Stirling Heat Engine to Stirling Heat Pump : How is it done?

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hello moderators, if you do not feel this is 'close enough' to boring company news i understand if you want to delete it,

But this heat transfer technology will be a major reason why cities and counties will want bore tunnels all over the world in the thousands

👍︎︎ 2 👤︎︎ u/lazy2late 📅︎︎ Apr 11 2021 🗫︎ replies
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One of the greatest gifts our modern  human technologies have brought us   is the ability to maintain safe comfortable  temperatures in our living and working spaces   without the need to find blocks of ice  to cool down or firewood to keep warm.   But of course we all now know the environmental  and climate costs of those technologies,   most of which use fossil fuels in one form or  another, either directly for heating or indirectly   via national electricity grids. According to  the International Energy Agency the use of air   conditioners and electric cooling fans accounts  for nearly 20% of the total electricity used in   buildings around the world, and that number  is much higher if you include mobile cooling   in private vehicles and on public transport  plus industrial and commercial refrigeration   for keeping food fresh and for chilling critical  products like pharmaceuticals. There's something   like 3.6 billion cooling appliances in use today  all over the world and that number is going up   by about 10 devices every second. And  as we move rapidly away from gas and oil   and towards electric heat pumps for space heating  even greater demand will be placed on our grids.   These things draw a lot of energy and many of them  use hydrofluorocarbons or HFCs as a refrigerant   gas. HFCs aren't quite as disastrous as the  CFCs that were banned by the Montreal Protocol   30 years ago. They don't wreck the ozone layer.  But they're still extremely potent greenhouse   gases - often hundreds of times more powerful than  carbon dioxide. So the race is on to find better   solutions to the rapidly growing challenge of  heating and cooling with better energy efficiency   and without potentially harmful emissions. Now  a British company looks like they've achieved   precisely that with an elegantly simple system  inspired by this thing - the sterling engine Hello and welcome to Just Have a Think. Stirling  engines are an example of an external combustion   engine. The energy that drives them comes  from outside the closed system, as opposed   to an internal combustion engine where the fuel is  burnt inside the combustion chamber. So how does   it work? Well in this little model I've got here  we've got two metal plates at the top and bottom   and then we've got this little block of foam  sitting in an enclosed chamber in the middle.   If I put the model onto something hot like  a cup of coffee the heat energy from the   coffee warms up the bottom plate and that  makes the air inside the chamber expand.   And as it expands it pushes this little piston  upwards. The piston is attached to the wheel   via this rod, so as the piston goes up, the  wheel starts to turn. But the wheel is also   attached to the foam block, so as it turns  it pushes the block downwards. That forces   the air to flow past the block and come into  contact with the top plate, which is cooler.   The cooling air contracts, pulling the piston back  down, which turns the wheel a little bit more.   And as the wheel continues to turn it pulls  the foam block back up, forcing the air back   down to the hot side, and the whole cycle starts  again. As long as there's a temperature difference   between the top plate and the bottom plate then  the engine will keep running. In fact you could   put this thing on top of a block of ice and it'd  still work, albeit with the wheel turning in the   opposite direction, because the top plate would  then be warmer than the bottom plate. The greater   the temperature difference between the two plates  the more efficiently the system will run, and   conversely if there's no temperature difference  at all the whole thing grinds to a halt.   But Stirling's invention is one of the few cycles  that can be run in reverse to effectively make it   a heat pump instead of a heat engine. If I use  the energy in my arm to manually turn the wheel,   or in a more sophisticated version if I attached  a drive shaft to it powered by a little electric   motor, then the expansion and compression of the  air would make one plate hot and the other plate   cold. And if that system was scaled up then you  could theoretically draw the heat or the cold off   from one plate or the other depending on whether  you wanted to heat a space or cooler space.   Sounds simple right? So why don't we run all our  heaters and coolers that way instead of using air   conditioning units that contain all that horrible  hydrofluorocarbon refrigerant fluid stuff?   Well it all has to do with something called  the Carnot cycle and whether a gas is expanding   isothermally or adiabatically. I know - science  jargon! I know. The full explanation of the   Carnot cycle is beyond the scope of this  video, but suffice to say it represents   the theoretical maximum efficiency of a heat pump  or a heat engine. Isothermal just means constant   temperature, so if a gas is expanded or compressed  isothermally it stays at the same temperature all   the time. It's much more normal though for a  gas to be compressed or expanded adiabatically,   which means its temperature increases or decreases  as it's compressed or expanded. To achieve the   ideal efficiency of the Carnot cycle a Stirling  heat pump would have to run 100% isothermally so   that the gas was able to lose all its heat energy  as it was being compressed and draw in enough heat   energy to stay at a constant temperature while it  was being expanded. That kind of energy exchange   might be possible for the gas molecules  right next to the outer wall of the chamber,   but the molecules in the middle of the chamber  are a very long way away, so to achieve a fully   isothermal cycle you'd have to run it extremely  slowly to allow time for all those molecules to   either give up or take in energy. That's just  not practical for any real world application.   You'd be waiting hours or days for your room to  cool down or heat up. So instead air conditioners   and refrigeration units around the world today use  vapor compressor heat pump technology that's been   around for more than 160 years and which relies  on those nasty refrigerants with very high global   warming potential or GWP. And they still only  achieve about 40% of the Carnot cycle efficiency.   But now this new system has been created that  takes the elegant simplicity of the Stirling cycle   and applies some good old engineering lateral  thinking to the challenge of heat energy transfer   to produce a working heat pump that can reach 60%  of Carnot without using any gases with high GWP   values. The design is the brainchild of hydraulic  engineer Michael Crowley and is being developed   by his company Fluid Mechanics who are specialists  in the design, analysis and modelling of hydraulic   systems. Several prototypes have been built and  tested since the beginning of the project back   in 2015. All of them are based on the principle of  pistons and cylinders to achieve a similar effect   to this version of a Stirling engine known as an  Alpha Type. Essentially the gas in the expansion   cylinder is heated externally and the gas in the  compression cylinder is cooled externally. That   sets up the temperature differential needed to  make the pistons move to rotate the drive shaft,   just like in my little model version. The gas  is able to flow between the two cylinders, which   it does via this channel known as a regenerative  heat exchanger. The heat pump developed by Fluid   Mechanics also has two cylinders, just like the  Alpha Type Stirling engine. In fact the working   model will actually have another pair of cylinders  at the back to optimize the mechanical balance of   the system. Each set of two pistons are attached  to each other via something called a Ross Yoke,   which is a clever piece of existing technology  designed to keep them out of phase with each other   by about 120 degrees. Again, very similar  to the Alpha Type Stirling engine. The gas   is expanding and compressing, and we've also got a  regenerative heat exchanger moving the gas between   the cylinders. So far so samey! But remember the  Fluid Mechanics system is set up to be a heat pump   not a heat engine. That means the drive shaft is  providing the input power to move the pistons up   and down rather than vice versa. So now we've  got to find a way of removing the heat from one   cylinder and the cold from the other. The Fluid  Mechanics system achieves that in two ways.   Firstly by using helium as the  working fluid rather than ambient air,   and secondly by adding a series of thin  metal fins to the bottom of each piston.   Helium molecules are much smaller than air  molecules so they can move much faster and that   means they can transport energy more quickly too.  In fact the thermal conductivity of helium is 10   times greater than air, and according to Michael  you could just as effectively use hydrogen gas   for exactly the same reasons. The helium gas is  held between the metal fins at the base of each   piston. The distance between the fins is just  two millimetres, so the average distance that   the helium molecule has to travel to get to a  fin is just 0.5 millimetres. And that means heat   transfer out of or into the gas is extremely  rapid indeed. As each piston completes a cycle   the fins are plunged into a sump of silicon oil  where they're quenched. Depending on which side   of the system the quenching takes place, the oil  is either heated up a bit or cooled down a bit.   A circulating pump moves the oil constantly  around an external circuit via a heat exchanger   where it heats up water on the hot side and cools  it down on the cold side. To measure the basic   system efficiency, Fluid Dynamics created this  test rig which looks a bit like something out   of Back to the Future, but is in fact a very  carefully calibrated scientific instrument.   Based on measurements of the pressures inside  the chambers, the rig demonstrated that it was   achieving 95% isothermal efficiency. Very close to  that theoretical maximum of the Carnot cycle, with   an overall real world working efficiency of about  60% once all the system losses are accounted for.   The performance of all heat pumps improves  as the temperature difference between what   you've got outside and what you want inside  gets smaller. It's a function known as the   Coefficient of Performance or COP. So if the  ambient temperature is 19 degrees C and you   want say your room or your car to be at 21C, then  your system will have no trouble at all. but if   it's 45 degrees Celsius outside and you're trying  to get to 18 degrees inside then the COP number   will drop significantly. That's the same for all  heat pump systems, and Fluid Mechanics' design   is no different. Nevertheless, early test  results suggest that the Fluid Mechanics system   will achieve a higher COP than a typical air  source heat pump available on the market today.   And their current 2.7 kilowatt prototype is  capable of generating a temperature difference of   60 degrees Celsius between hot and cold. The next  development model will be a 10 kilowatt unit with   improved technology that Fluid Mechanics expect to  reach temperature differences of about 80 degrees   Celsius. That could happily run an industrial  freezer in a building where the external   temperature was over 30 degrees Celsius, or if  it was configured as a heating device it could   provide hot water at about 60 degrees Celsius when  the external temperature was less than minus 10!   In principle the design can be scaled all the  way up to one megawatt of cooling capacity.   Something that's attracted interest and funding  from the navy, who currently cool their ships with   air conditioning units that leak refrigerant gases  all the time, making it extremely difficult for   them to achieve their emissions reductions targets  as part of the Paris Agreement. So there it is.   A system that achieves a 30% energy saving  versus the current technology with absolutely no   high GWP refrigerant gases and which, by the  way, also operates much more quietly than a   traditional refrigeration unit. And the potential  applications are everywhere, from air conditioners   in buildings to refrigeration units on lorries  and even cabin heaters in electric vehicles.   Fluid Mechanics reckon they're about  three years from full production capacity   but if they can successfully bring this  innovation to market then it could potentially   have a hugely beneficial impact on the energy  requirements of our rapidly warming world.   If you've got feedback and views on this one, or  if you work in the HVAC or refrigeration industry   and you've got insight that you can share,  then jump down to the comments section below   and leave your thoughts there. That's it for  this week though. Thanks as always to the amazing   folks who support this channel via Patreon and  help me keep the video content independent and   ad ad-free. And I must just give a quick shout  out to the folks who've joined since last time   with pledges of $10 or more a month. They are Bill  Urech, Phil Hall, Mike Palmer, Max Kroschel, Chuck   Tyler, Bill O'Connor, Yang Chang. Andrew Keller,  Lawrence Bottorff, Staniforth Hopkins, Scott BM,   Scott Adams, Sebastian Sirois, Chris Nenov and  Matthew York. And of course a big thank you to   everyone else who's joined since last time  too. You can get involved in that and get   the opportunity to exchange ideas and information  plus watch exclusive monthly news updates from me   and have your say on future programs  in monthly content polls by visiting   www.patreon.com/justhaveathink. And you can  hugely support the channel absolutely for free   by subscribing and hitting that like button and  notification bell. Dead easy to do all that - you   just need to click down there, or on that icon  there. As always, thanks very much for watching.   Have a great week, and remember to  just have a think. See you next week.
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Channel: Just Have a Think
Views: 257,969
Rating: undefined out of 5
Keywords: Stirling Engine, Heat Pump, Heating and Cooling, International Energy Agency, Climate Emergency, Climate crisis, climate change
Id: X1fiABe4x08
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Length: 14min 13sec (853 seconds)
Published: Sun Apr 11 2021
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