Author Topic: Talking Thermodynamics  (Read 139053 times)

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1365 on: September 09, 2020, 12:39:35 AM »
Hi All , ok ..interesting .. actually I just drink the apple juice as I am a teetotaller..apart from medicinal brews !! so if the surface of a container was polished microscopically would it slow or even stop the nucleation ??  I am thinking of another experiment that I will report on with this explanation..?!!! Hi Avtur   we use to put liquorice in coke bottles when I was young !!.. I suppose the process does actually give off some heat ? something else I learnt today was  that an explosion occurred in a recycling plant because all the coke bottles still had the lids on when they were being crushed, it was a very hot day and the pressure inside of them increased somewhat and when they got crushed the pressure was released sudenly and destroyed the machine .....

so thanks for the science lesson

Willy

Offline Zephyrin

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Re: Talking Thermodynamics
« Reply #1366 on: September 09, 2020, 11:05:00 AM »
In a fermenting liquid saturated with CO2, the gas in excess breaks down the intermolecular forces of the liquid to accommodate gas, and forms an interface between the liquid and gaseous phases; this phenomenon is costly in terms of energy, hence the spherical form of the bubbles; which I suppose is the best way to balance the different forces, gas pressure, surface tension...

In a liquid without disturbance for a while, the bubbles rise vertically to the surface, under the effect of Archimedes' thrust, and accumulate as foam precisely above their production area, and release the CO2.
If it was otherwise, or if it sticks to the wall of the glass, it is because a force is exerted on these small bubbles .

I only have experience of Champagne, where one easily observes also that bubbles are growing up while they rise in the glass.

Paul :
I suggest that you put a small spring or a shim elastic bronze on the valve of your loco so that it remains pressed against the port face even upside down...otherwise starting the engine will be impossible if the valve is not pressed firmly against it.
Repairing your locomotive will hopefully be a good remedy against these gloomy thoughts...
« Last Edit: September 09, 2020, 11:09:07 AM by Zephyrin »

Offline paul gough

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Re: Talking Thermodynamics
« Reply #1367 on: September 09, 2020, 11:35:39 AM »
Hi Zephrin, Thanks for the suggestion regarding support for getting the valve to seat with inverted cylinders. Sorry for sounding gloomy, I was in fact trying to be jocular. One reaches a point where existential threats force you to re-assess things somewhat, and I now take the view that it is best to laugh at adversity and attendant, prescribed, no option outcomes.  Regards, Paul Gough.

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1368 on: September 09, 2020, 12:06:18 PM »
hi All ..thanks.. and I have done the experiment... I bent a piece of studding to a W shape and put it in a square jar with the new apple juice. this was placed in the jar about 12 hours ago and the bubbles have taken up the shape of the  bent steel studding   {sort of}.  so there we have it !!! one could do this to identify your bottles of juice ..say in a shared house ,to mark out your ownership ?!!!

Willy

Offline AVTUR

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Re: Talking Thermodynamics
« Reply #1369 on: September 09, 2020, 12:51:50 PM »

I only have experience of Champagne, where one easily observes also that bubbles are growing up while they rise in the glass.


The Champagne industry did a lot of research on the development of bubbles when the great wine is poured into a glass. This was in the late 1980s and I would have loved to have been involved. Were you, Zephyrin?

It may not be thermodynamics but it is certainly fluid dynamics.

AVTUR
There is no such thing as a stupid question.

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1370 on: September 09, 2020, 12:56:45 PM »
Hi ..I suppose that anything that changes temp by even   .000000000000001 degree will fall into   Thermodynamics  ?????????????

Just thinking above my pay grade !!

Willy

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1371 on: September 09, 2020, 01:58:59 PM »
Hi Willy, just by coincidence, there was an article in the newspaper here, I think just last week, where climate scientists somewhere had put a sea water temperature difference of a trillionth of a degree into their climate model.  I read it three times, to be sure I had read it correctly.  It had a major effect on the ebb and flow of the el Nina/el nino pattern that has so much effect on our seasons.  Right up there with the flapping of a butterfly wing in the Amazon.  So clearly thermodynamics, but probably not much help to our understanding of our model engines. 

However, fluid dynamics can tell us a lot of useful stuff so that subject definitely belongs in this thread.

I was thinking of Avtur’s comment about rain seeding with silver compounds.  There were a lot of experiments in this country in the second half of the last century, but I have not seen much about it lately.  I looked up a couple of reliable sources and found that there was the general impression that in the right circumstances, it does produce statistically significant rainfall increases, the right circumstances do not occur very often.  And it requires very significant experimental design and statistical analysis to demonstrate any effect at all, compared with the normal highly variable nature of rainfall.  Then they were talking about perhaps 5%, and made the interesting comment, would that make any difference to Scotland, and would it be any use in Ethiopia?  Apparently the most successful experiments occurred in regions where there was significant air uplift due to mountains to carry the seeded air mass up high into the atmosphere.  And only in a very narrow air temperature range between the limits of “not going to rain anyway”, and “would have rained without seeding”.

So some of these things have a theoretical basis, and do actually occur, but the effect may not be enough to suit our purposes.

Not sure how you would indentify the difference between M and W to tell your glass from mine!  But this question has certainly started some interesting discussions.  Now we need to develop an engine powered by the CO2 generated in cider.

(Perhaps I had better return to Fluid mechanics.)

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

Offline paul gough

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Re: Talking Thermodynamics
« Reply #1372 on: September 09, 2020, 11:48:13 PM »
I went looking for some cork sheet, say 1-2 mm thick but only found rubberized cork gasket sheet from auto shops. Can anyone say if this material has insulating properties anywhere close to plain cork. Regards, Paul Gough.

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1373 on: September 10, 2020, 12:54:27 AM »
Hi Paul,

I found the thin Cork sheet in one of those $2 variety shops, sold as place mats.  They all seem to be independent, so I guess it depends on what they think they can sell in your area.

I would be concerned about a rubberised material becoming soft and sticky with heat, so might need a bit of an experiment to see if it is satisfactory.  Not sure if the rubber component affects the insulating properties a lot.  Certainly the thermal conductivity of the material is important, but the rubberised material would be a lot better than nothing if you can’t find an alternative.

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 #1374 on: September 10, 2020, 03:47:28 AM »
hi MJM ..interesting about cloud seeding ,,but could they just use dust ? rather than silver compounds ..very expensive   also do W 's become M's as you are down under as they say about the antiperdies  ??

Willy

Offline paul gough

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Re: Talking Thermodynamics
« Reply #1375 on: September 10, 2020, 07:03:24 AM »
Thanks for your thoughts MJM. We have a couple of those "Cheap Charlie" shops up here so I'll check those for the plain cork sheet. I seem to remember the rubberized stuff being rather cheap, and might try it wrapped around a tin and put it in the oven on a low heat and see what happens. Will also try to set a small piece of it alight to see if it is flammable. I had assumed it would have some heat tolerance being for automotive use, but only a presumption on my part.
 I forgot to answer your question about the engines valves in the PM. They are just small rectangular brass slide valves running on the upper surface of the brass cylinder block with drilled porting.

Willy, There would probably be specific reasons for using silver iodide for cloud seeding, but I remember from my uni geography course the size of the particles is critical  as well as the specific atmospheric circumstances that prevail to have any chance of success, which in this country seems to be rare. Oddly enough, when we have large intense bush fires they frequently engender powerful thunder storms often with significant rainfall. I think there might be a close relationship between the chemical and the physical for forming these minute droplets. Regards, Paul Gough.

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1376 on: September 10, 2020, 01:42:36 PM »
Hi Willy, The cloud seeding experiments in this country used either silver iodide or dry ice which is the solid phase of carbon dioxide.  I don’t know enough of the chemistry or cloud mechanics to understand why each was chosen, or if other compounds were tried.

Hi Paul, I hope you can find that cork.  With slide valves needing a little room for lift to discharge condensate, I think they will fall away from the valve face when not in operation, if you turn the cylinder over.  But the spring as Zephyrin has suggested should hold them against the face, but still allow a little lift when required.  My mill engine needs the same treatment, as the valve face in the vertical plane sometimes allows the valve to rest far enough off the face to allow the steam or air to pass straight through to the exhaust without pressurising the cylinder.  I am thinking of a little sliver of stainless steel shim that I have somewhere in my “potentially handy bits” box, with a slight bend as a leaf spring.

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 #1377 on: September 11, 2020, 03:54:07 AM »
Hi MJM , I have a flat bottomed Petri dish and doing the experiment again ,,,and after 4 hours the bubbles have only started to appear on just one of the arms ?? there may be something different about this arm but will only see it when the ex is done , and the w/m is removed ???

willy

Offline paul gough

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Re: Talking Thermodynamics
« Reply #1378 on: September 11, 2020, 11:42:45 AM »
Hi All, I carried out some simple kitchen tests on rubberised cork sheet. Branded 'Calibre CS0065, 375 x 400 x 1.6 mm' no country of origin on packet. The tests where carried out in a pot of boiling water on the gas stove and in the electric oven, with a supplementary 'insulation' test using a stainless electric kettle. Make sure the kitchen boss is away, as the odour becomes unpleasant at high temps.
A 30mm dia. 100mm long cylinder of sheet was submerged in boiling water for 15 minutes with no apparent degeneration of the material and no adverse affect after folding it over flat 6 times when it dried.
A 25 x 50 strip placed on oven paper on a tray in a pre-heated oven 75mm above element at 150 C. and soaked for 5 mins. then raised to 150 C. for 5 mins., finally at 250 C. for 5 mins. At 150 C it showed no indications other than slight odour, 200 C. stronger odour with slight darkening, 250 C. strong unpleasant odour and darker, about twice darkness of original but no other sign of degeneration. Folding over 6 times caused cracking to 50% of thickness. Material very slightly stiffer and slightly rougher surface texture.
Pristine material, boiled sheet, oven test sheet all ignited immediately in a butane stove flame.
Insulation test carried out as described above giving single thickness result of 30 seconds and double thickness of 65 seconds.
I think this material may prove resilient, for longer times, up to temperatures of 150 C. Approximately steam temp. at 60 psi or 4 bar.
It may prove superior as an insulator in environments where it is wet or in prolonged damp where other insulating materials degenerate or lose insulating properties. Comparative tests against plain cork are needed but I can't source any thus far. The test material has rather fine cork particles and I have seen another brand with significantly larger particles or granules, whether it is superior or otherwise I don't know. Hope this is of some use. Regards, Paul Gough.

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1379 on: September 11, 2020, 01:24:07 PM »
Hi MJM, so 12 hours later the bubbles are forming slowly ...but as there is nolid does the fermentation process take longer ?

Willy