Cold traps

Variants

A cold trap / cooling finger has the task of collecting and retaining the condensate from a gas flow, for example upstream of the vacuum pump.

As different substances may be present in the gas flow (e.g. water / solvents / acidic or alkaline gases), the condensation temperature of the substance to be condensed must be considered first. The material (glass or metal) and the geometry of the condensate freezing wall play a major role in a cold trap / cold finger. In order to increase the performance of a cold trap, it is sometimes fitted with baffles so that the gas in the condensation chamber is swirled more strongly and thus better condensation can take place on the cold inner wall of the cold trap.
In general, it should be noted that the liquid used for cooling (LN2 or CO2) should be at least 50°C colder than the condensation temperature of the substance that is to be condensed out of the gas flow. If, for example, a solvent such as methanol (melting point -98°C) or acetone (melting point -95°C) is to be filtered out of the gas flow, LN2 (approx. -196°C) is required as a coolant in order to achieve sufficient cooling capacity in the cold trap. The melting point of water is 0°C. This means that a mixture of CO2 and acetone (approx. -77°C) with water vapor would be sufficient.

To keep the performance of a cold trap/cooling finger constant, the coolant level (LN2 level) in the Dewar flask must also be kept constant. This can be achieved with an automatic LN2 level control. This type of level control ensures that the cold trap / cold finger is always supplied with sufficient LN2 coolant so that optimum condensation performance of the cold trap / cold finger is guaranteed. Complete LN2 level control systems for cold traps are available for this purpose.

A cold trap / cooling finger has the task of collecting and retaining the condensate from a gas flow, for example upstream of the vacuum pump.