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It Is A Steam-Engine... Using the term loosely

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Nigel Graham 212/01/2021 23:32:27
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BBC R4's current series 39 Ways To Save The Planet (1.45pm week-days) on "green" alternatives yesterday looked at the Dearman Engine, a British invention and company, whose present primary application is to replace the small diesel engine that drives the refrigerator-compressor on a refrigerated-goods lorry trailer.

They didn't go deeply into the mechanical details, but it soon became clear that Peter Dearman has adapted simple steam-engine principles to work on high-pressure nitrogen. The programme seemed to imply it runs on liquid nitrogen, missing the point that the liquid is the source of gaseous nitrogen, boiled as with gases like propane, by release and expansion through a regulator.

So it's a " steam " engine, only it's very cold " steam ", but its great advantages are of course no pollution, and it being naturally very quiet.

' ' ' '

Today's was about another British invention - greatly increasing a solar array's efficiency by incorporating a second layer whose different semiconductor material can use the higher light frequencies to which the conventional p-v cell is insensitive.

' ' ' '

I wish these all success!

" Save The Planet " ... It's not the planet we need worry about, but what's on it!

Michael Gilligan12/01/2021 23:47:44
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More details on the concurrent thread that I started yesterday: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=170361&p=1

MichaelG.

Tony Wright 112/01/2021 23:55:54
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My latest invention is for electric powered vehicles. It’s one for you electronics experts. Would it be possible to connect the up and down movement of the suspension to a generating device to charge the battery during travel ?Thus increasing it’s range .

Just a thought ! Tony Wright.

Paul Lousick13/01/2021 01:54:00
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Internal combustion engines in cars also use steam engine principles. Is it a steam engine ? No. Steam is defined as the gasseous form of water when it is heated. Cold steam is water or ice.

Tony,

It is be possible to harness the energy in the suspension movements and convert to electricity bu using a permanent magnet inside a coil. OK on a bumpy road but not much use cruising on a highway.

My portable 12v Engel refrigerator works on a similar principle and has a compressor that has only one moving part unlike many rotary type compressors. Instead a piston is connected to an electro dynamic device which is powered by the use of magnetic fields. Also more economical to run than one with a rotary type compressor.

engel_swing_motor_sawafuji_graphic.jpg

Paul

Tony Wright 113/01/2021 10:38:31
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With the state of the roads where I live ,there should be enough excess power to run the national grid 😂

SillyOldDuffer13/01/2021 18:42:07
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Posted by Paul Lousick on 13/01/2021 01:54:00:

Internal combustion engines in cars also use steam engine principles...

Paul

Pedant alert! Steam Engines, Steam Turbines, Petrol, Diesel, Jet Engines, Guns, Rockets Dearman, Stirling, muscles, Refrigerators and Hot Air Balloons all obey exactly the same physical laws. They are all Heat Engines. Understand one of them and the others make sense - they differ only in the details.

Heat Engines have a source of heat and a working fluid.

The working fluid can be steam, air, nitrogen, or almost anything else. It can be a gas, liquid (see Malone Engine), or even a solid. The fluid doesn't matter much; water is cheap for making steam, but internal combustion engines do better with air. The important part of the engine is Heat, which the engine converts into useful work. A known amount of energy translates exactly into a known amount of Work. Then power is the rate at which Work is done - another simple calculation.

Designing a heat engine, it's misleading to think pressure pushes the piston. Rather the piston does work by cooling the working fluid by expansion. Mending engines, the pressure model is fine, but it's not much use to engine designers. Design depends on thermodynamics, not guessing the dimensions and fuel requirements necessary to suck, squeeze, bang, and blow.

The steam engine isn't the mother of all heat engines because it was preceded by Newcomen's Engine, which, although it uses steam, it doesn't use steam pressure. It''s an Atmospheric Engine.

The form of a heat engine directly influences it's efficiency. Reciprocating steam engines are poor because there are so many places energy can leak. Heat radiates from the firebox, does no useful work bringing water up to boiling point, the boiler shell leaks heat, heat escapes up the chimney, and more heat is wasted in the pipework, piston and cylinder. A full-size steam railway locomotive is rarely over 5% efficient. Guns do much better, about 40%, because most of the energy produced by the propellant is applied direct to the projectile. Internal Combustion engines are also good - 25 to 40% - because the heat released by burning fuel is deep inside the cylinder, and acts directly on the piston.

The Dearborn engine is interesting but it's not a general purpose engine. The working fluid is nitrogen and the heat is provided by warm water, so relatively low power. For use in a refrigerated container, it's clever. Being very cold, liquid nitrogen can usefully be stored inside the refrigerator, from which it absorbs heat. Therefore insulating the Nitrogen isn't a major problem. When the engine runs, it drives a heat pump to cool the container. The engine's exhaust is freezing cold nitrogen and water that can be released inside the container to help keep it cold.

For refrigeration it's elegant and highly efficient. Not so good for powering a ordinary car because liquid nitrogen is expensive. Being pollution free is nice, but otherwise the benefit of a cold exhaust is wasted. Could be souped up by injecting steam rather than water, but making steam by burning fuel loses the anti-pollution benefit.

Dave

Michael Gilligan13/01/2021 19:00:29
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Posted by SillyOldDuffer on 13/01/2021 18:42:07:

[…]

The engine's exhaust is freezing cold nitrogen and water that can be released inside the container to help keep it cold.

[…]

.

can be ... but [at least in the present application] isn’t ... cooling is indirect

See the other thread.

MichaelG

Andy Stopford13/01/2021 19:24:47
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Just to add to SOD's explanation, thermal efficiency for a Carnot cycle engine depends on the difference between the peak temperature (say boiler temperature in a steam engine) and the temperature at the end of expansion (the exhaust temperature in most applications):

efficiency = peakT - endT / peakT

multiplied by 100 if you want it as a percentage.

This is just the theoretical efficiency, in practise there'll be all sorts of other losses, and I've presented it in a form which idiots like me can , hopefully, understand. It does show why diesel engines, say, with a very high combustion temperature are more efficient than steam engines, where the practical limit on maximum steam temperature is quite low.

Oh, and don't think you can get better than 100% efficiency by making it exhaust at below 0, the equation only works if you use Kelvin.

Nigel Graham 213/01/2021 21:42:18
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Gentlemen, I was being slightly tongue-in-cheek with my title.

I am aware that any engine that converts heat to mechanical energy is a heat-engine by definition, but in case I forget I have several of my Dad's old text-books on the subject. Most of their contents is above me I am afraid, as being degree-level mathematics.

What is significant perhaps about Peter Dearman's work is that he has produced a machine intended for genuinely useful work in specific applications.

Over the years a lot of inventors have tried assorted wheel re-inventions but without succeeding. Not perhaps in the League-of-Hopelessness of perpetual motion, but not really thinking of applications or even basic physics. I had a partial copy of the description of one such, and the waffle failed to disguise as new, a simple rotary-vane motor; but as far as I could glean about the working fluid and energy source, that didn't give us anything new either. (I think its heat source was the Sun.)

Back in the 1980s or so, agricultural academics were studying growing suitable crop-woods (species of hazel and willow, I think) for the raw material for a form of producer-gas that would fuel conventional petrol-engines modified to burn gas. Their idea was a power-source for places like remote farms - assuming the space and conditions for the trees of course. I do not know how far that progressed; nor what "green" types now would say about it. So nothing new in the equipment; but possibly not very much thought about application and need.

What Dearman has done is use the familiar and well-tested in an unusual combination to solve a particular problem. In other words, seen the problem and looked at how it can be solved by ingenious use of the readily-available and adaptable. Not tried to alter the familiar or fight the physics, call that novel then try to find uses.

'

Recently my local paper gave a splendid diagram showing how the heat is harvested for a household ground-heat pump: fluid circulated through a large array of pipes at shallow depth below the garden. I thought, unless I am missing something, you need only school-level physics to see the obvious flaw.

'

This all reminds me of an amusing spoof published in one of the railway "glossies " (an April edition?) back when BR was throwing its steam-locomotives away as fast as you could spell Dai Woodham. Illustrated by a line-drawing of a bizarre confection of Pacific wheels and motion turned end-for-end under the superstructure, coupled to half of a diesel locomotive body on a tender chassis, the mock-scientific text told us all of a hush-hush R&D project by British Rail(ways still then?) as a replacement for the steam loco. Allegedly the secret machine would evaporate a special fluid at high temperature and pressure, and by suitably conveying the vapour to the power-cylinders....

John Haine13/01/2021 21:55:33
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Posted by Nigel Graham 2 on 13/01/2021 21:42:18:

........

Recently my local paper gave a splendid diagram showing how the heat is harvested for a household ground-heat pump: fluid circulated through a large array of pipes at shallow depth below the garden. I thought, unless I am missing something, you need only school-level physics to see the obvious flaw.

.....

Given the number of such systems being installed, do share.

Nigel Graham 214/01/2021 00:00:02
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What was show was a set of large coils laid not far under the ground - probably just deep enough to avoid normal gardening.

It occurred to me to wonder what happens when you are relying on the system most - coldest days and limited insolation in Winter. Surely, unless the system is fitted with complicated thermostats that shut it down to avoid this happening (so defeating the object), it would be possible to draw heat from the ground more rapidly than Nature can replenish it... so defeating the object.

This is analogous to a water well. It is possible without proper control to extract water more quickly than the aquifer can supply it, creating a funnel-shaped volume of dry ground around it.

Also, that heat-pump system would be affected by the thermal properties of the surrounding ground - again analogous to the water-well whose recharge is controlled by the porosity and permeability of the rock. (Rock includes very solid stuff, multi-jointed ones like limestone, practically waterproof clay or water-logged sand and gravel).

You say many of these ground-heat systems have being installed. I wonder what proportion have actually proven their heating and financial worth over long spells of either frost and cold East winds chilling the soil, or slightly milder overcast with no sun but rain transferring the heat downwards?

As I said previously, I may be missing something but I'm certainly not rushing to buy a ground-source heat pump; not without I know the full performance I could expect, both in heat and in financial efficiency. I doubt anyway my garden would be large enough - the feature depicted a 3-bed suburban detached property, not a small Edwardian terrace, with land to match! A air-heat-pump might be more sensible... it might give a bit of background warmth while the ground-source users look out over their expensively-refrigerated lawns, and shiver.

Hopper14/01/2021 03:19:41
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Posted by Nigel Graham 2 on 13/01/2021 21:42:18:

Recently my local paper gave a splendid diagram showing how the heat is harvested for a household ground-heat pump: fluid circulated through a large array of pipes at shallow depth below the garden. I thought, unless I am missing something, you need only school-level physics to see the obvious flaw.

'

 

Its possible the engineers who designed and developed these systems know more about it than can be gleaned from a newspaper diagram.

Even if the ground were frozen solid at that depth at 32 degrees F, there is still plenty of useable heat available to be extracted by a heat pump system. It works the same way the refrigeration system on a freezer locker works. Heat is extracted from the freezer, where the temperature is already sub-freezing, usually around 0 degrees F, and then blown out the back of the refrigeration unit as hot air. Check it out at your local supermarket next time you are there. Massive amounts of heat being dumped overboard after being extracted from their freezer cabinets and coldstore rooms.

That's basic physics.

So the ground in your garden could be 0 degrees F and still provide heat via a heat pump to warm your house.

But unless you live on the Siberian tundra where there is permafrost down several metres, it's unlikely your garden beds will get anywhere near that cold below the surface.

People make the mistake of thinking ice is cold. But it's not really. Anything above absolute zero (minus 459 degrees F) contains heat energy that can be extracted. So ice at around 0 Farenheit is quite toasty stuff, relatively speaking. And ice at close to 32 Deg F is just about tropical. The Innuit build houses out of it to keep warm.

 

 

Edited By Hopper on 14/01/2021 03:24:58

SillyOldDuffer14/01/2021 09:43:08
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Posted by Hopper on 14/01/2021 03:19:41:
Posted by Nigel Graham 2 on 13/01/2021 21:42:18:

Recently my local paper gave a splendid diagram showing how the heat is harvested for a household ground-heat pump: fluid circulated through a large array of pipes at shallow depth below the garden. I thought, unless I am missing something, you need only school-level physics to see the obvious flaw.

'

...

Even if the ground were frozen solid at that depth at 32 degrees F, there is still plenty of useable heat available to be extracted by a heat pump system...

Worth considering where underground heat comes from too and how much!

Being surface creatures our experience of heat comes from the sun and fires. Easy to forget that the earth's core consists mostly of molten iron and that we are perched on a relatively thin crust of rock. We live on the slag on top of a giant cast-iron furnace.

Back to heat pumps. The sun doesn't penetrate more than a few metres deep because rock is a good insulator. Shallow caves are cool compared with the surface but deep mines are so hot working them is a major problem. Rock dug in the Mponeng Gold Mine is 66°C; the mine is 4km deep and the heat comes from the core.

A significant amount of heat percolates to the surface. Even though the temperature just below ground level is low, there's a lot of energy in it because the planet underneath is massive. From this a domestic heat pump extracts low-level heat; it's not going to drive a steam turbine, but it's an excellent way of warming a house. The heat is replenished naturally, often speeded by movement of water deep underground. Provided the pipes go deep enough the system doesn't depend on the weather.

The size of the planet explains another paradox. Stick ohmmeter probes against a rock and it measures a high resistance. How then does an electrical earth work? It's because although Planet Earth's surface is a rotten conductor compared with any metal, there's a lot of it. Whilst the earth return is made of high resistivity material, the return 'wire' is about 12000km thick. Tap into anything that bulky, and it becomes a good conductor.

The difference between heat and temperature is confusing. They're not the same. Temperature is like voltage: you can have lots of volts without danger provided there is no current behind them. The kilovolts made by rubbing a rubber balloon on a nylon jumper are harmless. In the same way, igniting a match looks spectacular, and it contains enough energy to inflict a painful burn, but there's far less thermal energy in it than a bucket of cold water. The problem with low-level thermal energy is how to extract it in useful form.

Dave

martin haysom14/01/2021 11:57:42
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, but its great advantages are of course no pollution ???? so long as you forget about how the liquid nitrogen was produced in the first place would it not be more efficient to use the liquid nitrogen to cool the fridge

Nigel Graham 214/01/2021 12:09:20
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Hopper & Dave -

With respect although you both explained how it works. you have not answered my question.

I ask, can such a system be relied on for at least some background warmth to a house throughout the Winter without risking depleting the heat energy from its ground faster than it will be replenished?

I am not convinced it could, not to any worthwhile extent anyway.

I do know the difference between heat and temperature, and that the system designers do understand the physics and engineering. Physics is immutable and predictable for all practical purposes - but though driven and regulated ultimately by physics, geological and meteorological processes are extremely variable and a ground-source heating system is very heavily dependent on the variables.

'

All heating systems are influenced heavily by a factor beyond their control - the external temperature and duration at that temperature. The ground can hold a lot of heat, but the amount and temperature available in a given spot and time are affected by the natural recharge from the surrounding geology and by solar radiation. Both of those variables are very much that - and the sun's contribution is a matter of seasonal daylight and weather (cloud cover and air temperature).

I live on the South-facing, coastal, dip slope of a ridge of various limestone, sandstone and clay strata with fairly thin soil cover. I think it quite possible that a system designed for a house near me would perform quite differently, and have very different re-charge characteristics, if installed in a similar home a mile North, on the deep clays below the scarp slope. Very different again if in a garden in the R. Frome valley 10 miles inland, in wet valley-gravels but North of a higher ridge that creates a distinct " North-South Divide " in local Winter air temperatures and frost.

It might even differ from garden to garden in the same street, depending on overshadowing in low Winter sunlight.

A ground-source heating system moves heat energy from ground to house. If it cools the ground faster than the natural re-warming from the Sun and from a steady but very small, locally individual, heat flux from the depths, its heat output and temperature within the house will diminish. Eventually, at some sort of equilibrium controlled also by the building's primary heating, it would have to stop and wait for Nature to catch up.

Just like the over-drawn water well, and just as affected by location.

A kitchen fridge moves heat from one space and discharges it in another until the desired interior air and food temperature is reached. If left undisturbed, the delay between successive refrigerating cycles is led by the slow return of heat through the walls and door-seal. A ground-heat system's recharge time is the analogical delay, and probably a lot slower.

'

Hence my concern that however properly designed individually for location and ground conditions, the concept of a ground-source heating system based on pipes under the garden, is essentially flawed.

(Those using direct, high-energy geothermal sources, as in parts of Cornwall and Iceland, are different and a rare exception. I believe there are also studies underway in extracting heat from the water flooding deep, abandoned mines: a reasonably reliable source provided again, artificial scale does not overtake Nature.)

Nigel Graham 214/01/2021 12:17:06
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Martin -

A good question, and in fact asked in the report. The Dearman company says it buys the gas it uses (a by-product of extracting oxygen from the atmosphere) from a processor using "renewable" energy.

More efficient than direct cooling by the liquid gas? Evidently not, but the system does combine mechanical refrigerating with gas cooling; and maybe relying more on the machine simplifies keeping the temperature constant.

Andy Stopford14/01/2021 16:44:47
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Nigel -

You're right in that there is some concern that widespread adoption of ground source heat pumps might freeze the ground under very highly concentrated housing and reduce the pumps' performance, but I don't think it is regarded as a problem for individual installations - if you've got a garden to put your heat exchangers under, you'll probably be OK.

David Mackay has information and calculations on the subject in Sustainable Energy Without The Hot Air:

https://withouthotair.com/c21/page_152.shtml

duncan webster14/01/2021 19:13:04
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According to Google the mean solar irradiance in January in London is about 1kWhr/m^2.day. By modern standards I have quite a big garden, so could accommodate 100 sqm of collection pipes, 100kWhr/day. Then you have to allow for the coefficient of performance which can be around 3, I think this means for every 1 kWhr of electricity I get 3 kWhr of useable heat, 2 kWhr must come from the garden, so my 100 kWhr/day becomes 150 kWhr useable, which sounds like quite a lot to me.

Air source heat pumps are a different matter. With our cold wet atmosphere if you try to extract much heat you get icing. Fiend of mine's son has such a system, it shifts vast amounts of air and is consequently very noisy

Hopper15/01/2021 00:15:32
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And solar is only one, probably minor, source of ground heat. Heat from the earth itself is obviously huge. Will it flow quickly enough to replenish the cooled garden area? Obviously it does on the many of these systems in use. It would be a matter of correct design for the ambient conditions with a large enough area cooled, suitable depth etc. And as previously pointed out, even if the ground were to become frozen, there is still heat to be extracted until it gets down to minus 493 degrees.

Nigel Graham 215/01/2021 12:23:19
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All these replies are re-inforcing my belief that at best, ground-heat systems could provide only modest and very intermittent background warmth to help the homes' main heating system; could serve only a single home with a big garden that faces South and is not overshadowed; and would save far less money or planet than claimed.

Andy -

I don't know how far the heat depletion would spread laterally from a pipe array. Since the heat sources (subterranean and solar) are to all intents and purposes perpendicular to the ground, a row of arrays in a street would receive equal amounts of heat, assuming same ground and shadow conditions for all. I suspect that for most ground neighbouring arrays would not affect each other much provided a few metres separation.

The bigger problem would be for blocks of flats However, I doubt such systems would be at all practical for them because they would need far more heat in total than feasible from what for many such buildings is very limited land area, often in the shade for much of a Winter's day.

I did not mean to imply "freezing" the ground. These systems would not do that. They would simply keep it cold - the plants and wildlife over-wintering in it would not be too impressed, though.

====

Duncan -

Mean solar irradiance - is that figure of the heat or of the total, energy density? I tried to look the figures up too, but found the presentation fractured and confusing, not really answering the question.

I assume that 3kW/hr is what you need to keep your home comfortable all day and night?

Your performance figures. Sorry, but that so-called coefficient of performance reads to me like heat-pump advertisers twisting what engineers call efficiency, to remove the revealing % sign.

You might obtain nearly 1kW/hr of heat from 1kW//hr of electricity, by direct resistance heating, so nearly 100% efficient. (A small amount of the electricity is lost as light.)

If C of P does mean efficiency, as indeed the figures suggest, the fluid in the pipes absorb only 2% of the sun's radiation hitting the ground; and the circulating pump would take, maybe a 100W?, further nibbling away at the overall efficiency.

It will be at a maximum for only a short time too around mid-day too, even if the garden is not overshadowed, and although dry ground might act rather like a storage heater, the heat actually put into the rooms will be small and might diminish fairly rapidly after dark.

So they are not very efficient systems at all physically, and despite costing little to run, probably not financially either efficient.

=====

Hopper -

Potentially the heat rising from within the Earth is indeed huge, derived from nuclear decay very deep down, mostly far below several tens of miles of Continental Crust. The heat diffuses through that without too much trouble, but then to reach your garden has to fight through a suite of rocks of combined local characteristics and depths of much greater variety than Heinz condiments.

To make life even harder for the heat energy, nearer the surface its path must be influenced considerably, possibly not quantifiably, by the local hydrology.

This means that whilst Duncan's example might suit London's leafy suburbs basking in balmy 1W/hr sunshine, it could be either even better or almost useless anywhere else.

Put it in one area here in Dorset, and its 2% efficiency in the London Clay may be <1% thanks to plentiful ground-water flowing through the Chalk and valley-gravels below thin soil cover. Its springs take the ground-heat way, but they support large watercress farms developed because the water is just warm enough to maintain the plants through the Winter.

Place the same array in a Devon or Cornish garden, and depending on exactly where, it might be 3% or more efficient thanks to small, natural nuclear heat sources within the mass of granite underlying much of that region.

So just taking mean weather and ground figures from a test location is not safe if we want to use the natural warmth of the ground seriously. The potential exists but exploiting it has to be based on thoroughly understanding the intended location's real temperatures and heat-flux from above and below, not the sellers' assumed " co-efficients of performance ".

===

I have had direct insights into how harnessing "free" energy is by no means as simple as stage-managed teenagers try to claim; and as engineers we know it isn't. My previous home faced SW, theoretically suited to a solar array. My brother, working then for a "renewable" energy company, explained that the small roof area, direction and over-shadowing rendered it not economical.

He had no commercial interest here as he lives and worked up in Scotland. I asked if his company built small-scale hydro-electric plant, in a country ideally suited to it. Such schemes are now quite common in England. He replied that although sound environmentally and potentially as business, the Scottish planning system rendered it uneconomical. I do not know if this still applies.

He installed a small solar array at his own home, near Glasgow. On a shed roof, it is rotated in azimuth by a small motor, taking less electricity than the approach gains. I think he also built a small roof-mounted solar water-heater, helping the hot water rather than central heating.

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