JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II THERMAL ENGINEERING I Previous Question Paper (December - 2017 - R13)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks and may have a, b, c as sub questions.
Part A
List out the assumptions made for the analysis of thermodynamic air cycles.
Answer
The common assumptions are: the working fluid is a fixed mass of air behaving as an ideal gas, all processes are internally reversible, combustion is replaced by a heat addition process from an external source, and the exhaust process is replaced by a heat rejection process to the surroundings.
Define chemical fuel.
Answer
A chemical fuel is a substance containing chemical energy that can be released through a chemical reaction, such as combustion with oxygen, to produce heat or perform work.
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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Part B
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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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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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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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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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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