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Author Topic: What's wrong with Thermodynamics?  (Read 11088 times)

Offline damocles

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Re: What's wrong with Thermodynamics?
« Reply #25 on: 16/02/2012 11:33:43 »
but would struggle to remember how many yards in a mile.
It is easy enough.
440 yards to the quarter mile (which used to be the track standard until someone changed it to a metric equivalent to the mile, 1600 meters), out of which you can derive the rest.

The only imperial measurement that I can think of that is still in common and official use is the mile

Don't you still use the gallon over there.
Which the British conveniently changed AFTER the US Adopted the British Queen Anne Gallon.

Do you use Calories for nutrition?



Here in Oz we use only litre for buying petrol or drinks, and we have also long abandoned the mile -- all distances are in km and speeds in km/h (not m/s but you cant have everything!). Everyone has long forgotten their weight except in kilogram, but most (older) people still think of their height in feet and inches, although timber, cloth, rope, etc is bought in metres or centimetres with gauge, widths etc in cm or mm. All property measurements are in hectare or sq km, though older people still think in acres. Pints, gallons of either variety are long forgotten, although a 200 litre drum (what might be called a barrel in the US?) is still called a 44 gallon drum. And food and dieting always work in kilojoule, or "killer-joule" as they are sometimes known.
 

Offline peppercorn

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Re: What's wrong with Thermodynamics?
« Reply #26 on: 16/02/2012 11:43:32 »
Don't you still use the gallon over there.
Which the British conveniently changed AFTER the US Adopted the British Queen Anne Gallon.

Do you use Calories for nutrition?

Confusingly, the gallon (Imperial) is only quoted w.r.t. fuel economy, but petrol and Diesel are sold in litres on the forecourt!  I learnt quite young that a gallon is about 4.5 litres, so is one of the few everyday tests of mental arithmetic :)

Oh, and beer barrels (firkins and kils) are also still derived from the gallon and obviously the pint still survives... for now ::)
« Last Edit: 16/02/2012 11:46:16 by peppercorn »
 

Offline peppercorn

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Re: What's wrong with Thermodynamics?
« Reply #27 on: 16/02/2012 12:03:35 »
How about the planet Mercury as the ideal heat engine 'platform'?
Am I right in thinking it has a permanently dark side? The cold dead rocky surface would act like the ideal cold reservoir 'sink' as well (following on from Damocles' point about a lack of thermal mass in space).
How one would transfer the 'work' back to our little blue sphere is an exercise I leave for the reader .... :D
 

Offline CliffordK

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Re: What's wrong with Thermodynamics?
« Reply #28 on: 16/02/2012 12:08:51 »
What about the Pound Sterling?  Which can't buy a Pound of Sterling anymore?
Isn't Britain the only country in the EU that chose to keep the Pound Sterling rather than adopt the Euro.  I wonder how long that will last?

What units are gold and silver measured in?

We commonly use 55 gallon drums, which is about 200L, but apparently it is bigger than a barrel of crude oil.

What about measurements for alcohol?
Pints?  Ounces?
Here in the USA,  there is a fifth, which apparently was initially 1/5 of a gallon, but converted to 750ml.
Of course, I wouldn't be surprised if the British call something a pint that isn't really a pint, just like the fifth is no longer based on a gallon.
(oh, I see Peppercorn got that squeezed in).
 

Offline damocles

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Re: What's wrong with Thermodynamics?
« Reply #29 on: 16/02/2012 12:41:56 »
How about the planet Mercury as the ideal heat engine 'platform'?
Am I right in thinking it has a permanently dark side? The cold dead rocky surface would act like the ideal cold reservoir 'sink' as well (following on from Damocles' point about a lack of thermal mass in space).
How one would transfer the 'work' back to our little blue sphere is an exercise I leave for the reader .... :D
Unfortunately Mercury does not have a permanently "dark" side. It is locked into a resonance, with a long day of about 58 days that is just 2/3 of its year of about 88 days.

The floor of a polar moon crater where a permanent shadow might fall is probably the best place to set up. It is also conveniently(?) (well, marginally less inconveniently!) local. The energy costs of the infrastructure to set up there could possibly be recovered in a millennium or two.
 

Offline peppercorn

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Re: What's wrong with Thermodynamics?
« Reply #30 on: 16/02/2012 12:54:56 »
If we ever get around (and don't destroy our home or ourselves first) to building the fabled space elevators there's potential for a pretty serious thermal gradient there!  And there's no need to come up with a fancy way to transport the power either.
 

Offline syhprum

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Re: What's wrong with Thermodynamics?
« Reply #31 on: 16/02/2012 13:54:52 »
One of the most annoying measures with have to put up with is the emasculated half Kilo, many things that are normally sold in 1/2 1/4 kilo packs in England come as 454 or 227 grams, in many stores for products that you normally buy by the Kilo the price is diplayed in large letters as so much the pound.
We are supposed to have gone metric by 1960 but we still have miles, pints, horse power pounds, stones and ounces, when I look for England on the map it seems we should be about where the Azores are. 
Clifford there are quite a few countries in the EU that don't use the Euro off the top of my head they are Sweden, Denmark, Hungary, switzerland, Iceland, Czech Republic and maybe some of the ex soviet block countries. 
« Last Edit: 16/02/2012 20:16:55 by syhprum »
 

Offline Geezer

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Re: What's wrong with Thermodynamics?
« Reply #32 on: 16/02/2012 18:06:47 »

What about the Pound Sterling?  Which can't buy a Pound of Sterling anymore?
Isn't Britain the only country in the EU that chose to keep the Pound Sterling rather than adopt the Euro.  I wonder how long that will last?


The UK (which includes England, Wales, Scotland and Northern Ireland) did not buy into the Euro and it was not the only country that didn't drink the Coolaid opted out rats!I cant turn off strikethrough.
 
Based on recent events, I have a suspicion that the GBP might be around a lot longer than the Euro :)
 

Offline imatfaal

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Re: What's wrong with Thermodynamics?
« Reply #33 on: 16/02/2012 18:37:13 »
The gallon is waning in popularity (petrol is sold in litres - and that was about the only thing you bought in gallons apart from beer for a party).  But I think the calorie or kilocalorie is still popular - although I think foodstuffs have the energy content in both calories and joules.

The pint is of course still used on a regular basis - as regular as possible in fact.  Although the barmaid managed to charge me over 14 quid for three pints at lunchtime so maybe it is time we moved to the slightly smaller demi
 

Offline Geezer

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Re: What's wrong with Thermodynamics?
« Reply #34 on: 16/02/2012 19:41:11 »
Although the barmaid managed to charge me over 14 quid for three pints at lunchtime so maybe it is time we moved to the slightly smaller demi

Fourteen quid!! It might be time you moved to another country (either that, or open a pub.)
 

Offline peppercorn

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Re: What's wrong with Thermodynamics?
« Reply #35 on: 16/02/2012 20:16:16 »
Dear me!  You weren't buying pints of Scotch again were you imatfaal?! ::)
 

Offline imatfaal

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Re: What's wrong with Thermodynamics?
« Reply #36 on: 17/02/2012 10:07:22 »
Fourteen quid!! It might be time you moved to another country (either that, or open a pub.)
  Or not be a pillock and stop going to pubs in Mayfair - but watching the world (well half of it) walking past in their finery is almost worth it.  Don might like to add one his bespoke little yellow men as a shameless ogler here.

Dear me!  You weren't buying pints of Scotch again were you imatfaal?! ::) 
That's the ticket; pint of Scotch with lager shots as a chaser.  Nope; I was with oiks who liked weird european lagers (who drinks a pint of peroni? apart from the ad man's perfect target) - without my pint of young's ordinary it would probably have been worse.  Although if you are in the area I would still recommend it - their shepherd's pie won best in the country about 5 years on the trot, and the young's is too good
 

Offline Geezer

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Re: What's wrong with Thermodynamics?
« Reply #37 on: 17/02/2012 10:28:15 »
That's all very well, but you could probably buy an an entire island in the Aegean for fourteen quid at the moment.

We trust that HM Inland Rev. would agree this was a "business lunch".
 

Offline imatfaal

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Re: What's wrong with Thermodynamics?
« Reply #38 on: 17/02/2012 10:35:41 »
That's all very well, but you could probably buy an an entire island in the Aegean for fourteen quid at the moment.

We trust that HM Inland Rev. would agree this was a "business lunch".
It was indeed a business lunch and I will be avoiding the cost entirely.  If you want an island with running water you might need to think over 20 quid - it's worth the extra investment
 

Offline yor_on

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Re: What's wrong with Thermodynamics?
« Reply #39 on: 17/02/2012 15:35:26 »

Actually, you do not just need a low temperature, you also need a large heat sink or "thermal bath" to dump the waste low grade energy that you will produce. And space is incredibly empty!

Also space, at least in the inner solar system as far out as the orbit of Jupiter, is really very hot! The prevailing temperature is thousands of degrees. Basically, the molecules and ions that are there, many of them from the "solar wind", will not hit you very often, but they will hit you very hard when they do -- high temperature, low heat content.

Could you explain how you mean there in more detail Damocles?  I've been wondering about that one. The sun is said to carry 'heat' to earth by EM radiation, but for a smaller heat source (thermos bottle) it seems as if the vacuum isolates? Why does that differ. Is it that radiation is a generally poor transmitter of 'heat/IR', or is there some another explanation to it, like different combinations of frequency's?

I'm not thinking of it as being just one part of the Radiation, Convection, Conduction cycles here, just asking about radiation.
 

Offline syhprum

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Re: What's wrong with Thermodynamics?
« Reply #40 on: 17/02/2012 19:26:48 »
In your "Thermos" the transmission of heat by radiation is inhibited by reflective silvered surfaces, the heat would soon leak in or out without these.
 

Offline damocles

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Re: What's wrong with Thermodynamics?
« Reply #41 on: 17/02/2012 21:29:35 »
From Yor-on
Quote
Could you explain how you mean there in more detail Damocles?  I've been wondering about that one. The sun is said to carry 'heat' to earth by EM radiation, but for a smaller heat source (thermos bottle) it seems as if the vacuum isolates? Why does that differ. Is it that radiation is a generally poor transmitter of 'heat/IR', or is there some another explanation to it, like different combinations of frequency's?

As a chemist, I am familiar with situations where "heat transfer" means loss of kinetic energy through the statistics of collisional transfer to vessel walls or surrounding medium. Radiative transfer is a relatively slow and inefficient process and only a tiny perturbation to conductive/convective processes. It can safely be neglected. I am used to neglecting radiation.

In the emptiness of space, there is no almost no opportunity for conductive/convective heat loss, and even if there were, the very thin interplanetary medium is probably at a temperature where heat gain rather than heat loss would follow. That was my point. I might have been wrong in failing to consider radiative heat loss, but I think not.

Radiative loss at a low temperature would involve infrared radiation at around 20 nm wavelength, is a process where spontaneous emission would have a characteristic time of the order of seconds. Spontaneous emission is a process with a characteristic rate that goes as the fourth power of the frequency, other things being equal: double the wavelength means one sixteenth of the emission rate. And radiators with lower temperature emit their radiation at longer wavelength. I would be surprised if any practical heat engine could operate at the low speeds that would be needed if it relied on radiative emission at 20 nm for cooling.

A cold planetary surface that has been continuously shielded from sunlight (solar radiation) for at least several days, and had the opportunity to achieve a really low temperature through its own emissions over that time, would have sufficient thermal mass to allow the possibility of rapid conductive/convective heat transfer -- hence the lunar polar crater floor suggestions.
 

Offline Geezer

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Re: What's wrong with Thermodynamics?
« Reply #42 on: 17/02/2012 23:58:17 »

In the emptiness of space, there is no almost no opportunity for conductive/convective heat loss, and even if there were, the very thin interplanetary medium is probably at a temperature where heat gain rather than heat loss would follow. That was my point. I might have been wrong in failing to consider radiative heat loss, but I think not.


Maybe you better let these guys know :)

http://en.wikipedia.org/wiki/Advanced_Stirling_Radioisotope_Generator
 

Offline CliffordK

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Re: What's wrong with Thermodynamics?
« Reply #43 on: 18/02/2012 05:48:29 »
In the emptiness of space, there is no almost no opportunity for conductive/convective heat loss, and even if there were, the very thin interplanetary medium is probably at a temperature where heat gain rather than heat loss would follow. That was my point. I might have been wrong in failing to consider radiative heat loss, but I think not.
Maybe you better let these guys know :)
http://en.wikipedia.org/wiki/Advanced_Stirling_Radioisotope_Generator

Wolfekeeper brought up the Stefan Boltzmann Law here.
http://www.thenakedscientists.com/forum/index.php?topic=42960.msg379543#msg379543

Which will determine the watts per square meter that can be radiated by temperature and energy.

It is not clear how much energy is reabsorbed on a convoluted surface in space, but perhaps if mirrored, the reabsorption would be minimized.  One might also design the surface of the entire space probe to be highly heat conductive, and thus use all the surface area of the entire probe as the radiator (and also warm the equipment in the probe slightly).

Anyway, we know that RTGs have been used in space probes for quite a while.

One concern that I have with the sterling engine is that it is rated for "≥14 year lifetime".  I guess I'd be a bit worried about moving parts off somewhere where there is little chance of maintenance. 

The Pioneer Probes have run out of power (more energy conversion efficiency might have helped, but it also depends on the design tolerances).

The Voyager Probes are now at 34 years and counting, with hopes to keep them operational for another decade or so (perhaps a half century total).  Is the Sterling Engine capable of a half century of continuous operation without maintenance?
 

Offline Geezer

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Re: What's wrong with Thermodynamics?
« Reply #44 on: 18/02/2012 05:56:52 »
btw, it's not Sterling as in money, is Stirling as in this place http://www.nationalwallacemonument.com/
 

Offline syhprum

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Re: What's wrong with Thermodynamics?
« Reply #45 on: 18/02/2012 08:56:36 »
I used to work near Smithfield market and always gave a slight shudder when I passed the plaque where Wallace met his awful fate.
(excuse irrelevent post)
 

Offline yor_on

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Re: What's wrong with Thermodynamics?
« Reply #46 on: 18/02/2012 22:33:13 »
Thanks Damocles. A nice answer. So what is the 'output' of the sun relative the heat/IR we receive on Earth? I guess it might be difficult to answer that one but it would be interesting to know the relation between those two. If we talk about photons the only way they 'annihilate' is through interactions, if we talk about waves we have quenching and reinforcing. And the waves from the sun are polychromatic, of a lot of different wavelengths. So how do the transfer of heat works, and if some get lost, to what does it lose?

I know, maybe for another thread this one, but I like when threads grow :)
 

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Re: What's wrong with Thermodynamics?
« Reply #46 on: 18/02/2012 22:33:13 »

 

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