10 Common Fluid Mechanics Questions Asked in The Interviews: Theory Series 03

 

1.     What is viscosity?

Answer: Viscosity is a measure of a fluid's resistance to flow. It determines the internal friction within the fluid. High-viscosity fluids are thick and flow slowly, while low-viscosity fluids are thin and flow more easily.

2.     Define pressure and its units of measurement.

 Answer: Pressure is the force exerted per unit area. It is defined as the ratio of force to the area over which the force is applied. The SI unit of pressure is Pascal (Pa), where 1 Pa equals 1 N/m². Other common units include bar, psi, and atm.

3.     Explain the difference between laminar and turbulent flow.

 Answer: Laminar flow is characterized by smooth and orderly movement of fluid particles in parallel layers, with minimal mixing between layers. Turbulent flow, on the other hand, is characterized by irregular and chaotic fluid motion, involving mixing and eddies.

4.     What is Bernoulli's equation?

Answer: Bernoulli's equation is a fundamental equation in fluid mechanics that relates the pressure, velocity, and elevation of a fluid along a streamline. It states that the total energy of the fluid remains constant along a streamline in the absence of external forces like friction or pumps.

5.     Define Reynolds number and its significance.

Answer: Reynolds number is a dimensionless quantity used to determine the flow regime of a fluid. It represents the ratio of inertial forces to viscous forces in the flow. It helps in predicting whether the flow is laminar or turbulent and provides insights into flow behavior.

6.     Explain the concept of buoyancy.

Answer: Buoyancy is the upward force exerted on an object submerged in a fluid. It is a result of the difference in pressure between the top and bottom surfaces of the object due to the fluid's weight. Buoyancy is governed by Archimedes' principle and plays a crucial role in understanding the behavior of floating and submerged objects.

7.     What is the continuity equation?

Answer: The continuity equation states that the mass flow rate of a fluid remains constant in a steady-state, incompressible flow. It relates the velocity and cross-sectional area of the flow and is based on the principle of conservation of mass.

8.     What is the difference between absolute pressure and gauge pressure?

Answer: Absolute pressure is the total pressure exerted by a fluid, including atmospheric pressure as a reference. It is measured relative to a perfect vacuum. Gauge pressure, on the other hand, is the pressure measured relative to the atmospheric pressure. It does not consider the atmospheric pressure in its measurement.

9.     Define the concept of specific gravity.

Answer: Specific gravity is a dimensionless quantity that represents the density of a substance relative to the density of a reference substance, usually water at a specific temperature. It provides a measure of how much denser or lighter a substance is compared to water.

10.  Explain the working principle of a Venturi meter.

Answer: A Venturi meter is a device used to measure the flow rate of a fluid in a pipe. It consists of a converging section, throat, and diverging section. As the fluid flows through the converging section, its velocity increases, causing a decrease in pressure according to Bernoulli's equation. The pressure difference is measured to determine the flow rate.

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10 Common Applied Thermodynamics Questions Asked in The Interviews: Theory Series 02

 

1.     What is the Brayton cycle? 

Answer: The Brayton cycle is a thermodynamic cycle that describes the operation of gas turbine engines. It consists of four processes: isentropic compression, constant pressure heat addition, isentropic expansion, and constant pressure heat rejection. The Brayton cycle is commonly used in gas turbine power plants and jet engines.

 

2.     What is the Otto cycle? 

Answer: The Otto cycle is a thermodynamic cycle that represents the operation of spark-ignition internal combustion engines, commonly used in automobiles. It consists of four processes: isentropic compression, constant volume heat addition, isentropic expansion, and constant volume heat rejection.

 

3.     Explain the concept of air-fuel ratio in combustion. 

Answer: The air-fuel ratio represents the ratio of the mass of air to the mass of fuel in a combustion process. It is a crucial parameter that influences the efficiency and performance of combustion systems. The stoichiometric air-fuel ratio is the ideal ratio at which complete combustion occurs, ensuring efficient utilization of fuel.

 

4.     What is a Rankine cycle? 

Answer: The Rankine cycle is a thermodynamic cycle that represents the operation of steam power plants. It consists of four processes: isentropic compression, constant pressure heat addition, isentropic expansion, and constant pressure heat rejection. The Rankine cycle is commonly used in steam power generation systems.

 

5.     Define specific volume and its importance in thermodynamics.

 Answer: Specific volume (v) is the volume occupied by a unit mass of a substance. It is the reciprocal of density and provides insights into the spacing between molecules or particles. Specific volume is an important property in thermodynamics as it influences the behavior and performance of substances during processes such as compression, expansion, and heat transfer.

 

6.     What is a regenerative cycle in thermodynamics?

Answer: A regenerative cycle is a thermodynamic cycle that utilizes the extraction of heat from the working fluid leaving the cycle to preheat the fluid entering the cycle. It improves the overall efficiency of the cycle by reducing the amount of heat required from external sources. The regenerative cycle is commonly used in steam power plants.

 

7.     Explain the concept of a compressor in thermodynamics. 

Answer: In thermodynamics, a compressor is a device used to increase the pressure and temperature of a gas by reducing its volume. Compressors play a vital role in various applications such as gas turbines, refrigeration systems, and air conditioning systems. They are typically classified as positive displacement compressors or dynamic compressors.

 

8.     What is the purpose of a condenser in a refrigeration system? 

Answer: A condenser is a component in a refrigeration system that removes heat from the refrigerant gas and converts it into a liquid state. It facilitates the rejection of heat to the surroundings, allowing the refrigerant to release the absorbed heat and cool down. The condenser plays a crucial role in the heat rejection process of a refrigeration cycle.

 

9.     Define the coefficient of performance (COP) in refrigeration systems. 

Answer: The coefficient of performance (COP) is a measure of the efficiency of a refrigeration system. It represents the ratio of the heat extracted from the refrigerated space to the work input to the system. A higher COP indicates a more efficient refrigeration system.

 

10.  Explain the concept of irreversibility in thermodynamics. 

Answer: Irreversibility refers to the deviation from an ideal reversible process in a thermodynamic system. In practical systems, various irreversibilities such as friction, heat transfer across finite temperature differences, and pressure losses occur. Irreversibilities lead to inefficiencies and decrease the overall performance of thermodynamic processes.

 

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10 Common Thermodynamics Questions Asked in The Interviews: Theory Series 01

  

1.     What is the First Law of Thermodynamics? 

Answer: The First Law of Thermodynamics states that energy cannot be created or destroyed in an isolated system. It can only change forms or be transferred from one system to another.

2.     What is the Second Law of Thermodynamics? 

Answer: The Second Law of Thermodynamics states that the total entropy of an isolated system always increases over time. It implies that natural processes tend to move towards a state of higher disorder or randomness.

3.     What is enthalpy and how is it related to thermodynamics? 

Answer: Enthalpy (H) is a thermodynamic property that represents the total heat content of a system. It is given by the sum of the internal energy (U) and the product of pressure (P) and volume (V) of the system, H = U + PV.

4.     Explain the Carnot cycle. 

Answer: The Carnot cycle is a theoretical thermodynamic cycle that represents the most efficient heat engine possible. It consists of four reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. The Carnot cycle operates between two heat reservoirs at different temperatures.

5.     What is entropy? 

Answer: Entropy (S) is a measure of the degree of randomness or disorder in a system. It quantifies the number of possible microscopic states that a system can have. Entropy tends to increase in natural processes, indicating an increase in system disorder.

6.     Define specific heat capacity and its relation to thermodynamics. 

Answer: Specific heat capacity (c) is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius. It is a material property that influences the amount of energy needed to change the temperature of a substance during a thermodynamic process.

7.     Explain the concept of work done in thermodynamics. Answer: In thermodynamics, work is defined as the energy transfer that occurs due to the application of a force over a distance. It represents the ability to perform mechanical tasks or produce changes in the system. Work can be done on or by the system, and it is typically expressed as the product of force and displacement.

8.     What is a heat exchanger? 

Answer: A heat exchanger is a device used to transfer thermal energy between two or more fluids at different temperatures. It facilitates the efficient exchange of heat by bringing the fluids in close contact without mixing them. Heat exchangers are widely used in various industrial and HVAC systems.

9.     What is the difference between an open system and a closed system in thermodynamics?

 Answer: In thermodynamics, an open system allows the transfer of both energy and matter across its boundaries. In contrast, a closed system only allows the transfer of energy across its boundaries but not matter. The concept of an isolated system does not permit the transfer of either energy or matter.

10.  Explain the concept of a phase diagram in thermodynamics. 

Answer: A phase diagram is a graphical representation that shows the relationships between different phases (solid, liquid, gas) of a substance under various combinations of temperature and pressure. It illustrates the conditions at which phase transitions occur and provides insights into the behavior of substances under different thermodynamic conditions.

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