Thermodynamics Mechanical previous year questions with answer

Ques 41 GATE 2017 SET-1

One kg of an ideal gas (gas constant, R = 400 J/kg.K; specific heat at constant volume, c_v = 1000 J/kg.K) at 1 bar, and 300 K is contained in a sealed rigid cylinder. During an adiabatic process, 100 kJ of work is done on the system by a stirrer. The increase in entropy of the system is ________ J/K.

Ques 42 GATE 2017 SET-1

The pressure ratio across a gas turbine (for air, specific heat at constant pressure, c_p = 1040 J/kg.K and ratio of specific heats, γ = 1.4) is 10. If the inlet temperature to the turbine is 1200 K and the isentropic efficiency is 0.9, the gas temperature at turbine exit is ________ K.

Ques 43 GATE 2017 SET-1

Moist air is treated as an ideal gas mixture of water vapor and dry air (molecular weight of air = 28.84 and molecular weight of water = 18). At a location, the total pressure is 100 kPa, the temperature is 30°C and the relative humidity is 55%. Given that the saturation pressure of water at 30°C is 4246 Pa, the mass of water vapor per kg of dry air is ________ grams.

Ques 44 GATE 2017 SET-1

Air contains 79% N₂ and 21% O₂ on a molar basis. Methane (CH₄) is burned with 50% excess air than required stoichiometrically. Assuming complete combustion of methane, the molar percentage of N₂ in the products is ________.

Ques 45 GATE 2016 SET-3

The INCORRECT statement about the characteristics of critical point of a pure substance is that

Ques 46 GATE 2016 SET-2

The internal energy of an ideal gas is a function of

Ques 47 GATE 2016 SET-2

The heat removal rate from a refrigerated space and the power input to the compressor are 7.2 kW and 1.8 kW, respectively. The coefficient of performance (COP) of the refrigerator is ________.

Ques 48 GATE 2016 SET-2

Consider a simple gas turbine (Brayton) cycle and a gas turbine cycle with perfect regeneration. In both the cycles, the pressure ratio is 6 and the ratio of the specific heats of the working medium is 1.4. The ratio of minimum to maximum temperatures is 0.3 (with temperatures expressed in K) in the regenerative cycle. The ratio of the thermal efficiency of the simple cycle to that of the regenerative cycle is ________.

Ques 49 GATE 2016 SET-2

A piston-cylinder device initially contains 0.4 m³ of air (to be treated as an ideal gas) at 100 kPa and 80°C. The air is now isothermally compressed to 0.1 m³. The work done during this process is ________ kJ. (Take the sign convention such that work done on the system is negative)

Ques 50 GATE 2016 SET-2

A reversible cycle receives 40 kJ of heat from one heat source at a temperature of 127°C and 37 kJ from another heat source at 97°C. The heat rejected (in kJ) to the heat sink at 47°C is ________.