Your attempt at reaching near isothermal operation is similar in some ways to (Fluid Mechanics Ltd) use of fins on the pistons dipping a fluid. But i think 304 stainless steel material choice might be a better choice than aluminum for similar reasons i point out in my prior comment on volumetric heat capacity, except you csn easilly control dead space with a fluid piston. I assume you still plan on moving both pistons at 90 degrees out of phase from eachother? It is probable that varying pressure effects condension and evporation of water. And the latent heat of condensation and evaporation over the surace area of the fins might work for you or work against you and lower the efficency. A low viscosity thermal transfer oil could avoid phase transion if it's a problem.
When evaluating choice of stirling regenerator material, one might want to consider volumetric heat capacity. Why? The simple answer is, because one wants to store as much heat energy as possible in a given volume of material and minimise power robbing dead space. Volumetric heat capacity is commonly expressed in Joules per degree Kelvin per cubic Meter, in other words, J/K/M³. Here is a short list materials and their Volumetric Heat Capacity 1) Iron: 3.6 (J/K/cm³) 2) Aluminum: 2.49 (J/K/cm³) 3) Fiberglass: 1.2 (J/K/cm³) As one can see, one cm³ of iron stores 3× as much energy as one cm³ of fiber glass for each degree rise in Kelvin. Someone might say "but fiberglass can be spun into high surface area fibers". Yes it can be, but so can iron be spun into steel wool. 😊If one starts with 1 cm³ of iron and 1 cm³ of fiberglass and shredded them both to the same surface area filling 2 cm³, then they will have the same 1 cm³ of material, the same 1 cm³ dead space, and the same surface area, but iron will store 3× as much energy for each degree kelvin rise. Mater of fact, one will need 3 cm³ of fiberglass, to store the same ammount of energy and have more than 3 cm³ dead space to allow the same air flow without adding additional back pressure. Now, someone might say "well maybe aluminum doesn't have as high a volumetric heat capacity as iron but aluminum is more conductive". Yes that's true but not only does thermal conductivity from the regenerator's hot side to the cold side reduce the effectiveness of the regenerator, but if the regenerator material is very thin then heat doesn't have far to penetrate and thermal conductivity is much less important to heating the mass of the regenerator over the duration of a 1/2 cycle. 304 stainless steel has a volumetric heat capacity of 3.8 (J/K/cm³) and about 1/5th the thermal conductivity of iron and the bonus that it is far more resistant to oxidation corrosion. One can look for a better material but 304 stainless steel is about as best i could find for volumetric heat capacity and lower thermal conductivity. One might use layers of screens or scrub pads, or thin corigated sheets for laminar flow which might reduce turbulence and back pressure but laminar flow is not as good for thermal heat transfer. One needs to maximize energy absorbed, minimize dead space, maximize surface area and not restrict air flow too much.
My thougts is to always compare the total gas heat capacity to the solid material heat capacity. When not use many bar of pressurized air(or other gas) only avarage pressure of the ambinet atmospheric pressure. Then the mass is so low of the air compared to ANY solid material plastic iron aluminium or what ever solid material I will use. I calculate that the mass of the aluminium foile in the cold isothermalizer is about 20 times the mass of the air I have in the system. Indeed if I would have a pressureized stirling engine with let say 25 bar pressure then probably the volumetric heat capacity of all the solid material make sens I guess. Thats my thougts but maybe I am wrong it should be easy to check my thougts of physics. Best regards. I feel more uncerten about the evaporator condensator effect when use atmospheric pressure and water. My guess is that the air get dry when it have run a full cycle. In fact one of the tradeoff in my design is to hold down the weights of the displacer on one hand on the other hand Give the isothermizer at least 10 times or more the mass (higher volumetric heat capacity) the then air. Why I use aluminium was because of practical reason it was easy to make structure and was easy to pick a reasonble thickness (I select 50um with respect to volumetric heat capacity and amout of the air) with respect to the total weight I also want to hold low. The total weight of the displacer and the acceleration energy is one of the dissadvantage of my innovation compared to the unusual fluidyne stirling. Some of the advantage on the other hand compared to the fluiduyne is that this machine follow discontinous movements. Another advantage of this machine it not need to have large U shaped tube in resonans with large amout of water.
@@Nissearne12 while the physics says high volumetric heat capacity (not specific heat capacity, or total mass) is the better metric to optimize for thermal performance, weight can be concern if the regenerator moves or doubles as the dusplacer because of two things. 1) It takes energy to accelerate a mass from one position and deaccelerate a mass to another position. Springs and flywheel conserve that energy. 2) unbalanced weigh. Furthermore, I fully understand the importance of material cost and availability and ease to work with. Engineering is sometimes an art of compromises.
Last summer I try to explain my thougts about theoretical losses and practical implication according to stirling or Ericsson heat engines ua-cam.com/video/_QB6GE5VrYg/v-deo.htmlsi=QrGiLW_twnHiO_c1
To jest bardzo interesujący projekt. Mam nadzieję że go zrealizujesz
Your attempt at reaching near isothermal operation is similar in some ways to (Fluid Mechanics Ltd) use of fins on the pistons dipping a fluid. But i think 304 stainless steel material choice might be a better choice than aluminum for similar reasons i point out in my prior comment on volumetric heat capacity, except you csn easilly control dead space with a fluid piston.
I assume you still plan on moving both pistons at 90 degrees out of phase from eachother?
It is probable that varying pressure effects condension and evporation of water. And the latent heat of condensation and evaporation over the surace area of the fins might work for you or work against you and lower the efficency. A low viscosity thermal transfer oil could avoid phase transion if it's a problem.
Like all your comments 😁👍 I have add some through of my crazy, funny innovation compared to Fluidyne Stirling as well to your first comments.
When evaluating choice of stirling regenerator material, one might want to consider volumetric heat capacity.
Why? The simple answer is, because one wants to store as much heat energy as possible in a given volume of material and minimise power robbing dead space.
Volumetric heat capacity is commonly expressed in Joules per degree Kelvin per cubic Meter, in other words, J/K/M³.
Here is a short list materials and their Volumetric Heat Capacity
1) Iron: 3.6 (J/K/cm³)
2) Aluminum: 2.49 (J/K/cm³)
3) Fiberglass: 1.2 (J/K/cm³)
As one can see, one cm³ of iron stores 3× as much energy as one cm³ of fiber glass for each degree rise in Kelvin.
Someone might say "but fiberglass can be spun into high surface area fibers". Yes it can be, but so can iron be spun into steel wool. 😊If one starts with 1 cm³ of iron and 1 cm³ of fiberglass and shredded them both to the same surface area filling 2 cm³, then they will have the same 1 cm³ of material, the same 1 cm³ dead space, and the same surface area, but iron will store 3× as much energy for each degree kelvin rise. Mater of fact, one will need 3 cm³ of fiberglass, to store the same ammount of energy and have more than 3 cm³ dead space to allow the same air flow without adding additional back pressure.
Now, someone might say "well maybe aluminum doesn't have as high a volumetric heat capacity as iron but aluminum is more conductive". Yes that's true but not only does thermal conductivity from the regenerator's hot side to the cold side reduce the effectiveness of the regenerator, but if the regenerator material is very thin then heat doesn't have far to penetrate and thermal conductivity is much less important to heating the mass of the regenerator over the duration of a 1/2 cycle.
304 stainless steel has a volumetric heat capacity of 3.8 (J/K/cm³) and about 1/5th the thermal conductivity of iron and the bonus that it is far more resistant to oxidation corrosion. One can look for a better material but 304 stainless steel is about as best i could find for volumetric heat capacity and lower thermal conductivity. One might use layers of screens or scrub pads, or thin corigated sheets for laminar flow which might reduce turbulence and back pressure but laminar flow is not as good for thermal heat transfer. One needs to maximize energy absorbed, minimize dead space, maximize surface area and not restrict air flow too much.
My thougts is to always compare the total gas heat capacity to the solid material heat capacity. When not use many bar of pressurized air(or other gas) only avarage pressure of the ambinet atmospheric pressure. Then the mass is so low of the air compared to ANY solid material plastic iron aluminium or what ever solid material I will use. I calculate that the mass of the aluminium foile in the cold isothermalizer is about 20 times the mass of the air I have in the system. Indeed if I would have a pressureized stirling engine with let say 25 bar pressure then probably the volumetric heat capacity of all the solid material make sens I guess. Thats my thougts but maybe I am wrong it should be easy to check my thougts of physics. Best regards. I feel more uncerten about the evaporator condensator effect when use atmospheric pressure and water. My guess is that the air get dry when it have run a full cycle. In fact one of the tradeoff in my design is to hold down the weights of the displacer on one hand on the other hand Give the isothermizer at least 10 times or more the mass (higher volumetric heat capacity) the then air. Why I use aluminium was because of practical reason it was easy to make structure and was easy to pick a reasonble thickness (I select 50um with respect to volumetric heat capacity and amout of the air) with respect to the total weight I also want to hold low. The total weight of the displacer and the acceleration energy is one of the dissadvantage of my innovation compared to the unusual fluidyne stirling. Some of the advantage on the other hand compared to the fluiduyne is that this machine follow discontinous movements. Another advantage of this machine it not need to have large U shaped tube in resonans with large amout of water.
@@Nissearne12 while the physics says high volumetric heat capacity (not specific heat capacity, or total mass) is the better metric to optimize for thermal performance, weight can be concern if the regenerator moves or doubles as the dusplacer because of two things. 1) It takes energy to accelerate a mass from one position and deaccelerate a mass to another position. Springs and flywheel conserve that energy. 2) unbalanced weigh.
Furthermore, I fully understand the importance of material cost and availability and ease to work with. Engineering is sometimes an art of compromises.
Last summer I try to explain my thougts about theoretical losses and practical implication according to stirling or Ericsson heat engines ua-cam.com/video/_QB6GE5VrYg/v-deo.htmlsi=QrGiLW_twnHiO_c1
ua-cam.com/video/_QB6GE5VrYg/v-deo.htmlsi=QrGiLW_twnHiO_c1