BE (2nd Semester)
Examination Nov-Dec- 2006
Basic Mechanical Engineering
1. (a) what do you mean by international temperature scale?
Distinguish clearly between the following:
(i)Closed system and open system.
(ii)Heat and work.
(iii) Point function and path function.
(iv) Enthalpy and internal energy
(b) Find the final temperature, pressure, work done and heat transfer if the fluid is compressed reversibly from volume 12 m3 to 2 m3 when the initial temperature and pressure of fluid are 20°C and 1 bar. The index of compression may be assumed as and 1.40 respectively.
Take Cp = 1.005 and Cv = 0.718 and R = 0.287 kJ/kgK .
2. (a) Define Clausius Inequality and prove it.
Define entropy and show that it is a property of the system.
(b) A diesel engine working on diesel cycle takes air at pressure 1 bar and temperature 30° C. The pressure at the end of compression is 30 bar and the cut-off is 6.02% of the stroke. Calculate:
(i) The compression ratio
(ii) The percentage clearance
(iii) The heat supplied
(iv) The heat rejected
(v) The thermal efficiency
(vi) The mean effective pressure.
Take = CP=1.005 and CV = 0.718 kJ/kg K.
3. (a) Explain why safety valves are needed in boiler? Draw a neat sketch of spring loaded safety valve and explain its working.
What do you understand by “Draught”? What are the different methods of producing draught?
(b) A vessel of volume 0.04 m3 contains a mixture of saturated water and saturated steam at a temperature of 250°C. The mass of the liquid present is 9 kg. Find the pressure, the mass, the specific volume, the enthalpy, the entropy and the internal energy.
4. (a) What is meant by fluxing? Why is it done? And illustrate about the properties of a good flux.
State the important functions of flux coating of electrodes used in manual metal arc welding process.
(b)Explain with the help of neat sketch, the principle of working of lathe. What is the lathe carriage? Explain its parts with the help of neat sketch.
5. (a) Prove that the volumetric strain of a cylindrical rod which is subjected to an axial tensile load
is equal to strain in the length plus twice the strain of diameter.
Derive an expression for volumetric strain for a rectangular fear which is subjected to
Three mutually perpendicular tensile stresses.
(b) A brass bar, having cross-sectional area of 1000mm2,is subjected to axial forces as shown in fig.1
Find the total change in length of the bar.
Take E= 1.05* 105N/mm2.