Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/19

Rh pressure P becomes

P=$W/g$ (V-$V/x$). . .  .  .  (2)

The work done per second is, obviously, the pressure in lbs. on the vane multiplied by the distance in feet through which the pressure is exerted; and the distance in feet traversed by the vanes in a second is the velocity of these in feet per second, or $V/x$.

Therefore the work is equal to

P × $V/x$ foot pounds.

inserting the value of P from (2);

the work in foot pounds=$W/g$ × (V-$V/x$) × $V/x$. . .  (3)

The efficiency is given by the ratio of the work done on the vanes to the energy possessed by the jet.

From Chapter I. the jet energy is $Wv²,/2g$ and the efficiency is therefore

Equation (3)÷$Wv²/2g$. . .  .  (4)

For example:-- Supposing the velocity of the jet is 300 feet per second, and the size of the nozzle is such that 2 lbs. of water or gas are discharged in one second, the energy of the jet=$Wv²/2g$=$2×300×300/2×32∗2$=2795 foot pounds, and assuming that the vane velocity is