Direkteoppvarming

Direkteoppvarming, also known as direct heating or direct resistance heating, is a method of heating where electrical energy is converted directly into thermal energy within the material being heated. This is typically achieved by passing an electric current through a conductive material. The resistance of the material causes it to heat up according to Joule's law, which states that the heat produced is proportional to the square of the current, the resistance, and the time for which the current flows.

In industrial applications, direct heating is often used for processes like forging, smelting, and welding. For instance, in resistance welding, the parts to be joined are heated by the current passing through them until they reach their melting point and fuse together. Direct resistance heating is also employed in furnaces where electrodes are immersed directly into the material to be melted or heated, such as in glass or metal production.

A common example of direct heating in everyday life is an electric toaster. The heating elements within the toaster are resistive wires that glow red hot when electricity passes through them, directly heating the bread placed above. Similarly, some electric stoves use direct heating elements. The efficiency of direct heating is generally high because the electrical energy is converted into heat precisely where it is needed, minimizing heat losses to the surroundings. However, it requires the material being heated to be electrically conductive.