ENGG. THERMODYNAMICS

Transcription

1 ENGG. THERMODYNAMICS Unit-1 [8 hrs] Introduction To Thermodynamics: Basic concepts of Thermodynamics, Closed & Open Systems, Forms of energy, Properties of a system, State and Equilibrium, Processes and Cycles, Temperature and Zeroth Law of Thermodynamics. The Ideal Gas equation of state, Difference between Gas and Vapor, Compressibility Factor, Internal energy and specific heats of gases, Universal Gas Constants. Unit-02 [8 hrs] First Law of Thermodynamics : Heat and Work, Mechanical forms of work, Non- Mechanical Forms of Work, applied to closed systems flow work and enthalpy, The Steady flow process and its applications. Introduction to Unsteady Flow process. 1) (A96) What is macroscopic and microscopic point of view? 2) (Nov 01) Explain control volume and control surface. 3) (NOV 04 )Differentiate between homogenous and heterogeneous system. 4) (Nov 02) Define system boundary and surroundings. 5) (A-96) Classify each of the following systems. Whether it is an open or closed system, (i) Piston and cylinder arrangement (ii) Air compressor (iii) Carburetor (iv) Radiator of an automobile (v) Pressure cooker and (v) Tea- kettle. 6) (May 02) What do you mean by thermodynamic equilibrium. 7) (Nov 01) What is the difference between thermal and thermodynamic equilibrium? 8) (Nov 04) Define Joules law, of internal energy and prove that energy is property of the system. 9) (Nov 04) Define state and process. 10) (Nov 04) Define and explain quasi-static process. 11) (Nov 04) Differentiate between reversible and irreversible process. 12) (Nov 04) State Boyel s law and Charls law and prove that characteristic gas equation is given by PV = MRT. 13) (Nov 02,A-96) Write Avogdro hypothesis and calculate the value of universal gas constant. 14) (A-96) Calculate the weight of the oxygen in the cylinder with capacity of 100 liters at a

2 temperature of 30 C, the pressure in the cylinder is maintained at 86 Bar. 15) (May 02) What are thermodynamic properties? Explain its types. 16) (May 02) Which law of thermodynamics is the basis or temperature management? Explain. 17) (Nov 02,May 02,W96)Explain Zeorth law, of Thermodynamics Give its applications. 18) (Nov 03) A The temperature scale of a certain thermometer is given by relation t = a.log n Y + b. where a and b are constants and Y is thermodynamic property of fluid in thermometer. If at ice and steam points the thermometer properties are found to be 1.5 and 7.5 respectively. What will be temperature corresponding to thermometer property or 3.5 on Celsius scale. 19) (May 02) Prove that internal energy is a property of the system. 20) (May 03, Nov02) Differentiate between (i) Intensive and extensive property (ii) Point function and path function (iii) Open system and closed system. 21) (A-96) What do you understand by Intensive and Extensive properties? Classify the following properties (i) Velocity (ii) Pressure (iii) Density (iv) Volume (v) Molecular weight and (vi) Temperature. 22) (Nov 02) Distinguish between flow process and non-flow process. 23) (Nov 02, A-9S) Explain reversible and irreversible process with suitable example. 24) (Nov 02, May 02) Distinguish between Point function and Path function. 25) (May 03,A95) Define thermodynamic work and prove that it is a path function. 26) (May 02) What do you understand by thermodynamic work? Explain how electric current is thermodynamic work. 27) (Nov 01) explain the concept of work in thermodynamics. How does it differ from the work in mechanics? 28) (May 03) Heat does not cause inevitably a temperature rise. Comment on this statement. 29) (Nov 04)Prove that in case of free expansion work transfer is zero. 30) (A-96) explain in brief (i) Free expansion process (ii) Throttling process and (iii) Hyperbolic process. 31) (Nov 03) Explain the following terms: (i) closed and open systems (ii) Zeroth law of thermodynamics (iii) quasi-static process.

3 32) (May 02) State the first law of thermodynamics for (i) Closed system and (ii) Open system. 33) (May 02, Nov 01, A-96) Discuss the limitations of the first law, of thermodynamics giving examples. 34) (Nov 01) Define extensive and intensive properties. Explain whether the following can be used as properties. (i) (ii) (iii) 35) An ordinary egg can be approximated as a 5.5 cm diameter sphere. The egg is initially at a uniform temperature of 8 O C and is dropped into boiling water at 97 0 c. Taking the properties of the egg to be = 1020 kg/m 3 and Cp = 3.32 kj/kg- C, determine how much heat is transferred to the egg by the time the average temperature of the egg rises to 70 C (18.3KJ). 36) A domestic refrigerator is loaded with food and door is closed. During a certain period the machine consumes 1KWh of energy and the internal energy of' the system drops by 5000KJ. Find the net heat transfer the system. (-8.6MJ). 37) A piston cylinder arrangement has a gas in the cylinder space. During a constant pressure expansion to a larger volume the work effect for the gas are 1.6KJ the net neat added to tile gas and cylinder arrangement is 3.2KJ and friction between the piston and cylinder wall amounts to.24kj. Determine the change in internal energy of the entire apparatus (gas, cylinder, piston). 38) In a system executing a non flow process, the work and heat per degree change of temperature arc given by dw/dt= 200 W-s/C and dq/dt= 160 J/C. What will be the change in internal energy of the system when its temperature changes from 55C to 95C. (-1600J) CLOSED SYSTEM 39) At the jog falls, water drops from the height of approximately 383m. Assuming that all the potential energy of water is changed into internal energy, estimate the rise in water temperature due to the fall. 40) (A-96) A spherical balloon has a diameter of 0.3m and contains air at a pressure of 1.5 bar. The diameter of the balloon increases to 0.4m due to heating and during this process

4 the pressure is proportional to diameter. Calculate the work done during this process. 41) (W-97) A spherical balloon of 1m diameter contains a gas at 150 KPa. The gas inside the balloon is heated until the pressure reaches 450 KPa. During the process of heating the pressure of the gas inside the balloon is proportional to the cube of the diameter of the balloon. Determine the work done by the gas inside the balloon. 42) (A-01) A certain balloon is constructed of a material such that the pressure inside is proportional to balloon diameter squared (d 2 ). This balloon contains 2 kg of all at 27 0 and 1 bar. The balloon is now heated until the final pressure inside reaches 500 kpa. How much work is done during the process? 43) (A-97) In a certain non-flow process pressure and specific volume are related by P=100/V-V 2 where P is in bar, v is. in m 3 /kg. Find the work done per kg in moving the piston from an initial volume of 0.01m 3 /kg to 0.6 m3/kg. 44) (Nov 04) The pressure and volume relation during a non-flow reversible process is given by * + bar. The volume changes from 6 m 3 to 2m 3. Calculate the work done. The heat rejected during the process is 200 kj. Determine the change in internal energy. 45) (May 03) A fluid system undergoes a non-flow frictionless process following the pressure - volume relationship as P= 5/ V + 2, where P is in bar and V is in m 3. During the process the volume changed from 0.2m 3 to 0.04m 3 and the system rejects 50 kj of heat. Determine the change in internal energy and enthalpy. 46) A gas is compressed from an initial volume of 0.42 m 3, to a final volume of 0.12 m 3. During the quasi-equilibrium process, the pressure changes with volume according to the relation P = av + b, where a = KPa/ m 3 and b = 600 KPa. Calculate the work done during the process. (-82.8 KJ). 47) During an expansion process, the pressure of a gas changes from 80 KPa to 400 KPa according to the relation P = av + b, where a = 860 KPa/ m 3 and b is a constant. The initial volume of the gas is 0.1m 3. Calculate the work done during the process. (90KJ). 48) (May 02, A98) A fluid is confined in a cylinder by a spring loaded, frictionless piston so that the pressure in the fluid is a linear function of the volume (p = a + b V ). The internal energy of the fluid is given by the following equation U = pV where U is in kj, p in kpa and V in cubic meter. If the fluid changes from an initial state of 170 kpa,

5 0.03m 3 to a final state of 400 kpa, 0.06 m 3 with no work other than that done on the piston, find the direction and magnitude or the work and heat transfer. 49) (A-2000) fluid is contained in a cylinder by a spring- loaded, friction less piston so that the pressure in the fluid is a linear function of the volume (p= a+ bv). The internal energy of the fluid is given by the equation U = p V. where U is in kj, p in kpa and cubic meter. If the fluid changes from an initial state of 190 kpa, and m 3 to a final state of 420 kpa and 0.07m 3 with no work other than that done on the piston, find the direction and magnitude of the work and heat transfer. 50) (Nov 02) A system of volume V contains mass m of a gas at pressure P and temperature T. The macroscopic properties of the system obey the following relationship ( ) ( ) where a, b and R are constants. Obtain an expression far the displacement work done by the system during a constant temperature expansion from volume V = 1m 3 to volume V 2 = 10m 3. Calculate the work done if the mass = 10kg, a= 15.7 b= 1.07 x 10-2 R = 278 J/Kg/-K. 51) (A-95) A piston cylinder arrangement contains a gas of amount 2 kg and expand from an initial pressure of 6 bar and volume of 0.2m 3 to a final pressure of 1 bar. The process of expansion follows the law Pv 1.2 = const. The internal energy is related by U = 240 (Pv) where u in KJ/kg, P is in bar, v is in m 3 /kg. (i) If the expansion is frictionless, find the changes ill heat transfer, internal energy and work transfer. (ii) If during expansion 33 KJ of heat is transferred to the system, find the work done. Explain the difference in work for the above two cases. 52) (W2000) 10 kg of gas undergoes a process for which where, P is the pressure in bar and V is the volume in m 3. The initial volume is 5 m 3 and the temperature is 200 C. The find volume is 10m 3 and the temperature is -100 C. If u = 0.71T + 2 kj/kg, where T is in K. Find (i)work done (ii) Change in internal energy (iii) Heat transfer. SSFE FIRST LAW 53) (May 03) State first law of thermodynamics and prove that for a non-flow system it leads to Q= U+W.

6 54) A-96)Discuss the various assumptions made in the analysis of steady flow system and write the energy equation for it, clearly stating the meaning of each term involve in it. 55) (May 03) Write down the general steady flow energy equation. Derive its simplified when used for following system (i) water turbine (ii) boiler (iii) Throttling device (ii) Condenser (iii) Nozzle (i) Centrifugal water pump (iv) Gas turbine. 56) (Nov 02) prove that the shaft work during a steady flow process is 57) (May 02) Clearly explain the difference between non-flow and steady flow processes. If the heat transfer Q in both processes is same and initial conditions are same, show that the relation between the work developed in two process is given by Where is the change in flow work and change in potential and kinetic energy is zero, in case of stead flow process. 58) (Nov 02) Starting from the basic concept of first law of 1 thermodynamics for flow process derive steady flow energy equation and apply it on nozzle for calculating the nozzle exit velocity. 59) Nov 01) Derive the steady flow energy equation (SFEE ) for a throttling device. 60) A-96) 0.2 kg of a fluid per second undergoes through a reversible process. The properties of fluid at the inlet are pressure 1.4 bar, density 1.25 kg/m 3 velocity 125m/sec, internal energy 900kJ/kg. The properties at the exit conditions are pressure 5 bar density 4- kg/m 3, velocity 180 m/sec, internal energy 700 kj/kg. During the passage, the fluid rejects 50 kj/sec and rises through 50 meter. Determine the work done during the process. COMPRESSOR 61) (A-01) The compressor of a large gas turbine receives air from the ambient at 95 kpa, 20 0 C with low velocity. At the compressor discharge air exists at 1.14 MPa, C with a velocity of 120 m/s power input to the compressor is 5500 kw. Determine mass flow rate of air. 62) W-95) Air enters the compressor of a gas turbine at 0.9 bar and l5 0 C with a velocity of 120 m/sec. The air leaves the compressor at pressure of 4 bar, 200 C with a velocity of 60 m/sec. The process is adiabatic. Calculate the reversible work and irreversibility of process.

7 63) (W-99) A compressor takes in 50 kg/min of air at 98 kpa and 18 0 C and delivers at 550 kpa and 68 0 C The diameters of the intake and delivery pipes are 450 mm and 200 mm respectively. The compressor is driven by motor of 1000 kw. Determine the air velocities in the intake and delivery pipes and assuming that all the energy from the motor is transmitted to the air, estimate the rate at which heat is transferred to or from the air during compression. 64) At entry to the reciprocating compressor of a refrigerator, the refrigerant Freon 12 has a pressure of 2 bar and temperature of C (h = kj/kg). At the exit from the compressor the Freon has a pressure of 8 bar and a temperature of 45 0 C (h= kj/kg). The flow is steady. Evaluate the shaft work assuming the compression is adiabatic. 65) A water-jacketed ammonia compressor delivers 2 kg/min of refrigerant with a sp. Enthalpy of 1465 kj/kg. The sp. enthalpy of ammonia ill the suction line is kj/kg. Power supplied to drive the compressor is kw. Determine the rate of heat transfer to the water packet. TURBINE 66) (W-95) A water air-cooled air compressor requires a work input of 20kN-m per kg of air delivered. The enthalpy of air leaving the compressor is 15.6 kj/kg greater than that entering. Heat lost to the cooling water is 105 kj/kg. From the first law analysis estimate the heat lost by compressor to the atmosphere. 67) W-2000) In a chemical plant CO 2 at 9bar and 17 0 C is passed through a turbine where it expands isentropically till its pressure falls to 1.1 bar. Neglecting the changes in velocity and elevation, find (i) Final specific volume and temperature (ii) If the mass flow rate is 5 kg/min; find out the power developed by the turbine. Take Cv = 0.84 kj/kg K for CO 2 and consider CO 2 is a perfect gas. 68) (W-97) Air is expanded reversibly and adiabatically in a turbine from 3.5 bar and 260 C to 1 bar. The turbine is insulated and the inlet velocity is negligible. The exit velocity is 150 m/s. Find the work output of the turbine per unit mass of airflow. Take for air, Cp = kj/kg-k and = ) (Nov 01) A gas at 8 bar, 800 C and 150 m/s is passed through a turbine. The gas comes

8 out of the turbine at 2 bar, 600 C and 300 m/s. The process may be assumed to be adiabatic. The enthalpy of the gas at entry and exit of the turbine are 950 kj/kg and 700 kj/kg respectively. Determine the power of the turbine if the gas flow is 5 kg/s and the outlet of the turbine is 5 m below the inlet. 70) (A-97) In a certain flow-process, air at a pressure of 12 bar, specific volume 0.6m 3 /kg and having internal energy of 800 kj/kg. If the velocity of gas at inlet and out let is 9 m/sec and 7 m/sec, determine the power developed by the turbine. The heat transfer in the form of radiation losses is 30 kj/kg. The outlet of turbine is 5 m above the inlet. Also find the ratios of diameters of inlet and outlet pipes. Take mass flow rate as 40 kg/min. 71) (W-96) In a gas turbine unit, the mass flow rate of gas through the turbine is 15 kg/s and the power developed by the turbine is 2000 kw. The enthalpies of the gases at inlet and outlet are 1260 kj/kg and 400 kj/kg respectively and the velocity of gases at the inlet and outlet are 50 m/s and 110 m/s respectively. Calculate (i) The rate at which heat is rejected to the turbine and (ii) The area of the inlet pipe when specific volume of gases at the inlet is 0.45 m3/kg. 72) (A-95) A stream of gases at 7.5 bar, C and 140 m/s is passed through a turbine of a jet engine. The stream comes out of the turbine a 1.0 bar, C and 280m/s. The process may be assumed adiabatic the enthalpy of gas at the entry and exit of the turbine are 950 kj/kg and 650 kj/kg of gas respectively. Determine the power of the turbine if the gas flow is 5 Kg/s. 73) (May 02) A centrifugal pump delivers 50kg of water per second. The inlet and outlet pressure are 1 bar and 4.2 bar respectively. The suction is 2.2m below the center of the pump and delivery is 8.5m above the center of the pump. The suction and delivery pipe diameters are 20cm and l0cm respectively. Determine the capacity of electric motor run the pump. NOZZLE 74) (Nov 04) One kg of fluid enters a nozzle with a velocity of 3300m/min and enthalpy of 2990 kj/kg. The enthalpy of fluid at the exit is 2760 kj/kg. The nozzle is placed horizontally; neglect the heat losses from the nozzle. Determine (i) The velocity of fluid at the exit (ii) The mass flow rate, the inlet area of the nozzle is 0.095m 2 and specific

9 volume at inlet is 0.19m 3 /kg. (iii) The exit area of nozzle if the specific volume at the exit is 0.5m 3 /kg. 75) (Nov 03) At the inlet to a certain nozzle the enthalpy of fluid passing is 2800 kj/kg and velocity is 50m/s. At the discharge end the enthalpy is 2600 kj/kg. The nozzle is placed horizontally neglect the heat losses from the nozzle. Determine (i) The velocity of fluid at the exit (ii) The mass flow rate, the inlet area of the nozzle is 900cm 2 and specific volume at inlet is 0.187m 3 1kg. (iii) if the specific volume at the exit is 0.948m 3 /kg find the ratio of inlet diameter to the exit diameter. 76) A nozzle is a device for increasing the velocity of steadily flowing stream of fluid. At the inlet to a certain nozzle the enthalpy of the fluid is 3025 KJ/Kg and the velocity is 60m/s. At the exit from the nozzle the enthalpy is 2790 KJ/kg. The nozzle is horizontal and there is negligible heat loss from it (a) Find the velocity at the nozzle exit, (b) If the inlet area is 0.1 m 2 and specific volume at the inlet is 0.19m 3 /Kg, find the rate of flow of fluid, (c) If the Specific volume at the nozzle exit is 0.5m 3 /kg, find the exit area of the nozzle. 688 m/s, 3.16 Kg/s, m2). HEAT EXCHANGER 77) (Nov 02,W-98) Air at a temperature of 15 0 C passes through a heat exchanger at a velocity of 30m/s where its temperature is raised to C. It then enters a turbine with the same velocity of 30m/s and expand until the temperature falls to C on leaving the turbine the aan is taken at a velocity of 60 m/s to nozzle where it expands until the temperature has fallen to C. If the air flow rate is 2 Kg/s, calculate (i) The rate of heat transfer to the air in the heat exchanger. (ii) The power output from the turbine assuming no heat loss (iii) The velocity at exit from the nozzle assuming no heat loss. 78) (May 02) A certain water heater operates under steady flow conditions receiving 4.2 kg/s of water at 73 C temperature, enthalpy a kj/kg. The water is heated by mixing with steam which is supplied to the heater at temperature C and enthalpy 2676 kj/kg. The mixture leaves the heater as liquid water at temperature 100 C and enthalpy 419 kj/kg. How much steam must be supplied to the heater per hour? 79) (A-2000) In a steam power station steam flows steadily through a 0.2 m diameter pipeline from the boiler to the turbine. At the boiler end the steam conditions are found to be p =

10 4Mpa, t = C, h = kj/kg and v = m 3 /kg. At the turbine end the conditions are found to be p= 3.5 MPa, t =392 C, h = kg and v = m 3 /kg. There is a heat loss of 8.5 kj/kg from the pipeline. Calculate the steam flow rate. 80) (W-2000) In a boiler and turbine plant the steady flow condition prevails 3600 kg of water per hour enter the boiler at specific enthalpy of 840 kj/kg and velocity of 300 m/minute at 5 m elevation. Water receives the heat at constant pressure in the boiler and increases the specific enthalpy to 3140 kj/kg and the steam formed enters the turbine. The steam leaves the turbine at velocity of 3000 m/min at an elevation of 1m and specific enthalpy of 2640 kj/kg. Heat losses from the turbine and the boiler to the surroundings arc 72,000 kj/hr. Determine the power output of turbine. 81) In a system power station steam flows steadily through a 0.2m diameter pipe line from the boiler to turbine. At the boiler end, the steam conditions are found to be P = 4 MPa, t = C, h = kj/kg and v =0.073 m3/kg. At the turbine end, the conditions are found to be P 3.5 MPa, t = C, h = kj/kg and v = m 3 / kg, There is a heat loss of 8.5 kj/kg from the pipeline, Calculate the steam flow rate. MIXING PROBLEMS 82) A hot-water stream at 80 C enters a mixing chamber with a mass flow rate of 0.5 kg/s where it is mixed with a stream of cold water at 20 C. If it is desired that the mixture leave the chamber at 42 C, determine the mass flow rate of the cold-water stream. Assume all the streams are at a pressure of 250 KPa. Answer : Kg/s. 83) Liquid water at 300 KPa and 20 C is heated in a chamber by mixing it with superheated steam at 300 KPa and 300 C (h = kj/kg). Cold water enters the chamber at a rate of 1.8 kg/so If the mixture leaves the mixing chamber at 60 C, determine the mass flow rare of the superheated steam required. Answer: Kg/s. 84) A certain water heater operates under steady flow conditions receiving 4.2 kg/s of water at 75 0 C, h = kj/kg. The water is heated by mixing with steam which is supplied to the heater at a temperature of C and h = 2676 kj/kg. The mixture leaves the liquid water at a temperature of l00 0 C and h = 419 kj/kg. How much steam must be supplied to heater per hr. IDEAL GAS

11 CONSATNT VOLUME 85) A certain gas occupies a space of 0.3 m 3 at a pressure of 2 bar and a temperature of 77 0 C. It is heated at a constant volume, until the pressure is 7 bar. Determine change in internal energy and enthalpy during the process. 86) A tank contains 5 m 3 of air at 20 bars. Calculate the change in internal energy of air if it is cooled to 27 0 C. The pressure of air after cooling is 1.2 bar, assume air to be ideal gas. CONSTANT PRESSURE 87) (Nov 03) One kg of gaseous Co 2 contained in closed system undergoes a reversible process at constant pressure. During this process 42kJ of internal energy decreases. Determine the work done during the process. Take Cp= 840 J/kg- 0 C, Cv = 600 J/kg- 0 C. CONSTANT TEMPERATURE 88) A mass of 2.5 kg of air at 250 KPa and 23 0 C is contained in a gas-tight, frictionless piston-cylinder device. The air is now compressed to a final pressure of 400 KPa. During the process, heat is transferred from the air such that the temperature inside the cylinder remains constant. Calculate the work input during this process. (100 KJ). 89) Nitrogen at an initial state of 300 K, 150 KPa, and 0.4 m 3 is compressed slowly in an isothermal process to a final pressure of 800 KPa. Determine the work done during the process.(100 KJ ). 90) A quantity of air has a volume of 0.4 m 3 at a pressure of 5 bar and at a temperature of 80 0 C. It is expanded in a cylinder at constant temperature to a pressure of 1 bar. Determine the amount of work done. ISENTROPIC 91) A certain gas is compressed isentropically until topic pressure becomes five times its original value. During the process the temperature. increases from 27 to and 130 kj of work is done on 1kg of gas. Find the specific heats Cp and Cv. the gas constant R and the molecular weight of gas. 92) The volume of 0.18 kg of a certain gas was 0.15m 3 at a temperature of 15 0 C and a pressure of 1 bar. After adiabatic compression to 0,056m 3 the pressure was found to be 4 bar. Find the gas constant, molecular mass, sp. and change of internal energy.

12 93) Air at 1.02 bar, 22C initially occupying cylinder volume of 0.015m 3 is compressed reversibly and adiabatically by a piston to a pressure of 6.8 bar calculate (a) The final temp. (b) the final volume, (c) the work done 011 the mass or the air in the cylinder (234.5C, m 3, 2.76KJ) POLYTROPIC 94) (May 03) Derive an expression for work done in polytropic process. 95) (W-99) Air contained in a cylinder fitted with a piston is compressed in quasiequilibrium process. During the compression process the relation between pressure and volume is pv 1.25 = constant. The mass of air is 0.1kg. The initial pressure is 100 kpa, and the initial temperature is 20 0 C. The final volume is 1/8 of the initial volume. Determine work and heat transfer. 96) (Nov 04) 3 Kg of an ideal gas is expanded from a pressure of 7 bar absolute and volume 1.5 m 3 to a pressure of 1.4 bar absolute and volume 4.5 m 3. The specific heat at constant volume for the gas is 1 kj/kg- K calculate (i) Gas constant (ii) Change in enthalpy (iii) Initial and final temperature. 97) (Nov 03) A closed system undergoes a polytropic process in which the heat added is 17 kj and the internal energy increases by 48 kj. The initial state is 130 Kpa and 0.15m 3 and the final pressure is 800 KPa. Calculate the final volume in the process. If the system were air what mass would be required? 98) (W -95) One kg of air is compressed reversibly and adiabatically from 1 bar and 20 0 C to 6 bar according to relation pv 1.4 = constant. Neglecting changes in kinetic and potential energies compute the work done in compression for the following cases: (i) Non flow process (ii) Steady flow process. What accounts for the difference between (a) and (b)? R = 287 J/kg-K. 99) (W-95) 5 kg of air is compressed in reversible steady flow polytropic process from bar and 40 0 to bar and during this process to a law, followed by the gas is pv 1.25 = C. Determine change in enthalpy. Cv = kj/kg-k and R = I/kg-K. 100) (A-96). The pressure and temperature of air in a cylinder are 1 bar and 54 0 C. The air is compressed according to law pv 1.35 = const, until the pressure is 8 bar. The volume of air initially is 0.035m 3 Determine i) Mass of air in the cylinder (ii) Temperature at the

13 end of compression (iii) Work done on the air during compression and (iv) The heat rejected during compression. R = kj/kg-k = ) (A-98) The pressure and temperature of air in a cylinder are 1bar and 44 0 C. The air is compressed according to Pv 1.25 = constant until the pressure is 7 bar. The volume of air initially is 0.035m 3. Find (i) mass of air in the cylinder. (ii) temperature at the end of compression. (iii) work done 011 the air during compression. (iv) the heat rejected from the air during compression. Take: R = kj/kg-k, =1.4. COMBINED 102) (A-99) A cylinder contains 1 kg of certain fluid at an initial pressure of 20bar. The fluid is allowed to expand reversible behind a piston according to a law Pv 1.2 = constant until the volume is doubled. The fluid is then cooled reversibly at constant pressure until the piston regains its original position heat is then supplied reversibly with the piston firmly locked in position until the pressure rises to the original value of 20 bar. Calculate the network done by the fluid for an initial volume of 0.05m ) (W-98) A mass of air initially at C and 7()() kpa and occupies 0.028m 3. The air is expanded at constant pressure to rn 3. A polytropic process with n = 1.5 is then carried out, followed by a constant temperature process which completes a cycle. All the processes are reversible (i) Sketch the cycle in P-v and Ts planes. (ii) Find the heat received and heat rejected in the cycle (iii) Find the efficiency of the cycle. 104) (Nov 02) When a system is taken from stale A and B as shown in fig along path ACB. 80 J of heat flow into the system and the system does 30 J or work (i) How much heat flows into the system along the path ADB if the work done is 10J (ii) The system is returned from state B to state A along the curved path BA. The work done on the system is 20J. Docs the system absorb or liberate heat and how much? (iii) If U A = 0, U D = 40J find the heat absorbed in the process AD and DB. 105) (May 02) Three gms of nitrogen at 6 atrn and C in a frictionless piston cylinder device is expanded according to a law PV 1.2 = constant until its volume is doubled, then compressed at constant pressure to initial volume and then compressed at constant pressure to initial volume and then compressed at constant volume to initial state. Calculate work done by the gas. Draw P- V diagram for the process.

14 106) (W-95) One kg of air initially at 20 0 C and 1 bar is to he reversibly compressed to a final state of 10 bar and C. This may be achieved by any of the 0 the following two processes (i) Heating of constant volume followed by cooling at constant pressure. (ii) Isothermal compressions followed by hearing constant pressure. Assuming are to behave like an ideal gas with Cp = kj/kg-k and Cv = kj/kg-k determine the work required, heat transferred and changes in internal energy of the air for each or process. Sketch the path followed by each process on a single diagram. 107) (A2000) A fluids system contained in a piston and cylinder machine passes through a complete cycle of four processes. The sum of all heat transferred during the cycle is -340 kj. The system completes 200 cycles per minute. Complete the following table and compute net ate of work output in kw. Process Q kj/min W (kj/min) E/ u ( kj/min) ) (A-02) An Ideal gas of 2060 Kpa, m 3 and 610K expands according to the law PV= C to six times the initial volume. The gas is further cooled to 303K according to the law, V - constant. Finally compressed back to initial condition according to the law PV = C. Find tile network done and heat transfer during the complete cycle. Also calculate thermal efficiency of the cycle. Show the Cycle all P- V and T -S diagrams. Take = ) (A-02) 0.5 Kg of air is compressed reversibly and adiabatically from 80kPa C to 0.4 MPa and is then expanded at constant pressure to the original volume. Sketch these processes on the p - v and T-S planes. Compute the heat transfer and work transfer for the whole path. 110) (May 03) Determine the work done by the air which enters into an evacuated vessel from atmosphere when the valve is opened. The atmosphere pressure is 1.02 bar and 1.5 cubic meters of air at atmospheric conditions enters into vessel. 111) (W-2000) An automobile tyre contains air at 2 bar gauge at 30 0 C. The barometer reads 750 mm of Hg. Due to long duration running of the automobile, the air temperature in the tyre rises to 80 0 C. Assuming air to be perfect gas and tyre to be rigid. find the rise in the pressure in the tyre due to running.

15 112) (W01) A cylinder fitted with piston has all initial volume of 1 m 3 and contains Nitrogen at 150 kpa, 25 C. The piston is moved until the pressure is 1MPa and temperature C. During this compression process work done on the Nitrogen is 20 kj. Determine the amount of' heat transfer. Make suitable assumption. Molecular weight of Nitrogen = ) Nitrogen gas has to be stored at 140bar and 30 0 C in a steel cylinder having 0.5m 3 capacity. The cylinder has to be protected against excessive pressure by fusible plug which will melt and allow the gas to escape if the temperature rises too high. How many kg of Nitrogen will the cylinder hold at the desired condition? And at what temperature must the fusible plug melt in order to limit the pressure in the receiver to 155 bar.