Q13. Carbon dioxide, initially at a pressure of 5 bar and a temperature of 300°C, is heated at constant volume in a cylinder to a temperature of 600°C. It then expands reversibly according to the law pV1.35 = constant until the pressure has returned to its original value.
(a) Sketch the processes on p-V and T-s diagrams.
(b) Calculate EACH of the following:
(i) The final temperature
(ii) The magnitude and direction of the total heat transfer per kg
(iii) The total change in specific entropy.
Note: For CO2, R = 0.189 kJ/kg K and g = 1.22
Q16. The layout of a gas turbine plant is illustrated in Fig Q2. The plant operates between pressures of 1.00 bar and 8.00 bar. The HP turbine drives the compressor, and the LP turbine drives the load. Air enters the compressor at temperature of 18°C. Combustion gases enter the HP turbine at 997°C. The isentropic efficiency of the compressor is 0.80, and that of each turbine is 0.88. For ALL processes, γ = 1.4 and Cp =1.005 kJ/kg K.
(a) Sketch the cycle on a T-s diagram.
(i) The temperature at HP turbine exhaust
(ii) The pressure at HP turbine exhaust
(iii) The thermal efficiency.
Q5. In a stage of a 50% reaction turbine the steam is dry and saturated at a pressure of 3.0 bar. The mean blade diameter is 800 mm, the blade height is 50 mm and the speed of rotation is 4500 rev/min. The absolute velocity of the steam at exit from the stage is in an axial direction. The blade outlet angle is 25°.
(a) Sketch the combined velocity diagram, showing all relevant velocities and angles.
(b) Determine EACH of the following:
(i) The blade power
(ii) The diagram efficiency.
Q14. Dry saturated steam enters the shell of a shell and tube condenser at a pressure of 0.091 bar and leaves as saturated liquid. The rate of heat transfer is 75 MW. The condenser has a total of 12000 tubes arranged in a single pass. Each tube has outside diameter 16 mm, wall thickness 1.2 mm and length 3.7 m. cooling water enters the tubes at a temperature of 25°C and leaves at 31°C. The specific heat capacity of the cooling water is 4.2 kJ/(kg K) and its density is 1000 kg/m3.
Determine EACH of the following:
(a) The mass flow rate of steam
(b) The mass flow rate of cooling water
(c) The logarithmic mean temperature difference
(d) The overall heat transfer coefficient, bared on the tube outside surface area
(e) The mean flow velocity of the cooling water in the tubes.
Q14. A single stage, single acting air compressor is used to charge a large air receiver. The bore diameter is 750 mm and the stroke length is 950 mm. The clearance volume is 0.03 m3 and the index of compression and expansion is 1.31. The mechanical efficiency is 87%. Suction pressure and temperature are 1.00 bar and 25°C respectively. The compressor runs at 300 rev/min.
(a) Calculate, for a delivery pressure of 6 bar, EACH of the following:
(i) The power input required
(ii) The rate of jacket cooling.
(b) Explain why the mass flow rate of air decreases as the delivery pressure rises.
(c) Calculate the maximum theoretical delivery pressure which this compressor can achieve from the given suction conditions.
Note: For air, R = 0.287 kJ/kg K and Cp = 1.005 kJ/kg K.
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