Climatic chambers can control both positive and
negative temperatures. For positive temperature control, the chambers use
electric heating elements, but for negative temperatures, there are different
cooling options. Most climatic chambers use a mechanical system based on
refrigerant gas compressors to perform the cooling.
There are several negative temperature ranges,
but the standard used and the type of material or sample being tested will
determine the negative range. The following must be taken into account: the
negative temperature range indicated in the standard, energy dissipation, mass,
and type of material, in order to calculate the cold group and determine
whether it is the most appropriate. For example, if you want to lower the test
temperature to -40°C with a large mass and high dissipation, a
single-compressor chamber will not be sufficient, and you will need to select a
two-compressor system with a larger negative temperature range.
There are several alternatives for lower
temperature ranges, based on mechanical cooling or an expandable refrigerant.
• Ambient +10°C. This lower limit is common for
non-cooled chambers. Since the fan generates its own heat, temperatures close
to ambient cannot be guaranteed. If a temperature close to ambient is desired,
a cooling system will be necessary.
• -25°C. This is a considerably lower range
that can be achieved by refrigerants commonly used in refrigerators or air
conditioners, using a refrigerant gas.
• -40°C. This type of cooling system is
commonly called single-stage, as there is only one compressor in the cooling
system.
• -70°C. Systems called cascade or dual-stage.
The high stage will be used to cool the low stage, allowing the temperature
limits to be lowered. The high stage will ensure no overpressure or
overheating.
• -86°C. To achieve this cooling, a triple
cascade cooling system is used. This is rare in climatic chambers, however, it
is common for ultra-low temperature freezers.
• -170°C. Chambers that reach these limits use
liquid nitrogen for cooling. Nitrogen is an inexpensive method for cooling a
chamber; however, prolonged use can be expensive. It is typically used for
tests requiring gradients close to 30°C/min with a small volume.
Remember, provide as much information as
possible to the DYCOMETAL technical department so they can configure the most
appropriate equipment for your solution.
