Question

A piston/cylinder device operating in a cycle with steam as the working fluid executes the following steps: (1) steam at 550 kPa and 200 degrees celsius is heated at constant volume to a pressure of 800 kPa. (2) It then expands, reversibly and adiabatically, to the initial temperature of 200 degrees celsius. (3) Finally, the steam is compressed in a mechanically reversible, isothermal process to the initial pressure of 550 kPa.

Please show all the steps, and please do not repost the same solution already offered on chegg.

Answer 1

thermal efficiency of a cycle = energy obtained / energy that costs

in Step 1.

energy input given = work done on the system = 0

in step 2.

we know that in step 1 it is constant volume process

therefore P/T = constant

hence final temperature T = 290.90deg C

hence for the reversible adiabatic process work =

work = 1889.54J

in Step 3

from step 2 we calculate the final pressure at the end of step2

using the T-P relation for adiabatic process

= constant

hence final pressure P = 215.57 KPa

therefore work done in step 3 = RT ln (P1/P2)

=-3683.29 J

thermal efficiency = 1889.54J / 3683.29J

=0.513 * 100 = 51.3%