EP3581871A1 - Metallic heat exchange pipe - Google Patents

Abstract

The invention relates to a heat exchanger tube (1), comprising a tube wall (2) and fins (3) which run around the outside of the tube (21) and which have a fin base (31), fin flanks (32) and a fin tip (33) and one between the Ribs formed primary groove (34), wherein the rib foot (31) projects essentially radially from the tube wall (2), and the rib flanks (32) along the primary groove (34) are provided with additional structural elements (4) which are spaced apart and which are made of Material of the rib flank (32) shaped material projections (4) are formed, which are arranged on the side of the rib flank (32). The material projections (4) are deformed in such a way that they touch the tube wall (2) in the region of the primary groove (34), so that local cavities (5) are formed. The cavities (5) have openings (51, 52) in the circumferential direction (U) of the ribs.

Description

The invention relates to a metallic heat exchanger tube with ribs running around the outside of the tube according to the preamble of claim 1.

Metallic heat exchanger tubes of this type are used in particular for the evaporation of liquids from pure substances or mixtures on the outside of the tube.

Evaporation occurs in many areas of refrigeration and air conditioning technology as well as in process and energy technology. Shell and tube heat exchangers are often used, in which liquids of pure substances or mixtures evaporate on the outside of the tube and thereby cool down brine or water on the inside of the tube. Such devices are referred to as flooded evaporators.

The size of the evaporators can be greatly reduced by intensifying the heat transfer on the inside or outside of the tube. As a result, the manufacturing costs of such apparatus decrease. In addition, the required amount of refrigerant drops, which can make up a not insignificant share of the total system costs with the chlorine-free safety refrigerants that are mainly used today. In the case of toxic or flammable refrigerants, the risk potential can also be reduced by reducing the filling quantity. Today's high-performance pipes are already four times more powerful than smooth pipes of the same diameter.

It is state of the art to manufacture such powerful tubes on the basis of integrally rolled finned tubes. Integrally rolled finned tubes are understood to mean finned tubes in which the fins are made of the wall material a smooth tube were formed. Various methods are known with which the channels located between adjacent ribs are closed in such a way that connections between the channel and the environment remain in the form of pores or slots. In particular, such essentially closed channels are formed by bending or folding the ribs ( US 3,696,861 A ; US 5,054,548 A ; US 7 178 361 B2 ), by splitting and compressing the ribs ( DE 27 58 526 C2 ; US 4,577,381 A ) and by notching and compressing the ribs ( US 4,660,630 A ; EP 0 713 072 B1 ; US 4,216,826 A ) generated.

The most powerful, commercially available finned tubes for flooded evaporators have a finned structure on the outside of the tube with a fin density of 55 to 60 fins per inch ( US 5,669,441 A ; US 5 697 430 A ; DE 197 57 526 C1 ). This corresponds to a rib pitch of approximately 0.45 to 0.40 mm. In principle, it is possible to improve the performance of such pipes by means of an even higher fin density or smaller fin pitch, since this increases the density of bladder nuclei. A smaller rib division inevitably requires equally fine tools. However, finer tools are subject to a higher risk of breakage and faster wear. The tools currently available enable the safe production of finned tubes with fin densities of up to 60 fins per inch. Furthermore, as the fin pitch decreases, the production speed of the pipes becomes slower, and consequently the manufacturing costs become higher.

It is also known that increased evaporation structures can be produced on the outside of the tube with a constant fin density by introducing additional structural elements in the area of the groove base between the fins. Since the temperature of the rib is higher in the area of the groove base than in the area of the rib tip, structural elements for intensifying the formation of bubbles in this area are particularly effective.

Examples of this are in EP 0 222 100 B1 ; US 5,186,252 A ; JP 4 039 596 B2 and US 2007/0 151 715 A1 to find. These inventions have in common that the structural elements on the base of the groove do not have an undercut shape, which is why they do not intensify the formation of bubbles sufficiently. In EP 1 223 400 B1 and WO 2014/072 047 A1 It is proposed to produce undercut secondary grooves at the bottom of the groove, which extend continuously along the primary groove. The cross section of these secondary grooves can remain constant or can be varied at regular intervals. In WO 2014/072 046 A1 It is proposed to create pyramid-like undercut structural elements on the bottom of the groove between the ribs, which are arranged at regular intervals along the primary groove.

The invention has for its object to provide a performance-enhanced heat exchanger tube for the evaporation of liquids on the outside of the tube.

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

The invention includes a metallic heat exchanger tube comprising a tube wall and fins surrounding the tube outer side, which have a fin base, fin flanks and a fin tip, and a primary groove formed between the fins, the fin foot projecting essentially radially from the tube wall, and along the fin flanks the primary groove are provided with additional structural elements spaced apart from one another, which are formed as material projections formed from the material of the rib flank and arranged laterally on the rib flank. The material projections are deformed in such a way that they touch the tube wall in the area of the primary groove, so that local cavities are formed. The cavities have openings in the circumferential direction of the ribs.

The invention is based on the consideration that to increase the heat transfer during evaporation, the process of bubble boiling is intensified. The formation of bubbles begins at the germ sites. These germ sites are mostly small gas or vapor inclusions. When the growing bubble has reached a certain size, it detaches from the surface. If the germ site were flooded with liquid in the course of the bubble detachment, the germ site is deactivated. The surface must therefore be designed in such a way that a small bubble remains when the bubble is detached, which then serves as the nucleus for a new cycle of bubble formation. This is achieved by forming local cavities on the surface which have openings in the circumferential direction of the ribs. The liquid and vapor are exchanged through the opening.

A cavity is formed from material of the rib flank which, shaped like a chip, contacts the tube wall in the area of the primary groove as a material projection. In a special case, it is the front edge, i.e. the area of a material projection that is the most distant from the rib flank in the course of the curvature. In other words: the deformed material projections have a point on the front, the front edges of which, or the surface portions immediately connected to these front edges by a conceivable rolling process in the manufacturing process, can come into contact with the tube wall in the region of the primary groove. A cavity is consequently formed from the material projection and the rib foot remaining radially within the material projection and the region of the primary groove adjoining the rib foot until the material projection contacts. The material projections are particularly preferably on both sides of the ribs arranged.

The length of the areas in the circumferential direction between two cavities can be between 0.2 mm and 0.5 mm. In this way, optimal coordination of the successive cavities and the areas in between is achieved.

In addition, the rib tips can be deformed in such a way that they cover and partially close off the primary grooves in the radial direction and thus form a helically surrounding, partially closed cavity. The rib tips can, for example, have an essentially T-shaped cross section with pore-like recesses through which the vapor bubbles can escape.

The particular advantage of the invention is that the effect of a cavity on the formation of bubbles is particularly great if the exchange of liquid and vapor is controlled in a targeted manner and the flooding of the bladder germ site in the cavity is prevented. The position of the cavities in the vicinity of the primary groove base is particularly favorable for the evaporation process, since the excess temperature is greatest at the groove base and therefore the highest driving temperature difference is available there for the formation of bubbles.

In a preferred embodiment of the invention, the cavities can form a cylindrical cavity. The material projections can deform increasingly with increasing distance from the rib flank, so that they curl up to the point of contact with the tube wall and a cylindrical tube is thereby formed. A cylinder-like cavity has two openings of essentially the same type in the circumferential direction of the ribs, via which a bubble germ supports the evaporation process of a fluid.

The maximum clear width of a cavity can advantageously be a maximum of half the longitudinal extent of the cavity. In this way, elongated cavities are formed, which represent bladder germ sites particularly efficiently and contribute to an increase in the heat transfer during evaporation. When the bubble growing out of the elongated cavity has reached a certain size, it detaches from the surface. After detachment, the elongated tube as the germ site is only partially flooded with liquid, which means that the germ site remains constantly activated. The dimension of the cavity is consequently designed such that when a bubble is detached, a small bubble remains, which then serves as the nucleus for a new cycle of bubble formation.

In a particularly preferred embodiment, fluid guide structures can be arranged on the rib flanks between the cavities. The bubbles formed in the evaporation process preferably originate in the cavities opened in the circumferential direction of the ribs, and the liquid flows through the fluid guide structures preferably radially along the rib flank near the closed regions of the cavity. The escaping bladder is not hindered by the inflowing liquid working medium and can expand undisturbed in the primary groove. The respective flow zones for the liquid and the vapor are ideally spatially separated from one another.

In a further advantageous embodiment of the invention, fluid guide structures can be arranged which extend from one cavity to the cavity adjacent in the circumferential direction of the ribs. As a result, the liquid flows particularly radially along the rib flank. The escaping bubble is not hindered by the inflowing liquid working medium and can expand in the primary groove until it detaches. The respective flow zones for the liquid and for the vapor are spatially separated by the fluid guide structures.

In a further advantageous embodiment, the fluid guide structures on the rib flanks can extend in a raised arc segment rising towards the rib tip. Through such fluid guide structures, the fluid is led to the cavities as bubble nuclei for evaporation.

The fluid guide structures on the rib flanks can advantageously extend in the radial direction as raised fluid guide surfaces. Raised fluid guiding surfaces can, due to comparatively sharp edges and the wetting behavior of the liquid fluid, be particularly effective for mass transport on the heat exchanger tube and thus for efficient heat exchange.

In a preferred embodiment of the invention, a fluid guide surface can end directed radially inwards at or in the immediate vicinity of a cavity. Structures of this type ensure targeted fluid guidance and thus efficient heat dissipation on the outside of the pipe.

A fluid guide surface can advantageously end radially outwards at or in the immediate vicinity of the rib tip. Thus, starting from the area of the fin tip, the liquid fluid is already guided radially in the direction of the tube wall for heat exchange along the fin flanks.

In a further advantageous embodiment of the invention, the fluid-guiding structures on the rib flanks can extend outward in the radial direction up to a maximum of half the rib height. For manufacturing reasons, the rib tip can be designed to be extremely narrow, as a result of which, in the radially inward direction, a rib only has a sufficient width and thus sufficient material in the central part and in the region of the rib foot in order to form a material projection from the flank.

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

Fig. 1

eine perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaustauscherrohres mit Werkstoffvorsprüngen,

Fig. 2

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

Fig. 3

eine perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaustauscherrohres mit Werkstoffvorsprüngen und erhabenen Fluidleitstrukturen, und

Fig. 4

eine weitere perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaustauscherrohres mit Werkstoffvorsprüngen und bogenartigen Fluidleitstrukturen.

In it show:

Fig. 1

2 shows a perspective partial view of a rib section of a heat exchanger tube with material projections,

Fig. 2

a detailed view of an in Figure 1 material projection shown with a curved boundary surface,

Fig. 3

a partial perspective view of a rib portion of a heat exchanger tube with material projections and raised fluid guide structures, and

Fig. 4

a further perspective partial view of a rib portion of a heat exchanger tube with material projections and arcuate fluid guide structures.

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

Fig. 1 shows a perspective partial view of a rib section of a heat exchanger tube 1 with four material projections 4. From the tube outer side 21, only a part of the circumferential, integrally formed ribs 3 is shown. The ribs 3 have a rib base 31 which attaches to the tube wall 2, rib flanks 32 and a rib tip 33. The rib 3 projects essentially radially from the tube wall 2. The rib flanks 32 are provided with additional structural elements which are designed as material projections 4 which attach laterally to the rib flank 32. The material projections 4 have front ends 41 which touch the tube wall 2 in the region of the primary groove 34. In this way, together with the rib base 31, cavities 5 form, which are in the circumferential direction U of the ribs Have openings 51, 52. Such cavities 5 preferably form bubble nuclei in the evaporation process of a fluid, which promote heat exchange.

In the embodiment shown, the boundary surfaces of the material projections 4 are convexly curved on the side facing away from the tube wall 2. In principle, however, with each material projection 4, other boundary surfaces can also be provided with a convex curvature. The remaining, non-convex boundary surfaces can either be flat or concave. The material of the integrally worked-out material projections 4 comes from the fin flank 32, with recesses 42 additionally being formed in the fin flank 32 due to a material shift during the manufacture of the heat exchanger tubes 1.

Fig. 2 shows a detailed view of a material projection 4 with a curved boundary surface and a tip 41 which touches the tube wall 2 in the region of the primary groove 34. The cavity 5 formed from the rib base 31 and the inside of the material projections 4 has an approximately cylindrical cavity.

The maximum clear width x _{1 of} a cavity 5 is considerably smaller than the longitudinal extension x _{2 of} the cavity 5. This creates elongated cavities which form bubble nuclei particularly efficiently and contribute to an increase in the heat transfer during evaporation. The dimension of the cavity is consequently designed such that when a bubble is detached in the evaporation process, a small bubble residue remains, which then serves as a nucleus for a new cycle of bubble formation. In operation, liquid fluid is preferably accumulated in the area of the recess 42, as a result of which there is increasingly liquid in the area of the bladder germ, which is available for evaporation. With usual structure sizes of Heat exchanger tubes 1 according to the invention with integrally rolled fins 3, the structural size of the material projections 4 and thus also the cavities 5 are typically in the submillimeter range.

Fig. 3 shows a perspective partial view of a rib section of a heat exchanger tube 1 with material projections 4 and raised fluid guide structures 6. From the tube outer side 21, in turn, only part of one of the circumferential, integrally formed ribs 3 is shown. The ribs 3 have a rib foot 31 which attaches to the tube wall 2, rib flanks 32 and a rib tip 33. The ribs 3 protrude radially from the tube wall 2. The rib flanks 32 are provided with additional structural elements which are designed as material projections 4. The fluid guide structures 6 formed essentially extend in the axial and radial directions of the tube 1.

In Fig. 3 two fluid guide surfaces 62 are assigned to each of the material projections 4. The fluid guide surfaces 62 are brought radially from the outside to the material projections 4. The surface of the tube 1 is enlarged by the fluid guide structures 6. Furthermore, the edges of the fluid guide surfaces 62 facing away from the rib flank 32 represent convex edges, on which the liquid fluid is preferably collected and directed to the cavity 5. In the Fig. 3 Fluid guide surfaces 62 shown are flat surfaces. However, surfaces of this type can also be curved in themselves or also assume a wavy shape.

As in Fig. 3 also shown, the axial extent of the fluid guiding surfaces 62 is smaller than the axial extent of the material projections 4. This results in pocket-like structures as recesses 42 on the rib flank 32. Consequently, in the case of a heat exchanger tube 1 designed in this way, liquid fluid can also collect in the pocket-like structures 42 are available for the evaporation process. The surface of the tube 1 is thus specifically covered with liquid fluid. This favors the Evaporation process, which increases the performance of the pipe.

Fig. 4 shows a perspective partial view of a fin section of a heat exchanger tube 1 with a plurality of material projections 4. From the tube outer side 21, in turn, only a part of the circumferential, integrally formed fins 3 is shown. The material of the integrally worked-out material projections 4 originates primarily from the rib flank 32, recesses 42 being produced by a material shift during the manufacture of the heat exchanger tubes 1. Starting from these recesses 42, fluid guide structures 6 run as arc segments 61, which rise on the rib flanks 32 0 toward the rib tip. Such fluid guide structures 6 consequently extend from a cavity 5 to the cavity 5 adjacent in the circumferential direction of the ribs 3. As a result, the liquid flows particularly efficiently radially along the rib flank 32 to the cavity 5.

LIST OF REFERENCE NUMBERS

1

heat exchanger tube

2

tube wall

21

Pipe outside

22

Pipe inside

3

Rib on the outside of the pipe

31

fin base

32

rib flank

33

fin tip

34

primary groove

4

Structural element, material lead

41

top

42

recess

5

cavity

51

opening

52

opening

6

Fluidleitstruktur

61

arc segment

62

Fluidleitfläche

x ₁

clear width of a cavity

x ₂

Longitudinal extension of a cavity

U

direction of rotation

A

pipe axis

Claims (10)

Metallic heat exchanger tube (1), comprising a tube wall (2) and ribs (3) running around the outside of the tube (21), which have a rib base (31), rib flanks (32) and a rib tip (33) and a primary groove formed between the ribs (34), the fin base (31) projecting essentially radially from the tube wall (2), and the fin flanks (32) along the primary groove (34) being provided with additional structural elements (4) which are spaced apart from one another and which are made of the material of the fin flank (32) shaped material projections (4) are formed, which are arranged laterally on the rib flank (32), characterized in that - That the material projections (4) are deformed such that they touch the tube wall (2) in the region of the primary groove (34), so that local cavities (5) are formed, and - That the cavities (5) in the circumferential direction (U) of the ribs have openings (51, 52). Metallic heat exchanger tube (1) according to claim 1, characterized in that the cavities (5) form a cylindrical cavity. Metallic heat exchanger tube (1) according to claim 1 or 2, characterized in that the maximum clear width (x ₁ ) of a cavity (5) is a maximum of half the longitudinal extent (x ₂ ) of the cavity (5). Metallic heat exchanger tube (1) according to one of claims 1 to 3, characterized in that fluid guide structures (6) are arranged on the rib flanks (32) between the cavities (5). Metallic heat exchanger tube (1) according to claim 4, characterized in that fluid guide structures (6) are arranged which extend from a cavity (5) to the cavity (5) adjacent in the circumferential direction (U) of the ribs (3). Metallic heat exchanger tube (1) according to claim 5, characterized in that the fluid guide structures (6) on the fin flanks (32) extend in a raised arc segment (61) rising towards the fin tip (33). Metallic heat exchanger tube (1) according to claim 4, characterized in that the fluid guide structures (6) on the rib flanks (32) extend in the radial direction as raised fluid guide surfaces (62). Metallic heat exchanger tube (1) according to claim 7, characterized in that a fluid guide surface (62) directed radially inwards at or in the immediate vicinity of a cavity (5). Metallic heat exchanger tube (1) according to one of claims 4, 7 or 8, characterized in that a fluid guide surface (62) directed radially outwards at or in the immediate vicinity of the fin tip (33). Metallic heat exchanger tube (1) according to one of claims 4 to 8, characterized in that the fluid guide structures (6) on the fin flanks (32) extend in the radial direction outward and extend to a maximum of half the fin height.

Images