BE (2nd Semester)
Examination Nov-Dec- 2007
Basic Mechanical Engineering
- (a) Define intensive property and extensive property and give one example of each.
Attempt any two parts of the following :
(b) Explain the following terms with necessary examples
(i) Control volume
(ii) Closed system
(iii) Zeroth Law
(c) Air at 30°C and 1 bar is compressed reversibly and polytropically from 5 m3 to 1 m3. Calculate the final temperature pressure, work done and the 4 heat transferred it the index of compression is 0.9. Assume Cp = 1.005, ; and C = 0.7178 kJ/kg K. P
(d) Air flows steadily at the rate of 0.5 kg/s through an air compressor, entering at 7 m/s velocity, 100 k Pa pressure, and 0.95 m3/kg volume, and leaving at 5 m/s, 700 kPa, and 0.19 m3/kg. The internal energy of the air leaving is 90 kJ/kg greater than that of air entering. Colling water in the compressor jackets absorbs heat from the air at the rate of 58 kW, Compute the rate of shaft, work input to the air in kW.
2. (a) Write Kelvin-Planck statement of Second Law of Thermodynamics.
(b) Show that all the reversible engines operating between the same source and sink will have the same efficiency.
One kg of water at 273 K is brought into contact, with a heat reservoir at 373 K. When the water has reached 373 K, find the entropy change of the water, of the heat reservoir, and of the universe. Take CP =4.187.
(c) Explain the working of vapour compression refrigeration cycle with the help of T-s and P-h diagrams.
In an Otto cycle, the temperature and pressure in the beginning of compression 310 K and 1 bar, respectively. The compression ratio and the maximum cycle temperature are 8 and 1500 K. Calculate the ajr standard efficiency, net work output and th6 mean effective pressure.
3. (a) What is saturated staem?
(b)Two kg of steam at a pressure of 20 bar exists in the following conditions :
(i)Wet steam with a dryness fraction of 0.9.
(ii)Superheated steam with temperature 250°C.
Calculate enthalpy and entropy with the help of steam table.
Take Cp = 2.302kj/kg K for superheated steam.
3 kg of steam at 10 bar and 2500 C undergoes a constant pressure process. The resulting steam is wet having dryness fraction 0.6. Calculate the
(i) Work done (ii) Change in enthalpy.
Assume non-flow process.
(c) How do you classify boilers? Give the list of boiler mountings and accessories.
4. (a) Write the name of gases used in gas welding.
(b) Draw and explain stress and strain curve for ductile and brittle materials . Mention different points of importance.
(c) How lathes can classify and write specification of any lathe.
5. (a) Define stress and strain.
(b)Find the relation between Bulk Modulus and Youns’s Modulus.
(c)The following data refer to a tensile test conducted on a mild steel bar:
(i)Diameter of the steel bar – 30 mm
(ii)Gauge length = 200 mm
(iii) Extension at a load of 100 kN is 0.139 mm
(iv) Load at elastic limit = 230 kN
(v) Maximum load 360 kN
(vi)Total extension 56 mm
(vii) Diameter of the rod at failure 22-25. mm
(1) The young’s Modulus (2) The percentage elongation (3) The percentage decrease in area.