A closed rigid tank contains 2 kg of water initially at 80 d

A closed rigid tank contains 2 kg of water initially at 80 degree C and a quality of 0.6. Heat Transfer occurs until the tank contains only saturated vapor Kinetic and potential energy effects ire negligible, For the water as a system, determine the amount of energy transferred by heat.

Solution

The initial state of the system is:

1) T₁=80C x=0.6 v₁=2.043kJ/kg u₁=1622kJ/kg

where v₁ and u₁ were obtained from steam tables.

The final state is

2) x=1 v₂=v₁=2.043kJ/kg

T₂=94.1C

u₂=2498kJ/kg

where T₂ and u₂ were obtained from steam tables.

Using the first law of thermodynamics we have

u = q - w

u = 2498 - 1622 = 876 kJ/kg

where w=0. This the total heat input is

Q = m q = 2*(876) = 1752 k