# Evaporation and Mass Flow Rate

Question 2: (20 points)

An insulated, vertical piston–cylinder device initially contains 10 kg of water, 5 kg of which is in the vapor phase. The mass of the piston is such that it maintains a constant pressure of 200 kPa inside the cylinder. Now steam at 0.8 MPa and 400°C is allowed to enter the cylinder from a supply line until all the liquid in the cylinder has vaporized. Determine (a) the final temperature in the cylinder and (b) the mass of the steam that has entered.

0.8MPa 400oC

2 Question 3: (20 points)

A well-insulated rigid tank contains 3 kg of a saturated liquid–vapor mixture of water at 200 kPa. Initially, three-quarters of the mass is in the liquid phase. An electric resistor placed in the tank is connected to a 120-V source, and a current of 10 A flows through the resistor when the switch is turned on. Determine how long it will take to vaporize all the liquid in the tank. Also, show the process on a T-v diagram with respect to saturation lines.

Question 4: (20 points)

Steam enters the condenser of a steam power plant at 20 kPa and a quality of 95 percent with a mass flow rate of 20,000 kg/h. It is to be cooled by water from a nearby river by circulating the water through the tubes within the condenser. To prevent thermal pollution, the river water is not allowed to experience a temperature rise above 10°C. If the steam is to leave the condenser as saturated liquid at 20 kPa, determine the mass flow rate of the cooling water required.

Question 5: (20 points)

Steam at 5 MPa and 600°C enters a two-stage 5MPa adiabatic turbine at a rate of 20 kg/s. The steam 600oC expands in the turbine to a...

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