Physicist-turned-chemist Svante Arrhenius led a life of stellar scientific achievement. He was the first
Swedish Nobel laureate, winning the prize for chemistry
in 1903. Lunar crater Arrhenius is named in his honor.
All in all, his life made more of an “impact” (crater, get
it?) than that of a humble technical contributor: although
the International Astronomical Association has honored
some 360 persons with named craters, including two
Pickerings, your columnist is not among them.
But I digress; Arrhenius also gave his name to the
Arrhenius equation that describes the relationship
between the rate of a chemical reaction and the absolute
temperature at which it occurs. As electronic engineers,
we care because the equation also predicts the increase
in failure rate of electronic components as temperatures
rise: the rate approximately doubles for every ten degrees
increase in temperature.
One consequence of the drive towards adding ever-more
features into ever-smaller enclosures is the increase in
internally-generated heat that must be removed to extend
the life of the product. Luckily, most enclosures are open
to the outside air: For these, forced-air convection cooling
is the most popular option. A fan forces cooler external
air to flow through the enclosure across the hot internal
components and out again through a vent, taking the heat
Conceptually it’s simple, but that’s not to say designing
a forced-air cooling system is straightforward. When air is
forced into an equipment enclosure, a force opposing the
air flow is generated due to the layout of the components
and the shape of the air stream inside the equipment. This
phenomenon is called ventilating resistance (also called
“system impedance” or “channel resistance”). Increasing
the component density increases the strain on the cooling
system because it increases the ventilating resistance, even
if the total heat generated remains the same.
If the enclosure must be sealed from the outside
environment, a different approach is called for, and
thermoelectric technology can be a cost-effective
The Peltier Effect is the underlying phenomenon behind
thermoelectric cooling (TEC) systems. In 1834, French
Physicist Jean Peltier found that when a current flowed
through two dissimilar conductors, the junction of those
materials either absorbed or released heat, depending on
the direction of the current flow.
Figure 1: The Peltier Effect. (Source: SRJC)
Applying DC across the PN junction forces electrons
in the n-type material and holes in the p-type away from
each other on the cold side and towards each other on the
hot side, carrying thermal energy with them.
Connect multiple PN junctions together, and you form
a Peltier element, shown in Figure 2: the p- and n-type
materials are stacked electrically in series and thermally in
parallel with a high-thermal.
By Paul Pickering, Technical Contributor