Question

500 g of saturated liquid water is contained in a piston-cylinder arrangement. The inside diameter of the cylinder is 100 mm. The water is heated at a constant pressure of 150 kPa until it becomes saturated vapor. Determine (a) the distance through which the piston is raised, and (b) the amount of energy transferred to the water.

Answer 1

At Pressure, P = 150 kPa

V_f = 0.001052 m³/kg , Vg = 1.163 m³?/kg , V_fg = 1.1579 m³/kg

h_f = 466.37 kJ/kg , h_g = 2693.23 kJ/kg , h_fg = 2226.21 kJ/kg

given, Mass m = 500 g = 0.5 kg

a)
Increased volume of the gas, V = m * (V_g - V_f ) = m*V_fg

= 0.5 * 1.1579 = 0.5789 m³

This increased Volume will cause piston displacement. s

  V =  *r²* s

since, diameter, d = 100 mm

so, radius, r = 100/2 = 50 mm = 0.05 m

0.5789 =   *0.05²s

so, piston displacement. s = 73.7 m

b)

Amount of energy transferred, E = m* h_fg

= 0.5 * 2226.21 = 1113.1 kJ