A centrifugal spin on a 500-year-old air compressor design • Hacker News Board

Re: A centrifugal spin on a 500-year-old air compressor design

#61

Post by chipsa » Fri, May 07, 2021, 1:38 PM UTC

tomkinstinch wrote: post #34

I wonder if a pump like this could be made smaller using a perfluorocarbon liquid like FC-70 (Perfluorotripentylamine)—nearly double the density of water, higher boiling point, non-flammable, and would not impart water vapor to the compressed air.

I wouldn't necessarily be able to say whether it'd be smaller, but it'd probably work. It works due to the air getting entrained in the liquid as it increases in pressure. So there shouldn't be a requirement that the air dissolve into the fluid or anything like that.

Re: A centrifugal spin on a 500-year-old air compressor design

#62

Post by LorenPechtel » Fri, May 07, 2021, 5:00 PM UTC

labcomputer wrote: post #16

breischl wrote: post #3

Earlier quoted context omitted.

I'm certainly no expert, but as they pointed out this is basically a trompe, which... >Compressed air from a trompe is at the temperature of the water, and its partial pressure of water vapor is that of the dewpoint of the water's temperature. If the water is cool, the compressed air can be made very dry by passing it through pipes that are warmer than the water. Often, ordinary outside air can warm the pipes enough…

> this is basically a trompe Is it though? They don't really explain how it works or show any diagrams, and they said it was "inspired by" the trompe. So I'm a bit confused on that point. It really looks more like a mashup of a centrifugal compressor and a diffusion pump. One where water instead of oil is used as the working fluid.

As I see it, the trompe has the problem of needing a lot of distance for gravity to operate it. This basically uses a centrifuge to increase the "gravity" and thus reduce the size.

Re: A centrifugal spin on a 500-year-old air compressor design

#63

Post by mnouquet » Fri, May 07, 2021, 5:15 PM UTC

londons_explore wrote: post #60

mnouquet wrote: post #48

Earlier quoted context omitted.

> Cut a pipe on the back of a fridge and it'll run open circuit just fine Try to run a plasma cutter, or a 1" impact wrench out of a fridge compressor...

Those things also don't need 400psi. A modified fridge compressor could have 4x the capacity at 100psi and be suitable for a small workshop.

Do you understand the concept of air flow at a specific pressure ? 15CFM at 90psi is no small feat.

Lowering working pressure does not increase CFM, pump have a fixed displacement at their most efficient RPM, it's not gonna change...

Re: A centrifugal spin on a 500-year-old air compressor design

#64

Post by labcomputer » Tue, May 11, 2021, 6:28 AM UTC

LorenPechtel wrote: post #62

labcomputer wrote: post #16

Earlier quoted context omitted.

> this is basically a trompe Is it though? They don't really explain how it works or show any diagrams, and they said it was "inspired by" the trompe. So I'm a bit confused on that point. It really looks more like a mashup of a centrifugal compressor and a diffusion pump. One where water instead of oil is used as the working fluid.

As I see it, the trompe has the problem of needing a lot of distance for gravity to operate it. This basically uses a centrifuge to increase the "gravity" and thus reduce the size.

Ah yup. I was misremembering what a tromp was--I was thinking one of those cyclic pumps that uses water hammer (but to compress air rather than pump water).