THERMODYNAMICS, HEAT AND MASS TRANSFER

TUTORIAL NO: 2

(PROPERTIES AND STATES OF SUBSTANCES)

1. The Liter-than-Air Balloon Company has a helium balloon that will be used in an attempted crossing of the Atlantic Ocean. The helium will initially be at 200C and 500 kPa. The balloon, a rigid sphere, has a radius of 25 m. Determine:(a) The mass of the helium.(b) As the balloon rises, the helium is heated by solar radiation to a temperature of

3000C. If the safe pressure limit is 1 MPa, are the balloonists in danger?(c) If a newer model of the balloon were to have its allowable mass cut by 26960 kg,

what gas could be used in place of helium?

2. A 1 m3 rigid tank with air at 1 MPa, 400 K is connected to an air line as shown in Figure P2.2. The valve is opened and air flows inside the tank until the pressure reaches 5 MPa, at which point the valve is closed and the temperature inside is 450 K.(a) What is the mass of the air in the tank before and after the process?(b) The tank eventually cools to room temperature, 300 K. What is the pressure inside

the tank than?

Figure P2.2

3. Fill in the blanks in the following table for the properties of water.

S.N. P, kPa T, 0C x, % v, m3/kg1 300 2002 300 653 200 0.10504 10000 0.05845 20000 1206 101.325 1007 120 0.620

4. A vessel having a volume of 0.6 m3 contains 3.0 kg of liquid water and water vapor mixture in equilibrium at a pressure of 0.5 MPa. Calculate:(a) The volume and mass of liquid.(b) The volume and mass of vapor.

5. A vessel of volume 0.04 m3 contains a mixture of saturated water and saturated steam at a temperature of 2500C. The mass of the liquid present is 9 kg. Find the pressure, the mass, the specific volume, the enthalpy, and the internal energy.

THERMODYNAMICS, HEAT & MASS TRANSFER TUTORIAL NO. 23

6. A piston encloses 1 kg of saturated water which is initially 10 % liquid on mass basis. The initial pressure is 1.0 MPa. The water is heated in the system shown until the water is at the saturated vapor state. The volume at the top stops is 0.19 m3. Determine the work done by the water and the final temperature and pressure.

Figure P2.6

7. 5 kg of H2O are contained in a closed rigid tank at an initial pressure of 20 bar and a quality of 50 %. Heat transfer occurs until the tank contains only saturated vapor. Determine the volume of the tank, in m3, and the final pressure, in bar.

8. Steam is contained in a closed rigid container. Initially, the pressure and temperature of the steam are 15 bar and 2400C, respectively. The temperature drops as a result of heat transfer to the surroundings. Determine the pressure at which condensation first occurs, in bar, and the fraction of the total mass that gas been condensed when the temperature reaches 1000C. What percentage of the volume is occupied by saturated liquid at the final state?

9. Water vapor is heated in a closed, rigid tank from saturated vapor at 1600C to a final temperature of 4000C. Determine the initial and final pressures, in bar, and sketch the process on T-v and P-v diagrams.

ANSWERS

1. 53770kg, No, Hydrogen 2. 8.7 kg, 38.7 kg, 3.3 MPa3. M, 0.7163; 133.6, 0.394; 1553.7, 0.823; 1000, M; M, 0.0584; M, 0.0010513; I, I;

198.48, 0.6954. 0.0015 m3, 1.404 kg; 0.5985 m3, 1.596 kg5. 3.973 MPa, 9.575 kg; 0.00418 m3/kg; 1188.32 kJ/kg; 1171.71 kJ/kg6. 15 kJ7. 0.252 m3; 39.6 bar8. 13.68 bar; 0.912; 0.64 %9. 617.66 kPa; 1000 kPa

THERMODYNAMICS, HEAT & MASS TRANSFER TUTORIAL NO. 24