Question

You are part of a team that is completing a mechanical-engineering project. Your team built a steam engine that takes in superheated steam at 300°C and discharges condensed steam from its cylinder at 40°C. Your team has measured its efficiency to be 30.0%.

(a) How does this efficiency compare with the maximum possible efficiency for your engine?
ε_{steam engine}/ε_max =   %

(b) If the useful power output of the engine is known to be 185 kW, how much heat does the engine release to its surroundings in 1.00 h?
  GJ

Answer 1

A.

Max efficiency is givenby:

e)max = 1 - Tc/Th = 1 - (273 + 40)/(273 + 300) = 0.4537

e)steam engine = 30% = 0.3

So,

e)steam engine/e)max = 0.3/0.4537 = 0.6612

B.

Power = 185 kW = 185*10^3 W

Energy = power*time

Total output energy in 1 hr = 185*10^3*3600 = 6.66*10^8 J

Total input energy = Total output energy/efficiency of steamed engine

Total input energy = 6.66*10^8/0.3 = 22.2*10^8 J

So

Energy released = energy input - energy output

Energy released = (22.2 - 6.66)*10^8 = 1.554*10^9 J = 1.554 GJ