6 TRG-TRC003-EN
notes
period one
Heat and Refrigeration
The third principle is that heat is transferred from one substance to another by
one of three basic processes: conduction, convection, and radiation. The device
shown is a baseboard convector that is commonly used for heating a space. It
can be used to demonstrate all three processes of transferring heat.
Hot water flows through a tube inside the convector, warming the inside
surface of the tube. Heat is transferred, by conduction, through the tube wall to
the slightly cooler fins that are attached to outside surface of the tube.
Conduction is the process of transferring heat through a solid.
The heat is then transferred to the cool air that comes into contact with the fins.
As the air is warmed and becomes less dense, it rises, carrying the heat away
from the fins and out of the convector. This air movement is known as a
convection current. Convection is the process of transferring heat as the result
of the movement of a fluid. Convection often occurs as the result of the natural
movement of air caused by temperature (density) differences.
Additionally, heat is radiated from the warm cabinet of the convector and
contacts cooler objects within the space. Radiation is the process of
transferring heat by means of electromagnetic waves, emitted due to the
temperature difference between two objects. An interesting thing about
radiated heat is that it does not heat the air between the source and the object it
contacts; it only heats the object itself.
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Figure 11
