EP2253922A2 - Metallic heat exchange pipe - Google Patents

Abstract

The tube (1) has a tube wall, and integrally formed ribs (3) running around on an outer tube (21) and having a rib foot (31), rib flanks (32) and a rib tip (33). The rib foot projects radially from the tube wall, and the rib flanks are provided with additional structural elements, which are formed as material projections (4) arranged laterally on the rib flanks. The material projections have a set of boundary faces (41, 42), where one of the boundary faces is curved convexly. The projections are spaced apart from each other in a circumferential direction.

Description

The invention relates to a metallic heat exchanger tube according to the preamble of claim 1.

Such metallic heat exchanger tubes are used in particular for the condensation of liquids from pure substances or mixtures on the tube outside. Condensation occurs in many areas of refrigeration and air conditioning technology as well as in process and energy technology. Frequently, shell-and-tube heat exchangers are used, in which vapors from pure substances or mixtures are liquefied on the outside of the pipe, thereby heating a brine or water on the inside of the pipe. Such apparatuses are referred to as tube bundle condensers or tube bundle liquefiers.

The heat exchanger tubes for shell and tube heat exchangers usually have at least one structured area and smooth end pieces and possibly smooth spacers. The smooth end or intermediate pieces limit the structured areas. So that the tube can be easily installed in the shell and tube heat exchanger, the outer diameter of the structured areas must not be greater than the outer diameter of the smooth end and intermediate pieces. The standard high performance pipes today are about four times more efficient than smooth pipes of the same diameter.

To increase the heat transfer during the condensation on the outside of the tube, various measures are known. Frequently, ribs are applied to the outer surface of the tube. As a result, the surface of the tube is primarily increased and thus the condensation intensified. For the heat transfer, it is particularly advantageous if the ribs are formed from the wall material of the smooth tube, since then there is an optimal contact between the rib and the tube wall. Nippled tubes in which the ribs have been formed from the wall material of a plain tube by means of a forming process are referred to as integrally rolled ribbed tubes.

It is state of the art to further increase the surface area of the pipe by inserting notches in the fin tips. Furthermore, the notches create additional structures that positively influence the condensation process. Examples of notches of the rib tips are from the documents US 3,326,283 and US 4,660,630 known.

Today, commercially available tubing for condenser on the outside of the tube has a rib structure with a rib density of 30 to 45 ribs per inch. This corresponds to a rib pitch of approx. 0.85 to 0.56 mm. Such rib structures are for example from the documents DE 44 04 357 C2 . US 2008/0196776 A1 . US 2007/0131396 A1 and CN 101004337 A refer to. The further increase in performance by increasing the rib density are limited by the Inundationseffekt occurring in shell and tube heat exchangers: With decreasing distance between the ribs is flooded by the capillary effect of the space between the ribs with condensate and obstructs the flow of condensate through the decreasing channels between the ribs.

Furthermore, it is known that in condenser tubes performance increases can be achieved by adding additional rib density additional Structural elements in the region of the rib edges between the ribs brings. Such structures may be formed by gear-like discs on the rib flanks. The resulting material projections protrude into the space between adjacent ribs. Embodiments of such structures can be found in the documents US 2008/0196876 A1 . US 2007/0131396 A1 and CN 101004337 A , In these documents, the material projections are shown as structural elements with flat boundary surfaces. The flat boundary surfaces are disadvantageous because the condensate formed on a flat surface does not experience any surface tension induced force that would remove it from the boundary surface. Thus, an undesirable liquid film forms, which can hinder the heat transfer sustainable.

The invention has the object of developing a performance-enhanced heat exchanger tube for the condensation of liquids on the outside of the tube with the same tube-side heat transfer and pressure drop and the same production costs. The mechanical stability of the tube should not be adversely affected.

The invention is represented by the features of claim 1. The other dependent claims relate to advantageous embodiments and further developments of the invention.

The invention includes a metallic heat exchanger tube having a tube wall and integrally molded ribs on the tube outside which have a rib root, rib flanks and a rib tip, the rib stem projecting substantially radially from the tube wall and the rib flanks provided with additional structural members , which are formed as material projections, which are arranged laterally on the rib side, wherein the material projections have a plurality of boundary surfaces. According to the invention, at least one of the boundary surfaces of at least one material projection is convexly curved.

The present invention relates to structured pipes in which the heat transfer coefficient is intensified on the pipe outside. As a result, the majority of the heat transfer resistance is often shifted to the inside, the heat transfer coefficient on the inside usually also needs to be intensified. An increase in the heat transfer on the inside of the pipe usually results in an increase in the pipe-side pressure drop.

The invention is based on the consideration that the integrally rolled finned tube has a tube wall as well as on the outside of the tube helically encircling ribs. The ribs have a ribbed foot, a rib tip and on both sides rib flanks. The rib foot is substantially radially from the pipe wall. The height of the rib is measured from the pipe wall to the fin tip and is preferably between 0.5 and 1.5 mm. The contour of the rib is curved concavely in the radial direction in the region of the rib foot and in the region of the rib flank adjoining the rib base. At the rib tip and in the region of the rib flank adjoining the rib tip, the contour of the rib is convexly curved in the radial direction. At approximately half the height of the rib, the convex curvature changes into a concave curvature. In the area of the convex curvature, resulting condensate is pulled away due to surface tension forces. The condensate collects in the area of the concave curvature and forms drops there.

The side of the rib flanks according to the invention additional structural elements in the form of material protrusions are formed. These material protrusions are formed from material of the upper rib flank by means of a Tool the material lifted and displaced similar to a chip, but is not separated from the rib edge. The material projections remain firmly connected to the rib. At the junction, a concave edge is created between the rib flank and the material projection. The material projections extend substantially in the axial direction of the rib edge in the space between two ribs. The material projections may in particular be arranged approximately at half the height of the ribs. By the material projections, the surface of the tube is increased.

Opposing material projections of adjacent ribs should not touch each other. Therefore, the axial extent of the material projections is usually slightly smaller than half the width of the space between two ribs. For example, for condenser tubes for the refrigerant R134a or R123, the width of the gap between two ribs is about 0.4 mm, thus the axial extent of the material protrusions is less than 0.2 mm.

The material projections are inventively limited by at least one convex curved surface. The convex shape improves the effect of the additional structural elements. Due to the surface tension, the condensate is drawn away from convexly curved surfaces and towards the concave edge at the point of attachment between the material projection and the rib flank. Therefore, the condensate film on the convexly curved boundary surface of the material projection becomes thinner and the thermal resistance becomes lower. The material projections are arranged approximately in the region of the rib flank, in which the convexly curved contour of the rib merges into the concavely curved contour. Condensate from the top of the rib and condensate from the material projection meet at the point of attachment and form a drop in the concave-shaped part of the rib.

At the in US 2007/0131396 A1 and US 2008/0196876 A1 shown later attached to the rib edges additional structures are elements with flat surfaces that do not have such advantageous properties.

The particular advantage is that can be greatly reduced by intensifying the heat transfer on the pipe inside in conjunction with a favorable heat transfer on the pipe outside the size of the condenser. As a result, the production costs of such apparatuses decrease. It is negatively influenced by the inventive solution neither the mechanical stability of a pipe nor the pressure drop. In addition, the necessary filling quantity of refrigerant, which can account for a not inconsiderable share of the total investment costs in the chlorine-free safety refrigerants that are predominantly used today, is decreasing. In the case of the toxic or flammable refrigerants which are normally only used in special cases, the danger potential can be reduced by reducing the filling quantity.

In a preferred embodiment of the invention, the local radius of curvature of the convex boundary surface can be reduced with increasing distance from the rib edge. At each point of the convex boundary surface, a local radius of curvature can be defined as the radius of the nodding circle. The Schmiegekreis lies in a plane perpendicular to the rib side plane. With an arbitrarily shaped boundary surface, this local radius of curvature changes. If such a surface is covered with a liquid film, pressure gradients arise in the liquid film due to the surface tension and the changing radius of curvature. These pressure gradients pull the fluid away from areas of small radius of curvature and toward areas of great radius of curvature. Particularly advantageous embodiments of the material projections are present when the local radius of curvature of its boundary surface with increasing distance from the rib edge gets smaller. The condensate is then pulled away from the areas of the material protrusions, which are remote from the rib flank, particularly efficiently and transported to the rib.

Advantageously, the convexly curved boundary surface may be the boundary surface of a material protrusion facing away from the pipe wall. The steam to be condensed can then flow unhindered to this surface.

In an advantageous embodiment of the invention, the curvature of the boundary surface may be convexly curved in a plane parallel to the rib flank, wherein the curvature of the convex boundary surface in a plane perpendicular to the rib flank is stronger than the curvature of the convex boundary surface in the plane parallel to the rib side. This additionally promotes the transport of the condensate in the lateral direction from the tip of the material projection to the rib.

The radius of an imaginary circle, referred to as the mean radius of curvature of the convex boundary surface, can be determined by measurements at three points. In a particularly preferred embodiment, the radius of this imaginary circle, which lies in a sectional plane perpendicular to the tube circumferential direction and which is defined by the points P1, P2 and P3, be less than 1 mm. P1 is the point where the convex boundary surface of the material protrusion adjoins the rib flank, P3 is the point where the convex boundary surface of the material protrusion is farthest from the rib flank, and P2 is the midpoint between P1 and P3 on the contour line of the convex Boundary surface of the material projection. If this radius of curvature were greater than 1 mm, then the surface tension forces resulting from the commonly used substances, such as refrigerants or hydrocarbons, would not be sufficiently high in gravity relative to the transport of the condensate to influence significantly.

Advantageously, the convex boundary surface of the material projection in the region of its tip over the farthest from the rib edge remote point P3 continue with convex curvature. In this case, the tip of the material projection is then usually curved helically. As a result, additional surface for the condensation is obtained in the available space between the ribs with the same rib spacing.

In a preferred embodiment of the invention, the material protrusions disposed on the rib flank may be circumferentially spaced. This creates additional edges where condensation takes place. Furthermore, the condensate collecting at the rib flank can flow away in the areas between two material projections to the ribbed foot.

In a further advantageous embodiment of the invention, the material projections arranged on the rib flank can be equidistant in the circumferential direction and spaced at least around their width. As a result, sufficient space for the collecting at the rib side condensate is created to ensure removal.

Embodiments of the invention will be explained in more detail with reference to the schematic drawings.

Fig. 1

eine perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaus- tauscherrohres mit Werkstoffvorsprüngen,

Fig. 2

eine Detailansicht eines in Figur 1 dargestellten Werkstoffvorsprungs mit einer konvex gekrümmten Begrenzungsfläche.

Fig. 3

eine weitere Detailansicht eines Werkstoffvorsprungs mit zwei konvex gekrümmten Begrenzungsflächen,

Fig. 4

eine weitere Detailansicht eines Werkstoffvorsprungs mit einer zweifach konvex gekrümmten Begrenzungsfläche,

Fig. 5

eine weitere Detailansicht eines Werkstoffvorsprungs mit einer über den am weitesten von der Rippenflanke entfernten Punkt hinausgehende Fortsetzung,

Fig. 6

eine perspektivische Teilansicht der Außenseite eines Wärmeaustauscher- rohrabschnitts,

Fig. 7

eine perspektivische Teilansicht der Innenseite eines Wärmeaustauscher- rohrabschnitts, und

Fig. 8

den Querschnitt eines Wärmeaustauscherrohrabschnitts.

Show:

Fig. 1

1 is a partial perspective view of a rib section of a heat exchanger tube with material projections,

Fig. 2

a detailed view of an in FIG. 1 shown material projection with a convex curved boundary surface.

Fig. 3

another detailed view of a material projection with two convex curved boundary surfaces,

Fig. 4

a further detailed view of a material projection with a doubly convex curved boundary surface,

Fig. 5

a further detailed view of a material projection with a continuation beyond the point farthest from the rib edge,

Fig. 6

3 is a partial perspective view of the outside of a heat exchanger tube section;

Fig. 7

a partial perspective view of the inside of a heat exchanger tube section, and

Fig. 8

the cross section of a heat exchanger tube section.

Corresponding parts are provided in all figures with the same reference numerals.

Fig. 1 shows a partial perspective view of a rib portion of a heat exchanger tube 1 with three material projections 4. From the outside of the pipe 21, only a part of the circumferential, integrally molded ribs 3 is shown. The ribs 3 have a rib foot 31, which attaches to the pipe wall, not shown here, rib flanks 32 and a rib tip 33. The rib 3 is substantially radially from the pipe wall. The rib flanks 32 are provided with the additional structural elements, which are formed as material projections 4, which attach laterally to the rib flank 32. These material projections 4 have a plurality of boundary surfaces 41 and 42. In the illustrated embodiment, the three boundary surfaces 42 of the material projections 4 are convexly curved on the side facing away from the tube wall. In principle, however, according to the invention, for each material projection 4, another boundary surface 42 or a plurality of boundary surfaces 42 may be provided with a convex curvature. The remaining, non-convex boundary surfaces 41, can either even or concave. The material of the integrally machined material projections 4 originates primarily from the rib flank 32, wherein recesses 34 are formed by a material displacement in the production of the heat exchanger tubes 1.

Fig. 2 shows a detailed view of a material projection 4 with a convex curved boundary surface 42. The remaining non-convex boundary surfaces 41 extend flat in this case. In the area of the convex surface, the condensate precipitating out of the gas phase is transported away due to the surface tension, as a result of which condensate accumulates increasingly in the area of the concave curvature or even on flat surface areas.

The mean radius of curvature RM of the convex boundary surface 42 of an imaginary circle K is defined by the three points P1, P2 and P3. This radius RM can be used as a characterizing measure for the expression of the convex surface. P1 is the point where the convex boundary surface 42 of the material protrusion 4 abuts the rib flank, P3 is the point where the convex boundary surface 42 of the material protrusion 4 is farthest from the rib flank, and P2 is the midpoint between P1 and P3 The contour line of the convex boundary surface 42 of the material projection 4. In conventional structure sizes of the heat exchanger tubes according to the invention with integrally rolled ribs, the average radius of curvature RM is typically in the submillimeter range.

A further detail view of a material projection 4 with two opposite convex curved boundary surfaces shows Fig. 3 , With this geometry, starting from the tip of a material projection 4, condensate is transported particularly effectively towards the rib flank. In principle, for the most efficient performance form, all boundary surfaces 42, including the side surfaces 41, have a convex curvature. However, in the course of the structuring of integral rib shapes and their material projections 4, such embodiments are subject to high process requirements.

As a further advantageous embodiment can also be in the further detail view in Fig. 4 represented material projection 4 with a doubly convex curved boundary surface 42 and flat side surfaces 41 realize. The curvature of the convex boundary surface in a plane perpendicular to the rib flank is stronger than the curvature of the convex boundary surface 42 in the plane parallel to the rib flank. Such curved surfaces additionally support the condensate drainage towards the rib flank.

Another exemplary embodiment shows Fig. 5 in a detailed view of a material projection 4 with flat side surfaces 41 and with a beyond the farthest from the rib edge remote point P3 addition continuing. In this case, the tip SP of the material projection 4 is spirally rolled towards the rib foot. As a result, additional surface for the condensation is obtained in the available space between the ribs. The mean radius of curvature RM of the convex boundary surface 42 of an imaginary circle K is again defined by the points P1, P2 and P3.

Fig. 6 shows a partial perspective view of the outside of a heat exchanger pipe section 1. A further partial perspective view of the inside of a heat exchanger pipe section, however, shows Fig. 7 , On the outside of the pipe 21, some of the integrally formed and circulating around the tube axis A ribs 3 are shown. The ribs 3 are radially from the pipe wall 2 and are connected via the ribbed 31 with this. At the rib edges 32 material projections 4 are formed, which attach laterally to the rib edge 32. Of the boundary surfaces of the material projections 4 are the from the pipe wall 2 facing away from boundary surfaces 42 convex. The remaining non-convex boundary surfaces 41 are in the embodiment according to Fig. 6 just. In Fig. 7 If the lateral boundary surfaces 41 are flat, the boundary surfaces 41 directed towards the interior of the tube are concave. The material of the integrally machined material projections 4 comes primarily from the rib flank 32 and only partially from the area of the rib tip 33, whereby recesses 34 are formed. The material projections 4 arranged on the rib flank 32 are equidistant in the circumferential direction U approximately at their width. Opposing material projections adjacent ribs 3 do not touch, since the axial extent of the material projections 4 is chosen smaller than half the width of the gap between two ribs 3. Spirally encircling internal ribs 5, which increase the heat transfer to the fluid in the interior of the heat exchanger tube 1 with respect to a smooth tube, are arranged on the inside of the tube 22.

Fig. 8 shows a cross-section of a heat exchanger pipe section 1. On the tube inside 22 are spirally encircling inner ribs 5. The ribs 3 on the tube outer side 21 are arranged in a regular sequence starting from the rib foot 31 perpendicular to the tube wall 2, the rib tip 33 is slightly flattened. The facing away from the pipe wall 2 boundary surfaces 42 of the rib edge 32 attaching material projections 4 are convex, the pipe interior 22 directed towards the boundary surfaces 41 are concave. Opposing material projections of adjacent ribs 3 in turn do not touch. As a result, the accumulating condensate sufficient space is created for removal.

LIST OF REFERENCE NUMBERS

1

heat exchanger tube

2

pipe wall

21

Pipe outside

22

Pipe inside

3

Rib on the tube outside

31

fin base

32

rib flank

33

fin tip

34

recesses

4

Material advantage

41

boundary surface

42

convex boundary surface

5

Rib on pipe inside

SP

Tip of a material projection

U

Tube circumferential direction

A

pipe axis

RM

mean radius of curvature

K

circle

P1, P2, P3

Points on convex boundary surface

Claims (8)

A metallic heat exchanger tube (1) having a tube wall (2) and integrally molded ribs (3) encircling the tube outside (21), having a ribbed foot (31), rib flanks (32) and a ribbed tip (33) (31) extends substantially radially from the tube wall (2) and the rib flanks (32) are provided with additional structural elements which are formed as material projections (4) which are arranged laterally on the rib flank (32), wherein the material projections (4 ) have a plurality of boundary surfaces (41, 42),
characterized,
in that at least one of the boundary surfaces (42) of at least one material projection (4) is convexly curved. A metallic heat exchanger tube (1) according to claim 1, characterized in that the local radius of curvature of the convex boundary surface (42) is reduced with increasing distance from the rib flank. Metallic heat exchanger tube (1) according to claim 1 or 2, characterized in that the convexly curved boundary surface (42) facing away from the pipe wall (2) boundary surface of a material projection (4). Metallic heat exchanger tube (1) according to one of claims 1 to 3, characterized in that the curvature of the boundary surface (42) is also convexly curved in a plane parallel to the rib flank (32), wherein the curvature of the convex boundary surface (42) in a plane perpendicular to the rib flank (32) is stronger than the curvature of the convex boundary surface (42) in the plane parallel to the rib flank (32). Metallic heat exchanger tube (1) according to one of claims 1 to 4, characterized in that the radius (RM) of an imaginary circle (K) lying in a sectional plane perpendicular to the tube circumferential direction (U) and the points P1, P2 and P3 is smaller than 1 mm, where P1 is the point at which the convex boundary surface (42) of the material projection (4) adjoins the rib flank (32), P3 is the point at which the convex boundary surface (42) of the Material projection (4) farthest from the rib edge (32) is removed and P2 is the midpoint between P1 and P3 on the contour line of the convex boundary surface (42) of the material projection (4). Metallic heat exchanger tube (1) according to claim 5, characterized in that the convex boundary surface (42) of the material projection (4) continues in the region of its tip (SP) beyond the farthest point of the rib flank (32) remote point P3 with convex curvature , Metallic heat exchanger tube (1) according to one of claims 1 to 6, characterized in that the ribs (32) arranged on the material projections (4) in the circumferential direction (U) are spaced. Metallic heat exchanger tube (1) according to one of claims 1 to 7, characterized in that the ribs (32) arranged on the material projections (4) in the circumferential direction (U) are equidistant and at least spaced by their width.

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