Author Topic: Talking Thermodynamics  (Read 121141 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

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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!

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1107 on: January 10, 2019, 02:31:37 AM »
Hi MJM,  A prosperous new year to you and I seem to be slowing down somewhat at the moment  I have been reading an 1892 book about electricity and there is a few pages on Thermocouples !! It suggests that Antimony and Bismuth are the best combinations  and I wonder how, in the last 120 years have we progressed further ? also we don't actually here much about thermopiles/couples apart from measuring devices.?  I can remember reading back in the sixties a chap in India listening to his transistor radio whilst smoking a Hookar with the device attached to it ??  Are there any actual electricity producing devices out there driven by heat. ??!!

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1108 on: January 10, 2019, 08:20:28 AM »
Hi Willy, A very happy New Year to you as well.  I was suspicious that you had not run out of questions.  Your work on the Easton and Anderson model is more than enough diversion though.  I am an avid follower, and always learning new techniques.

I would suggest there have been considerable advances in use of thermocouple effects.  Apart from the electronics to measure the voltage and display the temperature, and account for the necessary reference junction, many different metal combinations are used.  The “best” in any application depends on temperature range, cost, need for calibration and so on.  The common K type thermocouple uses a chrome alumel junction, and there are standard tables of output voltage with temperature.  (I don’t know what “alumel” is, some sort of nickel alloy, I believe.)  And then semiconductors are also being used, I assume in thermopile applications where many junctions are connected in series in a compact array.

You will find more information if you look up Peltier effect, or Seebeck effect, but even “thermocouple” will yield a wealth of information on the thermoelectric effect.  Possibly way too much!

The effect is used for cooling of industrial instrumentation in desert areas and for cooling computer chips, and there are also thermoelectric heaters and coolers available, even for use as a fridge in your car.  The drink heater/cooler devices are available in stores here.  They use many thermocouples in series to increase the power/heating/cooling output to a useful level.  I believe that the simple reversing the supply polarity changes it from a heater to a cooler.  Not very efficient in terms of current consumption but easy to control, and reliable, due at least in part to being solid state, no moving parts.

The process involves increase of entropy, but I won’t even try to explain that, or even suggest that I could.  But it is unlike many thermodynamic processes in that it is fully reversible, and you can produce current from a temperature difference or produce a temperature difference by supplying the current.

There are reports of watches powered by body heat with this effect, and battery-less radios for remote areas and emergency use.  The most spectacular example of use of the effect to produce electricity is in space craft.  You may have wondered how they use radioactive fuel sources to produce electricity.  I understand that the heat from the radioactive decay is used to heat the hot junction and the cold of outer space for the cold junction is used for a Peltier effect power generator which continues to work for many years long after space craft have travelled out of range of the sun’s heat for PV power generation.

So when you read your historical text, that is the direction it is all heading.  A tribute to the early work of Seebeck, Peltier, Thompson and others.

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

Offline Admiral_dk

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Re: Talking Thermodynamics
« Reply #1109 on: January 10, 2019, 11:57:31 AM »
Some of these are also used to create electricity today in areas where it do not matter that the hot side stays hot and you have a cooler side too.

Another "funny" use is a fan for a stove in the living room. You place it on the stove / oven and this is the hot side of the element and the fan that get is electricity from the element, blows air over the cold side + the stove, so it distributes the heat in the room.