Mechanical Engineer – Interview Questions

Followings are Interview Questions for Mechanical Engineer 

What are the four laws of thermodynamics?

Zeroth Law: If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

First Law (Law of Energy Conservation): Energy can neither be created nor destroyed, only transferred or transformed.

Second Law (Law of Entropy): The entropy of an isolated system tends to increase over time.

Third Law: As temperature approaches absolute zero, the entropy of a system approaches a minimum value.

What is the difference between heat and work in thermodynamics?

Heat (Q) is the transfer of energy due to a temperature difference, while work (W) is the transfer of energy due to a force acting through a distance. The first law of thermodynamics can be expressed as Q = ΔU + W, where ΔU is the change in internal energy of the system.

What is the Carnot cycle and its efficiency?

The Carnot cycle is a theoretical thermodynamic cycle consisting of reversible isothermal and adiabatic processes. Its efficiency (η) is given by the formula: η = 1 – (T_cold / T_hot), where T_cold is the temperature of the cold reservoir and T_hot is the temperature of the hot reservoir.

Define enthalpy and provide its equation.

Enthalpy (H) is a thermodynamic property representing the heat content of a system at constant pressure. It is given by the equation: H = U + PV, where U is the internal energy, P is the pressure, and V is the volume.

What is the Clausius-Clapeyron equation?

The Clausius-Clapeyron equation relates the vapor pressure of a substance to its temperature. It is given by the equation: ln(P2 / P1) = (ΔH_vap / R) * (1 / T1 – 1 / T2), where P1 and P2 are the vapor pressures at temperatures T1 and T2, ΔH_vap is the enthalpy of vaporization, and R is the gas constant.

Explain the concept of specific heat capacity.

Specific heat capacity (C) is the amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius (or Kelvin). It can be calculated using the equation: Q = mcΔT, where Q is the heat energy transferred, m is the mass, c is the specific heat capacity, and ΔT is the temperature change.

What is the difference between an adiabatic process and an isothermal process?

An adiabatic process is one in which there is no heat transfer to or from the system, while an isothermal process is one in which the temperature remains constant throughout the process. Adiabatic processes involve changes in internal energy, while isothermal processes involve heat transfer to maintain a constant temperature.

Define entropy and its relationship to the second law of thermodynamics.

Entropy (S) is a measure of the degree of randomness or disorder in a system. The second law of thermodynamics states that the total entropy of an isolated system can never decrease, only increase or remain constant.

Explain the concept of a heat engine and provide an example.

A heat engine is a device that converts heat energy into mechanical work. An example is a steam power plant, where heat energy from burning fuel is used to generate steam, which then drives a turbine to produce mechanical work.

What is the Rankine cycle and its significance in power plants?

The Rankine cycle is a thermodynamic cycle used in steam power plants. It consists of four processes: heating in a boiler, expansion in a turbine, condensation in a condenser, and compression in a pump. The Rankine cycle is widely used in power generation due to its ability to efficiently convert thermal energy into mechanical work.