Is my Math correct

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Fan/Pump Power
Original RPM
1,750.00
Original Power
8,365.00
2nd RPM
1,735.42
1,720.83
1,706.25
1,691.67
1,677.08
1,662.50
1,647.92
1,633.33
Power Rqd
8,158
7,954
7,753
7,556
7,362
7,172
6,985
6,801
% Change
-2.48%
-4.92%
-7.31%
-9.67%
-11.99%
-14.26%
-16.50%
-18.70%
0.99
0.98
0.98
0.97
0.96
0.95
0.94
0.93
0.975
0.951
0.927
0.903
0.880
0.857
0.835
0.813
 
Power varies as the cube of the speed of rotation. So there should be no surprise that you would see a significant reduction in power with a slight reduction in speed.

I checked the first three rows, and can confirm that the math is correct. I don't know what the bottom two rows are intended to represent.
 
ptonsparky said:
Fan/Pump Power
Original RPM
1,750.00
Original Power
8,365.00
2nd RPM
1,735.42
1,720.83
1,706.25
1,691.67
1,677.08
1,662.50
1,647.92
1,633.33
Power Rqd
8,158
7,954
7,753
7,556
7,362
7,172
6,985
6,801
% Change
-2.48%
-4.92%
-7.31%
-9.67%
-11.99%
-14.26%
-16.50%
-18.70%
0.99
0.98
0.98
0.97
0.96
0.95
0.94
0.93
0.975
0.951
0.927
0.903
0.880
0.857
0.835
0.813
Click to expand...

I agree with your calculations for power and the reduction as a percentage. The other two rows of figures are not labelled.
 
ptonsparky said:
The last two rows could be hidden although they are part of solution.
Click to expand...
OK.
The top one is the fraction of rated speed, the lower the fraction of rated power.
I wouldn't have used those in the calculation though.

(1735.42/1750)3 * 8,365.00 = 8,158.00

Job done.
 
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