Vapour Power and Refrigeration Cycles - Thermodynamic Cycles - Engineering Sciences Previous Year Questions

1

2007 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2007

In an ideal vapour compression refrigeration system, the process in the condenser is

A

heat addition at constant pressure

B

heat removal at constant volume

C

heat removal at constant pressure

D

heat addition at constant volume

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2

2007 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2007

Steam enters an adiabatic turbine steadily at 450°C and 4.0 MPa and leaves at 50 kPa. The minimum possible dryness fraction of the steam at the turbine exit is approximately

A

85 %

B

90 %

C

95 %

D

97 %

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3

2008 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2008

The above mentioned device is a

A

Turbine

B

Compressor

C

Nozzle

D

Diffuser

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4

2008 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2008

In a thermal power plant operating on a Rankine cycle, steam having enthalpy \(h = 2995.1\) kJ/kg and entropy \(s = 6.5422\) kJ/kg °C is produced at 3 MPa and 300 °C and is fed to a turbine where it expands to a condenser pressure of 5 kPa, where \(h_f = 137.77\) kJ/kg, \(h_{fg} = 2561.6\) kJ/kg, \(s_f = 0.4763\) kJ/kg °C and \(s_{fg} = 8.3960\) kJ/kg °C. At the entrance to the condenser, the quality and enthalpy of steam, respectively are approximately:

A

0.89, 1994.42

B

0.68, 1795.67

C

0.79, 2055.02

D

0.77, 2004.12

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5

2008 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2008

If for the isentropic process $\frac{T_2}{T_1}=\left(\frac{P_2}{P_1}\right)^{\frac{\gamma-1}{\gamma}}$ and $\gamma=1.4$, the isentropic efficiency of the turbine is

A

63%

B

73%

C

83%

D

93%

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6

2009 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2009

The thermal efficiency of an ideal Rankine cycle is less than that of a Carnot cycle operating between the same maximum and minimum temperature limits, because

A

heat addition does not take place at constant temperature

B

the expansion process is not reversible and adiabatic

C

heat rejection does not take place at constant temperature

D

the compression process is not reversible and adiabatic

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7

2009 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2009

The quality of steam at the exit of the turbine after an isentropic expansion is

A

0.47

B

0.72

C

0.88

D

0.94

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8

2009 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2009

If the steam leaves the turbine as saturated vapour, the power produced by the turbine in kW is

A

1640

B

2030

C

2340

D

8830

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9

2009 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2009

The refrigeration effect in kW is

A

1.71

B

3.84

C

4.33

D

4.83

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10

2009 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2009

The actual power input to the compressor in kW is

A

0.49

B

0.99

C

1.71

D

2.2

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11

2010 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2010

Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]: Assertion: Carnot cycle is not used in vapour power cycles. Reason: Pumping of a two phase mixture is difficult

A

Both [a] and [r] are true and [r] is a reason for [a]

B

Both [a] and [r] are true but [r] is NOT a reason for [a]

C

[a] is true but [r] is false

D

Both [a] and [r] are false

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12

2010 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2010

Work done by the turbine is

A

276.5 kJ/kg

B

303.9 kJ/kg

C

335.8 kJ/kg

D

361.3 kJ/kg

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13

2010 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2010

Heat addition in the boiler is

A

2000.9 kJ/kg

B

2514.6 kJ/kg

C

3028.2 kJ/kg

D

3554.5 kJ/kg

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14

2011 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2011

An ideal vapor compression refrigeration cycle uses R-134a as working fluid. The condenser pressure is 5 bar and evaporator pressure is 60 kPa. The refrigerant enters the compressor as saturated vapor and its specific enthalpy at the compressor exit is 267.98 kJ/kg. The other relevant data regarding R-134a are given below:

Pressure, bar	\(h_f\), kJ/kg	\(h_g\), kJ/kg	\(s_f\), kJ/kg·K	\(s_g\), kJ/kg·K
0.6	3.46	224.72	0.0147	0.9520
5	71.33	256.07	0.2723	0.9117

The COP of the cycle is approximately

A

2.55

B

3.55

C

4.11

D

5.11

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15

2013 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2013

If the required cooling is attained in 16 hours, the refrigeration plant capacity (in Tons) is

A

19

B

24

C

29

D

32

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16

2013 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2013

If the cooling is to be achieved in 8 hours, the power required (in Horse Power) to operate the plant having a Coefficient of Performance (COP) of 2.5 will be

A

47

B

65

C

89

D

96

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17

2013 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2013

What is the mass flow rate of the working fluid through the turbine, in kg/s, to first decimal place accuracy?

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18

2013 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2013

What is the power required to drive the compressor, to the nearest kW?

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19

2014 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2014

Steam is isentropically expanded in a turbine from 80 bar to 7 bar. At the inlet of the turbine (state 1) \(h_1\) is 3246 kJ/kg and \(s_1\) is 6.52 kJ/(kg.K).

Pressure = 7 bar
hf(kJ/kg)	hg(kJ/kg)	sf(kJ/(kg.K))	sg(kJ/(kg.K))
697	2763	2.0	6.7

The enthalpy of the steam exiting the turbine (state 2) in kJ/kg is

A

2663.87

B

2657.17

C

1986.87

D

3354.17

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20

2015 · Engineering Sciences · Thermodynamic Cycles · Vapour Power and Refrigeration Cycles

Engineering Sciences (XE) 2015

In an ideal Rankine cycle, increase in superheat of vapor at the exit of boiler leads to
(A) decrease in net work output from the cycle
(B) increase in cycle efficiency
(C) decrease in cycle efficiency
(D) decrease in quality of steam at the exit of the turbine

A

decrease in net work output from the cycle

B

increase in cycle efficiency

C

decrease in cycle efficiency

D

decrease in quality of steam at the exit of the turbine

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