Thermodynamics Mechanical previous year questions with answer
Ques 31 GATE 2017 SET-2
A calorically perfect gas (specific heat at constant pressure 1000 J/kg.K) enters and leaves a gas turbine with the same velocity. The temperatures of the gas at turbine entry and exit are 1100 K and 400 K, respectively. The power produced is 4.6 MW and heat escapes at the rate of 300 kJ/s through the turbine casing. The mass flow rate of the gas (in kg/s) through the turbine is
Ques 32 GATE 2017 SET-2
One kg of an ideal gas (gas constant R = 287 J/kg.K) undergoes an irreversible process from state-1 (1 bar, 300 K) to state-2 (2 bar, 300 K). The change in specific entropy (s2 - s1) of the gas (in J/kg.K) in the process is ________.
-198.9 is the correct answer.
Ques 33 GATE 2017 SET-2
The volume and temperature of air (assumed to be an ideal gas) in a closed vessel is 2.87 m3 and 300 K, respectively. The gauge pressure indicated by a manometer fitted to the wall of the vessel is 0.5 bar. If the gas constant of air is R = 287 J/kg.K and the atmospheric pressure is 1 bar, the mass of air (in kg) in the vessel is
Ques 34 GATE 2017 SET-1
The molar specific heat at constant volume of an ideal gas is equal to 2.5 times the universal gas constant (8.314 J/mol.K). When the temperature increases by 100 K, the change in molar specific enthalpy is ________ J/mol.
2909.9 is the correct answer.
Ques 35 GATE 2017 SET-1
A heat pump absorbs 10 kW of heat from outside environment at 250 K while absorbing 15 kW of work. It delivers the heat to a room that must be kept warm at 300 K. The Coefficient of Performance (COP) of the heat pump is ________.
1.67 is the correct answer.
Ques 36 GATE 2017 SET-1
One kg of an ideal gas (gas constant, R = 400 J/kg.K; specific heat at constant volume, cv = 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.
288 is the correct answer.
Ques 37 GATE 2017 SET-1
The pressure ratio across a gas turbine (for air, specific heat at constant pressure, cp = 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.
680 is the correct answer.
Ques 38 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.
14.9 is the correct answer.
Ques 39 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 ________.
73.5 is the correct answer.
Ques 40 GATE 2016 SET-3
The INCORRECT statement about the characteristics of critical point of a pure substance is that