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Refrigerators To Cool With Sound (Cool!)
T-Kir writes "A very interesting report from the BBC where researchers at Penn State University are developing a prototype fridge that cools using metal plates and sound waves. If successful, this technology would help remove the dependance on gases that contribute to global warming. Talk about Cool!"
You can also make refrigerators using a Stirling-engine like gas compression cycle. The guys at Medis Technologies have designed this. See here for the brief description. I guess instead of trying to extract mechanical work from a Stirling engine, they are just removing heat from one area and piping it off elsewhere. They claim this uses no greenhouse depleting gases, and it sounds plausible to me.
I'd worry about my ears more than Fido's. The article doesn't say the frequencies are ultrasonic, so it's possible human ears will need protection too. I can't imagine how much sound insulation you'd need to hold in 173dB. What happens if the chiller doesn't cut off when you open the fridge door? I'm picturing the last scene of Raiders of the Lost Ark where the Nazis get their faces melted off.
At ridiculous volumes and/or frequencies, sound has some amazingly powerful properties, but I'm skeptical as to how practical such a technology can be. Here's why:
A professor at my university was doing some personal research with a small team at his house on the properties of high-decibel sound. Based on incredibly complex differential equations, one could project two sound waves at ridiculously high frequencies and volumes to create a special kind of interference. This interference would in essence start a new sound (at a hearable frequency/volume) from where the two waves intersected, effectively making it seem like a controlled sound was being created out of thin air at any point in 3d-space.
I don't think I need to point out applications to this technology. BUT - he decided to discontinue the project before it was ever completed. He had several pets in his house (dog + cats) that he tried to keep away from the testing, but they were still being driven crazy by the sound. He also started developing nasty headaches and suspected that his high-range hearing was being destroyed.
Interestingly, one of the graduate students who worked with him on the project decided to continue the work on his own. From what I've heard, he had his work picked up and funded by the US military (DARPA, I think). When I heard this, it really didn't come as a surprise.
Experts agree: everything is fine.
It says compressed gas is needed to generate the sound. All that means is if someone breaks open the fridge it won't keep making 173dB noise. However sound conducts through many materials, solid, liquid and gas. While the chiller is running, you'll still have to soundproof 173dB of noise while taking into account things like heat exchanger tubes.
How's this for an experiment. Turn your stereo speakers up to the loudest (that's maybe 110dB if you have a killer stereo) and try to build a soundproof box around it that's smaller than your fridge.
Suddenly it seems a lot easier to soundproof.
There is also the issue of the density difference from the compressed gas media in the tube to atmospheric pressure (think about sound not transferring well from water to air or back), but I suspect that is a red herring given that you are going to a more dense material first before the atmosphere.
Incidentally, I think they have a compressed gas because you can't do 173dB in free air. You rip the air down to total vacuum in the low pressure parts before you get there.
Unrelated trivia note: Your hearing ends at 20Hz. If you put a mic on your body and pitch shift the 20Hz range up into audible frequencies you will find that your body is quite loud and distracting if you can hear it.