ou 43ME36 Pea mir Dye canitiee) (2013 - 2014) COIMBATORE INSTITUTE OF TECHNOLOGY (Government Aided Autonomous Institution) COIMBATORE 641 014 B.E. DEGREE EXAMINATIONS, APRIL 2018 (Third Semester) MECHANICAL ENGINEERING BRANCH |3ME36 APPLIED THERMOD’ (Common to P.7.B.E. Mech Il! Sem) Time : 3 Hours Max: 75 Marks STRUCTIONS ‘Answer all questions In Part A and as per choice in Part B. Part A and Patt B questions should be answered separately in the same answer sheet. ‘Question No.11 is compulsory. ; Use of Steam Tables, Refrigerant Tables, and Charts is.permitted. ‘Answers without proper units will be penalized. ae No Note: con {(@) For ideal gas air, R= 0.287 kJIkg-K, cp (©) For liquid water, cy = 4.2 kukg-K 1.005 kuikg-K, and y= 1.4 PART-A (10 x 2 = 20) 1. An air-conditioner rated for 5.25 KW of cooling effect operates for 8 hours each day with a COP . of 2.8, Electricity for the compressor costs Rs. 5.25 per kWh. Calculate the minimum monthly cost of operating this air-conditioner (1 month = 30 days). 2. For every kilo-joule of heat extracted from the cold space, estimate the minimum work required in an R-134a vapor compression cycle operating between 0.2 MPa ant 1.2 MPa. *3. Sketch an air-standard Otto cycle and an air-standard Diesel cycle in-T-s coordinates. In each sketch, number the end states for each process and identify those processes in which heat transfers take place. 4. Does the thermal efficiency of an ideal Brayton cycle increase, decrease, or remain the same if the specific heats ratio of the working fluid is decreased? 5. How is regeneration implemented in a gas turbine cycle? Why is it necessary? 6. Explain why reheating of stem tielps to improve the thermal performance of a basic Rankine oycle. : 7. What is cogeneration? How does cogeneration‘differ from combined-cycle, power generation? ‘8, What ié the minimum pressure in MPa above which steam should exist for a power cycle to be classified as a supercritical pressure cycie? What restrictions dictate the maximum steam pressure attainable in such a cycle? 9. Mention the role of friction in thé flow of steam through a nozzle. 40. Identify the difference between closed-type and open-lype feed water heaters. TB (14. 41, (ay Aone cylinder, single acting, 4-stroke engina.with a 15 cm bore rugs at 240 RPM. The area ofits indicator diagram is $05 mm? with a length that is 0.1 times the-engine stroke. The “spring constant’ of the indicator mechanism is 25 N/cm®. Find the indicated power of the engine. i © (b) An ideal Rankine cycle operates with steam entering the turbine at 10 bar, 300°C and ‘i {eaving it at 20 kPa. Caleulate the thermal efficiency of this cycle, © 12. An air-standard Otto cycle operates with a compression ratio of 8. The maximum temperature in the cycle is 2000 K. At start of the compression process, airs at 0.98 bar, 300 K. Calculate: (@) The maximum pressure in the cycle. @) (b) The temperature and pressure of ait at end of the expansion proces: (4 (©) The net cyclic work produced for every kg of air used. (4) (eR) Contd. +49. (a) Identity key differences in o eration of a petrol engine vs. a diesel engine. Explain why diesel engines give better fuel economy than petro! engines of the same cubic capacity. (4) (b) An airstaridard Diesel cycle has a cutoff ratio ‘of 2 with a thermal efficiency of 0.6. At start of the compressioh process, alr is at 0.98 bar, 300 K. Find the net cyclic work produced for mo every kg of air used, ifthe highest pressure in the cycles 5 MPa < 44, An R22-based standard vapour compression cycie operates between ~5°C and 30°C. (@) Sketch the cycle using clearly numbered state points on T-s and p-h diégrams; -@) © () Caleulate the refrigeration effect produced. @) {c) Calculate the heal rejected (@) Calculate,the cycle COP. in condenser. = @) : a (oR) 16, (@) List the key differences between a vapour absorption refrigeration system and a vapour Compression reffigeration eystom. Identify the kinds of ndusties where use of absorption refrigeration systems can b e recommended. @ (0) A BeltColeman cycle operates with ar a inlet to the compressor at 100 kPa and 298 K. High prescure air enters the turbine at 298 K. The compressor power iApAt is twice that of the : Rifaine power output, Calculate the pressure rato, the net power Input, and the cycle heat fejecton rate in order to produce a cooling effect of 6.25 KW. @ 416. Rankine cycle with a single stage of reheat operates with steart ent@ting the first turbine at 45. ar fO0"C. Mer fsertropie expansion to 5 bar, steams reheated at consian! preset to 350°C aot aooing the second turbine where it undergoes isentropic expansion to GEC Aboiler Pere eis used to pump saturated condensate tothe boiler pressure, For a net power output of 235 MW, calculate: + (a) The required mass flow rate of steam, @) (b), The required heat addition fates In the boller and re-heater. ray {6) The required mass fiow rate of condensate cooling ver water whose temperature rise must @) not exceed 5°C due to envi ironmental regulations. (OR) 47.A Rankine eyele with a single stage of regensration operates with steam, entering the turbine at 45 bar, 400°C. After isentropic ‘expansion to 5 bar, some steam is extracted and sent to an open ~ type feed water heater, while the remaining steam expands (9 2h isentropic manner to 60°C. 20Ed pumps raise saturated liduid condensate to the required pressures. Calculate: (a) The cycle thermal efficiency: ©) {b) The tequired mass flow rate of steam for @ net power output of 235 MW. @ {c). The required mass flowrate of condensate cooling river water whose temperature rise must not exceed 5°C due to environmental regulations. . @) 48. (@) Juslfy how for reversible polytropic compréssion undergone by ida gas air inside @ _18-(0) dusty pon compressor, te process work per kg ofa from state 1 to etate 28: () (b) A single-acting reciprocatin takes in atmospheric air at nk f i we 5G-n) 9 air compressor Raving a bore of 12 crand a stroke of 15 ¢7 4 bar and 25°C. The volumetric efficiency of the compressor is DOS, Calculate its air delivery rate in kg/hr when running at 1200 RPM. @ (OR) 49, A 2-stage air compressor compreeses ait from 4 bar and 26°C 10 4 bar. The first stage compresses air to 2.5 bar before itis cooled to 40°C before ‘entering the second stage. In both Stages, compression is nearly reversible and adiabatic. Caleutate: (@) The total work of compression and heat transfer in He intercooler. © {B) The percentage changes in total work of compression ‘and heat transfer in the intercooler if perfect infercooling were accomplished at an optimum pressure, 6)