### MODEL QUESTION BANK | MECHANICS OF MACHINES | BASIC THERMAL ENGINEERING | APPLY BASIC CONCEPTS, LAWS AND PRINCIPLES OF THERMODYNAMICS TO USE AND SELECT EQUIPMENTS/DEVICES/MACHINES WORKING ON THESE BASICS | DIPLOMA

Diploma in Mechanical Engineering IV Semester

Course title: MECHANICS OF MACHINES BASIC THERMAL ENGINEERING

APPLY BASIC CONCEPTS, LAWS AND PRINCIPLES OF THERMODYNAMICS TO USE AND SELECT EQUIPMENTS/DEVICES/MACHINES WORKING ON

THESE BASICS

REMEMBERING

1.    Define the terms: (i) system (ii) boundary and (iii) surroundings.

2.    Define the terms: i) Cycle (iv) Enthalpy (v) Entropy.

3.    State the comparison between closed system and open system.

4.    Define intensive and extensive property.

5.    Define specific heat at constant pressure and specific heat at constant volume.

6.    State the zeroth law and first law of thermodynamics.

7.    State first law and second law of thermodynamics.

8.    Define heat and work. Are these quantities a path function or point function? Explain.

9.    Define the following :

i)     Quasi-static process

ii)    Internal energy

10. Define steady flow process & write steady flow energy equation with notations.

UNDERSTANDING

1.      Explain open system with example.

2.      Explain the closed system with example.

3.     Differentiate between intensive and extensive properties of a system. Give three examples for each.

4.      Derive the characteristic gas equation.

5.      Establish that Cp-Cv=R.

APPLICATION

1. A closed system received a heat transfer of 120 kJ and delivers a work transfer of 150 kJ. Determine the change of internal energy.

2.  During the compression stroke of an engine, the work done on the working substance in the engine cylinder is 80 kJ/kg and the heat rejected to the surrounding is 40 kJ/kg. Determine the change of internal energy.

3.  A closed system undergoes a change in process in which 5 kJ of heat energy is supplied to the system. Determine the change in internal energy under the following conditions.

a.          i) 1 kJ of work is done on the system. ii)1.25 kJ of work is  done  by  the  system.

4. A piston - cylinder containing air expands at a constant pressure of 150 KPa from a temperature of 285 K to a temperature of 550 K. The mass of air is 0.05 kg. Determine the heat transfer, work transfer and change in internal energy during the process Cp =

1.01 kJ/kg K and Cv = 0.72 kJ/kg K.

5.  A cold storage is to be maintained at -5o while surroundings are at 35oC. The leakage from the surroundings into the cold storage is estimated to be 29 kW. The actual C.O.P. of the refrigeration plant is one - third of an ideal plant working between the same temperatures. Determine the power required to drive the plant.

6. In a compressor, the air has an internal energy at beginning of the expansion is 200 kJ/kg and after expansion the internal energy becomes 510 kJ/kg. The work done by the air during expansion is 150 kJ/kg. Determine the heat flow.

7. Determine the coefficient of performance and heat transfer rate in a condenser of a refrigerator in kJ/hr whose refrigeration capacity is 11000 kJ/hr if the power input is 1.5 kW.

8. The net work output of a cyclic process is 45 kN-m. If the heat input is 125 kJ, determine the efficiency of the cycle.

9.  One litre of hydrogen at 0oC is suddenly compressed to one-half its volume. Determine the change in temperature of the gas if the ratio of two specific heats for hydrogen is 1.4.

REMEMBERING

1.     List out the different thermodynamic processes on gases.

2.     State characteristics of throttling process

UNDERSTANDING

1.      Explain reversible and irreversible process.

2.      Explain free expansion process with sketch.

3.      Explain throttling process

4.     Construct the PV and TS diagram for i) Constant pressure process ii) Constant volume process iii) Constant temperature process.

5.      Derive expression for work done in constant temperature process with PV diagram.

6.     Derive expression for work done in constant entropy (Isentropic) process with PV diagram.

7.      Derive an expression for work done during polytrophic process.

APPLICATION

1. A quantity of gas occupies a space of 0.3m3 at a pressure of 2 bar and a temperature of 77oC which is heated at a constant volume, until the pressure is 7 bar. Determine (i) Temperature at the end of the process (ii) mass of the gas (iii) change in internal energy and (iv) change in enthalpy during the process.

Assume: Cp = 1.005 kJ/kg K, Cv = 0.714 kJ/kg K, R = 287 J/kg K.

2.  A quantity of gas has a volume of 0.14 m3, pressure 1.5 bar and temperature 100oC. If the gas is compressed at a constant pressure, until its volume becomes 0.112 m3, determine :

a.                             i)Temperature at the end of the compression ii)Work done in compressing  the gas

b.                     iii) Decrease in internal energy iv)Heat given out by the gas.

3.  If the values of Cp = 0.984 kJ/kg K and Cv = 0.728 kJ/kg K for an ideal gas. Determine the characteristic gas constant and ratio of specific heats for the gas. If one kg of this gas is heated at constant pressure from 25oC to 200oC. Estimate the heat added, ideal work done and change in internal energy. Also Determine the pressure and final volume if the initial volume was 2 m3.

4.  A volume of 0.5 m3 of gas at a pressure of 10 bar and 200oC is expanded in a cylinder to

1.2 m3 at constant pressure. Determine the amount of work done by the gas and the increase in internal energy. Assume Cp = 1.005 kJ/kg K and Cv = 0.712 kJ/kg K.

5.  A quantity of air has a volume of 0.4 m3 at a pressure of 5 bar and a temperature of 80oC. It is expanded in a cylinder at a constant temperature to a pressure of 1 bar. Determine the amount of work done by the air.

6.     0.1 m3 of air at a pressure of 1.5 bar is expanded isothermally to 0.5 m3 Determine the final pressure of the gas and heat supplied during the process.

7.  0.5 kg of gas is compressed isentropically in such a manner that the ratio of final pressure to initial pressure is 5.25. If the initial temperature is 100oC Determine; (i) work done (ii) change in internal energy. Assume: Î³= 1.4 and R = 287 J/kg K.

8. One kg of gas expands reversibly and adiabatically. Its temperature during the process falls from 515K to 390K, while the volume is doubled. The gas does 92 kJ of work in this process Calculate: The value Cp and Cv

9.     A gas of 0.15 m3 at NTP is expanded adiabatically in a cylinder to a volume of 0.3 m3, Determine the pressure at the end of expansion and the work during expansion. Take Cp=1.4 KJ/Kg K

10.  A certain quantity of air has a volume of 0.028 m3 at a pressure of 1.25 bar and 25oC. It is compressed to a volume of 0.0042 m3 according to the law PV1.3= C. Determine the final temperature and work done during compression. Also determine the reduction in pressure at a constant volume required to bring the air back to its original temperature.

11.  A gas has a molecular mass of 26.7. The gas is compressed through a ratio of 12 according to the law PV1.25 = C, from initial conditions of 0.9 bar and 333 K.

Assuming specific heat at constant volume Cv = 0.79 kJ/kg K. Determine per kg of mass, work done and heat flow across the cylinder walls. Gas constant and ratio of specific heat.

REMEMBERING

1.    Define: Air standard cycle, Reversible cycle.

2.    List the assumptions made in thermodynamic air standard cycle.

UNDERSTANDING

1.        Give the comparison between Otto, diesel and dual combustion cycles.

2.        Derive efficiency of Carnot cycle with PV diagram.

3.        Derive the efficiency of Otto cycle with PV diagram.

4.       With the help of P-V and T-S diagrams, derive an expression for the air standard efficiency of a diesel cycle.

5.        Derive an equation for the air standard efficiency of dual cycle.

6.       Explain with the help of P-V and T-S diagrams working of Carnot cycle .

7.       Explain with the help of P-V and T-S diagrams working of Otto cycle.

8.       Explain with the help of P-V and T-S diagrams working of Diesel cycle.

9.       Explain with the help of P-V and T-S diagrams working of Dual cycle .

APPLICATION

1.                       A Carnot engine working between 655 K and 320 K, produces 150 kJ of work. Determine thermal efficiency and heat added during the process.

2.                       A Carnot engine operates with a thermal efficiency of 70%. The minimum temperature of the cycle is 30oC. Determine the maximum temperature of the cycle.

3.                       An engineer claims his engine to develop 3.75 kW. On testing, the engine consumes

0.44 kg of fuel per hour having a calorific value of 42000 kJ/kg. The maximum temperature recorded in the cycle is 1400oC and minimum is 350oC. Determine whether the engineer is justified in his claim.

4.                       A Carnot cycle receives heat at 900oC and rejects at 50oC. Determine the efficiency of the cycle. If the cycle receives 4600 kJ of heat per minute, Determine the power developed by the engine.

5.            A Carnot cycle works with isentropic compression ratio of 5 and isothermal expansion ratio of 2. The volume of air at the beginning of the isothermal expansion is 0.3 m3. If the maximum temperature and pressure is limited to 550 K and 21 bar.

Determine; Minimum temperature in the cycle, Thermal efficiency of the cycle. Pressure at all salient points. Take ratio of specific heats as 1.4

6.                             In an Otto cycle, the beginning and end temperatures of a isentropic compression are 316 K and 596 K respectively. Determine the air standard efficiency and the compression ratio. Take Î³= 1.4.

7.                             A certain quantity of air at a pressure of 1 bar and temperature 70oC is compressed reversibly and adiabatically until the pressure is 7 bar in an Otto cycle engine. 460 kJ of heat per kg of air  is  now  added  at  constant  volume.  Determine: Compression ratio of the engine. Temperature at the end of compression. Temperature at the end of heat addition. Take for air, CP = 1 kJ/kg K and Cv = 0.707 kJ/kg K.

8.                               An Otto cycle has a cylinder diameter of 150 mm and a stroke of 225 mm. The clearance volume is 1.25X10-3 m3. Calculate the air standard efficiency of the cycle. Take Î³= 1.4.

9.                               In an air standard Otto cycle, the compression ratio is 6.5 and the compression begins at 1 bar and 313 K. The heat added is 2520 kJ/kg. Determine: The maximum temperature and pressure of the cycle. Work done per kg of air. Cycle efficiency. Take for air Cv = 0.713 kJ/kg K, R = 287 J/kg K = 0.287 kJ/kg K.

10.                     In an Otto cycle, air at 1 bar and 290 K is compressed isentropically until the pressure is 15 bar. The heat is added at constant volume until the pressure rises to 40 bar. Determine the air standard efficiency and work done during the cycle. Take Cv = 0.717 kJ/kg K and Ru = 8.314 kJ/kg mol K.

11.                        A diesel engine with a compression ratio is 13:1 and fuel cut off ratio is at 8% of the stroke. Determine the air standard efficiency of an engine. Take, for air Î³= 1.4.

12.                        A diesel cycle operating with the temperatures at the beginning and end of compression are 57oC and 603oC respectively. The temperatures at the beginning and end of expansion are 1950oC and 870oC respectively. Determine the ideal efficiency of the cycle. Take Î³ = 1.4. If the compression ratio is 14 and the pressure at the beginning of compression is 1 bar. Determine the maximum pressure of the cycle.

13.                        An ideal diesel engine has a diameter 150 mm and stroke 200 mm. The clearance volume is 10 percent of the swept volume. Determine the compression ratio and the air standard efficiency of the engine if the cut-off takes place at 6 percent of the stroke.

14.                        A diesel engine has a compression ratio of 15. Heat addition at constant pressure takes place at 10% of the stroke. Determine the air standard efficiency of the engine. Take Î³ = 1.4 for air.

15.                        The compression ratio of an ideal air standard diesel cycle is 15. The heat transfer is 1465 kJ/kg of air. Determine the pressure and temperature at the end of each process and determine the cycle efficiency, if the inlet conditions are 300 K and 1 bar. Take Î³= 1.4 and Cv = 0.712 kJ/kg K, Cp = 1 kJ/kg K for air.

16.                        An engine working on dual combustion cycle, has a compression ratio 10 and cut off takes place at of the stroke. If the pressure at the beginning of compression  is 1 bar and maximum pressure 40 bar, determine the air standard efficiency of the cycle. Take Î³= 1.4.

17.                        An engine working on dual combustion cycle with cylinder diameter of 30 cm and a stroke of 42 cm. The clearance volume is 1800 cm3 and cut off takes  place at 6% of the stroke. The explosion pressure ratio is 1.4. Determine the air standard efficiency of the engine. Assume Î³= 1.4 for air.

REMEMBERING

1.    Define IC engine and give the classification of IC engines.

2.    Define the following terms i) cylinder bore ii) swept volume iii) compression ratio.

3.    Define brake power, indicated power, mechanical efficiency.

4.    Define: Indicated thermal efficiency, Brake mean effective pressure, Brake thermal efficiency.

5.     Define : Air standard efficiency, Volumetric efficiency, Relative efficiency

UNDERSTANDING

1.    Explain with diagram internal combustion engine indicating the component parts.

2.    Explain with neat diagram the working of two stroke petrol engine.

3.    Explain with neat diagram the working of four stroke petrol engine.

4.    Explain with neat diagram the working of two stroke Diesel engine.

5.    Explain with neat diagram the working of four stroke diesel engine.

6.    Explain with diagram Rope brake dynamometer

7.    Explain the concept of heat balance sheet.

APPLICATION

1.                   A heat engine has a piston diameter of 150 mm, length of stroke 400 mm and mean effective pressure  5.5  bar.  The  engine makes 120                                                         explosions per minute. Determine the mechanical efficiency of the engine, if the engine BP is 5 kW.

2.                   A diesel engine uses 6.5 kg of oil per hour of calorific value 30000 kJ/kg. If the BP of the engine is 22 kW and mechanical efficiency 85%. Determine : 1) Indicated thermal efficiency, 2) Brake thermal efficiency 3) Specific fuel consumption in kg/BP/hr.

3.                   During the test on single cylinder diesel engine, working on the four stroke cycle and fitted with a rope brake, the following readings are taken:

Effective diameter of brake wheel = 360 mm; Dead load on brake = 200 N; Spring balance reading = 30 N; Speed = 450 rpm; Area of indicator diagram = 420 m2; Length of indicator diagram = 60 mm; Spring scale = 1.1 bar per mm; Diameter of cylinder = 100 mm; Stroke = 150 mm; Quality of oil used = 0.815 kg/hr; Calorific value of oil = 42000 kJ/kg.Determine  brake power, indicated power, mechanical efficiency, brake thermal efficiency and

brake specific fuel consumption.

4.                       A test is carried out on a single cylinder four stroke petrol engine gave the following results :

Cylinder diameter = 0.3 m; piston movement = 0.52 m; clearance volume = 0.0092 m3; explosions per minute = 110, indicated mean effective pressure = 7 bar; mass of the fuel = 28 kg/hr; calorific value of fuel = 19228 kJ/kg and take Î³ = 1.4 for air. Determine :i) Indicated thermal efficiency ii) Air standard efficiency iii) Relative efficiency.

5.                       The following observations were made during a test on a single cylinder 4 stroke cycle diesel engine.

Speed                    -                                   150 rpm Circumference of brake drum      -                             920 rpm Load on brake drum         -                                                     150 mm Spring balance reading     -                             25 N

Area of indicated diagram-                                                      950 mm2 Length of indicated diagram                                                      -           60 mm

Spring constant     -                       0.035 N/mm2/mm

Cylinder diameter -                       80 mm

Length of stroke    -                       110 mm

C.V. of fuel                        -                                   45430 kJ/kg Fuel consumed              -                       0.85 kg/hr

6.                       Determine :     i) Mechanical efficiency ii)   Indicated  thermal  efficiency iii) BMEP

7.                       A four stroke diesel engine has a cylinder bore of 150 mm and a stroke of 250 mm. The crank shaft speed is 300 rpm and fuel consumption is 1.2 kg/hr, having a calorific value of 39900 kJ/kg. The indicated mean effective pressure is 5.5 bar. If the compression ratio is 15 and cut off ratio is 1.8. Determine the relative efficiency. Assuming  = 1.4  for the air.

8.                       A four stroke four cylinder petrol engine gave the following details:

i.     Stroke = 95 mm; Bore = 65 mm; Speed = 3000 rpm; Clearance volume

= 65 cm3; Relative efficiency on brake thermal efficiency is 45%; CV of petrol is 46300 kJ/kg. Torque developed is 70 N-m. Determine i) Specific fuel consumption, ii) Brake power, iii) BMEP. Take = 1.4 and

= 80%.

9.                       A petrol engine consumes 0.28 kg of fuel per BP-hr, calorific value of fuel is 44000 kJ/kg, mechanical efficiency is 80% and compression ratio is 5.8. Determine (a) Brake

thermal efficiency, (b) Indicated thermal efficiency, (c) air standard efficiency, (d) Relative efficiency, take = 1.4 for air.

10.              An I.C. engine uses 6 kg of fuel having calorific value 44000 kJ/kg in one hour. The I.P developed is 18 kW. The temperature of 11.5 kg of cooling water was found to rise through 25 0C per minute. The temperature of 4.2 kg of exhaust gas with specific heat 1 kJ/kgK was found to rise through 220 0C. Construct heat balance sheet for the engine.

8.     A gas engine working on four stroke constant volume cycle, gave the following results when loaded by friction brake during a test of an hour’s duration :

Cylinder diameter 240 mm; Stroke length 480 mm; Clearance volume 445010--6 m3; Effective circumference of the brake wheel 3.86 m; Net load on brake 1260 N at overall speed of 226.7 rpm; Average explosions/min 77; mep of indicator card 7.5 bar; Gas used 13 m3/hr at 15 0C and 771 mm of Hg; Lower calorific value of gas 49350 kJ/m3 at NTP; Cooling jacket water 660 kg raised to 34.2 0C; Heat lost to exhaust gases 8%. Determine: i) IP ii) PB, iii) Indicated thermal efficiency                                                         iv) Efficiency ratio. Also Construct a heat balance sheet for the engine.

9.     31. A test on a single cylinder 4 stroke oil engine having bore 18 cm and stroke 36 cm yielded the following results : Brake torque 0.44 kN-m, MEP 7.2 bar, fuel consumption

3.5 kg/min, cooling water flow 4.5 kg/min, water temperature rise 360C, A/F ratio 25, exhaust gas temperature 4150C, Room temperature 210C, Specific heat of exhaust gases

1.05 kJ/kgK,           calorific value 45200 kJ/kg, speed = 286 rpm. Construct up a heat balance sheet on kJ/min basis.

CO5:  CALCULATE HEAT TRANSFER FOR GIVEN HEAT TRANSFER SYSTEM

UNDERSTANDING

1.    Derive an expression for heat transfer through a slab.

2.    Derive an expression heat transfer through a composite wall.

3.    Derive an expression for the quantity of heat flow through boiler tubes.

4.    Explain with line diagram thermal conductivity and thermal resistance of a material.

5.    Explain with line diagram radial heat transfer by conduction through thick cylinder.

APPLICATION

6.    A boiler is made of iron plates 12 mm thick, if the temperature of the outside surface be 120 0C and that of the inner is 100 0C, Determine (i) heat transfer per hr and (ii) mass of water evaporated per hour. Assume that the area of heating surface is 5 m2. Take K for iron as 84 W/mK and latent heat of water at 100 0C is hfg = 2260 kJ/kg.

7.    Heat is conducted through a wall of room made of composite plate with a conduction of 134 W/mK and 60 W/mK and thickness 36 mm and                                                                      42 mm respectively. The temperature at the outer face is 96 0C and 8 0C. Determine the temperature at the interface of the two materials.

8.    A furnace wall is made up of bricks of 200 mm thick. The inner and outer surfaces of the wall have temperature of 800 0C and 200 0C. Determine the heat loss. If the outside temperature becomes 25 0C, after the furnace wall is covered with insulator of 100 mm thick, Determine the reduction in heat loss.

a.     Take Kbrick = 4.5 W/mK, Kinsulator = 0.5 W/mK.

9.     Glass windows of a room have a total area of 10 m2 and the glass is 4 mm thick. Determine the quantity of heat that escapes from the room by conduction per second when the inside surfaces of windows are at 25 0 and the outside surfaces at 100 The value of K is 0.84 W/mK.

10.  The walls of a room having the parallel layers in contact of cement, brick and wood of thickness 20 mm, 300 mm and 10 mm respectively. Determine the quantity of heat that passes through each m2 of wall per minute. If the temperature of air in contact with the wall is 5 0C and 300 C inside. The values of K for cement, brick and wood are 0.294,

0.252 and 0.168 W/mK respectively.

11.  Determine the rate of heat flow per square metre through the furnace wall made of 3 cm thick iron metal and covered with an insulating material of                                                                     0.4 cm thick. Take K iron = 51 W/mK and K insulator = 0.15 W/mK. The temperatures of the outside and inside surfaces of the wall are 400 0 and 64 0C respectively.

REMEMBERING

1.    List the classification of gas turbine.

2.    State the applications and limitations of gas turbine.

3.    State the application of gas turbine and fuel used in gas turbine.

4.   Identify the    difference between the closed cycle gas turbine and a open cycle gas turbine.

UNDERSTANDING

1.      Explain closed cycle gas turbine with schematic diagram.

2.      Explain open cycle gas turbine with schematic diagram.

3.      Explain with neat diagram closed cycle gas turbine with intercooling and reheating

4.      Explain with neat diagram the turbo-jet engine.

5.      Explain with neat diagram the working of Ram-jet engine.

Explain the working principle of rocket engine with line diagram.