Thermoelectric cooler with fast-acting heater chromatograph

 

(57) Abstract:

The invention relates to a thermoelectric semiconductor refrigerators designed for cooling or temperature control of the capillary chromatographic column and rapid heating for gas analysis using a chromatograph. Thermoelectric cooler consists of a thermopile cooling, matrix, radiator, fan and is equipped with a heater in the form of a ceramic tube of small diameter with metallic belts, onto which the thin-walled tube, elektroshlifovalnaya from belts and is made of vysokoteploprovodnyh material. Inside the ceramic tube is inserted a wire spiral. On the ends of the ceramic tube napivayutsa thin conductive caps with a hole. The diameter of the hole caps and wire spiral exceeds 0.1-0.2 mm maximum diameter of the capillary chromatographic column. Capillary mounted on a heater mounted on the cooled matrix, and semi-cylindrical recessed groove of the matrix corresponds to the outer diameter thin-walled tubes of the heater. The current terminals of the heater is removed from the refrigerator and attached to the two article the key from breaking the electric circuit of the heater and turning it back on, and time relay for 5-10 seconds to be sure the power supply of the heater when the temperature on the capillary +(150-180)oC. the Technical result is crisp, high-quality chromatogram of the sample gas, the reduction in time and cost reduction of the process gas analysis in the chromatograph, using artificial cryofocusing. 1 Il.

The invention relates to a thermoelectric semiconductor refrigerators designed for cooling or temperature control of the capillary chromatographic column and rapid heating for gas analysis using a chromatograph. The aim of the invention is the creation of a functional structure of a thermoelectric refrigerator with quick heater.

While conducting gas analysis using a chromatograph for a number of tasks required to complete the cooling column or part thereof. Herself column is placed in the working chamber chromatograph /1, S. S. 45-60; 2, c.with. 190-200/.

In thermoelectric device (refrigerator) for gas analysis /3, S. 453/ thermopile provides the temperature in the chamber 0oC, which is condensed naphthalene hot hydrocarbon ha is camping in the capillary loop by cooling with liquid nitrogen.

In subsequent operations while conducting gas analysis required: fast heating a local area of the column for 5-10 seconds to a temperature of +(150-180)oC depending on the assigned tasks and complete heating of the entire chromatographic column to a temperature of 120-150oC, which is its own heating system working chamber chromatograph using the built-in camera, heater and fan.

(2, S. 190) presents a constructive solution - prototype, in which the above is solved as follows. On a separate plot column is worn thin Nickel tube with an inner diameter of 1 mm and a wall thickness of 0.1 mm Tube with integrated capillary is lowered into the tub, placed inside the working chamber of the chromatograph, and in the bath pour liquid nitrogen or carbon dioxide. The cost of such a cooling system is up to 40-50% of the cost of the chromatograph. At the end of the cooling process of plot columns on the ends of thin-walled Nickel tube served bit currents up to 50 a and voltage up to 1 C. the Tube is heated for a few seconds (3-8), heating the inside area of the capillary to the desired temperature.

Using the design of the refrigerator Nickel tubes will require a significant increase of its capacity due to shunting of heat on the tube. In addition, for the implementation of this technical solution requires special high-current power supply and the introduction into the working chamber chromatograph wires of large cross section.

Thermoelectric refrigerator is able to work himself in the reversible thermal heating mode, however, the amount of heat in the refrigerator usually limit value +(60-70)oC because of possible reduction in its reliability. Reversible heating from the initial temperature -40oC is 2-5 min and more.

The present invention is the creation of a thermoelectric cooler for a gas chromatograph, which provide not only cooling a separate section of the capillary chromatographic column to a temperature of about -40oC, but fast heating it to temperatures +(150-180)oC for 5-10 sec, convenient in installation and dismantling as in the working chamber of the chromatograph, and the chromatographic column, reliable.

Features quick-acting heater, made in the form of a ceramic tube of small diameter, for example 3.5 mm, with metal edge bands that are wearing thin-walled tube, elektroshlifovalnaya from belts and Alena wire helix; on the ends of the ceramic tube napivayutsa thin conductive caps with a hole, and the hole diameter of the caps and wire spiral exceeds 0.1-0.2 mm maximum diameter of the capillary chromatographic column; capillary put on him by the heater is mounted on the cooled matrix, and semi-cylindrical recessed groove of the matrix corresponds to the outer diameter thin-walled tubes of the heater; the current terminals of the heater is removed from the refrigerator and attached to the two racks screw clamp frame via quick connectors; a control unit provided with two lock systems from breaking the electric circuit of the heater and turning it back on, and time relay for 5-10 sec for de-energizing the power supply of the heater when the temperature on the capillary 150-180oC.

The proposed design solution thermoelectric cooler with fast-acting heater allows you to:

to produce cooling (temperature control) a separate section of the capillary chromatographic column to a temperature of about -40oC;

- to produce rapid heating of the individual (local) section of the capillary chromatographic column to temperate refrigerator in the working chamber chromatograph, as well as the installation of the capillary chromatographic column in the refrigerator;

to simplify the process gas analysis in the chromatograph using a thermoelectric cooler.

Guaranteed positive effect of increasing the reliability of the refrigerator with quick heater and facilities collaboration refrigerator and chromatograph is achieved due to the fact that the refrigerator is equipped with fast-acting heater, made in the form of a ceramic tube of small diameter, such as a 3.5 mm, thereby increasing the dimensions of thermoelectric refrigerator; ceramic tube has a metallic end bands; on the ceramic tube set tube from vysokoteploprovodnyh material, such as copper or brass, thereby providing a thermal contact with a cooled matrix thermopile, and the tube elektrosokirani from metallic belts ceramic tube; inside the ceramic tube inserted wire helix; on the ends of the ceramic tube napivayutsa thin conductive caps with a hole, and the diameter of the caps and wire spiral exceeds 0.1 - 0.2 mm limit of avatele; capillary mounted on a heater mounted on the cooled matrix, and semi-cylindrical recessed groove of the matrix corresponds to the outer diameter thin-walled tubes of the heater that allows Assembly capillary Assembly with the heater on the cooled matrix thermopile for a few seconds; the current terminals of the heater is removed from the refrigerator and attached to the two racks screw clamp frame via quick connectors for fast replacement of the heater in case of its failure; the control unit has two interlocking systems from breaking the electric circuit of the heater and turning it back on, thereby eliminating repeated actuation of the heating mode of the capillary without prior cooling, and time relay for 5-10 sec for de-energizing the power supply of the heater when the temperature on the capillary +(150-180)oC, while the temperature of the capillary is determined uniquely by the operating time of the heater.

The drawing shows a General view of thermoelectric cooler with fast-acting heater chromatograph.

Here:

1 - thermopile, 2 - matrix, 3 - radiator, 4 - fan 5-the wizard, 15 - screw, 16 - groove, 17 cable, 18 - block, 19 - ceramic tube of 20 tube 21 to the coiled wire, 22 - cap, 23 connector, 24 - metallic belt.

Fast-acting heater (Fig. below, the incision) is made in the form of standardized ceramic tube 19 having an outer diameter of 3.5 mm and an inner diameter of 1.5 mm Tube is manufactured by extrusion with high enough accuracy.

At the ends of the tube there are two oppozitnyj metallic belt 24 with a width of 1.5-2 mm Metallization is carried out in a traditional way - burn refractory material in paste form, for example of molybdenum, with subsequent coating electroplated layer of Nickel with a thickness of 2-5 μm. You can also burn silver-containing paste in the environment of hydrogen, however, the adhesion of the coating to the tube in this case the result is low.

The ceramic tube 19 is placed on a sliding fit thin-walled tube 20 from vysokoteploprovodnyh material, such as copper or brass. The tube wall thickness of 0.25-0.3 mm, the length of the tube 20 is selected so that its ends do not reach the metallized areas 24 ceramic tube 19 0.5-1 mm

Inside the ceramic tube 19 is set PR is or Constantan. The wire diameter is selected based on the voltage of the heater and may be in the range of 0.1-0.3 mm Wire tight spiral coil to a coil wound on technological mandrel and Monterosa in a ceramic tube 19. Length of winding a wire helix on the mandrel should be 5-8 mm less than the length of the ceramic tube due to thermal linear expansion of the wire heater in the process. To output a wire helix 21 of the ceramic tube 19 there is a corresponding radial groove.

On the ends 24 of the ceramic tube 19 are installed and napivayutsa thin conductive caps 22, made for example of brass with a thickness of 0.2 mm Soldering caps can be a standard solder, such as tin with two percent additive bismuth - avoid "tin plague". On tokoyo wire spiral napivaetsya single point plug connector 23. Conductive caps 22 and the gap with the tube 20 is covered by a thin layer of insulating heat-resistant silicone or fluorine-containing varnish.

The caps 22 have aligned holes, and the hole diameter of the caps and wire spiral exceeds 0.1-0.2 mm predelivery him heater (sections b-B and b-C) mounted on the cooled matrix, moreover, the semi-cylindrical recessed groove of the matrix corresponds to the outer diameter thin-walled tube 20 of the heater. The groove in the matrix 2 is produced by milling.

The current terminals of the heater 23 is withdrawn from the fridge and fixed on two legs 14 of the screw clamp 12, 13 of the frame 11. For this purpose, the rack has a single point lock quick-release connector (the connector has a standard solution in Fig. at specified) that allows you to plug in the power supply to the heater from the power supply and control of thermoelectric cooler.

The control unit thermoelectric refrigerator is equipped with two locks. The first lock was not possible to include the refrigerator in the cooling mode if not connected electric heater or the electric circuit. The second interlock prevents re-enable the heating mode without carrying out pre-cooling of the capillary, thereby increasing the reliability of the system: thermoelectric refrigerator - fast heater.

In addition, the control unit thermoelectric cooler provides electronic time relay for 5-10 sec is stachivaya power of the heater when the temperature on the capillary +(150-180)oC from its initial value -40oC in cooling mode. Obviously, the duration of fast-acting heater and electric power consumption, component 12-18 watts, uniquely determine the value of the temperature on the capillary.

The temperature of the capillary is determined by the pre-experimental method by replacing the capillary thermocouple type MC or HC with an outer diameter corresponding to the diameter of the inlet of the heater.

Thermoelectric cooler with fast-acting heater chromatograph operates as follows.

The door opens to the working chamber of the chromatograph and installation of frame 11 in the chamber.

The end of the capillary, intended for connection to the supply system of the sample gas chromatographic column, is passed through the through holes of the heater (see cross-section B-B), is mounted and sealed into the appropriate slot on the intake tract of the working chamber.

The current terminals of the heater 23 are installed in the bore of the connector (Fig. not specified), mounted on the two legs 14 of the retainer frame 11.

The window frame 11 is mounted to the housing 5 terminterest cooled recessed matrix 2, the shape and dimensions corresponding to the outside diameter of the heater tube 20).

The capillary and the current terminals of the heater is placed in the groove of a heat insulation 7 of the housing (see Fig., the view from the top) and excreted from the body.

The cover 6 is put on the case. The operator during installation must ensure that the capillary and the current terminals of the heater just got into the groove of the matrix 2. For this purpose, the housing may be coated subtle risks. Connect the power supply to the heater. Thermoelectric cooler with fast-acting heater is ready for operation.

Time of installation of thermoelectric cooler in the working chamber of the chromatograph may be no more than 2-5 minutes

Using a power supply and control mode cooling thermoelectric refrigerator. The time of his exit at the required temperature is within 5-10 minutes of consumed electric power of thermoelectric refrigerator does not exceed 50 watts.

Fan 4 resets heat from the hot junctions of thermopile 1.

The cooled die 2, touching the thin-walled tube 20 from vysokoteploprovodnyh material provides cooling the entire volume Nadu the capillary and the matrix will not exceed 2-3oC.

When thermopile 1 in cooling mode is cryofocusing the sample gas. Immediately after completion of the cooling process (power from thermopile 1) enters the heating mode. The supply voltage of the heater can be selected in such a way that it corresponded to the limiting value of the voltage of thermopile in cooling mode. Thus greatly simplifies the power supply thermoelectric refrigerator.

Heater power is a quantity that is inversely proportional to the heating time of the capillary to a temperature of +(150-180)oC from the initial temperature -40oC. the length of time of heating 5-10 sec the power of the heater is 18-12 W.

As shown by preliminary experimental study of the heater, ceramic tube 19, being a good thermal insulator, it is not possible to heat the outer tube 20 of the heater to temperatures above 50-60oC, although the temperature on a wire helix 21 reaches during operation of the heater 500-600oC.

Introduction to the control unit thermoelectric refrigerator lock system from the secondary of the heater b>Upon completion of the refrigerator cover 6 is removed from the housing 5. From the groove of the matrix 2 is dismantled fast-acting heater with capillary and is released from the cooling body.

The refrigerator case 5 with built-in structural elements is removed from the frame 11, and from the working chamber of the chromatograph.

To conduct further operations of chemical analysis gas chromatograph using complete heating throughout the chromatographic column to a temperature of 120-150oC, but without the participation of thermoelectric cooler.

The working chamber chromatograph closes and turns on its own heating system with built-in camera-in heater and fan.

Fast-acting heater (see Fig. view b-B) with built-in capillary naturally remains inside the working chamber, without being destroyed.

The proposed thermoelectric cooler with fast-acting heater allows to realize the following benefits:

- to obtain a clear and high-quality chromatogram of the sample gas due to the fact that the sublimation of the analyzed pre-cryofocusing gas chromatography is in the chromatograph, using artificial cryofocusing; installation time of thermoelectric refrigerator in the working chamber, as mentioned above, 2-5 minutes

Currently IHPM, Moscow made and passed preliminary tests in the laboratory of analytical chemistry, Moscow state thermoelectric cooler for gas chromatograph (Fig. IHPM 062.00.00).

Successful experimental work on the creation of fast-acting heater for thermoelectric refrigerator and design documentation for a new modification thermoelectric cooler with fast-acting heater (Fig. IHPM 063.00.00).

Sources of information

1. Chromatographic analysis of the environment, Per. s angl., edited by C. G. Berezkin, ed. "Chemistry", M., 1979, S. S. 45-65.

2. K. I. Skodinski in. A. Brazhnikov and other Analytical chromatography", ed. "Chemistry", M., 1993, S. C. 190-200.

3. Anatychuk L. N. thermoelements and thermoelectric devices Handbook, "Naukova Dumka", Kiev, 1979, S. C. 420-436, 453, 456.

Thermoelectric cooler with fast-acting heater chromatograph consisting of a thermopile cooling, coupled with her cooled matrix the user wherein the fast-acting heater is made in the form of a ceramic tube of small diameter, with metallized end belts, onto which the thin-walled tube, elektroshlifovalnaya from belts and is made of vysokoteploprovodnyh material inside the ceramic tube inserted wire spiral; on the ends of the ceramic tube soldered thin conductive caps with a hole, and the hole diameter of the caps and wire spiral exceeds 0.1 - 0.2 mm maximum diameter of the capillary chromatographic column; capillary mounted on a heater mounted on the cooled matrix, and semi-cylindrical recessed groove of the matrix corresponds to the outer diameter thin-walled tubes of the heater; the current terminals of the heater is removed from the refrigerator and attached to the two racks screw clamp frame via quick connectors, the control unit is equipped with two locks from breaking the electric circuit of the heater and turning it back on, and the relay time for 5 - 10 seconds to shut off power of the heater when the temperature on the capillary +(150 - 180)oC.

 

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