Laboratory cooler
Laboratory cooler are the condensation of gases and vapors used in a chemical laboratory equipment. Different cooler types are used depending on the intended use and working temperature. The cooling effect is based on heat transfer processes on the cooling surfaces of the cooler. In addition to the coolant temperature , an important criterion for the cooling effect is the size of the cooling surface, as the amount of heat that can be transferred is proportional to the area of the cooler. The cooling surface is an important design feature of a cooler. Large cooling surfaces are achieved using special shapes such as cooling spirals.
In terms of application, a distinction is made between product coolers and reflux coolers . In the case of the former, the condensate resulting from the distillation is discharged as a product. On the other hand, reflux condensers are designed to condense and return the vapors to the distillation flask.
Product coolers , such as Liebig coolers or serpentine coolers , are used “descending” to separate the distillate, which is collected in a receiving vessel, possibly using a spider or an attack according to Anschütz-Thiele .
Reflux condensers are always used in a vertical arrangement. With this structure, the condensate flows back into the flask, from which it rises due to an external heat supply or the heat of reaction released .
Cooling media
In most cases, flowing water is used as the coolant. In the case of very volatile condensates , such as acetaldehyde , the cooling water can be cooled to lower temperatures using a cooling thermostat and then circulated.
For high-boiling media with boiling points above 120 ° C, standing water is sufficient in many cases. At temperatures above 160 ° C, the ambient air is often sufficient as a cooling medium.
The cooling media are fed into the cooler according to the counterflow principle .
Cooler types
Allihn or spherical cooler
The tube of the Allihn cooler is wider than the Liebig cooler and is constricted spherically at intervals. This results in a significantly larger cooling surface and stronger swirling of the steam. This type of cooler, which is also still inexpensive, is used almost exclusively as a reflux cooler. It is named after the German glassblower Felix Richard Allihn (* around 1854, † 1915).
Dimroth cooler
The Dimroth cooler consists of a cooling spiral that is located inside a pipe. This type of cooler has a large cooling surface and is mainly used as a reflux cooler, but can also be used as a product cooler. It is named after Otto Dimroth .
Liebig cooler
The Liebig cooler (named after Justus von Liebig ) consists of a straight glass tube with a water jacket. It is mainly used as a product cooler in distillations that can also take place under high vacuum . Thanks to its simple structure, the Liebig cooler is inexpensive, robust and easy to clean. Due to the small cooling surface, the cooling effect is relatively small, which is why it is less suitable as a reflux condenser.
Intensive cooler
An intensive cooler is a combination of a Liebig cooler (outer cooling jacket) and a Dimroth cooler (cooling coil inside). This type of cooler has the largest cooling surface. It is therefore particularly suitable for working with low-boiling media such as diethyl ether .
Screw cooler according to Friedrichs
The Friedrichskühler, a cooler with a similar structure to a cold finger , was invented by Fritz Walter Paul Friedrichs, who published a concept for the cooler in 1912 . It consists of a spiral-shaped glass tube that is arranged around a large inner cylindrical body. The cooling medium enters through the cold finger of the inner cylinder; Rising vapors must escape up along the colder spiral. The cooler also has a very large cooling surface, so it is also suitable for the distillation of low-boiling compounds such as diethyl ether.
Air cooler
An air cooler consists of a single-walled tube in which the vapors are condensed by the ambient air as a cooling medium. Air coolers can be used as reflux coolers and product coolers for high-boiling media (boiling point greater than 150 ° C). One form of air cooler is the Vigreux column without a jacket.
Snake cooler
In the coil cooler, the riser pipe winds in a spiral shape through the jacket through which the coolant flows. Due to the design, the cooler must always be operated vertically. Because the condensate remains in the cooling coil for a long time, it is cooled down to almost the coolant temperature. Coil coolers are therefore often installed downstream of other cooler types with better condensation performance (Allihn cooler or Dimroth cooler) in order to cool the distillate and not used as a stand-alone reflux condenser.
Condensation of the smallest amounts of substance
The cold finger or hanging cooler is used to condense the smallest amounts of substance . This type of cooler can also be used for sublimations . The product to be isolated usually condenses in crystalline form on the cooler surface.
photos
Allihn or spherical cooler
Graham or snake cooler
Dimroth cooler
Cooler after Friedrichs
Cold finger
Graham or snake cooler
Intensive cooler
Cooler after Friedrichs
Cold finger with vacuum nozzle
Spherical cooler
Dimroth cooler
Radiator materials
Laboratory coolers are made almost exclusively from laboratory glass, for example borosilicate glass . In special cases, for example when distilling solutions containing hydrofluoric acid , coolers made of PTFE are also used.
In chemical technology, special heat exchangers , such as tube bundle heat exchangers or plate heat exchangers made of various materials ( stainless steel , polyetheretherketone , graphite , Hastelloy , tantalum , and many others) are used to cool larger quantities of material .