# Question Paper Dec 2011

GUJARAT TECHNOLOGICAL UNIVERSITY

BE SEM- I  II Winter Examination-Dec.-2011

Subject Name: Elements of Mechanical Engineering

Instructions:

1. Attempt any five questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of Steam Tables and Mollier’s Chart is permissible

Q-1 (a) What is flow and non-flow process?                                                                                      3

(b)  Define : (i) Sensible heat                (ii) Enthalpy of evaporation                                            4

(iii) Heat of superheat            (iv) Dryness Faction.

(c) Calculate the enthalpy per kg of steam at 10 bar pressure and a temperature of 300 °C. 7 Find also the change in enthalpy if this steam is expanded to 1.4 bar and dryness fraction

of 0.8. Take specific heat of superheat steam equal to 2.29 kj/kgK.

Q-2 (a) What is adiabatic process? Prove with usual notations the law of governing adiabatic                 7

process process as PVY = Constant.

(b) 0.67 kg of gas at 14 bar and 290 °C is expanded to four times the original volum according 7 to the law PV13 = Constant.

Caluculate : (1) The original and final volume of the gas.

(2)  The final temperature of the gas .

(3)  The final pressure of the gas. Take R = 287 J/kgK.

Q-3 (a) Differentiate between petrol engine and diesel engine.                                                            3

(b)  Derive equeation for air standared efficiency of otto cycle.                                                    4

(c) In an ideal constant volume cycle the pressure and temperature at the beginning of the comperession are 97 kPa and 50 °C respectively. The volume ratio is 5. The heat supplied 7 during the cycle is 930 kj/kg of working fluid.

Calculate : (1) The maximum temperature attained in the cycle.

(2)  The thermal efficiency of the cycle.

(3)  Work done during the cycle/kg of working fluide.

Q-4 (a) State the function of the following :                                                                                      3

(1)    Pressure gauge

(2)    Fusible plug

(3)    superheater

(b)  With neat sketch describe the working of two stroke cycle petrol engine.                                 4

(c)  With neat sketch describe the construction and working of Cochran boiler.                               7

Q-5 (a) Give classification of governor. Explain working of any one with neat sketch.                          3

(b) Classify the centrifugal pump and explain with neat sketch the vertex type centrifugal              4 Pump.

(c) Classify the air compressor . Differentiate between reciprocating compressor and                     7 rotary compressor.

Q-6 (a) What is refrigerant? State the most widely used refrigerant.                                                     3

(b)  With neat sketch explain vapour compression refrigeration cycle.                                           4

(c)  Explain with neat sketch split air conditioner. State its advantages.                                         7

Q-7 (a) What is zeroth law of thermodynamics.                                                                                 3

(b)  With simple sketch explain working of disc clutch.                                                                4

(c)    Write short note on: Type of belt drive.                                                                               7