S.E. (Mechanical) (First Semester) EXAMINATION, 2012 APPLIED THERMODYNAMICS (2008 PATTERN) Time : Three Hours Maximum Marks : 100


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1 Total No. of Questions 12] [Total No. of Printed Pages 8 Seat No. [4162]111 S.E. (Mechanical) (First Semester) EXAMINATION, 2012 APPLIED THERMODYNAMICS (2008 PATTERN) Time : Three Hours Maximum Marks : 100 N.B. : (ii) (iii) (iv) (v) (vi) Answer three questions from Section I and three questions from Section II. Answers to the two Sections should be written in separate answerbooks. Neat diagrams must be drawn wherever necessary. Figures to the right indicate full marks. Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. Assume suitable data, if necessary. SECTION I UNIT I 1. (a) Write a note on reversibility. [4] Prove that KelvinPlanck statement and Clausius statement are equivalent. [6] P.T.O.
2 At steady state, a refrigerator cycle removes 18,000 kj/h of energy by heat transfer from a space maintained at 40ºC and discharges energy by heat transfer to the surroundings at 20ºC. If the actual COP of the cycle is 25% of that of the theoretical cycle operating between thermal reservoirs of these two temperatures, determine power input to the cycle in kw. [6] 2. (a) Write a note on Principle of Increase of Entropy. [4] State and prove Clausius Inequality. [8] Two kg of air is heated at constant pressure of 200 kpa to 500ºC. Calculate entropy change if the initial volume is 0.8 m 3. [4] UNIT II 3. (a) Derive an expression for available energy of nonflow system. [6] Sketch the following processes on PV and TS planes : Reversible adiabatic (ii) Isothermal. [4] [4162]111 2
3 0.25 kg of air at a pressure of 140 kn/m 2 occupies 0.15 m 3 and from this condition is compressed to 1.4 MN/m 2 according to 1.25 PV = C. Determine : Change in internal energy of air (ii) Work done and (iii) Heat transfer. [6] 4. (a) Prove that reversible adiabatic ideal gas process law is K PV = C where K is ratio of specific heats. [6] Explain : Helmholtz function (ii) Gibbs function. [4] One kg of air is contained in a rigid tank at 500 kpa and 700 K. Calculate maximum useful work : if the system changes to dead state (ii) when the air is cooled in tank to 400 K. Take dead state as 20ºC and 100 kpa. [6] 5. (a) Define : UNIT III Dryness fraction at wet steam (ii) Degree of superheat. [4] [4162] P.T.O.
4 Explain Rankine cycle with TS diagram. [6] Two kg of saturated steam is contained in 0.2 m 3 rigid vessel. Heat is transferred to the surroundings at 30ºC until the quality reaches to 20%. Calculate work done, entropy change and heat transfer. [8] 6. (a) Explain separating calorimeter with the help of a neat sketch. Show the process on hs plane. [8] Define : Work ratio (ii) Specific steam consumption. [4] A Carnot vapour power cycle operates between 20 kpa and 800 kpa steam pressures. Calculate net work per cycle and cycle efficiency. [6] SECTION II UNIT IV 7. (a) Explain the method of writing the complete combustion equation of a fuel with air with the help of an example. [5] Differentiate between mass fraction and mole fraction. [5] [4162]111 4
5 In a bomb calorimeter the following observations were recorded : Weight of coal tested = 3.0 gm Weight of water in the calorimeter = 1.4 kg Water equivalent of calorimeter = 0.9 kg Rise in temperature of jacket water = 9ºC The coal contains 3% moisture by weight and room temperature is 25ºC. If one kg of moisture at 0ºC requires 2470 kj to evaporate to form dry and saturated steam, calculate the lower calorific value of coal. [6] 8. (a) Name the apparatus used for measurement of C.V. of gaseous fuels and discuss its working with the help of neat sketch. [8] A sample of fuel has the following percentage composition C = 86%, H 2 = 8%, S = 3%, O 2 = 2% and Ash = 1% for an airfuel ratio of 12 : 1. Calculate : Mixture strength as a percentage rich or weak (ii) Volumetric analysis of dry products of combustion. [8] [4162] P.T.O.
6 UNIT V 9. (a) Discuss the different methods of capacity control used for reciprocating compressor. [6] Define clearance ratio in air compressor. What is its effect on work and volumetric efficiency? [4] A single stage single acting reciprocating air compressor has air entering at 1 bar, 20ºC and compression occurs following polytropic process with index 1.2 up to delivery pressure of 12 bar. The compressor runs at the speed of 240 rpm and has L/D ratio of 1.8. The compressor has mechanical efficiency of Determine the isothermal efficiency and cylinder dimensions. Also find out the rating of drive required to run the compressor which admits 1 m 3 of air per minute. [8] 10. (a) Draw PV and TS diagram for a single stage reciprocating air compressor without clearance. Derive the expression for work done when compression is : Isothermal and (ii) Isentropic. [6] Explain the working of Root blower with a neat sketch. [4] [4162]111 6
7 A reciprocating air compressor has four stage compression with 2 m 3 /min of air being delivered at 150 bar when initial pressure and temperature are 1 bar 27ºC. Compression occur polytropically following polytropic index of 1.25 in four stages with perfect intercooling between stages. For the optimum intercooling conditions determine the intermediate pressures and the work required for driving compressor. [8] UNIT VI 11. (a) Explain with neat sketches fusible plug and superheater. [8] A boiler uses 1350 kg of coal per hour. The temperature of flue gases is 660 K and outside ambient temperature is 300 K. If the draught produced by 30 m high chimney is 18 mm of water column. Determine : Air supplied per kg of coal burnt and (ii) Base diameter of the chimney. [8] 12. (a) Define equivalent evaporation from and at 100ºC and the boiler efficiency. [4] What is IBR? Explain some of its provisions. [4] [4162] P.T.O.
8 The following data relate to a trial on boiler using economiser, air preheater and superheater : Condition of steam at exit of boiler = 20 bar and 0.96 dry (ii) Temperature of steam at exit of superheater = 300ºC (iii) Steam evaporation rate/kg of fuel = 13 kg (iv) Room temperature = 30ºC (v) Temperature of feed water at exit of economiser t 1 = 50ºC. (vi) Temperature of air at exit of air preheater, t a = 70ºC, the temperature of flue gases at inlet to superheater, economiser, air preheater and exit of air preheater are 650ºC, 430ºC, 300ºC and 180ºC respectively. Assume that air supplied is 19 kg/kg of fuel of C.V. of 45,000 kj/kg. Find : (a) equivalent evaporation with and without economiser from and at 100ºC. Thermal efficiency of boiler with and without economiser. Thermal efficiency of superheater, economiser and air preheater. [8] [4162]111 8