Entropy Generation and Second-law Analysis - Entropy - Engineering Sciences Previous Year Questions

1

2007 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2007

Steady heat transfer takes place through a plane wall in the outward direction at the rate of 1500 W. The inner surface temperature of the wall is 27°C. The entropy generation is 0.25 W/K. The outer-surface temperature of the wall is

A

2.7°C

B

5.1°C

C

7.2°C

D

12.7°C

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2

2007 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2007

A large furnace can supply heat at a temperature of 1200 K at a steady rate of 3200 kW. The ambient temperature is 27°C. The availability of this energy is

A

0 kW

B

800 kW

C

1200 kW

D

2400 kW

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3

2007 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2007

Consider an isentropic process undergone by an incompressible liquid. The change in temperature experienced by the liquid is \(\Delta T = T_2 - T_1\). Which one of the following is correct?

A

\(\Delta T = 0\)

B

\(\Delta T > 0\)

C

\(\Delta T < 0\)

D

\(\Delta T\) depends on the liquid under consideration

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4

2008 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2008

Irreversibility of a given process in a system is equal to

A

Product of temperature of the surroundings and net change in entropy in the universe and it represents loss in total work available from the system.

B

Product of temperature of the surroundings and net change in entropy in the universe and it represents gain in total work available from the system.

C

Product of temperature of the system and net change in entropy in the universe and it represents loss in total work available from the system.

D

Product of temperature of the system and net change in entropy in the system and it represents loss in total work available from the system.

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5

2008 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2008

The approximate entropy change, when 10 kg of an ideal gas having specific heat at constant volume \(c_v = \frac{5R}{2}\) (given, R=287 J/kg K) is taken from an initial state of 100 kPa and 300 K to the final state of 200 kPa and 500 K, is

A

9.1

B

3.14

C

91.0

D

0.314

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6

2009 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2009

Atmospheric air ($R = 287$ J/kg·K; $\gamma = 1.4$) at 1 bar and 25 °C is compressed adiabatically to 2 bar and 105 °C. Which of the following statements is correct?

A

The process is possible but irreversible.

B

The process is possible and reversible.

C

The process is impossible.

D

The process is impossible and it is isentropic.

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7

2010 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2010

An insulated rigid container having 1 m³ volume has two compartments having equal volume separated by a thin membrane. Half of the container is filled with helium (R = 2.08 kJ/kg-K, Cv = 5.19 kJ/kg-K and Cp = 3.11 kJ/kg-K), while the remaining half is empty. Suddenly the membrane ruptures and helium fills the whole volume of the container. Temperature and pressure of helium before rupture are 500°C and 0.1 MPa respectively. The change in the entropy of helium is

A

0.019 kJ/K

B

0.045 kJ/K

C

0.112 kJ/K

D

0.675 kJ/K

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8

2010 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2010

Availability per unit mass associated with air (R = 287 J/kg·K, Cp = 1005 J/kg·K and γ = 1.4) flowing from a reservoir at 10 atm and 25°C when atmosphere is at 1 atm and 25°C is (Neglect changes in the potential and the kinetic energies)

A

98.4 kJ/kg

B

196.9 kJ/kg

C

492.3 kJ/kg

D

689.14 kJ/kg

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9

2012 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2012

The exergy (or availability) of a system at a specified state

A

depends on the conditions of the system alone

B

depends on the conditions of the environment alone

C

depends on the conditions of both the system and environment

D

depends neither on the conditions of the system nor the environment

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10

2012 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2012

32 kg of oxygen is mixed with 28 kg of nitrogen at the same temperature. The gases are at the same pressure of 103 kPa before and after mixing. If \( \bar{R} \) is the universal gas constant in kJ/kmol.K, the change in entropy of the mixture is

A

\(1.38\bar{R} \)

B

\(0.69\bar{R} \)

C

\(\bar{R} \)

D

\(0.34\bar{R} \)

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11

2012 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2012

Clausius inequality is written as

A

\(\oint \delta Q > 0 \)

B

\(\oint \delta Q < 0 \)

C

\(\oint \frac{\delta Q}{T} \leq 0 \)

D

\(\oint \frac{\delta Q}{T} > 0 \)

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12

2013 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2013

The fuel air mixture in a petrol engine is ignited with a spark plug at the end of compression stroke. This process

A

increases the entropy of the fuel air mixture but decreases the entropy of the spark plug

B

decreases the entropy of the fuel air mixture but increases the entropy of the spark plug

C

decreases the entropy of the fuel air mixture and of the spark plug

D

increases the entropy of the fuel air mixture and of the spark plug

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13

2013 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2013

For a reversible isothermal expansion of an ideal gas from a state 1 to a state 2,

A

s₁=s₂

B

s₁>s₂

C

s₁2

D

h₁>h₂

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14

2014 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2014

Entropy is a

A

Path function

B

Point function

C

Property independent function

D

Neither path nor point function

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15

2014 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2014

A metal block of mass 25 kg at 300 K is immersed in an infinitely large liquid nitrogen bath maintained at 77 K. The system comprising of the block and liquid nitrogen attains thermal equilibrium. The average specific heat of the metal is 0.45 kJ/(kg.K). The entropy generated during the process is ______ kJ/K.

A

17.28

B

32.5

C

47.8

D

-47.8

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16

2015 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2015

As per Clausius inequality, a system operating on an irreversible cycle transfers

A

more entropy to the sink than what it receives from the source

B

as much entropy to the sink as it receives from the source

C

less entropy to the sink than what it receives from the source

D

less entropy to the sink than that corresponding to a reversible cycle

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17

2015 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2015

Two moles of air at 1 atm, 21.1°C goes through an adiabatic device and separates into a hot stream of 0.4 moles at 1 atm, 176.3°C and a cold stream of 1.6 moles at 1 atm, −17.7°C, without any external work. It can be concluded that
(A) the total entropy change is zero
(B) the total entropy change for the process is positive
(C) the device violates Second Law of Thermodynamics
(D) the device violates First Law of Thermodynamics

A

the total entropy change is zero

B

the total entropy change for the process is positive

C

the device violates Second Law of Thermodynamics

D

the device violates First Law of Thermodynamics

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18

2015 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2015

An ideal gas of 1 kg mass enclosed inside a rigid vessel at the initial temperature 1200 K is employed as a heat source. The specific heat C_v of the gas is 718 J/kg K. The maximum work in kJ that can be developed by operating a heat engine between the ideal gas and the ambient at 300 K is

A

646.2

B

484.7

C

387.7

D

347.6

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19

2015 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2015

One kmol of hydrogen (molecular weight = 2 kg/kmol, specific heat ratio $\gamma$ = 1.4) at 1 bar, 300 K mixes with one kmol of nitrogen (molecular weight = 28 kg/kmol, specific heat ratio $\gamma$ = 1.4) at 1 bar, 300 K in an adiabatic vessel. The final mixture is also at 1 bar, 300 K. The entropy change (in kJ/K) for the process is

A

– 5.76

B

zero

C

5.76

D

11.53

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20

2015 · Engineering Sciences · Entropy · Entropy Generation and Second-law Analysis

Engineering Sciences (XE) 2015

Air enters a pipe at 1 bar and flows isothermally at the rate of 1 kg/s. Due to pipe friction, the pressure drop between two sections of the pipe is 7 % of the pressure at inlet section. For ambient temperature, \(T_0 = 300\) K, the rate of irreversibility (in W) between the two sections is ______.

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