Which of the following is true?

Question

A. A closed system is one where no heat or mass can cross the system boundary.
B. Step 2à3 in the Rankine Cycle (re: across the turbine) is characterized as an isobaric expansion.
C. An adiabatic process is one where the temperature is constant throughout the process.
D. In step 1à2 in the Rankine Cycle (re: across the boiler), heat is added to the system in order to convert water to steam.
E. None of the above are true.

Answer 1

A. Incorrect. A closed system is one in which no mass crosses the boundaries of the system, but heat (and work) can be transferred to or from a closed system.
B. Incorrect. The word isobaric means constant pressure. The fluid experiences a significant pressure drop as it travels through a turbine.
C. Incorrect. A constant temperature process is isothermal. Adiabatic means no heat is added or removed. An adiabatic system is not necessarily isothermal. In fact, when a chemical reaction or a phase change is occurring, adding or removing heat is how a system is maintained isothermal.
D. Correct. The primary purpose of the added heat is to boil the liquid, though ordinarily a change in temperature also occurs because the entering liquid is not at its boiling point.
E. Incorrect. Check again. One of the statements is true.