JNTU
JNTU B.Tech IV Year I Semester TURBO MACHINERY Previous Question Paper (February/March - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Show that for a perfect gas when it is adiabatically decelerated stagnation temperature is
Answer
For an adiabatic flow of a perfect gas, the energy equation derived from the steady flow energy equation (SFEE) between a point in the flow (static state T, V) and the stagnation point (stagnation state T0, V=0) is given by:
Since h = cpT and h0 = cpT0, this becomes:
Dividing by cpT:
Using the relations cp = (γR) / (γ - 1) and the speed of sound a = √(γRT), we have:
Substituting the Mach number M = V/a:
Show that the discharge through a nozzle is maximum when there is sonic condition at its throat.
Answer
The mass flow rate through a nozzle is given by m = ρAV. Using the isentropic flow relations, the mass flow rate can be expressed in terms of the stagnation pressure P0, stagnation temperature T0, and Mach number M:
To find the condition for maximum discharge, we differentiate the mass flow rate with respect to M and set the derivative to zero (dm/dM = 0). This differentiation leads to the condition:
This implies M = 1 at the section where the area A is minimum (the throat). Thus, the flow velocity at the throat is equal to the local speed of sound (sonic condition). This state is known as choked flow, where the mass flow rate reaches its maximum value for a given set of stagnation conditions.
Define critical pressure ratio? From fundamentals, derive the expression relating the critical pressure ratio to the index of expansion ‘n’ for expansion in nozzles?
Answer
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The inlet and exit conditions of steam supplied to a nozzle has enthalpy 3210 kJ/kg and 2930 kJ/kg. Taking velocity at inlet as 60 m/s. Find:
i) the exit velocity of steam
ii) mass flow rate of an inlet area of 0.1 m2 and specific volume of 0.19 m3/kg inlet. Neglect the effect of friction?
Answer
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Differentiate between (i) Radial and Axial flow machines (ii) Inward and Outward radial flow machines.
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Explain in detail the phenomenon of cavitation in pumps and also give the necessary precautions against cavitation?
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A centrifugal pump rotating at 1000 rpm delivers 160 litres/s of water against a head of 30 m. The pump is installed at the place where atmospheric pressure is 1 × 105 Pa (abs.) and vapour pressure of water is 3 kPa (abs.). The head loss in suction pipe is equivalent to 0.2 m of water then calculate:
(a) Minimum NPSH
(b) Maximum allowable height of the pump from free surface of the water in the sump?
Answer
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Explain the terms slip factor and power input factor as applied to centrifugal compressor.
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The free air delivered by a centrifugal compressor is 20 kg/min. The suction condition is 1 bar and 20°C. The velocity of air at the inlet is 60 m/s. The isentropic efficiency of the compressor is 0.68. If the total head pressure ratio of compressor is 3. Determine:
(i) The total head temperature of air at the exit of the compressor and
(ii) Power required to run the compressor assuming mechanical efficiency of 96%.
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Distinguish between normal shock and detached shock.
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The following data is pertaining to a centrifugal compressor: Overall diameter of the impeller - 60 cm; Speed - 14000 RPM; Slip factor - 0.9; Power input factor - 1.04; Eye tip diameter - 35 cm; Eye root diameter - 20 cm; Total mass flow - 20 kg/s; Inlet total head temperature and pressure - 25°C and 1.01 bar; Total head isentropic efficiency - 82%. Determine the total head pressure ratio and power required to drive the compressor, if the velocity of air at inlet is axial.
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At 1.02 bar and 30°C, air enters an axial flow compressor stage with an axial velocity of 180 m/s. The rotor stage has a tip diameter of 0.55 m and hub diameter of 0.5 m and rotates at a speed of 6500 RPM. The air enters the rotor and leaves the stator in the axial direction with no change in velocity or radius. The air is turned through 30° as it passes through rotor. Assuming constant specific heats and that the air enters and leaves the blade at the blade angles. Determine:
(i) mass flow rate
(ii) power requires
(iii) degree of reaction
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Explain the concept of surging in an axial flow compressor.
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Explain the working of a closed cycle gas turbine unit with flow diagram and T-s diagram.
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What are the advantages and dis-advantages of a closed cycle gas turbine over open cycle gas turbine?
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