Applied ThermodynamicsSpring-2011

Assignment No 5 Due Date- 19-04-2011

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Q-1: Helium gas expands from 125 kPa, 350 K and 0.25 m3 to 100 kPa in a Polytropicprocess with n = 1.667. How much work does it give out?

Q-2: Air at 1500 K, 1000 kPa expands in a polytropic process, n = 1.5, to a pressure of200 kPa. How cold does the air become and what is the specific work out?

Q-3

Q-4 Air goes through a Polytropic process from 125 kPa, 325 K to 300 kPa and 500 K.Find the Polytropic exponent n and the specific work in the process.

Q-5 In a sink 5 liters of water at 70oC is combined with 1 kg aluminum pots, 1 kg of flatware (steel) and 1 kg of glass all put in at 20oC. What is the final uniform temperature neglecting any heat loss and work?

Q-6 A house is being designed to use a thick concrete floor mass as thermal storage material for solar energy heating. The concrete is 30 cm thick and the area exposed to the sun during the daytime is 4 m × 6 m. It is expected that this mass will undergo an average temperature rise of about 3°C during the day. How much energy will be available for heating during the nighttime hours?

Q-7 A computer CPU chip consists of 50 g silicon, 20 g copper, 50 g polyvinyl chloride (plastic). It heats from 15oC to 70oC as the computer is turned on. How much energy does the heating require?

Q-8 A 250 L rigid tank contains methane at 500 K, 1500 kPa. It is now cooled down to 300K. Find the mass of methane and the heat transfer using ideal gas.

Q-9 A diffuser, shown in Fig. P6.28, has air entering at 100 kPa, 300 K, with a velocity of 200 m/s. The inlet cross-sectional area of the diffuser is 100 mm2. At the exit, the area is 860 mm2, and the exit velocity is 20 m/s. Determine the exit pressure and temperature of the air.

Q-10 A windmill with rotor diameter of 30 m takes 40% of the kinetic energy out as shaft work on a day with 20oC and wind speed of 30 km/h. What power is produced?

Q-11 A small expander (a turbine with heat transfer) has 0.05 kg/s helium entering at1000 kPa, 550 K and it leaves at 250 kPa, 300 K. The power output on the shaft is measured to 55 kW. Find the rate of heat transfer neglecting kinetic energies.

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