JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II THERMAL ENGINEERING – I Previous Question Paper (December - 2017 - R15)
Part A is compulsory. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
List out the assumptions made for the analysis of thermodynamic air cycles.
Answer
The air behaves as an ideal gas following the relation PV = mRT, the specific heats remain constant throughout the cycle, no chemical reactions occur, and the cycle is considered a closed system with no friction or heat loss.
Define chemical fuel.
Answer
A chemical fuel is a substance that contains stored chemical energy, typically in the form of carbon and hydrogen, which is released as heat energy through a rapid oxidation process known as combustion.
What is the function of a flywheel?
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Define octane number.
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What is the effect of cut-off ratio on the efficiency of diesel cycle when the compression ratio is kept constant?
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What are the functions of piston rings?
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What is meant by positive displacement compressor?
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What is meant by pressure coefficient?
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Differentiate between refrigeration and air conditioning.
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What are the properties of good refrigerants?
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Unit I
Describe with a suitable sketch the two stroke cycle spark ignition engine. How its indicator diagram differs from that of four stroke cycle engine?
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Explain the essential properties of a lubricant.
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Unit II
Describe the phenomenon of detonation in S.I engines. How can it be controlled?
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Describe the phenomenon of auto ignition. Explain how it is responsible for knocking in S.I. engines.
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Unit III
Explain the commonly used laboratory method for the measurement of air consumption.
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Explain what is meant by volumetric efficiency of a compressor. Explain how clearance volume affects it. Discuss the effects of clearance upon the performance of an air compressor.
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Unit IV
Explain surging and choking of compressors.
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Free air of 20 m3/min is compressed from 1 bar to 2.2 bar. Find: a) the I.P required if the compression carried out in roots blower, b) if the compression is carried out in vane blower. Assume that there is 25% reduction in volume before the back flow occurs and, c) the isentropic efficiency in each case.
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Unit V
A refrigeration system of 10.5 tones capacity at an evaporator temperature of 12°C and a condenser temperature of 27°C is needed in a food storage locker. The refrigerant ammonia is sub cooled by 6°C before entering the expansion valve. The vapour is 0.95 dry as it leaves the evaporator coil. The compression in the compressor is of adiabatic type. Find (a) Condition of vapour at the outlet of the compressor (b) Condition of vapour at the entrance of the evaporator (c) COP and (d) The power required. Neglect valve throttling and clearance effect.
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A Freon-12 refrigerator producing a cooling effect of 20 kJ/s operates on a simple vapour compression cycle with pressure limits of 1.509 bar and 9.607 bar. The vapour leaves the evaporator dry saturated and there is no under cooling. Determine the power required by the machine.
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