Energy Recovery’s Chief Scientist, Azam Thatte, Ph.D, explains how the PX G1300® pressure exchanger provides free compression in a CO2 refrigeration system, thus making it more energy efficient.
Watch the video here or read the transcript below.
Hello, this is Azam Thatte.
I am the Chief Scientist at Energy Recovery. In this science episode, we are going to dive deep into the heart of the transcritical rotary pressure exchanger and see how this pressure exchanger provides free compression in a CO₂ refrigeration system, making it more energy efficient.What you’re seeing on your screen is a fully coupled 3D physics-based model of the PX G. This model describes the processes occurring inside the PX G rotor:
- On the left side, you see the expansion process taking place in one half of the rotor.
- On the right side, you see the compression process occurring simultaneously in the other half of the rotor.
If you focus your attention on the right half, you’ll notice a low-pressure CO₂ gas entering the rotating duct of the pressure exchanger. This gas could be around 550 psi (if it’s coming from the receiver) or as low as 380 psi (if it’s coming directly from the evaporator). The gas is sealed in the rotating duct, and as the duct rotates, it eventually gets exposed to the high-pressure port.
At this moment, a compression wave (or acoustic wave) sets in, propagates back and forth inside the duct, and compresses the low-pressure flash gas into high-pressure, supercritical CO₂ at the same pressure as the gas cooler.
This compression requires no external mechanical or electrical energy. The PX G pressure exchanger achieves free compression by using expansion work recovery in the other half of the rotor.
On the left side of the animation, high-pressure, supercritical CO₂ (around 1500 psi) from the gas cooler exit enters the rotating duct of the pressure exchanger. The gas is sealed, and as the duct rotates, it gets exposed to the low-pressure port. Here, an expansion wave initiates, isentropically expanding the high-pressure, supercritical CO₂ into a low-pressure, two-phase liquid-gas mixture. This expansion process is more efficient than the isenthalpic expansion in a standard high-pressure expansion valve.
As the supercritical CO₂ expands to low pressure, it becomes colder, producing a liquid-gas mixture. This process generates more liquid after expansion through the pressure exchanger than through a standard high-pressure valve.
These compression and expansion processes occur inside each duct of the pressure exchanger rotor more than 1,000 times per minute. By recovering expansion work, the pressure exchanger provides free compression for a portion of the flash gas, reducing the energy consumption of the main compressor in a CO₂ refrigeration system.
This is the magic happening at the heart of the pressure exchanger. Hopefully, this video demystifies CO₂ refrigeration and Energy Recovery’s pressure exchanger technology for you.
Thank you for watching, and see you in future science episodes from Energy Recovery!