ACCURACY: In the fields of science, engineering, industry and statistics, accuracy is the degree of closeness of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results.

BERNOULLI: In fluid dynamics, Bernoulli”s principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid”s potential energy. Bernoulli”s principle is named after the Dutch–Swiss mathematician Daniel Bernoulli who published his principle in his book Hydrodynamica in 1738.

CALIBRATION: Calibration is the validation of specific measurement techniques and equipment. At the simplest level, calibration is a comparison between measurements-one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device.

CAVITATION: Cavitation is the formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Since the shock waves formed by cavitation are strong enough to significantly damage moving parts, cavitation is usually an undesirable phenomenon. It is specifically avoided in the design of machines such as turbines or propellers, and eliminating cavitation is a major field in the study of fluid dynamics.

CORIOLIS: The mathematical expression for the Coriolis force appeared in an 1835 paper by a French scientist Gaspard-Gustave Coriolis in connection with hydrodynamics, and also in the tidal equations of Pierre-Simon Laplace in 1778. Early in the 20th century, the term Coriolis force began to be used in connection with meteorology.

DENSITY: The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho).

FOULING: Fouling refers to the accumulation of unwanted material on solid surfaces, most often in an aquatic environment. The fouling material can consist of either living organisms (biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other surface-growth phenomena in that it occurs on a surface of a component, system or plant performing a defined and useful function, and that the fouling process impedes or interferes with this function.

KARMAN VORTEX STREET: A Kármán vortex street is a term used in fluid dynamics for a repeating pattern of swirling vortices caused by the unsteady separation of flow of a fluid over bluff bodies. It is named after the engineer and fluid dynamicist, Theodore von Kármán and is responsible for such phenomena as the “singing” of suspended telephone or power lines, and the vibration of a car antenna at certain speeds.

LAMINAR: Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. In fluid dynamics, laminar flow is a flow regime characterized by high momentum diffusion, low momentum convection, pressure and velocity independent from time. It is the opposite of turbulent flow. In nonscientific terms laminar flow is “smooth,” while turbulent flow is “rough.”

REPEATABILITY: Repeatability methods were developed by Bland and Altman (1986). The repeatability coefficient is a precision measure, which represents the value below which the absolute difference between two repeated test results may be expected to lie with a probability of 95 percent. The standard deviation under repeatability conditions is part of precision and accuracy.

REYNOLDS NUMBER: In fluid mechanics and heat transfer, the Reynolds number Re is a dimensionless number that gives a measure of the ratio of inertial forces (Vρ) to viscous forces (μ/L) and, consequently, it quantifies the relative importance of these two types of forces for given flow conditions.

STANDARD: A technical standard is an established norm or requirement. It is usually a formal document that establishes uniform engineering or technical criteria, methods, processes and practices. A technical standard can also be a controlled artifact or similar formal means used for calibration. Reference Standards and certified reference materials have an assigned value by direct comparison with a reference base. A primary standard is usually under the jurisdiction of a national standards body.

TRACEABILITY: The term traceability is used to refer to an unbroken chain of comparisons relating an instrument”s measurements to a known standard. Calibration to a traceable standard can be used to determine an instrument”s bias, precision, and accuracy.

TURNDOWN RATIO: Turndown ratio is a flow measurement term that indicates the range a specific flowmeter, or meter type, is able to measure with acceptable accuracy. It is also known as rangeability.

VISCOSITY: A measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms (and for fluids only), viscosity is “thickness”. Thus, water is “thin”, having a lower viscosity, while honey is “thick” having a higher viscosity.

The definitions provided here were compiled from entries in Wikipedia (www.wikipedia.org).

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