Final answer:
The problem involves a piston/cylinder with water undergoing a constant pressure process where temperature and quality change. The new quality and specific volume require reference to steam tables, and the P-v diagram depicts a horizontal line representing constant pressure with different volumes at states one and two.
Step-by-step explanation:
The student's question involves a constant pressure process in a piston/cylinder setup with water at a specific initial temperature, pressure, and quality. The quality of a two-phase mixture (liquid-vapor) refers to the percentage of the mass that is vapor. Since the initial quality is 25%, it means that 25% of the water mass is vapor and the rest is liquid. When the temperature is lowered by 20°C, the quality will change because the proportion of vapor will decrease as some of the vapor condenses into liquid. This change in quality can be found using steam tables or thermodynamic relationships for two-phase mixtures. Similarly, the specific volume, which is the volume occupied by a unit mass of water, will also change corresponding to the new temperature and quality.
To sketch the isobaric process on a P-v (pressure vs. specific volume) diagram, one would draw a horizontal line because the pressure remains constant. On this line, two points would be marked, one for state one with the higher specific volume and one for state two with the lower specific volume, demonstrating the reduction in temperature and potentially specific volume. State one would be at a higher specific volume than state two due to the higher temperature. The piston/cylinder device sketches would show the initial state with a higher volume and the final state with a potentially lower volume, depending on the change in quality.