Mechanical Engineering UPSC PYQ 2020

One stage comprising a pair of blade rings of a 50 percent reaction axial flow steam turbine has a mean ring diameter of 140 cm. The blade to steam speed ratio is 0.7. The speed of rotation is 3000 r.p.m. Determine the required entrance angle for the blading if the exit angle is 20°. Also, determine the work done per kg of steam flowing per second and the diagram efficiency. Calculate the percentage increase in diagram efficiency if the blades are designed for, and run at the best theoretical speed corresponding to the optimum operating condition, for the given steam speed and the exit angle.

Air enters the compressor of a gas turbine plant at ambient conditions of 100 kPa and 25 °C with negligible velocity, and exits at 1 MPa and 347 °C with a velocity of 90 m/s. The compressor is cooled at a rate of 1500 kJ/min and the power input to the compressor is 250 kW. Determine the mass flow rate of air through the compressor. For air, consider C_p = 1.005 kJ/kg-K, C_v = 0.717 kJ/kg-K and R = 0.287 kJ/kg-K.

An oil engine operating on air-standard dual cycle has cylinder bore of 250 mm and stroke length of 300 mm. The compression and expansion ratios are 10 and 6 respectively. The initial pressure and temperature of air before compression are 1.0 bar and 27 °C respectively. The heat added at constant pressure is twice the heat added at constant volume. Determine the pressure and temperature at all the salient points in the cycle, and the air-standard efficiency of the cycle. Also, calculate the clearance volume of the engine. Draw the P-V diagram of the cycle. Take, for air, \gamma = 1.4 and C_p = 1.005 kJ/kg-K.