MECHANICAL-ENGINEERING-PAPER-I-QP-ESEM-25-110825

Engineering Services (Main) Examination - 2025 NESP-O-MCHN MECHANICAL ENGINEERING PAPER—I Time Allowed : Three Hours Maximum Marks : 300 QUESTION PAPER SPECIFIC INSTRUCTIONS Please read each of the following instructions carefully before attempting questions There are EIGHT questions divided in TWO Sections. Candidate has to attempt FIVE questions in all. Question Nos. 1 and 5 are compulsory and out of the remaining, any THREE are to be attempted choosing at least ONE question from each Section. The number of marks carried by a question/part is indicated against it. Wherever any assumptions are made for answering a question, they must be clearly indicated. Diagrams/Figures, wherever required, shall be drawn in the space provided for answering the question itself. Unless otherwise mentioned, symbols and notations carry their usual standard meanings. Psychrometric Chart is given in Page No. 11. Attempts of questions shall be counted in sequential order. Unless struck off, attempt of a question shall be counted even if attempted partly. Any page or portion of the page left blank in the Question-cum-Answer Booklet must be clearly struck off. Answers must be written in ENGLISH only. NESP-O-MCHN/41 i PPO. (b) (¢) (d) (e) 2. (a) SECTION—A Prove that in case of forced vortex, the rise of liquid level at the ends is equal to the fall of liquid level at the axis of rotation. 2 Explain, with the aid of neat sketch, the working principle of a Pitot static tube. Further, explain how the Pitot static tube differs from the Pitot tube. 12 Using an ideal gas as working fluid, show that the thermal efficiency of an Ericsson cycle is identical to the efficiency of a Carnot cycle operating between the same temperature limits. 12 Distinguish between the following : (i) Thermodynamics and Heat transfer (ii) Free convection and Forced convection (ii) Black body and Gray body 12 Explain the effects of the following variables on the volumetric efficiency of an IC engine : () Types of fuel (ii) Valve overlap (iii) Inlet valve timing (iv) Exhaust residual (v) Exhaust gas recirculation (vi) Engine speed 12 () Enumerate, with the aid of illustrative sketches, the condition of equilibrium of a submerged body. 8 (i) A solid cone of relative density 0-70 floats in water. What should be its minimum apex angle so that it may float its apex downwards in stable equilibrium? 12 NESP-O-MCHN/41 2 (b) Ethylene glycol (1800 kg/hr) is cooled from 100 °C to 60 °C by cooling water that enters the annular space of a single-pass counterflow heat exchanger at 15 °C and has a mass flow rate of 1200 kg/hr. Calculate— (i) the overall heat transfer coefficient if convective heat transfer coefficient of water-side is 8-72 kW/m?-deg; (ii) the necessary length of copper tubing if it has an internal diameter of 1:25 m; (iti) also the length of the tube required if water flows in the same direction as ethylene glycol. For turbulent flow of fluid inside the tube, the Dittus-Boelter relationship Nu =0-023 (Re)°'8 (Pr)°'4 is to be used. The relevant physical properties of ethylene glycol at its bulk temperature of 80 °C are C, =2-64 kJ/kg-K; » =11-72 kg/hr-m; k =0-26x1079 kW/m-deg. 20 (c) A 4-cylinder, 4-stroke SI engine having 70 mm bore and 84 mm stroke runs at 4000 r.p.m. and uses a fuel having 84% carbon and 16% hydrogen by mass. The volumetric efficiency of the engine is 80%. The ambient conditions are 1:0 bar and 27 °C. The depression at the venturi throat is 0-65 bar. Assuming - the stoichiometric A/F ratio, calculate the fuel flow rate, the air velocity at the throat and the throat diameter. [Take, Raj, = 287 J/kg-K, Rene vapour = 98 J/kg-K] 20 3. (a) (i) Let us define a thermal time constant t= aad A mass m with an initial q uniform temperature 7) and then lower into a water bath with temperature T,,, and the heat transfer between mass and water has a heat transfer coefficient C, with surface area A and C, is specific heat at constant volume. Assume radiation to be negligible. Show, with the help of suitable equations, that for a quick response, thermocouple needs a small thermal time constant t while for a house, a large thermal time constant is needed. 10 (i) On a hot day of summer, a car is left in sunlight with all the windows closed. After some time, it is found that inside of the car is considerably warmer than the air outside. Why? 10 (b) (i) Establish a relation for the time taken to form a layer of ice on the surface of a pond. = (ii) Name the various types of insulating materials used in engineering and mention applications for which they are used. 8 NESP-O-MCHN/41 3 [PiTo. (c) () A cylinder/piston setup contains 1L of saturated liquid refrigerant (R-410A) at 40 °C. The piston now moves slowly, expands maintaining constant temperature to a final pressure of 500 kPa in a reversible process. Calculate the work done and heat transfer required to accomplish this process. State-1 Temper-| Pres- Specific volume, m? /kg Enthalpy, kJ/kg Entropy, kJ/kg-K | Internal energy, kJ/kg ature sure (CC) | (kPa) Yi ‘fo | Yo | *f | hfe | Ao | sf | Sfo | 89 | “>, | 4Fg | 4g 40 2420°7 | 0001025 | 0-00865 | 000967 | 124-09 | 159-04 | 283-13 | 0-4473 | 0-5079|0:9552| 121-61 | 138-11 | 259-72 State-2 500 kPa, -13-89 °C v (m3/kg) = 0:06775 u (kJ/kg) = 290-32 h (kJ/kg) = 324-20 s (kJ/kg-K) = 1-2398 (i) (1) 1 kg of water at 100 kPa, 120°C receives 50 kJ/kg in a reversible process by heat transfer. Which thermodynamic process, from the given below, will generate the largest entropy change? Justify your answer : A. Constant temperature B. Constant pressure C. Constant volume (2) How can you change entropy of a substance going through a reversible process? Keep in mind the second law of thermodynamics. 4. (a) A cooling tower cools water from 45 °C to 25 °C. Water enters the tower at a rate of 100000 kg/hr. Air enters the tower is at 20 °C with a relative humidity of 50%; the air leaving is at 40 °C with a relative humidity of 95%. The air enters at the bottom and leaves at the top. The barometric pressure is 92 kPa. Determine— (i) the required flow rate of atmospheric air in kg/hr; (i) the amount of water lost by evaporation per hour. NESP-O-MCHN/41 4 10 20 Saturated water—Temperature table Specific volume, Internal energy, Enthalpy, Entropy, ms/kg kJ/kg kJ/kg kJ/kg: Sat. Sat. Sat. Sat. Sat. Sat. Sat. Sat. Sat. Temp., _ press., liquid, vapor, liquid, Evap., vapor, liquid, Evap., vapor, liquid, Evap., vapor, T°C —— PraskPa vy Vg Uy Ug ug fy Ng hg S Sy Sy 0.01 0.6117 0.001000 206.00 0.000 2374.9 2374.9 0.001 2500.9 2500.9 0.0000 9.1556 9.1556 5 0.8725 0.001000 147.03 21.019 2360.8 2381.8 21.020 2489.1 2510.1 0.0763 8.9487 9.0249 10 1.2281. 0.001000 106.32 42.020 2346.6 2388.7 42.022 2477.2 2519.2 0.1511 8.7488 8.8999 15 1.7057 0.001001 77.885 62.980 2332.5 2395.5 62.982 24654 25283 0.2245 8.5559 8.7803 20 2.3392 0.001002 57.762 83.913 2318.4 2402.3 83.915 2453.5 2537.4 0.2965 8.3696 8.6661 25 3.1698 0.001003 43.340 104.83 2304.3 2409.1 104.83 2441.7 2546.5 0.3672 8.1895 8.5567 30 4.2469 0.001004 32.879 125.73 2290.2 2415.9 125.74 2429.8 2555.6 0.4368 8.0152 8.4520 35 5.6291 0.001006 25.205 146.63 2276.0 2422.7 146.64 2417.9 2564.6 0.5051 7.8466 8.3517 40 7.3851 0.001008 19.515 167.53 2261.9 2429.4 167.53 2406.0 2573.5 0.5724 7.6832 8.2556 45 9.5953 0.001010 15.251 188.43 2247.7 2436.1 188.44 2394.0 2582.4 0.6386 7.5247 8.1633 50 12.352 0.001012 12.026 209.33 2233.4 2442.7 209.34 2382.0 2591.3 0.7038 7.3710 8.0748 55 15.763 0.001015 9.5639 230.24 «= 2219.1 2449.3 230.26 2369.8 2600.1 0.7680 7.2218 7.9898 60 19.947 0.001017 7.6670 251.16 2204.7 2455.9 251.18 2357.7 2608.8 0.8313 7.0769 7.9082 65 25.043 0.001020 6.1935 272.09 2190.3 2462.4 272.12 23454 2617.5 0.8937 6.9360 7.8296 70 31.202 0.001023 5.0396 293.04 2175.8 2468.9 293.07 2333.0 2626.1 0.9551 6.7989 7.7540 75 38.597 0.001026 = 4.1291 313.99 2161.3 2475.3 314.03 23206 2634.6 1.0158 6.6655 7.6812 80 47416 0.001029 3.4053 334.97 2146.6 2481.6 335.02 2308.0 2643.0 1.0756 6.5355 7.6111 85 57.868 0.001032 2.8261 355.96 2131.9 2487.8 356.02 22953 2651.4 1.1346 6.4089 7.5435 90 70.183 0.001036 2.3593 376.97 2117.0 2494.0 377.04 2282.5 2659.6 1.1929 6.2853 7.4782 95 84.609 0.001040 1.9808 398.00 2102.0 2500.1 398.09 2269.6 2667.6 1.2504 6.1647 7.4151 100 101.42 0.001043 1.6720 419.06 2087.0 2506.0 419.17 2256.4 2675.6 1.3072 6.0470 7.3542 105 120.90 0.001047 1.4186 440.15 2071.8 2511.9 440.28 2243.1 26834 1.3634 5.9319 7.2952 110 143.38 0.001052 1.2094 461.27 2056.4 2517.7 461.42 2229.7 2691.1 1.4188 5.8193 7.2382 115 169.18 0.001056 1.0360 48242 2040.9 25233 482.59 22160 26986 1.4737 5.7092 7.1829 120 198.67 0.001060 0.89133 503.60 2025.3 2528.9 503.81 2202.1 2706.0 1.5279 5.6013 7.1292 125 292,23 0.001065 0.77012 524.83 2009.5 2534.3 525.07 2188.1 2713.1 1.5816 5.4956 7.0771 130 270.28 ~——-0.001070 0.66808 546.10 1993.4 2539.5 546.38 2173.7 2720.1 1.6346 5.3919 7.0265 135°. .Si9i22 0.001075 0.58179 567.41 1977.3 2544.7 567.75 2159.1 27269 1.6872 5.2901 6.9773 140,361.53 0.001080 0.50850 588.77 1960.9 25496 589.16 2144.3 27335 1.7392 5.1901 6.9294 145 415.68 0.001085 0.44600 610.19 1944.2 25544 610.64 2129.2 27398 1.7908 5.0919 6.8827 (b) For the velocity profile of laminar boundary layer u 1 — =sin( 3 x) es 25, find the expressions for— (i) boundary layer thickness; (i) shear stress; (iii) average coefficient of drag. 20 NESP-O-MCHN/41 5 PPT.O. (c) (b) (c) (a) (i) A 4-cylinder, 4-stroke engine has cylinder dia 10-0 cm and stroke length 10-0 cm. The engine is connected to an eddy current dynamometer, and 80-0 kW of power is dissipated by the dynamometer. Assuming engine mechanical efficiency as 85% at 4500r.p.m. and the dynamometer efficiency as 95%, calculate— (1) the frictional power lost; (2) the brake mean effective pressure; (3) the engine torque at 1500 r.p.m.; (4) the engine specific volume. 10 (ii) A single-cylinder SI engine is operated with gasoline of calorific value 44 MJ/kg and density 780 kg/m°, During each combustion cycle when the flame reaches up to a height of 2 cm, combustion reaction stops due to closeness of the wall and dampens out all fluid motion while conducts heat anyway. The boundary layer of unburnt charge is formed in the combustion chamber of 4cm dia and fuel is distributed equally throughout the combustion chamber having unburnt charge layer of approximately 0-1 mm thickness. Find the fraction of the unburnt fuel and resulting heat loss. 10 SECTION—B Enumerate the advantages of using steam condenser in a steam power plant. Explain the significance of vacuum efficiency and condenser efficiency. 12 Derive an expression for acceleration head impressed on the flow in case ofa reciprocating pump. Assume that the piston has simple harmonic motion. 12 What is the need of mine ventilation? Explain, with a sketch, the working of mine air-conditioning system. Also mention the various heat sources in mines. 12 Briefly discuss the impact of the following variables on the performance ofa concentrating solar collector : () Fluid inlet temperature (ii) Mass flow rate of fluid (ii) Concentration ratio (iv). Type of absorber surface i2 NESP-O-MCHN/41 6 (e) (i) Mention any four advantages of a high-pressure boiler. 4 (ii) Briefly explain, with the aid of an illustrative sketch, the working principle of LaMont boiler. 8 6. (a) Ina vapour compression refrigeration cycle based ice plant of 20 TR capacity using NH, as refrigerant, the following data are used for the calculations : The temperatures of water entering and leaving the condenser are 20 °C and 27 °C, and the temperature of brine in the evaporator is -15 °C. Before entering the expansion valve, ammonia is cooled to 20 °C and ammonia enters the compressor dry saturated. Calculate— (i) the compressor power required; (ii) the flow rate of cooling water circulated in the condenser; (iii) the COP of the plant for 1 TR capacity. Show the cycle on t-s and p-h diagrams. Use the properties given in the table : Saturation | Entropy, kJ/kg-K Enthalpy, kJ/kg Sp. heat, kJ/kg-K temperature (°C) Liquid Vapour Liquid Vapour Liquid Vapour -15 0-4572 5:5490 112:34 | 142654 4-396 2:303 25 1-:1242 5:0391 298-90 1465:84 4-606 2-805 20 (b) For a hot and humid summer condition, an air-conditioning system needs to be designed for meeting an industrial demand and the following data are used : Outside conditions : 32 °C DBT and 65% RH Required inlet air conditions : 25 °C DBT and 60% RH Amount of free air circulated is 250 m°/min, coil dew point temperature is 13 °C. The required condition is achieved by cooling and dehumidification initially and then by heating. NESP-O-MCHN/41 7 [PEe: Calculate the following : () The cooling capacity of the cooling coil and its by-pass factor (i) The heating capacity of the heating coil in kW and surface temperature of the heating coil if the by-pass factor is 0:3 (ii) The mass of water vapour removed per hour Show the psychrometric processes involved on Psychrometric Chart. [Psychrometric Chart is given in Page No. 11] (c) (i) Draw and explain in detail each of the constant head characteristics of Pelton, Francis and Kaplan turbines. (i) A Francis turbine was installed in a power plant system. For first few years of operation, it gave noise or vibration frequency around 15 Hz. But after 10 years of operation, the noise/frequency coming out of it is around 100 Hz. Can you explain the different causes of this increase in noise or vibration and suggest the remedies for it? Can you also suggest the places where the errors are located? (iti) Describe the significance of specific speed in turbine sizing, if any. 7. (a) Compare running costs of winter heating system of a conference hall for which 50000 kJ/hr of heating is required using the following three methods of heating : () Vapour compression cycle based heating (i) Direct heating using fuel (iii) Electric heating Take the following data for calculation : COP of VCRC system = 3:0 Fuel charges for light diesel oil = €64/L Specific gravity of oil = 0:87 Heating value of fuel = 42 MJ/kg Combustion efficiency = 0-80 Electricity charges = €8-5/unit Now-a-days in winter season, which is the most common system being used and why? NESP-O-MCHN/41 8 20 10 20 () (c) 8. (a) Air enters a turbojet engine at 10x104 kg/hr at 25°C and 1:03 bar, and is compressed adiabatically to 192°C and four times the pressure. Products of combustion enter the turbine at 815 °C and leave the compressor at 650°C to enter the nozzle. Calculate the isentropic efficiency of the compressor, the power required to drive the compressor, the exit speed of gases, and the thrust developed when flying at 900 km/hr. Assume that isentropic efficiency of turbine is same as that of compressor and the nozzle efficiency is 90%. Assume for air y, =1-4, C, =1-005 kJ/kg-K and for gases assume y, =1-3 and R=1-147 kJ/kg-K. () A small rural village having 40 houses with 5 members each is located remotely. Design a solar photovoltaic system to meet the daily energy needs, considering 24 x 7 energy requirements. Assume the following data for solar panel : Peak power = 80 W Voltage at peak power = 17-6 V Current at peak power = 4:55 A Operating factor = 0:8 0-85 5 hr/day Mismatch factor Sunshine hours State clearly, if any assumptions are made. (i) What are the important factors affecting the solar cell performance? Discuss in brief. () A blast furnace gas has the following volumetric compositions : CO, = 10% CO = 30% Hy = 15% Ny = 58:5% Determine the theoretical volume of air required for the complete combustion of 1 m° of the gas. Also determine the percentage composition of dry flue gases by volume. Consider that air contains 21% of O, and 79% of No by volume. (i) How does ash in the coal affect power plant economics? 20 10 10 14 NESP-O-MCHN/41 9 [Pitwo: (b) (i) What is the need of alternative fuels for transportation? Compare the utility of bio-diesel and bio-alcohol in Indian context. 10 (i) A wind turbine is operating at wind speed of 7-0 m/s to pump water at a rate of 5-O m°/hr with a lift of 6-0 m. Calculate the radius of the rotor and the tip speed ratio. Assume : Water density = 1000 kg/m? Water pump efficiency = 45% Efficiency of rotor to pump = 80% Power coefficient = 0:25 Air density = 1-2 kg/m? Angular velocity of the rotor = 60 r.p.m. 10 (c) Gas at 8 bar and 300 °C expands to 4 bar in an impulse turbine stage. The nozzle angle is 65° with reference to the exit direction. The rotor blades have equal inlet and outlet angles, and the stage operates with optimum blade speed ratio. Assuming that the isentropic efficiency of the nozzle is 0-9 and velocity at entry to the stage is negligible, deduce the blade angle used and the mass flow required for this stage to produce 75 kW. [Given, C, =1-15 kJ/kg-K, y = 1-333] 20 kkk NESP-O-MCHN/41 10 130 185 140 145 0.35 है ಕ 0.032 2 ற 0.031 1௦.40 5 0.030 | চু 7 / £ ८ + -Fo.029 |, i గీ 008 5 © மய்ய, ୦ [তদ ০৪৪ ‘BES. 0026 ळ کو‎ ಸ اقب‎ ००25 | உ 25 7 پا راک‎ వై 0.024 | 9.50 = ಜ್‌ ட்‌ எ ][ 1 10023 हैं ५०५ I (~ Ni ੫ [0.022 ର 2 | ద్‌ 11001 ০5৪ 2 نا‎ વી | கக Sif ર + 0.020 2 ଠୁ | 7 | 10.019 7 0.60 n + ட! +f بی 8و2‎ ह| | 0,017 19:65 | 3 ਤੇ व وو‎ 0018 ૦.70 + ৪ 0.95 0.015 | > 0.75 St ર | 0014 foots (9৪০ - ଓ न - وریہ لن‎ ६ ૦૦5 % ও ಎಳ್ಳ = ହ 0.01 [655 5 ےئ‎ 1 + 0.010 ౬1.00 ಕ 1 स] ടു | ઝા ଃ ےا وت‎ ੍ 220186-71 1 17114112 (> ¦-1 [:0.007 ے‎ ೨೧೨ ப ப பு | ا‎ 1 2 755 - ਰਸ ॥ ید‎ 18.005 இ ನೀತ 99 ° ୩ ଆ IN سد‎ 7 न |) [< 3 ॥ 1. ੫ ਟਲ 212 ല്‍ - இய TS | he दै २0७4 ଠି > ` 4 ತ್ಯೆ aa رس‎ ಕ್ಷ 0 ತೆ ms. .004 01௨ nae BS ae = = [~व : 153੫1 7 5 meth Sk ০০০ ਨੂੰ 2 کے یک نے‎ ® SS دا جا نر‎ `. 5 | ങ്ക ® ‰« . ୬୯ लेन ত্র 5 ) ૧-૧ SS | [- ಸ | NI سا‎ விபி لہ‎ \ મળા छ ર स 19 11111111. 1111 ^ SOR وت‎ -10 પ 5 ০ 5 ٠ت‎ 15. 20 25 \ 30 35 40 જ્‌ 50 یب‎ DRY BULB TEMPERATURE, °C 0.75 ೧330 0.80 13/૯૦ BELOW 0 °C PROPERTIES AND ENTHALPY DEVIATION LINES ARE FOR ICE 0.85 m/kg 0.90 m/kg SPECIFIC VOLUME, ஈட DRY AIR SENSIBLE HEAT FACTOR 26BS—816 11 NESP-O-MCHN/41