Perma Pure Baldwin-Series 10410 - Manual (Page 6)

Section C: Principle of Operation 6
as a small heat pump with no
moving parts. The Peltiers
operate on direct current and
may be used for heating or
cooling by reversing the
direction of current flow. This
is achieved by moving heat
from one side of the module to
the other with current flow and
the laws of thermodynamics.
A typical single stage Peltier
(figure 1) consists of two
ceramic plates with p- and n-
type semiconductor material
(bismuth telluride) between the
plates. The elements of
semiconductor material are
connected electrically in series and
thermally in parallel.
When a positive DC voltage is applied to the n-type thermo-electric element,
electrons pass from the p- to the n-type thermo-electric element and the cold side
temperature will decrease as heat is absorbed. The heat absorption (cooling) is
proportional to the current and the number of thermo-electric couples. This heat is
transferred to the hot side of the Peltier element where it is dissipated into the heat
sink and surrounding environment.
The Baldwin™-Series Thermo-Electric Coolers remove the moisture from the
sample gas by cooling the gas as it passes through a laminar impinger (heat
exchanger). A diagram showing the gas flow path through an impinger is shown in
the Appendix. The heat exchanger, made of 316L stainless steel, Durinert
®
(a
corrosion-resistant inert coating over 316L stainless steel), PVDF (Kynar), or glass,
is mounted within a thermally insulated heat transfer block bored to receive the heat
exchanger without a mechanical lock. This assembly allows the easy removal of any
heat exchanger simply by slipping it out of the cooling block by hand. The heat
transfer block cools the heat exchanger through the heat pumping action of the
peltier element. The heat transfer block is on the cold side of the thermo-electric
element and the heat sink is on the hot side of the thermo-electric element. The
heat from the heat transfer block is pumped to the heat sink where it is then
dissipated into the air by the heat sink fan. See figure 2. The desired temperature is
maintained by a closed loop control system, which is implemented through an
analog proportional controller. The controller uses a type K thermocouple in the
heat transfer block located very close to the cold side of the peltier element as the
input sensor.
Figure 1: Thermo-electric element (Peltier)