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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER-VIII EXAMINATION WINTER 2017
Subject Code: X81901 Date:02/11/2017
Subject Name: Thermal Engineering
Time:02:30PM TO 5:00PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of Steam table and mollier chart are permissible.
Q.1

What is critical Pressure? Derive the expression of critical pressure ratio to have maximum mass flow for a nozzle. Explain also its significance. Consider expansion of steam is isentropic.
07

Explain the effect of variation of back pressure in a convergent-divergent nozzle.
07
Q.2

What do you mean by compounding of steam turbine? State types of it and explain any one in detail.
07

A steam nozzle is to be designed for a mass flow rate of 8 kg/s of steam from 8 bar and 350°C to a back pressure of 1 bar. The nozzle efficiency is 0.93 and the frictional loss is assumed to take place in the diverging portion of the nozzle only. Assume a critical pressure ratio of 0.5457. Determine the throat and exit area.
07
OR

Steam issues from the nozzle at angle of 22° at a velocity of 450m/s. The friction factor is 0.86. for a single stage turbine designed for maximum efficiency, Calculate: the blade velocity the moving blade angles for equiangular blades the blade efficiency the stage efficiency if nozzle efficiency is 94% the power developed for a mass flow rate of steam of 5 kg/s.
07
Q.3

Define degree of reaction. For reaction turbine, derive relationship of degree of reaction with velocity of flow, blade velocity and blade angles.
07

Explain Reheating cycle used for steam turbine with neat sketch. State its advantages and disadvantages.
07
OR
Q.3

Why governing of steam turbine is required? Explain throttle control governing with neat sketch.
07

Explain regenerative feed heating by bleeding process used for steam turbine.
07
Q.4

Compare between open cycle and close cycle gas turbine.
07

Air enters the compressor of an open cycle, constant pressure gas turbine at 1 bar pressure and 27°C temperature. The pressure of air after compression becomes 4 bar. The isentropic efficiencies of compressor and turbine are 78% and 84% respectively. The air fuel ratio use is 75:1. If the rate of flow of air is 2.5 determine the power developed and thermal efficiency of the cycle. Take Cp= 1.005 kJ/kg K and both for air and gases. The calorific value of fuel used =42000 kJ/kg.
07
OR
Q.4

Discuss the effect of operating variables on thermal efficiency of gas turbine.
07
2

In an open cycle regenerative gas turbine power plant the air enters the compressor at 1 bar and 27°C. The pressure ratio and maximum cycle temperature 6.5 and 727°C respectively. The isentropic efficiencies of compressor and turbine are 0.85 and 0.86 respectively. The combustion efficiency and regenerative effectiveness are 92% and 0.62 respectively. Calculate thermal efficiency air rate and work ratio.
07
Q.5

Explain pass out turbine with neat sketch.
07

Draw schematic diagrams T-S diagram of following gas turbine cycle
Open cycle gas turbine with reheating
Open cycle gas turbine cycle regeneration
Open cycle gas turbine cycle with inter cooling, reheating and regeneration
07
OR
Q.5

Explain the turbojet Engine with T-S diagram. Draw variation of pressure, temperature and velocity across the turbojet engine components.
07

Explain with a neat schematic diagram combined (steam and gas) cycle power plant. State its merits.
07