Air Motors

2025

• 60% efficient, Livermore [1]. Implies standard air motors are 10-20% efficient. But even with that - that is good.
• Compressor efficiency calculation, hard core - [2]
• Compressors are 60% efficiency and up [3]
• Anecdotal - 7% efficient [4]
• 1/2 to 2 hp drum mixers [5]
• 30 CFM to 1 hp [6]
• 28 cfm/hp [7]
• 1/2 hp specs - [8]. 1.4 cfm @90 PSI with 200 rpm.
• This one claims air motor piston - 40-50% efficient [9]. But if you include compressor - it is another half of this for 20%. So in practice - want 8 hours of night power? Need 300W - fans, 250W HD desktop, etc. 12W for LED bulbs.
• 1/3 hp motor $300 [10]
• 1/2 hp is $500 [https://www.ebay.com/itm/303335987408?chn=ps&mkevt=1&mkcid=28&google_free_listing_action=view_item&srsltid=AfmBOoqc6x7jpKH-9gG1M2xB6OuVcmgccG6NqUJ22Y6SdG6NaK0V38l08b0&gQT=1

2021

• This one says 70% efficient - really? [11]
• CFM of 20 gets 0.5 hp about. 1 cu m is 35 cf. 1 cu m at 190 atm is 7000 cf, at 20 cfm gives 350 minutes or almost 6 hours.
• Piston type mixer motor - 7 cfm, 0.2 hp - $250 - [12].
  • One k-type cylinder gets me 35 minutes of this power. That's at least a start, but too short duration for practical use. Adiabatic.
• 14 cfm gets me the right power - 0.4 hp or 300W.
• 17 cfm - 0.33 hp - 250 W - [13]

Power Out

• 1 cubic meter of air storage - at 200atm - gets you 7000 cfm at stp. Since we need to save 10 atm to run, have 190 atm available - so 5% negligible loss - most is usable air. This is 500 minutes of air - 8 hours - of 300W - or 2.4kW hrs! This is just plain adiabatic.
  • One Type K tank gets 120Whrs.
• Thus, having access to 1 cu m of stored air - is key - for an inefficient storage system.
• Going to isothermal - we are 2.5x better
• Compressed air with heat would be the way to go - where we store the thermal energy of compression via a heat exchanger.

Pipe

• 2" pipe - 10' - is $33. It is about 6l volume for 10'. 8 of these equal a Type K cylinder in volume. Same price.
• Metals depot - 12" schedule 40 pipe, 6' long, is $726. That is 1/2 cu meter. Getting there for storage - but working pressure is 370 psi and burst is 3000 psi. Needs reinforcement.
• How about 12" PVC - 3D printed, reinforced with fiberglass winding? That sounds like a possible idea for 2000 PSI air tanks on the cheap. $100 for pipe, then winding after that.
• Or - Type IV pressure vessels, all composite, from HDPE liner and wound with 500,000 psi+ tensile strength fiber (glass or carbon)