RU2577502C1 - Bimetallic gravitational heat pipe - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: invention relates to heat-transfer devices, namely to gravitational heat tubes intended mainly for use in cooling soil. Gravitational heat pipe has sealed housing 2 with zones of evaporation, transport zone 3 and condensation zone 4. Housing made with possibility of filling with liquid heat carrier is represented by top and bottom steel cylindrical tube 1, which in condensation zone 4 is enclosed in tube 5 from aluminium alloy with ribs 6. Feature of the gravity-assisted heat pipe is the fact that steel cylindrical pipe 1 is produced by hot galvanizing coating layer 11 on the outer and inner surface 13, and that in zone of condensation 4 tightly contacts with inner surface of tube 5 by its outer surface through layer 11.

EFFECT: technical result consists in preventing blocking of the upper part of the condensation zone uncondensed gases and eliminating factors deteriorating thermal contact between steel cylindrical tube 1 in condensation zone and aluminium ribs 6, as well as in reduction of increase of the effect of these negative factors in time.

1 cl, 2 dwg

Description

The invention relates to heat engineering, and more specifically to heat transfer devices, namely, gravitational heat pipes, mainly intended for use in cooling the soil in order to strengthen the foundations and foundations of various structures, supports of pipelines and power lines, embankments of roads and railways, etc., constructed on permafrost soils and in areas with deep seasonal freezing.

Known structural diagram of the gravitational heat pipe, which is a sealed filled with coolant tubular body with zones of evaporation, condensation and transport zone. In such a heat pipe, the steam moves upward due to the pressure difference between the saturated steam in the zones of evaporation and condensation, and the reverse movement of the liquid is carried out under the influence of gravity (Polytechnical Dictionary. M., "Soviet Encyclopedia", 1989, S. 524 [1] ) Such a heat pipe transfers heat absorbed by the heat carrier and is given to it during condensation in an external medium that is in direct contact with the outer surface of the pipe in the condensation zone. The advantage of a gravitational heat pipe is the ability to function without energy supply under the influence of only environmental factors, such as gravity, temperature and air velocity, radiation of natural and man-made objects.

To ensure more intense heat transfer, the body of the gravitational heat pipe in the condensation zone is usually equipped with a fin, which together with the part of the pipe body on which it is placed, has a radiator (see, for example, RF patents No. 2349852, publ. March 20, 2009 [2]; No. 2384672, published on March 20, 2010 [3]; No. 2384671, published on March 20, 2010 [4]).

It is advisable to carry out the fins from a material with a higher thermal conductivity than that of the pipe body material. The most common combination of materials is that the body of the gravitational heat pipe is made of steel and the fins in the condensation zone are made of aluminum alloy (A. Abrosimov, S. Zaletaev. Soil coolers. Designs and calculation methods. Ed. Palmarium Academic Publishing, 2012, p. . 20, 44 [5]).

The heat transfer capacity of a gravitational heat pipe is largely determined by the heat transfer efficiency in the condensation zone, which can be negatively affected by a number of interrelated factors. First of all, as the experience of operating gravitational heat pipes shows, the upper part of the radiator fins may remain unheated during the operation of the pipe, i.e. actually does not participate in the performance of its function of cooling the condensation zone. This can be explained by the fact that non-condensable gases are inevitably present inside the pipe due to non-ideal evacuation before filling with coolant. The residues of nitrogen and water vapor present in the atmospheric air, being lighter than the majority of coolant vapors, accumulate in the upper part of the pipe and block the access of the coolant vapor to the pipe wall, which results in blocking the condensation zone for part of its length, which turns off the corresponding part finned radiator. However, experience also shows that a further improvement in the quality of evacuation of the pipe before filling with coolant, being technically complex and expensive, practically does not eliminate the described reason for the decrease in the efficiency of the pipe. The authors found that these light non-condensable gases are mainly released from the inner surface of the pipe wall along its entire length in all three zones. This surface in the real conditions of production and storage of the workpiece of the future gravitational heat pipe is corroded and therefore has a very developed surface adsorbing these gases from the air. During operation of the pipe, these gases are desorbed into the inner space of the pipe, which leads to the phenomenon noted above, almost independently of the quality of evacuation before filling with coolant, and the degree of blocking of the upper part of the condensation zone can increase gradually as desorption occurs.

Corrosion of the surface of the pipe affects the efficiency of heat transfer through the fin fin and other ways. In accordance with a common method for producing a bimetallic radiator, an aluminum pipe is put on a steel pipe, then aluminum is pressed onto the steel with rollers on the roller stand, while deforming aluminum to form ribs. The uneven distribution of the efforts of pressing aluminum to steel causes the appearance of local delamination caused by axial runout of the elements of the roller stand, such as the eccentricity of the steel pipe and rollers relative to the axis of the stand. Flaking, in turn, leads to an increase in contact thermal resistance between the pipe body in the condensation zone and its fins and can negate the advantages given by the bimetallic design of the radiator of the condensation zone.

In addition, in extreme climatic conditions of operation of a bimetallic gravitational heat pipe at high humidity, electrochemical corrosion develops at the contact point of steel and aluminum, since the steel-aluminum contact pair has a relatively large electric potential. Corrosion destroys the surface layers of the wall of the steel casing at the contact point, which leads to an increase in contact thermal resistance and to a deterioration in the heat transfer characteristics of the pipe, leveling the advantages of the bimetallic structure, and this deterioration increases with time.

The bimetallic structure known from the book [5], in which the steel cylindrical body in the condensation zone has aluminum alloy fins, is closest to the proposed gravitational heat pipe.

The present invention is aimed at increasing the heat transfer capacity of a gravitational heat pipe by simultaneously overcoming all of the above factors that reduce the heat transfer efficiency in the condensation zone through a finned radiator, namely, to eliminate blocking of the upper part of the condensation zone and to reduce thermal resistance between the steel pipe body and the finned radiator, as well as weakening the growth of the influence of these factors over time.

Below, when revealing particular cases of the implementation of the proposed gravitational heat pipe, other types of technical result can be mentioned, which are ultimately associated with an increase in the heat transfer ability of the heat pipe and its durability while maintaining performance indicators.

The proposed gravitational heat pipe, like the specified closest known pipe [5], has a sealed housing with evaporation zones, a transport zone and a condensation zone, made with the possibility of filling with a liquid coolant and made in the form of a steel cylindrical pipe that is muffled from above and below, which in the condensation zone it is enclosed in a finned tube made of aluminum alloy.

To achieve the above technical result in the proposed gravitational heat pipe, in contrast to the closest known pipe, said steel cylindrical pipe has a coating layer obtained by hot-dip galvanizing on its entire inner and outer surface. Moreover, it tightly contacts through the specified layer with its outer surface in the condensation zone with the inner surface of the specified finned aluminum alloy pipe.

Due to the presence of a zinc coating layer obtained by hot galvanizing on the inner surface of a steel cylindrical pipe, the desorption of non-condensable gases into the inner space of the body of the gravitational heat pipe is prevented during its operation. As a result, the amount of these gases is limited to that which occurred as a result of evacuation before filling the pipe with coolant and remains stable over time.

Due to the presence of the zinc coating layer obtained by hot-dip galvanizing on the outer surface of the steel cylindrical pipe, there is no void between this surface and the inner surface of the aluminum finned tube, the formation of which, possible during knurling during the manufacture of the gravitational heat pipe, could lead to an increase in contact thermal resistance between the steel cylindrical body and aluminum finned tube. At the same time, the presence of this layer reduces the contact electric potential (since the steel-aluminum contact pair is replaced by the steel-zinc pair) and thereby contributes to the suppression of electrochemical corrosion in the proposed design, and due to the reduction of corrosion, prevents the said contact thermal resistance from changing over time, namely, its increase during operation of the pipe.

It should be noted that the above-described mechanism of action of the specified hot-dip galvanized layer on both surfaces of a steel cylindrical pipe does not consist in traditional corrosion protection, since the conditions for the manufacture and storage of a workpiece of a cylindrical body of a gravitational heat pipe are such that its surface is already corroded before galvanizing .

The protection implemented by the traditional method against further corrosion of the entire surface of the cylindrical body of the gravitational heat pipe, including the outer surface located in more unfavorable conditions, is an indirect consequence of the described measures taken to increase the heat transfer properties of the gravitational heat pipe by increasing the efficiency of its condenser.

It should also be noted that all these effects in the implementation of the invention with the implementation of the characteristic characterizing the presence of a layer of zinc coating obtained by hot galvanizing, are inseparable from each other and appear together. Moreover, the implementation of any of these effects separately without the simultaneous receipt of others would require very serious additional costs and overcome specific technological difficulties. This is because hot dip galvanizing of the entire pipe (its inner and outer surfaces) is technologically simpler than galvanizing only one of these surfaces, and even more easier than galvanizing only part of the outer surface related to the condensation zone. But it would be especially difficult to galvanize only the inner surface.

At the same time, the presence of a zinc coating layer obtained by hot-dip galvanizing provides not only well-known corrosion protection per se (which is not so intense inside the pipe as outside), but also weakening the previously unknown and discovered by the authors mechanisms for reducing the heat transfer ability specific to gravitational heat pipes, including those manifested in harsh operating conditions specific to them.

The proposed gravitational heat pipe is illustrated by drawings, which schematically show:

- in FIG. 1 - gravitational heat pipe installed in the soil cooled by it;

- in FIG. 2 - condensation zone on an enlarged scale in the presence of a coating layer obtained by hot-dip galvanizing of the outer and inner surfaces of the steel cylindrical pipe of the casing and on an even larger scale - a fragment of galvanized steel cylindrical pipe of the casing with aluminum fins.

Gravity heat pipe (Fig. 1) has a sealed enclosure with evaporation zones 2, transport zone 3 and condensation zone 4. The housing is made with the possibility of filling with a coolant fluid through a fitting with an adapter not shown in the drawing and is made in the form of a steel cylindrical pipe 1 plugged from above and below. In the condensation zone 4, a steel cylindrical pipe 1 is enclosed in an aluminum alloy pipe 5 having a fin 6, which, together with the aluminum pipe itself and part of the pipe 1, acts as a radiator in the condensation zone. As the aluminum alloy can be used, for example, alloys AD-0, AD-1. The steel cylindrical pipe 1 contacts its outer surface with the inner surface of the aluminum pipe 5 through the indistinguishable drawing scale of FIG. 1 coat of hot dip galvanized coating. As a material for the manufacture of a cylindrical pipe 1 can be used, for example, steel grade St. 20, which forms the best pairs with the specified aluminum alloys.

Obtained by hot galvanizing, the coating layer of the surface of the steel cylindrical pipe 1 is present on its entire outer and inner surface in all three zones 2-4. Said layer (keys 11 and 13) is shown in FIG. 2, representing an image of only the transport zone 4. As in FIG. 1 at 5 in FIG. Figure 2 shows an aluminum alloy pipe, and position 6 shows the finning of this pipe. At the bottom of FIG. 2 shows, on an enlarged scale, a fragment 100 of the upper part of this figure. This fragment covers part of the wall of the steel cylindrical pipe 1, part of the layer 11 obtained by hot-dip galvanizing the coating on the outer surface of the pipe 1, part of the layer 13 obtained by hot-galvanized coating on the inner surface of the pipe 1 and part of the pipe 5 is made of aluminum alloy with ribs 6. It can be seen that in the case shown in the drawing, in separate places (position 12), the deformed surface of the pipe 5 can contact directly with the surface of the steel cylindrical pipe 1, and in other places through the zinc material roof 11. In the absence of such a coating, position 11 at the bottom of FIG. 2 and other similar drawing elements would correspond to voids that increase contact thermal resistance.

In the manufacture of the proposed gravity pipe, the cylindrical steel pipe 1 is subjected to hot galvanizing by immersion of molten zinc in a bath. The coating thickness is 80 ÷ 150 microns. After that, an aluminum pipe 5 of the required length is put on a galvanized steel pipe and rolled out with rollers to form a bimetallic capacitor with a radiator.

As can be seen from the above brief description of the process of obtaining a zinc coating, the most technologically advanced version of the design, providing for the presence of hot-dip galvanized coating of a steel cylindrical pipe 1 simultaneously over all three zones and on both sides on the outer and inner surfaces. Such a coating is easier to obtain than just for the part of the pipe corresponding to the condensation zone, or only for its outer surface; it is all the more difficult to obtain a coating of only the inner surface.

The presence of a layer of zinc coating on the inner surface of the pipe prevents desorption into the working space of the pipes of light non-condensable gases, the accumulation of which in the upper part of this space could make it impossible for the evaporated coolant to contact the pipe wall 1 in the condensation zone 4 and thereby block the transfer of heat from the coolant to the top parts of a finned radiator.

Due to the presence of a zinc coating on a part of the outer surface of the steel cylindrical pipe 1 corresponding to the condensation zone 4, good thermal contact of this surface with the inner surface of the pipe 5 made of aluminum alloy is ensured in this zone. This is due to the fact that during the compression process during the manufacture of the radiator of the gravitational heat pipe, the zinc coating material fills the shallow cavities present on the steel billet of the cylindrical pipe 1 and voids between these surfaces are eliminated, which could increase the thermal resistance (see the text related to positions 11 and 13 on the lower part of Fig. 2). At the same time, the electrochemical properties of the interaction of metals in contact with each other change. The consequence of this is a decrease in the intensity of corrosion of the steel cylindrical pipe 1 and the occurrence during operation of the gravitational heat pipe, which is usually generated by corrosion of voids between the contacting surfaces, which could increase the contact thermal resistance, is prevented. As a result, the heat transfer properties of the gravitational heat pipe become more stable over time, which is especially important when operating in harsh environmental conditions, especially for pipes immersed in the ground to protect railway embankments, foundations of structures, power transmission towers, etc.

It should be noted that some technical techniques are known that relate to radiators of heat engineering devices, the use of which as applied to the radiator of a gravitational heat pipe could help increase its heat transfer ability. In particular, in the patent of the Russian Federation No. 2450880, publ. 05/20/2012 [6], it is proposed to change the rolling technology with the use of specialized equipment, providing, ultimately, a more tight contact of the surfaces of steel and aluminum pipes. However, this way, associated with the complication of the technological process for manufacturing the finned condensation zone, does not eliminate the already noted drawback of the traditional bimetallic design associated with electrochemical corrosion in the steel-aluminum contact pair. In the author's certificate of the USSR No. 434252, publ. 06/30/1974 [7], a radiator design with a lead insert between steel and aluminum pipes is proposed, and in USSR author's certificate No. 460918, publ. 02/25/19751974 [8], - cladding of a steel pipe before putting aluminum, lead, tin or zinc on it. The mentioned technical solutions [6] - [8], being more difficult to implement, are at the same time aimed only at a partial solution to the problem of increasing the heat transfer capacity of the pipe - by improving the thermal contact of the steel pipe with an aluminum radiator. However, they do not affect the specific task of gravitational heat pipes to prevent the phenomenon of blocking the condensation zone by non-condensing gases. The present invention solves this problem, i.e. is a complete solution.

From the point of view of the principle of action, the proposed gravitational heat pipe does not differ from the closest known pipe to it [5]. When used for cooling the soil, the pipe body is installed so that the transport zone 3 is above the surface of the soil 10 (Fig. 1). The pipe body is filled with liquid coolant. The volume of filling is determined so as to prevent the condensate stream 7 from drying out, droplets 8 of which move along the wall of the steel cylindrical pipe 1 to the lower part, where there should always be a slight excess of condensate 9. The return of condensate from the condensation zone 4, where the heat Q is removed, to the evaporation zone 2, where the heat Q is supplied to the pipe, occurs through the transport zone 3 under the action of gravity in the oncoming steam flow. In this case, the condensate stream occupies a small part of the cross section of the steel cylindrical pipe 1 of the body of the gravitational heat pipe. Therefore, the steam flow passes almost unhindered from the evaporation zone 2 to the condensation zone 4 through the transport zone 3.

Such a hydrodynamic picture determines both the low inertia of the soil freezing process and the easy (according to the required temperature difference) start-up of the gravitational heat pipe.

The circulating vapor-liquid coolant flow transfers heat from the soil 10 to the condensation zone 4, where it is transmitted by convection to the surrounding air and radiation to the surrounding space through the fins 6 of the radiator. During the described process, the soil around the heat supply zone of the cooler is frozen.

Information sources

1. Polytechnical dictionary. M .: "Soviet Encyclopedia", 1989, p. 524.

2. RF patent No. 2349852, publ. 03/20/2009.

3. RF patent No. 2384672, publ. 03/20/2010.

4. RF patent No. 2384671, publ. 03/20/2010.

5. A. Abrosimov, S. Zaletaev. Soil coolers. Designs and calculation methods. Ed. Palmarium Academic Publishing, 2012, p. 20, 44.

6. RF patent No. 2450880, publ. 05/20/2012.

7. Copyright certificate of the USSR No. 434252, publ. 06/30/1974.

8. Copyright certificate of the USSR No. 460918, publ. 02/25/1975.

Claims (1)

Gravity heat pipe having a sealed housing with evaporation zones, a transport zone and a condensation zone, made with the possibility of filling with a heat-transfer fluid and made in the form of a steel cylindrical pipe muffled from above and below, which is enclosed in an aluminum alloy finned tube in the condensation zone, characterized in that said steel cylindrical pipe has a coating layer obtained by hot-dip galvanizing on its entire inner and entire outer surface, through which the latter in the conde zone sation in close contact with the inner surface of said finned tube of aluminum alloy.

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