The power of a windmill depends—first, on the diameter of the wheel; and second, on the velocity of wind. To increase the diameter of the wheel is to increase its power in proportion to the area of the squares. Table I gives the horse-power of several sizes of mills working in a fifteen-mile wind: if the wind velocity be increased or diminished, the power of the windmill will increase or decrease in the ratio of the squares of the velocity. Table V will show the comparative power or force of the wind in velocities from eight to forty miles per hour for each square foot of surface.
Rules for approximately determining size of windmill to use.
The daily water consumption must be given as a basis for calculation. Divide this by 8 to find the hourly capacity of windmill, as if loaded aright the mill will pump on an average eight hours daily.
Multiply the quotient by total water lift in feet and with the co-efficient given in Table II.
The product will in Table I show what mill to use.
The size of the cylinder and discharge pipe will be found in Table III.
Fig. 466.
Table I gives the maker’s number of the pumping mill, and the number of gallons each will raise one foot high per hour, with a wind having a velocity of fifteen miles per hour. Example: No. 9 pump will raise 24,000 gallons of water one foot high in one hour. Now if the water is to be raised 50 feet then by dividing 24,000 by 50 the quantity raised becomes 480 gallons per hour.