Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/31



THE size of a model turbine is determined by the maximum evaporation of the boiler which is to furnish the steam. A standard rule has been to reckon on one cubic inch of water 'per minute per 100 square inches of heating surface. Five cubic inches evaporation from this surface has been obtained, and designs promising as much as ten cubic inches have been published. We will have one cubic inch, and if the evaporation is more or less than this quantity areas will have to be increased or reduced in exact proportion. One cubic inch of water weighs 0⋅036 lb., and the table overleaf gives the corresponding volumes of steam both in cubic inches and feet at the respective pressures considered.

Assuming that the boiler pressure is 30 lbs. (gauge), the volume of steam delivered to the turbine per minute is 0⋅33 cubic feet, weighing, of course, 0⋅036 lbs.; hence the volume and weight 27