Fluid: A fluid deforms continuously under the influence of shear stress, no matter how small .
Internal flow: The flow in a pipe or duct is internal flow if the fluid is completely bounded by solid surfaces.
External flow: External flow is the flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe.
Open channel flow: The flow of liquids in a pipe is called open-channel flow if the pipe is partially filled with the liquid and there is a free surface , such as the flow of water in rivers and irrigation ditches.
Incompressible flow: A fluid flow during which the density of the fluid remains nearly constant is called incompressible flow.
Incompressible fluid: A fluid whose density is practically independent of pressure (such as a liquid) is commonly referred to as an “incompressible fluid,” although it is more proper to refer to incompressible flow.
Compressible flow: A flow in which density varies significantly is called compressible flow.
Forced flow: In forced flow, the fluid is forced to flow over a surface or in a tube by external means such as a pump or a fan .
Natural flow: In natural flow, any fluid motion is caused by natural means such as the buoyancy effect that manifests itself as the rise of the warmer fluid and the fall of the cooler fluid.
Mach number: The Mach number of a flow is defined as the ratio of the flow velocity to the local speed of sound in the same medium.
No slip Condition: A fluid in direct contact with a solid surface sticks to the surface and there is no slip. This is known as the no-slip condition.
Boundary layer: When a fluid stream encounters a solid surface that is at rest, the fluid velocity assumes a value of zero at that surface. The velocity then varies from zero at the surface to the freestream value sufficiently far from the surface. The region of flow in which the velocity gradients are significant and frictional effects are important is called the boundary layer.
Steady-flow process: A process is said to be steady if it involves no changes with time anywhere within the system or at the system boundaries.
Stress: Stress is defined as force per unit area, and is determined by dividing the force by the area upon which it acts.
Normal Stress: The normal component of a force acting on a surface per unit area is called the normal stress
Shear Stress: The tangential component of a force acting on a surface per unit area is called shear stress.
Pressure: In a fluid at rest, the normal stress is called pressure.
System: A system is defined as a quantity of matter or a region in space chosen for study.
Surroundings: The mass or region outside the system is called the surroundings.
Boundary: The real or imaginary surface that separates the system from its surroundings is called the boundary.
Closed system: A closed system (also known as a control mass or simply a system) consists of a fixed amount of mass, and no mass can cross its boundary.
Open system: An open system, or a control volume, is a properly selected region in space.
Intensive properties: Intensive properties do not depend on the size (extent) of the system.
Extensive properties: Extensive properties do depend on the size (extent) of the system.
Specific gravity: The specific gravity, or relative density, is defined as the ratio of the density of a substance to the density of some standard substance at a specified temperature . (the standard is water at 4°C, for which ρH2O = 1000 kg/m3).
Vapor pressure: The vapor pressure of a pure substance is defined as the pressure exerted by a vapor in phase equilibrium with its liquid at a given temperature.
Partial pressure: The pressure of a vapor or gas, whether it exists alone or in a mixture with other gases, is called the partial pressure.
Cavitation: In the flow of a liquid, cavitation is the vaporization that may occur at locations where the pressure drops below the vapor pressure.
Total energy: The sum of all forms of the energy a system possesses is called total energy. In the absence of magnetic, electrical, and surface tension effects, the total energy of a system consists of the kinetic, potential, and internal energies.
Flow energy: Flow energy or flow work is the energy needed to push a fluid into or out of a control volume. Fluids at rest do not possess any flow energy.
Newtonian fluid: Fluids whose shear stress is linearly proportional to the velocity gradient (shear strain) are called Newtonian fluids.
Viscosity: Viscosity is a measure of the “stickiness” or “resistance to deformation” of a fluid.
Surface tension: The magnitude of the pulling force at the surface of a liquid per unit length is called surface tension σ(s).
Capillary effect: The capillary effect is the rise or fall of a liquid in a small-diameter tube inserted into the liquid.
Absolute pressure: The actual pressure at a given position is the absolute pressure and is measured relative to the absolute vacuum.
Gage or gauge pressure: Difference between absolute pressure and atmospheric pressure, known as Gauge Pressure.
Vacuum pressure: Pressure below the atmospheric pressure is the Vacuum Pressure.
Pascal’s Law: Pascal’s law states that the pressure applied to a confined fluid increases the pressure throughout by the same amount.
Centre of pressure: The resultant hydrostatic force acting on a submerged surface is the resultant of the pressure forces acting on the surface. The point of application of this resultant force is called the centre of pressure.
Buoyancy force: The upward force a fluid exerts on an immersed body is called the buoyant force.
Fluid kinematics: Fluid kinematics is the study of how fluids flow and how to describe fluid motion.
The Lagrangian method : In the Lagrangian description of fluid motion, individual fluid particles (fluid elements composed of a fixed, identifiable mass of fluid) are followed.
The Eulerian description: In the Eulerian description of fluid motion, we are concerned with field variables, such as velocity, pressure, temperature, etc., as functions of space and time within a flow domain or control volume.
Pathline: A pathline is the actual path traveled by an individual fluid particle over some time period. It indicates the exact route along which a fluid particle travels from its starting point to its ending point. Unlike streamlines, pathlines are not instantaneous, but involve a finite time period.
Streamline: A streamline is a curve that is everywhere tangent to the instantaneous local velocity vector. It indicates the instantaneous direction of fluid motion throughout the flow field.
Streakline: A streakline is the locus of fluid particles that have passed sequentially through a prescribed point in the flow.
Timeline: A timeline is a set of adjacent fluid particles that were marked at the same instant in time.
Translation: A fluid particle moves from one location to another.
Rotation: A fluid particle rotates about an axis drawn through the particle.
Linear strain or extensional strain: A fluid particle stretches in a direction such that a line segment in that direction is elongated at some later time.
Shear strain: A fluid particle distorts in such a way that two lines through the fluid particle that are initially perpendicular are not perpendicular at some later time.
Mass flow rate: Mass flow rate is the amount of mass flowing through a cross-section per unit time
Volume flow rate: Volume flow rate is the amount of volume flowing through a cross-section per unit time.
Mechanical energy: Mechanical energy is the form of energy that can be converted to mechanical work completely and directly by a mechanical device such as a propeller.
Mechanical efficiency: Mechanical efficiency is defined as the ratio of the mechanical energy output to the mechanical energy input.
Streamwise acceleration: The acceleration of a fluid particle along a streamline is called streamwise acceleration, and it is due to a change in speed along a streamline.
Normal acceleration: Normal acceleration (or centrifugal acceleration, is the acceleration of a fluid particle in the direction normal to the streamline, and it is due to a change in direction.
Static pressure: Static pressure (P)is the actual pressure of the fluid.
Dynamic pressure: Dynamic pressure ρV2/2 is the pressure rise when the fluid in motion is brought to a stop isentropically.
Hydrostatic pressure: Hydrostatic pressure (ρgz) is not pressure in a real sense since its value depends on the reference level selected, and it accounts for the effects of fluid weight on pressure.
Stagnation pressure: The sum of the static and dynamic pressures is called the stagnation pressure
Pressure head: The pressure head P/ρg is the height of a fluid column that produces the static pressure P.
Velocity head: The velocity head V2/2g is the elevation needed for a fluid to reach the velocity V during frictionless free fall.
Elevation head: The elevation head z is the height of a fluid relative to a reference level.
Hydraulic grade line: The curve that represents the sum of the static pressure and the elevation heads, P/ρg + z, is called the hydraulic grade line or HGL.
Energy grade line: The curve that represents the total head of the fluid, P/ρg + V2/2g + z, is called the energy line or EGL.
Irreversible head loss: Irreversible head loss is the loss of mechanical energy due to irreversible processes (such as friction) in piping expressed as an equivalent column height of fluid, i.e., head.
Useful pump head: Useful pump head is the useful power input to the pump expressed as an equivalent column height of fluid.
kinetic energy correction factor: The kinetic energy correction factor is a correction factor to account for the fact that kinetic energy using average velocity is not the same as the actual kinetic energy using the actual velocity profile (the square of a sum is not equal to the sum of the squares of its components). The effect of kinetic energy factor is usually negligible, especially for turbulent pipe flows. However, for laminar pipe flows, the effect of α is sometimes significant.
Newton’s first law: Newton’s first law states that “a body at rest remains at rest, and a body in motion remains in motion at the same velocity in a straight path when the net force acting on it is zero.” Therefore, a body tends to preserve its state or inertia.
Newton’s second law: Newton’s second law states that “the acceleration of a body is proportional to the net force acting on it and is inversely proportional to its mass.”
Newton’s third law: Newton’s third law states “when a body exerts a force on a second body, the second body exerts an equal and opposite force on the first.”
Dimension: A dimension is a measure of a physical quantity (without numerical values).
Unit: A unit is a way to assign a number to the dimension.
The law of dimensional homogeneity:The law of dimensional homogeneity states that every additive term in an equation must have the same dimensions.
