MEPCO SCHLENK ENGINEERING COLLEGE, SIVAKASI

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RMK College of Engineering & TechnologyDEPARTMENT OF MECHANICAL ENGINEERING

UNIVERSITY QUESTIONS

ME 6301- Engineering Thermodynamics

Compiled by Dr.P.K.Devan

Professor, Mech. Engg UNIT-IShort Questions

1. State the First law for a closed system undergoing a change of state.2. What are point functions and path functions and give examples for each?3. What is meant by internal energy?4. A rigid tank is insulated around both its sides and ends. It is separated initially into two equal volumes by a partition. When one side contains 1 kg of gas at 100 kPA and 345oC, the other side remains evacuated. If the partition is removed, find pressure and temperature.5. Briefly explain the concept of continuum6. What is a PMM 1? Why is it impossible?7. IS it correct to say total heat or heat content of a closed system?8. Define process and cycle with one example each.9. Distinguish between heat and temperature.10. Define: (a) system (b) Cycle11. An insulated rigid vessel is divided into two parts by a membrane. One part of the vessel contains air at 10 MPa and other part is fully evacuated. The membrane ruptures and the air fill the entire vessel. Is there any heat or work transfer during the process? Justify your answer.12. Explain mechanical, chemical and thermal equilibrium.13. Show that work is path function and not a property.14. Mathematically state the steady flow energy equation and apply it to a condenser.15. Prove that an isolated system, there is no change in internal energy.16. Determine the molecular volume of any perfect gas at 600 N/m2 and 30oC. Universal gas constant may be taken as 8324 J/kg mole-K.17. Indicate the practical application of steady flow energy equation.18. What is the relationship between a system and its environment when the system is (a) Adiabatic (b) Isothermal19. What is meant by enthalpy?20. What is heat?21. Prove that cpcv = R.22. State Zeroth law of thermodynamics. What is its application?23. What is the convention for positive and negative work?24. What are the corollaries to the first law of thermodynamics?25. Distinguish between intensive and extensive properties by giving examples.26. Deduce an expression for the work done by a gas in a system during the reversible polytropic process.27. What is thermodynamic property? How are they classified?28. Is it possible to compress an ideal gas isothermally in an adiabatic cylinder device? Explin.29. Define thermodynamic system and surroundings.30. State Zeroth law and First law of Thermodynamics.

Big Questions

1. A piston and cylinder machines contains a fluid system which passes through a complete cycle of four processes. During a cycle, the sum of all heat transfers is -170 kJ. The system completes 100 cycles per min. Complete the following table showing the method for each item and compute the net rate of work output in kW.

Process Q(kJ/min)W (kJ/min)E (kJ/min)

ab 02170--------

bc 210000--------

cd -2100--------36000

da ---------------------

2. Air flows steadily at the rate of 0.5 kg/s through an air compressor, entering at 7 m/s velocity, 100 kPa pressure and 0.95 m3/kg volume and leaving at 5m/s, 700 kPA and 0.19 m3/kg. The internal energy of the air leaving is 90 kJ/kg greater than that of the air entering. Cooling water in the compressor jackets absorbs heat from the air at the rate of 58 kW.

(i) Compute the rate of shaft work input to the air in kW.

(ii) Find the ratio of the inlet pipe diameter to outlet pipe diameter.3. (i) Deduce the expression for the displacement work in an isothermal process.(ii) 3 kg of nitrogen gas at 6 atm and 160oC is expanded adiabatically to double its volume then compressed at constant pressure to its initial volume and then compressed again at constant volume to its initial state. Calculate the net work done on the gas. Draw the pV diagram for the processes. Specific heat ratio of nitrogen is 1.44. (i) Describe steady flow energy equation and deduce suitable expression for the expansion of gas in a gas turbine with suitable assumptions. (ii)Air expands by isentropic process through a nozzle from 784 kPa and 220o C to an exit pressure of 98 kPA. Determine the exit velocity and the mass flow rate, if the exit area is 0.0006 m2.5. Air of mass 0.5 kg is compressed reversibly and adiabatically from 80 kPa, 60o C to 0.4 MPa and is then expanded at constant pressure to the original volume. Sketch the process on pv plane and determine the heat transfer and work transfer. For air assume R=0.287kJ/kgK and cv=0.713 kJ/kgK.6. Air at 101.325 kPa, 20oC is taken into a gas turbine power plant at a velocity of 140 m/s through an opening of 0.15 m2 cross-sectional area. The air is compressed, heated, expanded through a turbine and exhausted at 0.18 MPA, 150 oC through an opening of 0.10 m2 cross sectional area. The power output is 375 kW. Calculate the net amount of heat added to the air in kJ/kg. Assume the air obeys the law pv=0.287(t+273), Where p is the pressure in kPa, v is the specific volume in m3/kg, and t is in temperature in oC. Take cp= 1.005 kJ/kg.k.7. A closed system consists of 1 kg of air which is initially at 1.5 bar and 67oC. The volume doubles as the system undergoes a process according to the law PV1.2=C. Find the work done, heat transfer and the change in entropy during this process. For air R=0.287 kJ/kg.K and =1.4.8. (i) Apply the steady flow energy equation to a Turbine and deduce an expression for work.

(ii) An air compressor takes in air at 100 kPA, 17oC and delivers it at 1 MPa, 600 K to a constant pressure cooler which it exits at 300 K. Making suitable assumptions find the specific compressor work and specific heat transfer. For air R=0.287 KJ/kgJK and =1.49. (i) A blower handles 1 kg/sec of air at 293 K and consumes a power of 15 kW. The inlet and outlet velocities of air are 100 m/sec and 150 m/sec respectively. Find the exit air temperature, assuming adiabatic conditions. Take cp=1.005 kJ/kg-K.

(ii) A room for four persons has two fans, each consuming 0.18 kW power and three 100 W lamps. Ventilation air at the rate of 0.0222 kg/sec enters with an enthalpy of 84 kJ/kg and leaves with an enthalpy of 59 kJ/kg.. If each persons puts out heat at the rate of 0.175 kJ/sec, determine the rate at which heat is to be removed by room cooler, si that a steady state is maintained in the room.10. (i) One litre of hydrogen at 273 K is adiabatically compressed to one half of its initial volume. Find the change in temperature of the gas, if the ratio of two specific heats for hydrogen is 1.4. (ii) The velocity and enthalpy of fluid at the inlet of a certain nozzles are 50 m/sec and 2800 kJ/kg respectively. The enthalpy at the exit of nozzle is 2600 kJ/kg. The nozzle is horizontal and insulated so that no heat transfer takes place from it. (a)Find velocity of fluid at exit of the nozzle.(b) Mass flow rate, if the area at inlet of nozzle is 0.09 m2 and specific volume of the fluid is ______________ . (c) Exit area of nozzle, if the specific volume at the exit of the nozzle is 0.495 m3/kg.11. (i) Derive an expression for the work transfer in an isothermal process.

(ii) Identify any four reasons for irreversibility in a process (iii) A work done by substance in a reversible non- flow manner is in accordance with V=(15/P) m3, where p is in bar. Evaluate the work done on or by the system as pressure increases from 10 to 100 bar. Indicate whether it is compression process or expansion process. If the change in internal energy is 500 kJ, calculate the direction and magnitude of heat transfer.12. (i) Define internal energy and prove that it is a point functions.

(ii) Establish the relationship between the specific heat at constant pressure and specific heat at constant volume.(iii) In a gas turbine installation, the gases enters the turbine at the rate of 5 kg/sec with a velocity of 50 m/sec and enthalpy of 900 kJ/kg and leave the turbine with 150 m/sec. and enthalpy of 400 kJ/kg. The loss of heat from the gases to the surroundings is 25kJ/kg. Assume R=0.287 kJ/kg-K, cp=1.004 kJ/kg-K and inlet conditions to be at 100 kPA and 27o C. Determine the diameter of the pipe. 13. (i) Prove that the change in entropy during a polytropic process is given by s2-s1=cv(n-k/n-1) log (T2/T1). Where k-ratio of specific heats and n-index of compression or expansion. (ii) A closed system consists of 1 kg of air which is initially at 1.5 bar and 67oC. The volume doubles as the system undergoes a process according to the law pV1.2=constant. Find the work transfer and change in entropy.14. (i) Deduce an expression for the work done by a system during a polytropic process.

(ii) Air flows steadily at the rate of 0.5kg/sec through an air compressor entering at 7 m/s velocity, 100 kPa pressure and 0.95 m3/kg specific volume and leaving at 5 m/s, 700 kPa and 0.19 m3/kg. The internal energy of air leaving is 90 kJ/kg greater than that of the air entering. Cooling water in the compressor jackets absorbs heat at the rate of 58 kW. Calculate the rate of shaft work input to the compressor.15. (i) From the first law and using the ideal gas property relations prove that PV = constant represent the reversible adiabatic process. (ii) A system receives 200 kJ of energy as heat at constant volume. Then it is cooled at constant pressure when 50 kJ of work as done on the system while it rejects 70 kJ of heat. Supposing the system is restored to the initial state by an adiabatic process, how much work will be done by the system.16. Air in a closed vessel of fixed volume 0.15m3 exerts a pressure of 12 bar at 250oC. If the vessel is cooled so that the pressure falls to 3.5 bar, determine the final temperature, heat transfer and change of entropy.17. A gas flows steadily through a rotary compressor. The gas enters the compressor at a temperature of 16oC, a pressure of 100 kPa and an enthalpy of 391.2 kJ/kg. The gas leaves the compressor at a temperature of 245oC, a pressure of 0.6 MPa and an enthalpy of 534.5kJ/kg. There is no heat transfer to or from the gas as it flows through the compressor. Evaluate the external work done per unit mass when the gas velocity at entry is 80m/s and that at exit is 160 m/s.18. A gas of mass 1.5 kg undergoes a quasi-static expansion which follows a relationship P=a+bV, where a and b are constants. The initial and final pressures are 1000 kPa and 200 kPa respectively and the corresponding volumes are 0.20 m3 and 1.2 m3. The specific internal energy of the gas is given by the relation u=1.5Pv 85 kJ/kg where P is in kPa and v is in m3/kg. Calculate the net heat transfer and the maximum internal energy of the gas attained during expansion.19. A room for four persons has two fans, each consuming 0.18 kW power and three 100 W lamps. Ventilation air at the rate of 80 kg/hr enters with an enthalpy of 84 kJ/kg and leaves with enthalpy of 59 kJ/kg.. If each persons puts out heat at the rate of 630 kJ/h, determine the rate at which heat is to be removed by room cooler, si that a steady state is maintained in the room.20. A mass of air is initially at 260oC and 700 kPa and occupies 0.028 m3. The air is expanded at constant pressure to 0.084 m3. A polytropic process with n=1.5 is then carried out, followed by a constant temperature process. All the processes are reversible. a. Sketch the cycle in the pv and TS planes

b. Find the heat received and heat rejected in the cycle.

c. Find the efficiency of the cycle.21. Air at a temperature of 15oC passes through a heat exchanger at a velocity of 30 m/s where its temperature is raised to 800oC. It then enters a turbine with the same velocity of 30 m/s and expands until the temperature falls to 650oC. On leaving the turbine, the air is taken at a velocity of 60 m/s to a nozzle where it expands until the temperature has fallen to 500oC. If the air flow rate is 2 kg/s, calculate

a. The rate of heat transfer to the air in the heat exchangerb. The power output from the turbine assuming no heat loss and .c. The velocity at exit from the nozzle, assuming no heat loss. Take the enthalpy of air as h=cpt, where cp is the specific heat equal to 1.005 kJ/kg-K and t the temperature.22. (i) 5 kg of air expands in to isothermally from 1m3 to 5.0 m3. Assuming air to be an ideal gas with constant specific heats, compute the change in entropy of air during the process.

(ii) What are the limitations of the First law of thermodynamics as applied to various thermal systems.23. Steam flows steadily through a turbine with a mass flow rate of 3 kg/s. The steam is at 70 bar and 500oC while entering the turbine and at 0.2 bar on leaving the turbine. The expansion process may be considered as isentropic. Determine the turbine output power.24. (i) Derive the general energy equation for a steady flow system and apply the equation to a nozzle and derive an equation for velocity at exit.

(iii) In an air compressor, air flows steadily at the rate of 0.5 kg/sec. At entry to the compressor, air has a pressure of 105 kPa and specific volume of 0.86 m3/kg and at exit those corresponding values are 705 kPa and 0.16 m3/kg. Neglect Kinetic and Potential energy change. The internal energy of air leaving the compressor is 95 kJ/kg greater than that of air entering. The cooling water in the compressor absorbs 60 kJ/sec of heat from the air. Find power required to drive the compressor.25. (i) Prove that internal energy is a property. (ii) 1 kg of gas at 1.1 bar, 27oC is compressed to 6.6 bar as per the law pv1.3=constant. Calculate work and heat transfer, if

a. When the gas is ethane with molar mass of 30 kJ/k mol and cp of 2.1 kJ/kgK.

b. When the gas is Argon with molar mass of 40 kJ/k mol and cp of 0.52 kJ/kgK26. In an isentropic flow through nozzle, air flows at the rate of 600 kg/hr. At inlet to the nozzle, pressure is 2 MPa and temperature is 127oC. The exit pressure is 0.5 MPa. Initial air velocity is 300 m/s determine (i) Exit velocity of air (ii) Inlet and exit area of nozzle.27. A centrifugal pump delivers 2750 kg of water per minute from initial pressure of 0.8 bar absolute. The suction is 2 m below and the delivery is 5 m above the centre of pump. If the suction and delivery pipes are 15 cm and 10 cm diameter respectively, make calculation for power required to run the pump.28. (i) What is thermodynamic system? Explain the classification of thermodynamic system

with suitable examples.

(ii) An air compressor draws in air at 1 bar pressure,0.5m3/kg specific volume and 5 m/s velocity and delivers at 7 bar pressure, 0.15 m3/kg specific volume and 7.5 m/sec velocity. If the enthalpy of air at delivery is 170 kJ/kg greater than that at inlet and the rate of airflow is 15 kg/min. Estimate the power of the compressor in kW and the ratio of pipe diameters at inlet and outlet. Assume a heat loss of 7300 kJ/min to the cooling water and surrounding air. 29. (i) Write down the steady flow energy equation clearly indicating the various terms.

(ii) A steady flow thermodynamic system receives fluid at the rate of 7 kg/min with an initial pressure of 2 bar, initial velocity 145 m/s, internal energy 820 kJ/kg and density 25 kg/m3. The fluid leaves the system with a final pressure of 7.5 bar, velocity 180 m/s, internal energy 750 kJ/kg and density 5 kg/m3. If the fluid receives 100 kJ/kg of heat during passing through the system and rises through 65 meters, determine the work done during the process.30. Air at 10oC and 80kPa enters the diffuser of a jet engine steadily with a velocity of 200 m/sec. The inlet area of the diffuser is 0.4 m2. The air leaves the diffuser with a velocity that is very small compared with the inlet velocity. Determine

(i) The mass flow rate of the air and`(ii) The temperature of the air leaving the diffuser.31. Air of mass 0.5 kg is compressed reversibly and adiabatically from 80 kPa, 60oC to 0.4 MPa and is then expanded at constant temperature to the initial pressure and compressed at constant pressure to the initial state. Determine the net work transfer.32. (i) Define the terms thermodynamic equilibrium, properties, cycle and work done.

(ii) Air in closed stationary system expands in a reversible adiabatic process from 0.5 MPa, 15oC to 0.2 MPA. Find the final temperature, and per kg of air, the change in enthalpy, the heat transferred and the work done.

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UNIT-IIShort Questions

1. Why the second law of thermodynamics is called a directional law of nature?2. The coefficient of performance of a heat pump is 5. Find the COP of refrigerator if both are reversible devices interacting between same source temperature and sink temperature.3. What do you understand by the concept of entropy?4. What is loss of availability? How is related to entropy of universe?5. What is PMM II?6. Mention any four factors which render processes irreversible.7. 1 kg water boils melt at constant atmospheric pressure and at 100oC to form liquid water. If the latent heat of vaporisation of water is 2258 kJ/kg, calculate the entropy change during this process.8. What do you understand by a reversible process?9. What are the two major conclusions deduced from the Carnot principle.10. What are the limitations of first law of thermodynamics?11. State the Kelvin-Plank and Clausius statements.12. Write the necessary conditions for reversible process.13. A reversible heat engine operates between a source at 800oC and a sink at 30oC. What is the least rate of rejection per kW network out put of the engine?14. 1 kg of ice melts at constant atmospheric pressure and at 0oC to form liquid water. If the latent heat of fusion of ice is 333.3 kJ/kg, calculate the entropy change in this process.15. Explain the terms source and sink.16. What do you understand by the entropy principle?17. State the second law of thermodynamics. Also write its physical significance.18. A domestic food freezer maintains a temperature of -15oC. The ambient air is at 30oC. If heat leaks into the freezer at a continuous rate of 1.75kJ/sec, what is the least power necessary to pump this heat out continuously?19. In some refrigerator systems, approximately the power requirement is 1 kW for every ton of refrigeration. Find the COP achieved.20. State the Clausius statement of second law of thermodynamics.21. State few example of irreversible process.22. Deduce the relationship between the COP of heat pump and refrigerator.23. What is meant by thermodynamic temperature scale? How do you device such scale? 24. What is the process involved in a Carnot cycle, sketch the same in P-V and T-S diagram.

BIG QUESTIONS1. (i) Give the Clausius statement of second law.

(ii) A house hold refrigerator is maintained at a temperature of 275 K. Every time the door is opened, warm material is placed in side, introducing an average of 420 kJ, but making only a small change in the temperature of the refrigerator. The door is opened 20 times a day and the refrigerator operates at 15% of the ideal COP. The cost of work is Rs 2.50 per kWhr. What is the bill for the month of April for this refrigerator? The atmosphere is at 303 K.2. (i) What is a thermal energy reservoir?

(ii) Establish the inequality of Clausius.3. (i) State Carnot theorem.

(ii) An inventor claims to have developed an engine which receives 1000 kJ at a temperature of 160oC. It rejects heat at a temperature of 5oC and delivers 0.12 kWh of mechanical work. Is this a valid claim? Justify your answer through Clausius inequality.

(iii) A refrigerator operating between two identical bodies cool one of the bodies to a temperature T1. Initially both the bodies are at temperature T1. Deduce the expression for the minimum specific work input, taking their specific heat as c.4. (i) Deduce the expression for the entropy change in terms of pressure and temperature.

(ii) One kg of ice at -10oC is allowed to melt in atmosphere at 30 oC. The ice melts and the water so formed rises in temperature to that of atmosphere. Determine the entropy change of universe and write your comment based on principle of increase in entropy. The specific heat of ice is 2 kJ/kg-K and its latent heat is 335 kJ/kg.5. Two Carnot engines A and B are operated in series. The first one receives heat at 870 K rejects to the reservoir at temperature T. The second engines receives the heat rejected by the first engine and inturn to the reservoir at 300 K. Calculate the temperature in oC for the following cases.

(i) Work output of the engine is equal

(ii) The efficiency of the two engines is equal.6. A Carnot engine operates between source temperature T1 and sink temperature T2. It is decided to increase the efficiency by either increasing the source temperature or decreasing the sink temperatures by the finite amount. Establish which is more effective.7. (i) State and prove Carnot theorem. (ii) A reversible power cycle is used to drive a reversible heat pump cycle. The power cycle takes in Q1 heat unit at T1 and rejects Q2 at T2. The heat pump abstracts Q4 from the sink at T4 and discharges Q3 at T3. Develop an expression for the ratio Q3/Q1 in terms of the four temperatures. What must be the relationship of the temperatures for Q3/Q1 to exceed a value of unity?8. (i) What are the conditions for reversibility? Explain.

(ii) A heat exchanger circulates 5000 kg/hr of water to cool oil from 150oC to 50oC. The rate of flow of oil is 2500 kg/hr. The average specific heat of oil is 2.5 kJ/KgK. The water enters the heat exchanger at 21oC. Determine the net change in entropy due to heat exchange process and the amount of work obtained if cooling of oil is done by using the heat to run a Carnot engine with sink temperature of 21oC.9. (i) Deduce Clausius inequality and interpret it.

(ii) An ideal gas of 0.12 m3 is allowed to expand isentropically from 300 kPa and 120oC to 100 kPa. 5 kJ of heat is then transferred to the gas at constant pressure. Calculate the change in entropy for each process. Assume =1.4 and cp=1.0035 kJ/kgK. If these two processes are replaced by a reversible polytropic expansion, find the index of expansion between original and final states. What will be the total changes in entropy?10. A gas is flowing through a pipe at the rate of 2 kg/s. Because of inadequate insulation the gas temperature decreases from 800 to 790oC between two sections in the pipe. Neglecting pressure losses, calculate the irreversibility rate due to this heat loss. Take To=300 K and a cp=1.1 kJ/kg-K. For the same temperature drop of 10oC when the gas cools from 80oC to 70oC due to heat loss, what is the rate of entropy degradation? Take the same values of To and cp. What is the inference you can draw from this example?11. Two reversible heat engines A and B are arranged in series, A rejecting heat directly to B. Engine A receives 200 kJ at a temperature of 421oC from a hot source, while engine B is in communication with a cold sink at a temperature of 4.4oC. If the work output of A is twice that of B, Find

(i) The intermediate temperature between A and B

(ii) The efficiency of each engine

(iii) The heat rejected to the cold sink12. One kg of ice at -5oC is exposed to the atmosphere which is at 20oC. The ice melts and comes into thermal equilibrium with the atmosphere. (i) Determine the entropy increase of the universe. (ii) What is the minimum amount of work necessary to convert the water back to ice at -5oC? Assume cp of ice as 2.093 kJ/kg-K and the latent heat of fusion of ice as 333.3 kJ/kg . 13. (i) Derive the COP of heat pump.

(ii) In a Carnot heat engine 5 kg of air acts as the working substance. The peak cycle temperature is 930 K and the maximum pressure is 8.4x103 kPa. The heat addition per cycle is 4.2 kJ. Determine the maximum cylinder volume if the minimum temperature during the cycle is 315 K.14. Two kg of air at 500 kPa, 80oC expands adiabatically in a closed system until its volume is doubled and its temperature becomes equal to that of the surroundings which is at 100 kPa, 5oC for this process, determine

(i) The maximum work

(ii) The change in availability

(iii) The irreversibility.

For air cv=0.718 kJ/kg-K, u=cvT and R=0.287 kJ/kg-K.15. Establish the inequality of Clausius and express entropy change in irreversible process.16. (i) Two reversible adiabatic lines cannot intersect. Is this statement true or false? Justify the answer.

(ii) A reversible engine operates between a source at 972oC and two sinks, one at 127oC and another at 27oC. The energy rejected is same at both the sinks. What is the ratio of heat supplied to the heat rejected? Also calculate the efficiency.17. (i) What are the conditions for reversibility?

(ii) Differentiate between heat pump and refrigerator.

(iii) 50 kg of water is at 313 K and enough ice at -5oC is mixed with water in an adiabatic vessel such that at the end of the process all the ice melts and water at 0oC is obtained. Find the mass of ice required and the entropy change of water and ice. Given cp of water = 4.2 kJ/kg-K, cp of ice =2.1 kJ/kg-K and latent heat of ice=335kJ/kg.18. A heat engine operating between two reservoirs at 1000 K and 300 K is used to drive heat pump which extracts heat from the reservoir at 300 K at a rate twice that at which engines rejects heat to it. If the efficiency of the engine is 40% of the maximum possible and the co-efficient of performance of the heat pump is 50% of the maximum possible, make calculations for the temperature of the reservoir to which the heat pump rejects heat. Also work out the rate of heat rejection from the heat pump if the rate of supply of heat to the engine is 50 kW.19. One kg of air is contained in a piston cylinder assembly at 10 bar pressure and 500 K temperature. The piston moves outwards and the air expands to 2 bar pressure and 350 K temperature. Determine the maximum work obtainable. Assume the environment conditions to be 1 bar and 290 K. Also make calculations for the availability in the initial and final states.20. (i) Prove that Kelvin-Plank statement and Clausius statement of second law of thermodynamics are equivalent.

(ii) Two reversible heat engines A and B are arranged in series with A rejecting heat directly to B through an intermediate reservoir. Engine A receives 200 kJ of heat from reservoir at 421oC and engine B is in thermal communication with a sink at 4.4oC. If the work output of A is twice that of B find (i) the intermediate temperature between A and B, (ii)the efficiency of each engine and (iii)the total heat rejected to the cold sink.21. State and prove Clausius inequality and hence deduce that the property entropy exist.22. A steam turbine receives steam at a pressure of 1 MPa, 300oC. The steam leaves the turbine at a pressure of 15 kPa. The work out put of the turbine is measured and is found to be 600 kJ/kg of steam flowing through the turbine. Determine the efficiency of the turbine.

23. A heat pump uses water in a river at 6oC as an energy source and it delivers heat at 65oC to a building. It operates at 65% of its maximum possible COP between these temperatures and is powered by a 1.5 kW motor. What is the heat out put to the building?

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UNIT-IIIShort Questions

1. If water is at 65oC at 1 atm., what is the state of water? What is its specific enthalpy?2. Plot the standard Rankine cycle on T-s diagram and label all the processes assuming the steam to be dry and saturated at the end of expansion.3. Define saturation state of steam.4. Why Carnot cycle is not practicable for steam power plant?5. Define triple point and identify the triple point of water.6. Steam in pipe line with a pressure with pressure of 1000 kPa flows through a throttling calorimeter where pressure is 100 kPa and temperature is 120oC. What is the initial quality of steam if enthalpy remains constant during throttling?7. Define the term quality and give expressions to determine the entropy of wet steam of given quality x, in terms of entropy of standard liquid and dry saturated vapour.8. What is a pure substance? Give examples.9. How evaporation differ from boiling?10. What do you understand by pure substance? Give some typical example.11. What is critical point? What are the properties of water at critical point?12. Define critical pressure and temperature for water.13. Sketch the Rankine cycle on a p-V plane and name the various processes.14. Determine whether water at the following states is a compressed liquid, a superheated vapour or a mixture of saturated water-steam: (a) 18 MPa, 0.003 m3/kg (b) 130oC, 200 kPa.

Big Questions1. 3 kg of steam at 18 bar occupy a volume of 0.2550 m3. During a constant volume process, the heat rejected is 1320 kJ. Determine final internal energy. Find dryness fraction and pressure, change in entropy and work done.2. (i) Briefly explain the process of super heated steam formation with the help of T-s diagram.

(ii) A steam power plant runs on a single regenerative heating process. The steam enters the turbine at 30 bar and 400oC and steam fraction is withdrawn at 5 bar. The remaining steam exhausts at 0.10 bar to the condenser. Calculate the efficiency, steam fraction and steam rate of the power plant. Neglect pump work.3. A cyclic steam power plant is to be designed for a steam temperature at turbine inlet of 633 K and an exhaust pressure of 8 kPa. After isentropic expansion of steam in the turbine, the moisture content at the turbine exhaust is not to exceed 15%. Determine the greatest allowable steam pressure at the turbine inlet and calculate the Rankine cycle efficiency for these steam conditions. Estimate also the mean temperature of heat addition.4. In a reheat steam cycle, the maximum steam temperature is limited to 773 K. The condenser pressure is 10 kPa and the quality at turbine exhaust is 0.8778. Had there been no reheat , the exhaust quality would have been 0.7592. Assuming ideal processes, determine (i) reheat pressure (ii) the boiler pressure (iii) the cycle efficiency (iv) the steam rate. 5. (i) Draw p-T diagram and label various phases and transitions. Explain the process of sobaric heating above triple point pressure with the help of p-T diagram.

(ii) 2 kg of water at 200 oC are contained in a 20m3 vessel. Determine the pressure, nthalpy, mass and volume of vapour within the vessel.6. Draw Rankine cycle with one open type feed water heater. Assume the condition of the steam before entering the turbine to be superheated. Sketch the cycle on T-s diagram.

(i) In an ideal reheat cycle, the steam enters the turbine at 30 bar and 500oC. After expansion to 5 bar, the steam is reheated to 500oC and then expanded to the condenser pressure of 0.1 bar. Detrmine the cycle thermal efficiency and mass rate of steam. Take power output as 100 MW.7. (i) A vessel having a volume of 5 m3 contains 0.05 m3 of saturated liquid water and 4.95 m3 of saturated water vapour at 0.1 MPa. Heat is transferred until the vessel is filled with saturated vapour. Determine the heat transfer, work done and change in entropy for the process.

(ii) Explain with neat sketch the construction of the Mollier diagram and give its use in thermodynamic representation.8. Determine the volume change when 1 kg of saturated water is completely vaporised at a pressure of (i) 1 KPa (ii) 100 kPa and (iii) 10,000 kPa9. Steam at 7 bar and 0.9 dryness fraction expands isothermally to 1.8 bar. Calculate the change in internal energy and enthalpy using steam tables.10. Estimate the quantity of heat required to produce 5 kg of steam at 6 bar from water at 0oC, when the steam is 80% dry and when it is at 300oC. Take cp of superheated steam as 2.3 kJ/kg-K.11. Steam at 20 bar, with a degree of superheat of 80oC is supplied by a boiler at 1.5 kg/sec to a turbine. It is expanded isentropically to 0.07 bar. Determine the quality of steam after expansion, heat supplied in the boiler in kW, heat rejected in the condenser in kW, power generated and thermal efficiency neglecting pump work.12. In a single heater regenerative cycle the steam enters the turbine at 30 bar, 400oC and the exhaust pressure is 0.10 bar. The feed water heater is a direct-contact type which operates at 5 bar. Find (i) the efficiency and the steam rate of the cycle and (ii) the increase in mean temperature of heat addition, efficiency and steam rate as compared to the Rankine cycle ( with out regeneration ) Neglect pump work.13. One kg of steam is contained in an elastic balloon of spherical shape which supports an internal pressure proportional to its diameter. The initial condition of steam is saturated vapour at 110oC. Heat is transferred to steam until pressure reaches 200 kPa. Determine: (i) Final temperature (ii) Heat transferred. Take cp=2.25 kj/kg-K. 14. (i) Draw the p-T diagram of pure substance and label all the phases and phase changes?

(ii)What do you understand by dryness fraction? What is its importance?

(iii) A rigid tank of 0.03 m3 capacity contains wet vapour at 80 kPa. If the wet vapour mass is 12kg, calculate the heat added and the quality of the mixture when the pressure inside the tank reaches 7 MPa.15. (i) What are the major problems of Carnot vapour cycle?

(ii) What are methods for improving the performance of Rankine cycle?

(iii) Steam enters the turbine at 3 MPa and 400oC and is condensed at 10 kPa. Some quantity of steam leaves the turbine at 0.6 MPa and enters open feed water heater. Compute the fraction of steam extracted per kg of steam and cycle thermal efficiency.16. 1 kg of steam initially dry saturated at 1.1 MPa expands in a cylinder following the law pV1.3=C. The pressure at the end of expansion is 0.1 MPa. Determine (i) The final volume (ii) Final dryness fraction (iii) work done (iv) The change in internal energy (v) The heat transferred.17. Steam at a pressure of 2.5 MPa and 500oC is expanded in a turbine to a condenser pressure of 0.05MPa. Determine for Rankine cycle (i) the thermal efficiency of Rankine cycle (ii) Specific steam consumption.

If the steam pressure is reduced to 1MPa and the temperature is kept same 500oC. Determine the thermal efficiency and specific steam consumption. Neglect feed pump work.18. Ten kg of water at 45o C is heated at a constant pressure of 10 bar until it becomes superheated vapour at 300oC. Find the changes in volume, enthalpy, internal energy and entropy.19. In a steam generator compressed liquid water at 10 MPa, 30oC enters a 30 mm diameter tube at the rate of 3 lit/sec. Steam at 9 MPa, 400OC exits the tube. Find the rate of heat transfer to the water.20. A vessel of volume 0.04 m3 contains a mixture of saturated water and saturated steam at a temperature of 250oC. The mass of the liquid present is 9 kg. Find the pressure, the mass, the specific volume, the enthalpy and the internal energy.

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UNIT-IVShort Questions

1. What do you mean by equation of state?2. State the Daltons law of partial pressure.3. Have you encountered any ideal gas? If so, where?4. What is coefficient of expansion?5. What is equation of state? Write the same for an ideal gas.6. What is the significance of compressibility factor?7. What are reduced properties? Give their significance.8. Define Joule-Thomson coefficient. 9. Sketch a skeleton compressibility chart and show the constant reduced temperature characteristics on it.10. How does the Van der Waals equation differ from the ideal gas equation of state?11. Deduce the expression for the gas constant of the mixture of two non reacting ideal gases A and B.12. Explain the construction and give the use of generalised compressibility chart.13. What are the unique features of Vader Waals equation of state?14. What is compressibility factor? What does it signify? What is its value for Vander Waals gas at critical point?15. State the Avagodros law and state its significance.16. Write the Maxwells equations and its significance.17. A system contains air in the form of liquid-vapour mixture in equilibrium. Can this mixture be treated as pure substance? Justify your answer.Big Questions

1. (i) A certain gas has cp= 0.913 and cv=0.653 kJ/kg-K. Find the molecular weight and the gas constant R of the gas.

(ii) Derive the Clausius Clapreyon equation.2. (i) Derive Maxwells equations.

(ii) Prove T ds = cv dT + T (p/T)v dV3. (i) Prove that the total pressure is a sum of partial pressures.

(ii) A closed vessel has a capacity of 0.5 m3. It contains 20% nitrogen and 20% oxygen, 60% carbon dioxide by volume at 20o C and 1 MPa. Calculate the molecular mass, gas constant, mass percentage and the mass of mixture.4. (i) Derive Tds relations in terms of temperature & pressure changes and temperature 7 volume changes.

(ii) Derive Joule Kelvin effect with the help of T-p diagram.5. Explain the Joule Thomson effect with the help of T-p diagram and derive the expression for Joule Thomson coefficient. Show that the value of this coefficient for an ideal gas is zero.6. (i) What are the difference between real and ideal gases?

(ii) Write down the van der Waals equation of state for real gases and how is it obtained from ideal gas equation by incorporating real gas corrections?

(ii) A tank contains 0.2 m3 of gas mixture composed of 4 kg of nitrogen, 1 kg of oxygen and 0.5 kg of CO2. If the temperature is 20oC, determine the total pressure, gas constant and molecular mass of the mixture.7. Calculate the pressure of steam at temperature of 500oC and a density of 24 kg/m3 using

(i) The ideal gad equation

(ii) The Van der Waals equation

(iii) The compressibility factor and

(iv) The steam table8. Prove that cp-cv = -T(V/T)p2 (P/V)T. What are the facts one can infer from the above equation?9. Using Maxwell relations cp-cv = TV2/KT. 10. A mixture of ideal gas consist of 3 kg of N2 and 5 kg of CO2 at a pressure of 300 kPa and a temperature of 20oC. Find

(i) The mole fraction of each constituent

(ii) The equivalent molecular weight of the mixture

(iii) The equivalent gas constant of the mixture

(iv) The partial pressures and the partial volumes.11. Prove that cp of ideal gas is a function of temperature only.12. A mixture of 2 kg of oxygen and 2 kg Argon is in an insulated piston cylinder arrangement at 100 kPa, 300 K. The piston now compresses the mixture to half its initial volume. Find the final pressure, temperature and piston work. Molecular weight of oxygen is 32 and for Argon is 40. Ratio of specific heats for oxygen is 1.39 and for Argon is 1.667.13. Deduce the Maxwells relations and from the third relation deduce the Clausius-Clapeyron equation. Also apply this equation to the vaporisation process for pure substance.14. Entropy is a function of any two properties like p and V, P and T etc. For pure substance with the help of Maxwells equation, Prove

(i) Tds=cvdT + T(/K).dv

(ii) Tds=cpdT-V..dp.T

(iii) Tds=[Kcv/].dp + [cp/v].dv15. Determine change of internal energy and change of entropy when the gas obeys Vander Waals equation. 16. 0.45 kg of CO and 1 kg of air is contained in a vessel of volume 0.4 m3 at 15oC. Air has 23% of O2 and 76.7% of N2 by mass. Calculate the partial pressure of each constituent and total pressure in the vessel. Molar masses of CO,O2 and N2 are 28,32 and 28 kg/k-mol.17. Explain the flow process of ideal gas through throttle valve. Derive the expression for Joule Thomson coefficient and deduce its value for an ideal gas.18. Derive Tds equation when

(i) T and V independent

(ii) T and P independent

(iii) P and V independent.19. A mixture of ideal gases consist of 3 kg of N2 and 5 kg of CO2 at a pressure of 300 kPa and at 20oC. Find (i) the mole fraction of each constituent, (ii) equivalent molecular weight of the mixture (iii) equivalent gas constant of the mixture (iv) the partial pressures and partial volume (v) volume and density of the mixture and (vi) cp and cv of the mixture. Assume the value of cp/cv for CO2=1.286 and for N2=1.4.

***********UNIT-VShort Questions

1. What is specific humidity and how do you calculate it?2. What is meant by adiabatic saturation temperature?3. Define specific humidity.4. Define dew point temperature5. What is sensible heating?6. If the relative humidity of air is 60% at 30oC, what is the partial pressure of water vapour?7. What is thermodynamic wet bulb temperature?8. What is dew point temperature? How is it related to dry bulb and wet bulb temperature at the saturation condition?9. What is adiabatic mixing and write the equation for that?

Big Questions

1. (i) Draw the psychrometric chart and show any two psychrometric processes on it.

(ii) A sample of moist air at 1 atm. and 25oC has a moisture content of 0.01% by volume. Determine the humidity ratio, the partial pressure of water vapour, the degree of saturation, the relative humidity and the dew point temperature.2. (i) Describe the process of adiabatic mixing of two streams and deduce the ratio of masses of two streams in terms of humidity and/or enthalpy.

(ii) The temperature of the windows in a house on a day in winter is 5oC. When the temperature in the room is 23oC and the barometric pressure is 74.88 cm Hg, what would be the maximum relative humidity that could be maintained in the room without condensation on the window panes? Under these conditions, find the partial pressure of the water vapour and air, the specific humidity and the density of the mixture.3. In a laboratory test, a sling psychrometer recorded dry bulb and wet bulb temperatures as 303 K and 298 K respectively. Calculate (i) vapour pressure (ii) relative humidity (iii) specific humidity (iv) degree of saturation (v) dew point temperature (vi) enthalpy of the mixture.4. (i) 1 kg of air at 313 K dry bulb temperature and 50% relative humidity is mixed with 2 kg of air at 293 K dry bulb temperature and 293 K dew point temperature. Calculate the temperature and specific humidity of the mixture.

(ii) Show the following processes on a skeleton psychrometric chart.

(a) Dehumidification and cooling

(b) Heating and dehumidification5. (i) Describe the adiabatic cooling process and deduce the expression for the enthalpy

(ii) Air at 20oC, 40% relative humidity is mixed adiabatically with air at 40oC, 40% RH in the ratio of 1 kg of former with 2 kg of latter (on dry basis). Find the final condition (humidity and enthalpy) of air.6. (i) Draw the cooling and dehumidification process and explain Sensible Heat Factor (SHF), Bypass Factor and effectiveness of coil.

(ii) A stream of air at 101.32 kPa, 18oC and relative humidity of 30% is flowing at the rate of 14.15 m3/min. A second stream at 101.32 kPa, 38oC and RH of 50% is flowing at the rate of 8.5m3/min.. The two steams are mixed adiabatically to form a third stream at 101.32 kPa. Determine the specific humidity , the relative humidity and the temperature of the third stream.7. Atmospheric air at 1.0132 bar has DBT of 32oC and a WBT of 26oC. Compute:

(i) The partial pressure of water vapour

(ii) The specific humidity

(iii) The dew point temperature

(iv) The relative humidity

(v) The degree of saturation

(vi) The density of the vapour in the mixture (vii) The enthalpy of mixture.8. An air water vapour mixture at 0.1 MPA, 30oC, 80% RH has a volume of 50 m3. Calculate the specific humidity, dew point, wet bulb temperature, mass of dry air and mass of water vapour.9. (i) Explain the adiabatic saturation process using T-s diagram and derive an expression to determine the specific humidity of unsaturated air entering the adiabatic saturator.

(ii) Air at 20oC, 40% relative humidity is mixed adiabatically with air at 40oC, 40% RH in the ratio of 1 kg of former with 2 kg of latter (on dry basis). Find the final condition (humidity and enthalpy) of air.10. Explain in detail about the following.

a. Sensible heating or cooling

b. Cooling and dehumidification.

c. Heating and dehumidification.11. The atmospheric air at 30oC DBT and 70% RH enters a cooling coil at the rate of 200 m3/min. The coil temperature is 14oC and the bypass factor is 0.1. Determine

(i) The temperature of air leaving the coil

(ii) Capacity of the cooling coil in TR

(iii) The amount of water vapour removed

(iv) Sensible Heat Factor for the process.12. The volume flow rate of air is 800 m3/min of re-circulated at 22oC DBT and 10oC dew point temperature is to be mixed with 300 m3/min of fresh air at 30oC DBT and 50% RH. Determine the enthalpy, Specific volume, Humidity ratio and dew point temperature of the mixture.

13. (i) Differentiate between

Dry bulb temperature and wet bulb temperature

Wet bulb temperature and wet bulb depression

(ii) Air at 16oC and 25% RH passes through a heater and then through a humidifier to reach final dry bulb temperature of 30oC and 50% RH. Calculate the heat and moisture added to the air. What is sensible heat factor?14. (i) In an adiabatic mixing of two streams, derive the relationship among the ratio of mass of streams, ratio of enthalpy change and ration of specific humidity change.

(ii) Saturated air at 20oC at a rate of 1.167 m3min is mixed adiabatically with the outside air at 35oC and 50% RH at a rate of 0.5 m3/sec. Assuming adiabatic mixing condition at 1 atm., determine specific humidity, relative humidity, dry bulb temperature and volume flow rate of the mixture.15. A room 7 m x 4 m x 4 m is occupied by an air water vapour mixture at 38oC. The atmospheric pressure is 1 bar and the relative humidity is 70%. Determine humidity ratio, dew point temperature, mass of dry air and mass of water vapour. If the mixture of air water vapour is further cooled at constant pressure until the temperature is 10oC. Find the amount of water vapour condensed.16. Air at 20oC, 40% RH is mixed adiabatically with air at 40oC, 40% RH in the ratio of 1 kg of the former with 2 kg of later. Find the final condition of air. Draw the process in chart also as diagram.17. (i) Indicate the application of psychrometry in industry

(ii) The air in a room has a pressure of 1 atmosphere, a dry bulb temperature of 24oC and a wet bulb temperature of 17oC. Compute the following:

i. The specific humidity

ii. The dew point temperature

iii. The relative humidity

iv. The degree of saturation.

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