Pte 13ME36 (To be filed by the candidate) (2013 batch onwards) COIMBATORE INSTITUTE OF TECHNOLOGY (Government Aided Autonomous Institution) COIMBATORE 641 014 BE. DEGREE EXAMINATIONS, APRIL 2017 (Third Semester) MECHANICAL ENGINEERING BRANCH 13ME36 APPLIED THERMODYNAMICS. (Common to PT BE Mech. IIt Sem.) Time : 3 Hours + Max: 75 marks INSTRUCTIONS, Answer all questions in Part A and as per choice in PART B. Part A and Part B questions should be answered separately in the same answer sheet. Question No.11 is compulsory. | Approved Steam tables, Refrigeration Tables and Mollier chart are permitted. PAaRTA (0 xX2=20) . Define the term mean effective pressure. ‘Write the principle of supercharging. ‘What are the effects of clearance on volumetric efficiency in reciprocating air compressors? Distinguish between isentropic and isothermal efficiencies in air compressors. “What are the advantages of regeneration in gas turbine power plants? ‘Name any four fuels used in gas turbines. Distinguish between reheat and regeneration in steam turbine power plants. ‘What are the effects of friction in steam nozzles? ‘What are called azeotropic refrigerants? (0. How will you define by-pass factor in air conditioner? PARTB (5X 11=55) (Q.No. 11 is compulsory) No ae pre sae see 11. A 4-cylinder two-stroke cycle petrol engine develops 30 kW at 2500 rpm. The mean effective pressure on each piston is 8 bar and mechanical efficiency is 80%, Calculate the diameter and stroke of each cylinder of stroke to bore ratio 1.5. Also calculate the fuel consumption of the engine, if brake thermal efficiency is 28%, The calorific value of the fuel is 43900 ki/ke. , 12. A single acting two stage compressor with complete intercooling delivers 10.5 kg/min of air at 16 bar. The suction occurs at 1 bar and 27 °C. The compression and expansion processes are reversible, polytropic index n=1,3, Caleulate: (i) The power required to drive the compressor The isothermal efficiency : (iii) The free air delivery (iv) The heat transferred in intercooler ‘The compressor runs at 440 rpm (0) Ifthe clearance ratios for L.P and HLP cylinders ae 0.04 and 0.06 respectively, calculate the swept and clearance volumes for each cylinder. cor) Contd...13. The requirement is to compress air at 1 bar and 25 °C and deliver it at 160 bar using multi-stage compression and intercoolers. The maximum temperature during compression must not exceed 125 °C and also cooling in the intércooler is done so as not to drop the temperature below 40 °C. The law of compression followed is pv’? = constant for al stages. Calculate: (@) Number of stages required ii) Work input per kg of air, and Heat rejected in the intercoolers. Take R=0.287 ki/kg K, Cy= 0.71 kivkg K. 14.Find the required air fuel ratio in a gas turbine whose turbine and compressor efficiencies are 85% and 80%, respectively. Maximum cycle temperature is 875 °C. The working fluid can be taken as air (Cp = 1.0 ki/kg K, y = 1.4) which enters the compressor at 1 bar and 27°C. The pressute ratio is 4. The fuel used has calorific value of 42000 kifkg, There is a Joss of 10% of calorific value in the combustion chamber. (OR) 15. In a gas turbine the compressor is driven by the high pressure turbine. The exhaust from the high pressure turbine goes to a free low pressure turbine which runs the load. The air flow rate is 20 ke/s and the minimum and maxinum temperatures are respectively 300 K and 1000 K. The compressor pressure ratio is 4. Calculate the pressure ratio of the low pressure turbine and the temperature of exhaust gdses from the unit, The compressor and turbine are isentropic. Cp of air and exhaust gases = 1 ki/kg K and y= 1.4. 16. An impulse turbine having a set of 16 nozzles receives steam at 20 bar, 400 °C. The pressure of steam at exit is 12 bar. If the total discharge is, 260 kg/min and nozzle efficiency is 90%, find the cross sectional area of the exit of each nozzle. If the steam has a velocity of 80 m/sec at entry to the nozzles, find the percentage increase in discharge. (OR) 17. @) Iustify the statement “Nozzles are more efficient than diffusers”. @) (b) Derive the following expression for nozzle flow: @) ’ da _ 1 dp [oa A yp| M ‘The symbols have -usual meanings. 18. A vapour compression reftigerator uses R-12 as refrigerant and the liquid evaporates in the evaporator at -15 °C, The temperature of this refrigerant at the delivery from the compressor is 15 °C when the vapour is condensed at 10 °C. Find the coefficient of , performance, if @) there is no undereooling (i) the liquid is cooled by 5 °C before ~* expansion by throttling. “Take Cpat constant pressure for the superheated vapour as 0.64 ki/kg K and that for liquid as 0.94 ki/kg K. The other properties of refrigerant are as follows: Enthalpy (/kg) _ Specific Ent Tk Temperature °C |——~Tiguid "Vapour Liquid ‘Vapour -15 22.3 180.88 0.0904 0.7051 10 45.4 191.76 0.1750 0.6921. (OR)13ME36 19.A commercial refrigerator operates with R-I2 between!.2368 bar and 13.672 bar. The vapour is dry and saturated at the compressor inlet. Assuming isentropic compression, determine the theoretical coefficient of performance of the plant. The isentropic discharge temperature is 64.86 °C. If the actual coefficient of performance of the plant is 80% of the theoretical, calculate the power required to run the compressor to obtain a reftigerating capacity of 1 TR. If the liquid is subcooled through 10 °C after condensation, calculate the power required. The properties of R-12 are Saturated Enthalpy (ki/kg) Entropy (kikg K) Temperature |, Saturated Co) Pressure (bar) Liquid Vapour Liquid Vapour 23 1.2368 1333__|_176.48_| 0.055 [0.7126 35 13.672 90.28 [207.95 | 0.3197 | 0.6774 Properties of superheated R-12 Enthaly Er Tempacras | mresurecou) | Tata | amor 64.86 13.672 220.6 0.7126 Assume specific heat of liquid to be 1.055 ki/kg K. KX