How Heat Energy Travels
Heat can only be transferred between objects—or areas within an object—with different temperatures. This transfer happens spontaneously only in the direction of the colder body. Energy transfer by heat can occur between objects by convection, conduction and radiation:
This is the transfer of heat generally using heated air as the transfer medium between the heat source and the object to be heated. This is the way most homes are heated with hot water heating the surrounding air through radiators. Hot air systems are most suitable where the object to be heated has a large mass in relation to its surface area.
This form of heating occurs via physical contact between a heat source and the object to be heated. Conduction is particularly effective where the heat source can be enclosed and be in indirect contact with the substance to be heated. Immersion heaters are a good example of this and used extensively for heating water, bitumen and oil
When heat is transferred as invisible electromagnetic waves of energy from a heat source to the object to be heated, we refer to it as “radiative heating“.
Along with ultraviolet, microwave, radio frequency, and induction transfers, infrared radiation is one means to pass heat. Vibration and rotation of molecules in a source (quartz tube or ceramic element), heat energy, travels as infrared light waves. The resulting energy is controlled and directed specifically to and on people and objects.
This energy is not absorbed by air and does not create heat until it is absorbed by an opaque object. The sun is a source of infrared energy travelling at the speed of light and converting to heat upon contact with the ground, people, buildings floors and any other opaque objects. There is however no ultraviolet component (for example, sun-tanning rays) in electric infrared.
Electric infrared energy travels in straight lines from the heat source and difuses as a function of the square of the distance. Intensity would therefore decrease in a proportional manner.
In the electromagnetic spectrum infrared radiation occupies a wave region of considerable width and therefore has been further split into three sub regions as follows:
|Near infrared region—short wave||0.75 to 1.5 micrometres|
|Intermediate infrared region—medium wave||.5 to 4 micrometres|
|Far infrared region—long wave||4 to 10 micrometres|
It has been shown that for a given temperature there is a definite wavelength at which the radiated power is maximum. Furthermore the wavelength of the maximum is found to vary in direct proportion to the absolute temperature. Therefore we can give approximate temperature ranges tothe above wave length split as follows:
|Near infrared region—short wave||740 to (3,000-5,200)°K|
|Intermediate infrared region—medium wave||(92.5-140) to 740°K|
|Far infrared region—long wave||(10.6-18.5) to (92.5-140)°K|
Infra red emitters are therefore manufacture to fit into these categories as follows:
|Short Wave Emitters||Generally consisting of a high temperature resistance winding enclosed in a sealed quartz tube containing a small amount of halogen gas. Short wave emitters are characterized by the presence of a bright white light.|
|Medium Wave Emitters||Generally consist of a resistance winding enclosed in an un-evacuated quartz tube. Medium wave is generally characterized by the presence of orange or red light.|
|Long Wave Emitters||Generally consist of a resistance wire embedded in magnesium insulation in a steel tube or cast into ceramic and are generally characterized by the lack of any visible light.|
Each of these wave lengths and elements have their own particular advantages and disadvantages when solving a particular heating application.