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BE Mechanical Engineering VI Sem 2010
Answer the following
(a) What is the difference between work transfer and heat transfer?
(b)Classify the following processes as heat or work. Give reasons.
• -Temperature rise of a gas in a cylinder when it is compressed by the piston.
• -Heating of a room when an electric iron is plugged in.
• -Solar heating of a room.
• -Heating of an insulated room by burning candles.
(c)Write the statement of First law of thermodynamics.
(i)Nitrogen at an initial state of 300 K, 150 kPa and 0.2 m3 is compressed by an adiabatic process to a final pressure of 800 kPa. Find the total work done.
(ii) Air at a flow rate of 4.2 kg/m3 leaves a diffuser that has an exit to inlet area ratio of 2:1 with a velocity of 120 m/s. It enters the diffuser with a velocity of 380 m/s find the density of the air as it enters the diffuser.
A mass of 15kg of air in a piston cylinder device is heated from 250C to 770C by passing current through a resistance heater inside the cylinder. The pressure inside the cylinder is kept constant at 300kPa during the process and a heat transfer of 60KJ occurs from the device to the surroundings. Determine the electrical energy supplied.
Liquid water at 300 kPa and 20oC enters a mixing chamber a rate of 1.8 kg/s where it is mixed with superheated steam at 300 kPa and 300oC. If the mixture leaves the mixing chamber at 60oC, determine the mass flow rate of the super heated steam.