18) Principle of peltier modules used in gas coolers / driers

The basic function of a peltier element is the reversed thermoelectric effect that is used to measure temperatures with thermocouples. The so-called Seebeck effect causes two different metals, if welded together or held in close contact, to produce a particular voltage depending on the temperature.

A peltier element uses this effect to transport heat from one side of a particular body to the other side when a current is applied.

This is used in the Peltier cooler to bring the gas quickly to the dew point. The Peltier element is not a very efficient means of cooling something, when the purely energetic efficiency is considered. It has certain advantages that lead to its use in this type of equipment. It is small and light, making it ideal for any type of portable instrumentation. It contains no coolant which may be either flammable or of a type that is restricted due to environmental considerations. The time between set-up and operational temperature is relatively short due to the low mass and lack of any medium. There is no liquid medium to create airlocks or other problems that can lead to a shortened lifetime. In the case of damage, the semiconductor element can be simply replaced with no worries about refilling a coolant system and checking for leaks, which would be practically impossible in the field. The element is also relatively inexpensive, especially when compared to systems consisting of pump, evaporator and condenser. As spare part it will be available easily worldwide, not requiring specialised parts from the original manufacturer. The major disadvantages are the relatively high current consumption and the necessity of connecting several Peltier elements after each other to achieve the desired cooling effect. A heat sink with fan will be needed to transport the temperature away from the body. The ambient temperature will therefore play a major role in the cooling effects that can be achieved with this equipment. The Peltier element will only achieve a temperature differential, there is no way of programming an exact temperature into the device. Any temperature control desired must be applied separately.

To increase the cooling effect it is common practice to build a bank of Peltier elements, with the cold side of one in contact with the hot side of the next. Greatly increased cooling can be achieved in this way, but the power consumption will rise accordingly.

Peltier elements are used in many industries where size and weight are at a premium over power consumption. These articles are to be found in all those newest computers with extremely fast processors as an extra aid to cooling.