BTME 20 Third Semester B. Tech Mechanical Engineering Examination July/August 2012 Thermodynamics Time:-3Hours Max. Marks: - 75 SECTION-A Attempt any five Questions. (5*5) 1. Define atomic mass and molecular mass. 2. Derive the combustion equation of gas ears fuel. 3. A producer gas used as a fuel has the following volumetric composition H2 28%, CO12%, CH4 2%, co2 16% and N2 42 %. Find the volume of air required for complete contusion of 1m(3) this gas. Air contains 21% by volume of oxygen. 4. Derive the general expression for change of entropy of a perfect gas. 5. 0.5 kg of a perfect gas is heated from 100’c to 300˚c at a constant pressure of 2.8 bars. It is then cooled to 100˚c at constant volume. Find the overall change in entropy take cp=1KJ/KG k and cu=0.72 kj/kg k. 6. 1 kg of air occupier 0.084 m³ at 12.5 bar and 537˚c. it is expanded at a constant temperature to a final volume of 0.336m³. Calculate. 7. Explain the working of single stage reciprocating system. SECTION-B Attempt any two Questions. (10*2) 8. Explain in brief about magneto ignition system. 9. Two boilers discharge equal amounts of steam in to the same main. The steam from one is at 18 bars and 380˚c, and from the other at 18 bars and 0.95 qualities. Determine the equilibrium conditions, after mixing 2, the loss of entropy by the high temperature steam, 3. The gain in entropy by the low temperature steam, and 4. Net increase or decrease of entropy. 10. What is super heater? Explain in brief. SECTION-C Attempt any two Questions. (15*2) 11. A 30m high chimney is used to discharge hot gasses at 297˚c to the atmosphere which is at 27˚c find the mass of air actually used per kg of fuel, if the draught produced is 15mm of water. If the cool burnt in the combustion chamber contains 80% carbon, 6%moisture and remaining ash, determine the percentage of excess air supplied. 12. A steam turbine receives super heated steam at a pressure of 17 bars and having a degree of superheat of 110˚c. The exhaust pressure is 0.07 bar and the expansion of steam takes place is entropic ally. Calculate 1. The heat supplied 2. The rejected, 3.net work done and 4, the thermal efficiency. 13. Determine the cylinder dimensions of a double acting , 11 kw indicated power, air compressor which compressor air from 1 bar to 7 bar according to the law pu (1.4)= constant. The average piston speed is 150m/s. assume stroke to diameter ratio of 1.5 and neglect clearance.