Will this be more efficient than the Sterling engine?

[Terrysv]

Hi everyone,I am hoping to discuss the value of a design.
The original idea was intended to receive the thermal energy from the exhaust from an internal combustion (IC) engine and produce additional power. The working principle is much like a Stirling engine except that instead of a regenerator it relies on a phase change to create a substantial efficiency advantage over the Stirling design. Water as an example will expand about 1600 times its volume when boiled. Water vapor, nitrogen and all other gases change at a linear rate when the temperature changes. Therefore a chamber with a very small quantity of water at its phase change equilibrium will require a fraction of the energy required to produce the same pressure change as is common in a Stirling engine.

The engine is a closed cylinder with many sliding vanes creating chambers that increase and decrease in volume. Other than a drive shaft and perhaps a valve stem to add a liquid and pressurize the unit there is no entrance or exit for the working fluid (it is not a water wheel). The external radius will have attached heat exchange surfaces or insulation as is required to handle the intended thermal exchange. The activity in the circular cycle of each chamber can be visualized when separated into quadrants (red outline), including two areas where the chamber volume changes very little, one large (3) and one small (1) and two where the chamber volume is either increasing (2) or decreasing (4) when the rotor is turned (clockwise).

Before starting a cylinder allowing the conduction transfer of thermal energy though the circular wall of the outside circumference is closed. Confined in the formed chambers of the closed cylinder is a specified pressure of gas and a less than 3% by volume quantity of working phase change liquid. A gas such as helium is specified for its heat transfer coefficient and the liquid is specified for its boiling point at the pressure and temperature range anticipated.

The cycle starts by transferring thermal energy into the chambers adjacent to the quadrant having the small average chamber volume (1). The transferred thermal energy both expands the gas contained and causes the liquid contained to boil (change phase), increasing the pressure. The increased pressure pushes the chamber through the next quadrant, where the volume is increasing, (2) turning the rotor. As each chamber moves though the quadrant having the large average volume (3), the thermal energy is transferred out, causing the gas to contract and the boiled vapor to condensate, reducing the pressure contained. The reduced pressure will now cause the described chambers to move through the quadrant having a declining volume, (4) then back to the start, carrying with it the quantity of condensate ready to be expanded to vapor again.
Thank you in advance for contributing to this idea.

 

[russ_watters]

The working principle is much like a Stirling engine except that instead of a regenerator it relies on a phase change to create a substantial efficiency advantage over the Stirling design. Water as an example will expand about 1600 times its volume when boiled. Water vapor, nitrogen and all other gases change at a linear rate when the temperature changes. Therefore a chamber with a very small quantity of water at its phase change equilibrium will require a fraction of the energy required to produce the same pressure change as is common in a Stirling engine.

Well, I think if you include the heat of vaporization, you will find the efficiency is lower, not higher. However if having a liquid enables you to recover more energy due to better heat transfer you still might see an overall benefit.

 

[jack action]

I'm not sure if you mean that all your fluid is liquid when in phase 1, but if that is the case, it cannot be in phase 3: Liquid is incompressible.

Even if the fluid is only partially liquid, the biggest challenge of this type of design is proper lubrication/sealing of the sliders: Oil and water don't mix well and too much water tends to remove the needed oil film.

 

[Tom.G]

Reminds me of a Wankel Engine.

 

[Mech_Engineer]

It seems to me the O.P. is possibly describing a Rankine Cycle steam engine. Calculation of efficiency for a Rankine Cycle vs. Stirling Cycle can be done by anyone with some education/understanding of thermodynamics.

https://en.wikipedia.org/wiki/Rankine_cycle

The efficiency of the Rankine cycle is limited by the high heat of vaporization of the working fluid. Also, unless the pressure and temperature reach super critical levels in the steam boiler, the temperature range the cycle can operate over is quite small: steam turbine entry temperatures are typically around 565°C and steam condenser temperatures are around 30°C. This gives a theoretical maximum Carnot efficiency for the steam turbine alone of about 63% compared with an actual overall thermal efficiency of up to 42% for a modern coal-fired power station.

The Carnot efficiency is a useful tool for comparing theoretical maximum efficiency between two differing processes, all you need is the high and low temps for the process. Take for example the Rankine cycle's max temperature of about 565 °C vs. its low temperature of 30 °C; this results in an estimated Carnot efficiency of 63%. Still, to compare two cycles apples-to-apples you have to look at their individual parameters and do some old-fashioned calculation.

 

[billy_joule]

Reminds me of a Wankel Engine.

It's a rotary vane motor, they're found in many air tools. Also used as pumps.
https://en.m.wikipedia.org/wiki/Rotary_vane_pump

There are a few experimental (organic) Rankine cycle systems that use them as expanders (turbines). The papers can be found online.

A die grinder with a rotary vane motor can be bought for less than 15USD so a rough prototype would be cheap. I can't see it lasting long, most expanders are damaged by condensation, let alone boiling.

 

[RonL]

If you compare your illustration to the Rotary_vane_pump linked by billy_joule, you can see the rotation is produced by a flow through process. My mind sees your pump to need power applied to the shaft to get rotation, the sliding vanes need some stationary or high pressure to push against.
I just can't quite see the rotation I think you are implying. :)

RonL

 

[jack action]

My mind sees your pump to need power applied to the shaft to get rotation

Isn't this true with any combustion engine?

 

[RonL]

Isn't this true with any combustion engine?

My air motors have flat plate surfaces that seal the sliding vanes into individual chambers, until each vane crosses a port of intake or exhaust, I can't grasp the red line portion of the OP drawing, when the vanes move past the dotted red line what happens in each chamber ?
Did I misunderstand that this is a power provider design, driven by waste heat ? I'll go back and look again.

 

[Terrysv]

Thank you for this, your response is great.
Please let me try to describe the cycle with some probable numbers to answer some of your questions. Think of it as a heat exchanger with a counter flow middle man. The cycle could be viewed as a self-contained organic Rankine cycle, without most of the ancillary equipment. If it were to be installed on a thermal solar location with a lower temperature a liquid like ammonia or silicone oil will be installed in place of the water.

http://www.greencarcongress.com/2014/06/20140604-orc.html

https://en.wikipedia.org/wiki/Organic_Rankine_cycle

In my drawing the red lines only indicate how the circular path can be understood during the cycle of the 12 chambers moving clockwise. The engine needs to be warmed up before it functions properly. The sliding vanes and rotor are lubricated with graphite. The chambers are more like a pressure cooker than a tea kettle and will be pre filled with 10 bar of helium and 1% of the volume is water. If too much water is present the absorbed thermal energy and be moved by the sliding vane much like a squeegee, reducing the efficiency. Most Stirling engines are pressurized with helium or hydrogen for the superior heat transfer coefficient.

(1) As a sample chamber enters the first of four quadrants at the 4:30 point of the drawing and will start to acquire thermal energy with a conduction transfer. Heat from a source like the exhaust header of an IC engine is channeled through the adjacent “hot in” passage of area 1. With 10 bar of helium pressure present the water contained will start to change phase (boil) at about 180°C. A sample chamber enters the first of the four areas at 200°C and is able to acquire 50°C, bringing the temperature up to 250°C, with a few milliliters of water remaining. The additional energy will increase the pressure of the saturated steam from 14.5 bar to 38.7 bar. It is the 24.2 bar of additional pressure that will push the chamber through to (2) the second area where the volume is increasing, allowing the pressure to expand, similar to the Wankel engine after the combustion event. (3) When the chamber enters the third area starting at around the 10:30 point of the cycle and continuing to the 1:30 area of the drawing it will transfer the 50°C of energy out to the adjacent “cold in” passage, causing the pressure to drop. (4) Finally the chamber will move through the fourth area, bringing the condensate from the previously saturated steam with it.

 

[jack action]

My air motors have flat plate surfaces that seal the sliding vanes into individual chambers, until each vane crosses a port of intake or exhaust, I can't grasp the red line portion of the OP drawing, when the vanes move past the dotted red line what happens in each chamber ?
Did I misunderstand that this is a power provider design, driven by waste heat ? I'll go back and look again.

It is a closed system with an external combustion («Heat Exchanger»). There is also an external «Heat Sink» to cool down the enclosed fluid. It is some kind of rotating Stirling engine with that regard:

Alpha-type Stirling engine. There are two cylinders. The expansion cylinder (red) is maintained at a high temperature while the compression cylinder (blue) is cooled. The passage between the two cylinders contains the regenerator.

 

[RonL]

Thank you for this, your response is great.
Please let me try to describe the cycle with some probable numbers to answer some of your questions. Think of it as a heat exchanger with a counter flow middle man. The cycle could be viewed as a self-contained organic Rankine cycle, without most of the ancillary equipment. If it were to be installed on a thermal solar location with a lower temperature a liquid like ammonia or silicone oil will be installed in place of the water.

http://www.greencarcongress.com/2014/06/20140604-orc.html

https://en.wikipedia.org/wiki/Organic_Rankine_cycle

In my drawing the red lines only indicate how the circular path can be understood during the cycle of the 12 chambers moving clockwise. The engine needs to be warmed up before it functions properly. The sliding vanes and rotor are lubricated with graphite. The chambers are more like a pressure cooker than a tea kettle and will be pre filled with 10 bar of helium and 1% of the volume is water. If too much water is present the absorbed thermal energy and be moved by the sliding vane much like a squeegee, reducing the efficiency. Most Stirling engines are pressurized with helium or hydrogen for the superior heat transfer coefficient.

(1) As a sample chamber enters the first of four quadrants at the 4:30 point of the drawing and will start to acquire thermal energy with a conduction transfer. Heat from a source like the exhaust header of an IC engine is channeled through the adjacent “hot in” passage of area 1. With 10 bar of helium pressure present the water contained will start to change phase (boil) at about 180°C. A sample chamber enters the first of the four areas at 200°C and is able to acquire 50°C, bringing the temperature up to 250°C, with a few milliliters of water remaining. The additional energy will increase the pressure of the saturated steam from 14.5 bar to 38.7 bar. It is the 24.2 bar of additional pressure that will push the chamber through to (2) the second area where the volume is increasing, allowing the pressure to expand, similar to the Wankel engine after the combustion event. (3) When the chamber enters the third area starting at around the 10:30 point of the cycle and continuing to the 1:30 area of the drawing it will transfer the 50°C of energy out to the adjacent “cold in” passage, causing the pressure to drop. (4) Finally the chamber will move through the fourth area, bringing the condensate from the previously saturated steam with it.

Do you have a side view ? my mind can't comprehend what keeps the quadrants from equalizing when a black vane section moves past a red dotted line of the quadrant. I think I know exactly what your thoughts are (and think you have a good idea) the mechanics just seem to elude me at this point.
Best wishes in your success as per this idea.

RonL

 

[Nidum]

This contraption would be very unlikely to work at all let alone provide any useful energy recovery from IC engine exhaust gas .

I see a long list of difficulties but let us start with the problem which RonL asks about :

Where are there any differences of area and / or differences of pressure in the vane system which would generate any torque on the rotor ?

 

[Terrysv]

Do you have a side view ? my mind can't comprehend what keeps the quadrants from equalizing when a black vane section moves past a red dotted line of the quadrant. I think I know exactly what your thoughts are (and think you have a good idea) the mechanics just seem to elude me at this point.
Best wishes in your success as per this idea.

RonL

Here is an 3d cutaway image with red pencil lines indicating the 4 area of the cycle the thermal exchange passages removed.and one without the pencil lines.

 

[Terrysv]

This contraption would be very unlikely to work at all let alone provide any useful energy recovery from IC engine exhaust gas .

I see a long list of difficulties but let us start with the problem which RonL asks about :

Where are there any differences of area and / or differences of pressure in the vane system which would generate any torque on the rotor ?

The torque comes from the 24.2 bar increase in pressure created by the saturated steam produced by increasing the temperature in the chamber as it is moved past the heated sidewall. The pressure expands similar to the power event in a Wankel Engine moving the rotor forward. The sidewall is heated by the adjacent passage where the hot exhaust gas is being channeled, before being discarded.

 

[RonL]

Here is an 3d cutaway image with red pencil lines indicating the 4 area of the cycle the thermal exchange passages removed.and one without the pencil lines.
View attachment 103176

Sorry I can't see it. Unless there is a high pressure input that pushes each vane toward a low pressure outlet, there will be no movement of the rotor. This is the same as lifting oneself by pulling up on the bootstraps. The shape of the chamber being a wedge will not move the front vane forward if the same pressure is pushing back on the rear vane.

 

[Tom.G]

From Post #6

...a rough prototype would be cheap.

Since a prototype would be so cheap, how about just build one to avoid all this "I suppose", non-productive chatter. Hot side could be heated with a propane torch for proof of concept. Someone else can come up with a cheap-and-dirty way for the cold side. (afterthought: A water spray perhaps?)

The shape of the chamber being a wedge will not move the front vane forward if the same pressure is pushing back on the rear vane.

Actually, I see how the temp., therefore the pressure, could be higher at the 7-o'clock position than at the 5-o'clock position. Note that the image in the OP shows a counter-flow hot-side heat exchanger.

 

[jack action]

Sorry I can't see it. Unless there is a high pressure input that pushes each vane toward a low pressure outlet, there will be no movement of the rotor. This is the same as lifting oneself by pulling up on the bootstraps. The shape of the chamber being a wedge will not move the front vane forward if the same pressure is pushing back on the rear vane.

Actually it will because the area are different and force is pressure times area, so the greatest area gives the greatest force. The vane motor is a proven concept in both pneumatics and hydraulics (http://enginemechanics.tpub.com/14105/css/Vane-Type-Motor-161.htm).

 

[Nidum]

The action of a vane motor depends on a through flow of fluid acting on net differential areas .

This engine has no through flow of fluid and there are no net differential areas .This engine is symmetrical about a vertical centre line . Forces on vanes causing clockwise motion are balanced by forces on vanes causing anti clockwise motion .

 

[Terrysv]

The action of a vane motor depends on a through flow of fluid acting on net differential areas .

This engine has no through flow of fluid and there are no net differential areas .This engine is symmetrical about a vertical centre line . Forces on vanes causing clockwise motion are balanced by forces on vanes causing anti clockwise motion .

Correct the two sides are the same on a vertical line. Steam is clear, therefore what you see coming from a boiling kettle is condensate. A graph of steam pressure shows a curved line because the vapor is changing the pressure at one rate, while the water becoming vapor effects the pressure at a different rate. When running, a chamber at 3 o clock will have more condensate in the form of water water droplets than a chamber at the 9 o clock position.

 

[RonL]

It's taking a little bit of time, but I'm starting to see the similarity between the heat expanding gas and a steady supply of compressed air.
Because of the leakage of sliding vanes, keeping the gas and liquid quantities at a consistent value in the chambers as the cycle takes place, I would think will be a big challenge.
A slow speed high torque machine, but anything that works will have a use in some application.
This might help me through a mind problem I have been having with one of my ideas.
I will keep an eye on this thread, thanks
Ron

 

[Terrysv]

It's taking a little bit of time, but I'm starting to see the similarity between the heat expanding gas and a steady supply of compressed air.
Because of the leakage of sliding vanes, keeping the gas and liquid quantities at a consistent value in the chambers as the cycle takes place, I would think will be a big challenge.
A slow speed high torque machine, but anything that works will have a use in some application.
This might help me through a mind problem I have been having with one of my ideas.
I will keep an eye on this thread, thanks
Ron

Hi RonL There is no supply of compressed air. The cylinder is closed and sealed with the rotor, vanes and some graphite (for lubrication). The seal on the crankshaft needs to be sufficient to hold the anticipated pressure. After sealing a small quantity of water and the helium or hydrogen is added. When the hot and cold passages are transferring the thermal energy into the cylinder a reaction will occur.
The one thing not shown this far is how a single dead end port will distribute the helium content evenly. This will probably be the same valve stem used to add the helium. As each chamber passes this dead end port it will deposit or withdraw an amount of the gas, without affecting the reaction.

 

[RonL]

Hi RonL There is no supply of compressed air. The cylinder is closed and sealed with the rotor, vanes and some graphite (for lubrication). The seal on the crankshaft needs to be sufficient to hold the anticipated pressure. After sealing a small quantity of water and the helium or hydrogen is added. When the hot and cold passages are transferring the thermal energy into the cylinder a reaction will occur.
The one thing not shown this far is how a single dead end port will distribute the helium content evenly. This will probably be the same valve stem used to add the helium. As each chamber passes this dead end port it will deposit or withdraw an amount of the gas, without affecting the reaction.

The exact reason I was having a hard time visualizing your design, the time factor for adding heat and removing heat, is my other thought and why I made the comment about slow speed and high torque.
The design should be a simple enough project that can be tested and proven with little investment, I would encourage you to move forward with it :)

Ron

 

[Terrysv]

I would encourage you to move forward with it :)

Thanks RonL, Yes I am perusing this, it is a patent pending design. My feeling is this design will be several times more efficient than a Stirling engine. The recuperator in the Stirling engine will at best double the pressure changes of a heat transfer, while a liquid to vapor change produces larger pressure change per unit of energy transfered. The one caveat is if too much water is available then the efficiency will drop fast.

 

[russ_watters]

My feeling is this design will be several times more efficient than a Stirling engine.

That isn't possible because more than double would make it more than 100% efficient, violating the laws of thermodynamics (even less than double likely would).

This question requires real thermodynamic analysis, not just guesswork.

 

[Mech_Engineer]

That isn't possible because more than double would make it more than 100% efficient, violating the laws of thermodynamics (even less than double likely would).

This question requires real thermodynamic analysis, not just guesswork.

Agreed. Since the heat source has approximate max temp of about 600 Celsius, the maximum efficiency which can be achieved (Cannot efficiency) is about 64%. It's possible due to the practical considerations of this concept it could not reach more than half of this.

 

[Terrysv]

That isn't possible because more than double would make it more than 100% efficient, violating the laws of thermodynamics (even less than double likely would).

If Sterling engine makes a claim of 30% efficiency then without the recuperator it should get 15%. So now it is a question of calculating how much heat needs to be transferred to get the pressure required to achieve those values. I questioned if a Stirling engine could in fact achieve the 30% or if so then at what temperatures are they working with. We need to remember some engines burning fuel and have exhaust valves have trouble reaching 30%. Air changes pressure at one rate and the phase change of water is at another rate when heated. Hence the original question.

 

[russ_watters]

If Sterling engine makes a claim of 30% efficiency then without the recuperator it should get 15%. So now it is a question of calculating how much heat needs to be transferred to get the pressure required to achieve those values. I questioned if a Stirling engine could in fact achieve the 30% or if so then at what temperatures are they working with. We need to remember some engines burning fuel and have exhaust valves have trouble reaching 30%. Air changes pressure at one rate and the phase change of water is at another rate when heated. Hence the original question.

You're still just guessing. You know your temperatures, right? So calculate the efficiency of the Stirling engine!

 

[Terrysv]

Hello everyone, I am going to try show the advantage of using liquid vapor phase equilibrium in my design compared to the expansion of a more common diesel engine using Amonton's law in a new thread.

 

[berkeman]

Please don't multi-post here. Just post your new work here in this thread that is being followed by very helpful people...

 

[Terrysv]

Hello everyone,
I am going to try show the advantage of using liquid vapor phase equilibrium in my design compared to the expansion of a more common diesel engine using Amonton's law. All gases expand at about the same rate when heated (33%) and water expands at about 1600 times when boiled requiring a lot less energy is to produce an equal pressure change in a quantity of saturated water.
If a piston in a typical diesel engine compresses a volume of air to 41 bar at 450°C and then the combustion event brings the pressure up to 70 bar at 1667°C. Therefore using Amonton's law we know that enough fuel needs to be spent to bring the temperature of the volume of compressed gas up 1217°C to get the pressure desired. A liquid to vapor phase change will need an increase of 33.5°C to convert enough saturated water into the same volume and pressure of saturated vapor.
The benefit of using a phase change in a closed cycle engine is that most of the thermal energy is retained in the condensation and this retained energy is able to get out of its own way during the compression part (4) of the cycle.

Description of the cycle and the activity in a sample chamber:
Section 1 (4:30 to 7:30) the chamber path, has a small volume with a low volume change as the chamber moves past in a clockwise direction.
A chamber of compressed air, with a minimal quantity of saturated water present is preheated to 41 bar at 253.3°C. The chamber will accumulate an additional 33.5°C as it passes by the adjacent reverse flow heat exchange, bringing the contents up to 70 bar at 286.8°C, replacing only the quantity of thermal energy that was rejected on the previous cycle. The additional pressure gained is produced by the quantity of saturated water becoming a compressible water vapor.

Section 2 (7:30 to 10:30) of the chamber path, has an increasing volume.
The 70 bar at 287°C of pressure is declining from adiabatic expansion.

Section 3 (10:30 to 1:30) of the chamber path, has a large volume with a low volume change as each chamber moves past in a clockwise direction.
The chamber pressure is dropping as the water vapor is returning to a liquid state as the thermal energy is rejected to the reverse flow heat sink. Without having an exhaust valve all the remaining thermal energy is retained in the condensate.

Section 4 (1:30 to 4:30) of the chamber path, has a declining volume.
The chamber having lost a quantity of thermal energy is now gaining pressure and thermal energy from adiabatic compression arriving at the cycle starting point with 41 bar at 253°C.

 

[berkeman]

Thread locked temporarily for Moderation...

 

[NascentOxygen]

Are the vanes welded to the cylinder wall?

 

[Nidum]

Are the vanes welded to the cylinder wall?

May as well be - it wouldn't make any difference . This engine is not going to function anyway . #13 and #19 .

 

[Terrysv]

Hi NascentOxygen
No the vanes slide driving the rotor with the pressure generated by a liquid to vapor phase change of the working liquid.

Just enough working liquid is installed in the hermetically sealed cylinder. The advantage of this design over a Stirling engine or other hot air engines is first the operating temperature is lower. Second is that after the heat sink event all the remaining energy in each chamber is carried in the form of liquid condensate to the heat exchanger to be expanded into a compressed gas. These compressed gases can easily double the mole content of the product available for adiabatic expansion.

The Wikipedia page titled Charles’s law has an animation and also contains a modern statement referencing a “dry gas”. The phase change of the just enough water in the chamber changes the graph on the right to look more like a steam pressure chart. Since the chambers are closed similar to the combustion chamber in a Wankel engine it will cause the rotor to move.
Cheers.
Below I have pasted a better drawing and here is a link to Charles law. https://en.wikipedia.org/wiki/Charles's_law