Author Topic: Talking Thermodynamics  (Read 143783 times)

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1305 on: April 20, 2020, 02:33:09 AM »
Hi MJM, I wast doing  some washing in the bath recently and noticed that after a while these ridges of detritus had occurred ? I left the water in the tub and eventually this pattern appeared..So is this some sort of thermodynamic action or vibration activity ?? and I was wondering how it is formed ..Any ideas and does this have any detrimental effect on the vessel over time ?

thanks willy

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1306 on: April 20, 2020, 01:37:28 PM »
Hi Willy, I am glad to see that your mind is turning back to the great questions of life again.  It shows even better than your thermometer that you are well.

Very hard to diagnose from this distance, and I am not really a water expert.  I would not put it down to any obscure thermodynamics though.

Only you would know if you were washing something very dirty, been crawling around in the allotment perhaps, or if your water from the tap is fresh from the Thames.  Or even just rusty pipes.

You mention leaving it sit for a while before all this appeared, so suspended mud particles could have settled, or if the water is exceptionally hard, meaning it has a high concentration of calcium salts, you could get a bit of precipitation after some cooling and evaporation.  Calcium salts are not very soluble so it is not difficult to reach the solubility limit.

But basically, that is a very long winded way of saying “I have no idea!” 

I hope appropriate to the spirit of your question.

All well here.  Getting a bit more time in the shop, though getting used to doing everything differently takes a huge amount of time.  First zoom meeting today, plus a phone consultation with the doctor.  Life is relatively normal.  But we both miss the company of others.  Communication is so much better than in the time of the Spanish flu, but not the same as normal human interaction, especially with family.  But it gives an idea of the life of my in-laws, a couple with nearest neighbours 3 miles away, the kids away at boarding school, and a road into town that was not for the timid in the cars of the day.  Once a week into town at best, but only in good weather.   The phone line was a party line that all could listen too, and the post mistress always listened, and she would patch you through to the requested number, if anyone was home at the other end. 

Stay well, and consider it “ shelter in place”, just as they advise when the bushfire cuts the exit roads.

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 #1307 on: April 21, 2020, 03:42:40 AM »
Hi MJM , the reason I asked you was because I thought you may have had experience with this phenomenon. as you have said you worked on refineries with lots of liquid holding vessels.?? anyway thanks for the message. I am allowed to go out for exercise here in Norwich, England !! and am spending about 5 hours a day there... Glad you are ok .. I do live next to a main rd so it may be lots of traffic causing vibrations ?? 

Willy

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1308 on: April 21, 2020, 01:02:10 PM »
Hi Willy, over 40 years in refineries and related hydrocarbon processing plants, some in an operating company, so close to operation of these plants, and mostly on design and construct teams.  Always a team effort, none of these things happen without a great team, and the site work and commissioning activities provide a wide range of interesting experiences. 

When it comes to the patterns in your bath, there are a few important factors that are clear.

First, they are the result of having impurities in the water.  As the water drains, there is a rim of moisture in the edge of the bath that remains a little after the level has lowered.  Evaporation from this thin film is a bit quicker than from the general water surface, and leaves the impurities behind, clearly visible on the white enamel.

As the last of the bath drains out, the bath is left a little damp so a bit of a film over the surface as it dries due to evaporation, again leaving that trace behind.  Any disturbance to the surface at around this final stage will cause little waves and then there is often a little variation in gradient.  It could be vibration due to that traffic, especially if the frequencies coincide with the natural frequency of the water surface, and it might explain those patterns.  But might not be significant.  Needs closer observation to see if you can pick anything.  It is surprising how often natural frequencies do coincide, and these coincidences can do incredible damage to steel and concrete structures, from piping to bridges.

Similarly the nature of the impurities is important.  Whether dissolved salts, or dispersion of mud and the like, or most likely a combination, needs closer observation and analysis.  You can see colloidal particles and larger under a microscope, but dissolved salts can’t be seen, so some kind of analysis is required, but the laboratory equipment required is beyond most of us to access.  They would probably be calcium salts which are not very soluble so can form precipitates even with quite low concentrations.  Iron oxides from rusty pipes are also possibly involved.  These sort of deposits tend not to redissolve easily next time you fill the bath so they build up.  And they definitely build up in a boiler if we don’t actively do something about it.  I would not want to use that water in a boiler.

So you can see there is quite a bit of factual information that points to possibilities, but observation, analysis is required to understand what is going on.

But that might give you some clues as to what you might look for.

I grew up on a street where our trams passed our front gate, making a lot of noise which we grew surprisingly used to, a bit like your traffic.  And I have been in houses over underground railways, and they definitely cause vibration.  But I never connected these things with what marks the water leaves in the bath.  But our water supplies are also very good, so not such an obvious problem.  But overall, the best way to avoid those deposits is to wipe out the bath when you have drained it, but before it dries.  This way, your cleaning cloth takes away the remaining solids, and can be washed in the laundry using lots more water.  Simple enough action to reduce the amount of heavy cleaning required.

So plenty of relevant general information is available, but this has to be applied to specific situations to identify any particular case.

I hope that helps.  Or am I missing your real question?

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

Offline scc

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Re: Talking Thermodynamics
« Reply #1309 on: April 21, 2020, 09:13:45 PM »
Re reply 1299    most compound traction engines have this device, usually called a "snifter". On Burrells it is operated by a spring loaded button. This gives instant HP steam to the LP cylinder with obvious results. It's only used in short bursts to start or save an imminent stall on a hill.             Regards                Terry

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1310 on: April 22, 2020, 02:03:47 AM »
Hi MJM ,thanks for the reply and the design of the detritus occurs in nature quite a lot...thinking about zebras for instance !!! and the wave motion on sandy beaches .? I do use the bath water as a 'grey' water supply for plants and washing the car and things and I only empty the bath when I need to so the plug remains in until it is emptied.

Hi Terry, interesting about the 'snifter' valve ..I thought on a locomotive the "snifter/snifting" valve was to stop the engine sucking in the exhaust smoke when the engine was coasting ? I have not heard about this valve before either.!

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1311 on: April 22, 2020, 05:19:35 AM »
Hi Terry, it’s great that those threads from long ago are still being read.  I would love to have more of you experience added to the conversation.  Theory takes us so far, but then there has to be practice to demonstrate it.  So please do revive the discussion if you see anything needing correction.

Like Willy I had only heard the term “snifter” in the context of ensuring that locomotives don’t get into trouble when coasting down hill.  So letting the cylinders draw in air when coasting down hill with the throttle closed.

I was more familiar with the “Simpling valve” (Apple does not like the spelling!) to add hp steam to the lp cylinder, or do you use that word in another context?

Willy, I also had in mind ripples in the sand at the waters edge, but you beat me to it.

Makes a lot of sense to use the bath water for gardening, especially in this country, but I thought you had plenty of water.  Or has population density pushed the consumption that far?

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

Offline Hugh

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Re: Talking Thermodynamics
« Reply #1312 on: April 22, 2020, 12:10:25 PM »
Hi MJM, I wast doing  some washing in the bath recently and noticed that after a while these ridges of detritus had occurred ? I left the water in the tub and eventually this pattern appeared..So is this some sort of thermodynamic action or vibration activity ?? and I was wondering how it is formed ..Any ideas and does this have any detrimental effect on the vessel over time ?
thanks willy

I think it's the result of a harmonic in the way the water (subtly) sloshes around in the bath. In essence, your bathwater is behaving a bit like a guitar string, except instead of a vibration running through the string, you have a waves. Like putting your finger on the fretboard of a guitar, I'm willing to bet that the stripes of dirt would be closer together if your bath was shorter.

Anyway, the waves push the dirt particles in your bath towards the points where the vibrational amplitude is smallest, where they eventually end up when the waves lose steam and die down.

You might imagine that this kind of behaviour could be used as a way to push every small particles around, and you'd be right. This is the foundation for devices for sorting and analysing cells (e.g. when detecting cancer). You can even use it to "levitate" things:

Hugh

Offline AVTUR

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Re: Talking Thermodynamics
« Reply #1313 on: April 22, 2020, 12:35:49 PM »
I have tried thinking about this and I agree with Hugh that it is probably a wave effect. However I would have expected the detritus to be washed up at the wave peak since it would have the lowest velocity. Just like a tide line on a beach.

There could be another effect that enhances the collection of detritus and that is aggregation. The particles in the water get caught by those already deposited on the dirty solid surface. If the surface was clean they would easily get washed away. This effect is seen in some obscure chemical reactions.

AVTUR
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Offline Hugh

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Re: Talking Thermodynamics
« Reply #1314 on: April 22, 2020, 02:15:05 PM »
I have tried thinking about this and I agree with Hugh that it is probably a wave effect. However I would have expected the detritus to be washed up at the wave peak since it would have the lowest velocity. Just like a tide line on a beach.

Sort of, but I think the bathtub conundrum is actually a standing wave phenomena in which crud settles in the nodal points where amplitude and velocity are both zero. Perhaps this shows it a bit more clearly:

I think a real mind bender is contemplating why the sand under the water at the beach is often rippled.

Hugh

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1315 on: April 23, 2020, 01:09:21 AM »
Hi MJM, et al, this is quite interesting and when I made violins I was very interested in the acoustical properties of the timber I was using...but that is a different story. I have spent a few hours looking at those videos so no work tonight !! I suppose the resonance of the chatter when parting off is the closest we will get to this phenomenon and ways of dealing with it ...like sticking some chewing gum on a long boring tool?
willy

Offline AVTUR

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Re: Talking Thermodynamics
« Reply #1316 on: April 23, 2020, 09:26:24 AM »
Willy

You are taking this thread to exciting places - Spring, Mass, Damper systems. Just as complicated as thermodynamic and fluid flow.

Hugh

I am not sure Willy's detritus is a standing wave.

AVTUR
There is no such thing as a stupid question.

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1317 on: April 23, 2020, 12:53:44 PM »
It’s great to see more people joining the conversation.  I am quite sure that many other forum members have knowledge in all these areas, and mass spring damper systems offer plenty of scope.  They appear in so many interesting areas.  Possibly even another current but unrelated thread that I am following on this forum.

I am with you Hugh on the ripples in the sand.  Some places the sand is quite smooth and some rippled.  In one area I know quite well, those ripples are over a meter peak to trough in a tidal stream.  More commonly they are very close together, which implies a higher frequency than typical waves.  So some harmonic effect between different wave patterns perhaps.

I also think it is hard to be very sure, we have not seen the situation, and we don’t want too much information about anyone’s bath habits.  But a standing wave, if the traffic rumbles happens to force a natural frequency, or alternatively the effect of removing the water a bit at a time, giving a water limit which moves in steps, or as you mention, Avtur, some sort of chemical effect.  There is a water treatment process which absorbs the turbidity particles at one pH and rejects them at a different pH (I just can’t remember which side of the process was acidic and which alkaline).   So these obscure chemical reactions are definitely another possibility.

Willy, I have to present another opinion on whether the acoustic properties of the violin or the lathe tool chatter are different matters.  The maths is the same on all these problems which involve mass, springs and dampers as Avtur suggested.  Even including the chewing gum.  So another interesting discussion from your observations.  I am glad you took the time to put the observation into another of your thought provoking questions.

Some understanding of the behaviour of mass spring damper systems is helpful in so many situations.

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 #1318 on: April 24, 2020, 01:15:57 PM »
Ni MJM , It has just occurred to me that I live in a medieval house with a cellar  which is where my workshop is and there is a wooden floor separating them ... and my lathe is actually directly under the bath !! the lathe has a 1425  3/4 HP single phase motor  so the mathematics could possible correlate the waves in the bath !?!?!    there is always a reason for 'things' so this may be the answer ??

Willy

Offline scc

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Re: Talking Thermodynamics
« Reply #1319 on: April 24, 2020, 09:29:25 PM »
MJM , you are correct to call it a simpling valve, it's correct name.  The uncouth gang that I work with call it the snifter , so that is the term I use.
    Regards   Terry