II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 ENGINEERING THERMODYNAMICS (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ?????
1. (a) Explain the terms state, path, process and cyclic process. (b) Discuss the macroscopic and microscopic point of view of thermodynamics. [8+8]
2. Prove that the formula T b Va-b ekT = Constant for an adiabatic expansion of the gas, if Cp = a + KT and Cv = b + KT, where a, b and K are constants and T in degrees K. [16]
3. (a) What is absolute temperature scale? Develop this scale from Carnot theorem (b) A reversible engine during a cycle of operation interacts with three thermal reservoirs maintained at 200K,300K and 400K. It receives 5 MJ of heat from the reservoir at 400K and produces a net positive work of 840 kJ. Find the amount and direction of heat interaction with other reservoirs. [8+8]
4. (a) Explain third law of Thermodynamics. (b) A tank holds 1 kg of air at 100 kPa, 400 C, and another tank holds 1 kg of air at 200 kPa, 400 C. The atmosphere is at 100 kPa, 200 C. In which tank is the stored energy is greater? Determine the availability of the air in each tank. [6+10]
5. (a) What is p-v-T surface? Draw a portion of such a surface. (b) Write a short note on Vander Waal’s equation. (c) Determine the compressibility factor for O2 at i. 100 bar and - 700 C ii. 5 bar and 300 C [4+4+8]
6. A mixture of 25% Nitrogen and 75% Hydrogen by volume is compressed. Isentropically from 300 K and 100 kPa to 500 kPa in the ?rst stage of multistage compressor in a fertilizer plant. The compression to still higher pressure is acheived in subsequent stages after the gas mixture is passed through the intercooler. Find the temperature of the gas mixture after compression as well as the work required per unit mass of the mixture. Also evaluate the entropy change for each gas. Assume that the mixture behaves like an ideal gas. [16]
7. (a) Derive an expression for the e?ciency of the ideal cycle for the diesel engine in terms of the compression ratio, the cut o? ratio and adiabatic index. (b) In a car working on Otto cycle has initial pressure 1 bar and pressure after compression 10 bar. Calculate i. the compression ratio. ii. The percentage clearance iii. The thermal e?ciency.
8. A steam power plant has the range of operation from 40 bar dry saturated to 0.05 bar. Determine (a) The cycle e?ciency and (b) work ratio and speci?c fuel consumption for (c) car not cycle (d) Rankine cycle
set-2
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 ENGINEERING THERMODYNAMICS (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ?????
1. (a) Show that work is a path function and not a state function. (b) Justify the statement that work and heat are not properties. [8+8]
2. (a) Two kg of air expands polytropically (n=1.25) from a pressure of 15 bar and temperature of 300o C to a pressure of 1.5 bar, then heated at constant pressure to initial volume. Find i. Work done ii. Change in enthalpy iii. Heat transer. (b) Show that the heat transfer in polytropic process ?-n ?-1 times of work
3. (a) What is absolute temperature scale? Develop this scale from Carnot theorem (b) A reversible engine during a cycle of operation interacts with three thermal reservoirs maintained at 200K,300K and 400K. It receives 5 MJ of heat from the reservoir at 400K and produces a net positive work of 840 kJ. Find the amount and direction of heat interaction with other reservoirs. [8+8]
4. (a) Derive expression for the Gibbs Function of a mixture of inert ideal gases. (b) Show that on a Mollier diagram (h-s diagram) the slope of a constant pressure line increases with temperature in the superheat region. [8+8]
5. Steam at a pressure of 6.8M N/m2 and at a temperature of 3750 C is isentropically expanded to a pressure of 1.0M N/m2 . It is then reheated at constant pressure it has a temperature of 3000 C. It is further isentropically expanded to a pressure of 0.14M N/m2 . Using steam table, determine (a) the condition of steam after both isentropic expansion, (b) the heat transfer per kg of steam to carry out the constant pressure process. Sketch the processes on T-s and h-s diagram. [16]
6. Air has a dry bulb temperature of 270 C and a wet bulb temperature of 200 C . If the barometer reads 1 bar, Calculate (a) the humidity ratio (b) the relative humidity (c) the dew point (d) the enthalpy of mixture per kg of dry air.
7. (a) Explain the Atkinson cycle with the help q P-V and T-S diagrams. (b) An engine working on Atkinson cycle takes air at 1 bar and 250 c. The air is compressed isoentropically by a compression ratio 6:1. The heat is added at constant Volume resulting the ?nd pressure to be 20 bars. Then the air is expanded to a pressure of 1 bar calculate i. pressure and temperature at various points on the cycle. ii. Work done per Kg of air. iii. Cycle e?ciency.
8. (a) How does the increase in condenser temperature a?ect C.O.P. Also explain the in?uence of evaporator temperature on C.O.P. Which of the two temperatures have more in?uence on C.O.P? (b) Explain the actual vapour compression system on P-H chart clearly showing the typical variation from theoretical systems. [8+8]
set-4
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007 ENGINEERING THERMODYNAMICS (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ?????
1. The readings tA and tB of two centigrade thermometers A and B, agree at the ice point (0o C) and the steam point (100o C), but elsewhere are related by the equation tA = l + m tB + n tB 2 where l, m and n are constants. When both the thermometers are immersed in a well stirred oil bath, A registers 510 C while B registers 50o C. (a) Determine the reading on B when A reads 25o C and (b) Discuss which thermometer is correct. [16]
2. One kg of ?uid enters a nozzle with a velocity of 300m/min and enthalpy of 2990 kJ/kg. The enthalpy of the ?uid at exit is 2760 kJ/kg. The nozzle is placed horizontally and neglects the heat loss from the nozzle. Determine (a) The velocity of the ?uid at the exit (b) The mass ?ow rate, if the inlet area of the nozzle is 0.095m2 and the speci?c volume at inlet is 0.19m3 /kg. (c) The exit area of the nozzle if the speci?c volume at exit is 0.5m3 /kg. [16]
3. (a) What is absolute temperature scale? Develop this scale from Carnot theorem (b) A reversible engine during a cycle of operation interacts with three thermal reservoirs maintained at 200K,300K and 400K. It receives 5 MJ of heat from the reservoir at 400K and produces a net positive work of 840 kJ. Find the amount and direction of heat interaction with other reservoirs. [8+8]
4. (a) Deduce an expression for the non-?ow availability for a system. (b) A 2-kg piece of iron is heated from room temperature of 25o C to 400o C by a heat source at 600o C. What is the irreversibility in the process? Assume for iron Cp =0.450kJ/kgK. [6+10]
5. (a) Derive Clausius-Clayperon equation and explain its signi?cance. (b) Find the value of co-e?cient of volume expansion ß and isothermal compressibility k for a Vander Waal’s gas obeying (p + a/v 2 ) (v-b) = RT [8+8]
6. (a) De?ne i. Mole fraction ii. Mass fraction (b) The volumetric analysis of a dry ?ue gas in a boiler trial is given in Percentage as 13% CO2 , 1.5% CO, 3.5% O2 and 82% N2 . Determine the percentage gravimetric analysis. Also ?nd the speci?c gas constant of the mixture.[6+10]
7. (a) Explain with the help of suitable graphs the variation of the e?ciency of the diesel cycle with compression ratio and cut-o? ratio. (b) In an air standard diesel cycle, the compression ratio is 15.Compression begins at 0.1MPa, 400 c. the heat added is 1.675 MJ/Kg. Find i. ii. iii. iv. v. vi. The The The The The The maximum temperature of the cycle. work down per Kg of air. cycle e?ciency. temperature at the end of the isentropic expansion. cut-o? ratio. mean e?ective pressure of the cycle.
8. (a) Sketch the Rankine cycle on P-V and T-S diagram and explain clearly di?erent process of the cycle. State in what respect it di?ers from carnot cycle working between the same temperature limits. (b) Dry and saturated steam at pressure 11 bar is supplied to a turbine and expended isentropicelly to a pressure or 0.07 bar. Calculate the following. i. ii. iii. iv. Heat supplied Total change of entropy Heat rejected Theoretical thermal e?ciency
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