Answer to Question #88528 in Molecular Physics | Thermodynamics for Anikwue Grace

Question

Determine the temperature, volume, internal energy, enthalpy, entropy and density of 2kg of
steam at a pressure of 2MM/m2 and with a dryness fraction of 0.85.

Answer 1

For this problem we need h,S diagram

On this diagram find a point where across two lines: pressure 20 bar and dryness fraction 0,85

For it we have

Entropy per kg

$$S=5.7565 (\frac{kJ}{kg\cdot K})$$

Enthalpy per kg

$$i=2516 (\frac{kJ}{kg})$$

Volume per kg

$$\frac{V}{m}=0.0878 (\frac{m^3}{kg})$$

Find internal energy from this equation

$$i=U+pV$$

Internal energy

$$U=i-pV$$

For temperature use this equation

$$T=\frac{di}{dS}$$ $$T=\frac{2550-2516}{5.7565-5.826}-273=216 ^\circ C$$

Density

$$\rho=\frac{m}{V}=11.4 (\frac{kg}{m^3})$$

So, for 2 kg mass of steam and pressure 20 bar, we have

Volume

$$V=0.0878*2=0.1756 (m^3)$$

Internal energy

$$U=5032-2\cdot 10^{3} \cdot 0.1756=4681 (kJ)$$

Enthalpy

$$i=2516*2=5032 (kJ)$$

Entropy

$$S=5.7565*2=11.513 (\frac{kJ}{K})$$

Density

$$\rho=11.4 (\frac{kg}{m^3})$$