DE102018004701A1 - Metallic heat exchanger tube - 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), the rib foot (31) projecting essentially radially from the tube wall (2), and the rib flanks (32) along the primary groove (34) with additional spaced apart structural elements (4), which are provided as Material of the rib flank (32) shaped material projections (4) are formed, which are arranged laterally on the rib flank (32). The material projections (4) are deformed such that they touch the tube wall (2) in the area 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 circumferential ribs on the outside of the tube according to the preamble of claim 1.

Such metallic heat exchanger tubes 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. Frequently, shell-and-tube heat exchangers are used, in which liquids from pure substances or mixtures on the outside of the pipe evaporate, cooling brine or water on the inside of the pipe. Such apparatuses are referred to as flooded evaporators.

By intensifying the heat transfer on the outside of the pipe or the inside of the pipe, the size of the evaporator can be greatly reduced. As a result, the production costs of such apparatuses decrease. In addition, the necessary filling quantity of refrigerant, which can account for a not inconsiderable share of the total investment costs in today's predominantly used chlorine-free safety refrigerants, is decreasing. In the case of toxic or flammable refrigerants, the risk potential can also be reduced by reducing the filling quantity. The standard high-performance pipes are about four times more efficient than smooth pipes of the same diameter.

It is state of the art to produce 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 were formed from the wall material of a smooth tube. 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 surroundings 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 tubes 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 manufacture of finned tubes with fin densities of up to 60 fins per inch. Furthermore, with decreasing fin pitch, 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. 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 propose to produce undercut secondary grooves on the bottom of the groove between the ribs, 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 produce pyramind-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 other dependent claims relate to advantageous embodiments and further developments of the invention.

The invention includes a metallic heat exchanger tube, comprising a tube wall and ribs surrounding the tube outside, which have a rib base, rib flanks and a rib tip and a primary groove formed between the ribs, the rib base projecting essentially radially from the tube wall, and the rib flanks along the primary groove are provided with additional structural elements spaced apart from one another, which are designed 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 of the process of bubbling is intensified. The formation of bubbles begins at germinal sites. These germinal sites are usually small gas or steam inclusions. When the growing bubble reaches a certain size, it detaches from the surface. If, in the course of bladder detachment, the germinal site is undesirably flooded with liquid, then the germinal site is deactivated. The surface must therefore be designed in such a way that when the bubble is detached, a small bubble remains, which then serves as a germinal point for a new bubble formation cycle. This is achieved by forming local cavities on the surface which have openings in the direction of rotation of the ribs. Through the opening of the exchange of liquid and steam.

A cavity is formed of material of the rib flank, which, similar to a chip formed as a material projection contacts the pipe wall in the primary groove. In a special case, this is the end edge, ie the region of a material projection which is furthest away from the rib flank in the course of curvature. In other words, the deformed material projections have on the front side, as it were, a tip whose front edges or the surface portions directly adjoining these front edges by a conceivable curling operation in the production process can come into contact with the pipe wall in the area of the primary groove. A cavity is consequently formed from the material projection and the rib foot remaining radially inside the material projection and the region of the primary groove adjoining the rib foot until the contact of the material projection. The material projections are particularly preferably arranged on both sides of the ribs.

The length of the areas in the direction of rotation between two cavities can be between 0.2 mm and 0.5 mm. As a result, an optimal coordination of the successive cavities and intermediate areas is achieved.

In addition, the rib tips may be deformed such that they cover the primary grooves in the radial direction and partially close, thus forming a helically encircling, partially enclosed cavity. The rib tips may have, for example, a substantially 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 when the exchange of liquid and steam is controlled in a controlled manner and the flooding of the bubble nucleation point in the cavity is prevented. The location of the cavities in the vicinity of the primary groove bottom is particularly favorable for the evaporation process, since the excess temperature is greatest at the bottom of the groove and therefore the highest driving temperature difference is available there for bubble formation.

In a preferred embodiment of the invention, the cavities can form a cylinder-like cavity. The material projections can deform increasingly with increasing distance from the rib edge, so that they curl up virtually to the contact with the tube wall and thereby forms a cylindrical tube. A cylinder-like cavity has in the direction of rotation of the ribs two substantially similar openings through which a bubble germ supports the evaporation process of a fluid.

Advantageously, the maximum clear width of a cavity can be at most half the longitudinal extent of the cavity. As a result, elongated cavities are formed, which represent particularly efficient bubble nucleation sites and contribute to an increase in the heat transfer during evaporation. As the bubble growing out of the elongated cavity reaches a certain size, it detaches from the surface. After detachment, the elongated tube is only partially flooded with liquid as a germination site, whereby the germinal site remains constantly activated. The dimension of the cavity is thus designed so that upon detachment of a bubble, a small bubble remains, which then serves as a nucleation site 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 preferably flows radially through the fluid guide structures 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 remain undisturbed in the Extend 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 guiding 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 efficiently radially along the rib flank. The escaping bubble is not hindered by the inflowing liquid working medium and can expand until it breaks away in the primary groove. Through the Fluidleitstrukturen the respective flow zones for the liquid and for the steam are spatially separated.

In a further advantageous embodiment, the fluid guide structures may extend on the rib flanks in a raised arc segment rising toward the rib tip. By such Fluidleitstrukturen the fluid is led to the cavities as Blasenkeimstellen for evaporation.

Advantageously, the fluid guide structures can extend on the rib flanks in the radial direction as raised fluid guide surfaces. Raised fluid guide surfaces can provide particularly effective for a material transport to the heat exchanger tube and thus for efficient heat exchange due to relatively sharp edges and the wetting behavior of the liquid fluid.

In a preferred embodiment of the invention, a fluid guide surface can end radially inwardly at or in the immediate vicinity of a cavity. Such structures provide a targeted fluid management and thus efficient heat dissipation on the outside of the tube.

Advantageously, a fluid guide surface may terminate radially outward at or in the immediate vicinity of the fin tip. Thus, starting from the region of the rib tip, the liquid fluid is already guided radially along the rib wall for heat exchange along the rib wall.

In a further advantageous embodiment of the invention, the Fluidleitstrukturen at the rib edges in the radial direction outward maximally up to half of the rib height can extend. For manufacturing reasons, the fin tip can be made extremely narrow, whereby radially inwardly directed a rib only in the middle part and in the region of the rib foot has a sufficient width and thus enough material to form a material projection from the flank.

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

• 1 eine perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaustauscherrohres mit Werkstoffvorsprüngen,
• 2 eine Detailansicht eines in 1 dargestellten Werkstoffvorsprungs mit einer gekrümmten Begrenzungsfläche,
• 3 eine perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaustauscherrohres mit Werkstoffvorsprüngen und erhabenen Fluidleitstrukturen, und
• 4 eine weitere perspektivische Teilansicht eines Rippenabschnitts eines Wärmeaustauscherrohres mit Werkstoffvorsprüngen und bogenartigen Fluidleitstrukturen.

In it show:

• 1 2 shows a perspective partial view of a fin section of a heat exchanger tube with material projections,
• 2 a detailed view of an in 1 material projection shown with a curved boundary surface,
• 3 a partial perspective view of a rib portion of a heat exchanger tube with material projections and raised fluid guide structures, and
• 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 in all figures with the same reference numerals.

1 shows a partial perspective view of a fin portion of a heat exchanger tube 1 with four material projections 4 , From the outside of the pipe 21 is only part of the circumferential, integrally formed ribs 3 displayed. Ribs 3 have a ribbed foot 31 that on the pipe wall 2 attaches, rib flanks 32 and a rib tip 33 , The rib 3 stands essentially radially from the pipe wall 2 from. The rib flanks 32 are provided with additional structural elements that serve as material projections 4 are formed on the side of the rib flank 32 begin. The material advantages 4 have front tips 41 on which the pipe wall 2 in the area of the primary groove 34 touch. This forms together with the costal foot 31 wells 5 from which in the direction of rotation U the rib openings 51 . 52 respectively. Such cavities 5 prefer to form bubble nuclei in the evaporation process of a fluid, which promote heat exchange.

In the embodiment shown, the boundary surfaces are the material projections 4 on the of the pipe wall 2 opposite side convexly curved. In principle, however, with every material head start 4 other boundary surfaces can also be equipped with a convex curvature. The remaining, non-convex boundary surfaces can either be flat or concave. The material of the integral protrusions 4 comes from the rib flank 32 , due to a material shift in the manufacture of the heat exchanger tubes 1 additional recesses 42 in the rib flank 32 arise.

2 shows a detailed view of a material projection 4 with a curved boundary surface and a tip 41 which the pipe wall 2 in the area of the primary groove 34 touched. The ribbed foot 31 and the inside of the material projections 4 formed cavity 5 has an approximately cylindrical cavity.

The maximum clear width x ₁ a cavity 5 is much less than the longitudinal extent x ₂ the cavity 5 , This creates elongated cavities, which form bubble nuclei particularly efficiently and contribute to an increase in 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 the nucleus for a new cycle of bubble formation. In the area of the recess 42 liquid fluid is preferably accumulated during operation, as a result of which there is increased liquid in the area of the bladder germ, which is available for evaporation. With the usual structure sizes of the heat exchanger tubes according to the invention 1 with integrally rolled ribs 3 is the structure size of the material projections 4 and with it the cavities 5 typically in the submillimeter range.

3 shows a partial perspective view of a fin portion of a heat exchanger tube 1 with material projections 4 and raised fluid guide structures 6 , From the outside of the pipe 21 is in turn only part of one of the circumferential, integrally formed ribs 3 displayed. Ribs 3 have a ribbed foot 31 that on the pipe wall 2 attaches, rib flanks 32 and a rib tip 33 , Ribs 3 stand radially from the pipe wall 2 from. The rib flanks 32 are provided with additional structural elements that serve as material projections 4 are trained. The trained fluid guide structures 6 extend essentially in the axial and radial direction of the tube 1 ,

In 3 are to each of the material tabs 4 two fluid control surfaces each 62 assigned. The fluid guide surfaces 62 are radially from the outside to the material projections 4 introduced. Through the fluid guide structures 6 becomes the surface of the pipe 1 increased. They also represent the rib flank 32 opposite edges of the fluid guide surfaces 62 convex edges on which the liquid fluid preferentially accumulates and to the cavity 5 is directed. In the 3 shown fluid guide surfaces 62 are flat surfaces. However, surfaces of this type can also be curved in themselves or assume a wavy shape.

As in 3 also shown is the axial extent of the fluid guide surfaces 62 smaller than the axial extension of the material projections 4 , This creates on the rib flank 32 pocket-like structures as recesses 42 , Consequently, in such a heat exchanger tube 1 also liquid fluid in the pocket-like structures 42 collect and be available for the evaporation process. It becomes the surface of the pipe 1 thus specifically covered with liquid fluid. This favors the evaporation process, which increases the performance of the pipe.

4 shows a partial perspective view of a fin portion of a heat exchanger tube 1 with several material projections 4 , From the outside of the pipe 21 is in turn only part of the circumferential, integrally formed ribs 3 displayed. The material of the integral protrusions 4 comes primarily from the rib flank 32 , due to a material shift in the manufacture of the heat exchanger tubes 1 recesses 42 arise. Based on these recesses 42 run fluid guidance structures 6 as arc segments 61 that on the rib flanks 32 0 Rise to the tip of the rib. Such fluid guide structures 6 thus extend from a cavity 5 for the direction of rotation of the ribs 3 adjacent cavity 5 , As a result, the liquid flows particularly efficiently radially along the rib flank 32 to the cavity 5 after.

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

primary groove

4

Structural element, material projection

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

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 3696861 A [0005]
• US Pat. No. 5,054,548 [0005]
• US 7178361 B2 [0005]
• DE 2758526 C2 [0005]
• US 4577381 A [0005]
• US 4660630 A [0005]
• EP 0713072 B1 [0005]
• US 4216826A [0005]
• US 5669441 A [0006]
• US 5697430 A [0006]
• DE 19757526 C1 [0006]
• EP 0222100 B1 [0007]
• US 5186252 A [0007]
• JP 4039596 B2 [0007]
• EP 1223400 B1 [0007]

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) spaced apart from one another, which are made of the material of the fin flank (32) formed material projections (4) are formed, which are arranged laterally on the rib flank (32), characterized in that - the material projections (4) are deformed in such a way that they the tube wall (2) in the region of the primary groove (34) touch so that local cavities (5) are formed and - that the cavities (5) have openings (51, 52) in the circumferential direction (U) of the ribs. Metallic heat exchanger tube (1) after Claim 1 , characterized in that the cavities (5) form a cylindrical cavity. Metallic heat exchanger tube (1) after 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 the 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) after 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) after Claim 5 , characterized in that the fluid guide structures (6) extend on the rib flanks (32) in a raised arc segment (61) rising towards the rib tip (33). Metallic heat exchanger tube (1) after 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) after 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 the Claims 4 . 7 or 8th , characterized in that a fluid guide surface (62) directed radially outwards ends at or in the immediate vicinity of the rib tip (33). Metallic heat exchanger tube (1) according to one of the Claims 4 to 8th , characterized in that the fluid guide structures (6) on the rib flanks (32) extend outward in the radial direction and extend to a maximum of half the rib height.

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