An insulated rigid tank contains 5 kg of a saturated liquid-vapor mixture of water at a. Initially, three-quarters of the mass is in the liquid phase. An electric resistor placed in the tank is connected to a 110-V source, and a current of 8 A flows through the resistor when the switch is turned on. (a) Determine how much time it will take to vaporize all the water in the tank, and (b) show the process on a T-v diagram with respect to the saturation lines.

2.67 hours

Explanation:

If three quarters of the mass are in liquid phase, I have a mass of water:

m1 = 3/4 * 5 = 3.75 kg

The latent heat of vaporization of water is of

ΔHvap = 2257 kJ/kg

The heat needed to vaporize it is:

Q = m * ΔHvap

Q = 3.75 * 2257 = 8464 kJ

If I have a resistor connected to 110 V, with a current of 8 A, the heat it dissipates through Joule effect will be:

P = I * V

P = 8 * 110 = 880 W = 0.88 kW

With that power it will take it

t = Q / P

t = 8464/0.88 = 9618 s = 160 minutes = 2.67 hours2.