Difference between forward and reverse refrigerator. Refrigerator - glass laboratory device Straight glass refrigerator

A direct condenser (Fig. 26 b) is used to distill solvents from the reaction medium, to separate mixtures of liquids into components, or to purify liquids by distillation.

A reflux condenser (Fig. 26a) is used in installations for synthesis to dissolve substances. The vapors entering the reflux condenser are cooled, condensed, and the resulting liquid flows back into the reaction flask.

Figure 26. – Application of direct and reverse refrigerator.

Water (Fig. 27) Air (Fig. 28)

Refrigerators are classified according to the type of cooling agent that fills the inner “jacket”:

Water s running water;

Water with still water;

Air.

An air cooler is used to condense liquid vapors from
T. kip. >150 C, water with running water – boiling point. liquids< 120 С, водяной с непроточной водой - с Т. кип. жидкости от 120 до 150 С.

According to the structure of the inner tube

Based on the design of the inner tube, the cooling jacket, and, consequently, the cooling surface, refrigerators are distinguished:

- “pipe in pipe”;

Ball;

Serpentine;

Combined, etc. (Fig. 29).

The use of a specific type of refrigerator is determined by required intensity cooling.


A	b	V	G	d	e	and	h

And	To	l	m	n	O	P

Figure 29. Refrigerators of various designs.

Air cooler (Fig. 29 a, o)

It is one of the simplest refrigerators in design and is a long glass tube. Such a refrigerator is used only when working with high-boiling liquids (boiling point >150°C), since the cooling effect of air is small. The refrigerator can be used as direct or reverse. As a reverse refrigerator, such a refrigerator is ineffective: the movement of the liquid predominantly corresponds to laminar flow and the substance is easily “thrown out”. As a downward condenser, such a refrigerator can be used at a low distillation speed.

Weigel-Liebig refrigerator (more often Liebig, English. Liebig condenser)
(Fig. 29 b, p)

It was first proposed in 1771 by Weigel and then used
Liebig. Mainly used as a downdraft cooler. It is ineffective as a reflux condenser, because... has a small cooling surface and laminar vapor flow. For this purpose, it is used for relatively high-boiling (boiling temperature > 100 0 C) compounds. Since atmospheric moisture condenses on the outer surface of the refrigerator, which can get inside the flask through capillary leaks in the joint, the joints on the refrigerator and flask should be thoroughly lubricated. It is also recommended to put a cuff made of dry filter paper on the refrigerator above the joint. Higher boiling liquids (boiling point >160 0 C) at the junction of the tubes (Fig. 30) can cause internal stress, which causes cracks or complete destruction of the glass.

Figure 30. Locations of possible cracks due to sudden temperature changes

The heat transfer coefficient for Liebig refrigerators with a length of 300 to 1000 mm varies from 105 to 35 W/(m 2 K), i.e. decreases with increasing length of the refrigerator.

A Liebig refrigerator can also perform the functions of an air refrigerator if it is positioned vertically and the steam of a high-boiling liquid is directed into the jacket through the upper branch, and condensate is taken from the lower one. As a result of heating, a continuous vertical flow of cold air will appear in the central tube. In this case, the most efficient refrigerators are those with a wider central tube and, if possible, a smaller diameter surrounding jacket.

Refrigerator Vesta(English West condenser) (Fig. 29 c)

It is a modification of the Liebig refrigerator, the difference from which is the smaller distance between the inner and outer tubes, which allows increasing the speed of movement of the coolant. The Vesta refrigerator has twice the heat transfer coefficient of the Liebig refrigerator and is more effective for cooling the vapors of low-boiling liquids.

Allina ball cooler (English Allihn condenser) (Fig. 29 d)

Is a typical reflux condenser. Due to their larger cooling surface, Allina refrigerators are shorter than Weigel-Liebig refrigerators. It is convenient to insert the stirrer axis through the ball cooler and introduce it into the reactor various substances, well washed into the flask with condensate and heated by it. Typically, the number of balls in such refrigerators ranges from 3 to 8. In terms of efficiency as a reflux refrigerator, the Allina refrigerator is inferior to the Dimroth refrigerator (Fig. 29g, h ), withstands significant temperature changes. To avoid choking, when the condensate does not have time to flow back into the flask with boiling liquid, the reflux ball cooler is installed in an inclined position, but the slope should not be too great so that the condensate does not accumulate in the balls. The accumulation of condensation leads to a decrease in the effective cooling surface of the refrigerator.

Coil refrigerator(Graham's refrigerator)

(English: Graham condenser) (Fig. 29 d, f)

Never used as a reverse, because Condensation that does not flow well enough along the folds of the coil may be thrown out of the refrigerator and cause an accident. A vertically mounted coil refrigerator is the most efficient downdraft refrigerator, especially for low-boiling substances.

Dimroth refrigerator (eng. Dimroth condenser), (Fig. 29 g, h)

Very efficient reflux condenser. It has the highest heat transfer coefficient, reaching 120 W/(m 2 K). It can also be used as a downdraft if the relatively large distillate losses on the coil can be neglected. The junction of the coil with the jacket is located outside the zone with a large temperature difference, therefore, when using such a refrigerator when working with liquids boiling above 160 0 C, there is no fear of complications. For more efficient cooling it is used Dimroth refrigerator with double jacket (Fig. 29 h).

To improve the performance of jacketed refrigerators, increasing heat transfer, a turbulent flow of coolant is created. To do this, the liquid supply and discharge tubes of the jacket are soldered so that their axes are located tangentially to the jacket (Fig. 14 i) . Then the water or other coolant will begin to move in a spiral in the refrigerator.

Friedrich's refrigerator (Friedrichs, Friederichs)
Friedrich condenser, (Fig. 29 i, j)

In such a refrigerator, vapors wash a coil tube with running water and the walls of an internal wide cylindrical tube, outside of which flows water coming from the coil. This steam intensive refrigerator is essentially a combination of the Liebig and Dimroth refrigerators. It is very effective for fractional distillation of liquid mixtures, since condensate practically does not linger in it.

Schirm-Hopkins refrigerator (usually the Hopkins refrigerator, Fig. 29 l).

It consists of a jacket through which steam is passed, and a “finger” located inside the jacket - a device through which liquid refrigerant flows. When using this type of refrigerator, the steam flow rate should be as low as possible.

Cooling finger Cold fingers, (Fig. 29 m)

This specially shaped reflux condenser (it does not need to be specifically fixed in the cooling system) is used primarily in devices for semi-micromethods. If the "cooling finger" is inserted into the reaction vessel on a stopper, the device does not need to be sealed.

Dewar refrigerator (Fig. 29 n)

A mixture of dry ice (solid carbon dioxide) with acetone or alcohol, or liquid nitrogen is used as a cooling agent in such a refrigerator.


Justus Liebig (1803-1873)	James Dewar (1842-1923)

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Fridge is a device for condensing steam using a cooling medium, most often water.

Depending on the method of use, the following types of refrigerators are distinguished:

Direct refrigerator (descending) - used to condense vapors and remove the resulting condensate from the reaction system. The condensate is collected in a receiver flask.
Reflux refrigerator - used for condensing vapors and returning the condensate to the reaction mass. Such refrigerators are usually installed vertically.

Figure 1 shows the various design types of refrigerators.

Fig.1 Construction types refrigerators
a-air cooler
b-ball air cooler
v-Liebig refrigerator
g-ball refrigerator
d-coil refrigerator
Staedeler e-fridge
w-refrigerator Dimrot
z-refrigerator combining the principles of Liebig and Dimroth refrigerators
and - "cooling finger"

Air cooler(Fig. 1-a)
It is one of the simplest refrigerators in design and consists of a long glass tube. Such a refrigerator is used only when working with high-boiling liquids (boiling point >150°C), since the cooling effect of air is small. The refrigerator can be used as direct or reverse. As a reverse refrigerator, this type of refrigerator is ineffective: the movement of the liquid predominantly corresponds to laminar flow and the substance is easily “thrown out”. As a descending refrigerator, such a refrigerator can be used at a not too high distillation speed for substances with a boiling point >150°C.

Ball air cooler(Fig. 1-b)
Used as a reverse. Ball coolers are more efficient than conventional (straight in design) air coolers due to their larger heat transfer surface. Such refrigerators have found application for semi-microsynthesis, where the amount of heat removed is small and for condensation of even low-boiling substances air cooling turns out to be quite sufficient. (If necessary, the refrigerator can be wrapped in damp filter paper in this case.)

Liebig refrigerator(Fig. 1-c)
It is used primarily as a downdraft up to approximately 160°C. A coolant for substances with a boiling point. The Liebig refrigerator consists of two glass tubes sealed one inside the other. Liquid vapor moves through the inner tube, and cooling agent (cold water) moves through the outer tube (jacket).
As a reverse refrigerator, such a refrigerator is ineffective, since it has a small cooling surface and laminar vapor flow; for this purpose, it is used only for relatively high-boiling (bp >100°C) compounds. Atmospheric moisture condenses on the outer surface of the refrigerator, which can get inside the flask through capillary leaks in the joint, so the joints on the refrigerator and flask should be thoroughly lubricated. It is also recommended to put a cuff made of dry filter paper on the refrigerator above the joint. Higher boiling liquids at junction A (Fig. 1-c) can cause internal stress, which causes cracking of the glass. Therefore, Liebig refrigerators cannot be made of non-heat-resistant glass.

Figure 2 shows an example of using a Liebig refrigerator for a simple distillation.

Fig.2 Installation for simple distillation.
1-Wurtz flask
2-Liebig refrigerator
3-along
4-bulb receiver

It should be separately noted that the cooling agent (water) is supplied exclusively from the bottom up. When refrigerant is supplied from top to bottom, filling the refrigerator jacket will be incomplete, which will make cooling ineffective. In addition, with such a supply, the refrigerator may fail (crack) due to local overheating of the jacket.

Ball cooler(Fig. 1-d)
Used exclusively as a reverse. Since this refrigerator has spherical expansions, the flow of vapors in it becomes turbulent; The cooling effect of such a refrigerator is significantly higher than that of the Liebig refrigerator. However, atmospheric moisture also condenses on its outer surface and junction A is also dangerous. The coolant is supplied from bottom to top. It is convenient to insert the stirrer axis through the ball cooler and introduce various substances into the reactor, which are well washed into the flask by the condensate and heated by it. Typically, the number of balls in such refrigerators ranges from 3 to 8. To avoid choking, when the condensate does not have time to flow back into the flask with boiling liquid, the reflux ball refrigerator is installed in an inclined position, but the slope should not be too large so that condensate does not accumulate in the balls . The accumulation of condensation leads to a decrease in the effective cooling surface of the refrigerator.

Coil refrigerator(Fig. 1-d)
It is never used as a return, since condensate, which does not flow well enough along the folds of the coil, can be thrown out of the refrigerator and cause an accident. A vertically mounted coil refrigerator is the most efficient downdraft refrigerator, especially for low-boiling substances.

Staedeler refrigerator(Fig. 1st)
A modification of the coil refrigerator in which the cooling vessel can be filled with a mixture of ice and table salt, solid carbon dioxide with acetone, etc. Such a refrigerator can be used for condensation of substances boiling at very low temperatures.

Dimroth refrigerator(Fig.1-g) Very efficient reflux condenser. It is also used as a downdraft if the relatively large losses of distillate on the coil can be neglected. The junction of the coil with jacket A is located outside the zone with a large temperature difference, therefore, when using such a refrigerator when working with liquids boiling above 160°C, there is no fear of complications. Since the outer jacket of the refrigerator is air when room temperature, atmospheric moisture does not condense on its surface (see above). True, low-boiling substances can “crawl” along inside shirts and thereby “pull” the cooling zone. The Dimroth condenser is therefore not suitable as a return condenser for relatively low-boiling substances, such as ether. At the upper open end of the refrigerator, atmospheric moisture easily condenses on the water supply hoses, so it is equipped with a calcium chloride tube.

Immersion refrigerator - “cooling finger”(Fig. 1-i)
This specially shaped reflux condenser (it does not need to be specifically fixed in the cooling system) is used primarily in devices for semi-micro methods. If the “cooling finger” is inserted into the reaction vessel on a stopper, the device should not be sealed.

General Note: It is necessary to constantly ensure that the circulation of water through the refrigerator jacket does not stop, since turning off the refrigerator can lead to fires and explosions!

Refrigerators- serve for condensation of boiling liquid vapors in distillation apparatuses. Depending on the operating conditions, the liquid is processed in the refrigerator while cooling the vapors (condensate) and must either be discharged to the receiver or returned to the vessel in which the heating is carried out. This difference in the purpose of refrigerators determines their shape and name. Refrigerators designed to collect condensate are called direct or downward, and refrigerators from which condensate is returned to the process are called reverse.

Direct refrigerators (Liebig). Liebig refrigerators, consisting of a long glass tube (forshtos), one end of which is expanded, are very common in laboratories. This tube is passed through a glass or metal jacket or coupling, and secured with pieces of rubber tubing fitted to the ends of the coupling. Sometimes there are Liebig refrigerators in which the refrigeration tube is soldered to the jacket.

At the ends of the coupling (perpendicular to its axis) there is one outlet. Rubber tubes are put on them, one of which, located near the narrow end, is connected with a water tap, and the other is diverted into the waste pipe. When the tubes are connected in this way, the water in the refrigerator moves towards the vapors of the cooled liquid. When connecting the refrigerator, the following rules must be observed: water must always enter the refrigerator from the lower lower end and exit from the upper raised end. The cooling jacket (coupling) must always be filled with water. Otherwise, during prolonged distillation, the refrigeration tube becomes very hot and may burst at the border with the water level.

When used for a long time, a reddish-yellow coating of iron oxides that enter with water from the refrigerator often forms in the refrigerator jacket. water pipes. Plaque interferes with the visibility of the refrigeration tube and must be removed periodically. To do this, the refrigerator is disconnected from water tap, release all the water and pour 10-16% hydrochloric acid into the refrigeration jacket, while clamps are put on the rubber tubes near the outlets. Carefully turning the refrigerator, dissolve the deposit of iron oxides in hydrochloric acid, then pour out the acid, connect the refrigerator again to the water supply and run the water for 5-6 minutes. It is possible to distill a liquid using a Liebig refrigerator only when the temperature of its vapor does not exceed 150°C.

Reflux condensers can be ball (Allina refrigerators), coil and other forms. In ball refrigerators, the tube consists of spherical extensions, while in coil refrigerators it is coiled in the form of a spiral. This shape of the tubes increases the cooling surface and at the same time more complete condensation of vapor occurs.

The Allina refrigerator is installed only in a vertical position, but not in an inclined position, since in the latter case condensed liquid will collect in the balls, interfering proper selection factions.

Ball Soxhlet refrigerator most often used as the reverse. Cooling water enters through a small outlet into the internal spherical cavity and flows out of the right process. Liquid vapors pass between inner surface and the outer wall. Thus, the vapors are cooled from both surfaces at once; with the outside - air, and with the inside - cold water.

There are a number of special refrigerators, for example, refrigerators in which the refrigeration tube has the shape of a spiral (Fig. 14, position 6). This is done in order to increase the cooling surface without increasing the size of the refrigerator.

Refrigerators Domrata are universal, as they can be used as downstream and reverse. The refrigerator can withstand significant temperature changes. Its advantage is that on its outer walls there are water vapors from environment do not condense.

Related information:

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Chemical refrigerators

Distillation unit with Liebig downward condenser (5)

Refrigerator (chemistry)- a laboratory device for condensing vapors of liquids during distillation or heating (boiling). Used to distill solvents from a reaction medium, to separate mixtures of liquids into components (Fractional distillation) or to purify liquids by distillation.

Types of refrigerators

Reverse, or rising, condensers are used when carrying out a reaction at the boiling point of the reaction mixture, but without distilling off the liquid; they ensure condensation of vapors and flow of condensate back into the reactor along the walls of the refrigerator.

The simplest type of laboratory refrigerator is the air refrigerator, which is usually just a glass tube that is cooled by ambient air. It is used exclusively when working with high-boiling liquids (preferably with a boiling point of at least 120 °C), which, when working with a water refrigerator, due to the large temperature difference, could cause a crack in the glass of the refrigerator.

Application

When working with liquids with a boiling point below 120 °C, water coolers of various shapes are used - Liebig, ball, coil, etc. For distillation with an inclined downward condenser, the Liebig refrigerator is most convenient (except in the case of distillation of liquids with a very low boiling point, such as diethyl ether). Finger-shaped refrigerators are usually used as reverse refrigerators or for condensing vapors during sublimation

Installation

Chemical refrigerators can be used either as reverse or as downward (they differ in the position and method of fastening when installing the device).

The top of the condenser is connected to a Wurtz flask or a tube extending from the flask containing the original mixture. The lower part is connected to an allonge, through which the product of synthesis or distillation enters the receiver.

Difference between forward and reverse refrigerator. Refrigerator - glass laboratory device Straight glass refrigerator

Types of refrigerators

Application

Installation

see also

2010.