Heat gun

A heat gun is a device used to emit a stream of hot air, usually at temperatures between 100 °C and 550 °C (200-1000 °F), with some hotter models running around 760 °C (1400 °F), which can be held by hand. Heat guns usually have the form of an elongated body pointing at what is to be heated, with a handle fixed to it at right angles and a trigger, in the same general layout as a handgun, hence the name.

Construction

A heat gun comprises a source of heat, usually an electrically heated element, but sometimes a gas flame; a mechanism to move the hot air such as an electric fan, unless gas pressure is sufficient; a nozzle to direct the air, which may be a simple tube pointing in one direction, or specially shaped for purposes such as concentrating the heat on a small area or thawing a pipe but not the wall behind; a housing to contain the components and keep the operator safe; a mechanism to switch it on and off such as a trigger; a handle; and a built-in or external stand if the gun is to be used hands-free. Although not called such, a hair dryer is a form of low-temperature heat gun. Gas-powered soldering irons sometimes have interchangeable hot air blower tips to produce a very narrow stream of hot air suitable for working with surface-mount devices and shrinking heat shrink tubing.

Heat

In physics, heat is energy as it spontaneously passes between a system and its surroundings, other than as work or with the transfer of matter. In thermodynamics, finer detail of the process of transfer is in principle unspecified. When there is a suitable physical pathway, heat transfer occurs from a hotter to a colder body. The transfer can be direct, by contact, from the source to the destination body, as in conduction combined with radiation, or remote, as in radiation without conduction; or indirect, by conduction and radiation through a thick solid wall, or by way of an intermediate fluid body, as in convective circulation.

Originally, quantity of heat transferred was measured by how much it changed the states of participating bodies, for example, as amount of ice melted, or change in temperature, without work or matter transfer. Such measurement is possible because many bodies, over most temperature ranges, expand reversibly on being heated. This is called thermal expansion.

Gun

A gun is a normally tubular weapon or other device designed to discharge projectiles or other material. The projectile may be solid, liquid, gas or energy and may be free, as with bullets and artillery shells, or captive as with Taser probes and whaling harpoons. The means of projection varies according to design but is usually effected by the action of gas pressure, either produced through the rapid combustion of a propellant or compressed and stored by mechanical means, operating on the projectile inside an open-ended tube in the fashion of a piston. The confined gas accelerates the movable projectile down the length of the tube, imparting sufficient velocity to sustain the projectile's travel once the action of the gas ceases at the end of the tube or muzzle. Alternatively, acceleration via electromagnetic field generation may be employed in which case the tube may be dispensed with and a guide rail substituted.

The first devices identified as guns appeared in China around CE 1000. By the 12th century the technology was spreading through the rest of Asia, and into Europe by the 13th century.