A 750-L rigid tank, shown in Fig P6.122 initially contains water at 250C, 50% liquid and 50%

Question:

A 750-L rigid tank, shown in Fig P6.122 initially contains water at 250°C, 50% liquid and 50% vapor, by volume. A valve at the bottom of the tank is opened, and liquid is slowly withdrawn. Heat transfer takes place such that the temperature remains constant. Find the amount of heat transfer required to the state where half the initial mass is withdrawn