Mechanical Engineering Thermodynamics - Lec 16, pt 6 of 6: Stirling Engine Operation

Summary

This video delves into the mechanics and applications of the Stirling engine, powered by thermal energy from burning kerosene. The process involves four key steps: heat addition, constant volume, heat rejection, and final compression. The working mechanism, including the pistons, regenerator, and PV diagram, is explained step by step. The video also highlights the challenges of building a balanced, low-friction Stirling engine, with a focus on sealing gases like helium or hydrogen. Applications include environmentally friendly solar-powered engines, domestic water heating, and even cryogenic cooling for electronics, showcasing the versatility of the Stirling cycle.

Takeaways

• 😀 The Sterling engine is powered by thermal energy, typically from burning kerosene, to drive mechanical work.
• 😀 The engine uses a lamp, similar to an oil-burning lamp, to provide heat for the Stirling engine’s operation.
• 😀 The engine’s pistons work in a cycle, requiring a kickstart to get going, and then operate via the thermal energy input.
• 😀 The Sterling engine operates in four key steps, which include expansion, constant volume, compression, and regenerator processes.
• 😀 The first step involves expansion at constant temperature, where heat is added to the hot cylinder, causing the gas to expand.
• 😀 The second step involves a constant volume process where the gas passes through a regenerator, transferring heat into it.
• 😀 In the third step, heat is rejected during a compression process, maintaining constant temperature while doing work on the gas.
• 😀 The final step involves another constant volume process, where the gas moves through the regenerator in the opposite direction, completing the cycle.
• 😀 Sterling engines can be used in environmentally friendly applications, such as solar-powered engines developed by Sandia National Labs.
• 😀 The Sterling engine is versatile, being used for domestic water heating, electricity generation, cryogenic cooling, and even refrigeration of sensitive electronics.

Q & A

What is the main source of energy for the Sterling engine in the video?

The Sterling engine is powered by thermal energy, which is supplied by burning kerosene in a lamp, resembling an old oil-burning lamp.

What is the function of the regenerator in the Sterling engine?

The regenerator is responsible for retaining thermal energy as the working gas moves between the two cylinders, ensuring efficient heat exchange during the cycle.

What happens during the expansion process in the Sterling engine?

During the expansion process (from step 1 to step 2), heat is added to the hot cylinder, causing the gas to expand at a constant temperature (isothermally), doing work in the process.

How is the constant volume process implemented in the Sterling engine?

In the constant volume process (from step 2 to step 3), the pistons move in unison, maintaining a fixed volume while the working fluid passes through the regenerator, transferring heat to it.

What occurs during the compression process of the Sterling engine?

During the compression process (from step 3 to step 4), the gas in the cold cylinder is compressed at constant temperature. Heat is rejected from the gas as it is compressed, which causes the gas to cool.

How does the Sterling engine achieve its isothermal processes despite gas expansion and compression?

The Sterling engine maintains isothermal processes by exchanging heat with the environment. During expansion, heat is added to the gas, and during compression, heat is removed, allowing the engine to maintain a constant temperature in both the hot and cold cylinders.

What is the mechanical challenge of building a Sterling engine?

Building a Sterling engine involves mechanical challenges such as balancing the pistons, minimizing friction, and creating airtight seals to prevent gas leaks while avoiding excessive friction.

What are some environmentally friendly applications of the Sterling engine?

One environmentally friendly application is the use of solar energy to heat the hot cylinder, as demonstrated by Sandia National Labs. This system uses concentrated solar power instead of burning fuels like kerosene.

What is WhisperGen, and how does it use the Sterling engine?

WhisperGen, a company based in New Zealand, uses the Sterling engine in systems that generate electricity and heat domestic water, often powered by methane as the fuel.

How can the Sterling engine be used for refrigeration?

When the Sterling engine cycle is reversed, it can function as a refrigeration system. It is capable of cooling down to very low temperatures, making it useful for cryogenic cooling or for cooling sensitive electronics.