Centrifugal

Centrifugal (pronounced sen-trif-yuh-guhl or sen-trif-fugh-guhl)

(1) Moving or directed outward from the centre (as opposed to centripetal); tending, or causing, to recede from the centre.

(2) Pertaining to or operated by centrifugal force

(3) In botany, especially as applied to certain inflorescences, developing or progressing outward from a centre or axis, as in the growth of plant structures, usually to describe where the flowers in the centre or tip open first while those on the edge open last.

(4) In botany, having the radicle turned toward the sides of the fruit, as some embryos.

(5) In physiology, an alternative word for efferent, the process of transmitting nerve impulses away from the central nervous system.

(6) A machine for separating different materials by centrifugal force (now almost universally called a centrifuge).

(7) A rotating perforated drum holding the materials to be separated in such a machine.

(8) In the plural (as centrifugals), the crystals separated from the syrup in centrifugals, often then sent to second carbonatation tanks and mixed with juices being treated.

1687: From the New Latin centrifugālis (literally “center-fleeing”), the construct being the Latin centri- (an alternative combining form of centrum (center) + fugiō (to flee; escape) or fugō (to chase away, put to flight), from fugere (to flee) + al (the Latin adjectival suffix).  The -al suffix was from the Middle English -al, from the Latin adjectival suffix -ālis, or the French, Middle French and Old French –el & -al.  It was use to denote the sense "of or pertaining to", an adjectival suffix appended (most often to nouns) originally most frequently to words of Latin origin, but since used variously and also was used to form nouns, especially of verbal action.  The alternative form in English remains -ual (-all being obsolete).  The word was coined by Sir Isaac Newton (1642–1727) in Principia Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy (1687)), following the Dutch mathematician Christiaan Huygens (1629-1695) who created the new Latin centrifugālis.  In Newton’s words the original construction was vis centrifuga.  The noun centrifuge dates from 1887 (although the “centrifuge machine had been first described in 1765) and the first versions were designed to separate cream from milk, the word a noun use of the adjective centrifugal dating from 1801, from the Modern Latin centrifugus.  Centrifugal is a noun & adjective, centrifugalism is a noun, centrifuge & centrifugate are nouns & verbs, centrifugalize is a verb and centrifugally is an adverb; the noun plural is centrifugals.

The effect of centrifugal force, preserved by frozen water: 1972 AMC Matador.  As the wheel rotates, centrifugal force moves moisture outwards from the centre.  In sub-zero temperatures, ice forms in the shape of the direction.

Building on René Descartes' (1596–1650) theories of linear inertia, Newton’s description of centrifugal force emerged from his work in the 1660s studying the movement of planets; what is now known as centrifugal force he then termed an “endeavour to recede” and calculated the equation showing an inverse-square relation with distance from the centre.  In what was at the time thought by some counter-intuitive, Newton demonstrated the mathematics for calculating centrifugal and centripetal forces are identical.

1929 4½ Litre “Blower” Bentley raced in the 1930 Le Mans by Tim Birkin (1896–1933).  The Roots-type supercharger is mounted at base of the radiator, between the headlamps.

The physics of centrifugal force offered immediate possibilities to engineers, even before fuel-powered machines which creating reciprocating motion became widely used.  One of the best known applications (still in use today) was the supercharger, a device which “force-feeds” the fuel-air mixture in internal combustion engines (ICE).  As a general principle, all else being equal, to gain more power from an ICE, what is needed is a greater throughput of the fuel-air fixture from which energy can be extracted, the two most obvious solutions being to increase internal displacement or to increase the pressure with which the mixture is fed.

Principle of a “Roots Blower”, the Roots-type supercharger.

In the mid 1850s, brothers Philander Higley Roots (1813-1879) and Francis Marion Roots (1824-1889) of Indiana’s Roots Blower Company developed a strikingly efficient air pump with lobed rotors to provide a feed of pressurized air into the blast furnaces used in steel-making, an idea picked up in Germany by Daimler-Benz which patented a version intended for the ICE; at this point was born what came to be known as the “Roots-type supercharger”, a system which meshed two-lobed rotors in an 8-shaped chamber, the rotors capturing air at the inlet, trapping it for delivery it to the outlet.  In a Roots blower, there is no compression of air, just acceleration, making it ideal for low RPM ((crankshaft) revolutions per minute) applications including diesels and the big aero-engines developed during World War II (1939-1945).

Principle of a centrifugal supercharger.

The centrifugal supercharger differs in that it uses impellers, a type of fan which siphons air from its centre and directs it outwards.  Analysis of sketches from Antiquity have suggested the idea of an impeller may be truly old but one of the first to produce a workable design was Leonardo Da Vinci (1452–1519) and they came widely to be employed in the seventeenth & eighteenth centuries to ventilate mine-shafts.  Very simple in principle, in a centrifugal supercharger an impeller is located in a round housing with an inlet & outlet, the impeller as it rotates siphoning and circulating air from one point to another.  Under this system, air slows down as it is expelled but it can gather vast quantities, thus greatly increasing the pressure, something achieved by spinning at tens or even hundreds of thousands of RPM.

Principle of a centrifugal governor.

A centrifugal governor is a mechanical device which is used to control the speed of an engine by regulating the flow of fuel so a constant speed can be maintained, engineers calling this "proportional control".  Known also as "centrifugal regulators" and "fly-ball governors", centrifugal governors were invented by Dutch mathematician Christiaan Huygens (1629-1695) for the purpose of regulating the distance and pressure between millstones in seventeenth century windmills.  From here they were adapted for use in steam engines where their simplicity and reliability proved ideal for controlling the aperture through which steam entered a cylinder.  Doing reliably mechanically what could also be done unreliably using electronics, centrifugal governors remain in use on stationary ICEs and turbines but are seen also on decorative clocks, implemented often in a more deliberately intricate form that the starkly functional mechanisms designed by engineers.

Short clip of a centrifugal governor in operation by the Charles River Museum of Industry & Innovation.