Thermodynamics - Thermodynamics and Marine Engineering - Naval Architecture & Marine Engineering Previous Year Questions

1

2022 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2022

Which of the following are TRUE for pressure, temperature and density of a thermodynamic system?

A

path functions

B

point functions

C

inexact differentials

D

exact differentials

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2

2022 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2022

For a simple vapour compression refrigeration, which of the following thermodynamic cycles (1-2-3-4) are possible? Here, \( T \), \( P \), \( s \) and \( h \) indicate temperature, pressure, specific entropy and specific enthalpy, respectively.

A

B

C

D

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3

2022 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2022

An Otto cycle has states 1 and 2 at the beginning and the end of the compression stroke, respectively. The states 3 and 4 are at the beginning and the end of the expansion stroke, respectively.
Let the compression ratio of the cycle be \( r \), specific heat ratio of air be \( \gamma \), specific heat of air at constant volume be \( C_v \), and \( P \), \( v \), and \( T \) be pressure, specific volume and temperature of the air, respectively. Then, which of the following expressions represent the thermal efficiency of the cycle?

A

\(1 - \frac{1}{r^{\gamma-1}} \)

B

\(1 - \frac{T_3-T_4}{T_2-T_1} \)

C

\(\frac{(p_3v_3-p_4v_4)-(p_2v_2-p_1v_1)}{C_v(T_3-T_2)(\gamma-1)} \)

D

\(1 - r^{\gamma-1} \)

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4

2022 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2022

An air standard Otto cycle has a compression ratio of 6 and a mean effective pressure of 1000 kPa. Assume that the specific heat ratio \(\gamma\) as 1.4 and specific gas constant \(R\) as 0.287 kJ/kgK for the air. If the pressure and temperature at the beginning of the compression stroke are 100 kPa and 300 K, respectively, then the specific work output of the cycle is __________ kJ/kg (rounded off to one decimal place).

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5

2022 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2022

If methane (\(CH_4\)) gas reacts with air at a stoichiometric proportion, then the air-fuel ratio of the combustion process is __________ (rounded off to one decimal place).

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6

2022 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2022

In a vapour compression refrigeration cycle using R134 as the refrigerant, the enthalpies are (i) 240 kJ/kg at the beginning of the compression, (ii) 275 kJ/kg at the end of the compression and (iii) 96 kJ/kg at the beginning of the throttling.
Then the coefficient of performance of the cycle is __________ (rounded off to one decimal place).

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7

2023 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2023

The vapor quality of steam in the turbine of a Rankine cycle can be improved by employing

A

regeneration of steam

B

intercooler

C

reheating

D

cogeneration

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8

2023 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2023

A closed system undergoing a thermodynamic cycle consisting of two reversible isothermal and two reversible adiabatic processes is shown in the following figure. If $\delta Q$ is the infinitesimal heat transfer and T is the instantaneous temperature, then the value of the contour integral $\oint \frac{\delta Q}{T}$

A

is positive

B

is negative

C

is zero

D

cannot be determined

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9

2023 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2023

In a marine steam power cycle employing regeneration, the feed water heater for waste heat recovery is placed after the

A

boiler

B

turbine

C

condenser

D

pump

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10

2023 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2023

A vertical frictionless piston-cylinder arrangement contains air of mass 1 kg. During a process, 50 J of heat is transferred from outside to the system such that the piston is raised slowly by 0.1 m from its initial equilibrium position. The mass of the piston is 1 kg, and the diameter is 0.1 m. Assume that g = 9.81 m/s², and P_atm = 100 kPa. The change in internal energy of the air in J (round off to two decimal places) lies between

A

28.45 and 28.55

B

-28.55 and -28.45

C

-29.55 and -29.45

D

129.45 and 129.55

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11

2023 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2023

An insulated nozzle has an inlet cross-sectional area of 314 cm². Air flows through the nozzle with an inlet temperature of 300 K at a steady rate of 1.256 m³/s. The velocity at the exit is greater than that at the inlet by 210 m/s. Assume a constant Cp = 1.004 kJ/kg·K. The temperature (in K) of air at the exit of the nozzle lies between

A

330 and 331

B

269 and 270

C

320 and 321

D

277 and 278

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12

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

Consider an ideal Rankine cycle as shown in the figure, where \(T\) and \(S\) represent the temperature and entropy respectively. The overall efficiency of the cycle can be improved by

A

increasing the pressure at which heat is added

B

decreasing the pressure at which heat is rejected

C

employing an intercooler

D

superheating the steam

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13

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

Which of the following statement(s) is/are correct for a thermodynamic closed system?

A

The entropy change is positive for a reversible adiabatic process

B

The entropy change is positive for a reversible cycle

C

The entropy change is positive for a reversible isothermal heat addition process

D

The entropy change is negative for a reversible isothermal heat rejection process

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14

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

Which one of the following \(p-h\) plots represents the ideal vapour compression cycle with intercooling?
Here, \(p\) and \(h\) denote pressure and specific enthalpy respectively.

A

B

C

D

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15

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

Which one of the following psychrometric processes is represented by the line 1-2 in the figure?

A

Cooling and humidification

B

Cooling and dehumidification

C

Heating and humidification

D

Heating and dehumidification

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16

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

A 4-cylinder, 4-stroke diesel engine operating at 3000 rpm has a compression ratio \(r\) of 12 and cut-off ratio \(r_c\) of 2.5. The temperature rise during the heat addition process is 2400 K. The efficiency of an air-standard diesel cycle is given by \(\eta = 1 - \frac{1}{r^{\gamma-1}} \left( \frac{1}{\gamma} \frac{r_c^{\gamma}-1}{r_c-1} \right)\). Assume the working fluid as air with a mass flow rate of 0.05 kg/s, \(\gamma = 1.4\), and \(C_p = 1.004\) kJ/kg·K.

The power output of the engine is ______ kW (rounded off to the nearest integer).

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17

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

Consider a gas turbine combustor with air as the working fluid. The flow enters the device at 500 K and leaves at 1400 K with a mass flow rate of 0.1 kg/s. The changes in kinetic energy and potential energy of the flow are neglected. Assuming \(C_p = 0.717\) kJ/kg-K and \(R = 0.287\) kJ/kg-K, the rate of heat addition is _____ kW (rounded off to the nearest integer).

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18

2024 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2024

A new absolute temperature scale is proposed based on a Carnot engine operating between hot and cold reservoirs of temperatures \(T_L\) and \(T_H\) respectively. Let \(Q_L\) and \(Q_H\) be the respective heat transfers, with the relation given by \(\frac{T_L}{T_H} = \frac{Q_L}{Q_H}\). On the new scale, the difference between the steam and ice points of water is 500 units and the efficiency of the engine is 0.268. The steam point of water on this scale is __________ units (rounded off to the nearest integer).

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19

2025 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2025

A closed system is undergoing a reversible process 1-P-2 from state 1 to 2, as shown in the figure, where X and Y are thermodynamic properties. An irreversible process 2-Q-1 brings the system back from 2 to 1.
The net change in entropy of the system and surroundings during the above-mentioned cycle are ______ respectively.

A

positive and negative

B

negative and positive

C

zero and negative

D

zero and positive

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20

2025 · Naval Architecture & Marine Engineering · Thermodynamics and Marine Engineering · Thermodynamics

Naval Architecture & Marine Engineering (NM) 2025

An ideal Brayton cycle (1-2-3-4) consisting of two isentropic and two isobaric processes is shown in the T-s plot, where T is the temperature and s is the specific entropy of the system. Which one of the following plots represents the corresponding actual cycle 1-2'-3-4' (denoted by dashed lines) between the same two pressures p₁ and p₂?

A

B

C

D

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