Heat engine with with state change and no cooling

In summary, there are two different engines discussed in the conversation. The first one is a rocket engine that uses cold solid fuel and heat to create a reaction mass. The second engine has a cylinder and piston, and uses a gas that can be heated and expanded to do work. However, there are some limitations and challenges, such as fuel loss and the need for a continuous supply of energy. A thermodynamic analysis is suggested to support the claims made about these engines.
  • #1
goran d
32
0
I will look at two different engines, which need heater, and no cooler, to operate.
First one:
A rocket engine, which, instead of burning fuel, simply heats up cold fuel in solid form so the heated and evaporated substance is used as a reaction mass. The nozzle of the rocket engine is in vacuum, so there is no limit on the exit pressure. The gas expands so much, that the vast majority of it is cooled so much that it turns back into solid. This engine starts with cold solid fuel, adds heat, does work, and then ends up again with solid cold exhaust, which can be reused. The only drawback is that there are losses as, I think, it isn't possible to convert 100% of the exhaust to solid.

The second one:
This engine doesn't have the fuel loss problem.
The engine has a cylinder and a piston that can move inside of it. For the purpose of this description we assume the volume between the piston and cylinder is minimal when the piston is in top position. In between the cylinder and the piston there is a substance that's gaseous under environment temperature, for example carbon dioxide. There is a heat exchanger in the top part of the cylinder, which can heat up to environment temperature. At the bottom side of the cylinder there is an attached vacuum camera so that the piston doesn't receive air pressure.

The engine works as follows:

Initial state: The piston is in top position. The substance is cold, mostly in solid phase, with minimal amount of gas.
Stage 1: The piston is held in top position. The heat exchanger heats up the substance until it all evaporates and reaches environment temperature, greatly increasing pressure.
Stage 2: The piston moves down. The substance expands, and pushes the piston, doing work in the process. The expansion continues until the substance is so cold that it solidifies, leaving only negligible amount of gas. Note that due to no air pressure on the piston, the expansion does useful work during the whole stage 2, since it doesn't need to overcome air pressure.
Stage 3: The piston moves up, doing work on the remaining gas, compressing it. It continues until it reaches top position. Note that the useful work in stage 2 is much greater than the work in stage 3, since in stage 3 only a negligible amount of gas is compressed.
At the end of Stage 3, the engine is back in the initial position.
 
Last edited:
Science news on Phys.org
  • #2
Did you do, or rather you should do a thermodynamic analysis to back up your claims.

This engine starts with cold solid fuel, adds heat, does work, and then ends up again with solid cold exhaust, which can be reused
One problem is the collection of the "solid cold exhaust" for reuse.
 
  • #3
"Did you do, or rather you should do a thermodynamic analysis to back up your claims."

Unfortunately I don't know how to model state change.
 
  • #4
goran d said:
The gas expands so much, that the vast majority of it is cooled so much that it turns back into solid. This engine starts with cold solid fuel, adds heat, does work, and then ends up again with solid cold exhaust, which can be reused.

The gas MUST leave the vehicle in order to generate thrust.

Stage 2: The piston moves down. The substance expands, and pushes the piston, doing work in the process. The expansion continues until the substance is so cold that it solidifies, leaving only negligible amount of gas. Note that due to no air pressure on the piston, the expansion does useful work during the whole stage 2, since it doesn't need to overcome air pressure.
Stage 3: The piston moves up, doing work on the remaining gas, compressing it. It continues until it reaches top position. Note that the useful work in stage 2 is much greater than the work in stage 3, since in stage 3 only a negligible amount of gas is compressed.
At the end of Stage 3, the engine is back in the initial position.

This seems plausible to me, as you would need a continuous supply of energy to heat the "fuel" up, so it doesn't seem to violate any laws of physics to me.
 
  • #5


I find these two engines intriguing and innovative in their approach to utilizing heat energy. However, I do have some observations and concerns that I would like to address.

Firstly, let's discuss the rocket engine. While it is true that this engine does not have the issue of fuel loss, it does have the limitation of not being able to convert 100% of the exhaust to solid. This means that there will still be some loss of energy in the form of gas. In addition, the use of solid fuel can also be a limiting factor as it may not be readily available or easily replenished. It would also be important to consider the efficiency of the heat transfer process and the potential for heat loss during the conversion of solid fuel to gas.

Moving on to the second engine, I can see how the use of a piston and cylinder can be an effective way to harness the energy of expanding gas. However, there are a few concerns that need to be addressed. Firstly, the use of carbon dioxide as the working substance may not be ideal as it has a relatively low specific heat capacity, meaning that it may not be able to hold a significant amount of heat energy. This could limit the overall efficiency of the engine. In addition, the description mentions that the heat exchanger is heated to environment temperature, which may not be sufficient to provide a significant amount of heat energy. It would be important to consider the efficiency of the heat exchange process and the potential for heat loss during the expansion and compression stages.

Furthermore, both of these engines rely on a state change in their working substance, which can be a complex and energy-intensive process. It may be worth exploring other alternatives that do not require a state change, such as using a gas turbine or a Stirling engine.

Overall, these engines show potential for utilizing heat energy without the need for a cooling system. However, further research and development are needed to address the concerns and limitations mentioned above. I would be interested in seeing more data and analysis on the efficiency and practicality of these engines in real-world applications.
 

What is a heat engine with state change and no cooling?

A heat engine with state change and no cooling is a thermodynamic system that converts heat energy into mechanical work without any cooling process. This type of heat engine operates by utilizing the change in state of a working substance, such as a gas or liquid, to produce mechanical work.

How does a heat engine with state change and no cooling work?

A heat engine with state change and no cooling works by taking in heat energy from a high temperature source and using it to cause a change in the state of the working substance. This change in state, such as expansion or vaporization, produces mechanical work which can then be used to perform tasks such as powering an engine or generator.

What are some examples of heat engines with state change and no cooling?

Some examples of heat engines with state change and no cooling include steam engines, internal combustion engines, and gas turbines. In these systems, the working substance undergoes a change in state, such as steam expanding in a piston, to produce mechanical work without the need for any cooling process.

What are the advantages of using a heat engine with state change and no cooling?

The main advantage of using a heat engine with state change and no cooling is its efficiency. These types of engines can convert a larger percentage of the heat energy into mechanical work compared to traditional heat engines with cooling processes. They can also be more compact and have fewer moving parts, making them easier to maintain.

What are the limitations of a heat engine with state change and no cooling?

One limitation of a heat engine with state change and no cooling is that it can only operate between a limited range of temperatures. This means it may not be suitable for all applications. Additionally, these engines may require specialized materials and designs to withstand the high temperatures and pressures involved in the state change process.

Similar threads

  • Thermodynamics
Replies
8
Views
423
Replies
22
Views
2K
Replies
5
Views
905
Replies
1
Views
721
Replies
26
Views
2K
Replies
56
Views
3K
Replies
11
Views
2K
Replies
3
Views
905
  • Thermodynamics
Replies
20
Views
1K
Back
Top