Stirling cycle explained
Working gas/refrigerant:
The HoegTemp Stirling heat pump uses helium as the working gas. Hydrogen & nitrogen can also be used.
The Stirling cycle heat pump operates by expanding the helium at low temperatures and compressing it at high temperatures.
The helium is compressed and expanded by the compression piston (1), depending on whether the piston moves up or down.
During this process the helium is transferred between the high-temperature zone (red) and the low-temperature zone (blue).
During compression (on the hot side), the gas releases heat to the heat sink.
During expansion (on the cold side), the gas absorbs heat from the heat source, such as waste heat.
The displacer piston (2) moves the gas through the hot and cold side heat exchangers (3 & 5) and the regenerator (4).
This internal gas temporarily holds energy as it moves between the hot and cold regions and, depending on the stage in the Stirling cycle, it withdraws or deposits thermal energy via the heat exchangers to the process system in your plant or facility.
Regenerator (thermal sponge)
The regenerator is a porous material (often a mesh or matrix of metal) that sits between the hot and cold spaces.
It temporarily stores and releases heat during the hot or cold gas flow as it passes by.
When the gas flows from hot to cold, it deposits heat into the regenerator.
On the return trip, the gas picks up that heat again, improving efficiency.
To summarise:
The heat is stored internally in:
The working gas — as internal energy; and
The regenerator — as thermal energy is absorbed and released during the cycle.
How is the heat released into a usable form?
In many Stirling high-temperature heat pump systems, the released energy is transferred into a water circuit.
It is released via the heat exchanger, where the hot gas from the machine transfers its thermal energy to the water, heating it up for use in heat and steam applications.
Enerin’s HoegTemp achieves a one step temperature lift process for steam, hot water and thermal oil up to 482°F (250°C), from sources as low as -22°F (-30°C).
Read more about our HoegTemp high-temperature heat pumps HERE.