5 ms·

Can anyone tell me why they use Helium rather than say Nitrogen? I thought I read somewhere that we are running out of He.

xeromal 4y ago
We're running out of cheap helium. For applications like this, I'm sure it'll be fine.
mechhacker 4y ago
Helium is a more effective heat transfer medium with lower molecular weight. Hydrogen would be more efficient but it tends to cause issues with the containing material and leaks.
jnsaff2 4y ago
From this [0] NPR piece: Helium is the only element on the planet that is a completely nonrenewable resource. On Earth, helium is generated deep underground through the natural radioactive decay of elements such as uranium and thorium. "It takes many, many millennia to make the helium that's here on the Earth," says Sophia Hayes, a chemist at Washington University in St. Louis. The helium seeps up through the Earth's crust and gets trapped in pockets of natural gas, where it can be extracted. Like hydrogen, its immediate predecessor on the periodic table, helium is lightweight. But unlike hydrogen, it doesn't readily combine with other elements. So, once helium reaches the surface, it can easily escape the Earth's gravitational pull. Other resources, such as oil and gas, may turn into pollution or be difficult to recycle. But only helium physically disappears from the planet. "It's the one element out of the entire periodic table that escapes the Earth and goes out into outer space," Hayes says. [0] - https://www.npr.org/2019/11/01/775554343/the-world-is-constantly-running-out-of-helium-heres-why-it-matters https://www.npr.org/2019/11/01/775554343/the-world-is-consta...
Someone 4y ago
FTA: Because helium remains a gas until -200 C, we can achieve higher temperatures inside our heat pump core N₂ boils at −195.8 °C, but that will be higher at 30 bar. Next question: why do they need gas at lower temperatures to achieve higher temperatures? Do temperatures inside that acoustic wave vary that much?
- BlueTemplar 4y ago
  Probably because the higher delta allows for higher power density and keeps the device reasonably small ?
FRidh 4y ago
To improve the COP you need a gas with a high ratio of specific heats and low Prandtl numbers. The Prandtl number is the ratio of viscosity to thermal diffusivity. Helium works fairly well for this, though adding xenon, argon or krypton improves it even further. Really cool to see a company getting this in the market. I'm surprised though to see a standing-wave device instead of a traveling-wave device.

xeromal 4y ago

We're running out of cheap helium. For applications like this, I'm sure it'll be fine.

mechhacker 4y ago

Helium is a more effective heat transfer medium with lower molecular weight. Hydrogen would be more efficient but it tends to cause issues with the containing material and leaks.

jnsaff2 4y ago

From this [0] NPR piece: Helium is the only element on the planet that is a completely nonrenewable resource. On Earth, helium is generated deep underground through the natural radioactive decay of elements such as uranium and thorium. "It takes many, many millennia to make the helium that's here on the Earth," says Sophia Hayes, a chemist at Washington University in St. Louis. The helium seeps up through the Earth's crust and gets trapped in pockets of natural gas, where it can be extracted. Like hydrogen, its immediate predecessor on the periodic table, helium is lightweight. But unlike hydrogen, it doesn't readily combine with other elements. So, once helium reaches the surface, it can easily escape the Earth's gravitational pull. Other resources, such as oil and gas, may turn into pollution or be difficult to recycle. But only helium physically disappears from the planet. "It's the one element out of the entire periodic table that escapes the Earth and goes out into outer space," Hayes says. [0] - https://www.npr.org/2019/11/01/775554343/the-world-is-constantly-running-out-of-helium-heres-why-it-matters https://www.npr.org/2019/11/01/775554343/the-world-is-consta...

Someone 4y ago

FTA: Because helium remains a gas until -200 C, we can achieve higher temperatures inside our heat pump core N₂ boils at −195.8 °C, but that will be higher at 30 bar. Next question: why do they need gas at lower temperatures to achieve higher temperatures? Do temperatures inside that acoustic wave vary that much?

BlueTemplar 4y ago
Probably because the higher delta allows for higher power density and keeps the device reasonably small ?

FRidh 4y ago

To improve the COP you need a gas with a high ratio of specific heats and low Prandtl numbers. The Prandtl number is the ratio of viscosity to thermal diffusivity. Helium works fairly well for this, though adding xenon, argon or krypton improves it even further. Really cool to see a company getting this in the market. I'm surprised though to see a standing-wave device instead of a traveling-wave device.