مكثف (مخبر)

يظهر في الصورة مكثفان مختلفان. الأول (يسار) مكثف فيغريو ويستخدم كمود تجزئة، والثاني مكثف ليبيغ الذي يبرد البخار الساخن ويكثفه إلى سائل

المكثف في المخبر هو قطعة من الأدوات الزجاجية المخبرية ويستخدم في تبريد البخار أو الموائع الساخنة. يتكون المكثف من أنبوب زجاجي كبير يحتوي على أنبوب زجاجي أصغر من سابقه يمتد على كامل طوله حيث يمر ضمنه المائع الساخن.

تكيف نهاية الأنبوب الزجاجي الداخلي عادة وفق وصلات زجاجية مصقولة بحيث يسهل تثبيتها مع الأدوات الزجاجية الأخرى. تترك النهاية العليا عادة مفتوحة للضغط الجوي، أو تهوّى باستخدام صنبور (bubbler) أو أنبوب تجفيف (Drying tube) لمنع دخول الماء أو الأكسيجين.

ويكون الأنبوب الزجاجي الخارجي عادة مزود بفتحتين ناتئتين يمكن وصلهما لتمرير سائل تبريد، إما أن يستعمل ماء الصنبور العادي أو يستعمل مزيج من الماء ومضاد التجمد. وللحصول على أفضل مردود، وللحفاظ على تدرج حراري مباشر وصحيح لتقليل خطر الصدمة الحرارية التي تصيب الأداة الزجاجية المجاورة، يدخل المبرد من جهة نهاية المكثف ويخرج من الجهة الأخرى. ويمكن توصيل عدة مكثفات على التسلسل حين لا يفيد تدفق سائل التبريد في تبريد السطح الداخلي للمكثف.

Simple, Fluid-Cooled Condenser Design, Operation

Liebig (straight type)

simple cold finger (short path)

Left: Example of simple condenser design to expose vapor flow to cold surface. Shown is a Liebig fluid-cooled condenser (schematic). Circulating cooling water is shown in blue. The white rectangular area is a cutaway view of the central tube through which vapor and condensate flow, direction of which depends on the procedure. Trapezoids at top and bottom are ground glass joints that connect condenser to rest of apparatus (for example, in a reflux, to a boiling flask at bottom, drying tube at top). Right: Example of condenser use in a simple laboratory operation. A short-path distillation apparatus (schematic), for purification of a low boiling liquid from higher boiling or non-volatile impurities. Shown in a cutaway view, red and blue indicating heating and cooling (for example, circulating cooling water in blue). White areas around the cooled condenser are a cutaway view of path through which vapor flows to condenser (1→2) and the condensate flows from condenser to a pre-weighed collection flask (2→6). An exploded view, insofar as flasks 1 and 6 are shown disattached (where trapezoids represent matching ground glass joints allowing tight seals of apparatus parts). Impure liquid is placed in boiling flask 1, and heated with stirring (or other assistance to boiling to prevent bumping see text). Vapor rises diagonally to the right, coming in contact with a cold finger type of condenser, 2, chilled by fluid flow through ports 3 and 4. As warm gaseous material boiled from flask 1 comes in contact with cold surface of condenser 2, the gaseous material changes state to liquid (condenses, and falls, guided by the offset, pointed tip of the cold finger, to the right, through a funneled tip into collection flask 6, which is correspondingly cooled, to prevent any loss of product through adventitious heating and evaporation. After the distillation is completed (often not to complete dryness of 1), the apparatus can be disassembled and a rough yield determined by weight of flask and contents, followed by analysis (such as NMR or LC-MS) to confirm identity and purity of the product). Note, if the distillation is at ambient (normal) pressure, port 5 is attached to a drying tube (a tube open to air, packed with a desiccant); if it is a vacuum distillation, port 5 allows attachment of the vacuum pump.

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 أمثلة للعمليات

Condensers are often used in reflux, where the hot solvent vapors of a liquid being heated are cooled and allowed to drip back. This reduces the loss of solvent allowing the mixture to be heated for extended periods. Condensers are used in distillation to cool the hot vapors, condensing them into liquid for separate collection. For fractional distillation, an air or Vigreux condenser is usually used to slow the rate at which the hot vapors rise, giving a better separation between the different components in the distillate. For microscale distillation, the apparatus includes the pot, and the condenser fused into one piece, which reduces the holdup volume, and obviates the need for ground glass joints preventing contamination by grease and precluding leaks.

Simple distillation with Minimal Added Theoretical Plates

[Legend]

Shown in a cutaway view, blue indicating cooling flow and bath, red and yellow indicating heat. White areas in the short Vigreux section, 3, above boiling flask 2, and in Liebig condenser 5, and in vacuum take-off adapter 10, and receiving flask 8 represent the path through which vapor flows to the Liebig condenser (2→3→5) and the condensate flows from the condenser to a pre-weighed collection flask (5→10→8). Per usual, trapezoids represent matching ground glass joints allowing tight seals of apparatus parts. Impure liquid 15 is placed in boiling flask 2, and on a hotplate-stirrer (1, 13) equipped with silicone oil bath 14, and heated with stirring (11, 12) or other otherwise prevented from bumping (see text). Vapor rises vertically, coming first in contact with the Vigreux indentations in distillation head 3, and when the reflux reaches the height of the downspout of the adapter (point of bulb of thermometer 4), vapor proceeds downward to contact Liebig condenser, 5, chilled by fluid flow through ports 6 and 7. As the warm gases boiled from flask 2 come into contact with the cold surface of condenser 5, the gaseous volatile changes state to liquid (condenses), and proceeds to the right, through the drip tip of take-off adapter 10 into collection flask 8. which is correspondingly cooled in bath 16 to prevent loss of product evaporation. After distillation is complete (often not to complete dryness of 15), the apparatus can be disassembled, a rough yield determined, and analysis for identity and purity as described above. Likewise,a as noted, distillation at ambient pressure has port 9 is attached to a drying tube while in a vacuum distillation, port 9 allows attachment of the vacuum pump.

Common Air-Cooled Condenser Schematics

Vigreux
(finger indentations)

Snyder
(floating inverted teardrops)

Widmer
(concentric tube,
rod-and-spiral)

Left: Vigreux-type air condenser, illustrating defining Vigreux indentations as rows of orthogonal fingers projecting into the central vapor space. Used in vertical position, with vapor flowing from bottom opening to top. Center: Snyder-type air condenser, with circular indentations below and Vigreux indentations above inverted, hollow glass teardrops resting in and intermittently stoppering the circular opening made by those indentations. Right: Widmer-type air con-denser, with four concentric glass tubes and a central glass rod-and-spiral to increase surface area and vapor-condensate interaction, where the 4th and 3rd outer cylinders form an insulating dead air chamber (shaded). Vapor rises from a boiling flask into space 1, proceeds up the space between the 3rd and 2nd cylinders for full column length—follow the red arrows—doing a U-turn at top and proceeding down the space between the 2nd and 1st (innermost) cylinders for the full length of column to space 2. Vapor again does a U-turn at the column bottom, proceeding up spiral path created by the Dufton-type tight fitting rod-and-spiral inside the innermost cylinder. Arriving at space 3, vapor is then directed via a distillation head (glass branching adapter) to cooling and collection. Not shown in any cases are the boiling flasks, or the drying tubes (reflux application), or the distillation head and other downstream apparatus (distillation applications).

 الأنواع المبردة بالسوائل

 مكثف ليبگ

مكثف ليبگ

•  مقالة مفصلة: مكثف ليبگ

 مكثف آلين

The Allihn condenser or "bulb condenser" or simply "reflux condenser" is named after Felix Richard Allihn (1854–1915). The Allihn condenser consists of a long glass tube with a water jacket. A series of bulbs on the tube increases the surface area upon which the vapor constituents may condense. Ideally suited for laboratory-scale refluxing.

Further Common Fluid-Cooled Condenser Schematics

Allihn (straight type)

Graham (coiled type)

Dimroth (cold finger, coiled type)

Friedrichs
(cold finger,
spiral type)

As noted in the images above, circulating coolant is in blue, the white is a cutaway view of the vapor-condensate space, and notes about joints and flow directions are also as above.

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