This article is about the HVAC feature. For bell-mouth spillways, see spillway.
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Inlet bellmouths (right) on the two turboshaft engines of a heavy-lift helicopter
In building services engineering and HVAC, a bell mouth is a tapered expanding or reducing opening in the end of a ventilation duct, so named because the taper can resemble that of a bell shape. They are primarily designed and used for return air or extract air purposes within building ventilation systems, more commonly located within ceiling voids or other similar plenum. The bellmouth cross-sectional area is normally double that of the duct area so that the air velocity entering the bellmouth is low (to reduce noise, turbulence and pressure drop), and gradually increases to the normal design velocity of the ductwork. The angle of the bellmouth is normally tapered at about 45° as a balance between keeping the bellmouth short without causing too much turbulence or excessive pressure drop. Bellmouths can be manufactured to suit either circular or rectangular ductwork sections.
The bell-mouth shape allows the maximum amount of air to be drawn into the duct with minimum loss.
Cosworth Formula One engine, with bell-mouthed inlet trumpets for each cylinder, known as a velocity stack
A bell-mouth inlet duct is a form of convergent inlet air duct used to direct air into the inlet of a gas turbine engine. The area of a convergent duct gets smaller as the air flows into the engine. A bell-mouth inlet duct is extremely efficient and is used where there is little ram pressure available to force the air into the engine. Bell-mouth ducts are used in engine test cells and on engines installed in helicopters.
Examples of the effects of different shape (bellmouth)inlets are shown in the referenced "Good Fabs" article[1]
^"How to optimise the inlet bell mouth". March 2017.
a bellmouth is a tapered expanding or reducing opening in the end of a ventilation duct, so named because the taper can resemble that of a bell shape...
gate. The bell-mouth spillway in Covão dos Conchos reservoir in Portugal is constructed to look like a natural formation. The largest bell-mouth spillway...
Ass to mouth (abbreviated as ATM or A2M in pornography) is a slang term associated with the porn industry describing anal sex immediately followed by...
October 13, 2021. Média, Bell. "Zach Goode Named New Smash Mouth Singer". www.iheartradio.ca. Retrieved June 10, 2022. "Smash Mouth". Childers, Chad (March...
tower bell such that it swings in a complete circle from mouth upwards to mouth upwards and then back again repetitively. Full-circle tower bell ringing...
are meant to be shut down temporarily. Some commonly used strainers are bellmouth strainers, foot valve strainers, basket strainers. Most processing industries...
is sometimes called an inverted bell curve. A bell Standing bell (rin) Bell-mouth spillway at Llyn Celyn Inverted-bell beaker from Atting during the Beaker...
and can withhold 52,000,000 m3 (42,157 acre⋅ft) of water. The dam has a bell-mouth spillway with a maximum discharge of 81 m3/s (2,860 cu ft/s). Watersport...
2011 film Submarine was filmed on the reservoir walkway. The Reservoir's bell-mouth spillway (also known as plug hole) featured prominently in the opening...
speed of oscillation when the bell is mouth upwards at the balance-point when little effort is required. Swinging bells are sounded by an internal clapper...
discharge of 2,440 cubic metres (86,000 cu ft) per second, and an emergency bellmouth spillway with a capacity of 1,860 cubic metres (66,000 cu ft) per second...
recovery, Bell required more than 70 facial stitches, had to have his jaw wired shut for two months, and underwent surgery on his chin and mouth. In July...
Alexander Graham Bell (/ˈɡreɪ.əm/, born Alexander Bell; March 3, 1847 – August 2, 1922) was a Scottish-born Canadian-American inventor, scientist and...
then exhaust into the fourth stage, the classic chimney (U.S.: stack) bell-mouth. It was Chapelon's theory that such a multi-stage mixing and suction arrangement...
20 August 2022. Phares, Heather. "Mouth by Mouth – His Name Is Alive". AllMusic. Retrieved 28 September 2016. Bell, Mike (6 June 1993). "Recent Releases"...
Mary Flora Bell (born 26 May 1957) is an English woman who, as a juvenile, killed two preschool-age boys in Scotswood, an inner suburb of Newcastle upon...
but discharges into a tunnel under the side of the valley, via a large bell-mouth drop-shaft overflow in one corner, a feature not normally seen on Pennine...
credits include Busy Tonight, The Amber Ruffin Show, Saved by the Bell, and Big Mouth. Jackson was raised in Florida. She received her bachelor's degree...
co-creator Kristen Bell". Entertainment Weekly. Retrieved 2024-04-18. "'Big Mouth,' 'Central Park' will recast Jenny Slate's and Kristen Bell's biracial characters"...
used with a hydro turbine. It has a bell-mouth shape and its salient feature is a flat plate deflector near the mouth. The term hydraucone was introduced...
(rather than circular) section, the bellmouth has a distinctive "cutaway" profile, and the outer surfaces of the large bells feature 36 studs or bosses, symmetrically...
of metal sliding on metal. This reduces friction, uneven wear and "bell-mouthing" of the valve guide. Roller rockers can also be used in overhead cam...
shoreline. Near the dam on the southeast side of the reservoir is an open bell-mouth spillway, 72 feet (22 m) in diameter, which is known as the Glory Hole...
rung full circle (mouth uppermost to mouth uppermost), being held up by a rope and wheel until a note is required. Bolognese bell ringing is a tradition...
catchment area is 149 square kilometres (58 sq mi). The uncontrolled bell-mouth spillway has a diameter of 32 metres (105 ft) and is capable of discharging...
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