Made Easy Online Test Series(Thermoal)

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SCORE CARD TIME MANAGEMENT QUESTIONS REPORT SOLUTION

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Solution Report For THERMODYNAMICSRepresent whole test solution with correct and incorrect answers.

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Q.No

Question Status

Q.1

Attempt Correct Correct Ans. b Solution

In a new temperature scale X, the boiling and freezing point of water at

one atmosphere are 200X and 100X respectively, is corrected with

centigrade scale. The reading 0X on the centrigrade scale (in C) is

a. 100

b. 1 00

c. 250

d. 150

Q.2

a. 1 , 2, 5 and 6

b. 5, 6, 7 and 8

c. 1, 2, 3 and 8

d. 1, 2, 3 and 4

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Attempt Incorrect Your Ans. a Correct Ans. b

Solution

Q.3

Attempt Correct Correct Ans. a Solution

A gas expands from pressure P1to pressure . If the expansion

process is isothermal, the volume at the end of expansion is 0.5 m 3. If

the expansion process is adiabatic, the volume (in m3) at the end of

expansion will be closer to

[Take for gas = 1.4]

a. 0.316

b. 0.50

c. 0.10

d. 0.812

Q.4


During steady flow compression process of a gas with mass flow rate of

2 kg/s, increase in specific enthalpy is 15 kJ/kg and decrease in K.E. is 2

kJ/kg. The rate of heat rejection to the environment is 5 kW. The power

(in kW) needed to drive the compressor is

a. 31

b. 39

c. 34

d. 21

Q.5

The gear box of a machine is operating under steady state. The input

shaft receives 55 kW from a prime mover and transmits 52 kW to the

output shaft, the rest being lost due to friction etc. The gear box surface

is at an average temp. of 57C and looses heat to the surroundings at

27C. The rate of entropy production (W/K) inside the gear box is

a. 10

b. 9.1 103

c. 9.1

d. 10 103
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Attempt Incorrect Your Ans. a Correct Ans. c

Solution

Q.6

Attempt Correct Correct Ans. d Solution

Match the List-I (Equipment in the refrigeration) with List-II (Purpose) and

select the correct answer from the codes given below the lists:

a. a

b. b

c. c

d. d

Q.7

Attempt Incorrect Your Ans. d Correct Ans. a

Solution

Two insulated tank containing ideal gases at different pressures and

temperatures are connected to each other and gases are allowed to mix.

The process that occurs can be called ___________ process.

a. Constant internal energy

b. Constant enthalpy

c. Free expansion

d. Reversible adiabatic

Q.8

Consider the following statements:

P. Two constant entropy lines cannot intersect

Q. Once-through boilers never have a steam drum

R. In a centrifugal compressor the axial component of the fluid velocity

produces rotational effect on the rotor

S. The suction pipe diameter of a refrigerator plant should be less than


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Not Attempt Correct Ans. c Solution

the discharge pipe diameter.

T. The clearance volume of reciprocating compressor is given as a

percentage of stroke volume.

Which of the above statements are correct?

a. P, Q, and R

b. R, S and Tc. P, Q, and T

d. Q, R and S

Q.9

Attempt Correct Correct Ans. b Solution

Air is flowing steadily through a thermally insulated duct. The pressure

and temperature of the air measured at two different stations are as

follows:

Considering air as an ideal gas, the direction of flow of air in the duct

a. from A to B

b. from B to A

c. air will not flow in the duct

d. None of the above

Q.10

The mathematical conditions at the critical point for a pure substance

would be

a.

b.
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Attempt Incorrect Your Ans. c Correct Ans. d

Solution

c.

d.

Q.11


5 kg of gas is compressed in a device from a volume of 1.9m3 to a

volume of 1.4m3. During this time, the pressure remains constant at 200

kN/m2, and it is found that internal energy decreases by 12 kJ. How

much energy was transferred as heat (in kJ) to the gas in this process.

a. 112

b. 112

c. 88

d. 88

Q.12

Attempt Correct Correct Ans. 666.67 (666.0-667.2) Solution

A 1000 resistor carrying a current of 10 A for 2 sec is kept at a

constant temperature of 27C by a stream of cooling water. Entropy

change of the universe is ________ J/K.

Q.13

Attempt Incorrect Your Ans. 26 Correct Ans. 1.00

Solution

The internal energy of a certain system is a function of temperature

alone and is given by formulaE = 25 + 0.25 t kJ. If this system execute a

process for which the workdone by it per degree temperature increase

is 0.75 kN-m, the heat-interaction per degree temperature increase is

_________ k J.

Q.14
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Attempt Correct Correct Ans. 177 (176-178) Solution

A steel flask of 0.04 m3 capacity is to be used to store air at 100 bar,

27C. The flask is to be protected against excessive pressure by a

fusible plug which will melt and allow the air to escape if the temperature

rises too high. The temperature at which fusible plug must melt in order

to limit the pressure of a full flask to a maximum of 150 bar is ______

(C).

[Take air as perfect gas andR = 287 J/kg-K]

Q.15

Attempt Correct Correct Ans. 2.5 (2.4-2.6) Solution

A system expands from state 1 (P1, V1, T1)to the state 2 (P2, V2, T2) in

a reversible non-flow process as defined below

(a) A constant-pressure process followed by a constant-volume process(b) A constant-volume process followed by a constant-pressure process

Workdone ratio of the above two processes is _________, if

Q.16

Attempt Incorrect Your Ans. 114.15 Correct Ans.

97.29 (96.8-97.8)Solution

Air enters a compressor in steady flow manner at 140 KPa and 17C and

leaves it at 350 KPa and 127C. During the flow change in enthalpy and

kinetic energy are 110.55 kJ/kg and 3.6 kJ/kg respectively. The

minimum reversible work input required is ________ kJ/kg.

[Given: Environment temperature is 7C]

Q.17

The weight placed on the steam exhaust port of a domestic pressure

cooker never allows the pressure to build up above 250 KPa inside the

cooker. The latent heat of vaporization of water is 2257 kJ/Kg at 100C

and 101.325 KPa. The temperature (C) at which water boils in the

cooker is

a. 514.4

b. 224.6

c. 400.6


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Not Attempt Correct Ans. d Solution

d. 127.6

Q.18

Attempt Correct Correct Ans. dSolution

A heat engine receives half of its heat supply at 1000 K and half at 500 K

while rejecting heat to a sink at 300 K. What is the maximum thermal

efficiency (in %) of the heat engine?

a. 50

b. 45

c. 65

d. 55

Q.19

Not Attempt Correct Ans. d Solution

A wind mill is being used to generate pollution free power from the

kinetic energy of wind. What is the maximum possible power output (in

kW) from such a wind mill for a steady air velocity of 36 kmph, if the

diameter of its blades is 10 m?

[Assume air is at 27C and 101 kPa, Take R = 287 J/kgK]

a. 84.12

b. 52.18

c. 92.48

d. 46.10

Q.20

Not Attempt Correct Ans. c Solution

Air enters an adiabatic nozzle at 20 bar and 50C with a velocity of 80

m/s and leaves with a velocity of 300 m/s. If the area ratio of the nozzle is

4 : 1, and nozzle efficiency is 80%. The exit pressure (in bar) of the air is

[TakeCp= 1.0 kJ/kgK for air]

a. 15.2

b. 14.5

c. 18.6

d. 16.2


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Q.21

Not Attempt Correct Ans. a

Solution

A piston cylinder device contains 0.05 m3 of gas initially at 180 kPa. At

this state, a linear spring that has a spring constant of 150 kN/m is just

touching the piston but exerting no force on it. Now heat is transferred to

the gas, causing the piston to rise and to compress the spring until the

volume inside the cylinder doubles. If the cross-sectional area of the

piston is 0.25 m2, then the total workdone (in kJ) by the gas will be

a. 12

b. 14

c. 15

d. 18

Q.22

Not Attempt Correct Ans. b Solution

Long cylindrical aluminium rods ( = 2700 kg/m3andCp = 0.973 kJ/kg-K)

of 5 cm diameter are heat treated from 20C to an average temperature

of 400C by drawing them at a velocity of 10 m/min through a long oven.

The rate of heat transfer (in kJ/s) to the rods in the oven is

a. 19596.22

b. 326.6

c. 53

d. 426.7

Q.23

Not Attempt Correct Ans. a Solution

A 250 m3 rigid tank contains compressed air at 1 MPa and 300 K. If the

environment conditions are 100 kPa and 300 K, then the maximum work

(in MJ) that can be obtained from this air is

a. 350.6

b. 120.76

c. 29

d. 350646.22

Q.24


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Attempt Incorrect Your Ans. a Correct Ans. c

Solution

A Lenoir cycle comprises the following processes:

(i) Isochoric heat addition of 470 kJ/kg.

(ii) Adiabatic expansion to its original pressure with loss of 140 kJ/kg in

internal energy.

(iii) Isobaric compression to its original volume with heat rejection of 400

kJ/kg.

What will be the overall heat transfer and workdone during the cyclerespectively?

a. 140 kJ and 140 kJ/kg

b. 35 kJ and 70 kJ/kg

c. 70 kJ and 70 kJ/kg

d. 70 kJ and 35 kJ/kg

Q.25


What will be the temperature rise (in C) due to water falling over a height

of 1000 m? Change in internal energy of water is related to the

temperature change by equations,U= 4.2t kJ/kg (Heret is in C).

[Assume water comes to rest after falling)

a. 4.6

b. 23

c. 0.23

d. 2.3

Q.26

Two heat engine cycles (1 2 3 1 and 1 2 3 1) are shown

below on T S co-ordinates.

On pressure volume co-ordinates, the above cycles are best
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represented as:

a.

b.

c.

d.

Q.27

A reversible heat engine operates with three thermal reservoirs and

delivers 50 kW power. The engine absorbs 1000 kJ/s from a reservoir at

600 K. The temperature of the other reservoirs are 400 K and 300 K. The

thermal efficiency (in %) of the engine is

a. 15.2

b. 8.2
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c. 27.2

d. 2.7

Q.28

Attempt Correct Correct Ans. 800 (799-801) Solution

The ratio of work input needed to isentropically compress the saturated

steam from 1 bar to 5 bar and work input needed to isentropically

compress the saturated water for the same pressure ratio is

_________.

Q.29

Not Attempt Correct Ans. 7.5 (7.3-7.7) Solution

A rigid insulated tank contains 1 kg of air at 2 bar and 27C. A paddle

wheel inside the tank is rotated by an external motor till the temperature

rises to 77C. The exergetic efficiency of the process is ________ %.

[Assume surrounding air is at 27C and Cvfor air = 0.72 kJ/kgC]

Q.30

Attempt Incorrect Your Ans. 75 Correct Ans.0.357 (0.34-0.37)

Solution

Considering steady heat transfer through a 10 m 15 m brick wall of a

house of thickness 50 cm. On a day when the temperature of the

outdoors is 7C and the indoor temperature is maintained at 27C. the

temperature of the inner and outer surfaces of the brick wall are

measured to be 25C and 9C, respectively, and the rate of heat transfer

through the wall is 1500 watt. Rate of total entropy generation

associated with this heat transfer process is ________ W/K.

Q.31

A 100 kg block of iron casting at 500 K is thrown into a large lake that is

at a temperature of 285 K. The iron block eventually reaches thermal

equilibrium with the lake water. Assuming on average specific heat of


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0.45 kJ/kgK for the iron, the entropy generated during the process is

______ kJ/K.

Q.32


Two rigid tanks, each filled with 50 kg of air, have temperature of 900 K

and 300 K. A heat engine placed between the two tanks extracts heat

from the high temperature tank, produces work, and rejects heat to the

low temperature tank.

Maximum work obtained from the tank is ________ kJ.

Q.33

Attempt Incorrect Your Ans. .9375 Correct Ans.1.87 (1.80-1.94)

Solution

A 1200 kg vehicle travelling at 90 km/hr impacts a plunger attached to a

piston-cylinder arrangement. If all of the energy of the vehicle is

absorbed by the 100 kg of liquid contained in the cylinder. The maximum

temperature rise of the liquid is ________ C. The specific heat of the

liquid is 4.0 kJ/kgC.

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