noamross
23-02-2014, 02:45 AM
Hi all,
I'm not an expert on this topic but I have an idea for a hobby project that I hoped I could get some feedback on here.
I'm interested in trying to make a pedal-powered ice-cream-and-frozen-drink maker that runs a compressor directly. I'd like to know the feasibility of this. Some back-of the envelope calculations:
- A typical biker can put out about 200 watts (~1/4 hp) continuously
- I'd be aiming to cool about 1 quart of liquid from room temperature to frozen. Given the specific heat and heat of fusion of water, this amounts to change of energy of 120 Watt-hours.
- If the coefficient of performance of the system is 2, then one should be able to cool the liquid in about 20 minutes (120 W-h/ (2* 200 W)).
So this seems theoretically possible, but one would need a compressor and refrigerant system that fits the bill. It would have to be a compressor that could be efficient when run by an external belt/crank giving about 1/4 HP. One can use gearing to increase RPM, but it would be best if the RPM required were < 2000 RPM. And the refrigerant should evaporate at a below-freezing temperature.
Main questions:
- I'm sure I'm missing some major considerations - what are they?
- What compressor would fit this bill? I thought that maybe something designed for A/C of compact car might do. As far as I can tell, all compressors designed for small fridges (or countertop ice cream machines) are hermetically sealed combined motor/compressor units.
- What refrigerant would make sense? If this could be done with propane, it would make the DIY aspect easier.
Thanks for your help!
I'm not an expert on this topic but I have an idea for a hobby project that I hoped I could get some feedback on here.
I'm interested in trying to make a pedal-powered ice-cream-and-frozen-drink maker that runs a compressor directly. I'd like to know the feasibility of this. Some back-of the envelope calculations:
- A typical biker can put out about 200 watts (~1/4 hp) continuously
- I'd be aiming to cool about 1 quart of liquid from room temperature to frozen. Given the specific heat and heat of fusion of water, this amounts to change of energy of 120 Watt-hours.
- If the coefficient of performance of the system is 2, then one should be able to cool the liquid in about 20 minutes (120 W-h/ (2* 200 W)).
So this seems theoretically possible, but one would need a compressor and refrigerant system that fits the bill. It would have to be a compressor that could be efficient when run by an external belt/crank giving about 1/4 HP. One can use gearing to increase RPM, but it would be best if the RPM required were < 2000 RPM. And the refrigerant should evaporate at a below-freezing temperature.
Main questions:
- I'm sure I'm missing some major considerations - what are they?
- What compressor would fit this bill? I thought that maybe something designed for A/C of compact car might do. As far as I can tell, all compressors designed for small fridges (or countertop ice cream machines) are hermetically sealed combined motor/compressor units.
- What refrigerant would make sense? If this could be done with propane, it would make the DIY aspect easier.
Thanks for your help!