How do you get the most power from a Stirling?
Posted: Thu Mar 17, 2005 1:34 am
One is temperature differential. The more the better because the
maximum efficiency is TH-TC/TH*100. Degrees Kelvin of course.
Example TCold = 300K (27C)
THot = 500K (227C)
Maximum efficiency = 500-300/500 * 100 = 40 Percent absolute max.
Power almost varies as the square of the temperature difference
because both the pressure and amount of expansion/contraction volume
vary with temperature.
Another is how fast you can heat and cool the operating gas. The
faster you heat and cool the gas relates directly to how much power
is made. Faster heating and cooling will result in higher cycle
speeds. Lets call one heating phase and one cooling phase combined a
cycle for the example below. Lets assume each cycle can generate 500
ft.lbs of work. Note: 1horsepower = 33000 ft.lbs per minute. (or 746
watts).
At 10 seconds per cycle = 6 cycles per minute @ 500 ft.lbs per cycle
this would be 3000 ft.lbs per minute. 3000/33000 = 0.0909 horsepower
At 1 second per cycle = 60 cycles per minute @ 500 ft.lbs per cycle
this would be 30000 ft.lbs per minute. 30000/33000 = 0.909 horsepower.
At 0.1 second per cycle = 600 cycles per minute @ 500 ft.lbs per
cycle this would be 300000 ft.lbs per minute = 9.09 horsepower.
As you can see above the 3 examples all have the same hot and cold
temperatures but a tremendous difference in power output because of
how fast the gas is heated and cooled.
maximum efficiency is TH-TC/TH*100. Degrees Kelvin of course.
Example TCold = 300K (27C)
THot = 500K (227C)
Maximum efficiency = 500-300/500 * 100 = 40 Percent absolute max.
Power almost varies as the square of the temperature difference
because both the pressure and amount of expansion/contraction volume
vary with temperature.
Another is how fast you can heat and cool the operating gas. The
faster you heat and cool the gas relates directly to how much power
is made. Faster heating and cooling will result in higher cycle
speeds. Lets call one heating phase and one cooling phase combined a
cycle for the example below. Lets assume each cycle can generate 500
ft.lbs of work. Note: 1horsepower = 33000 ft.lbs per minute. (or 746
watts).
At 10 seconds per cycle = 6 cycles per minute @ 500 ft.lbs per cycle
this would be 3000 ft.lbs per minute. 3000/33000 = 0.0909 horsepower
At 1 second per cycle = 60 cycles per minute @ 500 ft.lbs per cycle
this would be 30000 ft.lbs per minute. 30000/33000 = 0.909 horsepower.
At 0.1 second per cycle = 600 cycles per minute @ 500 ft.lbs per
cycle this would be 300000 ft.lbs per minute = 9.09 horsepower.
As you can see above the 3 examples all have the same hot and cold
temperatures but a tremendous difference in power output because of
how fast the gas is heated and cooled.