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ENGINEERING THERMODYNAMICS 2

SCEE08006

2021

Question 1

One mole of gas is enclosed in a cylinder/piston assembly. The gas expands reversibly and isothermally at 25 °C from the pressure of 20 atm to 1 atm.     Calculate heat, work and specific internal energy change in the process for:

An ideal gas.                                                                                               (10)

A non– ideal gas following the equation of state:

P =

where R = 8.3145 J mol– 1 K– 1 and B in [L mol– 1] is:

B = 0.0458 −                                                       (25)

b).                                                                                                               (5)

Explain why this equation of state is not able to provide a value for the

saturation pressure and which modification of the equation enables

that.                                                                                                                       (10)

 

Question 2

A Brayton cycle working with air has a compression ratio of 6, between a          minimum temperature of 30 °C and a maximum temperature of 1200 °C. The    iso– entropic efficiency of the compressor is 70% and the isentropic efficiency of the turbine is 80%.

showing the heat and work exchanged.                                                   (5)

For the irreversible cycle, find the network, the flow rate producing

10 MW and the entropy generated in compression and expansion.        (25)

Find the efficiency of the reversible cycle and of the irreversible

cycle.                                                                                                        (10)

Compare the efficiencies of the reversible and irreversible Brayton

cycles with that of the corresponding internally reversible Carnot

cycle.                                                                                                        (10)

Properties:

The specific heat of air is constant at cp = 1 kJ kg– 1  K– 1 ;

The ratio k = cp/cv = 1.4