FLUID MECHANICS VIVA QUESTIONS AND ANSWERS

Q: What is fluid mechanics?

A: Fluid mechanics is the study of fluids in motion and at rest. It involves the study of the physical properties of fluids, the forces acting on fluids, and the behavior of fluids when subjected to various external forces.

Q: What are the different types of fluids?

A: There are two types of fluids: liquids and gases. Liquids have a fixed volume and take the shape of their container, while gases have neither a fixed volume nor a fixed shape.

Q: What is viscosity?

A: Viscosity is a measure of a fluid’s resistance to flow. It is the internal friction within a fluid that opposes the motion of a solid object moving through it or the motion of different layers of the fluid moving past each other.

Q: What is Bernoulli’s equation?

A: Bernoulli’s equation is a mathematical equation that describes the conservation of energy for a fluid in motion. It states that the sum of the pressure, kinetic energy, and potential energy of a fluid flowing along a streamline is constant.

Q: What is the difference between laminar and turbulent flow?

A: Laminar flow is a smooth, orderly flow of fluid in which the fluid moves in parallel layers, while turbulent flow is a chaotic, irregular flow in which the fluid mixes randomly and flows in eddies and swirls.

Q: What is the Reynolds number?

A: The Reynolds number is a dimensionless number that describes the ratio of inertial forces to viscous forces in a fluid flow. It is used to predict whether the flow will be laminar or turbulent.

A: Steady flow is a flow in which the properties of the fluid at any point do not change with time, while unsteady flow is a flow in which the properties of the fluid at any point change with time.

Q: What is the difference between compressible and incompressible flow?

A: Compressible flow is a flow in which the density of the fluid changes significantly due to changes in pressure and temperature, while incompressible flow is a flow in which the density of the fluid remains constant.

Q: What is the difference between a streamline and a pathline?

A: A streamline is a line that is everywhere tangent to the velocity vector of a fluid at a given instant, while a pathline is the actual path traced out by a fluid particle as it moves through space over time.

Q: What is the difference between a boundary layer and a shear layer?

A: A boundary layer is a thin layer of fluid near a solid surface in which the flow velocity is very low due to the effects of viscosity, while a shear layer is a region of rapidly changing velocity near the interface between two fluids of different velocities.

Q: What is the difference between a subsonic and supersonic flow?

A: Subsonic flow is a flow in which the velocity of the fluid is less than the speed of sound, while supersonic flow is a flow in which the velocity of the fluid is greater than the speed of sound.

Q: What is the difference between a convergent and divergent nozzle?

A: A convergent nozzle is a nozzle in which the cross-sectional area decreases in the direction of flow, while a divergent nozzle is a nozzle in which the cross-sectional area increases in the direction of flow.

Q: What is the difference between a pump and a turbine?

A: A pump is a device that is used to increase the pressure and flow rate of a fluid, while a turbine is a device that is used to extract energy from a fluid flow to produce mechanical work.

Q: What is the difference between a positive displacement pump and a centrifugal pump?

A: A positive displacement pump delivers a fixed volume of fluid for each stroke or revolution, while a centrifugal pump delivers a variable volume of fluid depending on the flow resistance.

Q: What is the difference between a steady and unsteady heat transfer?

A: Steady heat transfer is a process in which the rate of heat transfer does not change with time, while unsteady heat transfer is a process in which the rate of heat transfer changes with time.

Q: What is the difference between a conduction and convection heat transfer?

A: Conduction heat transfer is the transfer of heat through a solid material or a stationary fluid due to temperature gradients, while convection heat transfer is the transfer of heat by the motion of a fluid.

Q: What is the difference between natural and forced convection heat transfer?

A: Natural convection heat transfer is the transfer of heat due to the natural buoyancy-driven flow of a fluid, while forced convection heat transfer is the transfer of heat due to the forced flow of a fluid by an external source.

Q: What is the difference between a thermal conductor and a thermal insulator?

A: A thermal conductor is a material that allows heat to flow through it easily, while a thermal insulator is a material that resists the flow of heat through it.

Q: What is the difference between a heat sink and a heat source?

A: A heat sink is a device that absorbs and dissipates heat away from a system, while a heat source is a device that generates heat to be transferred to a system.

Q: What is the difference between a laminar and turbulent boundary layer?

A: A laminar boundary layer is a thin layer of fluid near a solid surface in which the fluid moves in parallel layers, while a turbulent boundary layer is a layer of fluid near a solid surface in which the fluid moves in an irregular, chaotic manner.

Q: What is the difference between a stagnation point and a separation point?

A: A stagnation point is a point on a solid surface where the fluid velocity is zero, while a separation point is a point on a solid surface where the fluid flow separates from the surface.

Q: What is the difference between a lift and drag force?

A: A lift force is a force perpendicular to the direction of flow that acts on an object immersed in a fluid, while a drag force is a force parallel to the direction of flow that acts on an object immersed in a fluid.

Q: What is the difference between a steady and unsteady lift force?

A: A steady lift force is a lift force that remains constant with time, while an unsteady lift force is a lift force that varies with time.

Q: What is the difference between a laminar and turbulent flow?

A: A laminar flow is a smooth, orderly flow in which fluid particles move in parallel layers without any mixing, while a turbulent flow is a chaotic, irregular flow in which fluid particles mix and flow in eddies and swirls.

Q: What is the difference between a Bernoulli’s equation and a continuity equation?

A: Bernoulli’s equation describes the conservation of energy in a fluid flow, while the continuity equation describes the conservation of mass in a fluid flow.

Q: What is the difference between a compressible and incompressible flow?

A: A compressible flow is a flow in which the density of the fluid changes with changes in pressure and temperature, while an incompressible flow is a flow in which the density of the fluid remains constant.

Q: What is the difference between a Newtonian and non-Newtonian fluid?

A: A Newtonian fluid is a fluid in which the shear stress is proportional to the rate of deformation, while a non-Newtonian fluid is a fluid in which the shear stress is not proportional to the rate of deformation.

Q: What is the difference between a single-phase and two-phase flow?

A: A single-phase flow is a flow in which only one phase of a fluid is present, while a two-phase flow is a flow in which two phases of a fluid, such as liquid and gas, are present.

Q: What is the difference between a nozzle and a diffuser?

A: A nozzle is a device that increases the velocity of a fluid by reducing the cross-sectional area of the flow passage, while a diffuser is a device that decreases the velocity of a fluid by increasing the cross-sectional area of the flow passage.

Q: What is the difference between a laminar and turbulent jet?

A: A laminar jet is a smooth, well-defined flow of fluid that maintains its shape over a long distance, while a turbulent jet is a chaotic, irregular flow of fluid that spreads out and becomes turbulent quickly.

Q: What is the difference between a stagnation pressure and dynamic pressure?

A: Stagnation pressure is the pressure at a point where the fluid velocity is zero, while dynamic pressure is the pressure that results from the velocity of the fluid.

Q: What is the difference between a laminar and turbulent pipe flow?

A: A laminar pipe flow is a smooth, orderly flow in which fluid particles move in parallel layers without any mixing, while a turbulent pipe flow is a chaotic, irregular flow in which fluid particles mix and flow in eddies and swirls.

Q: What is the difference between a Couette flow and Poiseuille flow?

A: Couette flow is a type of flow between two parallel plates, where one plate moves and the other is stationary, while Poiseuille flow is a type of flow in a circular pipe, where the flow is driven by a pressure gradient.

Q: What is the difference between a free and forced vortex flow?

A: A free vortex flow is a type of flow in which the fluid rotates around a central axis without any external forces, while a forced vortex flow is a type of flow in which the fluid is forced to rotate by external forces.

Q: What is the difference between a flow in a porous media and a flow in a solid media?

A: A flow in a porous media is a flow in which the fluid flows through a material with interconnected pores, while a flow in a solid media is a flow in which the fluid flows through a solid material with no interconnected pores.

Q: What is the difference between a weir and a flume?

A: A weir is a device that is used to measure the flow rate of a liquid over a raised structure, while a flume is a device that is used to measure the flow rate of a liquid through a channel or a conduit.

Q: What is the difference between laminar and turbulent boundary layer?

A: A laminar boundary layer is a thin, smooth layer of fluid that forms at the surface of a solid body in a fluid flow and moves in parallel layers, while a turbulent boundary layer is a thicker layer of fluid that forms at the surface of a solid body in a fluid flow and is characterized by chaotic, eddying motion.

A: Steady flow is a flow in which the flow properties, such as velocity and pressure, do not change with time, while unsteady flow is a flow in which the flow properties change with time.

Q: What is the difference between a stagnation point and a separation point?

A: A stagnation point is a point on a solid surface where the velocity of the fluid is zero, while a separation point is a point on a solid surface where the fluid flow separates from the surface.

Q: What is the difference between a converging and diverging nozzle?

A: A converging nozzle is a nozzle that narrows down as it goes from the inlet to the outlet, while a diverging nozzle widens as it goes from the inlet to the outlet.

Q: What is the difference between a cavitation and a flashing flow?

A: Cavitation is the formation of vapor bubbles in a liquid due to a decrease in pressure, while flashing flow is the sudden boiling of a liquid due to a decrease in pressure.

Q: What is the difference between a Pitot tube and a hot wire anemometer?

A: A Pitot tube is a device used to measure fluid velocity by measuring the difference between stagnation pressure and static pressure, while a hot wire anemometer is a device used to measure fluid velocity by measuring the heat transfer rate between a hot wire and the fluid.

Q: What is the difference between a laminar and turbulent mixing?

A: A laminar mixing is a mixing process in which the fluid particles mix in a smooth and orderly manner, while a turbulent mixing is a mixing process in which the fluid particles mix in a chaotic and irregular manner.

Q: What is the difference between a subcritical and supercritical flow?

A: A subcritical flow is a flow in which the fluid velocity is less than the velocity of small amplitude waves, while a supercritical flow is a flow in which the fluid velocity is greater than the velocity of small amplitude waves.

Q: What is the difference between a hydrostatic and dynamic pressure?

A: Hydrostatic pressure is the pressure that arises from the weight of a fluid at rest, while dynamic pressure is the pressure that arises from the motion of a fluid.

Q: What is the difference between a Couette viscometer and a rotational viscometer?

A: A Couette viscometer is a device used to measure the viscosity of a fluid by measuring the torque required to rotate an inner cylinder in a fluid-filled outer cylinder, while a rotational viscometer is a device used to measure the viscosity of a fluid by measuring the torque required to rotate a spindle in a fluid.

Q: What is the difference between a jet and a spray?

A: A jet is a narrow, high-speed stream of fluid that maintains its shape over a long distance, while a spray is a fine, mist-like dispersion of fluid particles that is created by breaking up a fluid into small droplets.

Q: What is the difference between a laminar and turbulent flow regime?

A: Laminar flow is a smooth, predictable flow of fluid with no fluctuations, while turbulent flow is characterized by fluctuations and eddies that cause the fluid to mix in a chaotic manner.

Q: What is the difference between a flow rate and a velocity?

A: Flow rate is the volume of fluid that passes through a given point in a specific time period, while velocity is the rate at which fluid moves past a specific point.

Q: What is the difference between a uniform and non-uniform flow?

A: A uniform flow has the same velocity and direction at all points, while a non-uniform flow has varying velocity and direction at different points.

Q: What is the difference between a compressible and incompressible fluid?

A: A compressible fluid is one whose density changes with pressure and temperature, while an incompressible fluid has a constant density regardless of pressure and temperature.

Q: What is the difference between a streamline and a streakline?

A: A streamline is a continuous line that represents the path of a fluid particle in steady flow, while a streakline is the path that fluid particles have followed over a period of time.

Q: What is the difference between a steady and unsteady boundary layer?

A: A steady boundary layer is one where the velocity profile remains constant with time, while an unsteady boundary layer changes with time.

Q: What is the difference between a velocity head and a pressure head?

A: Velocity head is the kinetic energy of a fluid per unit weight and is measured as v^2/2g where v is the fluid velocity and g is acceleration due to gravity. Pressure head is the potential energy per unit weight of a fluid and is measured as p/ρg where p is the pressure and ρ is the fluid density.

Q: What is the difference between a pitot-static tube and a pitot tube?

A: A pitot-static tube is a device used to measure both the velocity and pressure of a fluid, while a pitot tube is used only to measure the velocity of a fluid.

Q: What is the difference between an isentropic and an adiabatic process?

A: An isentropic process is a thermodynamic process in which the entropy of the system remains constant, while an adiabatic process is one in which no heat is transferred to or from the system.

Q: What is the difference between a manometer and a barometer?

A: A manometer is a device used to measure the pressure of a fluid in a closed container, while a barometer is used to measure the atmospheric pressure.

Q: What is the difference between an axial and a radial flow pump?

A: An axial flow pump is one in which the flow of fluid is parallel to the axis of rotation, while in a radial flow pump, the flow is perpendicular to the axis of rotation.

Q: What is the difference between a weir and a spillway?

A: A weir is a device used to measure the flow rate of a liquid over a raised structure, while a spillway is a structure used to allow excess water to flow over a dam or other barrier.

Q: What is the difference between a nozzle and a diffuser?

A: A nozzle is a device used to increase the velocity of a fluid, while a diffuser is a device used to decrease the velocity of a fluid.

Q: What is the difference between a static and dynamic pressure sensor?

A: A static pressure sensor measures the pressure of a fluid that is not in motion, while a dynamic pressure sensor measures the pressure of a fluid that is in motion.

Q: What is the difference between a centrifugal and a positive displacement pump?

A: A centrifugal pump uses centrifugal force to move fluids through the pump, while a positive displacement pump uses a mechanical means to move fluids through the pump.

Q: What is the difference between a propeller and a turbine?

A: A propeller is a device that converts rotational motion into a thrust force for use in propulsion, while a turbine is a device that converts the energy of a fluid into rotational motion for use in power generation.

Q: What is the difference between a boundary layer and an inviscid flow region?

A: A boundary layer is the thin layer of fluid near a surface where the effects of viscosity are significant, while an inviscid flow region is the area of fluid outside of the boundary layer where viscosity can be ignored.

Q: What is the difference between a stagnation and static pressure?

A: Stagnation pressure is the pressure that would exist if a fluid were brought to rest isentropically, while static pressure is the pressure of a fluid in motion relative to a reference point.

Q: What is the difference between a velocity potential and a stream function?

A: A velocity potential is a scalar function that satisfies Laplace’s equation and can be used to determine the velocity field of an incompressible fluid, while a stream function is a scalar function that satisfies continuity and can be used to determine the streamlines of an incompressible fluid.

Q: What is the difference between a vortex and a eddy?

A: A vortex is a rotational flow field in a fluid, while an eddy is a swirling motion that can occur in both laminar and turbulent flow.

Q: What is the difference between a hydraulic and pneumatic system?

A: A hydraulic system uses a liquid, usually oil, to transmit power, while a pneumatic system uses a gas, usually compressed air, to transmit power.

Q: What is the difference between a centrifugal and a reciprocating compressor?

A: A centrifugal compressor uses centrifugal force to compress gas, while a reciprocating compressor uses a piston and cylinder to compress gas.

Q: What is the difference between a laminar and a turbulent boundary layer?

A: A laminar boundary layer is one where the flow is smooth and ordered, while a turbulent boundary layer is one where the flow is chaotic and disordered.

Q: What is the difference between a vortex tube and a heat exchanger?

A: A vortex tube is a device that separates a compressed gas into hot and cold streams, while a heat exchanger is a device used to transfer heat from one fluid to another.

Q: What is the difference between a laminar and a turbulent jet?

A: A laminar jet is one that is smooth and predictable, while a turbulent jet is one that is chaotic and unpredictable.

Q: What is the difference between a hydraulic head and an elevation head?

A: Hydraulic head is the sum of pressure head and velocity head in a fluid system, while elevation head is the potential energy per unit weight of a fluid due to its position relative to a reference point.

Q: What is the difference between a pitot tube and a venturi meter?

A: A pitot tube measures fluid velocity by measuring the pressure difference between stagnation pressure and static pressure, while a venturi meter measures fluid flow rate by measuring the pressure difference between a constriction and the upstream and downstream points.