Question 1)a) Define the following
(i) Process
(ii) Intensive property
(iii) open system
(iv) Thermodynamic equilibrium
b) Show that internal energy is a property of the system.
c) Air at a temperature of 15°C passes through a heat exchanger at a velocity of 30 m/s where its temperature is raised to 800°C. It then enters a turbine with the same velocity and expands until the temperature falls to 650°C. On leaving the turbine air is taken at a velocity of 60 m/s to a nozzle where it expands until the temperature has fallen to 500°C. If the air flow rate is 2 kg/s, Calculate:
(i)Rate of heat transfer to air in the heat exchanger
(ii)Power output from the turbine assuming adiabatic conditions
(iii) Velocity at the exit of the nozzle. Take enthalpy of air as Cpt where Cp is the specific heat of air (=1.005 kJ/kgK) and t is the temperature.
Question 2)a) Derive the expression for thermal efficiency of a diesel cycle in terms of compression ratio, cut off ratio and ratio of specific heats.
b) A two stage air compressor receives 0.238 m3/s of air at 1 bar and 27°C and discharges it at 10 bar. The polytropic index of compression is 1.35. Assuming perfect inter cooling, determine
(i) the minimum power required for compression
(ii) Power needed for single stage compression to the same pressure
(iii) Maximum temperature in both cases.
Question 3)a) With neat sketches explain the effect of super heating and subcooling on the vapor compression refrigeration cycle.
b) Derive an expression for volumetric efficiency of a reciprocating air compressor in terms of clearance ratio and the pressure ratio.
c) In a gas turbine plant working on Brayton cycle, air at the inlet is at 27°C and 0.1MPa. The pressure ratio is 6.25 and maximum temperature is 800°C. The turbine and compressor efficiencies are each 80%. Find:
(i) Turbine exhaust temperature
(ii) cycle efficiency