BE (2nd Semester)
Examination Nov-Dec- 2009
Basic Mechanical Engineering
1. (a) Define thermodynamic work. How does it differ from work in mechanics?
(b)Define internal energy of the system. Show that the internal energy is a property of the system.
(c)During an expansion process, the pressure of a gas change from 103 kPa to 689 kPa according to the relation, p= aV + b, where a = 1230 kPa/m3 and b is constant. If the initial volume of gas is 0.198 m . Calculate the work done during the process.
(d) Steam enters a steam turbine with a velocity . of 40 m/sec, enthalpy 2500 kJ/kg and leaves with a velocity of 90 m/sec and enthalpy 2030 kJ/kg. Heat loss from the turbine insulation to the surrounding are 2400 kJ/min and the steam flow rate is 7200 kg/hr. Find the power developed by the turbine in kW. Neglect change in potential energy.
2. (a)What are the causes of irreversibility of a process ?
(b)Write Kelvin-Plank and Clasius statements of the second law of thermodynamics, and establish equivalence between them.
(c)Two identical body of mass m and specific heat Cp are at temperature T1 and T2 (T, > T2). A heat engine is operated between these two bodies to obtain maximum possible work W max until both the body attained a lowest possible temperature Tf show that
Tf= √T1T2 And W max= mc P (√T1-T2)2
(d) In an air standard dual cycle, the compression ratio is 15. Compression begins at 0.1 MPa, 40°C. The maximum pressure is limited to 6 MPa and the heat added is 1.675 MJ/kg. Compute
(i) the heat supplied at constant volume per kg of air.
(ii) the heat supplied at constant pressure per kg of air.
(iii) the work done per kg of air.
(iv)the cycle efficiency.
(v)the temperature at the end of constant volume heating.
(vi)the cut-off ratio.
(vii) them e.p. of the cycle.
3. (a)Define boiler draught. How natural draught is produced?
(b) One kg of steam at a pressure of 20 bars exist in the following conditions.
(i) Dry and saturated
(ii) Dryness fraction, x = 0.9.
(iii) Degree of superheat = 37.6°C Calculate
(vii) Internal energy for each condition of the steam. Use steam table.
(c) Draw the phase equilibrium diagram on p-v co-ordinate for water and label it completely. Also show triple point and critical point on the phase diagram and explain it.
(d) Describe the function of air preheater, economizer and superheater. Sketch a block diagram showing relative position of these accessories with respect to boiler and indicate flow path of air flue gas and water on it.
4. (a) Define welding and weldability.
(b) What is oxyacetylene gas welding? Compare low pressure gas welding and high pressure gas welding on the basis of storage of acetylene, acetylene pressure and design of welding torch.
(c) Classify welding electrode. Explain the function of flux coating on welding electrode.
(d)How is a lathe specified? Explain with a neat sketch relevance of each of the specification points.
5. (a) Differentiate between ducite material and brittle material and give two examples of each.
(b) Define the following terms:
(i) Elastic Limit.
(ii) Modulus of elasticity Lateral strain.
(iii) Lateral strain.
(iv) Poisson’s ratio.
(v) Volumetric strain calculate:
(vi)Modulus of rigidity
(vii) Bulk modulus
(c) The following data relate to a bar subjected to a tensile test within elastic limit
Diameter of the bar d= 40 mm
Tensile load P= 102 kN
Gauge length l= 30 mm
Extension of the bar ᵟl= 0.12mm
Change in diameter ᵟd=0.0052mm
(i) Linear strain
(ii) Lateral strain
(iii) Modulus of elasticity
(iv) Poisson’s ratio
(v) Modulus of rigidity
(vi) Bulk modulus
(d) The bar shown in figure is subjected to a tensile load of 100 kN. Find the diameter of the middle portion if the stress is limited to 150 MN/m2. Also find the length of the middle portion if the total elongation of the bar is 0.22 mm. Take modulus of elasticity 200 CN/m2.