Final answer:
The initial state of water at 150 degrees Celsius and a vapor quality of 0.8 is a two-phase mixture of liquid and gas. Vapor quality refers to the proportion in the vapor phase, indicating that 80% of the water is vapor and 20% is liquid. When all liquid water has evaporated at the constant temperature, the tank contains only superheated vapor.
Step-by-step explanation:
The initial state of water given its temperature of 150 degrees Celsius and a vapor quality of 0.8 is a two-phase mixture in which the substance exists partially in the liquid phase and partially in the gas phase.
In thermodynamics, the term 'vapor quality' refers to the fraction of a mixture that is in the vapor state at a particular temperature and pressure.
Given the information that the temperature remains constant during the vapor discharge process, we can deduce that the water stays in a saturated vapor state until all the liquid phase has evaporated.
When considering the heating curve of water, the initial thermal condition reported (150 degrees Celsius) falls into the region where water is a superheated vapor, because it is above the boiling point of water at 1.00 atm pressure (which is exactly 100 degrees Celsius).
However, since we have a mixture with a vapor quality of 0.8, it suggests that not all the liquid has turned into vapor; there is still 20% of the mass in the form of liquid water. Once the remaining liquid water is evaporated and the valve is closed, only superheated vapor will be present in the tank.
According to the heat of vaporization of water and the description of the process, a considerable amount of heat would need to be added initially to reach the point where vapor quality is 0.8.
Even though the details of this heat addition are not provided in the question, understanding the properties of water and its states is essential in grasping this concept.