Thermodynamics Mechanical previous year questions with answer

Ques 21 GATE 2023

Consider a fully adiabatic piston-cylinder arrangement as shown in the figure. The piston is massless and cross-sectional area of the cylinder is A. The fluid inside the cylinder is air (considered as a perfect gas), with γ being the ratio of the specific heat at constant pressure to the specific heat at constant volume for air. The piston is initially located at a position L₁. The initial pressure of the air inside the cylinder is P₁>>P₀, where P₀ is the atmospheric pressure. The stop S₁ is instantaneously removed and the piston moves to the position L₂, where the equilibrium pressure of air inside the cylinder is P₂>>P₀.
What is the work done by the piston on the atmosphere during this process?

Ques 22 GATE 2022 SET-2

Which one of the following is an intensive property of a thermodynamic system?

Ques 23 GATE 2022 SET-2

Consider 1 kg of an ideal gas at 1 bar and 300 K contained in a rigid and perfectly insulated container. The specific heat of the gas at constant volume c_v is equal to 750 J∙kg^-1∙K^-1. A stirrer performs 225 kJ of work on the gas. Assume that the container does not participate in the thermodynamic interaction. The final pressure of the gas will be ___________ bar (in integer).

Ques 24 GATE 2022 SET-2

Wien’s law is stated as follows: λ_mT = C, where C is 2898 µm∙K and λ_m is the wavelength at which the emissive power of a black body is maximum for a given temperature T. The spectral hemispherical emissivity (𝜀 ) of a surface is shown in the figure below (1Å = 10^-10m). The temperature at which the total hemispherical emissivity will be highest is __________ K (round off to the nearest integer).

Ques 25 GATE 2022 SET-2

In a vapour compression refrigeration cycle, the refrigerant enters the compressor in saturated vapour state at evaporator pressure, with specific enthalpy equal to 250 kJ/kg. The exit of the compressor is superheated at condenser pressure with specific enthalpy equal to 300 kJ/kg. At the condenser exit, the refrigerant is throttled to the evaporator pressure. The coefficient of performance (COP) of the cycle is 3. If the specific enthalpy of the saturated liquid at evaporator pressure is 50 kJ/kg, then the dryness fraction of the refrigerant at entry to evaporator is _________.

Ques 26 GATE 2022 SET-1

The Clausius inequality holds good for?

Ques 27 GATE 2022 SET-1

A polytropic process is carried out from an initial pressure of 110 kPa and volume of 5 m³ to a final volume of 2.5 m³. The polytropic index is given by n = 1.2. The absolute value of the work done during the process is _______ kJ (round off to 2 decimal places).

Ques 28 GATE 2022 SET-1

In a steam power plant based on Rankine cycle, steam is initially expanded in a high-pressure turbine. The steam is then reheated in a reheater and finally expanded in a low-pressure turbine. The expansion work in the high-pressure turbine is 400 kJ/kg and in the low-pressure turbine is 850 kJ/kg, whereas the pump work is 15 kJ/kg. If the cycle efficiency is 32%, the heat rejected in the condenser is ________ kJ/kg (round off to 2 decimal places).

Ques 29 GATE 2022 SET-1

An engine running on an air standard Otto cycle has a displacement volume 250 cm³ and a clearance volume 35.7 cm³. The pressure and temperature at the beginning of the compression process are 100 kPa and 300 K, respectively. Heat transfer during constant-volume heat addition process is 800 kJ/kg.. The specific heat at constant volume is 0.718 kJ/kg.K and the ratio of specific heats at constant pressure and constant volume is 1.4. Assume the specific heats to remain constant during the cycle. The maximum pressure in the cycle is ______ kPa (round off to the nearest integer).

Ques 30 Gate 2021 Set-1

In the vicinity of the triple point, the equation of liquid-vapour boundary in the P – T phase diagram for ammonia is ln P= 24.38 - 3063/ T , where P is pressure (in Pa) and T is temperature (in K). Similarly, the solid-vapour boundary is given by ln P=27.92-3754 / T . The temperature at the triple point is _______K (round off to one decimal place).