Question

A rigid, insulated tank that is initially evacuated is connected through a valve to a supply line that carries helium at 200 kPa and ${120}^{o}C$. Now the valve is opened, and helium is allowed to flow into the tank until the pressure reaches 200 kPa, at which point the valve is closed. The flow work of the helium in the supply line is closest to

• A. 730 kJ/kg
• B. 890 kJ/kg
• C. 930 kJ/kg
• D. 816 kJ/kg

Answer 1

The correct option is D 816 kJ/kg

Specific volume is calculated as :

$v=\frac{R{T}_{line}}{P}=\frac{2.0769\times (120+273)}{200}$

$(\because RforHe=\frac{\overline{R}}{4}=\frac{8.314}{4}=2.079kJ/kg.K)$

$=4.0811m^3/kg$

The flow work can be calculated as :

$W_{flow}=P\times v=200\times 4.0811=816.2kJ/kg$