Various devices are known for heating a gas, such as air, and gas heating devices have been employed for numerous industrial and domestic applications, such as cooking and room heating, and in many appliances such as hair dryers and clothes dryers. In an electrical gas heater, an electric heating element is energized and gas is caused to flow past the element. The air may flow past the element either naturally or by being forced by a blower or fan.
The most common electric heating element used today is a resistance heating wire, such as a nickel chromium wire, that is wound into a heating coil. These wire-type heating elements are effective at generating heat, but frequently need to operate at very high temperatures in order to provide sufficient heat to the surrounding gas. The flux of radiant heat of the heating element is proportional to the fourth power of its temperature, thus when the heating element is operated at high temperatures (e.g., when it becomes red hot), the element transfers heat predominantly by radiation. Gasses do not absorb radiative heat well, so much of this radiant energy does not heat the gas flowing past the element, but instead radiates to and heats up the surrounding structures. The conventional wire-based electric heating elements are therefore not very efficient in heating gas, due to this radiant heat loss. Furthermore, the intense radiant heat generated by the wire heating element can heat up surrounding structures to dangerous temperatures, which can pose a safety risk. For example, in the case of a clothes dryer, the radiant heat from the heating element can heat components of the dryer that are accessible to users, which can result in burns.
USPTO Backgrounds
USPTO Backgrounds