Author Topic: Talking Thermodynamics  (Read 124984 times)

Offline MJM460

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Re: Talking Thermodynamics
« Reply #1125 on: March 26, 2019, 11:01:16 AM »
Hi Pete, thanks for looking in and explaining that.

Hi Willy, sorry to hear that you are not fully back to your previous self, but it is good that you are at least making some progress.  Time on the allotment might be the medicine you need, along with some sunshine.

Basically the heat balance is slightly different when starting a cold engine that it is for a hot engine.  When those glow plug engines are cold there is not enough heat of compression to get to ignition point.  Once they are running, as Pete says there is excess heat available and the compression ratio is enough.  Really the thermodynamics is the same in each case.  The little compression ignition or Diesel engines have a higher compression ratio so they can start on compression heat alone from cold.

On larger size engines, many little marine Diesel engines are fitted with glow plugs and operating these before attempting to start the engine makes them start a lot easier in my experience.  Similarly, my car is a diesel, and I notice the start sequence involves running glow plugs for a short  period before it starts.  All computer controlled of course.  I believe a similar principle is used even for quite large engines.  But these are really beyond my experience.  Perhaps some of the marine engineers on the forum will come in and tell us all more about them.  I think the same might apply to Diesel engines in construction machinery. 

The differences between all these systems basically revolves around how much heat is required to get those first few pops each start.

Hi simplyloco, thanks for looking in.  Yes, those are the pumps used on farms that I was referring to in the earlier post.  Thanks for looking that out and posting. 

Wasteful of course is not a strict technical term.  The second law of thermodynamics means that you cannot use all the energy in the water to pump it all back to the height at which it started, some of that energy is ďlostĒ.  However the water is not lost, that part not pumped continues itís merry way down hill, and is appreciated by those downstream, and no matter how well they are set up some always continues.  I believe that if well set up, there is not the obvious spillage evident in that video, though I never had much to do with them.  The limitations not only mean the water cannot all be returned to the original height, you probably canít pump it all to any height using the ram pump, though you can move it all up some of the way simply by containing it in a pipe.  The difference with the ram is that some water must be passed through to establish the velocity that the device suddenly stops so the change of momentum develops the pressure.  It is using the kinetic energy, and can develop enough pressure to raise some of the water above the initial height, thus converting kinetic energy to potential energy, and of course losing some in the process.  Each time the check valve closes, the flow stops, and has to be re-established by a bypass flow after the pressure pulse.  I just canít remember what makes the check valve flip closed.

A simple pipe down the hill then up the other side is simply using the potential energy of the height, and can raise the water surface up to the original height under conditions of no flow, and all the flow to some smaller height, the difference in height being energy lost in overcoming friction in the pipe.  Obviously you would normally just use the pipe if you have access to the water at enough height, and accept the extra complexity of the ram if you need more pressure that resulting from the height at the point you have access to the water.

In both cases, the energy ďlossĒ is not really lost, it simply is dissipated as heat, and can always be accounted for if you look hard enough.  And it may even be useable to some extent if you have a use for low temperature heat.  Though recovering the heat from friction in the pipe would be a challenge.

Now we just need more information on Willyís heating system using water hammer.

Good to see the odd question coming through again.

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 #1126 on: March 26, 2019, 08:01:52 PM »
Quote
a battery is used to cause initial detonation

Are you talking about War equipment or engines Willy  ;)

Hopefully you only get a combustion  ;D

OK, joke aside, the coil 10Kpete mentioned, is made from Platinum (and a few other ingredients) and is a catalyst that "combines Methanol and Oxygen" and while it works much better at high temperature (initiated by the battery), there has been cases where engines has started without being connected to a battery  :zap:
The heat from combustion will keep it working as long as there is fuel and oxygen in the right amounts.
I haven't heard of a limit to going up in size, except for the extreme cost of running your car on that stuff + a complete "overhaul" everytime you shut it of again - hygroscopic effect will ruin the engine otherwise (don't ask how I know). Another reason, is that an ignition system where you can change the timing at will on the fly is much more useful on bigger engines where every single gram doesn't count as much.

I do hope that you soon get better Willy - best wishes

Per
« Last Edit: March 26, 2019, 08:05:33 PM by Admiral_dk »

Offline derekwarner

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Re: Talking Thermodynamics
« Reply #1127 on: March 27, 2019, 03:27:51 AM »
Trust you are progressing Willy...keep up that  :DrinkPint: [medecine] ......

We touched briefly on accumulators and water hammer, however the world of fluid engineering uses hydraulic accumulators for thousands of applications from a convenient precharged storage of energy in weapons missile launchers, to impact adsorbing solutions in the landing gear of jet planes to taking simple pressure harmonics from a fluid thats energy was created via any rotational device [multi element piston pump]

To take this one stage further, a single acting boiler feed make up water pump, using the humble o-ring principal loads the o-ring in a dynamic manner and deforms the soft elastomer to effect the seal in the pump cylinder to reach the boiler relief valve setting......and so yes, we are talking low pressure of say 3 Bar

One factor not well understood is the effect of the collapsing pressure field that sealing elements are subjected to

So our simple rotary pump at 120 pulsations per minute has the o-ring being pressurized every 2 seconds to 3 Bar, then re-subjected to the collapsing pressure field to the partial draw of vacuum as the pump check ball closes [all within milli-seconds frequency]

This is similar to hitting your own head with a hammer each 2 seconds :hammerbash: and expect to walk away without a headache

So the wonderful model steam people from REGNER in Germany have recognized this and produced a miniature model accumulator suitable for direct mounting on the discharge side of a piston pump and suitable for low pressure water applications

The feature here is the accumulator is not filled with a gas precharge, but a Nitrile elastomer ball, which by nature is deformable due to the unique cellular formation of the Nitrile ball itself

So the net total consequence here is that the velocity of the collapsing pressure field is minimized by the discharge of the energy stored within the accumulator........this in theory will save the Nitrite elastomer o-ring from premature failure

I plan to install one such accumulator in the very near future, however am not sure the conventional Pressure Gauges UK model gauge will record & display anything but a flutter each 2 seconds

Derek

« Last Edit: March 27, 2019, 05:08:27 AM by derekwarner_decoy »
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Offline MJM460

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Re: Talking Thermodynamics
« Reply #1128 on: March 27, 2019, 11:34:31 AM »
Hi Admiral DK, thanks for posting about the catalytic function of the glow plug in those little engines. I for one did not know about that.  I guess while the basic intent of all glow plugs is to provide a little heat to aid in starting a cold engine, tweaks such as catalytic action will greatly enhance the function. 

Do you know if the glow plugs in full size Diesel engines and automotive diesels also have a catalytic component for diesel fuel, or are they simple heaters?

Hi Derek, you are quite right about the great variety of applications for hydraulic accumulators, but in most cases, these are intended to minimise any water hammer induced vibration or damage, with no intention of recovering any energy.  Willyís original question was about a (fire station?) heating system which used the energy causing the water hammer for building heating, so a slightly different emphasis.  Hence on to ram pumps which use that kinetic energy for pumping some of the water.

Those model accumulators are certainly interesting, the nitrile ball will not require the periodic recharge that is the main issue with most gas cushioned systems.  It will be interesting to see how it performs in your model, and how much effect it has on the pressure gauge.  However, I am not sure if it will help the piston o-ring, as I assume the pump discharge check is in between and would isolate the ring from the accumulator.  And of course the pressure reduction in the cylinder is necessary to the pump function as there will be no intake of water for the next stroke until the cylinder pressure is below the pressure of the water at the inlet.  Worth experimenting with.

I have come across explosive decompression of o-rings when they are depressured even what seems quite slowly, and certainly not requiring frequent decompression.  Very special o-ring materials are required in these services.  But I was dealing with natural gas at 5000 psi!  I am sure it occurs at somewhat lower pressure as well, but I am not sure at what lower pressure it ceases to be a problem.

I wonder if the main reason for o-ring failure when they are used as piston rings is simply wear and tear due to wall friction.  I always understood that o-rings were basically static seals, meant to deform but not ideal for sliding.  I know they are used and with success.  And the catalogues even mention specific o-ring materials for this type of service.    I have at times wondered if they simply wear to fit at a close clearance in higher speed applications, some times called an ablative seal, though I expect they slide quite nicely in slower speed, well lubricated applications.

Thanks for looking in,

MJM460





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Offline Admiral_dk

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Re: Talking Thermodynamics
« Reply #1129 on: March 27, 2019, 10:25:35 PM »
Quote
Do you know if the glow plugs in full size Diesel engines and automotive diesels also have a catalytic component for diesel fuel, or are they simple heaters?

I would be very surprised if they are anything other than "just a heater", but I honestly don't know for sure.

Offline steam guy willy

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Re: Talking Thermodynamics
« Reply #1130 on: March 28, 2019, 02:02:54 AM »
Hi MJM  et al , more interesting stuff to think about........... ;D  Just a quick observation when i was cooking my tea    When i lit the gas stove   (Natural gas) I get the nice blue flame....however i decided to use my hoover in the kitchen with the effect on the gas flame to become flickering and orange ?? I don't know why this should happen unless microscopic particles are getting past the filter and interfering with the oxygen levels ?? The before and after  photos  !!!

Willy

Offline derekwarner

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Re: Talking Thermodynamics
« Reply #1131 on: March 28, 2019, 05:10:56 AM »
Willy....[I hope not too much  :DrinkPint: medecine]........certainly no gas accumulators involved.....I also have a natural gas cooking stove in the kitchen, however couldn't replicate your flame flicker variance with a large hand guided new fangeled design bagless Dyson vacuum cleaner over the kitchen tiles

The exhaust air from the Dyson is advertised as being passed through a series of filter cone jets that increase the velocity of the air, then a swirling action prior to two filter banks....so I suspect  the exhaust air is presented in a different manner [direction & cushion] to your Hoover
machine

So from this, I do understand the significance of the blue flame and also that the orange flicker is usually an indication of the carburizing flame due to lack of oxygen however suspect the volume of air & hence oxygen % is remaining virtually constant, and so the surrounding air to your gas oven top cooking jet is being subjected to turbulence :Mad: & causing the flicker from blue to orange flame? ..

Lest wait & see what MJM thinks........

_____________________________
Sealing elements in Fluid Systems

This is a huge subject in itself  :happyreader: however not really centered around Talking Thermodynamics....suffice to say that o-rings are the least costly dynamic sealing elements available and as such Industry makes great use of their ability/cost in a whole range of applications

Derek 
« Last Edit: March 28, 2019, 05:30:32 AM by derekwarner_decoy »
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Offline Jo

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Re: Talking Thermodynamics
« Reply #1132 on: March 28, 2019, 07:59:59 AM »
So from this, I do understand the significance of the blue flame and also that the orange flicker is usually an indication of the carburizing flame due to lack of oxygen however suspect the volume of air & hence oxygen % is remaining virtually constant, and so the surrounding air to your gas oven top cooking jet is being subjected to turbulence :Mad: & causing the flicker from blue to orange flame? ..

At home I cook on bottled propane gas. Normally the flame is blue but just as the bottle empties and the auto switch over connects to another bottle of gas the flames flicker and go orange due to the pressure drop (there is also a slight smell of propane at the time ::) ). From experience I would question if Willy's gas also suffered from a slight pressure drop..

Jo
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Offline MJM460

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Re: Talking Thermodynamics
« Reply #1133 on: March 28, 2019, 12:42:25 PM »
Hi Willy, that one is a bit of a puzzle.  The vacuum cleaner does not actually consume any oxygen, well only at the power station producing the electric power perhaps, so not likely to be lower oxygen content of the air in your kitchen.  Assuming this happens every time you run the vacuum cleaner while cooking, and with your natural gas it would be unlikely that a change of gas composition would arrive by coincidence each time you clean.  Does it happen every time or just occasionally?

Your suggestion of fine dust blown out of the vacuum cleaner is certainly a possibility.  There is a whole branch of chemical analysis based on flame colour changes when various substances are passed through a flame.  So silica in dust, or other minerals would cause various colours, or carbon based material might arrive at the flame and glow yellow before finding enough oxygen, could be a reasonable explanation.  But if there is really that much dust kicked up by the cleaner, and considering your recent health history, it might be worth wearing a dust mask while vacuuming, as that dust will also be entering your lungs.

Similarly, as Derek points out, the exhaust from the cleaner could be producing turbulence which conceivably could affect the amount of air drawn into the burner, but a bit of a long shot unless the vacuum cleaner outlet is quite close to the stove.  Perhaps a little more likely if the stove is on a very low setting.

We have an electrostatic air cleaner, and Inhave noticed that there is no extra sparking even when the cleaner is quite close to the air inlet, but our vacuum cleaner also has a fine filter on the air outlet.  It seems to be quite effective.  But we also only have an electric stove in the house, so no hope of observing that here.  Certainly an interesting observation.

Hi Jo, thanks for posting.  That auto changeover sounds like a good idea, nothing worse than running out of gas just after starting to cook a meal in the oven and not noticing.  But I hope you have something that tells you it has switched over so you donít just empty the second bottle.  As you suggest, the slight pressure drop during the changeover probably means a moment or two of less efficient air induction at the burner.

Derek, I agree totally with your comment on the number of applications of o-rings as sealing elements, even in sliding applications.  The ones I am most familiar with are in mechanical seals for pumps and compressors, where they only deform with no significant sliding, but there are also many applications where sliding seals are performed by o-rings.  And the manufacturers catalogues do recommend the correct formulations for these applications.

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 #1134 on: March 31, 2019, 02:24:42 AM »
Hi MJM, thanks for that... I was annealing a piece of brass in the blue flame  and the flame above was going yellow of the same hue as before ? !!! a new question... I was looking at this picture of a boiler burner and it shows the take off pipe of the parrafin canister coming from the top . It also shows a bike pump connector, I suppose a bit like a primus stove. So, what is actually happening in the tank when it is pressurised with air to send a combustable gas to the burner ?? the liquid paraffin is quite heavy and one would think the air should just stay above it ??  Perhaps this is another unintuitive process !!!

Offline Jo

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Re: Talking Thermodynamics
« Reply #1135 on: March 31, 2019, 08:47:38 AM »
Hi Jo, thanks for posting.  That auto changeover sounds like a good idea, nothing worse than running out of gas just after starting to cook a meal in the oven and not noticing.  But I hope you have something that tells you it has switched over so you donít just empty the second bottle. 

This is the changeover regulator. When it switches over bottle the internal valve rotates and the arrow in the white handle turns red showing it is pointing at an empty bottle. When you replace the bottle you have to remember to point the arrow at the bottle that was being used  ;) I have a couple of spare full propane bottles that I use for silver soldering kicking around if I forget  ::)

Jo
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Offline MJM460

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Re: Talking Thermodynamics
« Reply #1136 on: March 31, 2019, 11:07:26 AM »
Hi Willy, Just by coincidence, our household gas heater was being serviced Friday.  The serviceman gave a good blow to move some dust which was difficult to get at with a brush, and the flame took on that yellow appearance for a few moments.  So a strong air jet could explain your stove, but I doubt that your vacuum cleaner was sitting that close to the burner.  So more likely your guess of impurities in the air.  I have not tried brass in the flame but copper usually gives a green tinge in the same manner, but carbon based dust particles, or possibly silica in sandy dust might be the explanation as we discussed before.

I think you will find that the burner operation is easily explained by assuming that the catalogue picture is not a complete engineering drawing.  I am reasonably confident that inside that tank the outlet pipe is extended to the bottom of the tank.

The burner usually has an evaporating coil which picks up the necessary heat to evaporate the liquid.  The control valve then controls the vapour flow to the air mixing and combustion area.

First the tank is filled, then the pump is used to add some air so there is enough fuel pressure to push the liquid over to the burner and to push the vapour through the jet.  You usually have a little tray which you fill with meths and light to evaporate the first fuel until there is enough heat from the burner flame.

Initially you generally fill the tank perhaps half full, and pressurise the remainder with air.  As the fuel is used, the level drops so lowering the air pressure, and to run for a long time, you need to pump in a bit more air to maintain the pressure.  However, some heat conduction along the pipe probably helps a little to raise the vapour pressure of the fuel.

I remember using a primus stove on that principle for cooking when camping, and I also had a Coleman Shellite lamp (it might still be in the cupboard).  And my father had two blow lamps for heating one of those large copper soldering irons for roof spouting work.  Unfortunately they disappeared long ago, before I realised that they would have been very useful for extra heat for silver soldering.  I have even been in country buildings where lights on this principle were the only source of lighting before electricity was connected.  They continued in use in remote areas long after electricity was connected in towns.

I assume the pipe arrangement was so that once you release the pressure, the flame goes out, but also there was minimal likelihood of fuel leakage which might occur if the fuel outlet came directly from the bottom of the tank.

Hi Jo, I have not seen one of those automatic changeover valves, but it sounds like they still need a little attention to ensure the needle is pointing the right way.  And of course the really good part is that you often have a spare big bottle of gas for when a big silver soldering job comes along!

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 #1137 on: March 31, 2019, 10:44:25 PM »
HI MJM, Thanks for the reply, I have found this diagram of a primus stove and yes the tube out to the burner does go down to the bottom of the vessel  so the pump pressure does push just the liquid fuel to the burner. way back in the 50's i lived in a house with no electric and we had Primus stoves and Tilley lamps...when we had guests in the evening that mother didn't want to stay too late i was told to fill the lamps  only half full so when they started to flicker due to low pressure the quests would take the hint and elect to depart !! as soon as they had gone down the road  we would pump them back up and the house would suddenly become a blaze of light again !!!Here
 is a pic........

Willy

Offline derekwarner

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Re: Talking Thermodynamics
« Reply #1138 on: April 01, 2019, 01:24:12 AM »
Willy...MJM....I remember going gold panning to Hill End near Oberon in mid Western New South Wales with my Dad & Pa & others ...in 1954 ..so I was about 6 years old

No bridge over the Turon River...no electricity, no gas [prior to the availability of Primus gas equipment] cold swim in the river for a bath  :lolb:.......wood stove, tilly lamps [Dad had a 22 rifle to warn :Director: the Foxs away

Am pretty sure the Tilly lamp functioned on vapor pressure of the volatile liquid  [methylated spirit?]

So irrespective of the discharge point of admitted air into the lamp body, it became the pressure vessel..so pressurized air would create a vapor pressure above the top level of the fluid, which was admitted into small holes or oriface in the discharge tube

So the speed or velocity of this rising vapor pressure was enhanced by additional ventuti bringing in air [oxygen] to complete the combustion

Pretty sure, that Miners Safety Lamps work on a near similar principal....so even with today's technology [electronic methaneometers & the like], Miners Safety Lamps are still used in  underground Coal Mines

Derek [these are my words now, not the words of a 6 year old  :shrug: ]
« Last Edit: April 01, 2019, 01:27:29 AM by derekwarner_decoy »
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Offline MJM460

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Re: Talking Thermodynamics
« Reply #1139 on: April 01, 2019, 12:39:59 PM »
Hi Willy, yes, I still have one of those Primus stoves in my garage.  And Tilley is the other name I remember.  I see Derek also knew of those.

Hi Derek, I canít remember whether the Tilley was a petrol (shellite) fuel or kerosene.  The kerosene ones usually used meths in the little tray under the burner and evaporator cool for the initial heat up.  I think the Shellite ones had a slightly different procedure. 

I have found that I do still have the Coleman light in the cupboard, I will try and look out how it is lit, perhaps tomorrow.  It definitely uses shellite fuel.  Come to think of it, the power company has notified us that we will have no power tomorrow, so I might even need it if they donít finish by evening!

The mining safety lights have a configuration that prevents flame spread some how, canít remember the details.   Somebody might look up Davey safety light, or is it Davy, but itís getting late here tonight, I was out for dinner.

Thanks to all for looking in.

MJM460

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