Perma Pure Baldwin-Series M325 - Manual (Page 5)

Section C: Principle of Operation 5
C: P
RINCIPLE OF
O
PERATION
Thank you for purchasing a Perma Pure Baldwin™-Series Thermo-Electric Cooler. This
Modular Series features a unique slim design leaving additional space to install or access
other sample conditioning system components. A unique drop-down door on the Modular
Series provides easy access to electronic boards and the power supply. All electronic
boards (control, relay, and display) are mounted on the door for easy access.
The process of sampling combustion product stack gas or exhaust from internal combustion
engines requires a method to remove the moisture from the sample, without removing the
gas components of interest. The Baldwin-Series cooler is an ideal way to decrease the dew
point of combustion gases to a repeatable, stable, constant low dewpoint. The Baldwin
cooler prevents water condensation in sample pre-filters, sample pumps, and gas analyzers.
For gas analyzers where water vapor is an interferant, a stable, repeatable dewpoint
becomes a part of the gas analyzer performance specification. Baldwin-Series coolers
provide this constant low water concentration, resulting in an accurate component gas
measurement.
All Baldwin-Series coolers use thermo-electric elements (Peltiers) to cool the sample gas to
the desired dew point temperature. A thermo-electric cooler is best illustrated 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
elements. This heat is transferred to the hot side of the Peltier element where it is
dissipated into the heat sink and surrounding environment.
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
Figure 1: Thermo-electric element (Peltier)