Page 186 - Intro Predictive Maintenance

Thermography 177

RADIO

INFRARED
VISIBLE
ULTRA-
VIOLET
X-RAYS
GAMMA RAY

Figure 8–5 Wavelengths.

become shorter crest to crest and the energy being emitted has increased, entering the
visible band on the spectrum. By contrast, (infrared energy) when the coil comes off
of the coilers it has been cooled. Energy is lost. The wavelength have increased crest
to crest and decreased in frequency.

8.4.2 Heat Transfer Concepts
Heat is a form of thermal energy. The first law of thermodynamics is that heat given
up by one object must equal that taken up by another. The second law is that the trans-
fer of heat takes place from the hotter system to the colder system. If the object is
cold, it absorbs rather than emits energy. All objects emit thermal energy or infrared
energy through three different types or modes: conduction, convection, and radiation.
It is important to understand the differences among these three forms.

Conduction
Conduction is the transfer of energy through or between solid objects. A metal bar
heated at one end will, in time, become hot at the other end. When a motor bearing
is defective, the heat generated by the bearing is transferred to the motor casing. This
is a form of conduction.

Convection
Convection is the transfer of energy through or between fluids or gases. If you took
the same motor mentioned previously and placed a fan blowing directly on the hot
bearing, the surface temperature would be different. This is convection cooling. It
occurs on the surface of an object. An operator must be careful to identify the true
cause and effect. In this case, the difference between good and bad source heating and
the surface cooling is caused by convection.