EP1223400A2 - Tube for heat exchanger and process for making same - Google Patents

Abstract

A metallic heat exchanger tube, especially for vaporizing liquids comprising pure materials and mixtures on the outside of the tube, comprises integral ribs (3) on the outside of the pipe, which have a foot (13) that extends radially from the pipe wall (18). Grooves between the ribs have cut-outs in the base. The cut-outs are in the form of cut-back secondary grooves (7).

Description

The invention relates to a metallic heat exchanger tube, especially for the evaporation of liquids from pure substances or mixtures on the outside of the pipe, according to the generic term of claim 1.

Evaporation occurs in many areas of refrigeration and air conditioning technology as well as in process and energy technology. In the Tube heat exchangers are often used in technology which liquids of pure substances or mixtures on the Evaporate the outside of the pipe and thereby on the inside of the pipe cool down a brine or water. Such devices are called flooded evaporators.

By intensifying the heat transfer on the outer tube and the inside of the tube can be the size of the evaporator greatly reduce. This will increase the manufacturing costs of such apparatus. In addition, the necessary filling quantity drops of refrigerants that are mainly used today chlorine-free safety refrigerants not to be neglected Make up part of the total investment costs can. With toxic or flammable refrigerants by reducing the filling quantity, the potential danger decrease. The high-performance pipes that are common today are about three times more powerful than smooth pipes same diameter.

State of the art

The present invention relates to structured Pipes where the heat transfer coefficient is on the outside of the pipe is intensified. Since this is the main part of the Thermal resistance is often shifted to the inside the heat transfer coefficient must be on the inside usually also be intensified. An increase the heat transfer on the inside of the tube usually has an increase in the pipe-side pressure drop.

Have heat exchanger tubes for shell and tube heat exchangers usually at least one structured area as well smooth end pieces and possibly smooth intermediate pieces. The smooth end or intermediate pieces limit the structured Areas. So that the tube can be easily inserted into the tube bundle heat exchanger can be installed, the outer diameter the structured areas should not be larger than the outer Diameter of the smooth end and intermediate pieces.

To increase the heat transfer during evaporation, the Bubble boiling process intensified. It is known that the formation of bubbles at germ sites begins. These germ spots are mostly small gas or vapor inclusions. Such Germination can already be done by roughening the surface produce. If the growing bubble is a certain size reached, it detaches from the surface. If in In the course of the blister detachment the germ site by inflowing If liquid is flooded, the inclusion of gas or steam displaced by liquid. In this case the Germ site inactivated. This can be done by an appropriate one Avoid designing the germ sites. For this it is necessary that the opening of the germination point is smaller than that under the Opening cavity.

It is state of the art to base such structures of integrally rolled finned tubes. Under integral rolled finned tubes are understood to be finned tubes, where the fins are made of the wall material of a smooth tube were formed. There are different procedures here known with which the located between adjacent ribs Channels are closed in such a way that connections between channel and environment in the form of pores or slits stay. Because the opening of the pores or slits is smaller than the width of the channels, the channels represent suitably shaped Cavities represent the formation and stabilization of bladder germ sites favor. In particular, such are essentially closed channels by bending or folding the Rib (US 3,696,861, US 5,054,548), by splitting and upsetting the rib (DE 2,758,526, US 4,577,381), and by notches and Compression of the rib (US 4,660,630, EP 0.713.072, US 4,216,826) generated.

The most powerful, commercially available finned tubes for flooded evaporators on the outside of the tube a rib structure with a rib density of 55 to 60 Ribs per inch (US 5,669,441, US 5,697,430, DE 197 57 526). This corresponds to a rib pitch of approx. 0.45 to 0.40 mm. In principle it is possible to improve the performance of such Pipes through an even higher fin density or smaller fin pitch to improve, as this increases the density of the bladder germs is increased. A smaller rib division is required inevitably equally fine tools. Finer tools However, there is a higher risk of breakage and faster Subject to wear. The tools currently available enable a safe production of finned tubes with fin density of a maximum of 60 ribs per inch. Furthermore, with decreasing rib pitch the production speed of the Pipes are smaller and consequently the manufacturing costs are higher.

It is known that increased evaporation structures with the same fin density on the outside of the pipe can be generated by placing the bottom of the groove between structured the ribs. EP 0.222.100 proposes the bottom of the groove by means of a notched disk with indentations to provide. The indentations on the bottom of the groove can be V-, Have a trapezoidal or semicircular cross-section additional bladder germ sites represent. The by such Structures especially in the area of small heating surface loads achievable performance increases are not sufficient more the demands of the market. Furthermore, the impressions a weakening of the core wall of the tube and lead to a reduction in the mechanical stability of the Tube.

Task:

It is said to be a performance-enhanced heat exchanger tube Evaporation of liquids on the outside of the pipe same tube-side heat transfer and pressure drop as well same manufacturing costs are produced. The mechanical The stability of the pipe should not be adversely affected.

Brief description of the invention

The task is the one mentioned in a heat exchanger tube Type in which the area between the Ribs of helical primary grooves are arranged, solved according to the invention, that the recesses in the form of undercut secondary grooves are trained.

• in einer Schnittebene ein nicht abgeschlossenes Gebiet X zu finden ist,
• dieses Gebiet X mittels einer Strecke AB abgeschlossen werden kann,
• eine Strecke PQ mit P, Q ∈ Rand von X gefunden wird, so daß PQ parallel zu AB und die Länge von PQ größer ist als die Länge von AB.

An undercut groove (see Fig. 1) is present when

• an incomplete area X can be found in a sectional plane,
• this area X can be closed off by a route AB,
• a distance PQ with P, Q ∈ edge of X is found, so that PQ is parallel to AB and the length of PQ is greater than the length of AB.

An undercut secondary groove provides for education and Stabilization of bladder germ sites much cheaper Conditions than the simple ones proposed in EP 0.222.100 Indentations. The location of the undercut secondary grooves in the proximity of the primary groove bottom is for the evaporation process Particularly favorable because the wall overtemperature at the bottom of the groove is largest and therefore the highest driving force there Temperature difference for blistering is available.

Claims 2 to 15 relate to preferred embodiments of the heat exchanger tube according to the invention.

According to the invention, after the ribs have been formed, suitable additional tools material from the field of Rib flanks displaced towards the bottom of the groove, so that not there Completely closed cavities emerge that are the desired ones represent undercut secondary grooves. The cavities extend from the primary groove bottom to the tip of the rib, with a maximum of 45% of the rib height H, typically Extend to 20% of the rib height H. The rib height H is from the deepest part of the bottom of the groove through the largest roller was formed up to the tip of the rib of the fully formed finned tube measured.

The invention relates to claims 16 to 22 furthermore various processes for the production of the invention Heat exchanger tube.

Detailed description:

The invention is illustrated by the following examples explained in more detail:

Fig.1:

die Prinzipskizze einer hinterschnittenen Nut;

Fig.2:

schematisch die Herstellung eines erfindungsgemäßen Wärmeaustauscherrohres mit hinterschnittenen Sekundärnuten, die auf der Rohraußenseite mit im wesentlichen konstanten Querschnitt schraubenlinienförmig umlaufen;

Fig.3:

eine Teilansicht eines erfindungsgemäßen Wärmeaustauscherrohres mit hinterschnittenen Sekundärnuten, die mit im wesentlichen konstanten Querschnitt schraubenlinienförmig umlaufen;

Fig.4:

schematisch die Herstellung eines erfindungsgemäßen Wärmeaustauscherrohres mit schraubenlinienförmig verlaufenden, hinterschnittenen Sekundärnuten, deren Querschnitt in regelmäßigen Abständen variiert ist;

Fig.5:

eine Teilansicht eines erfindungsgemäßen Wärmeaustauscherrohres mit schraubenlinienförmig verlaufenden, hinterschnittenen Sekundärnuten, deren Querschnitt in regelmäßigen Abständen variiert ist;

Fig.6:

schematisch die Herstellung eines erfindungsgemäßen Wärmeaustauscherrohres mit hinterschnittenen Sekundärnuten, die im wesentlichen quer zur Richtung der Primärnuten verlaufen;

Fig.7:

eine Teilansicht eines erfindungsgemäßen Wärmeaustauscherrohres mit hinterschnittenen Sekundärnuten, die im wesentlichen quer zur Richtung der Primärnuten verlaufen;

Fig.8:

das Foto einer erfindungsgemäßen hinterschnittenen Sekundärnut am Nutengrund, die mit im wesentlichen konstanten Querschnitt schraubenlinienförmig umläuft;

Fig.9:

ein Diagramm, das den Leistungsvorteil durch die hinterschnittenen Sekundärnut am Nutengrund dokumentiert.

It shows:

Fig.1:

the schematic diagram of an undercut groove;

Figure 2:

schematically the production of a heat exchanger tube according to the invention with undercut secondary grooves, which run on the outside of the tube with a substantially constant cross-section helically;

Figure 3:

a partial view of a heat exchanger tube according to the invention with undercut secondary grooves, which run with a substantially constant cross section helically;

Figure 4:

schematically the production of a heat exchanger tube according to the invention with helical, undercut secondary grooves, the cross section of which is varied at regular intervals;

Figure 5:

a partial view of a heat exchanger tube according to the invention with helical, undercut secondary grooves, the cross section of which is varied at regular intervals;

Figure 6:

schematically the production of a heat exchanger tube according to the invention with undercut secondary grooves, which run essentially transversely to the direction of the primary grooves;

Figure 7:

a partial view of a heat exchanger tube according to the invention with undercut secondary grooves, which extend substantially transversely to the direction of the primary grooves;

Figure 8:

the photo of an undercut secondary groove according to the invention on the groove base, which revolves in a helical manner with a substantially constant cross section;

Figure 9:

a diagram that documents the performance advantage through the undercut secondary groove on the groove base.

The integrally rolled finned tube 1 according to FIGS. 2 to 7 has on the outside of the tube helical ribs 3, between which a primary groove 4 is formed. material the rib flanks 5 are suitably shifted so that in the area of the bottom 6 of the groove are not completely closed, the undercut secondary grooves according to the invention represent. Material of the rib tips 8 is such relocated that the rib spaces with formation of Channels 9 are closed except for pores 26.

The finned tube according to the invention is produced by a rolling process (see US Pat. Nos. 1,865,575 / 3,327,512) by means of the devices shown in Figures 2/4/6.

A device is used which consists of n = 3 or 4 Tool holders 10, in each of which a rolling tool 11 is integrated. The tool holder 10 are each 360 ° / n offset on the circumference of the finned tube. The tool holder 10 are radially deliverable. They are in turn a stationary roller head (not shown).

The smooth pipe entering the device in the direction of the arrow 2 is driven by the driven rolling tools arranged on the circumference 11 set in rotation, the axes of the rolling tools 11 run obliquely to the pipe axis. The rolling tools 11 consist of several side by side in a manner known per se arranged rolling disks 12, the diameter in Arrow direction increases. The centrally arranged rolling tools 11 form the helical circumferential ribs 3 from the tube wall of the smooth tube 2, being in the forming zone the tube wall is supported by a rolling mandrel 27. The rolling mandrel 27 can be profiled. The along the pipe axis measured distance between the centers of two adjacent ribs referred to as the rib pitch T. The rolling disks are on hers profiled outer circumference such that the shaped ribs 3rd have a substantially trapezoidal cross-section. Only in the transition area 13 between the rib flank 5 and the bottom of the groove 6 the rib deviates from the ideal trapezoidal shape. This Transition area 13 is usually referred to as a rib base. The radius formed there is required to be one unimpeded material flow during the rib formation enable.

After the formation of the essentially trapezoidal ribs 3 by the rolling tool 11 in the area of the bottom 6 of the Primary grooves 4, the undercut secondary grooves according to the invention 7 generated. Here, three different embodiments can be used Find application:

Embodiment 1:

After the last disc of the rolling tool 11 is a cylindrical disc 14 is engaged, the diameter is smaller than the diameter of the largest roller disc (Fig. 2). The thickness D of this cylindrical disc 14 is somewhat larger than the width B of the formed by the rolling disks 12 Primary groove 4, here the width B of the primary groove 4 on the Point is measured at which the rib flank 5 in the radius area of the fin base 13 passes over. Typically is the thickness D of the cylindrical disc 50% to 80% of the rib pitch T. The cylindrical disc 14 displaces material from the rib flank 5 towards the bottom 6 of the groove. The displaced material is determined by the appropriate choice of tool geometry shifted such that there are 6 material projections above the groove base 15 forms and thus directly at the bottom of the groove 6 not completely closed cavity 7 is formed (Fig. 3). This cavity 7 runs in the circumferential direction with almost constant cross section. The cavity 7 represents one undercut secondary groove according to the invention.

It may prove useful to have the disk 14 on it Lateral surface along its circumference with a completely or sectionally concave profile, so as to avoid displacement to favor the material of the rib flank 5.

Since the diameter of the cylindrical disc 14 is smaller than the diameter of the largest rolling disc of the rolling tool 11, the deepest point of the primary groove base 6 through the cylindrical disc 14 is not machined. The pipe wall 18 is accordingly in the formation of the undercut secondary grooves 7 not weakened.

Embodiment 2:

This embodiment is an extension of the embodiment 1 represents: After the cylindrical disc 14 is in the second embodiment, a gear-like notched disk 16 engaged, the diameter of which is larger than the diameter the cylindrical disc 14, but at most as large like the diameter of the largest rolling disc of the rolling tool 11 (Fig. 4). The formed by the cylindrical disc 14 in Circumferential direction with constant cross-section Cavity is through the notched disk 16 through in the circumferential direction regularly arranged impressions 17 divided. It This creates circumferential, undercut circumferential Secondary grooves 7, the cross section of which at regular intervals is varied (Fig. 5). The notched disk 16 can be straight or be helical.

Since the diameter of the gear-like notched disk 16 is not is larger than the diameter of the largest rolling disc of the Rolling tool 11, the lowest point of the primary groove bottom 6 by the gear-like notched disk 16 deepened. The tube wall 18 is accordingly in the formation of the undercut secondary grooves 7 according to embodiment 2 not weakened.

Embodiment 3:

After the last disc of the rolling tool 11 is a gear-like washer 19 is engaged, the Diameter of the notched disk 19 is at most as large as that Diameter of the largest roller disc (Fig. 6). The thickness D 'of Notched disk 19 is slightly larger than the width B of the Rolling disks 12 shaped primary groove 4, here the width B of the primary groove 4 is measured at the point where the Rib flank 5 merges into the radius area of the rib foot 13. The thickness D 'of this notched disk is typically 50% to 80% of the rib pitch T. The notched disk 19 can be straight or helical. The notched disk 19 displaces Material from the area of the rib flanks 5 and from the Radius area at the fin base 13 and leaves each other there spaced indentations 20. The displaced material preferably in the unprocessed area between each Impressions 20 relocated so that there are pronounced Dams 21 on the bottom of the groove 6 arise, which are transverse to the primary Grooves 4 run between the ribs 3. The following now Rolling disc 22 of constant diameter deforms the upper Areas of these dams 21 in the direction of the pipe circumference, so that between the deformed upper regions 23 of the dams 21 and the groove bottom 6 small cavities 7 between two neighboring ones Dams 21 are formed (Fig. 7). Make these cavities 7 the undercut secondary grooves according to the invention. The diameter of the roller plate 22 must be chosen smaller are called the diameter of the base washer 19th

Since the diameter of the gear-like notched disk 19 is not is larger than the diameter of the largest rolling disc of the Rolling tool 11, the lowest point of the primary groove bottom 6 by the gear-like notched disk 19 no further deepened. The tube wall 18 is accordingly in the formation of the undercut secondary grooves 7 according to embodiment 3 not weakened.

After the undercut secondary grooves 7 on the bottom 6 were generated, the rib tips 8 by means of a notched gear-like notched disk 24. This is in the figures 2/4/6 shown. Subsequently, the notched rib tips by one or more compression rollers 25. The ribs 3 thus have a substantially T-shaped Cross section, and the grooves 9 between the ribs 3 are up closed on pores 26 (see FIGS. 3/5/7).

The fin height H is the lowest on the finished finned tube 1 Place the bottom of the groove 6 up to the tip of the ribs completely shaped finned tube measured.

The undercut secondary grooves 7 according to the invention Bottom 6 of the primary grooves 4 extend from the bottom 6 of the groove Rib tip down, with a maximum of 45% of the rib height H, typically up to 20% of the rib height H.

8 shows the photo of an undercut according to the invention Secondary groove 7 at the bottom of the groove 6. The cutting plane is vertical to the circumferential direction of the pipe. Here is an example shown according to embodiment 1. The recognizable asymmetry the structure is due to unavoidable tolerances in tool and Due to raw material dimensions. The projections 15 exist made of material from the rib flanks 5 to the bottom 6 of the groove was relocated.

Fig. 9 shows the performance of two structured in comparison Pipes on the evaporation of the refrigerant R-134a the outside of the pipe, one of the pipes with undercut Secondary grooves on the groove base was carried out. shown is the external heat transfer coefficient above the heating surface load. The saturation temperature is 14.5 ° C. It can be seen that the undercut secondary grooves on A performance advantage is achieved that is small Heating surface loads over 30%, with large heating surface loads is about 20%.

Structures with undercut secondary grooves on the bottom of the groove are also proposed in EP 0.522.985. Here is however, the structure is on the inside of a pipe. Around the mechanical stability of such pipes in particular To ensure expansion of the pipes, the secondary grooves be as flat as possible. This is through the in EP 0.522.985 described acute-angled geometry of the secondary grooves reached. In the case of evaporation of refrigerants on the pipe side there is usually a higher pressure in the pipe than on the outside of the pipe. Under internal pressure is due to the notch effect from the acute-angled edges of the Secondary grooves an increased mechanical load on the wall of the pipe. This must be compensated for by a thicker tube wall become. This safety margin in the pipe wall however leads to an increased use of materials and thus to increased costs.

In the undercut design proposed here Secondary grooves 7 in the area of the primary groove base 6 on the However, there is no weakening on the outside of finned tubes the tube wall 18 instead, since to form the secondary grooves 7 only material from the area of the rib flanks 5 and possibly from the radius area 13 above the bottom of the groove 6 is used.

Claims (22)

Metallic heat exchanger tube, in particular for the evaporation of liquids from pure substances or mixtures on the outside of the tube, with integral fins (3) formed on the outside of the tube, the base (13) of which projects essentially radially from the tube wall (18), whereby in the area of the groove base ( 6) of the primary grooves (4) extending between the ribs (3), recesses are arranged, characterized in that the recesses are designed in the form of undercut secondary grooves (7). Metallic heat exchanger tube according to claim 1, characterized in that the ribs (3) and the primary grooves (4) run helically. Metallic heat exchanger tube according to claim 1, characterized in that the ribs (3) and the primary grooves (4) extend in an annular manner. Metallic heat exchanger tube according to claim 1, characterized in that the ribs (3) and the primary grooves (4) run in the axial direction. Metallic heat exchanger tube according to claim 2, 3 or 4, characterized in that the undercut secondary grooves (7) run in the direction of the primary grooves (4) with an essentially constant cross section. Metallic heat exchanger tube according to claim 2, 3 or 4, characterized in that the cross section of the undercut secondary grooves (7) running in the direction of the primary grooves (4) is varied at regular intervals. Metallic heat exchanger tube according to claim 2, 3 or 4, characterized in that the undercut secondary grooves (7) run essentially transversely to the direction of the primary grooves (4). Metallic heat exchanger tube according to one or more of claims 1 to 7, characterized in that the undercut secondary grooves (7) extend up to a maximum of 45% of the fin height H. Metallic heat exchanger tube according to claim 8, characterized in that the undercut secondary grooves (7) extend up to a maximum of 20% of the fin height H. Metallic heat exchanger tube according to one or more of claims 1 to 9, characterized in that the ribs (3) have a uniform height H. Metallic heat exchanger tube according to one or more of claims 1 to 9, characterized in that the fin tips (8) are notched. Metallic heat exchanger tube according to claim 10 or 11, characterized in that the ribs (3) have a substantially T-shaped cross section. Metallic heat exchanger tube according to one or more of claims 1 to 12, characterized in that it has smooth ends and / or smooth intermediate areas. Metallic heat exchanger tube according to one or more of claims 1 to 13, characterized in that it is designed as a seamless tube. Metallic heat exchanger tube according to one or more of claims 1 to 13, characterized in that it is designed as a longitudinally welded tube. A method of manufacturing a heat exchange tube according to claim 2, in which the following process steps are carried out: a) Helical ribs (3) are rolled out on the outer surface of a smooth tube (2), in that the rib material is obtained by displacing material from the tube wall to the outside by means of a rolling process and the resulting finned tube (1) is rotated by the rolling forces and / or is advanced according to the resulting fins (3), the fins (3) being formed from the otherwise undeformed smooth tube (2) with increasing height, b) the smooth tube (2) is supported by a rolling mandrel (27) therein, c) after the ribs (3) have been shaped out, material is displaced by radial pressure from the rib flanks (5) and / or from the transition region (13) on the rib base, forming the undercut secondary grooves (7) to the groove base (6). Method according to claim 16 for producing a heat exchanger tube according to claim 5, characterized in that the radial pressure in method step c) is generated by means of a cylindrical disk (14),
whose diameter is smaller than the diameter of the largest roller disc (12) and whose thickness D is at least 50% and at most 80% of the fin pitch T. Method according to claim 17 for producing a heat exchanger tube according to claim 6, characterized in that method step c) is followed by method step d),
in which the base of the groove (6) by further radial pressure by means of a toothed-wheel-type notched disk (16),
whose diameter is larger than the diameter of the cylindrical disc (14), but at most as large as the diameter of the largest roller disc (12), is deformed in places in this way,
that in the circumferential direction regularly spaced indentations (17) arise. Method according to claim 16 for producing a heat exchanger tube according to claim 7, characterized in that the radial pressure in method step c ') is generated by means of a toothed-wheel-type notched disk (19),
the diameter of which is smaller than the diameter of the largest roller disk (12), as a result of which indentations (20) spaced apart from one another are produced, and
that step d ') follows,
in which the undercut secondary grooves (7) are produced by further radial pressure using a cylindrical roller plate (22). Method according to claim 18 or 19, characterized in that in each case a straight or helically toothed notched disk (16, 19) is used. Method according to one of claims 17 to 20 for producing a heat exchanger tube according to claim 11, characterized in that in a further method step e) the fin tips (8) are notched by radial pressure by means of a gear-like notched disk (24). Method according to one of claims 17 to 21, characterized in that in a method step f) by further radial pressure the rib tips (8) are compressed to an essentially T-shaped cross section by means of at least one compression roller (25).

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