Question Bank Thermal Engineering Diploma IV Sem

Q1. Calculate the gas pressure using a mercury manometer with one limb open to atmosphere

as shown in Fig.. Barometer reading is 76 cm and density of mercury is 13.6 103 kg/m3. Take g

= 9.81 m/s2.

Q2. An incompressible gas in the cylinder of 15 cm diameter is used to support a piston, as

shown. Manometer indicates a difference of 12 cm of Hg column for the gas in cylinder.

Estimate the mass of piston that can be supported by the gas. Take density of mercury as 13.6

103 kg/m3.

Q3. A vessel of 5 m3 capacity contains air at 100 kPa and temperature of 300K. Some air is

removed from vessel so as to reduce pressure and temperature to 50 kPa and 7C respectively.

Find the amount ofof air removed and volume of this mass of air at initial states of air. Take R =

287 J/kg.K for air.

Q4. A cylindrical vessel of 1 m diameter and 4 m length has hydrogen gas at pressure of 100

kPa and27C. Determine the amount of heat to be supplied so as to increase gas pressure to 125

kPa. For hydrogen take Cp = 14.307 kJ/kg.K, Cv = 10.183 kJ/kg K.

Q5. Write short notes on the following: Thermodynamic properties, state, path, process,

closed system, isolated system, open system, extensive and intensive properties.

Q6. A gas at 65 kPa, 200C is heated in a closed, rigid vessel till it reaches to 400C.

Determine the amount of heat required for 0.5 kg of this gas if internal energy at 200C and

400C are 26.6 kJ/kg and 37.8 kJ/kg respectively.

Q7. Carbon dioxide passing through a heat exchanger at a rate of 50 kg/hr is to be cooled

down from 800C to 50C. Determine the rate of heat removal assuming flow of gas to be of

steady and constant pressure type. Take cp = 1.08 kJ/kg K.

Q8. A gas contained in a cylinder is compressed from 1 MPa and 0.05 m3 to 2 MPa.

Compression is governed by pV1.4 = constant. Internal energy of gas is given by;U= 7.5 pV

425, kJ.where p is pressure in kPa and V is volume in m3. Determine heat, work and change in

internal energy assuming compression process to be quasi-static. Also find out work interaction,

if the 180 kJ of heat is transferred to system between same states. Also explain, why is it

different from above.

Q9. An air compressor requires shaft work of 200 kJ/kg of air and the compression of air

causes increase in enthalpy of air by 100 kJ/kg of air. Cooling water required for cooling the

compressor picks up heat of 90 kJ/kg of air. Determine the heat transferred from compressor to

atmosphere.

Q10. 3 kg of air at 1.5 bar pressure and 77C temperature at state 1 is compressed

polytropically to state2 at pressure 7.5 bar, index of compression being 1.2. It is then cooled at

constant temperature to its original state 1. Find the net work done and heat transferred.

Q11. Show that for a polytropic process.

where Q and W are heat and work interactions and n is polytropic index.

Q12. Water in a rigid, insulating tank is set in rotation and left. Water comes to rest after some

time due to viscous forces. Considering the tank and water to constitute the system answer the

following.

(i)Is any work done during the process of water coming to rest?

(ii)Is there a flow of heat?

(iii)Is there any change in internal energy (U)?

(iv)Is there any change in total energy (E)?

Q13. Determine the power available from a steam turbine with following details; Steam flow

rate = 1 kg/s Velocity at inlet and exit = 100 m/s and 150 m/s Enthalpy at inlet and exit = 2900

kJ/kg, 1600 kJ/kg Change in potential energy may be assumed negligible.

Q14. Determine the heat to be supplied to a Carnot engine operating between 400C and 15C

and producing 200 kJ of work.

Q15. A reversible heat engine operates between two reservoirs at 827C and 27C. Engine

drives a Carnot refrigerator maintaining 13C and rejecting heat to reservoir at 27C. Heat input

to the engine is 2000 kJ and the net work available is 300 kJ. How much heat is transferred to

refrigerant and total heat rejected to reservoir at 27C?

Q16. In a winter season when outside temperature is 1C, the inside of house is to be

maintained at 25C.Estimate the minimum power required to run the heat pump of maintaining

the temperature. Assume heating load as 125 MJ/hr.

Q17. A cold storage plant of 40 tonnes of refrigeration capacity runs with its performance just

1/4th of its Carnot COP. Inside temperature is 15C and atmospheric temperature is 35C.

Determine the powerrequired to run the plant.[Take: One ton of refrigeration as 3.52 kW]

Q18. 0.5 kg of air executes a Carnot power cycle having a thermal efficiency of 50%. The heat

transfer to the air during isothermal expansion is 40 kJ. At the beginning of the isothermal

expansion the pressure is 7 bar and the volume is 0.12 m3. Determine the maximum and

minimum temperatures for thecycle in Kelvin, the volume at the end of isothermal expansion in

m3, and the work and heat transfer for each of the four processes in kJ. For air CP = 1.008 kJ/kg .

K, Cv= 0.721 kJ/kg. K

Q19. A cold body is to be maintained at low temperature T2 when the temperature of

surrounding is T3. A source is available at high temperature T1. Obtain the expression for

minimum theoretical ratio of heat supplied from source to heat absorbed from cold body.

Q20. State the Kelvin Planck and Clausius statements of 2nd law of thermodynamics.

Q21. Write short notes on the following: Heat reservoir, Heat engine, Heat pump and

refrigerator.

Q22. Describe Carnot cycle and obtain expression for its efficiency as applied to a heat engine.

Q23. Show that coefficient of performance of heat pump and refrigerator can be related

as;COPRef = COPHP 1

Q24. Why Carnot cycle is a theoretical cycle? Explain.

Q25. Assume an engine to operate on Carnot cycle with complete reversibility except that 10%

of work is required to overcome friction. For the efficiency of reversible cycle being 30%, what

shall be the efficiency of assumed engine? For same magnitude of energy required to overcome

friction, if machine operated as heat pump, then what shall be ratio between refrigerating effect

and work required

Q26. Oxygen is compressed reversibly and isothermally from 125 kPa and 27C to a final

pressure of 375kPa. Determine change in entropy of gas?

Q27. Determine the change in entropy of universe if a copper block of 1 kg at 150C is placed

in a seawater at 25C. Take heat capacity of copper as 0.393 kJ/kg K.

Q28. Determine change in entropy of universe if a copper block of 1 kg at 27C is dropped

from a height of 200 m in the sea water at 27C. (Heat capacity for copper= 0.393 kJ/kg.K)

Q29. Define the entropy. Also explain how it is a measure of irreversibility?

Q30. Discuss the significance of Clausius inequality.