GATE XE exam:gate PYQs & Answers — Page 83

Questions 821–830 of 1772. Imported answers require independent review unless marked reviewed.

An air-conditioning system consists of an insulated rigid mixing chamber designed to supply air at 24 °C to a building. The mixing chamber mixes two air streams: (i) a cold air stream at 10 °C and mass flow rate

(kg/s), and (ii) a stream of fresh ambient air at 30 °C and mass flow rate

(kg/s). Assume air to be an ideal gas with constant specific heat (

kJ/(kg K),

). Neglect change in kinetic and potential energies as compared to change in enthalpy. Under the steady state condition, the ratio of the mass flow rates of the two streams (

) is

Your answerChoose one option.

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An ideal gas mixture consists of 80% N₂ and 20% O₂ on mass basis. If the total pressure is 300 kPa, then the partial pressure of N₂ (in kPa) is

(Molecular weights of N₂ = 28 kg/kmol and O₂ = 32 kg/kmol)

Your answerChoose one option.

246.15

230.34

254.78

213.54

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On the basis of the ideal gas equation and van der Waals equation, the temperatures of a gas at pressure 10 MPa and specific volume 0.005 m³/kg would be, respectively

(Assume gas constant

kJ/(kg K),

m⁶ kPa/kg² and

m³/kg)

Your answerChoose one option.

166.67 K and 235.89 K

166.67 K and 206.40 K

166.67 K and 267.21 K

166.67 K and 240.90 K

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An ideal Brayton cycle operates between maximum and minimum temperatures of

and

, respectively. For constant values of

and

, the pressure ratio (

) for maximum work output is

(

is the specific heat ratio of air)

Your answerChoose one option.

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An insulated rigid tank of volume 10 m³ contains air initially at 1 MPa and 600 K. A valve connected to the tank is opened, and air is allowed to escape until the temperature inside the tank drops to 400 K. The temperature of the discharged air can be approximated as the average of the initial and final temperatures of the air in the tank. Neglect kinetic and potential energies of the discharged air. Assume that air behaves as an ideal gas with constant specific heat so that internal energy

and enthalpy

. Then, the final pressure of the air in the tank is ______ MPa (round off to 2 decimal places).

Assume

kJ/(kg K),

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Steam enters a steam turbine at 5 MPa and 600 °C and exits as saturated vapor at 50 kPa. Under steady state condition, the turbine loses heat to the surroundings at the rate of 50 kJ per kilogram of steam flow through the turbine. The ambient temperature is 300 K, and the heat transfer to the surroundings takes place at the outer surface of the turbine at a temperature of 450 K. The irreversibility per unit mass of steam flowing through the turbine is ______ kJ/kg (round off to 2 decimal places).

Neglect the change in kinetic and potential energies of the steam, and use the following property values:

Superheated steam at 5 MPa, 600 °C

m³/kg,

kJ/kg,

kJ/(kg K)

Saturated vapour at 50 kPa

m³/kg,

kJ/kg,

kJ/(kg K)

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A heat engine receives heat at 1000 K and rejects heat to the environment at 300 K. The efficiency of the heat engine is half of the efficiency of a Carnot engine operating between the above mentioned temperature limits. The work output from the heat engine is completely used to drive a refrigerator that steadily removes heat from a cold space at 260 K at a rate of 5.2 kW, and rejects the heat to the same environment at 300 K. The COP (coefficient of performance) of the refrigerator is half of the COP of the Carnot refrigerator operating between the same temperature limits as that of the refrigerator. Then, rate of heat supplied to the heat engine is ______ kW (round off to 2 decimal places).

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A room contains air at 25 °C, 100 kPa and 80% relative humidity. If the saturation pressure of water vapor at 25 °C is 3.1698 kPa, then the specific humidity of air is ______ kg of water vapor / kg of dry air (round off to 4 decimal places).

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An insulated rigid container is divided into two parts by a thin partition. One part of the container contains 6 kg of saturated liquid-vapor mixture with a dryness fraction of 0.7 at 0.3 MPa. The other part contains 12 kg of saturated liquid at 0.6 MPa of the same substance. When the partition is removed and the system attains equilibrium, the final specific volume of the mixture is ______ m³/kg (round off to 2 decimal places).

Use the following property values:

At 0.3 MPa:

m³/kg,

m³/kg

At 0.6 MPa:

m³/kg,

m³/kg

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During a steady state air-conditioning process, air enters a heating section at 15 °C with 40% relative humidity and leaves at 30 °C. Assuming the heating section takes place at 100 kPa, the relative humidity of the air at exit is ______ % (round off to nearest integer).

Saturation pressures of water vapor at 15 °C and 30 °C are 1.7057 kPa and 4.2469 kPa respectively.

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GATE XE exam:gate PYQs

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