ALUMINUM CLAD OBLONG TUBE FOR AIR COOLING SYSTEM
CONDENSING PLANT

BACKGROUND OF THE DISCLOSURE

Field

The teachings in accordance with the exemplary embodiments of this present disclosure generally relate to an aluminum (AL) clad oblong tube for air cooling system condensing plant which is a core element of an air-cooling module applied to a heavy duty power generating plant.

Background

An atomic power plant or a thermoelectric power plant uses fuels such as uranium, kerosene and coal to generate heat, and uses the heat to circulate water in a system and to generate steam. The generated steam turns a turbine to generate electricity, where the turbine-passed steam is cooled by a condenser to become water again.

Particularly, a water-cooling method, in which water is used to cool a condensing process in the steam circulation power generating method, needs a large amount of cooling water, such that sea water is usually used as cooling water in the condenser. Thus, the atomic power plant or the thermoelectric power plant is usually built near seaside to smoothly get supplied with and discharge the sea water that is used as cooling water.

However, the sea water used as cooling water is discharged in a heated state by passing through a cooling system of the power plant. The sea water discharged to the sea from the power plant in the heated state amounts to hundreds of tons per hour. The sea water in the heated state increases temperature of sea water to create various environmental problems such as destructing marine ecosystem, to name a few.
Furthermore, an amount of cooling water to be supplied to steam condenser is absolutely Insufficient in land-locked countries, such that there arises a problem of using a water-cooling condenser as a cooling system.

Recently, in view of the aforementioned problem, power plants using air-cooling condenser have been proposed, and are widely used in up-countries in China and US, for example, where sea water supply is insufficient. Although the power station using air-cooling condenser is disadvantageous in that facilities become bulky over the existing water-cooling condenser, the power station using air-cooling condenser has come into limelight as environment-friendly power generating facilities due to the fact that it can be advantageously installed at an inland area instead of seaside area to provide a relative flexibility in selecting a location for a power plant over a power plant that must use the water-cooling condenser, and can be free from fear of creating a marine pollution caused by temperature rise in sea water resultant from input/output of cooling water.

The air-cooling condenser uses a large number of tubes, where the tube may be categorized into two types based on the shape, that is, an AL (aluminum) clad oblong tube and a MRG (Multi Row Galvanized) tube. The steam condensing tube for power plant has a structure in which an aluminum fin is brazed to both sides of clad tube made of aluminum and steel stacks. An external surface of aluminum in the steam condensing tube for power plant is oxidized after brazing to be denaturalized into aluminite, such that no surface corrosion is generated in the air above a predetermined level.

Furthermore, a borderline between an aluminum fin and aluminum clad material on external surface of the fused clad tube is a coupled tissue of completely fused metal that has an advantageously perpetual heat transfer effect without any corrosion.

The steam condensing tube for power plant must maintain 5~10 times larger cross-section than that of a cylindrical small tube (r*~2") to have a relatively large cross-sectional area, whereby inside air of non-condensable gas can be rapidly removed to allow a rapid initial start operation and to advantageously dispense with an inner freezing of condensing water during winter operation due to larger flow of condensing water than that of a tube with a small cross-section.

Meanwhile, the conventional heat exchange type cylindrical MRG tube is externally attached with cooling pins for increasing heat transfer effect using various methods. The metal fusion method is an electric resistance welding method using same kind metals, which is the closest method for obtaining an intrinsic tube effect by the welded cooling fins. However, the electric resistance welding method is disadvantageous in that each fin is thickened and difficulty arises in arranging a large number of pins in order to allow each of the cooling fins to have an adequate cross-section for electric resistance welding. The disadvantage results in degradation of cooling effect caused by decreased heating surface.

In order to solve the aforementioned disadvantages, the cooling fins may be embedded into the surface of the tube, but the embedment leads to decreased performance of entire facilities due to rapid degradation of heat transfer capability of intrinsic function of the tube caused by generation of galvanic corrosion at the borderline 2~3 months after exposure to air upon start of operation.

The conventional MRG tube has been largely
applied, for domestic and foreign consumption, for heat transfer by air-cooling heat exchange, because the steam condensing tube is poor in pressure-resistance, but high in manufacturing cost over the MRG tube. However, the steam condensing tube is relatively excellent over the MRG tube, because steam condensation is easy if degree of vacuum is high and differential vacuum pressure is applied to an interior of the steam condensing tube.

Since 1990s, the conventional steam condensing tube for power plant developed and used particularly for European countries and US has a high defect rate in brazing process of aluminum pins and clad tubes due to outdated manufacturing method to act as a factor increasing a manufacturing cost of product.

In order to braze the clad tubes and aluminum fins according to the conventional method, steel fixed frames are vertically arranged between which an aluminum fin, a clad tube and an aluminum fin are sequentially arranged, and a portion where the aluminum fin and the clad tube face each other is coated with flux, wrapped with steel wire and inputted into an electric heating furnace. Then, the aluminum fins are depressed inside the high-temperature furnace by self weight of the steel fixing frames to be fused to upper/lower surfaces of the clad tube.
However, if the aluminum fins are partially and excessively heated, and applied with an excessive power, chances are the aluminum fins are fused to the clad tube and to the frame as well. Under these circumstances, a torch is used to separate the aluminum fin from the frame, where the product may be inevitably damaged and no longer unusable.

Furthermore, the clad tube is made of an alloy of carbon steel and aluminum 1050, and the aluminum fin of strip fin is made of aluminum alloy post-processed to allow aluminum 4XXX, which is an Al-Si alloy, to be exposed to a surface of aluminum alloy 3003. At this time, the aluminum 4XXX, a non-heated alloy using silicon (Si) as main additive component, is used as a welding material. The aluminum 4XXX is relatively expensive over aluminum alloy 3003 generally used for construction materials, vehicle materials and various other raw materials.

The reason of using relatively expensive aluminum 4XXX for a strip fin is to form filters in good condition in the course of the aluminum alloy 4343 or 4045 material exposed to the strip fin being brazed inside by heating with clad tube when the clad tube and the strip fin are brazed. However, an actual aluminum 4XXX part forming the filter is only an area where the clad tube and the strip fin are mutually contacted in the entire strip fin, and other areas require no use of aluminum alloy 4343 or 4050, and therefore there is a need to be improved in terms of cost-reduction aspect.

SUMMARY

The present disclosure has been made to solve the foregoing disadvantages of the prior art and therefore an object of certain embodiments of the present disclosure is to provide an aluminum clad oblong tube for air cooling system condensing plant configured to reduce a material cost and to improve a manufacturing process.

Technical subjects to be solved by the present disclosure are not restricted to the above-mentioned description, and any other technical problems not mentioned so far will be clearly appreciated from the following description by the skilled in the art. That is, the present disclosure will be understood more easily and other objects, characteristics, details and advantages thereof will become more apparent in the course of the following explanatory description, which is given, without intending to imply any limitation of the disclosure, with reference to the attached drawings.

An object of the invention is to solve at least one or more of the above problems and/ or disadvantages in whole or in part and to provide at least advantages described hereinafter.

In order to achieve at least the above objects, in whole or in part, and in accordance with the purposes of the disclosure, as embodied and broadly described, and in one general aspect of the present invention, there is provided an aluminum (AL) clad oblong tube for air cooling system condensing plant configured to fix and couple a clad tube and a fin strip member through a brazing process, the aluminum clad oblong tube comprising:

a clad tube formed at both ends with openings to have at least a pair of flat heat transfer units;
a fin strip member configured to emit heat transferred through an interior of the clad tube to air by being accommodated at the pair of heat transfer unit; and a pair of foil members interposed between the clad tube and the fin strip member, wherein the foil member includes an aluminum layer and a flux coating layer formed on a surface facing the clad tube and the fin strip member.

Preferably, but not necessarily, the clad tube may include a first member forming a body, and a second member arranged at an exposure surface of the first member.

Preferably, but not necessarily, the first member may be formed with a carbon steel material, and the second member may be formed with an aluminum material.

Preferably, but not necessarily, the second member may be formed with a pure aluminum having purity of over 99.00%.

Preferably, but not necessarily, the fin strip member may be a non-heated Al-Mn alloy with Mn as a main additive component and having various physical properties through a cooling process.
Preferably, but not necessarily, the fin strip member may be an aluminum alloy 3003 whose Si, Fe, Cu, Mn and Zn contents are respectively 0.6%, 0.7%, 0.05-0.20%, 1.0-1.5% and 0.10%.

Preferably, but not necessarily, the fin strip member may be formed by bending a plate material several times in same size, where a bent surface is brought into contact with the clad tube.

Preferably, but not necessarily, the aluminum layer of Al-Si alloy may be aluminum alloy 4XXX.

Preferably, but not necessarily, the aluminum layer of Al-Si alloy may be an aluminum alloy 4343 whose Si and Cu contents are respectively 10.0% and 4.0%.

Preferably, but not necessarily, the aluminum
layer of Al-Si alloy may be an aluminum alloy 4045 whose Si content is 12.0%.

Preferably, but not necessarily, the aluminum layer of Al-Si alloy may be an aluminum alloy 4154 whose Si content is 9.3-11.9%, whose Cu content is 3.3-4.7% and whose Mn and Cr contents are within 0.15%.

Preferably, but not necessarily, the flux coating layer may be formed by being coated on upper and bottom exposure surfaces of the aluminum layer.

In another general aspect of the present disclosure, there is provided an aluminum (AL) clad oblong tube for air cooling system condensing plant, the aluminum clad oblong tube comprising:

a clad tube configured to have an opening at both ends, and have at least a pair of flat heat transfer units;

a fin strip member accommodated to the pair of heat transfer units to emit the heat transferred through an interior of the clad tube to air; and
a paste coated between the clad tube and the fin strip member, wherein the paste is formed by mixing flux material and aluminum material in a gel state to allow the clad tube and the fin strip member to be fixedly coupled through brazing process.

Preferably, but not necessarily, the clad tube may include a first member forming a body, and a second member arranged at an exposure surface of the first member.

Preferably, but not necessarily, the first member may be formed with a carbon steel material, and the second member may be formed with an aluminum material.

Preferably, but not necessarily, the second member may be formed with a pure aluminum having purity of over 99.00%.

Preferably, but not necessarily, the fin strip member may be a non-heated Al-Mn alloy with Mn as a main additive component and having various physical properties through a cooling process.
Preferably, but not necessarily, the fin strip member may be an aluminum alloy 3003 whose Si, Fe, Cu, Mn and Zn contents are respectively 0.6%, 0.7%, 0.05-0.20%, 1.0-1.5% and 0.10%.

Preferably, but not necessarily, the fin strip member may be formed by bending a plate material several times in same size, where a bent surface is brought into contact with the clad tube.
Preferably, but not necessarily, the aluminum layer of Al-Si alloy may be aluminum alloy 4XXX.
Preferably, but not necessarily, the paste may include an alloy 4045 having contents of aluminum 88% and silicone 12%.

Preferably, but not necessarily, the paste may include an alloy 4047 having contents of aluminum 87%, silicone 12.7% and other elements.
Preferably, but not necessarily, the aluminum layer of Al-Si alloy may be an aluminum alloy 4154 whose Si content is 9.3-11.0%, whose Cu content is 3.3-4.7% and whose Mn and Cr contents are within 0.15%.

Preferably, but not necessarily, the paste may be coated on the heat transfer unit of the clad tube.

Preferably, but not necessarily, the paste may be coated on a surface opposite to the heat transfer unit of the fin strip member.

ADVANTAGEOUS EFFECTS

An exemplary embodiment of the present disclosure thus discussed has an advantageous effect in that material of fin strip member coupled to an aluminum clad tube is formed with aluminum alloy 3003 alone which is a simple forged-roll product, and aluminum alloy 4XXX filler material necessary for brazing is foil member or paste for use only on a local area connected to the clad tube, whereby material cost can be dramatically reduced.

Another advantageous effect is that aluminum alloy 4XXX necessary for brazing of clad tube and fin strip member is formed in a foil shape, interposed between the clad tube and the fin strip member, and brazed in a heating furnace, whereby a separate process of coating flux material can be omitted to reduce the number of work processes.

Still another advantageous effect is that use of flux material can be reduced to decrease discharge of environmentally polluting materials that may be generated in the course of brazing process. That is, KA1F4 + K3A1F6 components in the components forming the flux may emit very hazardous HF (Hydrofluoric acid), because these components may evaporate in a high temperature atmosphere due to reaction (3KA1F4 + 3H20 -+A1203 + K3A1F6 +6HF) with water (H20) existing in the atmosphere and increased steam pressure to maintain molecular states. In other words, the atmosphere is of a high temperature in the entire space to emit the very hazardous HF. However, flux material can be minimally used according to the exemplary embodiment of the present disclosure to reduce generation of pollutant materials.

Still further advantageous effect is that corrosion and/or weathering can be minimized to enhance durability of product, because foil of aluminum alloy 4032 or 4043 material or paste arranged at a connected area between the clad tube and fin strip member forms a protective coated layer of 35 to 50um thickness through the brazing process.

Still further advantageous effect is that the brazing strength may be enhanced, and capillary phenomenon can be advantageously generated to allow even brazing of the entire product, because the filler metal of aluminum alloy 4343 or 4045 material formed in the foil or paste shape is wetted to a strip fin direction in the clad tube to allow the brazing fillet to be formed in a better thicker manner.

Still further advantageous effect is that weight can be lighter by 10% over the post-treatment process of the existing aluminum alloy 3003 material, aluminum alloy 4343 or 4045 material, because the fin strip member can be configured with a simple forged roll product of aluminum alloy 3003 material, whereby structural stability can be obtained for the aluminum (AL) clad oblong tube for air cooling system condensing plant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an aluminum clad oblong tube for air cooling system condensing plant according to a first exemplary embodiment of the present disclosure.

FIG. 2 is an exploded perspective view of FIG. 1.
FIG. 3 is an enlarged cross-sectional view taken on "A" of FIG. 2.

FIG. 4 is an enlarged cross-sectional view taken on "B" of FIG. 2.

FIG. 5 is a schematic perspective view illustrating an aluminum clad oblong tube for air cooling system condensing plant according to an exemplary embodiment of the present disclosure.

FIG. 6 is an exploded perspective view of FIG. 9 according to a first exemplary embodiment of the present disclosure.

FIG. 7 is an enlarged view taken on "C" of FIG.6.

FIG. 8 is an exploded perspective view of FIG. 9 according to a second exemplary embodiment of the present disclosure.

FIG. 9 is an enlarged cross-sectional view taken on "D" of FIG. 8.

DETAILED DESCRIPTION

Now, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present disclosure, certain layers, sizes, shapes, components or features may be exaggerated for clarity and convenience. Accordingly, the meaning of specific terms or words used in the specification and claims should not be limited to the literal or commonly employed sense, but should be construed or may be different in accordance with the intention of a user or an operator and customary usages.

Therefore, the definition of the specific terms or words should be based on the contents across the specification.

FIG. 1 is a perspective view illustrating aluminum clad oblong tube for air cooling system condensing plant according to a first exemplary embodiment of the present disclosure, FIG. 2 is an exploded perspective view of FIG. 1, FIG. 3 is an enlarged cross-sectional view taken on "A" of FIG. 2, and FIG. 4 is an enlarged cross-sectional view taken on "B" of FIG. 2.

Referring to FIGS. 1 and 2, the aluminum clad oblong tube for air cooling system condensing plant according to a first exemplary embodiment of the present disclosure may include a clad tube (10), a fin strip member (20) and a foil member (100).

The clad tube (10) is formed at both ends with openings to have at least a pair of flat heat transfer units. The clad tube (10) is preferably clad by aluminum or carbon steel material for complete fusion with the fin strip member (20) manufactured by using the aluminum material through a brazing work, and may be imultaneously welded with a plurality of heat transfer units along with tube sheets because of excellent weldability. The clad tube (10) is rounded at both ends as illustrated in FIGS. 1 and 2, and may be formed with flat heat transfer units at upper and lower surfaces as in FIGS. 1 and 2.
The heat may be received by the fin strip member (20) side through the flat heat transfer units.

According to the exemplary embodiment of the present disclosure, the clad tube may include a first member (11) and a second member (12) as illustrated in FIG. 3. The first member may be formed with a carbon steel material and the second member may be formed with an aluminum material arranged on an exposure surface of the first member (11).

The aluminum material and aluminum alloy are widely used in the industrial fields such as aerodynamic fields, household containers, industrial vehicles, civil engineering, architecture, ship building, chemical areas and food industries. Although aluminum is excellent in corrosion resistance due to protection of raw material by oxide film under pH4.5~8.5 environments, if the aluminum contacts Fe, Cu or Pb under corrosive environments, the aluminum corrodes to a great extent due to ionization phenomenon.

The aluminum corrodes severely if mercury of a million-to-1 unit is available. A pure aluminum is low in strength, and used for promotion in strength by precipitation hardening along with addition with various elements (Mn, Si, Mg, Cu, Zn, Cr, etc). The aluminum has no magnetism but about four times greater than common carbon steel in terms of heat and electric conductivity. The aluminum is a material low in weldability because of being twice greater than the common carbon steel in terms of coefficient of linear expansion.

According to the exemplary embodiment of the present disclosure, the second member (12) may be formed with a pure aluminum having purity of over 99.00%. Preferably, the second member (12) may be an aluminum alloy 1050 with aluminum purity of over 99.5%. The aluminum 1050 may include Si of 0.25%, Fe of 0.40%, Cu of 0.05%, Mn of 0.05%, Zn of 0.05% and titanium of 0.03%.
The aluminum alloy 1050, being close to pure aluminum, is advantageous in that it is excellent in corrosion-resistance, light reflectivity and heat transferability, and easy in weldability and formability, albeit being low in strength.

The fin strip member (20) may function to perform a cooling fin, and is accommodated to the pair of heat transfer units to emit heat transmitted through an interior of the clad tube (10) to the air. Referring to FIGS. 1 and 2, the fin strip member (20) may be formed by bending a plate material several times in same size to have a corrugated shape, where a bent surface is brought into contact with the heat transfer unit of the clad tube (10).

The fin strip member (20) may be a non-heated Al-Mn alloy with Mn as a main additive component and having various physical properties through a cooling process. Preferably, the fin strip member may be an aluminum alloy 3003 whose Si, Fe, Cu, Mn and Zn contents are respectively 0.6%, 0.7%, 0.05-0.20%, 1.0-1.5% and 0.10%.
The aluminum alloy 3030 is an excellent material in terms of weldability, corrosion-resistance and formability, albeit being high in strength, and is advantageous in that it can be easily manufactured with low cost to a relative degree using section rolling method.

The foil member (100) is interposed between the clad tube (10) and the fin strip member (20). According to an exemplary embodiment of the present disclosure, a pair of fin strip members (20) is installed at each of the pair of the heat transfer units formed on the clad tube (10). Thus, a pair of foil members (100) may be also provided to be interposed between the clad tube (10) and the fin strip member (20).
According to an exemplary embodiment of the present disclosure, the foil member (100) may include an aluminum layer (110) and a flux coating layer (120) and may be accommodated to the heat transfer unit. The aluminum layer (110), being an Al-Si alloy, may be an aluminum alloy 4032 whose Si, Fe, Cu, Mg, Zn and Cr contents are respectively 11.0-13.5%, 1.0%, 0.05-1.3%, 0.8-1.3%, 0.25% and 0.10%. Furthermore, the aluminum layer (110), being an Al-Si alloy, may be an aluminum alloy 4043 whose Si, Fe, Cu, Mn, Mg, Zn and Ti contents are respectively 4.5-6.0%, 0.8%, 0.05%, 0.05%, 0.10%, 0.25% and 0.20%.
The flux coating layer (120) may be coated on upper and bottom exposure surfaces of the aluminum layer (110), and may contact a heat transfer surface of the clad tube (10) and a bent surface of the fm strip member (20) respectively. Thus, the flux coating layer (120) may substitute a catalyst function of the brazing process performed by the conventional flux if the brazing process is adopted.
The brazing is a two base metal-bonding technique in which two base metals are bonded or joined by applying heat to filler metal without hurting the base metals at a temperature below a melting point of the base metal to be bonded at a temperature above 450°C. That is, the brazing is a technique of bonding two base metals by applying heat below a solidus temperature of the base metal using a filler metal having a liquidus temperature above 450°C.

The ideal brazing may be preferably to maintain an optimum temperature under which the brazing filler metal can be melted and permeated between two base metals, which are subjects to be bonded, and to add other various environmental characteristics thereto.

At this time, a physical property indicating the degree of affinity between the two base metals and the filler metal may be expressed by wetting, and a phenomenon in which the filler metal flows into a joint gap between the two base metals may be expressed as capillary action. At this time, it should be apparent that force of gravity works. However, the basic principle of brazing is that the filler metal flows into two base metals by capillary action according to wetting, when base metals are heated, added by the filler metal and the two base metals are bonded or joined. If wetting of the metal filler with the to-be-brazed base metals is bad, bonding or joint is not realized, and if a joint gap is large, the metal filler may not be completely filled between two base metals to create an incomplete bond.
In general, a liquidus metal may be difficult to be wetted, when the base metals are left unattended in the air for a long time during brazing, or become in inactive state by being bonded with oxygen in the air to generate an oxide during heating process. Thus, the generation of oxide must be restrained to enable the metal filler to be wetted by using flux during brazing or heating the metal filler in a reducing atmosphere or in a vacuum atmosphere. Furthermore, when the wetting is finished, the metal filler must well flow into a joint gap between the two base metals according to correct capillary action. Particularly, the capillary action has a bearing on accuracy of processed product to be brazed. That is, when a product is not ideally designed for brazing, it may be a cause for deteriorated workability, increased cost and increased defect rates. That is, the gravity is naturally generated during brazing, and therefore, products must be installed and assembled in consideration of gravity. The capillary action and the gravity have a great influence on flow of metal filler, and the wetting has a great bearing on the affinity of metal filler.

Particularly, when the metal filler is wet, the degree of wetting may be a criterion for determining affinity with base metals, and for determining whether the flux material or atmosphere works properly. In order to explain the wetting thus discussed, it is assumed that a liquidus drop is fallen on a flat solid state surface. At this time, it is also assumed that gravity is disregarded, and chemical reactions of solid phase, liquid phase and gaseous phase are disregarded. The wetting may be expressed by the following equation[Equation 1 ]
cose where, ySL is a surface tension of solid phase (of base metal), ySU is a surface tension of liquid phase (metal filler) and yLV is a surface tension at interface of solid phase. 6 is contact angle.

A border between occurrence of non-occurrence of wetting may be an angle of 90°. That is, it can be assumed that if the angle is less than 90°, the wetting has occurred, and if the angle is over 90°, wetting has not occurred. In general, the 0 angle is largely in between 10°to 40°during brazing, and is generally determined by a joint gap between base metals during brazing.
Furthermore, the capillary action is a very important physical phenomenon in the brazing process. Metal filler fluidity depends on force by capillary action phenomenon, viscosity, density of fusing metal and position relative to gravity of joined surface and the like. In general, viscosity that restrains the flow of metal filler has a correlation with temperatures. Here, it can be noted that an increased temperature has an influence on the viscosity.

That is, it may be said that increased temperature increases the fluidity of metal filler. At any rate, the capillary action is an important physical force during brazing as mentioned before, and has a close relationship with the joint gap, as explained before, and is also a close correlation with the types of metal fillers, viscosity, density, position relative to gravity of joined surface and heating method.

According to the exemplary embodiment thus discussed, material of fin strip member (20) joined with the aluminum clad tube (10) is formed only with aluminum alloy 3003 which is a commonly and widely used-forged roll aluminum product, and aluminum alloy 4XXX metal filler necessary for brazing is formed with foil member (100), which are only used for a local area connected to the clad tube (10), whereby used amount of relatively high-priced aluminum alloy 4XXX material can be greatly reduced to dramatically reduce the material cost.

Particularly, the aluminum alloy 4XXX material necessary for brazing of clad tube (10) and the fin strip member (20) is formed in a thin foil shape, and brazed in a heating furnace only by a process of being interposed between the clad tube (10) and the fin strip member (20), whereby a process of coating separate flux material can be omitted to reduce the number of work processes.

Furthermore, due to no separate use of flux material, discharge of environment-polluting materials generated in the brazing process can be greatly reduced. KA1F4 + K3A1F6 components among components forming the flux have a high vapor pressure to maintain molecular states by evaporating in a high temperature atmosphere, and react with moisture(H20) existing in the atmosphere(3KAlF4 + 3H20 -> A1203 + K3A1F6 + 6HF) to emit very hazardous fluoric gas (HF). This is because the entire atmosphere inside the heating furnace is in a high temperature state, and the flux reacts under the high temperature to emit a hazardous gas (HF). However, the use of flux material can be reduced to minimize the discharge of hazardous material according to the exemplary embodiment of the present disclosure,
Furthermore, the foil member (100) of aluminum alloy 4343 or 4045 arranged at a connected area in between the clad tube (10) and the fin strip member (20) forms a protective coating layer of 35 to 50/zm thickness to allow minimizing the corrosion and weathering during operation of an aluminum (AL) clad oblong tube for air cooling system condensing plant, whereby product durability can be enhanced.

In addition, because an aluminum layer (110) formed with aluminum alloy 4032 or 4043 material of foil member (100) is used for filler metal and wetted to a strip fin direction from the clad tube (10), a brazing fillet comes to be formed with thicker and better thickness over the prior art to enhance the brazing strength, whereby the capillary action is developed better to allow an even brazing for entire products.
Furthermore, material of fin strip member (20) is formed with aluminum alloy 3003 of forged roll aluminum product to enable making lighter by 10% than the conventional post-process of aluminum alloy 3003, 4343 or 4045 material, whereby structural stability of an aluminum (AL) clad oblong tube for air cooling system condensing plant can be secured.

FIG. 5 is a schematic perspective view illustrating an aluminum clad oblong tube for air cooling system condensing plant according to an exemplary embodiment of the present disclosure, FIG. 6 is an exploded perspective view of FIG. 9 according to a first exemplary embodiment of the present disclosure, FIG. 7 is an enlarged view taken on "C" of FIG. 6, FIG. 8 is an exploded perspective view of FIG. 9 according to a second exemplary embodiment of the present disclosure, and FIG. 9 is an enlarged cross-sectional view taken on "D" of FIG. 8.

Referring to FIGS. 5 and 6, the aluminum (AL) clad oblong tube for air cooling system condensing plant may include a clad tube (10), a fin strip member (20) and a paste (200).
The structure of clad tube (10) and fin strip member (20) is same as that of the first exemplary embodiment such that no further elaboration will be made thereto.

The paste (200) is interposed between the clad tube (10) and the fin strip member (20). The clad tube (10) may be formed with a pair of heat transfer units, to which a pair of fin strip member (20) may be installed. Thus, the paste (200) may be coated on surfaces each facing the clad tube (10) and the fin strip member (20).
Referring to FIGS. 6 and 7, the paste (200) according to the second exemplary embodiment of the present disclosure may be coated on heat transfer surfaces of clad tube (10), and referring to FIGS. 8 and 9, the paste (200) according to the third exemplary embodiment may be coated on bent surfaces of the fin strip member (20). Although not illustrated, all the heat transfer surfaces and the bent surfaces may be coated with the paste.

The paste (200) may be formed in a gel state mixed with brazing filler material of aluminum material, flux material and binder. The aluminum material is an Al-Si alloy which may include an alloy 4045 having contents of aluminum 88% and silicone 12%, or an alloy 4047 having contents comprised of aluminum 87%, silicone 12.7% and other elements.

The flux material may be evenly distributed by being mixed with the aluminum material at a predetermined ratio when the paste (200) contacts the heat transfer surfaces of the clad tube (20) and the fin strip member (20). Thus, the flux material may substitute the catalyst function of the conventional flux during the brazing process.

According to the exemplary embodiment thus discussed, material of fin strip member (20) joined with the aluminum clad tube (10) is formed only with aluminum alloy 3003 which is a commonly and widely used-forged roll aluminum product, and aluminum alloy 4XXX metal filler necessary for brazing is formed with the paste (200), which are only used for a local area connected to the clad tube (10), whereby used amount of relatively high-priced aluminum alloy 4XXX material can be greatly reduced to dramatically reduce the material cost.

Furthermore, because the paste (200) is used by mixing the aluminum material with flux material, the used amount of flux material can be reduced over the brazing process of coating with the flux material alone, discharge of environment-polluting materials generated in the brazing process can be greatly reduced. KA1F4 + K3A1F6 components among components forming the flux have a high vapor pressure to maintain molecular states by evaporating in a high temperature atmosphere, and react with moisture(H20) existing in the atmosphere(3KAlF4 + 3H20 -► A1203 + K3A1F6 + 6HF) to emit very hazardous fluoric gas (HF). This is because the entire atmosphere inside the heating furnace is in a high temperature state, and the flux reacts under the high temperature to emit a hazardous gas (HF). However, the use of flux material can be reduced to minimize the discharge of hazardous material according to the exemplary embodiment of the present disclosure,
Furthermore, the paste (200) of aluminum alloy 4045 or 4047 coated at a connected area in between the clad tube (10) and the fin strip member (20) forms a protective
coating layer of 35 to 50/zm thickness through the brazing process to allow minimizing the corrosion and weathering during operation of an aluminum (AL) clad oblong tube for air cooling system condensing plant, whereby product durability can be enhanced.

In addition, because the aluminum material formed with aluminum alloy 4045 or 4047 material of paste (200) is used for filler metal and wetted to a strip fin direction from the clad tube (10), a brazing fillet comes to be formed with thicker and better thickness over the prior art to enhance the brazing strength, whereby the capillary action is developed better to allow an even brazing for entire products.

Furthermore, material of fin strip member (20) is formed with aluminum alloy 3003 of forged roll aluminum product to enable making lighter by 10% than the conventional post-process of aluminum alloy 3003, 4345 or 4047 material, whereby structural stability of an aluminum (AL) clad oblong tube for air cooling system condensing plant can be secured.

Although the present disclosure has been described in detail with reference to the foregoing embodiments and advantages, many alternatives, modifications, and variations will be apparent to those skilled in the art within the metes and bounds of the claims. Therefore, it should be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within the scope as defined in the appended claims

WHAT IS CLAIMED IS:

1. An aluminum (AL) clad oblong tube for air cooling system condensing plant
configured to fix and couple a clad tube and a fin strip member through a brazing
process, the aluminum clad oblong tube comprising:

a clad tube formed at both ends with openings to have at least a pair of flat heat transfer units;
a fin strip member configured to emit heat transferred through an interior of the clad tube to air by being accommodated at the pair of heat transfer unit; and a pair of foil members interposed between the clad tube and the fin strip member, wherein the foil member includes an aluminum layer and a flux coating layer formed on a surface facing the clad tube and the fin strip member.

2. The aluminum clad oblong tube of claim 1, wherein the clad tube includes a first member forming a body, and a second member arranged at an exposure surface of the first member.

3. The aluminum clad oblong tube of claim 2, wherein the first member is formed with a carbon steel material and the second member is formed with an aluminum material.

4. The aluminum clad oblong tube of claim 3, wherein the second member is formed with a pure aluminum having purity of over 99.00%.

5. The aluminum clad oblong tube of claim 1, wherein the fin strip member is a non-heated Al-Mn alloy with Mn as a main additive component and having various physical properties through a cooling process.

6. The aluminum clad oblong tube of claim 5, wherein the fin strip member is an aluminum alloy 3003 whose Si, Fe, Cu, Mn and Zn contents are respectively 0.6%, 0.7%, 0.05-0.20%, 1.0-1.5% and 0.10%.

7. The aluminum clad oblong tube of claim 1, wherein the fin strip member is
formed by bending a plate material several times in same size, where a bent surface is
brought into contact with the clad tube.

8. The aluminum clad oblong tube of claim 1, wherein the aluminum layer of Al-Si
alloy is aluminum alloy 4XXX.

9. The aluminum clad oblong tube of claim 1, wherein the aluminum layer of Al-Si alloy is an aluminum alloy 4343 whose Si and Cu contents are respectively 10.0% and 4.0%.

10. The aluminum clad oblong tube of claim 1, wherein the aluminum layer of Al-Si alloy is an aluminum alloy 4045 whose Si content is 12.0%.

11. The aluminum clad oblong tube of claim 1, wherein the aluminum layer of Al-Si alloy is an aluminum alloy 4154 whose Si content is 9.3-11.9%, whose Cu content is 3.3-4.7% and whose Mn and Cr contents are within 0.15%.

12. The aluminum clad oblong tube of claim 1, wherein the flux coating layer is formed by being coated on upper and bottom exposure surfaces of the aluminum layer.

13. An aluminum (AL) clad oblong tube for air cooling system condensing plant, the aluminum clad oblong tube comprising:
a clad tube configured to have an opening at both ends, and have at least a pair of flat heat transfer units;

a fin strip member accommodated to the pair of heat transfer units to emit the heat transferred through an interior of the clad tube to air; and
a paste coated between the clad tube and the fin strip member, wherein the paste is formed by mixing flux material and aluminum material in a gel state to allow the clad tube and the fin strip member to be fixedly coupled through brazing process.

14. The aluminum clad oblong tube of claim

13, wherein the clad tube includes a first
member forming a body, and a second member arranged at an exposure surface of the first member.

15. The aluminum clad oblong tube of claim 14, wherein the first member is formed with a carbon steel material and the second member is formed with an aluminum material.

16. The aluminum clad oblong tube of claim 15, wherein the second member is formed with a pure aluminum having purity of over 99.00%.

17. The aluminum clad oblong tube of claim 13, wherein the fin strip member is a non-heated Al-Mn alloy with Mn as a main additive component and having various physical properties through a cooling process.

18. The aluminum clad oblong tube of claim 17, wherein the fin strip member is an aluminum alloy 3003 whose Si, Fe, Cu, Mn and Zn contents are respectively 0.6%, 0.7%, 0.05-0.20%, 1.0-1.5% and 0.10%.

19. The aluminum clad oblong tube of claim 13, wherein the fin strip member is formed by bending a plate material several times in same size, where a bent surface is brought into contact with the clad tube.

20. The aluminum clad oblong tube of claim 13, wherein the aluminum layer of Al-Si alloy is aluminum alloy 4XXX.

21. The aluminum clad oblong tube of claim

13, wherein the paste includes an alloy 4045 having contents of aluminum 88% and silicone 12%.

22. The aluminum clad oblong tube of claim 13, wherein the paste includes an alloy 4047 having contents of aluminum 87%, silicone 12.7% and other elements.

23. The aluminum clad oblong tube of claim 13, wherein the aluminum layer of Al-Si alloy is an aluminum alloy 4154 whose Si content is 9.3-11.0%, whose Cu content is 3.3-4.7% and whose Mn and Cr contents are within 0.15%.

24. The aluminum clad oblong tube of claim 13, wherein the paste is coated on the heat transfer unit of the clad tube.

25. The aluminum clad oblong tube of claim 13, wherein the paste is coated on a surface opposite to the heat transfer unit of the fin strip member.