Question

An expansion valve does work on
100 g of water. The system is isolated, and all of
the work is used to convert the 90°C water into
water vapor at 110°C. How much work does the
expansion valve do on the water?

Answer 1

Known :

m = 100 gr = 0.1 kg

T1 = 90°C

T2 = 110°C

Solution :

Since the system is isolated, we can assume that no heat transfer is allowed, hence the process is adiabatic

W = m • Cv • ∆T

W = (0.1)(4.2 kJ/kg·K)(110°C - 90°C)

W = 8.4 kJ/kg