||This article relies largely or entirely upon a single source. (October 2010)|
A heat shield is designed to shield a substance from absorbing excessive heat from an outside source by either dissipating, reflecting or simply absorbing the heat. It is often used as a form of Exhaust Heat Management.
Due to the large amounts of heat given off by internal combustion engines, heat shields are used on most engines to protect components and bodywork from heat damage. As well as protection, effective heat shields can give a performance benefit by reducing the underbonnet temperatures, therefore reducing the intake temperature. Heat shields vary widely in price, but most are easy to fit, usually by stainless steel clips or high temperature tape. There are two main types of automotive heat shield:
- The Rigid heat shield has, until recently, been made from solid steel, but is now often made from aluminium. Some high-end rigid heat shields are made out of aluminium sheet or other composites, with a ceramic thermal barrier coating to improve the heat insulation.
- The Flexible heat shield is normally made from thin aluminium sheeting, sold either flat or in a roll, and is bent by hand, by the fitter. High performance flexible heat shields sometimes include extras, such as ceramic insulation applied via plasma spraying. These latest products are commonplace in top-end motorsports such as Formula 1.
As a result, a heat shield is often fitted by both amateur and professional personnel during a phase of engine tuning.
Spacecraft which land on a body with an atmosphere, such as Earth, Mars and Venus, currently do so by entering at high speeds, depending on friction rather than rocket power to slow the craft. A side effect of this is aerodynamic heating, which in the case of an Earth (or Venus) reentry can be destructive. An aerodynamic heat shield consists of a protective layer of special materials to dissipate the heat. Two basic types of aerodynamic heat shield have been used:
- An ablative heat shield consists of a layer of plastic resin, the outer surface of which is heated to a gas which carries the heat away by convection. Such shields were used on the Mercury, Gemini and Apollo spacecraft.
- A thermal soak heat shield uses an insulating material to absorb and radiate the heat away from the spacecraft structure. This type was used on the Space Shuttle, consisting of ceramic or composite tiles over most of the vehicle surface, with reinforced carbon-carbon material on the highest heat load points, the nose and wing leading edges. Damage to this material on a wing caused the 2003 Space Shuttle Columbia disaster.
Some spacecraft also use a heat shield (in the conventional automotive sense) to protect fuel tanks and equipment from heat produced by a large rocket engine. Such shields were used on the Apollo Service Module and Lunar Module descent stage.
Heat shields are often used to protect heat-sensitive components used in various industrial processes.