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The Science of Heat Transfer: What Is Conduction?
</h1>
<p>
Heat is an interesting form of energy. Not only does it sustain life, make us
comfortable and help us prepare our food, but understanding its properties is key
to many fields of scientific research. For example, knowing how heat is
transferred and the degree to which different materials can exchange thermal
energy governs everything from building heaters and understanding seasonal change
to sending ships into space.
</p>
<p>
Heat can only be transferred through three means: <a
href="http://www.lyyrcable.com/bare-conductor/all-aluminum-conductors/"
target="_self">conduction</a>, convection and radiation. Of these, conduction is
perhaps the most common, and occurs regularly in nature. In short, it is the
transfer of heat through physical contact. It occurs when you press your hand onto
a window pane, when you place a pot of water on an active element, and when you
place an iron in the fire.<br/>
</p>
<p>
This transfer occurs at the molecular level — from one body to another —
when heat energy is absorbed by a surface and causes the molecules of that surface
to move more quickly. In the process, they bump into their neighbors and transfer
the energy to them, a process which continues as long as heat is still being
added.
</p>
<p>
The process of heat conduction depends on four basic factors: the temperature
gradient, the cross section of the materials involved, their path length, and the
properties of those materials.
</p>
<p>
A temperature gradient is a physical quantity that describes in which
direction and at what rate the temperature changes in a specific location.
Temperature always flows from the hottest to coldest source, due to the fact that
cold is nothing but the absence of heat energy. This transfer between bodies
continues until the temperature difference decays, and a state known as thermal
equilibrium occurs.
</p>
<p>
Cross-section and path length are also important factors. The greater the
size of the material involved in the transfer, the more heat is needed to warm it.
Also, the more surface area that is exposed to open air, the greater likelihood
for heat loss. So shorter objects with a smaller cross-section are the best means
of minimizing the loss of heat energy.
</p>
<p>
Last, but certainly not least, is the physical properties of the materials
involved. Basically, when it comes to conducting heat, not all substances are
created equal. Metals and stone are considered good conductors since they can
speedily transfer heat, whereas materials like wood, paper, air, and cloth are
poor conductors of heat.
</p>
<p>
These conductive properties are rated based on a “coefficient” which is
measured relative to silver. In this respect, silver has a coefficient of heat
conduction of 100, whereas other materials are ranked lower. These include copper
(92), iron (11), water (0.12), and wood (0.03). At the opposite end of the
spectrum is a perfect vacuum, which is incapable of conducting heat, and is
therefore ranked at zero.
</p>
<p>
Materials that are poor conductors of heat are called insulators. Air, which
has a conduction coefficient of .006, is an exceptional insulator because it is
capable of being contained within an enclosed space. This is why artificial
insulators make use of air compartments, such as double-pane glass windows which
are used for cutting heating bills. Basically, they act as buffers against heat
loss.
</p>
<p>
Feather, fur, and natural fibers are all examples of natural insulators. These
are materials that allows birds, mammals and human beings to stay warm. Sea
otters, for example, live in ocean waters that are often very cold and their
luxuriously thick fur keeps them warm. Other sea mammals like sea lions, whales
and penguins rely on thick layers of fat (aka. blubber) – a very poor conductor
– to prevent heat loss through their skin.
</p>
<h2>
LV & MV Aerial Bundle Cable (ABC)
</h2>
<p>
Aerial Bundle <a href="http://www.lyyrcable.com/aerial-bundled-cables/lv-abc-
cable/" target="_self">Cables</a>, often referred to as Aerial Bundled Conductors
or simply ABC, are cables for overhead line power, so called for combining
multiple single core cables together. With applications including temporary power
distribution to street lighting and secondary pole-to-pole service cables,
they are lightweight stranded aluminium conductors, both single core and multi-
cores. Whilst Aerial Bundle Cables are used in rural power distribution in
some countries, they are more commonly used in temporary power installations such
as on construction sites. As insulated cables they are often preferred to bare
conductors which are installed and separated by air gaps but where sparks and
shorts in the event of high winds may cause resulting bushfires in dry climates or
risk nearby property. The XLPE insulation material, and where relevant the
sheathing material, allows the ABC to be tightly bundled together – additional
steel wire supports similar to those in ACSR can also be incorporated as
catenary wires .
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