Physics Question

Question

(a.) steam flow through a turbine at the rate of 100 lb/min with ∆K=0 &Q=0. At entry, its pressure is 175 psia, its volume is 3.16ft^3/lb , and its internal energy is 1166.7 Btu/lb. At exit it's pressure is 0.813 psia, its volume is 854.6 BTU/lb. What horsepower is developed? (b). The same as (a.) except that the heat loss the turbine is 10 Btul lb of steam.

Answer 1

Assuming the missing outlet specific volume is 328 ft^3/lb, the answers are:

(a) approximately 861 hp

(b) approximately 837.5 hp

Note: 854.6 Btu/lb is the outlet internal energy, not its specific volume.

For steady flow, with no change in kinetic energy and negligible change in potential energy:

Power output = heat-transfer rate into turbine + mass flow rate * (h1 - h2)

Enthalpy includes internal energy and pressure-related flow energy:

h = u + pv

With pressure in psi and specific volume in ft^3/lb, convert the pressure-volume term to Btu/lb:

h = u + (144 * p * v) / 778

Inlet enthalpy:

h1 = 1166.7 + (144 * 175 * 3.16) / 778