Question

In a piston-cylinder setup, 50 liters of water at 200kPa and 25°C is heated under constant pressure until it completely evaporates.

a) The mass of the water,

b) its temperature in the last case,

c) The heat given to the water during evaporation,

d) its volume in the final state,

 

e) Show the P-V and T-V (Pressure, temperature and specific volume) graph that you will draw the whole system.

Answer 1

Solution;

$V=50litres=0.05m^3$

$P_1=P_2=200kPa$

$T_1=25°c=298K$

From the tables;

$v=0.0010031m^3/kg$

(a)

$m=\frac{V}{v}=\frac{0.05}{0.0010031}=49.85kg$

(b)

P=2bar

From the tables;

$T=120.2°c$

(c)

$\Delta H=m(h_2+h_1)$

$\Delta H=49.85(2707-505)=109.77MJ$

$d)$

$v_g=0.8856m^3/kg$

$V_2=0.8856×49.85=44.15m^3$

(e)