Author Topic: Talking Thermodynamics  (Read 93442 times)

Offline crueby

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Re: Talking Thermodynamics
« Reply #1095 on: November 14, 2018, 11:15:05 PM »
Hi MJM, a quick question ...In a steam engine we burn fuel in a boiler to generate steam to drive the engine to create power to do work .......... this fuel can be wood coal gas etc etc ... So in the human body we eat vegetation in the form of veg and this enables the body to function and work also keeping us warm and cool,  So how does the human body change the fuel/food into a functioning  work producing "engine"   ?? This may be more medical than technical, and is it still a thermodynamic Process ??

Willy
And please, no tech details or pics of your 'boilers' blow-down valve!

Sorry, couldn't resist that one...   :LittleDevil:

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1096 on: November 14, 2018, 11:23:04 PM »
Hi Chris , ok i promise !! :cartwheel: :Lol:  ,  if you promise !!

Offline crueby

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Re: Talking Thermodynamics
« Reply #1097 on: November 14, 2018, 11:25:00 PM »
Hi Chris , ok i promise !! :cartwheel: :Lol:  ,  if you promise !!
Deal!
Hmm, should make Zee agree too....

Offline Zephyrin

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Re: Talking Thermodynamics
« Reply #1098 on: November 15, 2018, 08:20:56 AM »
Quote
So how does the human body change the fuel/food into a functioning  work producing "engine"   
We are plain combustion engine, like any living organism, we use oxygen to burn carbon compounds (sugars, fat...) and produce carbon dioxide at the end in all the cells of our organism. The respiration brings oxygen to the blood that distribute it in all the cells of the body, removing CO2 in the same time. These combustion processes occur at moderate temperature and in aqueous medium through a long chain of enzymatic reactions, the oxidative metabolism; but they are combustion in the principle.
Energy is stored into the cells through ionic gradients and energy rich chemical bonds, used by the molecular processes underlying life, muscle contraction, conduction of the nervous influx etc...
The yield of these reactions is far better than a steam engine, with billions years of tuning.

Only green plants are able to use light energy directly to incorporate carbon dioxide from the air into organic compounds, in addition to the above processes.
« Last Edit: November 15, 2018, 06:02:38 PM by Zephyrin »

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1099 on: November 15, 2018, 09:52:16 AM »
Well said Zephyrin, I can’t add anything to that.  Chemical plants and biological organisms and plants all rely on the same thermodynamics and the other laws of physics to govern their particular variations of basic chemical reactions.

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 #1100 on: November 16, 2018, 12:07:55 AM »
Hi Zephyrin and MJM thanks for the reply..most informative...Next question about evaporation  In hot countries it is possible to keep milk cold by evaporation by placing a piece of muslin over the bottle and having it soaking up water from a dish. however if everything gets to ambient temperature say in a closed room does this still happen ?? or does there have to be external forces at work  ? ie  sunlight ,or a draft for something?? also are there definite parameters to follow to make this work properly and efficiently
Willy.

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1101 on: November 16, 2018, 11:18:31 AM »
Hi Willy, in this country, we call it a Coolgardie safe, though that term tends to be used for a whole food cupboard covered in hessian, and kept wet, rather than just a bottle.  The heat absorbed by the evaporation of the water keeps the whole safe closer to the dew point temperature than the dry air temperature and is low enough in low humidity climates to be useful in storing food if refrigeration is not available.  It also keeps the flies off the food.

But like those evaporative air conditioners we talked about previously, the system depends on evaporation of water, so relies upon a continuous supply of fresh low humidity air to carry away the water vapour.  If there is insufficient air flow around the outside of the device, the humidity rises to the point where there is insufficient evaporation for the thing to be effective.  It won’t work for very long in a closed room.

The name is historical, sorry the story eludes me for the moment.  The water bag on the front of the car works on a similar principal.

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 #1102 on: November 16, 2018, 04:37:58 PM »
Hi MJM , i sort of came to the same conclusion but wanted to make sure with the maths !!  So do equations with thermodynamics also have a bit about wind speed etc etc ??
Willy

Offline derekwarner_decoy

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Re: Talking Thermodynamics
« Reply #1103 on: November 17, 2018, 12:16:57 AM »
'The water bag on the front of the car works on a similar principal'.............

Goodness Willy...that brings back memories  :old: [maybe 65 years ago] driving from Sydney to Melbourne in an FJ Holden....complete with caravan & twin canvas water bags attached :killcomputer:  to the front bumper either side of the yellow fog light :o

Every now & then, Dad would stop & boil the Billy with water from a bag & with a metho burner stove  for the cup of tea.......more steam involved

From memory...these events only occurred just after a Township where Mum would purchase a little 1/4 pt bottle of fresh milk at a corner store......garages only sold petrol

Derek

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Offline MJM460

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Re: Talking Thermodynamics
« Reply #1104 on: November 17, 2018, 10:33:11 AM »
Hi Willy, understanding all the things going on with that evaporative cooling involves fluid dynamics as well as thermodynamics and heat transfer all acting together.  The complete calculation may be possible these days with computers running computational fluid dynamics or CFD.  I was taught the equations, though the lesson faded almost as quickly as the sound of the lecturers voice.  Computers able to solve the equations did not exist at the time. 

Without the full computing facility, the problem is approached by assuming the conditions are constant, so ignoring the effect of the increasing air humidity as the evaporation proceeds.  This is near enough if there is a reasonable air flow, so the air is continually being replaced by low humidity air.  I am not even sure how to calculate the the rate at which the water will evaporate for any given air humidity.  As with many such complex problems, the simplest approach is experiment.  Unfortunately I can’t shed much more light on it than that.

Hi Derek, wow! an FJ, probably a new one at that time? A fog light and two water bags, we only had one bag on a second hand old Ford and no fog lamp.  We used the water bag to provide a cool drink on long hot trips.  That water always seemed particularly good.  But it does bring back memories for both of us, and I am sure many others.  I am glad to see that you are still looking in.

Thanks to 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 #1105 on: November 19, 2018, 03:57:04 PM »
Hi, MJM  Something festive going on here in the frozen north !! Saw this cool vid of crystals growing in a bubble  !! Some complicated thermodynamics going on here ??

Willy

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1106 on: November 20, 2018, 10:32:55 AM »
Hi Willy, very cool, in every sense of the word. 

I have never seen such a thing, but I have very limited exposure to cold enough conditions, apart from a bit over three years living and working in Canada, and a some time skiing.  However, providing it is not a photoshop job, I suggest it is another example of unsteady state heat transfer phenomena. 

I would expect that the bubble was initially formed from humid air, then the ambient temperature subsequently reduced.  So, what would we expect could be happening, based on our understanding of thermodynamics?  Is it plausible?

First assuming the crystals are ice, some water is freezing to make the crystals, but the bubble looks like it is still liquid, so perhaps it has some soap liquid to make the bubble more long lasting.  That may have lowered its freezing point, so it can remain liquid while the water inside freezes.  However, I am a little uncomfortable with this, as it would be difficult to make sure the soap did not mix with the water inside. 

Or, is freezing a process which causes some separation of a soap/water mixture?  But why, in that case do the crystals form inside and not outside?  There may be an explanation in the difference in humidity (or water vapour partial pressure) inside the bubble compared with outside. 

In some conditions you get snow, and others you get solid ice, and it depends on the path through that vague area at the bottom of the water phase diagram, the solid/liquid boundary.  An area where I am not very familiar, but well understood by those operating snow making machines in the worlds ski fields.  Perhaps others from those colder climates can add something clearer.

I do know the ice can form quite quickly in the right conditions.  I remember serving a cool drink from the cooler in the back of the car to my Boy Scout Troupe on a winter camp experience.  It turned to a slushy in their cups.  (It was around -20F from memory.)  Turned out the “cooler” was actually keeping the drinks warm.  Only an Aussie would not see a problem with serving up cordial after a job well done.  They had just finished pitching their tents ready for the night.  Just as well I had my Newfie associate to make sure I didn’t overlook anything important.  All survived safely.

Anyway a cool video, one that would take some detailed knowledge of thermodynamics to deliberately produce the right conditions, or the simple answer, a lucky coincidence for the camera operator.  Or perhaps everyone who celebrates Christmas in cold climates sees it all the time.  I would like to hear from others to help us understand it more clearly.

Thanks for looking in.

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