Turbo Assignment II Last Date Monday 1st November

THERMODYNAMICS OF FLOW IN TURBO MACHINES

Assignment  2

(1)    Air flows through an air turbine where its stagnation pressure is decreased in the ratio of 5:1. The total to total efficiency is 0.8 and the air flow rate is 5 kg/s.. If the total power output is 500 kW, find,(i) Inlet total temperature (ii) The actual exit total temperature (iii) The actual exit static temperature, if the flow velocity is 100 m/s and (iv) the total to static efficiency of the device.

(2)    In a centrifugal compressor the air is compressed to double the pressure. The inlet temperature is 27⁰C and the final temperature is 107⁰C. Calculate the efficiency of the compressor and the power required to drive it if 30 kg/min of air is compressed.

(3)    Air enters a compressor at a static conditions of 150 kPa and 15 ⁰C. and a velocity of 50 m/s. At the exit the static conditions are 0.3 MPa and 100 ⁰C. and a velocity of 100 m/s. Evaluate the isentropic and actual changes in enthalpy and total to total efficiency.

(4)    Compute the polytropic efficiency of a turbine using air if the initial pressure is 4.2 bar, initial temperature is 713 K, final pressure is 1.4 bar and final temperature is 553 K.  Also calculate overall efficiency and turbine output.

(5)    Compressor A has total pressure ratio 4, total head adiabatic efficiency of 86% and an exit velocity of 134 m/sec at the point of measurement.  Compressor B has a static pressure of 6.2 bar, static temperature of 518K and velocity of 100 m/s. at the point of measurement.  Which compressor has the best polytropic efficiency? Assume the ambient pressure and temperature, are 1 bar and 228 K respectively.

(6)    Each stage of a four stage air compressor delivering 44 kg/s, operates at a pressure of 1.2 with a stage efficiency of 65%. Calculate overall efficiency and pressure ratio. Compute power required to drive the compressor if air temperature at inlet is 20⁰C. Find also the exit air temperature.

(7)    An air compressor has eight stages of equal pressure ratio of  1.35. The flow rate through the compressor and its overall efficiency are 50 kg/s and 82% respectively. If the condition of air at entry are 1 bar and 40⁰C, determine (i) the state of air at compressor exit (b) polytropic efficiency(iii) efficiency of each stage and (iv) power required to drive the compressor assuming,  η_mech = 90%. as well as power required in each stage.

(8)    An Air turbine has five stages of equal pressure ratio 1.75.  The flow rate through the turbine is 50 kg/s and its overall isentropic efficiency, h_S-S is 82%.  If the conditions of air at entry are 15 bar and 850°C, compute

(i)                  The Infinitesimal polytropic Stage efficiency

(ii)                The Finite stage efficiency of each stage assuming them to be equal.

(iii)       Reheat Factor

(iv)       Actual Total Power developed by the turbine if η_mech =90%.

(9)    In a turbine there are 10 stages each having a finite stage efficiency of 86% and Pressure ratio of 1.24 and inlet temperature is 727°C.  Compute

i)    The overall isentropic efficiency

ii)  The infinitesimal polytropic efficiency

iii)Reheat factor

iv)The specific work done by the turbine.

(10)The turbine inlet and condenser conditions in a 3 stage pressure compounded turbine are 40 bar and 400 C at inlet and 0.1 bar and 0.87 dryness fraction at outlet. After expansion in the first stage the steam conditions are 12 bar and 250 C. After expansion in the second stage steam is at a pressure of 2 bar and a quality of 0.98. Find the work done in each stage and stage efficiency. Also find the overall efficiency and Reheat factor .

(11)The steam is supplied to a 3 stage turbine at 30 bar and 400 C. The steam leaves the first stage at 7 bar ,  second stage at 1.5 bar and finally at 0.1 bar. If  each stage has  an efficiency of 0.7,find  condition of steam , over all efficiency  and  reheat factor.

(12)In a 4 stage pressure compounded turbine the steam is supplied at 30 bar, 300 C. The exhaust pressure is 0.1 bar and overall efficiency 0.72. Assuming that the work is equally divided between stages and the condition line to be straight, estimate the stage pressures, the stage efficiency and reheat factor.

13. Explain surging and stalling in compressors

14. Explain pumps in series and parallel.