January 2001
5F - 9
Functions - Cooling System
Service Manual Cafitesse 500
F.3.2 Function: Cooling System
The principle of thermoelectric cooling
●
For cooling of the flexi-packs the dispenser
is equipped with a thermoelectric cooling
system.
The element in such a system is called
Peltier element (1). (Fig. 1)
●
The Peltier element (1) consists of a
series of thermoelectric cooling cells. The
elements of the cooling cells consist of 2
bismuth semiconductor bridges made from
tellurium with different doping. (Fig. 1)
●
The amount of heat that is transferred is
proportional to the electric current and to
the amount of cooling cells contained in the
Peltier element.
●
127 cells are electrically connected in
series in the Peltier element.
Viewed thermally these cells are connected
in parallel.
The typical electric current is 3.5 A (in a
stable, cooled state of the system).
●
The Peltier element (1) acts as a heat
pump and transfers the heat energy from
the cold cooling compartment side to the
warm heat sink side. In addition to the
cooling power (typically 10 Watt) from the
cooling compartment (2) the electric loss of
the element (typically 35 Watt) is also trans-
ferred to the warm side. (Fig. 1)
Design of the cooling system
●
The design of the cooling system is shown
in fig. 1:
Insulation (7)
●
The two-part Styrofoam insulation serves to
reduce the heating effect of the surrounding
area. (Fig. 1)
●
Due to the relatively low refrigerating
capacity of the Peltier cooling a thick
insulation is necessary which helps to keep
the energy consumption of the system very
low.
Cooling compartment (2)
●
The cooling compartment (2) consits of a
diecast aluminium container with an additio-
nal surface (6) to fasten the Peltier element
(1). The incoming heat is taken up by the
container wall and led to the Peltier
element. (Fig. 1)
Peltier element (1)
●
The Peltier element is made from ceramic
plates. The cooling elements are situated
between these plates
●
Very important for a proper functioning of
system is a very good heat conduction from
the Peltier element (1) to both sides. This
is effected by plane contact surfaces on the
cooling compartment (2) and on the heat
sink (3). A silicon lubricant is used as
contact material. Because the silicon
lubricant has very low heat transferring
properties it is important to use only a
small amount and to spread it very evenly.
(Fig. 1)
CAUTION:
Take care that during
mounting no dust particles
gather between these two
planes.
