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.

Propeller

Propeller (pronounced pruh-pel-er)

(1) A person or thing that propels.

(2) A device with a hub to which are attached evenly spaced & shaped radiating blades, rotating on a shaft to pitch against air or water to propel an aircraft, ship etc.

(3) A wind-driven (usually three-bladed) device that provides mechanical energy, as for driving an electric alternator in wind plants (not a universal use).

(4) A steamboat thus propelled; a screw steamer (now rare).

(5) In fishing, a spinnerbait.

1780: The construct was propel + -er and the original sense was “one who or that which that propels”, an agent noun from the verb propel.  The verb propel was a mid-fifteenth century form from the Middle English propellen (to drive away, expel), from the Latin propellere (push forward, drive forward, drive forth; move, impel), the construct being pro- (the prefix here use in the sense of “forward direction, forward movement”) + pellere (to push, drive), from the primitive Indo-European root pel- (to thrust, strike, drive).  The meaning “to drive onward, cause to move forward” emerged in the 1650s.  The –er suffix was from the Middle English –er & -ere, from the Old English -ere, from the Proto-Germanic -ārijaz, thought most likely to have been borrowed from the Latin –ārius where, as a suffix, it was used to form adjectives from nouns or numerals.  In English, the –er suffix, when added to a verb, created an agent noun: the person or thing that doing the action indicated by the root verb.   The use in English was reinforced by the synonymous but unrelated Old French –or & -eor (the Anglo-Norman variant -our), from the Latin -ātor & -tor, from the primitive Indo-European -tōr.  When appended to a noun, it created the noun denoting an occupation or describing the person whose occupation is the noun.  The alternative spelling propellor dates from the early days of aviation in the first years of the twentieth century and is now extinct.  The standard abbreviation is “prop”, the use noted from military aviation since 1914.  Propeller is a noun; the noun plural is propellers.

Although the concept was used in antiquity and inventors and others (most famously Leonardo da Vinci (1452–1519))  had for centuries experimented, the use of the word in mechanical engineering dates from 1809 and was from nautical design describing the application of a “device for moving vessels on or under the water”.  In aircraft design the theory of the use of “propeller” appears in papers and drawings in the 1840s (in what were then described as “flying machines”) and models were built which demonstrated a “proof of concept” although it would be decades before lightweight engines of sufficient power existed to allow experiments in aerodynamics and construction to be powered.  The first known rendering of an aircraft propeller in a recognizably modern form dates from 1853.  The modern propeller uses two or (usually) more twisted, airfoil-shaped blades mounted around a shaft which are spun to provide propulsion of a vehicle through water or air, or to cause fluid flow, as in a pump.  The lift generated by the spinning blades provides the force that propels the vehicle or the fluid although this lift does not of necessity have to induce an actual upward force; its direction is simply parallel to the rotating shaft.

Lindsay Lohan getting off the propeller driven (technically a turbo-prop) NAPA Shuttle, The Parent Trap (1998).

The term “to disembark” was borrowed from nautical use and of late "to deplane" has entered English which seems unnecessary but the companion “to disemplane” seems more absurd still; real people continue to “get on” and “get off” aircraft.

The terms “impeller” & “propeller” both describe devices which use various implantations of the “rotating blade(s) design and are used in mechanical systems to take advantage of the properties of fluid dynamics to harness specific energy for some purpose.  A propeller is a type of rotating device with blades designed to propel or move a fluid (typically a gas or a liquid) by generating thrust; they are most associated with marine vessels, aircraft and some industrial applications.  In aircraft, propellers can be attached to wing-mounted engines or mounted just about anywhere on a fuselage although historically a location at the front has been most common.  In marine applications, propellers have on specialized vessels been located to the sides of the hull but they almost always emerge at or close to the stern.  An impeller is a rotating component with blades or vanes (almost always enclosed in a housing), typically used for fluid or air distribution, such as a pump or a compressor, the primary purpose being to increase flow or pressure.  The classic impellers those in centrifugal pumps where they spin, creating a flow of fluid (liquid or air) by imparting centrifugal force to the substance; in practice, impellers such accelerate liquids are more common.

So an impeller & propeller do much the same thing, using blades to propel some form of fluid.  The use of different terms is helpful because in practice they are very different devices and the distinction that one is external and the other located within a housing is handy and the origin of that seems to lie in the construct of impeller which came first, dating from circa 1680 (as an agent noun from the verb impel) in the sense of “someone or something which impels”.  What the design of an impeller does is use the energy from the rotation to increase the flow or pressure of the fluid and it that it’s the reverse of a turbine, the rotation of which extracts energy from, and reduces the pressure of the flow.  Engineers also have a number of highly technical rules about what is and is not defined as an impeller base on the whether the entry and exit of the fluids occur axially or radially but it seemed impossible to construct such definitions as absolutes so for most the simpler distinctions are more helpful.  In engineering, impellers have been recorded as a machine or component name since 1836.

News Corp website 22 January 2024.  To refer to a jet engine’s nacelle as a propeller could (almost) be defended on the basis it’s the jet engine which “propels” the aircraft but this is more likely an example of (1) the decline in the quality of journalists and (2) what happens when there are no sub-editors to correct the mistakes.  In time, artificial intelligence (AI) should improve things.    

The verb impel dates from the early fifteenth century and was from the Middle English impellen, from the Latin impellere (to push, strike against; set in motion, drive forward, urge on), the construct an assimilated form of in- (into, in, on, upon), from the primitive Indo-European root en- (in) + pellere (to push, drive), from the primitive Indo-European root pel- (to thrust, strike, drive).  The construct of the Latin impellō was in- +‎ pellō (push, drive), from the Proto-Italic pelnō or pelnaō, a nasal-infix present derived from the primitive Indo-European pelh- (to drive, strike, thrust).  The Latin prefix –in could be appended to create a negative (un-, non-, not etc) but here was used as an intensifier, another possible meaning (in, within, inside) coincidental to the mechanical devices being usually mounted within housings.

Propellers and impellers both use blades (although those of the latter are often in the form of a single piece wither cast, molded, or (occasionally) forged.  Turbines also use blade-like parts but these are called vanes and an industry which seems unable to decide on terminology is the burgeoning business of wind-power; the huge rotating assemblies on wind turbines are referred to variously as vanes, blades or rotors.  Rotor blades are familiar for the use in helicopters which is essentially an airframe where a large-scale propeller sits atop the structure, pointing upwards and rather than “propeller blades”, the accepted term is “rotor blades”, the design of which permits both lift and directional thrust although some exotic multi-engined machines have rotors in housings which, to maximize performance, can themselves be rotated to operate as conventional propellers.

Supermarine Seafang (1946) with contra-rotating propellers.  The Seafang was powered by the Rolls-Royce Griffon and was the final evolution of the Spitfire-derived Seafire and Spiteful, the trio all designed for use on Royal Navy aircraft carriers, the series enjoying success despite the basic design being hampered by the narrow undercarriage which made landings a challenge (something corrected on the Spiteful & Seafang).  Series production of the Seafang was contemplated but eventually only 18 were built because the jet-powered de Havilland Sea Vampire proved capable of carrier operations, surprising some at the Admiralty who doubted the jets could operate from anywhere but land.

The evolution of aircraft influenced propellers.  Once they had been fashioned from wood before the need for faster, more efficient shapes dictated the use of aluminium or other light metals.  By the time the first modern monoplane fighters appeared in the mid 1930s propellers were still two-bladed but as power increased over the years (something which accelerated during World War II (1939-1945)), three, four and five-bladed solutions were engineered.  The rising output however, although it permitted higher performance, created challenges for engineers, notably the “torque effect” which meant a tendency to cause the aircraft to roll in the direction of the propeller’s spin, a problem especially serious during take-offs.  In twin-engined aircraft the solution was to have the propellers rotate in opposite directions but in airframes with a single power-plant, sometimes used were contra-rotating propellers which, although introducing additional complexity and demanding additional maintenance, did offer advantages including: (1) harnessing more of an engine’s power, (2) increased thrust efficiency by a reduction in energy losses, (3) counteracting the torque effect, (4) improved low-speed manoeuvrability and ground-handling and (5) improved acceleration and climbing performance.

A flight of Republic P-47D Thunderbolts with under-wing drop-tanks.

The propeller also influenced other aspects of the aircraft.  When the prototype Republic P-47 Thunderbolt (1941-1945) first took to the air, it was the largest, heaviest single-seat piston-engined fighter ever produced (a distinction it still enjoys today).  Even the early versions used an engine rated at 2000 horsepower (later this would rise to 2800) and to harness this output demanded a large propeller.  The 12 foot (3.7 m) diameter of this four-bladed monster meant the landing-gear had to be extraordinarily long and the only way it could be accommodated was to have them retract inward, otherwise the heavy wing armament (8 x .50 inch (12.7 mm) M2 Browning machine guns (425 rounds per gun)) wouldn’t have fitted.

Chrysler XI-2220 V16.  The splined shaft is where the propeller attaches.

With things like the Thunderbolt, the Hawker Tempest and the later Supermarine Spitfires (and its derivatives), the piston-engined fighter achieved its final evolutionary form, the jet engine offering a path to performance unattainable while the physics of propellers imposed limits.  However, had the use of the A-Bombs not ended the war in 1945, development of the propeller aircraft would have continued because the early jets lacked thrust and reliability as well as suffering a rate of fuel consumption which rendered them unsuitable for long-distance operations.  With the war against Japan envisaged as lasting well into 1946, development of faster, more powerful piston engines continued although, given the parlous state of the Japanese military, it’s dubious at least there was much of a rationale for this but the military industrial complex is a creature of inertia and Chrysler’s research had perfected a new aero-engine for the Thunderbolt.  The XI-2220 was a 2,220 cubic inch (36.4 litre) V16 which was rated at a basic 2450 horsepower with some 4000 hp available when tuned for wartime use but with the end of the conflict, all such developments were cancelled and attention switched to the brave new world of jets and swept wings.  Thus ended the era of the big propeller-driven fighters, the V16 stillborn, as was the other extraordinary aero-engine on the drawing board: Britain's 32-cylinder Napier-Sabre H-32 which was a scaled-up version of their H24.

Auburn

Auburn (pronounced aw-bern)

(1) A reddish-brown or golden-brown color.

(2) Of something colored auburn (most often used to describe hair).

(3) A widely used locality name.

(4) As the Auburn system (also known as the New York system and Congregate system), a notably severe penal method created in the early nineteenth century and implemented in Auburn Prison, Auburn, New York.

1400–1450: From the late Middle English abron, abrune aborne & abourne (light brown, yellowish brown), a sixteenth century alteration (because of a conflation with the later spelling auburne with the Middle English broune & brun (brown) which also changed the spelling) of the earlier auborne (yellowish-white, flaxen) from the Middle French & Old French auborne & alborne (blond, flaxen, off-white) from the Medieval alburnus (fair-haired, literally “like white or whitish”) and related to alburnum (the soft, newer wood in the trunk of a tree found between the bark and the hardened heartwood, often paler in color than the heartwood) from alba & albus (white).  Since the meaning shifted from blonde to hues of red, auburn has tended to be used exclusively of women’s hair.  The noun use dates from 1852.  Auburn is often associated with the Venetian painter Tiziano Vecellio (circa 1490-1576; known usually in English as Titian), especially the works of his early career when the colors tended to be more vivid but the modern practice is to apply auburn to darker shades although there’s much imprecision in commercial applications such as hair dyes and what some call some sort of auburn, others might list as some variation of burgundy, brown, chestnut, copper, hazel, henna, russet, rust or titian.

The term “medieval scholar” is not of course oxymoronic though the language is replete with errors of translation and misunderstandings replicated and re-enforced over a thousand-odd years.  However, as English began to assume its recognizably modern form, nor were errors unknown and it does seem strange such a well-documented Latin word as alburnus (fair-haired, literally “like white or whitish”) which had evolved in Middle English as auburne could be conflated with the Middle English broune & brun (brown), leading eventually to the modern auburn having morphed from blonde to a range of reddish browns.  Some etymologists however suggests it was deliberate, the late fifteenth century blond being preferred while auburne was re-purposed to where it could be more useful in the color-chart.  The modern blond & blonde were from the Old French & Middle French blund & blont (blond, light brown, feminine of blond) thought most likely of Germanic origin and related to the Late Latin blundus (yellow) from which Italian picked up biondo and Spanish gained blondo.  It was akin to the Old English blondenfeax (gray-haired), derived from the Classical Latin flāvus (yellow) and in Old English, there was also blandan (to mix).  There exists an alternative etymology which connects the Frankish blund (a mixed color between golden and light-brown) to the Proto-Germanic blundaz (blond), the Germanic forms derived from the primitive Indo-European bhlnd (to become turbid, see badly, go blind) & blend (blond, red-haired)).  If so, it would be cognate with the Sanskrit bradhná (ruddy, pale red, yellowish).  In his dictionary (1863-1873), Émile Littré (1801–1881) noted the original sense of the French word was "a color midway between golden and light chestnut" which might account for the notion of "mixed."  In the Old English beblonden meant "dyed," so it is a possible root of blonde and the documentary record does confirm ancient Teutonic warriors were noted for dying their hair.

However the work of the earlier French lexicographer, Charles du Fresne (1610-1688), claimed that blundus was a vulgar pronunciation of Latin flāvus (yellow) but cited no sources.  Another guess, and one discounted universally by German etymologists, is that it represents a Vulgar Latin albundus from the Classical Latin alba & albus (white).  The word came into English from Old French where it had masculine and feminine forms and the English noun imported both, thus a blond is a fair-haired male, a blonde a fair-haired female and even if no longer a formal rule in English, it’s an observed convention.  As an adjective, blonde is now the more common spelling and can be applied to both sexes, a use once prevalent in the US although most sources note the modern practice is to refer to women as blonde and men as fair.  Even decades ago, style guides on both sides of the Atlantic maintained, to avoid offence, it was better to avoid using blond(e) as a stand-alone noun-descriptor of women.

Paintings by Titian (left to right), Portrait of a Lady (circa 1511), National Gallery, London, Flora (1515), Uffizi Gallery, Florence, St Margaret and the Dragon (circa 1559) Museo del Prado, Madrid & Portrait of a Lady in White (circa 1561), Gemäldegalerie Alte Meister, Dresden.

Even the understanding of auburn as “reddish brown” or “golden brown” has changed over the years.  The Venetian painter Tiziano Vecellio (circa 1490-1576 and known in English usually as Titian) lent the name “titian auburn” to the tint of reddish-brown hair which appeared so often in his work.  As so often happens in art, his output darkened as he aged so the term “titian auburn” as a literal descriptor of a particular tincture needs to be understood as a spectrum.  While his fondness for redheads seems not to have diminished with age, the vivid hues which characterized the flowing locks he favored in his youth were later sometimes rendered in more subdued tones.

Lindsay Lohan illustrates the shift from the Latin alburnus to the modern English Auburn.

(1) Alburnus as a Roman would have understood the description; now called blond or blonde depending on context.

(2) The classical understanding of “titian auburn”, a light and vivid shade reddish-brown.

(3) A more cooper-tinged hue, representative of what the hair-dye industry would call something like “light auburn”.

(4) This is a dark alburn; any darker and depending on the tint, it would be described either as burgundy or chestnut.

The Auburn Speedster

1935 Auburn 851 SC Speedster.

Under a variety of corporate structures, the Auburn company produced cars in the US between 1900-1937 and is remembered now for the Speedster 851 & 852, one of the most romantic designs of the mid-1930s.  Although Auburn, along with its corporate stablemates Cord and Duesenberg, succumbed to the affects of the Great Depression, the company’s financial problems long-predated the 1929 Wall Street crash, the conglomerate of the three manufacturers assembled in 1925 as a restructuring.  After this, in the growing economy of the 1920s Auburn began again to prosper and it was in 1925 the company introduced the model which would be the basis of the later 851 & 852.  Auburn-Cord-Duesenberg (A-C-D) actually enjoyed a logical structure in that the brand-names existed at different price points but it lacked any presence in the low-cost mass-market, relying instead on lower volume vehicles which relied on their style, engineering and value for money for their appeal.  Had the depression not happened, the strategy might have worked but, given the austerity of the 1930s, what’s remarkable is that A-C-D endured until 1937.             

1932 Auburn 12-160.  The color is said to be a 1932 factory option and is similar to the apple green with which Duesenberg painted their 6.9 litre (420 cubic inch) straight-eights.

Although now celebrated for their stylish lines, A-C-D’s cars were at the time also noted for innovation and the quality of their engineering.  Cord’s front-wheel-drive proved a cul-de-sac to which US manufacturers wouldn’t for decades return but other aspects of their designs were influential although A-C-D’s trademark quixotic offerings sometimes suggested a sense of disconnection from economic reality; in 1932, in the depth of the depression, Auburn announced a model powered by a 391 cubic inch (6.5 litre) V12, a perhaps questionable approach in an environment which had seen demand collapse for the twelve and sixteen cylinder Lincolns, Packard and Cadillacs.  Elegant and powerful, in less troubled times it would likely have succeeded but was wholly unsuited to the world into which it was released despite being priced from an extraordinary US$1,105; while that was 40% more than even the most expensive Ford V8, it was a fraction the cost of the more comparable Packard or Lincoln V12.

1936 Auburn 852 SC Speedster.

The Boattail Speedster was less ambitious but had already carved its niche.  It was designed in 1928 to create the signature product that encapsulated what A-C-D wished the Auburn marque to represent: fast, sleek, stylish and a value for money no other could match; had the company anticipated the slogan “grace, space & pace” it would have been well understood for what is now called a mission statement was exactly what made Jaguar such a success in the post-war years.  Using Lycoming's smooth, powerful and reliable straight-eight cylinder engine, sleek Speedster delivered the performance the lines promised, a genuine 100 mph (160 km/h) roadster which set speed records when taken to Daytona Beach.  The Speedster’s classic iteration was the 851 (the subsequent 852 all but identical), introduced in 1934, the design clearly a homage to the much-admired (if infrequently purchased) Duesenberg Weymann Speedster though where the Duesenberg was long and elegant, the Auburn was squat and sporty and for those who wanted something more charismatic still, the 280 cubic inch (4.6 litre) straight-eight could be ordered with a Schwitzer-Cummins centrifugal supercharger.  The market responded to the speed and the art deco style but the investment had been considerable, something the under-capitalized A-C-D undertook only because the improving economy provided some confidence sales would be sufficient to ensure profitability.  Had the recovery been sustained, A-C-D may have survived, unemployment in 1937 still high but significantly lower in the demographic which was their target market.  As in was, in mid-1937, the US economy suffered a sudden, sharp, recession which would last over a year, the effects lingering until late 1940 when the combined effected of increased armaments production and a presidential election had a simulative effect.  A-C-D, its finances in a perilous state since the Wall Street Crash, couldn’t survive and the companies all entered bankruptcy, Auburn succumbing in 1937.

A-C-D’s fate provides a cautionary tale which for decades was often ignored by those unable to resist the siren call to make beautiful, fast cars bearing their name.  Unless volumes were sufficient (thereby diluting the lure of exclusivity which tended to be much of the attraction) or else subsidized by the profits of some mass-market offering, enduring success was rare and few of those which did initially flourish were capitalized to the extent necessary to survive the inevitable downturns which disproportionally affects those depending on the more self-indulgent sectors sustained by discretionary expenditure.

Scavenge

Scavenge (pronounced skav-inj)

(1) To take or gather (something hopefully usable) from discarded material.

(2) To cleanse of filth, as in cleaning a street (in the UK “scavenger” was once a term for a municipal street sweeper).

(3) In internal combustion engines (1) to expel burnt gases from a cylinder

(4) As “oil scavenger”, a device used to remove excess or unwanted oil from certain areas of various types of engine.

(5) In metallurgy, to purify molten metal by introducing a substance, usually by bubbling a suitable gas through it (the gas may be inert or may react with the impurities).

(6) In democratic politics (in preferential voting systems), to negotiate with other candidates or party machines to obtain preferences (usually on a swap basis).

(7) To act as a scavenger; to search (applied especially to creatures which look for food among the carrion killed by others).

(8) In chemistry, to act as a scavenger (for atoms, molecules, ions, radicals, etc).

(9) In historical UK use, a child employed to pick up loose cotton from the floor in a cotton mill.

1635–45: A back formation from scavenger, from the Middle English scavager, from the Anglo-Norman scawageour (one who had to do with scavage, inspector, tax collector), from the Old Northern French scawage & escauwage (scavenge) and the Old French scavage & escavage, an alteration of escauvinghe (the Medieval Latin forms were scewinga & sceawinga), from the Old Dutch scauwōn (to inspect, to examine, to look at).  The verb scavenge in the 1640s was first a transitive verb in the sense of “cleanse from filth” while the intransitive meaning “search through rubbish for usable food or objects” was in use at least by the 1880s and the idea of “extracting & collecting anything usable from discarded material” dates from 1922.  Scavenge is a verb, scavenged, scavengering & scavenging are verbs & adjectives, scavengeable is an adjective and scavenger & scavengerism are nouns; the noun plural is scavengers.

Lindsay Lohan: Fear of scavengers.

The noun scavenger dates from the 1540s and described originally “a person hired to remove refuse from streets” (a job which would come later to be known as a “street sweeper”, a modification of the late fourteenth century Middle English scavager & scawageour, the title of the employee of London city who originally was charged with collecting tax on goods sold by foreign merchants.  The origin of that title was the Middle English scavage & scauage, from the circa 1400 Anglo-French scawage (toll or duty exacted by a local official on goods offered for sale in one's precinct), from the Old North French escauwage (inspection), from a Germanic source (it was related to the Old High German scouwon and the Old English sceawian (to look at, inspect) and from the same lineage came the modern English “show”.  In the 1590s it came into use in zoology to refer to creatures which look for food among the carrion killed by others.  The game of “scavenger hunt” seems to have gained the name in 1937 and one form of the word which went extinct was scavagery (street-cleaning, removal of filth from streets), noted in 1851.

Oil scavenge systems

In an internal combustion engine, an oil scavenger is a device used to remove excess or unwanted oil from certain areas of the engine, typically from the bottom of the engine's crankcase or oil pan.  The oil scavenger can help to prevent excessive oil pressure or foaming, something to be avoided because in high-performance engines operating under extreme conditions, excessive pressure can collapse pistons, a destructive process.  The core of the system is a scavenge-pump (some even suction mechanisms) which draw the excess oil from the engine and directs it back into the oil pan or an external reservoir.

Internal combustion engine with dry sump and oil scavenging system.

The classic use of oil salvage is in dry sump lubrication systems in which the oil that is supplied by the pressure pump drains off the engine as a frothy, thoroughly-mixed air-oil suspension into a relatively shallow, low-capacity, sump that is often contoured around the rotating crankshaft-assembly.  In this system, there are several scavenge pump stages that pump the aerated oil from the “dry” sump and into the external oil tank that has the dual-assignment of (1) storing the major amount of the engine oil supply and (2) de-aerating the mixture being returned by the scavenge pump(s).  After lubricating the various components, the oil flows into the sump at the bottom of the engine and from here the scavenge stages of the pump retrieves the highly-aerated oil, delivering the mix through a filter and then to a centrifugal and boundary-layer air-oil separation system in the oil tank. The air extracted from the scavenge oil exits the system through the breather and the result is cool, clean oil into the external tank ready for recirculation.

Aircraft turbine engine with oil scavenging system.

Oil salvage systems are especially critical in aviation.  In car engines, used oil is able to drain down into the oil pan, where it can be circulated back through the engine or cooling system but at altitude, gravity or air pressure may not be sufficient for oil to drain on its own and for these reasons aircraft are equipped with scavenge pumps to help pull the used oil out of the engine into a reservoir for cooling, de-aerating, and recirculation.  In hard-to-empty areas that are far from the oil sump (like the rear of the engine) a scavenge pump prevents the pooling of used oil.  The aircraft scavenge pump system does not have its own power source, but operates on a designated line from the main electrical system and on bigger aircraft powered by turbines with large oil capacity, as many as six scavenge pumps may operate in unison.

Cavitation

Cavitation (pronounced kav-i-tey-shuhn)

(1) The formation of pits on a surface.

(2) In fluid dynamics, the rapid formation and collapse of vapor pockets in a flowing liquid in regions of very low pressure (associated especially with devices such as rotating marine propellers or the impellers used in pumps.

(3) Such a pocket formed in a flowing liquid; the formation of cavities in a structure.

(4) In biology, the formation of cavities in an organ (used originally to describe those appearing in lung tissue as a result of consumption (tuberculosis)).

1868: The construct was cavit(y) + -ation.  Cavity was a mid-sixteenth century borrowing from Middle French cavité or the Late Latin cavitās, from the Classical Latin cavus (hollow, excavated, concave), the construct being cav +‎-ity (the nominal suffix).  The suffix -ation was from the Middle English -acioun & -acion, from the Old French acion & -ation, from the Latin -ātiō, an alternative form of -tiō (thus the eventual English form -tion).  It was appended to words to indicate (1) an action or process, (2) the result of an action or process or (3) a state or quality.  Cavitation is a noun, cavitate, cavitated & cavitating are verbs and cavitatory & cavitatory are adjectives; the noun plural is cavitations.

The original use of cavitation dates from 1868 and appeared in the literature of human pathology, describing “the formation of cavities in the body”, especially those appearing in lung tissue as a result of consumption (tuberculosis).  The use in fluid dynamics (particularly pumps and marine engineering) emerged in circa 1895 although oral use may have predated this: the verb cavitate (to form cavities or bubbles (in a fluid)) documented since 1892 so it was either a back-formation from cavitation or the construct was cavit(y) + -ate.  The related verbs were cavitated & cavitating.  The suffix -ate was a word-forming element used in forming nouns from Latin words ending in -ātus, -āta, & -ātum (such as estate, primate & senate).  Those that came to English via French often began with -at, but an -e was added in the fifteenth century or later to indicate the long vowel.  It can also mark adjectives formed from Latin perfect passive participle suffixes of first conjugation verbs -ātus, -āta, & -ātum (such as desolate, moderate & separate).  Again, often they were adopted in Middle English with an –at suffix, the -e appended after circa 1400; a doublet of –ee.  The noun supercavitation was a creation of plasma physics and described an extreme form of cavitation in which a single bubble of gas forms around an object moving through a liquid, significantly reducing drag.  As observational technology & techniques improved, the form ultracavitation also appeared to describe instances where instances of the phenomenon meant drag tended as close to zero as was possible.

Cavitation is an interesting aspect of fluid dynamics but it’s studied because it’s something which can cause component failure in devices like the pumps used for liquid, fluid & gas which can have catastrophic consequences for both connected equipment and people in the vicinity and beyond.  Such components typically feature robust construction but cavitation is a function of sustained operation (often 24/7) at high speeds and some vulnerable parts may be heavy and the fragmentation at high velocity of a heavy, reciprocating mass is obviously a serious problem.  Technically, it’s the formation of vapour- or gas-filled cavities in a flowing liquid when tensile stress is superimposed on the ambient pressure and one novelty in the science of cavitation was in 2021 noted by researchers in an oncology laboratory.  Using a gassy, explosive bacteria to destroy cancer cells by bombardment, the strikes were observed to produce a brief sonoluminescence (in physics, the emission of short bursts of light from imploding bubbles in a liquid when excited by sound), the cavitation bubbles producing a brief flash of light as they collapsed.

In the specific case of “pump cavitation”, the problem typically occurs when a hydraulic pumps which pumps liquids suffers a partial pressure drop.  What the change in pressure can induce is the formation of air bubbles, leading to cavity creation.  Inside the pump, the pressure shift transforms the liquid into a vapor which is then converted back to liquid by the spinning impellers.  The air bubbles thus are constantly moving inside the housing and as they implode during pressure changes, the surfaces of the impeller are eroded and it’s the creation of these tiny cavities which can accumulate sufficiently to weaken the structure to the point of failure.  The issue particularly affects centrifugal pumps but can occur in submersible devices.

Lindsay Lohan enjoying the effects of fluid dynamics.

Although something identified by engineers in the nineteenth century, the exact nature of cavitation wasn’t fully understood until the application in the 1950s of high-speed photography and the mathematical models developed then were later confirmed as close to exactly correct by computer simulations later in the century.  What was found was two causes of cavitation : (1) Inertial Cavitation in which a shock wave is produced by the collapse of bubble or void present in a liquid and (2) Non-inertial Cavitation which is initiated when a bubble in a fluid undergoes shape alterations due to an acoustic field or some other form of energy input.  Also observed were two behaviors of cavitation: (1) Suction Cavitation induced by high vacuum or low-pressure conditions which reduce the flow of fluid, bubbles forming near the eye of an impeller eye; as these bubbles move towards the pump’s discharge end, they are compressed into liquid, and they will implode against the impeller’s edge and (2) Discharge Cavitation which occurs when the pump’s discharge pressure becomes abnormally high, altering the flow of fluid, leading to internal recirculation, the liquid becoming “stuck” in a pattern between the housing (and the impeller) thereby creating a vacuum which in turn creates the air bubbles which will collapse and cavitate the impeller.

Representation of fluid dynamics under specific resonant conditions.

In fluid dynamics, a flow becoming “stuck” is often something to avoid but an aspect of the behavior can be exploited and it was a specific instance of certain “resonant conditions” Chrysler’s engineers exploited in 1959 when designing their Sonoramic induction system.  The idea wasn’t new, the math explained as early as 1863 and in racing cars it had been used for years but what Chrysler did was make it a focal point.  Sonoramic was an implementation of Sir Isaac Newton's (1642–1727) first law of motion, more commonly known as the law of inertia: “An object at rest tends to stay at rest and an object in motion tends to stay in motion” and it’s the second part which was exploited.  During the intake cycle of an engine, the fuel-air mix flows through the intake manifold, past the intake valve, and into the cylinder, then the intake valve shuts.  At that point, the law of inertia comes into play: Because the air was in motion, it wants to stay in motion but can’t because the valve is shut so it piles up against the valve with something of a concertina effect.  With one piece of air piling up on the next, the air becomes compressed and this compressed air has to go somewhere so it turns around and flows back through the intake manifold in the form of a pressure wave.  This pressure wave bounces back and forth in the runner and if it arrives back at the intake valve when the valve opens, it’s drawn into the engine.  This bouncing pressure wave of air and the proper arrival time at the intake valve creates a low-pressure form of supercharging but for this to be achieved all variables have to be aligned so the pressure wave arrives at the intake valve at the right time.  This combination of synchronized events is known as the “resonant conditions”.

Representation of cavitation in mechanical gears.

The behavior in pumps is now well understood and both design parameters and maintenance schedules are usually cognizant of cavitation and its potential consequences.  However, instances remain not infrequent, especially when pumps are fitted into systems by non-specialists, the most common causes being (1) low fluid pressure, (2) insufficient internal diameter of suction pipes, (3) excessive distances between a fluid source and a pump’s impeller(s), (4) pumps being run at too high a speed (which may be within a manufacturer’s recommendations but inappropriate for the system in which it’s installed), (5) too many fittings added to a suction pipe and (6) debris intrusion (often a consequence of inadequate filter cleaning & maintenance).  Cavitation is a function of speed and in devices such as slow-speed propellers (such as those in many marine applications), cavitation is not an issue, thus the frequent use of light, efficient, thin blades.