Author Topic: Talking Thermodynamics  (Read 108914 times)

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1140 on: April 18, 2019, 02:42:39 AM »
hi MJM ,  Just been thinking about flatulance.... So .... cows and us produce a gas called methane  !!! however is this gas just called methane , and does it also contain traces of butane propane and other flammable components ?? does what is produced depend on what is consumed ?? When i lived near marshes one could stir the dykes and bubbles of gas would appear so is this also a mixture of different gasses ??

Willy


Offline derekwarner

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Re: Talking Thermodynamics
« Reply #1141 on: April 18, 2019, 03:42:58 AM »
Goodness Willy, with MJM residing in Australia.....and Australia set to have our Federal Elections next [edit] in a few weeks, you may have placed MJM in a rather invidious position as one on the National Parties standing for election has a platform that cows should be banned due to their Methane flatulence  contribution to the Green House effect the World is suffering

1. If that referenced Party were to win Office, the next time one went to McDonalds .......it would be  1/4 Pounder of Kangaroo meat  :facepalm:

2. It appears that Kanga's fart's are low in Methane  :cussing:

3. Cows, or beef cattle are not a Native specie to Australia & should be dispensed with

....Courtesy of WIKI.....
....Beef Cattle in Australia. The First Fleet and On. When first settled, Australia had no native animals suitable for domestication. ... A bull, four cows ....and a bull calf of the Indian Zebu were bought at Cape Town, South Africa.
 
4. So if MJM did bravely respond, his comments could be seen as a Political Statement as which is I understand  would be contrary to the Guidelines,  :happyreader: Rules and Codes  of MEM...or lets wait & see how he treats this heat thermal transfer question  :slap:

Derek

« Last Edit: April 22, 2019, 10:54:58 AM by derekwarner_decoy »
Derek Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1142 on: April 18, 2019, 10:49:12 AM »
Well, what can I say?  Between politics, climate change and animal liberation, perhaps it would be safer to talk about religion! 

So mindful of all that, the methane from cows is a byproduct of their digestive processes.  I donít really know enough about the chemistry, but I would be sure there is more than methane involved, including some sulphur compounds and more, but I believe methane has been identified as a significant component, and of interest due to its green house gas contribution.  I donít know if those same digestive processes have the ability to produce longer chain hydrocarbons, or whether the breakdown of grass and the other things cows eat results in breaking off parts with more than one carbon.  That is a deeper level of chemistry than I ever studied.  I wonder if any other forum members have more knowledge in this area.

Marsh gas, or swamp gas that bubbles up from the swamp as you have observed, Willy, is also largely natural gas or methane which has been produced in the process of decomposition of plant materials in the bottom of the swamp.  Again, I am not sure what longer chain components might be formed in the process.

Both the cows digestion, and the rotting of plant matter are low pressure processes, and in general, low pressure favours products with lower molecular weight.  The formation of natural gas and oil deep underground occurs at very high pressure, generally thousands of psi, with higher temperature than near the surface, and these conditions lead to larger molecules as seen in oil and the lpg gases such as propane and butane.  So that might be a clue.   But also, favouring the heavy components does not mean only heavy components are produced, just that they are produced in much greater proportion then the lighter components.  Similarly, low pressure generally favours lighter molecules, but I would not be surprised if there was a small proportion of heavier components produced even in th elbow pressure reactions.

I hope that helps and that I will not need a helmet to shield me from the responses.

MJM460

The more I learn, the more I find that I still have to learn!

Online crueby

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Re: Talking Thermodynamics
« Reply #1143 on: April 18, 2019, 12:15:51 PM »
What about the methane production at one end and the hot air at the other end of a politician? Gotta be some high thermal efficiency in that production!  :Lol:

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1144 on: April 18, 2019, 08:31:37 PM »
HI MJM, well ...that opened a can of worms .methinks.!!!.or should that be beans !! thanks for the relevant info !! and other historical stuff !!!! In a boat any leaking propane can sink into the bilges and be quite dangerous, so how high can released methane rise into the atmosphere if no wind ??  also is the carbon atom heavier than the 4 hydrogen atoms and in an inclosed space would you get a thin layer of methane with other molecules of gases above and below it ??  thinking about oil retorts here...?

Willy
« Last Edit: April 18, 2019, 08:37:48 PM by steam guy willy »

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1145 on: April 19, 2019, 09:40:18 AM »
Hi Willy, worms or beans?  Quite a mouthful either way.  Or perhaps not!

Yes, propane molecules are heavier than methane molecules, so methane tends to migrate higher while propane, butane etc tend to accumulate lower down.  Like in the bilge of a boat as you say or a hole in the ground.

But the story is a bit more complicated than that.  They do not form layers in order of density, but rather all move somewhat randomly in all directions, so they all tend to spread and occupy the whole space, largely independently of each other, so in a given volume, the concentration is similar everywhere.

However, added to that random motion is the effect of collisions between molecules.  If you consider just the vertical component of the motion, all have gravity accelerating them towards the centre of the earth, and when two collide, the lighter one bounces off at higher velocity than the heavier one.  So the effect of all those collisions is to cause the lighter ones to go upwards a bit more than down, while the heavier ones tend to go down a bit more than they go up.  So in a very high column of a mixture of gases, the concentration of lighter components will be higher at the top while the concentration of the heavier ones will be higher at the bottom.  But all will be detectable at all heights.

In the boat, butane (MW 58) and propane (MW 44) are much heavier than Oxygen (MW 32) or Nitrogen (MW 28) so will tend to accumulate low down, but there will be an air fuel mixture everywhere just waiting to be found by a spark, and the air circulation tends to be less than outside in free air, especially in the bilges, so a fuel leak can easily build up faster than it is carried away by ventilation, and it eventually reaches a flammable concentration.  And you donít want to be on that boat when the air fuel mixture finds that spark.  I have seen it close by, fortunately a few hours after, and even more fortunately, some how no one was hurt.

In air, methane (MW 16) is lighter than oxygen and nitrogen, so tends to rise as a result of all those collisions.  The effect of gravity is taking energy from those molecules all the way up, so it gets colder and less dense as fewer molecules have enough energy to keep rising, until it is eventually lost to some other object in the solar system or more likely does more falling back so spreads no further.

Wind tends to add turbulence which mixes it all up a bit, but as turbulence tends to be random, it does not particularly add to the separation which is due to gravity added  to the turbulence.

Itís a bit of a simplified explanation,  and does not explain everything that happens, but itís close enough  for a basic understanding.

The hydrogen and carbon atoms in each molecule are strongly bound together, so they act as a single molecule, not as separate atoms in a mixture.

And in case you think there is no energy in those collisions, the pressure on the walls of a container of gas under pressure is the result of all those collisions as molecules hit the walls.

I hope that all makes the situation a little clearer.

MJM460
The more I learn, the more I find that I still have to learn!

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1146 on: April 19, 2019, 11:37:50 PM »
Hi MJM thanks very informative,,,Another question  does it take the same amount of energy to cool things down ,as it does to heat them up ?? conservation says yes but ....... also we can heat things up very quickly but can we cool them down very quickly as well ?? we can use microwaves to heat things up but what are the alternatives with cooling ??

Sorry my questions are so short  and takes a fraction of your time for your answers !!!  Also, Does all those collisions of the molecules on the walls of the containers have a detrimental effect on the containers ??

Willy

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1147 on: April 22, 2019, 10:44:19 AM »
Hi Willy, Iíve been off line for a couple of days, but have not forgotten your questions.  I think there are four.

If we heat something up from some temperature to a higher temperature, we do get all that heat back in cooling it back to the starting temperature.  Note that this is a different question to whether the heat required to heat something by say 100 deg, do we get the same amount back if we cool it by that same 100 degrees from the same starting temperature?  The amount of heat involved in these cases is usually different because for most materials, the specific heat is not constant but varies with temperature.  So the heat to increase a temperature from 100 to 200 deg is slightly different from the heat required to increase the temperature from 200 to 300 deg.  I hope that makes sense.

How fast we can heat or cool something depends mostly on temperature difference.  If we have a piece of steel at ambient temperature, we could use a blow torch with a flame temperature many hundreds of degrees hotter than the steel, which will heat it quite quickly.  If however we want to cool it quickly from ambient temperature, about the best we could do is to plunge it into liquid nitrogen, but the temperature difference would still only be about 200 degrees.  As the heat transfer is proportional to the temperature difference, cooling would obviously be slower.  Most refrigeration systems we are familiar with have a minimum temperature around -40 C, depending on just which refrigerant is used, so an even smaller temperature difference.

However, if we start at a much higher temperature, say a piece of steel extracted from a blacksmiths forge, cold water would have quite a high temperature difference, and boiling of the water when it hits the hot steel has a very good heat transfer coefficient.  This results in very rapid cooling.

I donít know of any way to make something to emit microwaves in order to cause cooling.  Microwaves are waves like light and radio waves and infrared heat, so similar to cooling by radiation, which again requires cooler surroundings.

I wonder if you are thinking of processes like peening in your last question.  Many hammer blows on a metal surface cause plastic deformation at the surface which modify the material properties.  However the collisions of gas molecules with the walls of a container are much lower that than the pressure under the hammer used for peening.  So definitely no detrimental effect at any pressure we are likely to encounter.  However, for very high pressures, especially pressures that cycle through a significant range, pressure vessels do have to be designed for fatigue, as a result of the cyclic loading of the vessel walls.  And that pressure is of course the sum total of all those collisions of the gas molecules with the vessel walls, but it is a load on the whole wall thickness, not just a surface effect.  The calculation procedure is covered in a similar manner in the ASME, BS and AS codes.

However, when the gas molecules collide with the molecules of the wall of the container, there is energy exchange resulting from the collisions.  If the gas is hotter than the container wall, the wall will be heated and the gas cooled.  Similarly if the gas is cooler, it will pick up energy from the walls and the container cooled.

I hope that answers the questions.  Thanks everyone for looking in.

MJM460
The more I learn, the more I find that I still have to learn!

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1148 on: April 23, 2019, 01:35:32 AM »
Hi MJM, thanks for the info ... very informative...
Willy

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1149 on: April 23, 2019, 11:43:44 PM »
Hi MJM, I learnt an interesting thing today at the local model engineers club meeting....They have a club loco that has not been used for some time and as one does when confronted with hand wheels you allways have to twiddle them !!! However on this loco none of them would turn and also the regulator seem to be stuck fast. !! on enquiring about this i was informed that when a locomotive has finished running and all the valves and cocks are turned off and the blowdown vale is operated, when the loco cools down the brass cocks and valves shrink slightly and then seize up. I have never heard of this before so was quite surprised at my ignorance about steam engines etc etc.  I was also told that when the boiler was refired every thing would expand and they would become free again.

Willy

Online Jo

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Re: Talking Thermodynamics
« Reply #1150 on: April 24, 2019, 07:01:34 AM »
on enquiring about this i was informed that when a locomotive has finished running and all the valves and cocks are turned off and the blowdown vale is operated, when the loco cools down the brass cocks and valves shrink slightly and then seize up.

Which is why it is good practise to open all the valves just after you have blown down and before you put the Loco away. If they are left closed they contract hard shut not only damaging the valve seats but risking that next time, when getting it out for running, someone will try forcing them open  :toilet_claw:

Jo
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Offline AVTUR

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Re: Talking Thermodynamics
« Reply #1151 on: April 24, 2019, 09:28:24 AM »
Sorry to jump in here but I have just seen steam guy willy's first question in Reply #1146 and could not resist answering it. No - Second Law of Thermodynamics.

I know, you have heard it before but in any such operation energy is lost to the outside, radiation, warming up the air due to convection, etc. Conservation of energy (First Law of Thermodynamics) still applies but the losses have to be accounted for.

AVTUR

There is no such thing as a stupid question.

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1152 on: April 24, 2019, 12:41:49 PM »
Hi Avtur,

Good to have you join the discussion, no need to apologise.

I am trying to follow what you are saying.  Are you by any chance referring to post no 1147 for Willyís question?

 MJM460
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Offline MJM460

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Re: Talking Thermodynamics
« Reply #1153 on: April 24, 2019, 12:54:54 PM »
Hi Willy, I donít have any experience of running a locomotive, but your comment and the reply do not surprise me.  With full size piping in the oil industry, the normal experience is that when you close or open a valve, when the gate seats, you wind the wheel back to release the pressure on the thread so the nut is in the midst of the backlash.  This does not release the seal, but does make it easier to open the valve when the time comes.

I am not sure if the issue is corrosion of the thread, or thermal expansion/contraction, that jams the valve.

I think Jo has the right answer, they donít jam if left open.  Thanks Jo.

MJM460

The more I learn, the more I find that I still have to learn!

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1154 on: April 25, 2019, 02:22:25 AM »
Hi MJM et al, thanks for the extra info...I can't believe i didn't, know this . However i have been working in isolation for most of my life , and that is what is so good about this forum and local clubs closer to home. When i first started making engines and boilers i always used brass with the copper , so there is no way they could get boiler certificates today. I have part built a 3 1/2" County Carlow that i started in 1969  with brass bushes , so that will be just a static model!!

Willy