Talking Thermodynamics

[MJM460]

Hi Willy, they probably help reduce the leaves in the pool, though it is easy to drop them in trying to remove the blankets or the leaves.  I think the main use here is that combination of retaining some solar heat, so the pool is a better temperature for swimming, and reducing evaporation, which reduces the water makeup required, a major consideration in very dry seasons in our climate, and possibly reduce the chemical use as well.  In your climate, the heat conservation is probably the main consideration.

Nothing strange going on, it is just a matter of the heat balance finding an equilibrium.  As the temperature rises due to the solar radiation, the heat losses, which you remember are proportional to temperature differences, all increase.  So the higher temperature increases evaporation from the remaining surface area, and heat loss through the base and sides of the pool also increase, as does the conduction through the blanket to the air above.  Eventually, the total losses equal the total oncoming heat, but it takes a long time, as the rate of temperature rise slows as the temperature approaches the equilibrium temperature.  Then the temperature ceases to rise until something else changes.  But compared with an open free surface for evaporation, the effect of reducing evaporative heat loss with that blanket is to increase the temperature of the water in the pool at which heat balance is achieved.

Perhaps I should have emphasised yesterday that I was primarily thinking of the physical sciences, physics and engineering stuff.  When you start looking at the biological sciences, the science gets very complex quite quickly.  But even so, an understanding of the basic chemistry reactions and processes still makes the next steps a little more understandable.

Thanks for following along,

MJM460

[steam guy willy]

Hi MJM I have been busy with the Organic group at the Royal Norfolk Show this week and it is quite strenuous for me...I had a sorbet with a friend and he said it was something the Arabs developed in the deserts but was not sure how they managed to freeze things there ?? any ideas ? !!

Willy....

[MJM460]

Hi Willy, gardening can become quite strenuous in patches, it is not all smelling the roses.  I hope you have good weather and a successful show.

Regarding the sorbet, I am sure they did not have refrigeration in the desert at the time you were thinking about, but inland on a large continent, with a clear sky, things radiate into the absolute zero of outer space, and get pretty cold.  The first time we went to Alice Springs in Central Australia, the van we were towing had pull out canvas tents to cover and enclose the beds which pull out from each end.  The morning we left, we were up a it earlier, and had to break half an inch of ice off the canvas in order to fold it all down for travelling.  Wasn't fun, as we were unprepared and had no gloves. 

They were resourceful people and developed some very clever science.  They would have to be to live in those areas.  Clear skies would not have been a problem, and I am sure that they would have discovered perhaps accidentally, then used the phenomenon more deliberately. They certainly had salt, and certainly would have known how a concentrated salt solution gets even colder than ice before it freezes.   I guess they would have used a concentrated salt solution open to the sky at night, much as we make slushies with those special mugs you put in the refrigerator to cool down, then use it to make the cold drink.  A bit of cool for food preservation and for heat relief would have been really appreciated and they will have learned many ways of storing a bit of cold for use during the day.  There are probably other salts or other compounds which work as well or better, and they would have been of high value.  Or maybe they only developed sorbet when they first had refrigeration.

I have not been totally forgetting about thermodynamics while I have been quieter lately.  I am still working on adding that insulation to the centre flue boiler.  I managed to cut out the required shapes for two layers from an A4 sheet of 3mm cork with nearly none left over at the end.  Of course that increases the diameter by 12 mm, so the circumference by over 38 mm.  So I am looking for suitable wood for a few more planks.  I will also need longer strips of brass for the banding to keep it all in place, as the originals will not extend that far.  I will post it up when I am nearer complete, and then repeat the boiler tests to see how much difference it makes.

Thanks for looking in,

MJM460

[MJM460]

Well, I have had a bit of a break but have come back to discuss items Willy raised in his Freelance Engine build.  I do not want to hijack that. 

Hi Willy, a good set of drought related questions, but hey, six weeks is not a drought.  Our more recent one here, around 2000, was about 10 years, then as the farmers say, a shower of rain does not break a drought, we had several more years of below average rainfall and now some areas are again in drought.  But if you are used to rain nearly every day, I guess six weeks is a long time.

Let's put aside the sugar question for a while, I will come back to that.

In addition to temperature, a significant determinant of rate of evaporation is humidity.  You will remember that humidity is the water vapour content of the atmosphere compared with the saturation or equilibrium pressure.  You can look up the saturation pressure in the steam tables for any temperature.  Fifty percent humidity means the water vapour pressure in the atmosphere is half of that.

Of course temperature is important.  At freezing temperature, zero degrees C, the saturation pressure is just 0.61 kPa, while at 30 degrees C, the saturation pressure is 4.25 kPa, or seven times as much, and 50 degrees, it is 12.35 kPa.  Each of these figures is the water vapour pressure in air at 100% humidity at that temperature.  Clearly warmer air can carry away more water.

Water at the liquid surface tends to approach the saturation pressure, but the closer it gets, the slower the evaporation, just like the rate of heat loss gets less as the temperatures get closer in heat transfer.

Then, dry air currents, or wind, can carry away the vapour from near the surface so the concentration is lower and evaporation proceeds quickly.  However, if the wind is moist humid air, the vapour pressure near the surface may not be reduced much and evaporation slows.

Even though the soil is not a liquid surface, water evaporates into the air from the soil, at a rate that depends on the humidity in the same way.  So while at low temperature, the amount of moisture in the air is less, and the amount that will evaporate is less, it is the humidity near the surface as determined by air dryness that determines if the moisture keeps evaporating or slows down.

I hope it is obvious that due to the lower water vapour pressure at lower temperature, the whole process is slower at low temperature, and it takes longer to loose a given mass of water.  However, at low temperature, lower humidity air will still increase evaporation rates, while even at higher temperature, high humidity will reduce evaporation rates.

At low temperature, not only are the mass transfer rates lower, but again, if you look at the steam tables, you can see that at 0 degrees, it takes 2501 KJ to evaporate 1 kg of water, while at 30 degrees, it takes 2430 kJ per kg, so slightly less heat to be supplied to evaporate the mass of water.  At 100 deg C it is only 2257, but fortunately we don't get those temperatures in the atmosphere.

As evaporating the water takes heat, and the heat comes from the water and surrounding soil it cools, so reduces the saturation pressure so also reduces the evaporation rate.  The difference between the dew point temperature and the ambient temperature can be considered a driving force for evaporation, but this is really just a different way of looking at the difference in water vapour pressure and saturation pressure, so not an additional effect.

So generally a complex question of heat and mass transfer.  Our bureau of meteorology actually publishes figures for net evaporation rates which tell you whether the evaporation is more or less than rainfall based on monthly averages.  I seem to remember that they even use a dish in a standard enclosure to measure this.  If I can find it quickly, I will attach some figures at the end of the post.

I couldn't find some simple figures to post, but the website has the following definition for evaporation :- "The average evaporation per day as measured by the Class A evaporation pan, for each month and over the year, calculated over the period of record. The term evapotranspiration is sometimes used interchangeably with evaporation, however the two are different. It is more common to use evaporation data when referring to open water surfaces and bare soil, and evapotranspiration when referring to land surfaces with vegetation."

The maps on the site show most of the country has figures in excess of 100 inches per year, while average rainfall in most of these areas is less than 20.  They keep the level in that pan roughly constant by adding water each day, or draining a bit after heavy rain as necessary.  I wonder what the maps look like for your country?

I suspect that impurities in water may affect the saturation pressure slightly, but probably not significant in reasonably clean water.  A bit like salt in water affecting the freezing point.  When the water evaporates, the impurities are left behind, and are detectable as a slight scum on the dish surface, though again, the quantity of impurities in rain water is quite low, so you may have to top up the dish a few times to let the scum build to the point where you can see it.  Just the same as the impurities in your boiler feed water build up, and end up fouling the boiler, even though not usually significant for just one fill.  That is why full size boilers and even cooling towers need some blow down to prevent the continuing buildup.

On the sugar question, yes, the sugar normally stays in the bottom of your cup if it is not well stirred, something I am sure we have all observed.  In addition, the sugar dissolved in liquid has a maximum concentration that varies with temperature, and any excess will not dissolve, and the excess solids usually settle at the bottom due to a density difference.  The reason the dissolved sugar does not mix well is interesting.  Under gravity, everything accelerates towards the centre of the earth at the same rate.  When you drop a feather and a bowling ball from the tower at Pisa, air resistance slows the feather more than the bowling ball, but in the big vacuum chamber at NASA, I have seen films demonstrating them falling at the same rate.  (Yes, I know it was supposed to be a cannon ball, but that does not go well in this PC world!  The physics is the same either way.)

In a liquid, there are many more collisions than in air, and in a collision between a light object and a heavy object, the law of conservation of momentum means the lighter object ends up with higher velocity.  If you follow this through, it tends to mean that the lighter objects are easily bounced upwards, while the heavier ones are not.  This leads to a bias towards a higher concentration of the lighter objects at the top and heavier at the bottom.  I suspect that is the reason for your observation. 

I hope that answers the questions.

Insulating my boiler has had many of the usual life caused interruptions, but it is proceeding.  Like J. L., I found the local stockist had no 1/4 inch wide brass strips.  It was actually only the day before his post.  But fortunately another shop, a bit further away had what I needed.  Eventually I will be able to repeat the tests with the extra insulation.

Thanks for looking in,

MJM460

[steam guy willy]

Hi MJM , thanks for that interesting and as thermodynamics depends on microscopic changes of temperatures as well as large changes does this mean that everything comes under the topics of thermodynamics ??

[MJM460]

Hi Willy, thermodynamics is about energy transfer so involves most things involving energy, heat or work.   It is hard to avoid in physics and chemistry, and there are many grey areas which overlap into fluid mechanics.  For example, my heat transfer book includes a detailed derivation for the velocity profile in the boundary layer when a fluid flows past a surface.  But thermodynamics is not the much searched for "explanation for everything" even if though that explanation will probably include some energy considerations.

In general subject boundaries are somewhat artificial.  Useful for dividing the whole body of knowledge into manageable chunks, but not all that useful as limits of application. 

Engineering tends to involve a little of everything which means there is always more to learn.

MJM460

[steam guy willy]

Hi MJM, ok cool..I had a look on the Norfolk rainfall website and it suggest that any rain that does fall can evaporate before it reaches the ground !!!  also there is a site in Model Engineer talking about steam production in boilers that is quite interesting... I don't know if you subscribe to the magazine and it is available on line...
Willy

[MJM460]

Hi Willy, if you look at the BoM radar images, you will often see areas of quite light rain which never actually reach the ground if you are standing under them.  It is not really unexpected.  Air density is higher at ground level and as you go up, the air density and temperature falls.  So, the water vapour is cool enough to condense high up, but as the droplets fall towards earth, they see warmer air and are heated above that condensation point, leaving just quite high humidity.  So not really unusual, and not limited to times of drought.

I do quite often read Model Engineer, but only through casual purchases at the news stand.  I have missed those articles, but it is good to see someone else exploring aspects of thermodynamics and boiler performance.  The Speedy locomotive boiler he is looking at appears to be quite efficient compared with my rather primitive pot boilers.  I agree totally about the small amount of heat taken up by the steam in the superheater.  It would be interesting to know more about the methods he has used to calculate the other losses.  Perhaps they are covered in other articles.

He is discussing a coal fired boiler, for which fuel measurement is more difficult than for a spirit fired burner.  I have concentrated on methylated spirit firing which is a bit easier to measure, and as you have probably noticed, even gas firing is even more difficult to control to steady fitting rate.  I suspect I need a little pressure controller for this.

MJM460

[steam guy willy]

Hi MJM, More on evaporation   If you have an enclosed vessel say half full of water and applied a moderate heat....would the water eventually all evaporate and then fill the space with increased oxygen and hydrogen ?  would this become a flammable mixture that might explode if the temperature became high enough ? or is this another silly question ?  it is 3.50 AM and today it was 32 degrees so sleeping is well nigh impossible !!!

[MJM460]

Hi Willy, not silly questions but perhaps highlighting a misconception which I am sure there will be others who share.  You are not alone.

The fundamental point is that when water evaporates, it is still water molecules, two hydrogen atoms and an oxygen atom tightly bound together by covalent bonds, in each molecule.  It does not break down into hydrogen and oxygen.  Evaporation is not the same as decomposition.

It takes a lot of energy to break that bond.  It is usually done by electrolysis, passing a DC electric current through the water.  You get bubbles of hydrogen at one electrode, and oxygen at the other.  It might be possible to do it with heat, but there is be no doubt that the required heat would never be mistaken for moderate.  More like extreme heat combined with low pressure.

Of course, if you go the electric route, it is best to keep the gases quite separate, as a mixture of hydrogen and oxygen is quite dangerous.  Hydrogen will burn in air over a wide range of concentrations.  And pure oxygen can make a fire with most substances, even things you do not normally consider flammable, like steel and concrete, with a suitable ignition source.

It is not a silly question because these days, in your science shop or electronics outlet, you can buy small size fuel cells which are used in one direction to produce the two gases when an electric current is applied, and the same device when the gases are supplied in the other direction, produces an electric current.  Our local electronics store has them sufficiently efficient to power a small model car as an alternative energy demonstration science kit.  I have been tempted to buy one, and perhaps use it to power a small model boat.  A catalyst in the cell facilitates the reaction so it is more efficient than trying to put the current through pure water.  And if you add salt to make it more conductive, you get some chlorine produced, so not a great idea.  Or you can use a solar panel to supply the current to make the gases, then use the fuel cell to creat electric power to drive a motor, or a hydrogen powered i.c. engine.

If, instead of using a fuel cell, you ignite the hydrogen and oxygen there is a lot of energy released, and it does not take very long!  Also, it does not take much heat to start it off.

So back to the original question about heating a container half filled with water until all the water has evaporated.  I guess when you start, there is air in the other half of the container, just as in your mountain top experiments.  Of course we could assume the vessel has been evacuated and so only contains liquid water and water vapour with the water vapour pressure at the equilibrium vapour pressure for the temperature.  If we try and remove the water vapour, we just boil the liquid water at that temperature.  So the best we could do is boil enough water to displace the air then seal the vessel with just water and water vapour.

When you heat the water some water evaporates and you raise the vapour pressure.  Now the volume of water vapour is around 1000 times the volume of liquid which evaporated to make the vapour.  If the vessel is closed thus constraining the volume, the evaporation will result in a very high pressure, but it will still be water molecules.  In fact, the high pressure will suppress any breakdown of those water molecules into separate hydrogen and oxygen molecules.  (High pressure tends to favour the reaction which results in the fewest molecules).

So a practical experiment involves either a tiny bit of water in a large vessel, or allowing the steam to escape, like your kettle.  That water vapour is not flammable, and in fact you can use a steam lance to extinguish a fire in the right circumstances, the steam basically occupies the space and so excludes oxygen which is necessary for fire to continue.

I hope that makes things clearer for you and all others pondering the same issues.

I know what you mean about sleeping when it is 32 degrees overnight.  In northern parts of this country it happens regularly in the appropriate season.  Definitely don't need heavy blankets!  I certainly need air conditioning, but people who have lived there for long enough to be acclimatised seem to do better.  But I don't believe it is common in your area.  I avoid that time of year, by only travelling there in the dry season.

Thanks everyone for looking in,

MJM460

[steam guy willy]

Hi MJM , Ok a lot clearer ..so going on with the questions  ...we talk about hydrocarbons  (methane .Butane ) but with a fuel cell that burns Hydrogen and Oxygen would this be called a Hydrohydrogen   or even a Hydrooxyhydrogen ?? .  The sumization with the question was summed up quite succinctly  when you stated that the high-pressure stops the bonds breaking down !!  When water evaporates does the H20 become lighter than the water molecule in the liquid, which may rise into the atmosphere somehow from it. and how high can it elevate ? on the news tonight they suggested closing the curtains during the day to keep the inside of the house cooler !!



willy

[MJM460]

Hi Willy, hydrocarbons is a convenient collective name for a group of chemical compounds in which  each molecule is made up of a number of atoms of hydrogen and carbon.  Hydrogen atoms have only one bond site, while carbon has four.  This means that each carbon atom can join to four other atoms.  The other atoms can be different or even other carbon atoms.  So carbon atoms can join to make long chains, branched chains, or rings.  The chains can even be joined in more than one place, called cross linking, which leads quite solid plastic materials.

Obviously the first one in the hydrocarbon series is methane, with one carbon.  Each of its bonding sites is joined to one hydrogen.  It is the main constituent of natural gas.

If two carbons are joined in one place, we get ethane and each carbon is joined to the other one and to three hydrogens.  Three carbons give propane, four gives butane and so on.  These are the so called straight chain parafinic hydrocarbons, and the series can get very long.  Each extra carbon raises the boiling point through oils to solid waxes.

But after three carbons, things start to get complicated.  The fourth can continue in a straight chain, or it can branch off the side of the chain formed by the first three.  So we get normal butane and ISO butane.  And even at two carbons, those two can join at two places called a double bond, which gives us ethylene, the building block for polyethylene plastic.  And they can join at three places, a triple bond, or acetylene, as we know very unstable, but I am not aware of the possibility of two carbons joining at all four sites.

All of these compounds have many similarities, so it is convenient to have a group name.  However, hydrogen is a single element, not really a member of any group that I am aware of, so there is no need for a group name.  A hydrogen powered engine would be a sufficiently complete description.

When the hydrocarbons burn, they combine with oxygen, and they are all quite good fuels, though the longer chains are perhaps more difficult.  But oxygen is not part of that group name.  Similarly burning implies joining with oxygen with the release of energy, whether the fuel is hydrogen or hydrocarbon.

It is important to understand that the forces that bond the atoms together in a compound are very strong forces that operate only over a very short range.  These forces are much stronger than gravity which tends to be a weak force but it operates over a long range.

These covalent bond forces are much stronger than the inter molecular forces that hold a liquid together.  To give you an idea, think of the energy in the latent heat, required to evaporate water, around 2000 KJ/kg.  Quite a step change from the heat necessary to raise the temperature from say zero, but still small compared with the energy involved in breaking those covalent bonds.  This occurs in chemical plant cracking furnace when ethane for example is heated to around 1000 deg C to break the bonds.  I am not sure how much energy per kg is required, or the exact temperature, but the high alloy steel pipes in the furnace are a very bright red.  Clearly a step change in energy compared with what is required for evaporation.

So back to those escaping water vapour molecules.  First, they are still unchanged molecules of H2O, each having the same mass as when it was in the liquid.  Well, perhaps not quite.  Einstein demonstrated that mass can be converted to energy, with the famous equation E=mc^2.   This means that as the molecule moves with increasing velocity, the mass does decrease, but this effect is minuscule until the velocity gets very close to the speed of light.  Unless you have a synchrotron in your basement (I am not sure if you can buy one on Amazon yet, but who knows?), the effect of this energy-mass conversion is zero for practical purposes. So the vapour molecules are not lighter.

However, the molecules are much further apart than in a liquid.  And the vapour occupies a much larger volume.  Basically it bounces around between the molecules sharing the space.  This motion is random and even at low pressure there are very large numbers of individual molecules.  Close to a liquid surface equilibrium vapour pressure is when there are the same number of molecules in the vapour space hitting and being captured by the liquid as there are escaping from the liquid.  Further from the liquid surface, there tends to be more coming from the liquid surface than there are in the space above coming back.  So the vapour spreads to fill the space, essentially independent of any other molecules, for example oxygen or nitrogen, which also occupy that space.

In a closed vessel, the water vapour essentially spreads through the whole volume, but in the atmosphere, much larger than any practical vessel, the slight increase in the gravitational force nearer the earth, means the water density, or number of atoms per cubic meter tends to be higher nearer the earth.  In the end, I understand that essentially none of the molecules have enough energy to completely escape the pull of gravity, and in effect the earth captures any stray hydrogens which happen to be wandering by in space.  As you go higher, there will be fewer water molecules, just as there are fewer oxygen and nitrogen molecules.  The height of the atmosphere is quite large of course.

Gravity is considered by physicists to be a weak force, not that it seems that way if you fall off a ladder.  But it acts equally on all mass, and does not result in great density differences with height until extreme heights.  But it is insignificant compared with the molecular forces that hold the atoms together in a molecule.

Again Willy, you have a talent for asking innocent looking little questions which lead to so many paths.  But perhaps that has covered the main issues you are thinking about.

The idea of closing the curtains to keep the house cooler in hot weather is a strategy of passive cooling.  The idea is that by closing the curtains, you reduce the heat input from the sun, and confine the warmed air on the inside of the window glass to the immediate area of the glass, where it is hopefully returned to the outside when it is cooler at night.  Of course it is even better if you open them at night when it is cooler outside, to help the heat from inside return to the atmosphere outside.  Best of the lot is to have blinds on the outside of the windows to prevent the Suns radiation entering the house at all.  Again it is even better if you raise the outside blinds at night.  With our plentiful bright sunshine I think these are fairly normal activities in this country.  It makes quite a difference, but you need to take maximum advantage of the night time cooling to obtain best advantage.  We have outside blinds on the west side, and trees on the east, eves and a roll up shade on the north side.  I have to admit we don't often open the west side curtains at night, it is easier to just leave them down for the summer.  Our north side eves shade the full wall height with the high summer sun in summer, and admit the sunshine over the full height of glass doors in winter when the sun is lower in the northern sky.  In spring and autumn the strategy is not so effective, but it helps a little.

In winter of course, we keep the house a little warmer and use less heating by closing the curtains at night and opening them to let the weak winter sun enter during the day.

Always worth employing these passive methods of heating and cooling to at least reduce heating and cooling energy costs.

Thanks for looking in,

MJM460

.

[paul gough]

Hi MJM, Not been around for a while. Had some issues with the blood pump for a few weeks a while back and after uncoupling from the medical system I decided to spend some time quietly recharging the system. So to dip my toe into the subject again I have been pondering methods I might try in getting some data from gauge 1 locos. One of which I would be pleased if you would comment on. If I embed a thermocouple into a drilled hole in the cylinder body, possibly by extending the depth of one of the cylinder cover bolt holes into the cylinder wall area. 1) do you think this would be a viable, 2) If so would it be better to use a bare thermocouple or a sheathed probe, 3) If bare probe wire, do you think it necessary to use a heat conducting grease or some such in the hole or would the tiny volume make this unnecessary. Hope I am not going over old ground, I cannot remember discussing these things and have yet to get through the 200 odd posts since I disconnected. Regards, Paul Gough.

[MJM460]

Hi Paul, it's good to see you back.  I have been worried about you, it seems with good reason.  I hope you are through the worst of it and now on the way to recovery.   But I know it's a long process.

I had my own issues over 25 years ago, though the damage remains.  It is worth finding and continuing a good rehab programme.  I am sure they have developed since I did it, but even then it was well worth while, and many of the things I learned are now just a normal part of my life style.  I have been quite active and well since.

Good to see you still thinking about those locos.  Basically, with thermocouples the decision of sheath vs. no sheath basically comes down to what you are measuring.  If you are measuring a liquid, I think the sheath is the best arrangement to protect the wiring and insulation, and have good thermal contact by immersion of the sheath.

Also in case of very hot gases, such as flue gas, the sheath is able to contain insulation able to withstand the temperature.

The next issue is pressure containment.  The best way to measure a fluid under pressure, such as steam, is to insert the thermocouple into a thermowell, essentially a long plug screwed into a fitting on the pipe or vessel, drilled with a blind hole to accommodate the thermocouple, so it does not compromise the pressure containment.  Actually quite similar to a drilled bolt, providing the outside of the bolt is in good thermal contact with what you want to measure.  And then the sheath is not required.  My thermocouples seem to need a 2,5 mm hole to actually fit, so I imagine your bolts are too small unless you have access to very small thermocouples.  Something in the back of my mind (?) I can't quite recall.  But if the bolt extended into the exhaust passage for example, in principal it should do the job.

The next issue is the position of the thermocouple.  It is important to place the thermocouple where it will measure the temperature you are interested in.  In a cylinder, the temperature varies quite a bit in quite a small space, so I think it would be difficult to be sure just what you were measuring.  So far I have used an extended plug, drilled for the thermocouple as a filler plug to measure steam/water temperature in the boiler, a sheathed thermocouple to measure flue gas, and a rather bulky machined elbow containing a little short thermowell at the engine inlet and exhaust, both as close to the engine as possible, for inlet and exhaust temperatures.  The engine inlet is assumed to be essentially the same as the superheater outlet for practical purposes, though the tubing and lubricator mean there will be a difference.

I have tried using a drop of glycerine as a heat transfer fluid to improve the thermal contact.  I have not found it particularly successful and seem to get variable results, possibly exacerbated by the temperature difference effects I mentioned with cylinders in a very short thermowell.  It seems that it is more useful to clip the thermocouple wire near the thermowell so it does not move around every time I touch the wire or meter.  When I think about it, the full size ones in the plants I am familiar with are quite firmly secured at the head of the thermowell.  In principal the fluid should improve thermal contact to improve speed of response and reduce stem effects so long as you don't completely flood the well, just a drop is enough in our model sizes.  And of course minimal usefulness in a horizontal well!

I think glycerine is suitable, but it's possible I am mistaken and should use something else.  My lack of obvious success with it starts to test my confidence.

I think the first things to work on measuring are the fuel consumption, and the steam temperature.  If you have a superheater, superheater outlet/cylinder inlet.  In your scale, you could make a more compact thermowell by soldering in a length of 1/8 in tube with the end plugged or squashed and silver soldered.  The small diameter will withstand a lot of external pressure.  It does not have to be the bulky screwed fitting you see in my photos.

Don't feel pressured to catch up with the posts you have missed.  They will help you get to sleep for quite a while, the main thing is to enjoy the learning that I hope is contained in them.  I really don't mind repeating if required.  It will eventually become just another part of what you know.

Great to have you back again, 

MJM460

[paul gough]

Thanks for the comments MJM. It is likely that being an investigator and possibly minor experimentalist will be the limits of my activity from now. So I try to think up ways to find out what is going on in our little locos, or as near as possible, so as to develop a deeper understanding of their behaviour and maybe discover something of value. All the things you list as important to determine would be part of the investigation, but, I feel there are other things that might be revealed.

 My idea of a drilling into the cylinder block deep enough to locate the thermocouple about midway along the cylinder stroke and at about 180 degrees to the steam chest would, I take it, be a thermo-well of sorts. The temps. would be something of a close approximation, (I would hope), to average internal cylinder temps. Such a measure might be useful in determining time and distance a loco might go, with standardised varying throttle and load before approaching steam chest temp. Provide a guide or comparison for each cylinder. Get an insight into the relationship of superheat temp and cylinder temp. See what transpires with and without cylinder insulation. Attempt to discover any effects linking up, (varying valve travel), may have on cylinder temp. Assess the value of this type of cylinder temp. measurement  against other measures. Utilise anything gained to improve investigation methods further.

All this leads me to ponder some form of 'test stand' I might be able to cobble together and also try to work out how I could apply a variable load while a loco was on the stand. If successful it might convince my friend to let me drill holes and insert wires all over the place in his locos for comparison. He is, at the moment, a bit sceptical about the worth of my inquiries.

One further question, that I cannot find a definitive answer for. Do the common 'needle' type valves used as regulators/throttles in our miniature sizes actually work as a locomotive throttle is supposed to, i.e. a variable orifice volumetric control rather than a pressure varying device?

Thank you for your concern regarding my health, much appreciated. Alas, advanced maturity has a price we all have to pay. Paul Gough.