Methods
of Heat Transfer and Material Properties
Heat has been quantified as the energy that moves in
and out of a system with relationship to its environment. It
is unimportant to catalog the change of heat within a
reaction, but instead to take not in the form by which it
influences the interaction between the system and the
environment. In this respect, there are three methods of heat
transfer that allow for heat to be added to a system:
- Convection - or the heat transfer by
motion of fluids or material through a system. When a pot of
water is heated on the stove top, the water at the bottom
expands and becomes less dense then the water above, rising
to the surface. This is followed by the cooler, more dense
water falling to replace the vacated position at the bottom
of the pot. This movement of a fluid to transfer thermal
energy is the essence of convection, more commonly referred
to as the "heat rises" rule, making air an excellent
convector of heat and other rigidly bound systems poor
convectors.
- Conduction - or the heat transfer through
coupled vibration and collisions through a system. When
someone sits on a metal chair, it feels much colder against
their skin even though the chair is at room temperature.
This relationship is due to the thermal conductivity
of the material, a physical property dependent on the
composition of the material. Conduction asserts that a good
conductive material is one that has strong bonds between
adjacent atoms and molecules, and is responsible for a
coffee mug or pan handle to heat up when the mug is filled
with hot coffee or the pan is placed on a hot stove. This
association makes air and fluids poor conductors of heat.
- Radiation - or the heat transfer via
electromagnetic waves through a system. The sun radiates
heat to the Earth through the vacuum of space, as does a
fire when one sits in front of it. All objects emit some
form of radiation, released as electromagnetic waves which
oscillate electric charges within the atoms and molecules
that make up an object or material. These waves transfer
energy from materials and bodies emitting radiation to those
that absorb it. Hence, certain objects and materials are far
greater at transmitting heat by radiation as a function of
temperature, surface area, and time. Not only this, but
materials are also graded by their ability to effectively
radiate, referred to as the emissivity of the
material surface. Thus all materials can be quantified and
measured for their ability and aptitude to radiate heat.
One last important material property is the specific
heat of an object, or the amount of heat per unit of mass
required to raise the temperature of a fluid or material by one
degree Celsius. This relationship between heat, temperature, and
mass only exists while a material is within a singular phase of
matter, as the temperature of a material does not change when it
is undergoing fusion or vaporization and adjusting its phase.
Nave, R. "Specific Heat." Specific Heat. Hyperphysics, n.d. Web.
18 Apr. 2015.