Funnel

A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, spillage would occur.

Funnels are usually made of stainless steel, aluminium, glass, or plastic. The material used in its construction should be sturdy enough to withstand the weight of the substance being transferred, and it should not react with the substance. For this reason, stainless steel or glass are useful in transferring diesel, while plastic funnels are useful in the kitchen. Sometimes disposable paper funnels are used in cases where it would be difficult to adequately clean the funnel afterward (for example, in adding motor oil to a car). Dropper funnels, also called dropping funnels or tap funnels, have a tap to allow the controlled release of a liquid.

The term funnel is sometimes used to refer to the chimney or smokestack on a steam locomotive and usually used in referring to the same on a ship. The term funnel is also applied to other seemingly strange objects like a smoking pipe or a kitchen bin.

Funnel (concurrent computing)

In Computer Science, a funnel is a synchronization primitive used in kernel development to protect system resources. First used on Digital UNIX as a way to "funnel" device driver execution onto a single processor, funnels are now used in the Mac OS X kernel to serialize access to the BSD portion of xnu.

A funnel is a mutual exclusion (mutex) mechanism that prevents more than one thread from accessing certain kernel resources at the same time. Each thread acquires a funnel when it enters a synchronized portion of the kernel, and releases it when it leaves. If a thread blocks (sleeps) while holding a funnel, the kernel forces the thread to automatically drop the funnel, thereby allowing other threads to enter the synchronized portion of the kernel.

Because a funnel is automatically dropped when a thread blocks, care must be taken to ensure that synchronized resources are acquired again after any blocking operation. Specifically, acquiring a funnel can be a blocking operation, so if multiple funnels are needed, they must be acquired at once. This limits the utility of funnels because it increases the granularity of locking when multiple funnels need to be held at once.

Funnel (ship)

A funnel is the smokestack or chimney on a ship used to expel boiler steam and smoke or engine exhaust. They are also commonly referred to as stacks.

Purpose

The primary purpose of a ship's funnel(s) is to lift the exhaust gases clear of the deck, in order not to foul the ship's structure or decks, and to avoid impairing the ability of the crew to carry out their duties.

In steam ships the funnels also served to help induce a convection draught through the boilers.

Design

Since the introduction of steam-power to ships in the 19th century, the funnel has been a distinctive feature of the silhouette of a vessel, and used for recognition purposes.

Funnel area

The required funnel cross-sectional area is determined by the volume of exhaust gases produced by the propulsion plant. Often this area is too great for a single funnel. Early steam vessels needed multiple funnels (SS Great Eastern had 5 when launched), but as efficiency increased new machinery needed fewer funnels.

Merchant ships