Heat shield

In engineering, a heat shield is a component designed to protect an object or a human operator from being burnt or overheated by dissipating, reflecting, and/or absorbing heat. The term is most often used in reference to exhaust heat management and to systems for dissipating frictional heat. Heat shields are used most commonly in automotive and aerospace. Heat shields protect structures from extreme temperatures and thermal gradients by two primary mechanisms. Thermal insulation and radiative cooling, respectively isolate the underlying structure from high external surface temperatures, while emitting heat outwards through thermal radiation. To achieve good functionality the three attributes required of a heat shield are low thermal conductivity (high thermal resistance), high emissivity, and good thermal stability (refractoriness). Porous ceramics with high emissivity coatings (HECs) are often employed to address these three characteristics, owing to the good thermal stability of ceramics, the thermal insulation of porous materials and the good radiative cooling effects offered by HECs. 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 under-bonnet 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 aluminum. Some high-end rigid heat shields are made out of aluminum sheet or other composites, with a ceramic thermal barrier coating to improve the heat insulation. The flexible heat shield is normally made from thin aluminum sheeting, sold either flat or in a roll, and is bent by hand, by the fitter.