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| == '''[[Choked flow]]''' ==
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| The '''choked flow''' (often referred to as '''critical flow''') of a flowing [[gas]] is a limiting point which occurs under specific conditions when a gas at a certain [[pressure]] and [[temperature]] flows through a restriction<ref>A [[valve]], a [[convergent-divergent nozzle]] such as a [[de Laval nozzle]], an [[orifice plate]] hole, a leak in a gas pipeline or other gas container, a [[rocket engine]] exhaust nozzle, etc.</ref> into a lower pressure environment.
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| As the gas flows through the smaller cross-sectional area of the restriction, its linear [[velocity]] must increase. The limiting point is reached when the linear gas velocity increases to the [[speed of sound]] ([[sonic velocity]]) in the gas. At that point, the [[mass]] flow rate (mass per unit of time) of the gas becomes independent of the downstream pressure, meaning that the mass flow rate can not be increased any further by further lowering of the downstream pressure. The physical point at which the choking occurs (i.e., the cross-sectional area of the restriction) is sometimes called the ''choke plane''. It is important to note that although the gas velocity becomes choked, the mass flow rate of the gas can still be increased by increasing the upstream pressure or by decreasing the upstream temperature.
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| The choked flow of gases is useful in many engineering applications because, under choked conditions, valves and calibrated orifice plates can be used to produce a particular mass flow rate. Choked flow in a [[de Laval nozzle]] as used in a [[rocket engine]] can be accelerated to [[supersonic]] linear velocities.
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| In the case of liquids, a different type of limiting condition (also known as choked flow) occurs when the [[Venturi effect]] acting on the liquid flow through the restriction decreases the liquid pressure to below that of the liquid [[vapor pressure]] at the prevailing liquid temperature. At that point, the liquid will partially "flash" into bubbles of vapor and the subsequent collapse of the bubbles causes [[cavitation]]. Cavitation is quite noisy and can be sufficiently violent to physically damage valves, pipes and associated equipment. In effect, the vapor bubble formation in the restriction limits the flow from increasing any further.<ref>[http://www.fisherregulators.com/technical/sizingcalculations/ Scroll to discussion of liquid flashing and cavitation]</ref><ref>[http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf Search document for "Choked"]</ref>
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| ===Conditions under which gas flow becomes choked===
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| All gases flow from upstream higher pressure sources to downstream lower pressure environments. Choked flow occurs when the ratio of the absolute upstream pressure to the absolute downstream pressure is equal to or greater than:
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| :<math>(1)</math> <font style="vertical-align:+15%;"><math>\big[(k+1)/2 \big]^{\,k/(k-1)}</math></font>
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| where <math>k</math> is the [[specific heat ratio]] of the discharged gas (sometimes called the [[isentropic expansion factor]] and sometimes denoted as <math>\gamma</math> ).
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| For many gases, <math>k</math> ranges from about 1.09 to about 1.41, and therefore the expression in '''(1)''' ranges from 1.7 to about 1.9, which means that choked velocity usually occurs when the absolute upstream vessel pressure is at least 1.7 to 1.9 times as high as the absolute downstream pressure.
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| ''[[Choked flow|.... (read more)]]''
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| {| class="wikitable collapsible collapsed" style="width: 90%; float: center; margin: 0.5em 1em 0.8em 0px;"
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| ! style="text-align: center;" | [[Choked flow#References|notes]]
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| {{reflist|2}} | | {{reflist|2}} |
| |}
| | </small> |
Latest revision as of 10:19, 11 September 2020
The Irvin pin. The eyes have always been red, but there are
urban legends about the meanings of other colors.
A pin from another company, possibly Switlik or Standard Parachute. This style is common in catalogs and auctions of military memorabilia.
The Caterpillar Club is an informal association of people who have successfully used a parachute to bail out of a disabled aircraft. After authentication by the parachute maker, applicants receive a membership certificate and a distinctive lapel pin.
History
Before April 28, 1919 there was no way for a pilot to jump out of a plane and then to deploy a parachute. Parachutes were stored in a canister attached to the aircraft, and if the plane was spinning, the parachute could not deploy. Film industry stuntman Leslie Irvin developed a parachute that the pilot could deploy at will from a back pack using a ripcord. He joined the Army Air Corps parachute research team, and in April 1919 he successfully tested his design, though he broke his ankle during the test. Irvin was the first person to make a premeditated free fall jump from an airplane. He went on to form the Irving Airchute Company, which became a large supplier of parachutes. (A clerical error resulted in the addition of the "g" to Irvin and this was left in place until 1970, when the company was unified under the title Irvin Industries Incorporated.) The Irvin brand is now a part of Airborne Systems, a company with operations in Canada, the U.S. and the U.K.[1].
An early brochure [2] of the Irvin Parachute Company credits William O'Connor 24 August 1920 at McCook Field near Dayton, Ohio as the first person to be saved by an Irvin parachute, but this feat was unrecognised. On 20 October 1922 Lieutenant Harold R. Harris, chief of the McCook Field Flying Station, jumped from a disabled Loening W-2A monoplane fighter. Shortly after, two reporters from the Dayton Herald, realising that there would be more jumps in future, suggested that a club should be formed. 'Caterpillar Club' was suggested because the parachute canopy was made of silk, and because caterpillars have to climb out of their cocoons and fly away. Harris became the first member, and from that time forward any person who jumped from a disabled aircraft with a parachute became a member of the Caterpillar Club. Other famous members include General James Doolittle, Charles Lindbergh and (retired) astronaut John Glenn.
In 1922 Leslie Irvin agreed to give a gold pin to every person whose life was saved by one of his parachutes. By 1945 the number of members with the Irvin pins had grown to over 34,000. In addition to the Irvin Air Chute Company and its successors, other parachute manufacturers have also issued caterpillar pins for successful jumps. Irvin/Irving's successor, Airborne Systems Canada, still provides pins to people who made their jump long ago and are just now applying for membership. Another of these is Switlik Parachute Company, which though it no longer makes parachutes, still issues pins.
