JNTU
JNTU B.Tech II MECHANICAL TECHNOLOGY Previous Question Paper (November/December - 2018 - 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
Explain why a roller follower is preferred to a knife edge follower.
Answer
A roller follower is preferred because it replaces sliding friction with rolling friction, which significantly reduces wear and tear on the cam surface. Additionally, it can withstand higher loads and operates more smoothly at higher speeds compared to a knife-edge follower.
Define the terms of angle of decent, angle of ascent and dwell.
Answer
Angle of ascent: The angle through which the cam rotates while the follower moves from its lowest position to its highest position.
Angle of descent: The angle through which the cam rotates while the follower returns from its highest position back to its lowest position.
Dwell: The period during which the follower remains stationary while the cam continues to rotate.
What is the effect of centrifugal tension on power transmission capacity of belt?
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What do you mean by chordal action?
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What do you mean by law of gearing? Define conjugate action.
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What do you mean by reverted gear train?
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What is the difference between the two stroke and four stroke engines?
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What is scavenging process?
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When is multi stage compression used for air?
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What is difference between the centrifugal and axial compressor?
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Part B
A tangent cam with straight working faces tangential to base circle of 50 mm diameter has a roller follower of 20 mm diameter. The line of stroke of the roller follower passes through the axis of the cam. The angle between the tangent faces of the cam is 60°. The speed of the cam is 200 rpm, and the lift of the follower is 15mm. Sketch the cam and determine:
The main dimensions of the cam
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The acceleration of the follower: i) At the beginning of the lift ii) Where the roller touches the nose.
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Draw the cam profile for following conditions: Follower type = Knife edged, in-line; lift = 50 mm; base circle radius = 50 mm; out stroke with SHM, for 60° cam rotation; dwell for 45° cam rotation; return stroke with SHM, for 90° cam rotation; dwell for the remaining period. Determine maximum velocity and acceleration during out stroke and return stroke if the cam rotates at 1000 rpm in clockwise direction.
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A leather belt required to transmit 10 kW with 1m diameter pulley running at 300 rpm. The angle of contact is 160° and coefficient of friction between belt and pulley is 0.32. If the allowable strength of belt is 1.25 N/mm2 and the belt thickness is 10mm, determine the width of the belt. Density of belt material is 1000 kg/m3.
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A V-belt having lap angle of 165° has a cross section area of 240 mm2 and runs in a groove of included angle 40°. The mass density of belt is 1500 kg/m3. The maximum stress is limited to 4 MN/m2. Find the maximum power that can be transmitted by two such belts. Take µ is 0.145. Find also the shaft speed at which power transmitted would be maximum if pulley diameter is 600 mm.
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A gear wheel having 20 teeth of involute form of module pitch 6mm with an angle of obliquity of 20°, drives another wheel of the same dimensions. Calculate:
The length of the arc of contact if the addendum is one module.
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If the addendum was altered so that the arc of contact was the maximum possible what would be the length of this arc, and the addendum required for this condition.
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An epicyclic gear train is composed on a fixed annular wheel having 150 teeth. Meshing with A is a wheel B which drives wheel D through an idle wheel C, D being concentric with A. Wheels B and C are carried on an arm which revolves clockwise at 100 rpm about the axis of A and D. If the wheels B and D have 25 and 40 teeth respectively. Find the number of teeth on C and the speed and sense of rotation of C.
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Explain briefly Otto cycle with the help of p-v and T-S diagram and derive an expression for ideal cycle efficiency.
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A four stroke petrol engine with a compression ratio of 6.5 to 1 and total piston displacement of 5.2×10-3 m3 develops 100kW brake power and consumes 33kg of petrol per hour of calorific value 44,300kJ/kg at 3000 rpm. Find brake mean effective pressure, brake thermal efficiency and air standard efficiency (γ=1.4) and air fuel ratio by mass. Assume a volumetric efficiency of 80%. One kg of petrol vapour occupies 0.26m3 at 1.013bar and 15°C take R for air 287J/kg K.
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Explain the working principle of single stage reciprocating air compressor, without clearance. Derive an expression for the work done when compression is isothermal and isentropic.
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A rotary vane compressor compresses 4.5 m3 of air per minute from 1 bar to 2 bar when running at 450 rpm. Find the power required to drive the compressor when:
The ports are so placed that there is no internal compression and
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The ports are so placed that there is 50% increase in pressure due to compression before the backflow occurs.
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