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Fluid Dynamics Glossary

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  • Absolute Pressure  -  A pressure at absolute zero can only exist in a total vacuum and any pressure above this is called absolute pressure.
  • ACFM  -  Actual cubic feet per minute is a unit of volumetric flow. It is primarily used by manufacturers of blowers and compressors to measure how much air is being moved across the equipment.
  • Acoustic Flowmeter  -  This type of flowmeter (ultrasonic) can give a continuous measurement of the flow rates of both open channel or pipe.
  • Actual Vapor Pressure  -  The measurement to the amount of water vapor that is in a volume of air.
  • Aeration  -  Aeration is the process where water is subjected to intimate air contacting for the purpose of removing contaminating gasses or to saturate it with dissolved oxygen.
  • Air Flow Rate  -
  • Air Flow Rate through Piping  -
  • Air Pipe Sizing  -
  • Air Pressure Loss through Piping  -
  • Air Velocity through Piping  -
  • Air–fuel Ratio  -  The mass ratio of air to fuel mixture present in an internal combustion engines. Because it is a ratio, it is unitless.
  • Amagat's Law  -  States that the volume of a mixture is equal to the sum of the partial volume of its components.
  • Archimedes Principle  -  The upward bouyancy force that is extended on a body that is completely or partially immersed in a fluid and is equal to the weight of the fluid that the body displaces.
  • Average Force  -  used when the instantaneous velocity is not measured precisely between two points.
  • Average Velocity  -  The average of any given velocities where the acceleration is constant.  The calculation for average velocity with zero accleration is shown below.
  • Avogadro's Law  -  When temperature and pressure are held constant, the volume of a gas is proportional to the number of moles of gas present.

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  • Barlow's Formula  -  Relates to burst pressure, the point just before or at when a pipe or tubing fails under pressure.Bernoulli's Equation  -  A way of describing the conservation of energy principle in an incompressible fluid.
  • Borda-Carnot Equation  -  A empirical description of the mechanical loss energy losses of the fluid due to a sudden flow expansion.
  • Boyle's Law  -  States that the volume occupied by a given mass of gas varies inversely with the absolute pressure if the temperature remains constant.
  • Brackish  -  A relative term used for water having a total dissolved solids concentration less than brine but more than in potable water.
  • Brake Horsepower  -  The engine's horsepower required to overcome the loss in power caused by the pump.
  • Bulk Modulus  -  The elastic relationship between an applied pressure that acts to change the volume of the substance and the ability of a substance to withstand changes in volume when under compression.
  • Bulk Modulus and Compressibility Relationship  -
  • Bulk Modulus of Elasticity  -  The elastic relationship between an applied pressure that acts to change the volume of the substance and the ability of a substance to withstand changes in volume when under compression.
  • Buoyancy  -  When a liquid applies upward force on an object that is completely submerged or floating.
  • Buoyancy Mass  -  The amount of matter an object has relative to the density of the liquid.

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  • Dalton’s Law  -  States that the total pressure of a gas mixture is equal to the sum of the partial pressures of the individual gas components of the mixture.
  • Darcy Flux  -  See Darcy Velocity
  • Darcy Friction Factor - Brkić  -  The Brkić approximation is one way of estimating the Darcy friction factor for use in pressure drop calculations.
  • Darcy Friction Factor - Free Surface Flow  -  Free surface flow describes flow that experiences zero shear forces.
  • Darcy Friction Factor - Laminar Flow  -  The equation on this page should be used only when the flow regime is fully laminar.  If the flow regime is transition flow or turbulant flow, other approximations for the Darcy Friction Factor should be made.
  • Darcy Velocity  -  The volumetric flow per unit area of a porous mediun.
  • Darcy's Law  -  The law states that this rate is directly proportional to the drop in vertical elevation between two places in the medium and indirectly proportional to the distance between them.
  • Density  -  The ratio of the amount of matter in an object compared to its volume
  • Dew Point  -  The temperature at which air must be cooled to become saturated with water vapor.
  • Dimensionless Numbers  -  See these articles, they contain a lot of fluid related information.
  • Discharge Coefficient  -  The ratio of actual discharge to the theoretical discharge.
  • Drag Force  -  The drag on a body as is moves through a fluid (gas or liquid).
  • Dry Gas  -  A natural gas with very little liquid hydrocarbons or water vapor. It consists of almost 100% of methane \((CH4)\).
  • Dynamic Shear Viscosity  -  The resistance to shearing flow of a fluid, where adjacent layers move parallel to each other in different ways.

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  • Engine Horsepower  -  The estimate of engine horsepower after a quarter mile run using the trap speed.
  • Evaporation  -  The condition that occurs when heat is absorbed by the surface of a liquid and it changes to vapor.

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  • Fan Efficiency  -  The ratio of input and output power.
  • Flow  -
  • Flow Coefficient  -  Described as the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.
  • Rate  -  The amount of fluid that flows in a given time past a specific point.
  • Fluid  -  A substance that deforms and changes position when put under stress.
  • Fluid Oxidation  -  A fluid degradation phenomenon that occurs when it is exposed to oxygen.  This leads to an increase in viscosity and TAN (total acid number) as well as the eventual formation of insoluble solids.
  • Fluid Power  -  Describes hydraulic and pneumatic transmit of power from one location to another.
  • Fluid Pressure  -  Fluid at rest, exerts a force perpendicular to any surface in comes in contact with.
  • Fluid Pressure at Depth  -  The pressure exerted on a fluid depends only on the depth of the fluid.
  • Fluid Velocity  -  How fast the process is traveling in a pipe.
  • Force  -  The push or pull of an object resulting in a change from rest or motion.
  • Friction  -  The mechanical resistance to the relative movement of two surfaces.
  • Friction Coefficient  -  The ratio between two contacting surfaces and the frictional force that resists the normal force of the object.    
  • Friction Loss  -  How much loss of flow through a pipe is due to the viscosity, the measure of the internal friction/resistance to the flow of a liquid near the surface of the pipe.

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  • Manning's Roughness Coefficient  -  Measures the frictional resistance exerted by a channel, culvert or pipe on the flow.
  • Mean Depth  -  The average water depth in a stream channel or conduit computed by dividing the cross-section area by the surface width.
  • Mechanical Efficiency  -  The ratio of theoretical power the pump needs to operate to the actual power delivered to the pump itself.
  • Mole Fraction  -  The number of molecules (moles) of a solution in a mixture divided by the total number of moles present in the solution.
  • Momentum  -  An object is the amount of mass in motion.

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  • Natural Gas  -  Has very little liquid hydrocarbons or water vapor. It consists of almost 100% of methane \((CH4)\).
  • Newton's Law of Viscosity  -  States that shear stress between adjacent fluid layers is porportional to the velocity gradients between the two layers.

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  • Operating Pressure  -  The operating pressure of equipment occurs when the plant or process is operating at steady state conditions. 

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  • Torricelli's Law  -  The fluid efflux velocity flowing through an orifice under gravity at the bottom of a tank filled to a depth.  This is the same velocity from the orifice as a falling body over the same height due to gravity.
  • Torricelli's Principle  -  See Torricelli's Law
  • Torricelli's Theorem  -  See Torricelli's Law
  • Total Acid Number (TAN)  -  Measures the fluid acidity and indication of fluid oxidation.  It is determined by the amount of potassium hydroxide in milligrams that it needs to neutralize the acids in one gram of fluid.
  • Total Discharge Head  -  The total of the friction, pressure, and static discharge.
  • Total Displacement  -  In engine design, the total displacement is the amount of volume displaced by engine cylinders.
  • Total Dissolved Solids  -  The matter that remains in water which remains in solution.
  • Total Head  -  The sum of the discharge flange and the sum of the suction flange.
  • Total Pump Efficency  -  The conversion of one form of energy into another form of energy.
  • Total Suction Head  -  The total of the friction, pressure, and static discharge.
  • Turbidity  -  The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye.
  • Turbulence  -  Any deviation from parallel flow in a pipe due to rough inner walls obstructions or direction changes.

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