To be a good thermal insulator, a material must be resistant to the conduction, convection and radiation of heat. A good insulator is made from an opaque, nonmetallic material without a crystalline structure, and its insulating properties may be enhanced by creating small air pockets inside its structure.Know More
The reason metals conduct heat so well is that metallic atoms have a poor hold on their outermost electrons. This allows the electrons to flow from one atom to another easily, and they carry energy as they move. When one end of a metallic object is heated, this increase in temperature excites the electrons and causes them to flow, carrying the heat along the object and heating it evenly. Insulating materials such as plastics resist the flow of electrons, reducing heat flow through the material.
Air pockets are another way to increase insulation. Under normal circumstances, air can transmit heat through convection, flows of air created by differences in temperature and pressure. If the air pockets inside a material are separated from one another, however, these flows cannot happen. The heat also cannot conduct through the trapped air, reducing its ability to flow through the material. Winter coats and other insulated clothing often utilize this technique, as do the insulating materials inside the walls and attics of residential homes.Learn more about Thermodynamics
Heat flows from one object to another by conduction, convection or radiation, depending on the physical state of the medium through which it must flow. Heat always flows from a region of high temperature to a region of lower temperature. Without a temperature difference, there can be no heat flow.Full Answer >
Heat transfer works by transferring energy from one substance to another via convection, conduction or radiation. Particles in a substance are able to store energy and transfer it to other particles, often in the form of heat.Full Answer >
The Nusselt number is the ratio of the amount of heat transferred across a surface in a fluid via convection to the amount of heat transferred via conduction. Both the convective and conductive heat flows are measured perpendicular to the surface.Full Answer >
According to HowStuffWorks, aluminum foil is a good insulator because it prevents the radiation of heat by reflecting it back at the source. Since aluminum foil reflects the emission of heat, it tends to be a better insulator than other materials that just slow down the flow of heat from one area to another.Full Answer >