Hacker News Reader

Comment by schiffern | Hacker News Reader

  >And have questions like: 'Why don't we have a device like a microwave oven for fast cooling?'"

Isn't that... just a blast chiller? (AKA a convection oven in reverse)

It's not commonly found in households, but that's different from saying "we don't have a device" that does this.

EDIT: Yes folks, I do understand how the principles of operation differ. Point being that the humble countertop convection oven definitely qualifies as "a device like a microwave oven for fast heating," and a blast chiller is just the reverse of that.

View on HN

For "cooling by radiation" there's, counterintuitively, laser cooling:

https://en.wikipedia.org/wiki/Laser_cooling

"Laser cooling relies on the change in momentum when an object, such as an atom, absorbs and re-emits a photon (a particle of light). For an ensemble of particles, their thermodynamic temperature is proportional to the variance in their velocity. That is, more homogeneous velocities among particles corresponds to a lower temperature. Laser cooling techniques combine atomic spectroscopy with the aforementioned mechanical effect of light to compress the velocity distribution of an ensemble of particles, thereby cooling the particles."

No, because I think microwaves heat in a very different way from radiant heat gain (or loss) such as in an oven or this chiller you're talking about. The internal water is heated directly.

Same mechanism, different frequency.

Microwaves and radiant heat are both primarily EM radiation at different frequencies.

The frequency of microwaves was chosen due to the resonant frequency of water and thus is absorbed in the area near the surface of most food items, with radiant and kinetic heating spreading to the interior.

There is some minor differences with convection but a conventional stove heating element doesn't care if it is the air or the food that absorbs the photons it is releasing.

I guess the near surface of the food being directly heated vs nichrome wire producing infrared radiation can be considered 'very different'

But the need to preheat a conventional oven for even cooking is because it is mostly radiant heat transfer of infrared radiation.

Microwaves penetrate the interior of objects (outside of metal) that are in their Faraday cages, leading the internal temperature of those objects to rise dramatically. Blast chillers work like reverse ovens, from the surface to the interior.

Microwaves target the resonant frequency of intermolecular hydrogen bonds and impart vibration. It's a very special mechanism that doesn't really lend itself to this sort of analogy.

Prior question was specifically about a quote and asked the question why a blast chiller isn't a reverse microwave.

Reply on news.ycombinator.com