Question

CoGeneration a) Explain how a Stirling Engine works b) Calculate the membrane area required for a 48 cell fuel-cell to provide 1500W when each cell provides 0.5V

Answer 1

Displacer piston Work piston Gas Flywheel Heat Cranks Heat source Heat exchanger sink

Working if striling engine:

Like steam engine or other internal combustion engine,a stirling engine converts heat energy to mechanical energy by a series of cycles.Lets consider a simplified displace-type stirling engine.what is happening is that the gas insde is alternatively expanding and contracting and in between moving from hot side of the cylinder to the cool side and back again.The dark blue work pistons job is to use energy from the expansion of the gas to drive the machine the engine is powering ,then compress the gas so the cycle can repeat.The green displacer pistons work is  to shuttle the gas from the hot side of the cylinder to the cold side and then back ,the two pistons ensure that the heat energy is repeatedly being moved from source to the sink and converted into useful mechanical work

1.cooling and compression

most of the gas is over on the right at the cooler end of the cylinder .As it cools and contracts giving up some of its heat,which is removed by the heat sink, at this stage both pistons move inward

2.Transfer and Regeneration

the displacer piston moves to the right and the cooled gas moves around it to the hotter part of the cylinder on the left ,the volume of the gas remains constant as it passes back through the regenerator to pick up some of the heat it previously deposited

3.Heating and expansion

most of the gas is now on the left in the hot end of the cylinder .It's heated by the fire so its pressure rises and it expands ,absorbing energy .As the gas expands.It pushes the work piston to the right,which drives the flywheel.In this part of the cycle ,the engine converts heat energy into mechanical energy

4.Transfer and cooling

the displace piston moves to the left and the hot gas moves around it to the cooler part of the cylinder on the right.The volume of the gas remains constant as it passes through the regenerator ,giving up some of its energy on the way .And the cycle repeats

Theoretical saying the following stages are repeated

1.Isothermal compression: where the volume of the gas decreases and pressure increases as it gives up heat to the sink

2.Isovolumetric heating:This is the second stage,in which the volume of the gas remains constant as it passes back through the regenerator and regains some of its previous heat

3.Isothermal expansion:in this stage the  gas absorbs energy from the source,its volume increases and its pressure decrease while the temperature remains constant

4.Isovolumetric cooling:in this stage volume of the gas remains constant as it trasnfer's through the regenerator and cools

Pressure Stirling Cycle Volume