KR19980070239A - Tube for heat exchanger - Google Patents

Abstract

In a tube having a concave portion formed by a bead, a groove, or the like on the upper and lower surfaces of a tube, a tube for a heat exchanger capable of improving the corrosion resistance of the tube and extending the life of the heat exchanger is provided.

In a tube for a heat exchanger formed by bending one plate or by overlapping two plates, the tube 2 is formed with a plurality of beads 11A, 11B having a concave shape in cross section. The top portion is joined to the opposing plate to form a plurality of dividing flow paths inside the tube, and the beads located at least on the uppermost side of the air flow among the beads 11A and 11B protrude upward from the bottom of the tube. Heat exchanger tube

Description

Tube for heat exchanger

The present invention relates to a flat tube for a heat exchanger provided with a convex portion on an outer surface of a tube by a bead, etc., which forms a plurality of flow paths inside the tube. It is an improvement.

In general, a multilayer heat exchanger is constructed in which a plurality of flat tubes are stacked in parallel so that both ends of each flat tube are connected to two header pipes, and an outlet joint for supplying and supplying a heat exchange medium to a predetermined portion of the header pipe is provided. Known. In such a heat exchanger, the heat exchange medium blown into the heat exchanger exchanges heat with external circulation air while passing through the flat tube, and is circulated through the header pipe a plurality of times and discharged.

For example, as shown in the cross-sectional shape of FIG. 8, a flat tube used in such a laminated heat exchanger is formed of a single brazing sheet formed in a predetermined elongated board shape into a flat tube shape, and the tip portion in the plate width direction is formed. The flat tube 20 is comprised by soldering together. In the figure, 20a and 20b show planar joints provided at the tip end of the plate width direction, and the joint areas 20a and 20b enlarge the joint area to ensure sufficient solder joint strength.

In addition, recently, the flat tube 20 has been promoted to reduce the thickness of the tube in order to reduce the amount of use of the material even a little to reduce the cost, or to achieve high heat exchange efficiency or light weight. In addition, the thinned flat tube 20 is provided with a plurality of beads 21 (21A, 21B) integrally to ensure structural strength.

That is, a plurality of beads 21A, 21B protruding integrally formed at a predetermined position in the width direction of the flat tube 20 at a height in contact with the inner surface of the tube opposite to the front end of the tube along the tube length direction are formed. These beads 21A and 21B form a plurality of media flow paths 22 and 22 in the tube tube to increase the contact area with the media to increase the heat exchange efficiency and to reinforce the beads 21. It acts as a function, improving the pressure resistance of the tube itself.

Moreover, the flat tube which joined two plates instead of the flat tube shape | molded by such a single plate is also known. Moreover, the tube formed in the flat shape by extrusion molding using the aluminum material or the aluminum alloy material is also known. The tube is provided with a partition wall for partitioning the internal flow path in the width direction and a plurality of partitioned flow paths. The flat tube extruded as described above may have grooves having a cross-sectional shape on the outer surface of the tube for the purpose of increasing the surface area, reducing the cost, reducing the weight, or discharging condensation water.

By the way, in the flat tube for the conventional heat exchanger mentioned above, as shown in FIG. 8, the dust (x) contained in the air in the concave part by the bead 21A provided in the upper surface of a tube which becomes a wind side. Is easily intensively buried, and since this dust (x) causes corrosion, the corrosion resistance of the tube is lowered, resulting in a closed end that shortens the life of the component.

In addition, in the case of the extruded tube as well as the concave part of the bead, in the concave part of the concave part provided in order to increase the surface area, reduce the weight, and save the material, the concave part gets dust and causes corrosion. It became a problem to become.

That is, in general, the heat exchanger is such that the air flows in the width direction of the tube, the heat radiation fins are installed on the upper and lower sides of the tube, the dust contained in the air on the tube surface upstream from the front surface of the tube for air flow It is easy to ask and the downstream tube surface tends not to get dirty. If the convex portion as described above is located on the wind face of the tube surface, this tendency is promoted, and the convex portion is concentrated with dust or the like contained in the air. In particular, even if dust accumulates on the concave portion of the tube surface, the accumulated dust may fall and be excluded. On the concave portion of the upper tube tube, it is difficult to remove the dust once. Dust will accumulate enough.

In addition, rain water or the like is directly sucked into the heat exchanger, or moisture is contained in the air, and condensation water is generated in the vicinity of the tube depending on the heat exchange conditions. Similarly, these water flows into the convex portion of the upper surface of the tube. There was also a possibility that dust attached to the car could be transported to the ear.

In addition, since the tube itself is made thinner, the cost is reduced or the weight is reduced, and the heat exchange efficiency with the external medium is increased. Thus, even if it is slightly corroded, the pressure resistance of the part may be lowered or the medium may leak, which may cause various problems. It is also anxious to cause.

In particular, in a vehicle-mounted heat exchanger, since the air for cooling is sucked in from the outside, the dust and the like contained in the air increase, and this tendency is promoted, which may cause shortening of the life of the tube.

On the other hand, what remove | eliminated the concave part of the bead which faces the outer surface of such a tube previously, and integrally joins (for example, Unexamined-Japanese-Patent No. 4-86489) is proposed.

However, in this case, there is a disadvantage in that the manufacturing process is complicated and the cost is increased.

Thus, the present invention provides a tube for a heat exchanger in which a bead or a groove is provided on the upper and lower surfaces of the tube so that it is difficult for dust to remain in the recess due to the beads on the upper surface of the tube, thereby increasing corrosion resistance and extending life. It is aimed at.

1 is a front view of a stacked heat exchanger according to a first embodiment of the present invention.

Fig. 2 is a cross sectional view of the flat tube, taken along line A-A in Fig. 1;

Figure 3 is a cross-sectional view of the flat tube of the first embodiment of the present invention.

Figure 4 is a cross-sectional view of the flat tube of the first embodiment of the present invention.

5 is a cross-sectional view of the flat tube of the second embodiment of the present invention.

6 is a cross-sectional view of the flat tube of the third embodiment of the present invention.

Figure 7 is a cross-sectional view of the flat tube of the fourth embodiment of the present invention.

8 is a cross-sectional view of a flat tube for a heat exchanger of the prior art.

* Explanation of symbols for main parts of the drawings

1: Stacked Heat Exchanger 2: Flat Tube

2A: Top tube 2B: Bottom tube

2a: junction 2b: junction

3: inlet header pipe 3a: inlet joint

4: outlet header pipe 5: wave pin

6: clogged cap 7: partition board

8 side plate 9 tube insertion hole

11A: Tube Top Bead

11a: Tube surface 凹 by bead on the top of the tube

11B: Bottom tube bead

11b: Tube surface 에 by bead at the bottom of the tube

12: Split flow path in the tube 13A: Tube upper side bead

13B: Tube bottom bead 14A: Tube top groove

14a: Tube surface 의한 by the groove on the top of the tube

14B: groove at the bottom of the tube

14b: Tube surface 의한 by the groove on the bottom of the tube

15: partition wall 20: flat tube

20a: junction 20b: junction

21: Bead 21A: Tube Top Bead

21B: Tube bottom bead 22: Split flow path in tube

x: dust

The invention according to claim 1 of the present invention is a tube for a heat exchanger formed by bending one plate or by overlapping two plates, wherein the tube has a plurality of beads each having a cross-sectional shape, and each of the beads Heat exchanger having a plurality of divided flow paths formed inside the tube by joining to the upper plate of the top of the bead, wherein the bead located at least upstream of the air flow among the beads protrudes upward from the bottom surface of the tube. It is a tube for use.

In this way, since the convex part by the bead is provided in the lower side of the tube at the most upstream tube facing the air flow, dust and the like are prevented from remaining in the concave part by the bead. As a result, even if a convex part is formed on the upper surface of the tube from the downstream side of the air flow, dust in the air is removed by a pin or the like mounted between the stacked tubes, and relatively clean air flows. Dust and the like remain on the ridges due to this. As a result, the corrosion resistance of the tube is improved, and the life of the heat exchanger can be extended. The most upstream part facing the air flow is most likely to be attached to dust or the like contained in the air, but even if the dust is collected by the bead, the recess is downward, so that dust or the like falls from the recess. It can be easily excluded to prevent the residue of dust and the like on the surface of the tube.

In the invention described in claim 2 of the present invention, in the invention of claim 1, the bead is joined to the flat part of the plate opposite to the top or the top of the bead formed on the opposite plate, and is located at the most upstream side of the air flow. It is formed on the lower surface of the bead tube, and at the same time, the bead positioned downstream of the air flow is a tube for heat exchanger is formed so as to alternately protrude to the tube upper surface and the tube lower surface.

In this way, when the beads formed in the tube are alternately provided on the upper and lower surfaces of the tube along the flow direction of air flow, the upper and lower sides become almost symmetrical in the cross section of the tube after molding, so that the molding becomes easy, and the upper and lower surfaces As the beads are formed in a symmetrical shape, residual stress generated in the tube material is equalized on the upper and lower surfaces, and the material strength is equalized on the upper and lower tubes, thereby improving the pressure resistance of the tube itself, thereby ensuring durability of the heat exchanger. It is possible to extend the life of the heat exchanger.

In the invention according to claim 3, in the heat exchanger tube formed by extrusion molding using an aluminum material or an aluminum alloy, the tube has a plurality of grooves having a cross-sectional shape on the outer surface of the tube, and an inner flow path. The partition wall which divides into a width direction is provided, and the groove part located in the most upstream side of the air flow among the said groove parts is a tube for heat exchangers of the structure formed in the lower surface of a tube.

In this way, when the groove is formed in the tube formed by the extrusion, the surface area can be increased to increase the heat exchange efficiency, and further, the material such as aluminum material or aluminum alloy to be used can be reduced, and the cost can be reduced. The weight of the tube can be reduced. In addition, since the convex portion formed by the uppermost groove facing the air flow is formed on the lower surface of the tube, it is difficult for the dust in the air to enter the gap between the convex portions. Since this fall is eliminated, it is possible to prevent the remaining of dust or water on the tube surface. As a result, the corrosion resistance of the tube is improved, and the life can be extended.

(Example)

In the following, a first embodiment of the present invention will be described with reference to Figs. In each of the embodiments to be described later, since the basic configuration of the laminated heat exchanger using the flat tube of the present example is common to each other, the same reference numerals will be used, and description thereof will be omitted.

In Fig. 1, this laminated heat exchanger (1) has a plurality of flat tubes (2, 2) of equal length between two vertically installed header pipes (3, 4) parallel to each other through a thin plate-like corrugated fin (5). It is laminated | stacked so that the both ends of these flat tubes 2 and 2 may be connected in communication with each header pipe 3 and 4, and is comprised. In addition, as shown in FIG. 2, the top portion of the wavy pin 5 is in contact with the flat tube 2 plane.

In addition, the upper and lower openings of the header pipes 3 and 4 are closed by the cap 6, and at the predetermined positions, the inlet joint 3a for placing the heat exchange medium from the outside and the heat-exchanged medium are discharged to the outside. The outlet joint 4a is connected in communication with each other, and the inside of each header pipe 3 and 4 is partitioned by a partition plate 7. In addition, 8 in FIG. 1 shows a side plate disposed above and below the laminated flat tube 2, and the side plate 8 protects the wave fins 5 and also serves as a heat exchanger 1. FIG. To strengthen the mechanical strength.

Then, the heat exchange medium fed from the inlet joint 3a is circulated meandering a plurality of times while heat-exchanging the tube 2 between the left and right header pipes 3 and 4, and is discharged from the inlet joint 4a. That is, the medium flowing into the heat exchanger 1 is distributed by meandering downward in the heat exchanger 1 in a predetermined number of flat tube groups.

As shown in Fig. 3 and Fig. 4, the tube 2 is formed by bending one plate made of a material, and joins the upper and lower ends 2b and 2a to protrude from the upper and lower surfaces 2A and 2B of the flat tube. A plurality of bead 11A, 11B is integrally provided. The beads 11A and 11B are alternately protruded in the inner direction of the tube from the upper and lower sides of the flat tube 2 at predetermined positions in the width direction of the flat tube 2, and are installed in a total of four rows. Five flow paths 12 and 12 having substantially the same cross-sectional area are formed. In addition, the contact area with the medium for distributing these flow paths 12 and 12 is increased to increase heat exchange efficiency, and at the same time, the beads 11A and 11B function as reinforcing members to improve the pressure resistance performance of the tube 2. I'm making it.

By appropriately setting the arrangement of these beads 11A and 11B, they are conveyed by the air flowing between the tubes 2 and 2 to the concave portions 11a and 11b formed on the tube outer surface by the beads 11A and 11B. To reduce the accumulation of dust, etc. as much as possible.

Moreover, since a flat brazing sheet | seat is shape | molded in the shape of a flat tube, it is easy to manufacture what has a substantially symmetrical shape up and down in the tube cross section after shaping | molding. That is, since the portions where the beads 11A and 11B are formed on the flat plate material are slightly different from those in which the residual force is present or different in the material strength, the moldability may be deteriorated or deformed. , 11B) is not preferable, and it is preferable to fabricate the upper and lower surfaces in a symmetrical shape as much as possible. Therefore, in this example, although the upper and lower surfaces of the tube 2 are not symmetrical in shape, the same number of beads 11A and 11B are provided on the upper and lower surfaces so as to satisfy this condition so as not to cause practical problems. .

That is, four rows of beads are alternately installed on the bottom surface of the tube along the width direction of the tube, that is, the flow direction of air flowing therethrough, and the first bead 11B (1) protrudes upward from the bottom surface of the tube. The second bead 11A (2) protrudes downward from the top of the tube, the third bead 11B (3) protrudes upward from the bottom of the tube, and the fourth bead 11A (4) It protrudes downward from the top of the tube.

Therefore, as shown in FIG. 4, the convex part 11b by the bead 11B is located in the lower surface of the tube 2 in the vicinity of the portion facing the air flow passing through the heat exchanger 1. Since the dust (x) is difficult to accumulate in the concave portion 11b, and dust and the like are likely to accumulate on the uppermost side in the flow direction of the air flow, the dust (x) or the like in the concave portion 11b by the bead 11B. This accumulation cannot be avoided, but even in this case, since it falls easily from the concave portion 11b, it is possible to prevent the dust x or the like from remaining in the concave portion 11b.

In addition, since the convex parts 11a and 11b by the beads 11A and 11B were alternately located in the upper surface and the lower surface of the tube 2 by the downstream of the airflow, the upper and lower sides of the tube 2 are upper and lower. Since dust in the air is caught on the heat radiating fins 5 and 5 provided in the air, it is thought that relatively clean air flows, and it is difficult to accumulate dust on the concave portions 11a and 11b by the beads.

In addition, it is assumed that dust in the air or dust removed from the beads 11B of the tube 2 is caught by the corrugated fins 5 and causes corrosion of the corrugated fins 5, but the heat exchange medium is distributed. The corroded pin 5 is less damage to the heat exchanger to reduce the damage caused by corrosion to a minimum.

3 and 4 indicate the flow direction of air, and the downward arrow in FIG. 4 indicates the falling direction of dust (x).

In this way, since the convex portion by the bead is located on the lower side of the tube at the uppermost side facing the air flow, dust and the like can be prevented from remaining. Even if the concave portion by the bead is formed on the upper surface of the tube downstream of the air flow, relatively clean air flows, so that dust or the like hardly remains on the concave portion by the bead. In addition, since the dust contained in the air is easily attached to the upstream side facing the air flow, the dust is located at the bottom of the tube even when the dust is caught in the recess by the bead. It can be easily dropped and eliminated to prevent dust or moisture from remaining on the surface of the tube, so that the corrosion resistance of the tube can be improved and the life can be extended.

Next, the flat tube for heat exchanger of this invention is demonstrated based on the 2nd Example shown in FIG. In addition, the arrow in the figure shows the flow direction of air.

The flat tube 2 for the heat exchanger of this example is provided with four beads in the same manner as in the above embodiment, but the arrangement is different, and since the convex part by the bead is provided on the upper surface of the tube, the dust and the like are further caused by the beads. Residual residue is reduced.

That is, four rows of beads are formed along the width direction of the tube, that is, the flow direction of the air flowing therein. The first and second beads protrude upward from the bottom of the tube, and the third and fourth beads It protrudes downward from the top of the tube. Air flow is gradually cleaned along the width direction of the tube due to the presence of heat sink fins. Therefore, if the bead protrudes from the bottom side to the upper side away from the part facing the air flow, The dust can be prevented from remaining in the part. In addition, the first and second beads 11B (1) and 11B (2) protruding upward from the bottom of the tube and the third and fourth beads 11A (3) and 11A (protruding downward from the upper surface) 4)) is formed so as to be symmetrical in the width direction of the tube so as not to cause deterioration in formability or problems of deformation.

Next, the flat tube for heat exchanger of this invention is demonstrated based on 3rd Example shown in FIG. 6, arrows indicate the flow direction of the air flow.

In the heat exchanger flat tube 2 of the present example, the second, third and fourth beads except for the first bead positioned at the most upstream side of the air flowing in the tube are located inside the tube at the upper and lower surfaces 2A and 2B of the tube 2. The bead 13A, 13B which protrudes is formed, and the protrusion amount of each bead 13A, 13B is set so that it may become about half of the height of the inside of the flat tube 2. The top portions of the beads 13A and 13B facing the upper and lower sides of the tube are joined to each other, and a plurality of split passages 12 and 12 are formed in the flat tube 2. And these beads 13A and 13B increase the contact area with the medium which distributes these flow paths 12 and 12, improve heat exchange efficiency, and function as a reinforcement member, and improve the pressure resistance performance as the tube 2, and so on. I'm making it.

Moreover, the 1st bead 11B (1) located in the tube width direction, ie, the most upstream of air flow, protrudes upward from the bottom of the tube. The protrusion amount of this bead 11B (1) is set to be approximately equal to the height in the tube of the flat tube 2, and the portion of the flat tube 2 to which the bead 11B (1) faces is unprocessed plane. It is formed in the upper surface of the bead 11B (1), and the flat tube 2 and the inner surface which join are joined.

In this way, the convex portion by the bead is located on the lower side of the tube on the uppermost side facing the air flow, thereby preventing dust and the like from remaining on the concave portion of the bead 11B (1).

Next, the flat tube for heat exchanger of this invention is demonstrated based on 4th Example shown in FIG.

The flat tube 2 for the heat exchanger of this example forms an aluminum material by extrusion molding unlike the above embodiment. The inside of the tube 2 is provided with partition walls 15 for partitioning the inner flow path in the width direction, and a plurality of partitioned flow paths 12 and 12 are provided. The extruded flat tube 2 is provided with a concave portion on the outer surface of the tube to increase the surface area, reduce the weight, and reduce the material required for fabrication to reduce cost.

That is, the extruded flat tube 2 has grooves 14A and 14B having a cross-sectional shape in the upper and lower surfaces 2A and 2B. The grooves 14A and 14B are alternately provided on the upper and lower surfaces 2A and 2B of the tube as in the above embodiment, and are arranged to reduce the accumulation of dust in the recesses provided on the upper surface.

In this example, four rows of grooves 14A and 14B are alternately provided on the tube-shaped lower surfaces 2A and 2B along the width direction of the tube, that is, the flow direction of the air flowing therein, and the first groove portion 14B ( 1)) is formed in the lower surface 2B of the tube, the second groove 14A (2) is formed in the upper surface 2A of the tube, and the third groove 14B (3) is formed in the lower surface of the tube 2B. The fourth groove 14A (4) is formed in the upper surface 2A of the tube.

In this way, since the first groove portion 14B (1) is formed in the bottom surface 2B of the tube in the vicinity of the portion facing the air flow, dust is formed on the recess portion 14b by the groove portion 14B (1). Etc. are prevented from remaining. Thus, even in the flat tube by extrusion molding provided with the groove part in order to reduce cost and weight reduction, corrosion resistance can be improved and the life of the heat exchanger 1 can be extended.

In the present example, four beads or grooves are formed in the flat tube, and five medium flow paths are formed in the tube, but the present invention is not limited thereto, and any number of beads or any number of grooves are formed. Applicable to

Similarly, this example applies to those provided with mutually spaced intervals between the rows of these beads or grooves in the tube width direction at approximately the same intervals, but is also applicable to those set at other arbitrary intervals. And, if there is no problem in the strength of the tube, all the beads may be formed to protrude upward from the bottom of the tube.

In addition, in the above embodiment, the beads were applied continuously in the tube length direction, but various beads were intermittently and spotted, but spaced at predetermined portions of the beads, and adjacent to each other in the tube. Naturally, it can be applied to the communication with the flow path.

In addition, in the present example, one plate is bent to form a flat tube. However, the flat tube formed by overlapping two plates is not limited thereto. Can be.

As described above, the invention according to claim 1 of the present invention is a tube for a heat exchanger formed by bending one plate or by overlapping two plates, wherein the tube has a plurality of beads having a concave shape in cross section. And a top of each bead is joined to an opposing plate to form a plurality of dividing flow paths inside the tube, and the bead located at least upstream of the air flow among the beads protrudes upward from the bottom of the tube. It is a tube for heat exchanger of the structure.

Therefore, since the convex part by the bead is provided in the lower side of the tube at the most upstream tube facing the air flow, dust and the like are prevented from remaining in the concave part by the bead. In this way, even if a concave portion is formed on the upper surface of the tube from the downstream side of the air flow, dust in the air is removed by a pin or the like mounted between the stacked tubes, and a relatively clean air flow flows. Dust and the like remain less in the ridges due to the id. As a result, the corrosion resistance of the tube is improved, and the life of the heat exchanger can be extended. In the uppermost part facing the air flow, dust contained in the air is most likely to adhere to the tube, but even when accumulated in the recessed portion by the bead, the recessed portion faces downward. It can be easily eliminated by dropping to prevent dust and residue on the tube surface.

In the invention described in claim 2 of the present invention, in the invention of claim 1, the bead is joined to the flat part of the opposing plate or the top of the bead formed on the opposing plate, the top of which is opposite, The upstream bead is formed on the bottom surface of the tube, and the bead located on the downstream side of the air flow is sequentially formed so as to protrude alternately to the top and the bottom of the tube.

In this way, when the beads formed in the tube are alternately provided on the upper and lower surfaces of the tube along the flow direction of the air flowing therein, the upper and lower sides become substantially symmetrical in the cross section of the tube after molding, so that the molding is easy and the upper and lower surfaces are symmetrical. As a bead is formed in a conventional shape, the residual stress generated in the tube material is equalized on the upper and lower sides, and the material strength is equalized on the upper and lower tubes, so that the pressure resistance of the tube itself can be improved, thereby ensuring durability of the heat exchanger. Thus, it is possible to extend the life of the heat exchanger.

In the invention according to claim 3, in the heat exchanger tube formed by extrusion molding using an aluminum material or an aluminum alloy, the tube is formed with a plurality of grooves having a cross-sectional shape on the outer surface of the tube, The partition wall which partitions a furnace in the width direction is provided, and the groove part located in the upstream of at least the most air flow among the said groove parts is a tube for heat exchangers of the structure formed in the lower surface of a tube.

In this way, when the groove is formed in the tube formed by the extrusion, the surface area can be increased to increase the heat exchange efficiency, and further, the material such as aluminum material or aluminum alloy to be used can be reduced, and the cost can be reduced. The weight of the tube can be reduced. In addition, since the convex part formed by the uppermost groove facing the air flow is formed on the lower surface of the tube, it is difficult for the dust in the air to enter the gap between the convex part, and even if the condensed part accumulates in the convex part, the accumulated dust etc. falls. Since it is excluded, the residue of dust or moisture can be prevented from the tube surface. As a result, the corrosion resistance of the tube is improved, and the life can be extended.

As described above, according to the present invention, in a tube provided with a bead or a groove on the upper and lower surfaces of the tube, it is difficult to accumulate dust in the convex portion due to the bead of the tube surface, so that the tube for the heat exchanger, which has high corrosion resistance and can extend its life, You can get it.

Claims (3)

In a tube for a heat exchanger formed by bending one plate or by overlapping two plates, The tube has a plurality of beads having a concave shape in cross section, and is joined to a plate opposite the top of each bead to form a plurality of split flow paths inside the tube. A tube for heat exchanger, characterized in that the bead located at least upstream of the air flow of the bead protrudes upward from the bottom surface of the tube. 2. The bead of claim 1, wherein the bead is joined to a flat portion of an opposing plate or to a top portion of a bead formed on an opposing plate, and a bead positioned most upstream of the air flow is formed at the bottom of the tube. And at the same time, the bead positioned downstream of the air flow is formed so as to project alternately to the tube upper surface and the tube lower surface in turn. In the heat exchanger tube formed by extrusion molding using an aluminum material or an aluminum alloy, The tube is provided with a plurality of grooves having a concave shape in cross section on the outer surface of the tube, and a partition wall for partitioning the inner flow path in the width direction. And a groove portion located at an upstream side of the air flow at least among the groove portions is formed on a lower surface of the tube.