GATE ME exam:gate PYQs & Answers — Page 65 — Exam Papers

Questions 641–650 of 1040. Imported answers require independent review unless marked reviewed.

Topic practice 1040 questionsPage 65 of 104

Air (ideal gas) enters a perfectly insulated compressor at a temperature of 310 K. The pressure ratio of the compressor is 6. Specific heat at constant pressure for air is 1005 J/kg.K and ratio of specific heats at constant pressure and constant volume is 1.4. Assume that specific heats of air are constant. If the isentropic efficiency of the compressor is 85 percent, the difference in enthalpies of air between the exit and the inlet of the compressor is ______ kJ/kg (round off to nearest integer).

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Water flows through a tube of 3 cm internal diameter and length 20 m. The outside surface of the tube is heated electrically so that it is subjected to uniform heat flux circumferentially and axially. The mean inlet and exit temperatures of the water are 10°C and 70°C, respectively. The mass flow rate of the water is 720 kg/h. Disregard the thermal resistance of the tube wall. The internal heat transfer coefficient is 1697 W/m

·K. Take specific heat

of water as 4.179 kJ/kg·K. The inner surface temperature at the exit section of the tube is ______ °C (round off to one decimal place).

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One kg of air, initially at a temperature of 127°C, expands reversibly at a constant pressure until the volume is doubled. If the gas constant of air is 287 J/kg.K, the magnitude of work transfer is ______ kJ (round off to 2 decimal places).

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Air is contained in a frictionless piston-cylinder arrangement as shown in the figure.

Diagram for Mechanical Engineering question 52

The atmospheric pressure is 100 kPa and the initial pressure of air in the cylinder is 105 kPa. The area of piston is 300 cm². Heat is now added and the piston moves slowly from its initial position until it reaches the stops. The spring constant of the linear spring is 12.5 N/mm. Considering the air inside the cylinder as the system, the work interaction is _____ J (round off to the nearest integer).

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For an ideal Rankine cycle operating between pressures of 30 bar and 0.04 bar, the work output from the turbine is 903 kJ/kg and the work input to the feed pump is 3 kJ/kg. The specific steam consumption is ______ kg/kW.h (round off to 2 decimal places).

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Moist air at 105 kPa, 30°C and 80% relative humidity flows over a cooling coil in an insulated air-conditioning duct. Saturated air exits the duct at 100 kPa and 15°C. The saturation pressures of water at 30°C and 15°C are 4.24 kPa and 1.7 kPa respectively. Molecular weight of water is 18 g/mol and that of air is 28.94 g/mol. The mass of water condensing out from the duct is ______ g/kg of dry air (round off to the nearest integer).

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For a Kaplan (axial flow) turbine, the outlet blade velocity diagram at a section is shown in figure.

Diagram for Mechanical Engineering question 54

The diameter at this section is 3 m. The hub and tip diameters of the blade are 2 m and 4 m, respectively. The water volume flow rate is 100 m³/s. The rotational speed of the turbine is 300 rpm. The blade outlet angle β is _____ degrees (round off to one decimal place).

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In a steam power plant, superheated steam at 10 MPa and 500°C, is expanded isentropically in a turbine until it becomes a saturated vapor. It is then reheated at constant pressure to 500°C. The steam is next expanded isentropically in another turbine until it reaches the condenser pressure of 20 kPa. Relevant properties of steam are given in the following two tables. The work done by both the turbines together is ______ kJ/kg (round off to the nearest integer).

Superheated Steam Table:

Pressure, (MPa)	Temperature, (°C)	Enthalpy, (kJ/kg)	Entropy, (kJ/kg.K)
10	500	373.6	6.595
1	500	348.4	7.621

Saturated Steam Table:

Pressure,	Sat. Temp. (°C)	Enthalpy, (kJ/kg)	Enthalpy, (kJ/kg)	Entropy, (kJ/kg.K)	Entropy, (kJ/kg.K)
1 MPa	179.91	762.9	2778.1	2.1386	6.596
20 kPa	60.06	251.38	2609.7	0.8319	7.9085

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The indicated power developed by an engine with compression ratio of 8, is calculated using an air-standard Otto cycle (constant properties). The rate of heat addition is 10 kW. The ratio of specific heats at constant pressure and constant volume is 1.4. The mechanical efficiency of the engine is 80 percent.

The brake power output of the engine is ______ kW (round off to one decimal place).

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Keeping all other parameters identical, the Compression Ratio (CR) of an air standard diesel cycle is increased from 15 to 21. Take ratio of specific heats = 1.3 and cut-off ratio of the cycle

.

The difference between the new and the old efficiency values, in percentage,

______ % (round off to one decimal place).

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