Nice handwaving dismissal. Why don't you tell me what absorption and re-emission of photons in Raman spectra mean if not absorption and re emission of photons, and maybe post a spectrum showing that nitrogen doesn't do that somehow, and perhaps you can wave your magic wand while you are at it and tell us why physics is wrong and you are right.

The fact is that it IS a WEAK greenhouse gas. If a planet had a nitrogen atmosphere, it would be blazing hot during the day, and freezing cold at night, but significantly less so than a planet with no atmosphere. The gas particles have a temperature and a heat capacity. Yes they are LOW, but they are non-zero. http://www.engineeringtoolbox.com/spesific-heat-capacity-gases-d_159.html

The original Titanic ran on coal, something like 800 tons a day. Natural gas has about twice the BTUs per weight.

I found this table:

http://www.engineeringtoolbox.com/elevation-speed-sound-air-d_1534.html

The slowest the speed of sound gets is 295.1 m/s or 968 ft./s between 10,000 and 20,000 feet, which translates to 1062 km/h or 660 mph, so no, it seems Kittinger did not reach the speed of sound at any altitude.

That might not be much of a problem. Helium is the least water-soluble monatomic gas. At STP (0 C, 1 atm), the solubility of helium is 1.7 ppm.

http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html

Helium pretty much just doesn't like staying anywhere, including in water.

It's not perfectly accurate

No, it's not. It isn't even remotely accurate.

The effect isn't due strictly to the pressure of the air. Having a little bit of high pressure air in your lungs isn't that different than having a lot of low pressure air.

Uh, yeah, it is. There's a vast difference between having 14.7 PSI in your lungs and having 3.5 PSI in your lungs (at 35,000 feet). Go to your local library and check out a physics or chemistry text book, then look up "partial pressure". There comes an altitude at which the air pressure is too low to supply sufficient oxygen to your body, even if you are breathing pure oxygen. You can't simulate that on the ground by simply exhaling and holding your breath. Period.

Mercury has SHIT thermal conductivity, what are you talking about?

http://www.engineeringtoolbox.com/mercury-d_1002.html

Thanks for your reply. my question is why would the pipe only to pull energy from lava a few meters away from itself? If I am extracting energy from the lava underneath, it seems like conduction would mean I'd be pulling from a much larger area. I'm not looking to drain all of the energy in one day or one year. Just enough to keep the system in some type of equilibrium. If the numbers I found for Mt. St Helen are correct, and even if I assume that this volcano is a thousand times larger, it doesn't seem like you'd need to extract that much energy over a period of a century (these suckers form really slow) to maintain an equiibirum position.

Again, I will admit I am nowhere near to being an expert on this... I'd love to find out why I'm wrong.

Well, I was proposing pulling heat from a 30 meter radius of rock into a pipe 15cm in radius, so a 40,000:1 ratio - if you're vaporizing water to steam, you're not going to make much of a dent in heat content of 40,000x the volume of rock (at 2.5g/cc density vs. steam at about 0.0016g/cc @ 50psi) so 62 million times the mass, but over days and days, you will bring the temperature down a little - but, at the same time, that rock will be being heated from below....

And, remember, to cover the whole area at this 62 million to 1 mass ratio will require 1.3 million pipes...

As I posted elsewhere, sunlight is very bright.

Blocking 80% of 107,500 lux is still brighter than the 100-150 lux recommended for workspaces.

You're not familiar with how bright the sun is, are you?

A reference I've used before at Engineering toolbox lists even an overcast day at 1000 lux, equivalent to the lighting required in an OR. Normal interior light levels are 1/4 of that, and full daylight is 10x brighter yet.

Removing 80% of full daylight is not so bad, assuming you don't live in a ship with tiny portals to the exterior.

The things I mentioned don't restrict conclusions to the domain of commuting. Since you have made speed an issue, and as I have already pointed out, the same justification you gave also justifies driving a car... people just don't have the time to waste.

As for your continued attempt to charge the cost of resting to the cost of going from A to B - I'm sorry but it is ludicrous and afaics only has one purpose - to try and make cycling look better than it actually is. Hopefully everyone else can see that if energy is expended for activity A then you can't charge it to activity B especially when A is going to happen regardless of whether or not B happens. I find the insistence on trying to do this is usually a characteristic of people with a "religion" about something - in this case bicycling.

As for your your claim that you can walk infinitely slowly, it is simply wrong. One might be able to move at a rate that approaches infinitely slow but you won't be walking. Walking is a very specific mode of pedestrian movement. It requires that you fall - you swing one limb out in front and then fall onto it - this is what defines walking, as opposed to say shuffling. You move your leg and torso forward until gravity causes you to continue to move forward. At this point you cannot stop this - you also can not make it slower until the forward leg finally contacts the ground again, and you most certainly cannot make it infinitely slow. This is how walking is defined. If you are not engaging in this cyclic pattern of falling and catching yourself then you may be shuffling, sliding, or any number of other things but you are not walking.

Finally to use a source you have supplied elsewhere ( http://www.engineeringtoolbox.com/met-metabolic-rate-d_733.html ) if you are walking at 2 Km/hr your total rate of energy expenditure is 675 BTU/hr and if you are cycling it is 1780 BTU/hr. They don't give the speed of cycling but they do put it in the same category as golf. This of course is before adjusting for the base rate - if you were simply standing not doing anything you would be using 430 BTU/hr so the actual net cost of walking over standing still is 245 BTU/hr and for cycling it is 1350 BTU/hr.

Finally, and as I've also pointed out before, the figures are for what is basically an optimum case for cycling. We should also see the figures for travelling over sand, up a hill, over rocky terrain, on ice, into a headwind, etc. etc.

Additional data, not entirely consistent with other sources: http://www.engineeringtoolbox.com/met-metabolic-rate-d_733.html . Their estimate for (slow, 2km/h) walking seems high -- at 90% above resting, it appears to still work out to 54 kCal/mile incremental, about the same as the Bicycling Science estimate for 4 mph. (.9 * 1h/2km * 75 kCal/h * 8km/5mi). This could still be consistent with the perception of reduced effort, since you are in fact expending that energy more slowly.

They assert that merely standing consumes 20% more energy than sitting, and about 50% more than "reclining". If the cyclist plays the recumbent card, victory is assured :-).

Comparing a gas to a liquid by volume is not very meaningful. Wikipedia's 35 mg/l is 0.0035% by weight, or 35 ppm. It's milligrams in one kilogram. Actually this source and this other source both give around 0.026 g/l or 26 mg/l , which is 0.0026% solubility of methane in water at 17 C and one atmosphere, or 26 ppm. Pretty much a trace.

I feel for you - I feel the same way when the tires refuse to spin when I am stuck in the snow.

However, I am not certain that your (or my) feeling is actually "correct" in this situation. Assuming that the computer system is actually working to prevent the wheels from slipping - I suspect that we are getting significantly more acceleration from the non-slipping (and non-screeching) tires than we would if they were spinning.

My memory from way back when was that rubber-road static was about double rubber-road kinetic but I cannot find actual numbers for kinetic friction coefficients:

http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
http://en.wikipedia.org/wiki/Friction#Static_friction

If one wheel is starting to slip, but the other isn't I don't know if your total acceleration is better than with both not slipping but at a lower rate. I suspect however that having unequal accelerating forces between the two drive wheels causes very difficult handling.

Your lungs are able to extract oxygen from air because there is more oxygen in the air than in the blood. Your blood carries this oxygen to the tissue, where the blood has more oxygen than the tissue - the oxygen then diffuses into the tissue.

In theory, you could do this with an adequate flow of surface seawater (which has a partial pressure of O2 very similar to that of air), but the fact that the oxygen content of seawater is minuscule compared to the oxygen content of air means that you're going to need an enormous water flow. You should be able to extract about a fourth of the oxygen in the seawater before the partial pressure will go low enough that no further net diffusion of oxygen will occur (human not under load typically extract about a fifth, but let's be conservative here). Given that the oxygen content of fresh water is about 0.0089 g/L H2O, that's about 12.5 mL O2 per liter of water. Humans need about 250 mL O2 per minute at rest, so you'll need to extract all the oxygen from 20 L/min of fresh water saturated with air in order to supply each person. However, they're going to need at least four times that flow due to the difficulty of extraction, so now we're up to 80 L/min of water flow at rest, even if you don't consider the efficiency of the exchange process.

The way around this is to do something that captures more of the oxygen content of the water - usually by binding it to some intermediate (as we, and fish, do - hemoglobin is one such). The problem is that the human heart can't handle that level of cardiac output for it to happen within an all-blood system, and that any molecule which can extract a large measure of the oxygen available in water isn't going to give it up easily - it will have an oxygen dissociation curve that lets go a significant amount of the oxygen only at very low tissue pO2. Unfortunately for us, "tissue" in this case is the breathing-air side of the artificial lung. So you can choose chemical sequestration, but that presents the same problem - unless you can figure out some way for humans to live with much lower tissue pO2, you're going to have to expend a lot of energy dissociating that oxygen from whatever carrier you use to get it up to a usable concentration for humans. Fish have much lower metabolic oxygen requirements and so can live with lower tissue pO2.

I found most of my recent answers on
http://www.mathsisfun.com/
and
http://www.engineeringtoolbox.com/

the first one explains a bit more in details what's going on, the second one is very useful if you know the basics and need the specific formula. Like "yeah, I know polar-to-cartesian coordinate transformation goes via atan in the one and cos/sin in the other direction, but what's the actual formula again?".

I'm wondering why they can't pump liquid nitrogen in there to cool it down. Didn't they do that at Chernobyl?

Water has a specific heat of 4.187 kJ/kgK and a heat of vaporization of 2,270 kJ/kg.

Liquid nitrogen has a specific heat of 2.042 kJ/kgK and a heat of vaporization of 199.1 kJ/kgK, and a specific heat of 1.04 kJ/kgK when gas.

So putting in 1 kg of water at 20 C and extracting it as steam at 100 C removes (4.187)*80 + 2270 = 2605 kJ of heat energy from the reactor.

Putting in 1 kg of liquid nitrogen at -200 C and extracting it at 100 C removes (2.042)*4 + 199.1 + (1.04)*296 = 515 kJ of heat energy from the reactor.

Per kg, water removes over 5x more heat energy than liquid nitrogen. The only reason to use liquid nitrogen is if you wanted to drop the temperature below the boiling point of water. AFAIK radioactive decay is not influenced by temperature, so there would be no benefit to doing that here.

If I had to guess, the Soviets had to encase an active pile in-situ with concrete. Concrete tends to be very temperature-sensitive when curing - too hot and it'll crack. So they probably used liquid nitrogen to drop the temperature to where the concrete which initially contacted the pile could cure without cracking.

Gasoline requires about ten times as much energy to ignite as hydrogen.

Could you explain why then gasoline has an auto-ignition temperature of 280 while hydrogen is at 500? See here.

TLDR: Molten salt has zero benefit as a nighttime storage system. Ordinary boiling water is a better choice by a factor of >500.

I can't find good data on the heat capacity of the particular salt used in this system, but heat capacities for salts in general are around 1 J/kg-K.. If you're dealing with a temperature change of 700 K, that means each kg of salt can store around 700 J of heat. To store enough heat to power a typical American household overnight (1 kw x 12 hours), you'd need 61 tonnes of salt.

Now, most power plants use water as the working fluid. The latent heat of vaporization of water means that steam stores *at least* 330,000 J per kg of water in the phase change alone, plus additional specific heat if the steam is stored above the boiling point, which I'm too lazy to calculate.

That means that plain old ordinary water, already used in every thermodynamic power plant ever made, is at least 500 times better at storing heat than salt is.

So how do you think normal driving for truck looks like ? In europe it is highway driving at constant speed, more or less constant load for hundreds miles.

To avoid each person having a different metric, we use standardized drivecycles. The drivecycle that the EU uses to model how people typically drive for vehicle mpg ratings is called the NEDC -- the New European Drive Cycle. It is a combination of urban and highway driving that approximates typical european driving patterns (which, by the way, are lower energy than typical US driving patterns -- hence the US uses FTP75 (city) and US06 (hwy), which are higher energy, and correspondingly leads to lower MPG figures for the same car in the US). You can see the NEDC here.

If you want to talk about pure highway driving, even that is not constant speed. Speed on the highway varies based on traffic density, random factors (passing, being passed, etc), current weather conditions, stops (gas, rest, etc), start and end accel/decel, exits (to surface streets or other highways), and driver randomness. Beyond speed, energy consumption varies based on weather and especially altitude changes. For an example, here are actual measurements taken from a vehicle in the US. Here's a test drive that starts with city and progresses to intra-urban freeway. Your mileage may vary.

(I have my own drive data recordings, but I am not at liberty to disclose them, so I'm linking to publicly available ones)

Highway driving runs an engine much more efficiently than city driving. You're closer to the peak efficiency (although not at it), you brake less, idling is basically eliminated, etc. Now, there's obviously a big downside -- your aero drag is *way* higher, and your rolling drag slightly higher (yes). In non-hybrid vehicles, the upsides outweigh the downsides (sometimes significantly). In hybrid vehicles, the downsides usually outweigh the upsides.

No this is not from wiki. It is from book called "Automobile fuels" (translated)

Right. Which is why I said, "If you had cited ... you would have..." instead of "You cited... you did." Understand? I'm pointing out that different sources give different numbers because there is no single correct number because they're not a single chemical mixture. You've picked one source to latch onto, when there *is no single answer*. Check other sources; you'll see what I mean. Mixtures vary from location to location and even day to day (for example, summer versus winter blends). They even change from year to year, as standards and refineries are always changing. Their energy densities vary, too. But overall, the *current global average* is about 15% denser for diesel than gasoline.

I don't know how many times I need to stress this, but let me do so once more: There Is No Single Fuel Called Gasoline Or A Single Fuel Called Diesel. How about this -- how about I cite a bunch of random sources?

Simetric: 820-950kg/m^3
Alan Harvey, National Institutes of Standards and Technology: 850kg/m^3 typical, but 825-890.
Engineering Toolbox: 810-960kg/m^3
MSDS: 810-880kg/m^3

Gasoline:
MSDS: 710-770 kg/m^3
Simetric: 737kg/m^3
Engineering Toolbox: 680-740kg/m^3

So how do you think normal driving for truck looks like ? In europe it is highway driving at constant speed, more or less constant load for hundreds miles.

To avoid each person having a different metric, we use standardized drivecycles. The drivecycle that the EU uses to model how people typically drive for vehicle mpg ratings is called the NEDC -- the New European Drive Cycle. It is a combination of urban and highway driving that approximates typical european driving patterns (which, by the way, are lower energy than typical US driving patterns -- hence the US uses FTP75 (city) and US06 (hwy), which are higher energy, and correspondingly leads to lower MPG figures for the same car in the US). You can see the NEDC here.

If you want to talk about pure highway driving, even that is not constant speed. Speed on the highway varies based on traffic density, random factors (passing, being passed, etc), current weather conditions, stops (gas, rest, etc), start and end accel/decel, exits (to surface streets or other highways), and driver randomness. Beyond speed, energy consumption varies based on weather and especially altitude changes. For an example, here are actual measurements taken from a vehicle in the US. Here's a test drive that starts with city and progresses to intra-urban freeway. Your mileage may vary.

(I have my own drive data recordings, but I am not at liberty to disclose them, so I'm linking to publicly available ones)

Highway driving runs an engine much more efficiently than city driving. You're closer to the peak efficiency (although not at it), you brake less, idling is basically eliminated, etc. Now, there's obviously a big downside -- your aero drag is *way* higher, and your rolling drag slightly higher (yes). In non-hybrid vehicles, the upsides outweigh the downsides (sometimes significantly). In hybrid vehicles, the downsides usually outweigh the upsides.

No this is not from wiki. It is from book called "Automobile fuels" (translated)

Right. Which is why I said, "If you had cited ... you would have..." instead of "You cited... you did." Understand? I'm pointing out that different sources give different numbers because there is no single correct number because they're not a single chemical mixture. You've picked one source to latch onto, when there *is no single answer*. Check other sources; you'll see what I mean. Mixtures vary from location to location and even day to day (for example, summer versus winter blends). They even change from year to year, as standards and refineries are always changing. Their energy densities vary, too. But overall, the *current global average* is about 15% denser for diesel than gasoline.

I don't know how many times I need to stress this, but let me do so once more: There Is No Single Fuel Called Gasoline Or A Single Fuel Called Diesel. How about this -- how about I cite a bunch of random sources?

Simetric: 820-950kg/m^3
Alan Harvey, National Institutes of Standards and Technology: 850kg/m^3 typical, but 825-890.
Engineering Toolbox: 810-960kg/m^3
MSDS: 810-880kg/m^3

Gasoline:
MSDS: 710-770 kg/m^3
Simetric: 737kg/m^3
Engineering Toolbox: 680-740kg/m^3

But, as you say, one big plus of hydrogen is that the flames tend to go upwards, fast, meaning that you're a lot safer than when around gasoline fumes when things start to burn.

At 20 miles you're pretty much in a vacuum.
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

hydrogen gas... Which has a narrow fuel air mix

I don't think so.

Flammability Concentration Limits
Hydrogen 4% to 75%
Gasoline 1.4% to 7.6%

The auto-ignition temperature is indeed higher for hydrogen, 500 Celsius compared to 280 for gasoline. I had not known that.

hydrogen gas... Which has a narrow fuel air mix

I don't think so.

Flammability Concentration Limits
Hydrogen 4% to 75%
Gasoline 1.4% to 7.6%

The auto-ignition temperature is indeed higher for hydrogen, 500 Celsius compared to 280 for gasoline. I had not known that.

This fiber was about 300 times more thermally conductive than normal polyethylene

Since I couldn't find in TFA the ACTUAL measured conductivity, I turned to the internets:

Using data from the first source I found, at its highest, HDPE's thermal conductivity is 0.51 W/mK. So this material's thermal conductivity in that dimension is about 153 W/mK, or about 3/5 that of Al (250 W/mK), 3/8 that of Cu (401 W/mK), and between 1/6 and 1/15 that of diamond (900–2,320 W/mK, according to wikipedia.

So all in all, while this is very fascinating research (and I enthusiastically encourage them to continue exploring this avenue), I'm not optimistic about practical applications for computers (at least in the remote future). They would at least have to double the conductivity, while at least matching aluminum's cost - a feat that may be too difficult to overcome.

Since neither the summary nor the article has been kind enough to expand on "300 times more thermally conductive than normal polyethylene", I figured I'd look it up.
Thermal Conductivity of some common Materials:
Polyethylene HD: 0.42 - 0.51 W/mK
Aluminium: 250W/mK
Copper: 401 W/mK

Best case scenario: 153 W/mK or 61% as conductive as aluminium, 38% as conductive as copper. Not exactly impressive for a heat sink

http://www.engineeringtoolbox.com/moisture-holding-capacity-air-d_281.html

I'm with you re: Venus vs. Mars for terraforming. In addition to all the points you raised, the gravity of Venus is about 90% that of earth (according to http://astrogeology.usgs.gov/Projects/BrowseTheSolarSystem/venus.html). Mars' gravity is approximately 1/3 that of earth. This is important because less gravity == less atmospheric pressure on the surface of the planet. Consequently, the density of the Martian atmosphere is 1% that of earth. That's really freaking thin, even if you are trying to breathe pure oxygen. This site shows that the density at 100,000 feet is roughly 1% that of sea level at earth, and from what I remember reading as a kid who thought the SR-71 was just the coolest airplane ever, pilots above 60,000 feet had to wear pressure suits because a simple oxygen mask couldn't provide enough pressure to sustain consciousness at those atmospheric pressures.

In other words, Total Recall notwithstanding, humans will not ever be able to breathe the atmosphere unaided on a terraformed Mars without some radical genetic engineering.

actually, the stall would be BEFORE big ice melts as heat capacity of ice is much higher, to say nothing of the huge amount of energy it takes to make the phase change to liquid water. so the stall should have been much earlier, not now!

The heat capacity of water is about 2x that of ice, and melting ice takes ~80x the energy of heating water 1C. So any stall should happen while the ice is melting, which is apparently now.

The total mass of the oceans is about 1.4*10^21 kg. The total mass of the atmosphere is about 5*10^18 kg. That means the oceans weigh about 300 times as much as the atmosphere.

The heat capacity of water is about 4000 J * kg ^ -1 * K ^ -1. The heat capacity of air is about 1 kJ * kg ^ -1 * K ^ -1, or about 1000 J * kg ^ -1 * K ^ -1.

So since there's 300 times as much water as there is air, and the heat capacity of water is 4 times larger, heating up the atmosphere by 1200 degree Celsius would take the same amount of energy as heating up the oceans by 1 degree Celsius. This may not prove or disprove your point, I just started thinking about numbers when you said "raising the temperature of a body of water by a few degrees".

Except we don't know exactly what raising the temperature of the oceans by one degree will do.

The total mass of the oceans is about 1.4*10^21 kg. The total mass of the atmosphere is about 5*10^18 kg. That means the oceans weigh about 300 times as much as the atmosphere.

The heat capacity of water is about 4000 J * kg ^ -1 * K ^ -1. The heat capacity of air is about 1 kJ * kg ^ -1 * K ^ -1, or about 1000 J * kg ^ -1 * K ^ -1.

So since there's 300 times as much water as there is air, and the heat capacity of water is 4 times larger, heating up the atmosphere by 1200 degree Celsius would take the same amount of energy as heating up the oceans by 1 degree Celsius. This may not prove or disprove your point, I just started thinking about numbers when you said "raising the temperature of a body of water by a few degrees".

That depends on how the system is designed. More often than not, those two variables are independant. If you're designing a system to use a constant temperature (to avoid thermal stress problems on valves and pipework), then changing the pressure is a matter of valving and/or adjusting the heat and feed input on the boiler to maintain the operating temperature. In which case a Mollier diagram is likely to be a lot more useful than that table.

When it comes to steam power, temperature and pressure aren't the most important factors. It's more about mass flow rates and enthalpy.

Should have put this in my first post. The thermal conductivity of copper is 401 W/mK, concrete is 0.42 W/mK. This gives us a ratio of approx 950:1, close to my guess of 1000:1. This according to: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

Concrete is 950 times less efficient than copper. I don't think the author has enough pipe. He may end up adding a small rad and fan in the basement on either the input or output pipe, doesn't really matter as it's a closed loop. Of course, this is all dependent on his PC, and he didn't state if it's a monster gaming system with SLI and a huge overclock or just an average browser/email box.

Given the height of said clouds - they're huge!

Granted. Well, pretty big.

I have trouble believing that's all rocket plume up there...

There used to be a perception that SlashDot had a scientifically and/or technically literate readership - I'll bet that's what they tell the advertisers anyway. So don't believe, work the numbers.
Given - a shuttle is worth 300 tonnes of water ; altitude is 115km ; a cirrus cloud is 0.002 g/m^3 water (from http://www-das.uwyo.edu/~geerts/cwx/notes/chap08/moist_cloud.html ) ; pressure at that altitude is about 2 Pa (estimate from the 71km figure in http://en.wikipedia.org/wiki/Atmospheric_pressure#Altitude_atmospheric_pressure_variation , which broadly agrees with http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html).
So, (actually, do I need to look at the atmospheric pressure? Not for a first approximation.) 300 tonnes of water would make a cloud of 300x1000x1000 (tonnes -> g) / 0.002 (g/m^3 -> m^3) = 150000000000 m^3 which equates (broadly) to a 3300 m radius sphere. A sphere of 3.3km radius at 115km range would subtend an angle of 0.028 radians or 1.6 degrees.
That's about the size of a thumb at arms length, or very easily visible. Including atmospheric pressure in the estimate would (I think) increase the apparent size of the cloud, as would the fact that the cloud is irregular and sheeted.

Sheesh - don't schools teach kids how to do a back-of-a-fag-packet calculation any more?

You're one to talk when you don't even know the different between the metric system and the imperial system.

The term "English System" is commonly used to refer to the Imperial System.

So, try again, bureaucrat.

This is widely accepted conventional wisdom about losing (or gaining) weight. And it does just seem right.

Not only does it seem right, according to the laws of physics:

mass can neither be created nor destroyed

from http://www.engineeringtoolbox.com/conservation-mass-d_182.html

Acetylene has a whole raft of problems, but we use it 'cause it's such a good fuel.

Storing hydrogen by someone who understands it is no big deal. Storing hydrogen by someone who either never had chemistry or barely passed it 5 to 50 years prior and who hasn't put a thought into it since isn't such a good idea. And that's most of the drivers on the road.

Here's a useful link: http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html

It puts H2 at 4%-75%, Acetylene at 2.5-81%; the only one worse is Silane (with which I'm generally unfamiliar). This is for air, btw, not oxygen, which expands the range. In contrast, gasoline is a nice, tight 1.4-7.6%. Of course, nobody is suggesting we fill cars full of acetylene. They do seem to be suggesting it for Hydrogen.

In the 2007 World Solar Challenge which was held last month there were cars with engines that are 95-97% efficient [1]. Why should mass-market models have to settle for a 22% efficiency?

Electrical motors constructed according NEMA Design B must meet the efficiencies as mentioned on this page [2].

Also, gasoline vehicles have faar more moving parts than electric vehicles. In a video about the Tesla roadster I believe a 1000-ish vs 12 moving parts was mentioned. Skipping all the pulleys, shafts, transmission, etc. really really helps to get a more efficient 'energy down to the wheels on the road' score.

I believe it's more efficient to generate electricity in a central location and charge the batteries in a car than it is to load an amount of petrol in a car. I believe a 'well to wheel' efficiency percentage for a gasoline car is somewhere in the 15-20% range.

[1] http://en.wikipedia.org/wiki/Nuna4
[2] http://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html
[3] http://www.triplepundit.com/pages/askpablo-well-to-wheel-efficie-002467.php

Finally: just to move away from the polluted air I would rather see electric cars than gasoline vehicles. Since I've seen a demonstration of the former, I'm completely sold... even though I absolutely loved the big V8 blocks before, I barely stand them anymore.

And the sound? Well.. I bet there's enough power in a Tesla roadster to drive a good set of speakers. ;)

Hey, Mr. AC...

http://www.engineeringtoolbox.com/air-composition- d_212.html

How much Nitrogen do you burn to get CO2? Or do you burn the CO2 to get MORE CO2? or do you use the Hydrogen to create fusion which allows fused Argon to decay into Carbon?

I think the "underwater" comment was an attempt at humor, albeit lame. In space, no one can hear you laugh.

Let's do the math, just coz I'm bored.

The specific heat capacity of stainless steel is 500j/Kg and from this site I'm going to assume the specific heat capacity of the explosive is the same as "sandy clay" (poor assumption, but this is /. and I can't be bothered doing more research) which is 1381j/Kg.

Lets assume a 5Kg mortar is 40% propellant, 30% explosive and 30% shell, and that you don't have to heat the propellant. The specific heat capacity of a 2.5Kg object with a 50/50 mix of steel and clay by weight is given by:

(2.5 / 2) * 0.5(500 + 1381) = 2351.25 Kj/K/Kg

Lets also say we want to heat the thing from ambient (35 degrees Celcius, coz remember we're in the desers of Iraq) to 100 degrees (I have no idea about explosives, despite the fact that I am a Muslim) in order to detonate it.

Assuming that all energy is absorbed evenly, the formula for energy required is:

e = 65K(delta) * 4.7025 Kj/K/Kg
= 152.83125 Kj

Given that watts are a measure of joules per second, assuming you have a quarter of a second "paint time" of the laser on the round, your lazer will need to emit:

(1/0.25) * 152.83125 Kj
= 611.325 W

(Please note: My assumptions are completely bullshit and this figure is probably way off, but it was fun doing them anyway.)

To put this into perspective, a 20g chocolate biscuit yeilds about 2,200 Kj. So really, forget the billion dollar laser program, just start lobbing chocolate biscuits at your enemy.

If this post wasn't bizarre enough, if you lob that chocolate biscuit fast enough at your enemny for e = mc^2 to come into play, then that same chocolate biscuit will yield:

e = 0.02 * (3*10^8)^2
= 1,800,000,000,000 Kj

Just sayin'.

I knew someone would say this. So the melting ice argument doesn't hold so we now go for thermal expansion? OK. To keep things simple. You need to heat water from 0 to 35 degrees Celsius in order to get an expansion of 1% in volume. Water at a balmy temperature of 35 degrees Celcius needs to be heated to 70 degrees to get another 1% expansion ( http://www.engineeringtoolbox.com/water-thermal-pr operties-d_162.html ) So that is a lot of temperature increase. Let's go for a stupid 10 degree global water temperature rise that would represent a water expansion of 0.3%. The average global water depth on earth is 3720 Meters. Let's assume for simplicity sake that all shores in the world are vertical. So water has nowhere to go but up. That would represent an 11 meter rise of sea level. Roughly every degree of water temperature rise causes the sea level to go up 1 meter but... It takes a hell of a lot of energy and time to cause a global water temperature rise of 1 degree Celsius. This temperature rise should not only occur in the top layers of the water but also at the ocean floors which is in places 16 KM deep. It would take thousands of years of solid solar radiation in order to accumulate enough heat to achieve such a temperature rise. So, you'd say "Think about the children" yeah and theirs, and theirs and so on. But... If we observe sea level rises today. What do you think would have caused it? Definitely not melting ice. Absolutely not the minuscule global temperature rises which would take tens of thousands of years to affect all of the water in all oceans. The global thermodynamic machine is a huge slow moving mechanism. It survived millions of years. It had massive meteor impacts and other huge devastating events. Here is some math again. A square meter of earth surface retains 5057953.92 joules per year of energy. Approx 43% of the solar energy. A lot is reflected back into space and some energy is used for the water circulation system (Convection). Anyway, back to our average water depth of 3720 meters. Over an area of 1 square meter that is 3720000 litres of water. Roughly 1 litre is 1 KG. It takes 2108 joules to raise the temperature of 1 litre of water by 1 degree Celsius. So the annual energy provided by the sun of 5057953.92 on a square meter can at best cause a temperature rise of 0.00064 degrees or 0.6 degrees Celsius per 1000 years. It will take 1500 years for the oceans to receive enough energy to cause a thermal expansion of 1 meter in a worst case scenario. The truth is, this planet is inherently stable. The massive ocean is a huge carbon sponge soaking up more carbon as it gets warmer. Releasing it as it gets colder. It is a stable control system. The tiny ants called humans are totally insignificant to the shear scale of this mechanism and your 10% emission reduction on your hybrid has absolutely no effect whatsoever either way. (And nor does my neighbours 1970's V8 engine)

If I push air on one side of the room, how long after does the air move where you are standing at the other end?

Answer: it depends on the speed of sound in air.

The answer to your question is the same, and it depends on the composition of the material making up the rod. At the scale that we normally interact with objects, the propagation speed for solids only looks instantaneous. In reality, it is quite slow compared to light. Even fairly rigid materials only have compressive propagation speeds of a few kilometres per second. Even if you were to make an inanimate carbon rod consisting of diamond (one of the fastest materials), the velocity would be only 12km/s. That's pretty slow compared to the speed of light (~300 000km/s).

For your 300 000 000 metre example, the light would be at the other end in about 1 second. If the rod was made of steel (about 5000m/s), it would move over 16 hours later ((300 000 000m / 5000m/s) / 3600s/hr) .

Somebody correct me if I messed that up.

This is for a tank made of very thick steel

Usually Sch. 40 carbon steel pipe + pipe caps, buttwelded.

Problem is that it's not actually high enough to be out of all the atmosphere. At 11 miles high(a good deal higher than 11km), around 10% of pressure of sealevel(11 miles is ~58k feet) remains.

Since gravity is the reason for the pressure increase, if you leave the top open and attempt to evacuate the tupe, you'll have a constant inpour of gas from the top to repressurize the tube. So you'd have to cap it off, somehow designing the cap to not interfere with the launching ship. Don't forget turbulance from the sudden movement as well!.

Now, make it 20 miles high and we'd be around the 1% pressure point. You'd still have to pump the thing out, just not as quickly.

My uncle is a rocket scientist. A couple decades ago, he was working on a NASA contractor test in Florida. One of the technicians was badly burned in a hydrogen fire. It was a hot day, and the tech walked right into the fire without seeing it. That doesn't happen with gasoline.

At depth, the groundwater is way over 100C, but the pressure keeps it liquid. As Dr Friedleifsson puts it: "On the surface, you boil your egg at 100 degrees; but if you wanted to boil your egg at a depth of 2,500m, it would take 350."

Sorry, but I HATE stupid analogies that only help make stupid people reading them, dumber. It would take 350C for the water to boil, but non-boiling 100C water will "boil" and egg just fine. It is a good thing that 340C water isn't hot enough to burn you down there, because it isn't "boiling". Sheesh....

Lets see, pressure of water to boil at 350C is around 1100 psi (guess from extending this chart). So the question is, can an egg in a shell withstand 1100 psi to even be boiled?

assuming 1.5% vol/vol. The article does not say but I'd guess mol/mol or mass/mass

See http://www.engineeringtoolbox.com/air-solubility-w ater-24_639.html