Stirling Engine: LDT and high heat input?

In summary, an LDT Stirling engine is a type of heat engine that operates on the Stirling cycle and has a low temperature difference between the hot and cold sides. It is designed to be more efficient at lower heat inputs and uses a regenerator to handle high heat input. The advantages of using an LDT Stirling engine include its suitability for renewable energy sources and simpler design, with potential applications in power generation, heating and cooling, and transportation. However, limitations include lower power output, difficulty with fluctuating heat inputs, and material requirements for high temperatures and pressure differentials.
  • #1
zytrahus
8
0
Hello,
I am working toward my new Stirling engine prototype for a particular application. Let me start with a small description of what I am going to try anyways:

I will experiment this with a small electrical heater:
- heat input: 50-100 W (heater thermall insulated on all sides but the die)
- die size: 20x20 mm
- die material: Copper
- thermocouple in the geometrical center of the die (top surface)

I will not control the hot side temperature as I will control the heat input (50-100 W). Depending on the overall thermal resistance of the device, I expect a temperature of 75-80 C on the hot side of the engine. Basically I would like to keep my heater temperature (thermocouple on top of the die) below 80 C.

I will keep water temperature between 20 and 30 C. So I expect a maximum temperature delta of 45-60 C.

I have equipment to measure/control heat input as well as cold temperature (chilled water). I can also measure output RPM.


---

Now my problem:
I know that stirling engine are be very good for thermal dissipation as it uses a gas that is pumped cycle-ly. But let's imagine a stirling engine that is thermally good, i.e. with a low overall thermal resistance... You can give it a lot of heat input and the hot side of the engine will not get too hot, which means a low delta of temperature between the two sides, hence a bad efficiency (cf Carnot). Anyways, even if the efficiency is like 5%, 200 W heat input, you could get 10 W output power.
Now since it's a LDT stirling engine, 'it is said'* that RPM are low. (*I have read about it but never actually seen equations - personnaly I think it's more of a design choice = choice of volumes sizes in order to reduce RPM...).

But here is my problem/understanding: low RPM = big thermal resistance: with low RPM I don't see how we can keep a low delta of temperature between the two sides because the gas used will not move enough energy per second to leep a low temperature. So the hot side temperature will increase, increasing the RPM, decreasing the thermal resistance. The efficiency is also increasing with the hot side temperature (cold side kept constant).
To me, it ends up like this: there is no real way to have both a low delta of temperature and also a large amount of heat input. I know it's possible in the range of DT=60-70C but I am not sure what the heat capacity would be ( check this out: http://www.bsrsolar.com/core1-1.php3 )

What I want, is to use a defined amount of heat and keep my die temperature below one defined maximum (cf description above). I would like to design a stirling engine capable of this job: thermal resisance of xxx C/W (according to my constraints, I already have a good idea of my goal). I know it's a little backward from usual designs as it's always all about delta of temperature and never about heat input...

But anyways, I would like to get advices to design the engine knowing the heat input and a rough idea of the DT.


any comment/thought on all this, please go ahead :D
 
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  • #2
</code>Your design should take into account the heat input as well as the maximum temperature of the die in order to achieve an acceptable efficiency. To do this, you will need to select a Stirling engine with the appropriate thermal resistance and design a cooling system that will maintain the die temperature within your desired range.The thermal resistance of the engine will determine how much heat is transferred and how quickly it can be done. This will affect the RPM of the engine since a higher thermal resistance will require more time to transfer the same amount of heat. You can use this information to select an engine that has the appropriate thermal resistance for your application.The cooling system will also have an effect on the RPM. The more efficient the cooling system, the lower the die temperature can be maintained, allowing the engine to run at a higher RPM. The type of cooling system you choose will depend on the size of the engine and the materials used.Finally, you will need to consider the geometry of the engine and the fluid dynamics of the working gas. This will affect the performance of the engine, as well as the temperature profile across the hot and cold sides of the engine. A proper design will ensure that the engine runs efficiently and at the desired RPM.In conclusion, designing a Stirling engine for a particular application requires careful consideration of the heat input and the maximum temperature of the die in order to achieve an acceptable efficiency. The thermal resistance of the engine and the efficiency of the cooling system must be carefully selected, and the geometry of the engine and the fluid dynamics of the working gas must be taken into account. With these considerations in mind, you should be able to design a Stirling engine that meets your needs.
 
  • #3


Hi there,

Thank you for sharing your prototype and the problem you are facing with your Stirling engine design. It seems like you have a good understanding of the principles and limitations of Stirling engines, and your goal of designing an engine that can handle a specific heat input while maintaining a low die temperature is certainly a challenging one.

One potential solution to your problem could be to focus on optimizing the thermal resistance of your engine. As you mentioned, a low thermal resistance can help to keep the temperature difference between the hot and cold sides low, which in turn can improve the efficiency of the engine. This could involve carefully selecting the materials and design of your engine, such as using materials with high thermal conductivity and minimizing the distance between the hot and cold sides.

Another approach could be to use a regenerator in your engine. A regenerator can help to store and transfer heat within the engine, which can improve its efficiency and potentially allow for a higher heat input without increasing the temperature difference between the hot and cold sides. This could be a useful addition to your engine design, especially if you are limited in the size of your hot and cold sides.

Overall, designing a Stirling engine that can handle a high heat input while maintaining a low die temperature will require a careful balance of various factors such as thermal resistance, materials, and regenerator design. I would recommend doing some further research and experimentation to find the best solution for your specific application. Best of luck with your prototype!
 

1. What is an LDT Stirling engine?

An LDT (Low Delta T) Stirling engine is a type of heat engine that operates on the Stirling cycle and has a low temperature difference between the hot and cold sides of the engine. It is designed to be more efficient at lower heat inputs compared to traditional Stirling engines.

2. How does a Stirling engine handle high heat input?

A Stirling engine is able to handle high heat input by using a regenerator, which is a device that stores and releases heat energy as the engine cycles. This allows the engine to maintain a constant temperature difference between the hot and cold sides, resulting in more efficient energy conversion.

3. What are the advantages of using an LDT Stirling engine?

One of the main advantages of an LDT Stirling engine is its ability to operate at lower temperature differences, making it more suitable for use with renewable energy sources such as solar or waste heat. It also has a simpler design and requires less maintenance compared to other heat engines.

4. What are the potential applications of LDT Stirling engines?

LDT Stirling engines have a wide range of potential applications, including power generation, heating and cooling systems, and transportation. They can also be used in remote or off-grid locations, as they do not rely on traditional fuel sources.

5. Are there any limitations to using LDT Stirling engines?

One limitation of LDT Stirling engines is their lower power output compared to traditional Stirling engines. They may also have difficulty operating with fluctuating heat inputs, making them less suitable for certain applications. Additionally, the materials used in the engine must be able to withstand high temperatures and pressure differentials, which can limit their use in some industries.

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