Code No: R31034 R10 Set No: 1 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec - 2014/Jan -2015 THERMAL ENGINEERING-II (Com. to Mechanical Engineering and Automobile Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks Note : Steam tables and mollier chart may be permitted 1. (a) Explain Rankine cycle with neat schematic layout, what are the processes involved in it? [8+7] (b)in a steam power cycle, the steam supply is at 15bar and dry and saturated. the condenser pressure is 0.4 bar. Calculate the rankine efficiencies of the cycle neglect pump work. 2. (a) Name any 4 boiler mountings, Explain their functions? (b)with a chimney of height 45metres,the temperature of flue gases with natural draught was 370 0 C. The same draught was developed by induced draught fan and the temperature of the flue gases was 150 0 C mass of the flue gases formed is 25kg per kg of coal fired. The boiler house temperature is 35 0 C. Assuming c p =1.004kJ/kg 0 K for the flue gases. Determine the efficiency of the chimney.? [5+10] 3. (a)what is the function of a nozzle, explain various types of nozzles with neat sketches? (b)a steam is expanded in a set of nozzles from 10 bar and 200 0 C to 5bar.What type of nozzle is it? neglecting the initial velocity find minimum area of the nozzle required to allow a flow of 3kg/s under the given conditions. Assume that expansion of steam to be isentropic. [7+8] 4. (a) What are the classifications of steam turbines, explain each one with example? (b) A single row impulse turbine develops 132.4 kw at a blade speed of 175m/s, using 2kg of steam per sec. steam leaves the nozzle at 400m/s. velocity coefficient of the blades is 0.9.steam leaves the turbine blades axially. Determine nozzle angle, blade angles at entry and exit, assuming no shock. [5+10] 5. (a) What is the Parson s Reaction turbine? (b) A 50% reaction turbine (with symmetrical velocity triangles) running at 400 rpm has the exit angle of the blades as 20 0 and the velocity of steam relative to the blades at the exit is 1.35 times the mean blade speed. The steam flow rate is 8.33 kg/s and at a particular stage the specific volume is 1.381 m 3 /kg. Calculate for this stage: i. The suitable blade height, assuming the rotor mean diameter as 12 times the blade height, and ii. The diagram work. [5+10] 1 of 2
Code No: R31034 R10 Set No: 1 6. (a) What is the function of a steam condenser, what are the requirements of a steam condensing plant? (b) Steam enters a condenser at 36 0 C and with barometer reading 760mm, if the vacuum of 695mm is produced find the vacuum efficiency? [5+10] 7. (a) What are the merits and demerits of a gas turbine over an I.C engine? (b) In a jet propulsion cycle air enters the compressor at 1 bar, 15 0 C. The pressure leaving the compressor is 5 bar and the maximum temperature is 900 0 C. The air expands in the turbine to such a pressure that the turbine work is just equal to the compressor work. On leaving the turbine, the air expands in a reversible adiabatic process in a nozzle to 1 bar. Calculate the velocity leaving the nozzle. Take Cp=1.0035 and γ = 1.4 for compressor and expansion processes. [4+11] 8. (a) What is the principle of jet propulsion, classify jet propulsive engines? (b) Explain the working of turbo jet propulsive engine with neat sketch? [8+7] 2 of 2
Code No: R31034 R10 Set No: 2 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec - 2014/Jan -2015 THERMAL ENGINEERING-II (Com. to Mechanical Engineering and Automobile Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks Note : Steam tables and mollier chart may be permitted 1. (a) Explain modified Rankine cycle with P-V &T-S diagrams? (b) The adiabatic enthalpy drop across the prime mover of the Rankine cycle is 840kJ/kg. The enthalpy of steam supplied is 2940kJ/kg, If the back pressure is 0.1bar find the specific steam consumption and thermal efficiency? [7+8] 2. (a) What is the use of Economizer in a boiler, Explain its working with neat sketch? (b) How much air is used per kg of coal burnt in a boiler having chimney of 32.3m height to create a draught of 19mm of water column when the temperature of flue gases in the chimney is 370 0 C and the temperature of the boiler house is 29.5 0 C? [8+7] 3. (a) What is the critical pressure ratio, derive an expression for maximum discharge through nozzle? (b) Steam having pressure of 10.5 bar and 0.95 dryness is expanded through a convergent-divergent nozzle and the pressure of steam leaving the nozzle is 0.85 bar. find the velocity at the throat for maximum discharge conditions. Index of expansion may be assumed as 1.135. Calculate mass rate of flow of steam through the nozzle. [8+7] 4. (a) Define and derive an expression for stage efficiency in case of a steam turbine. (b) A stage of steam turbine is supplied with steam at a pressure of 50bar and 350 0 C,and exhausts at a pressure of 5bar. The isentropic efficiency of the stage is 0.82 and the steam consumption is 2270kg/min. determine the power output of the stage. [8+7] 5. (a) What do you mean by compounding of steam turbines? Discuss various methods of compounding steam turbines? (b) Explain the difference between an impulse turbine and a reaction turbine? [10+5] 6. (a) Classify jet condensers, Explain the working of any one of jet condenser? (b) The outlet and inlet temperatures of cooling water to a condenser are 37.5 0 C and 30 0 C respectively, if the vacuum in the barometer is 706mm of mercury with barometer reading 760mm determine efficiency? [10+5] 1 of 2
Code No: R31034 R10 Set No: 2 7. A turbo-jet engine flying at a speed of 960 km/hr consumes air at the rate of 54.5kg/s. Calculate (a) Exit velocity of jet when the enthalpy change for the nozzle is 200 KJ/kg and velocity coefficient is 0.97. (b) Fuel flow rate in kg/s when air-fuel ratio is 75:1. (c) Trust specific fuel consumption. (d) Thermal efficiency of the plant when the combustion efficiency is 93% and calorific value of the fuel is 45000 KJ/kg. (e) Propulsive power. (f) Propulsive efficiency. Overall efficiency. [15] 8. (a) Explain the parts of rocket engine with neat sketches, mention the applications rockets? (b) A simple turbojet unit operates with a turbine inlet temperature of 1100 0 K, a pressure ratio is 4:1 and a mass flow of 22.7 Kg/Sec. under design conditions. The following component efficiencies may be assumed: Isentropic Compressor efficiency - 0.85 Isentropic Turbine efficiency - 0.90 Propelling nozzle efficiency - 0.95 Transmission efficiency - 0.99 Combustion chamber loss - 0.21 bar Calculate the design thrust and specific fuel consumption when the unit is stationary at sea level where the ambient conditions may be taken as 1.013 bar and 288 0 K. [5+10] 2 of 2
Code No: R31034 R10 Set No: 3 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec - 2014/Jan -2015 THERMAL ENGINEERING-II (Com. to Mechanical Engineering and Automobile Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks Note : Steam tables and mollier chart may be permitted 1. (a) In a Rankine cycle, the steam at inlet to turbine is saturated at a pressure of 35 bar and the exhaust pressure is 0.2 bar. Determine. i. The pump work ii. The turbine work iii. The Rankine efficiency iv. The Condenser heat flow. Assume flow rate of 9.5 kg/s (b) In a chimney of height 55mts, temperature of flue gases with Natural draught is 367 0 C.The temperature of waste gases by using artificial draught is 127 0 C. The temperature of outside air is 27 0 C. If air supplied is 19 kg/kg of fuel burnt, determine the efficiency of chimney. Assume Cp = 1.005 KJ/kg for flue gases. [8+7] 2. (a) What is static draught, what is the condition for maximum discharge through a chimney? (b) In a boiler test 1250kg of coal are consumed in 24 hours. the mass of water evaporated is 13000kg and the mean effective pressure is 7bar.the feed water temperature was 40 0 C,heating value of coal is 30000kj/kg. The enthalpy of 1kg of steam at 7 bar is 2570.7 kj. Determine i)equivalent evaporation per kg of coal ii)efficiency of the boiler [7+8] 3. (a) What are the objectives of a steam condenser in a steam power plant? (b) Explain the working of high level jet condenser, with the help of a neat sketch. [5+10] 4. In an impulse turbine the steam issues from the nozzle with speed of 600 m/s and blade speed is 120 m/s. the velocity is compounded by passing the steam through a ring of moving blades; through a ring of fixed blades and finally through a ring of moving blades. The nozzle angle is 18 0 and the blade exit angles and relative velocity coefficients are: 1st row moving: 20 0 & 0.8 fixed row : 25 0 & 0.85 2nd row moving: 30 0 & 0.9 Find the diagram efficiency under these conditions and the power output for steam flow rate of 5 kg/sec. [15] 1 of 2
Code No: R31034 R10 Set No: 3 5. In a stage of impulse reaction turbine provided with single row wheel, the mean diameter of the blades is 1metre.it turns at 3000 r.p.m. the steam issues from the nozzle at a velocity of 350m/sec and the nozzle angle is 20 0. The rotor blades are equiangular. The blade friction factor is 0.86. Determine the power developed if the axial thrust on the end bearing of a rotor is 118N. [15] 6. (a) Explain with neat sketch open cycle gas turbine plant.? (b) Enumerate the differences between open cycle gas turbine plant and closed Cycle turbine plant. [8+7] 7. (a) What are the important properties of a good propellant? (b) In a jet propulsion cycle air enters the compressor at 1 bar, 15 0 C. The pressure leaving the compressor is 5 bar and the maximum temperature is 900 0 C. The air expands in the turbine to such a pressure that the turbine work is just equal to the compressor work. On leaving the turbine, the air expands in a reversible adiabatic process in a nozzle to 1 bar. Calculate the velocity leaving the nozzle. Take Cp=1.0035 KJ/Kg 0 K and γ = 1.4 for compressor and expansion processes. [4+11] 8. (a) Explain with a neat sketch a Screw Propeller Unit. [8+7] (b) What are the fundamental differences between jet propulsion and rocket propulsion? * 2 of 2
Code No: R31034 R10 Set No: 4 JNT University Kakinada III B.Tech. I Semester Regular/Supplementary Examinations, Dec - 2014/Jan -2015 THERMAL ENGINEERING-II (Com. to Mechanical Engineering and Automobile Engineering) Time: 3 Hours Max Marks: 75 Answer any FIVE Questions All Questions carry equal marks Note : Steam tables and mollier chart may be permitted 1. (a) Is Rankine cycle effected by temperature variation? Explain. (b) A simple Rankine cycle works between pressures 28bar and 0.06bar the initial condition of the steam being dry saturated. calculate the cycle efficiency, work ratio and specific steam consumption [ 5+10] 2. (a) Define factor of evaporation & what are the heat losses in a boiler? (b) The following readings were obtained during a boiler trial of 6 hours duration mean steam pressure=12 bar; mass of steam generated=40000kg; mean dryness fraction=0.85; mean feed water temperature=30 0 C, coal used= 4000kg.calorific value of coal=33400kj/kg. Calculate i)factor of equivalent evaporation ii)equivalent evaporation from and at 100 0 C iii)efficiency of the boiler. [5+10] 3. (a) With the help of a neat sketch. Explain the working of counter flow jet condenser. (b) The following data were obtained from the test of a surface condenser : Condenser vacuum =711 mm of Hg; Hot water Temp=32 0 C; Inlet temp of circulating water = 14 0 C Outlet temp of circulating water is 28 0 C, Barometer reading is 760 mm of Hg. Calculate the vacuum efficiency and efficiency of condenser. [7+8] 4. In a single stage impulse turbine the nozzle angle is 25 0. The absolute velocity of steam at exit is 300 m/sec in a direction 120 0 to the direction of motion of the blades. Assuming equiangular blades and no axial thrust, determine (a) the blade angles, (b) the power developed per kg and (c) the diagram efficiency. [15] 5. (a) The following data refers to a particular stage of a Parsons Reaction turbine: Speed of the turbine = 1500r.p.m Mean diameter of the rotor = 1metre Stage efficiency=80 percent Blade outlet angle=20 0 Speed ratio= 0.7 Determine the available isentropic enthalpy drop in the stage. (b) What do you mean by combined velocity diagram with reference to steam turbines? [10+5] 1 of 2
Code No: R31034 R10 Set No: 4 6. (a) Derive the expression for thermal efficiency of a simple gas turbine plant. (b) What are the Principal components in closed cycle gas turbine and Explain them briefly, show the cycle on T-S diagram [8+7] 7. A turbo-jet engine flying at a speed of 960 km/hr consumes air at the rate of 54.5 kg/s. Calculate (a) Exit velocity of jet when the enthalpy change for the nozzle is 200 KJ/kg and velocity coefficient is 0.97. (b) Fuel flow rate in kg/s when air-fuel ratio is 75:1. (c) Trust specific fuel consumption. (d) Thermal efficiency of the plant when the combustion efficiency is 93% and calorific value of the fuel is 45000 KJ/kg. (e) Propulsive power. (f) Propulsive efficiency. Overall efficiency. [15] 8. (a) Explain the parts of rocket engine with neat sketches and mention the applications of rockets? (b) What is ramjet? Explain the working of a ramjet with a neat sketch [8+7] * 2 of 2