Refrigeration is required for many applications, ranging from cryogenic temperature
controllers used in electronic and biotechnology industries to the wide variety
of general-purpose food storage appliances used by consumers. Conventional
refrigerators fall into two categories, i.e., vapor compression systems or absorption
refrigerators. The former uses mechanical pumps to actuate the compression and
expansion of specific working fluids according to the principle of thermodynamics.
The latter utilises heat energy (e.g., solar energy, waste heat) as a primary mover
and a refrigerant/absorbent combination as the working fluid. The disadvantages of
absorption refrigerators are that they are bulky and have a relatively low coefficient
of performance [1].
Mechanically driven refrigerators have a high coefficient of performance and are
very reliable, in spite of their moving parts, operating for many years with little
requirement for maintenance. However, they are noisy and can only achieve their
potentially high coefficient of performance when the cooling power is large and the
load is stable. Most importantly, the working fluids used in these refrigeration systems
often escape into the atmosphere, where they are known to have harmful
environmental effects [2].
Systems employing the thermoelectric Peltier effect are generally less efficient
than vapour-compression systems but do represent the most direct way of utilising
electricity to pump heat. A schematic description of a Peltier module is shown in
Fig. 1. It is composed of a number of thermoelectric couples, connected electrically
in series and thermally in parallel, integrated between two ceramic plates, which
form the cold and the hot surfaces of the module. Peltier coolers have been used in
many applications [3,4], including measurement devices, biotechnology, medicine
and electronics and have numerous advantages. They are silent and “environmen-