Steam at a temperature T H = 205 C and p = 1.00 atm enters a heat engine at an u
ID: 1484890 • Letter: S
Question
Steam at a temperature TH = 205 C and p = 1.00 atm enters a heat engine at an unknown flow rate. After passing through the heat engine, it is released at a temperature TC = 100 C and p = 1.00 atm . The measured power output P of the engine is 300 J/s , and the exiting steam has a heat transfer rate of HC = 2400 J/s . Find the efficiency e of the engine and the molar flow rate n/t of steam through the engine. The constant pressure molar heat capacity Cp for steam is37.47 J/(molK) .
Part A:
What is the efficiency of the heat engine?
Express the efficiency numerically to three significant figures.
Explanation / Answer
a) Power output = 300J/s
Power of exiting steam = 2400J/s
Power Input = Power output + Power of exiting steam = 300 + 2400 = 2700J/s
e = Power output/power input = 300/2700 = 1/9 = 0.111 (Ans)
b) In 1 s; Heat input = 2700 J; H = n Cp delT for constant pressure process
so, 2700 = n * 37.47 * (205 - 100)
n = 0.686 in 1 second
So n/t = 0.686 mol/s