Heat transfer
Heat transfer It is possible with three basic physical modes. Conduction or conduction is the transfer of heat so that a part of the body is heated by direct contact with the heat source, and the adjacent parts are subsequently further heated. For example, if one end of a metal rod is placed in a furnace, heat is spread along the rod by conduction.
The rate of heat transfer, the greater the greater the temperature difference, and depends on the substance itself. Since good conductors of electrical charges (metals) are also good conductors of heat, thermal conductivity is primarily attributed to the motion of free electrons. Bodies that conduct heat well are called thermal conductors and those that conduct heat poorly are thermal insulators. Semiconductors of heat are bodies (such as quartz, marble, graphite, and some ores) that heat the water less than metal, but better than real insulators. Of technical metals, the best heat conductor is silver, copper, followed by aluminum, brass, and iron. Bad heat conductors are air, followed by hollow substances such as cork, asbestos, sawdust, rock wool, polystyrene and more. Hollow substances are poor conductors of heat because they contain many cavities, filled with air, which is a thermal insulator. Fluids are also poor conductors of heat. That water is a poor conductor of heat is shown by an experiment when ice is attached to a tube full of water at the bottom (attached so that it does not float), the water may already boil up and the ice will not melt.
Flow or convection is the transfer of heat into substances that can flow, that is, into liquids and gases (fluids). The flow is due to a change in density by heating. For example, if the water is heated from below, the lower layers of water are warmed up, spread out and their density reduced, and the heated water rises above the cold. Similarly, winds in the atmosphere are generated.
Thermal radiation or thermal radiation is the transfer of heat so that the heated body transmits electromagnetic radiation and the cooler body is heated by absorbing (absorbing) the radiation energy. Thus the Earth receives heat from the sun passing through the airspace. Heat rays propagate at the same speed of light as light rays. From the hot body, heat is spread on all sides by invisible heat rays. Different bodies rule differently according to heat rays. Glass that is translucent absorbs heat rays for light, while opaque ebony transmits heat rays. Water and ice are impermeable to heat rays, that is, they absorb them and therefore heat up.