DE102014108209A1 - heat exchangers - Google Patents

Abstract

Heat exchanger (1) comprising tubes (2) with outer ribs (3) and having the following features: 1. Several rows (R1, R2) of the tubes (2) are arranged one behind the other in the direction of flow (P); 1.2. The rows (R1, R2) are transverse to the direction of flow (P); 1.3. The tubes (2) of successive rows (R1, R2) are displaced by a transverse offset (VQ) parallel to the previous row (R1, R2), the transverse offset (VQ) being unequal to a transverse separation distance (TQ) transverse to the direction of flow (P) , or 1.4. the tubes (2) adjacent within a row (R1, R2) are offset from one another by a longitudinal offset (VL) running in the direction of flow (P), the longitudinal offset (VL) being smaller than a longitudinal pitch (TL) of the tubes (2) successive rows (R1, R2); 1.5. The transverse pitch (TQ) of the tubes (2) of a row (R1, R2) is greater than the average width (B) of the ribs (3) measured transversely to the plane of view (4) of the row (R1, R2), so that its gap (5) is present between the ribs (3) of adjacent tubes (2) of 0.1 to 0.5 times the mean width (B); 1.6. The quadrangular ribs (3) have winglets (6a, 6b).

Description

The invention relates to a heat exchanger with the features of claim 1.

Finned tube heat exchangers are generally used as air-cooled shell-and-tube heat exchangers. In order to efficiently carry out air-cooled heat exchangers, the highest possible heat transfer coefficients are sought. One measure to increase the heat transfer properties lies in the turbulence generation at the ribs. In doing so, turbulators redirect the flow of air in a particular way to improve fin efficiency. The fin efficiency is the ratio of the heat flow that the fin actually delivers to the ideal heat flow the rib would emit if it had the tube temperature along its entire length. It also includes ribbed tubes with corrugated ribs to the prior art, such as by the EP2379977B1 ,

The k-value to be improved by this measure, the heat transfer coefficient as a measure of the heat flow of a fluid through a solid body, such. A pipe wall, into a second fluid due to a temperature difference between the fluids. The heat flow Q. is calculated from the heat transfer coefficient k multiplied by the area of the heat exchanger A and the mean temperature difference Δθm of the two fluids, that is, between air (outside) and product (inside). At the same time electric power must be applied in forced-cooled systems to pass the cooling air by means of fans on the heat exchanger tubes and the ribs. The necessary electrical energy is proportional to the product of the volume flow v. and the pressure loss Δp across the heat exchanger: P _sl ~ V. · Δp. In order to keep the power consumption small, low pressure losses are sought, so that a larger volume flow can be transported. At the same time, a high volume flow also means that a larger amount of cooler air can be brought to the heat exchanger.

The applicant is known from his own practice to arrange heat exchanger tubes in several rows one behind the other. The aim is to transfer a high heat output to the heat exchanger with a small construction volume. For this purpose, the heat exchanger tubes can be arranged one behind the other so that a heat exchanger tube in the second row is effectively in the lee of the tube of the first row. The tubes of the successive rows are arranged in alignment in this sense. It is also known to arrange the heat exchanger tubes of immediately consecutive rows displaced relative to each other. In the shifted arrangement, the inflow surfaces of the downstream rows of tubes are not in the immediate lee of the tubes of the preceding row of tubes.

In order to keep the volume of construction of a heat exchanger as low as possible, so far as many pipes and ribs have been arranged in a small space. Therefore, the division, i. H. the distance between the tubes comparatively low. Between the individual ribbed tubes remains only a very small gap, so that the rib density is high overall. However, then the pressure loss is high and thus an increased electrical power for the fan required.

The invention has for its object to provide a heat exchanger, which has an improved k value.

The invention solves this problem by a heat exchanger having the features of patent claim 1.

The subclaims relate to appropriate, not self-evident embodiments of the inventive concept.

The heat exchanger according to the invention comprises tubes with outer ribs, wherein a plurality of rows of the tubes are arranged one behind the other in the flow direction. The surface penetrated by the flow is referred to as the viewing surface of the heat exchanger. The successively arranged rows of tubes run transversely to the direction of flow. The tubes of successive rows are offset by a transverse offset parallel to the previous row, that is, transverse to the direction of flow. The transverse offset is not equal to a transverse spacing, which is also measured transversely to the direction of flow. In other words, the tubes of the successive rows are not aligned in the direction of flow.

Alternatively, the adjacent tubes within a row are offset from each other by a longitudinal offset to be measured in the direction of flow. The tubes may be offset alternately to each other, so that in a sense results in a zigzag-shaped row. The longitudinal offset, that is, the offset in the flow direction, is smaller than a longitudinal pitch. The pitch spacing is measured between the tubes of successive rows.

The longitudinal offset is preferably half the size of the longitudinal pitch. This refers to the staggered arrangement of the tubes adjacent within a row. In the shifted arrangement in which the rows of tubes to each other are shifted, the transverse offset is preferably half as large as the transverse pitch. For the invention, the transverse spacing is an important quantity. It will also be referred to below as the pitch.

In the invention, it is provided that the transverse spacing of the tubes of a row is greater than the mean width of the ribs measured transversely to the plane of view of this row, so that a gap between the ribs of adjacent tubes is 0.1 to 0.5 times the mean Width is available. In addition, the quadrangular ribs have winglets.

This constellation of square ribs in combination with the mutually offset tubes, the intended average width of the gap and the winglets has surprisingly enormous positive effects on the heat transfer performance Q. such a heat exchanger. A possibility has been found to increase the k-value while improving the average temperature difference Δθm. There are many developments in which, for example, turbulence generation at the fins causes heat transfer improvement. As a rule, these changes result in the driving temperature difference Δθm being degraded, always under the condition of equal electrical energy which has to be introduced into the system.

The advantages of the invention can best be seen when the objective is a high heat exchanger performance at low electric power for the fans is assumed. These are the typical requirements for heat exchangers in industrial applications.

The electrical power of the fans is proportional to the product of volume flow and pressure loss. If the pressure loss can be reduced, it is possible to increase the flow rate with constant electrical power. The invention makes use of this. However, the increased volume flow does not lead to a reduction of the average temperature difference Δθm between air and the product to be cooled, but - in contrast to other solutions - to an improvement. In combination with the likewise improving k-value, the heat exchanger performance is significantly better than in systems without the inventive features and based on the same electrical power for the fans.

The goal of high heat exchanger performance at low electrical power is achieved by the combination of various measures: on the one hand, the pitch between adjacent pipes must be changed in a particular way. The modification of the pitch results in a reduction of the pressure loss between input and output sides and makes it possible to drive higher flow velocities at low electrical power. However, this alone does not improve the heat transfer coefficient. It must be added that the tubes are arranged offset or shifted to each other. The invention provides at least two rows of finned tubes one behind the other. The transverse offset is preferably selected so that the viewing surfaces of the tubes overlap as little as possible. As a result, the faces of the heat exchanger tubes facing the viewing surface lie directly in the air flow and experience maximum cooling. The tubes in the first row, d. H. in the first streamed row, give off heat, so that the cooling air at an assumed inlet temperature of 30 ° C over the path of the first rib z. B. heated to 45 ° C. The temperature difference Δθ1 in the region of the first rib is in this case 15 ° C. With this inlet temperature, the following row of tubes is then cooled. Here, the cooling air heats up, for example, from 45 ° C to 55 ° C. Accordingly, the temperature difference Δθ2 has fallen from 15 ° C to 10 ° C with respect to this fin row. In a third row, for example, the cooling air then heats up again from 55 ° C to 62 ° C. The temperature difference Δθ3 is only 7 ° C. This example shows that the average temperature difference Δθm between the product to be cooled in the tubes and the cooling air is significantly influenced by the arrangement and shape of the finned tubes. The flow guidance of the product also has a considerable influence on the mean temperature difference Δθm between product and cooling air. Overall, with the embodiment of the heat exchanger according to the invention, a high k value is achieved with a high average temperature difference Δθm. Although the temperature difference .DELTA.i related to a single row naturally decreases with the number of successive rows of tubes, the arrangement of the tubes with the gap between the ribs taking into account all the parameters is so favorable for the k value and at the same time for the average over all rows of tubes Temperature difference Δθm that result in very large heat flows with only a small increase in the size of the heat exchanger. Even if the volume of construction is not increased and therefore less material is installed due to the increased gap width, better heat transfer results than in systems without the features according to the invention.

The ribs of the heat exchanger are quadrangular in their basic form. They can be square or rectangular, so that their adjacent sides are parallel to each other. The adjacent sides can also be at an angle to each other. The ribs can therefore also be trapezoidal, with their width increases in the flow direction. In trapezoidal ribs is spoken in the context of this invention of a mean width of the ribs or average gap width. The width of the gap preferably decreases in the flow direction. The gap width is also greater than zero at the narrowest point and is preferably at least 1.0 mm.

Another important element of the invention are the winglets. The winglets may be polygonal, in particular quadrangular, for example trapezoidal. The winglets can also be triangular. The winglets are preferably exhibitions of the rib material. These exhibitions lead to the fact that in the immediate vicinity of the winglets openings are present in the ribs, through which the cooling air can flow. The winglets preferably have a height in a range of 70% to 100% of the rib spacing of a pipe. The winglets are not necessarily based on the adjacent rib of a finned tube, but bridge this distance only to a large extent. Preferably, the height of the winglets is in a range of 80% to 90% of the rib spacing. These values have shown the best results. The invention provides both winglets, which are integrally integral part of the rib, so also winglets, which are connected as separate components with the rib. The term "winglet" therefore does not mean that an opening adjacent to the winglet is necessarily present, but may preferably be arranged. The winglets are preferably perpendicular or within the scope of manufacturing tolerances substantially perpendicular to the ribs. If necessary, the winglets can also include angles other than 90 ° with the ribs.

The arrangement of the winglets also influences the k-value. The winglets are preferably located in the corner region of a rib and at a distance from the longitudinal sides and transverse sides of the rectangular ribs. Each rib has at least four winglets and especially these four winglets.

The winglets are preferably in the area of the diagonal of the quadrangular ribs, in particular in a range of 40% to 60% of the distance from a corner of a rib to the central tube passing through the rib.

The winglets have a base through which they are connected to the ribs. The orientation of the base also affects the k-value of the heat exchanger. Preferably, the base is at an angle of 20 ° to 50 °, in particular 20 ° to 40 °, to the adjacent longitudinal side of the rib. In particular, the angle is 30 °. It is assumed that the longitudinal side of the rib is parallel to the flow direction. For trapezoidal ribs, the term "longitudinal side" is to be equated with the flow direction or central longitudinal axis of the ribs. All winglets of a rib are preferably exposed to a single side of the rib. The winglets are for example isosceles triangles. You may have a base for this case, which is preferably longer than the other two legs of the triangle. The ratio between the length of the base and the height of the winglets is preferably in a range of 2: 1 to 5: 1.

The winglets can be square as well. In a trapezoidal shape, the winglet is connected to the rib via the wider base. Its narrower upper side points away from the rib. The ratio between the length of the base and the height of the winglets is in a range of 2: 1 to 8: 1. It is preferably 5: 1.

In addition to the winglets, turbulators may be arranged on the ribs, for example in the form of triangular or rectangular displays.

In order to simplify the assembly of the heat exchanger, the ribs are constructed mirror-symmetrically with respect to their longitudinal axis. That is, in each corner of the rib is a winglet. Turbulators can be arranged in the desired number parallel to the longitudinal sides. There is at least one turbulator at a distance from each longitudinal side.

In addition to the shape of the winglets, the shape of the ribs also has an influence on the k value. The rectangular ribs may have an aspect ratio of 1: 1 to 3: 1. This means that the ribs are square in the extreme case. The preferably longer longitudinal sides of such a rib point in the flow direction. The transverse sides are perpendicular to the flow direction.

The gap width of the gap between the ribs of one row is preferably 15% to 45% of the mean width of the ribs. In particular, the gap width is 15% to 30% of the average width of the ribs. These values have shown very good k-value improvements. The same applies to the trapezoidal ribs, in which an average gap width is assumed.

The tubes may be circular in cross-section. The tubes are preferably elliptical in cross section. Advantageously, the average width of the ribs is about twice as large as the short major axis of the ellipse. The ellipse has a width (short major axis) of z. B. 14 mm, so that the rib has an average width of about 28 mm. The gap between The ribs have a gap width in a range of 4 mm to 8 mm. With this configuration, k-value increases have been in the double-digit percentage range, which is a tremendous and unexpected increase in view of the decades of development in this technical field. The deltoid winglets, for example, contribute significantly to increasing the efficiency of the ribs as a means of generating turbulence. The arrangement according to the invention allows an increase in the k value calculated by CFD simulations and proven by practical tests, whereby the heat exchanger according to the invention can be produced less expensively with less use of material.

The invention will be explained in more detail with reference to the embodiments illustrated in the purely schematic drawings. It shows:

1 to 9 Sectional views through portions of heat exchangers of different embodiments in the plan view of the ribs of the heat exchanger.

10 a plan view of a single rib of a tube of a heat exchanger according to the embodiment of the 5 and 6 ;

11 a portion of a finned tube of the heat exchanger of 5 and 6 ;

12 a perspective view of the rib for a tube of a heat exchanger of 5 and 6 ;

13 a plan view of a single rib of a tube of a heat exchanger according to the invention the 3 and 4 ;

14 a perspective view of a ribs according to the 3 . 4 and 13 ;

15 in an enlarged view of a trapezoidal winglet on the rib according to 14 and

16 the relationship between the k value and the Δp value and the flow rate of different types of heat exchangers.

1 shows a sectional view through a portion of a heat exchanger 1 , The heat exchanger 1 includes a variety of elliptical tubes 2 with outer, rectangular ribs 3 , Several of the outside ribbed pipes 2 are arranged in successive rows R1, R2. The heat exchanger 1 is in this embodiment in the image plane from the bottom in the direction of arrow P on the outside of cooling air flowing. The cooling air can be sucked, for example. A non-illustrated fan requires this an electric power Pel. The fan generates a volume flow V., which at a flow velocity v through the viewing surface 4 is encouraged. The viewing area 4 is the flow facing the upstream side of the heat exchanger 1 ,

The pipes 2 are flowed through by a medium to be cooled or product. The medium can be liquid or gaseous. The medium gives heat to the pipe 2 and with it to the ribs 3 from. The cooling air absorbs the heat. As a result, the temperature of the cooling air of row R1 increases by the temperature difference Δθ1 and via the downstream tube row R2 of tubes 2 around the temperature difference Δθ2. Overall, there is a temperature increase Δθ of the cooling air and an average temperature difference between the cooling air and the product to be cooled of Δθm and a pressure drop Δp between the inlet and the outlet side of the heat exchanger 1 ,

In the embodiment of the heat exchanger according to 1 are the pipes 2 arranged in the flow direction one behind the other. This arrangement is referred to as staggered arrangement because the tubes 2 a row of tubes R1, R2 respectively do not lie on a straight line, but in the flow direction of the cooling air forward and backward are. The offset in the direction of the flow of cooling air between adjacent tubes is the longitudinal offset LV. It is half the size of the longitudinal pitch LT of the zigzag-shaped rows R1, R2.

In contrast to the staggered arrangement shows 2 a pushed arrangement in which the individual tubes 2 a row of tubes R1, R2 are moved transversely to the direction of flow of the cooling air to the transverse offset VQ. The transverse offset VQ is half the size of the transverse division TQ. The centers of a row of tubes R1, R2 are enclosed 2 on a common axis. This arrangement is referred to as a pushed arrangement.

The term "row" refers to the tubes, regardless of whether it is a pushed or staggered arrangement 2 a first streamed row R1 and the tubes 2 a subsequent row of tubes R2. The term "row" may also mean, in particular in the staggered arrangement, that the tubes 2 do not lie exactly on a line, but follow one another in a zigzag shape.

The invention provides both in the embodiment of the 1 as well as in the embodiment of 2 before that the individual pipes 2 a row R1, R2 in a particular one Transverse division distance QT or short pitch are arranged to each other. The pitch TQ is greater than that parallel to the viewing area 4 measured width B of a rib 3 , This results in a gap 5 with a gap width S which is in a range of 0.1 to 0.5 times the width B. The pitch TQ results from the sum of the width B of a rib 3 and the gap width S of a gap 5 (TQ = B + S).

While in the pushed arrangement in 1 the pipes 2 two successive rows R1, R2 are aligned in the flow direction one behind the other, are the tubes 2 in the embodiment of the 2 shifted by half the pitch TQ to each other. As a result, there are the flow-facing end faces of the tubes 2 in a position where they can be flowed directly by the sucked air. Unlike heat exchangers, where the gap 5 As small as possible, is the shading of the front side of the tubes 2 lower in the second row R2. As a result, the pressure loss Δp1 across the first row R1 is lower than in a heat exchanger 1 without corresponding average gap width S. Of course, the total pressure loss .DELTA.p between the inlet and outlet side is lower than in an arrangement without a correspondingly wider column 5 ,

The advantages that arise in the embodiment of the 2 were also in the embodiment of the 1 detected. The larger gap width S leads to a reduction of the pressure loss, but not necessarily to a reduction of the heat transfer coefficient K.

The in the 1 and 2 Reference numerals are used for the same components in the following embodiments. To avoid repetition is only to the differences compared to the embodiments of 1 and 2 received. The description of 1 and 2 is therefore to be understood across the other embodiments.

In addition to the shifted or staggered arrangement and the intended gap width S have the ribs 3 in their corner E so-called winglets 6a ( 10 ). In addition to the winglets 6a can in the area of the long sides 7 turbulators 13 be arranged as they are in the 3 and 4 can be seen. The embodiments of the 3 and 4 differ from those of 1 and 2 exclusively by the additional turbulators 13 on the ribs 3 , Details of the turbulators 13 and to the shape of the ribs 3 are in the 13 to 15 shown.

The 5 and 6 show alternative winglets 6b which, unlike the first four embodiments, are not trapezoidal but triangular. Incidentally, the staggered arrangement of the ribs corresponds 3 in the 5 . 6 that of the 1 and 2 , The description there is used to avoid repetition.

In the same way as with the additional turbulators 13 provided ribs 3 as they are in the 7 and 8th are substantially the embodiment of the 3 and 4 , with the difference that the winglets 6b in the corners E are triangular and not trapezoidal. Incidentally, the explanation of the 3 and 4 respectively. 1 and 2 Referenced.

The embodiment of the 9 is essentially the same as that of 6 that is, there is an array of ribs 3 in a pushed arrangement. The only difference from the embodiment of the 6 is that the ribs 3 are trapezoidal. The dimension of the rib 3 in this case refers to the mean width B or the middle gap width S. The gap width S decreases in the flow direction, for example from 9 mm to 1 mm. Incidentally, the description of the 6 respectively. 2 Referenced.

10 shows a rib in a single representation 3 with winglets 6b in their corner areas E. All pipes 2 and ribs 3 are identically designed. Every rib 3 owns four winglets 6b , One winglet each 6b is in the corner E both at a distance from the long side 7 as well as from a transverse side 8th arranged. The aspect ratio between the long side 7 and transverse side 8th is in a range of 1: 1 to 1: 3. The long major axis is HA1 and the short major axis is the elliptical tube 2 is marked HA2. The short major axis HA2 in this example has a length L2 of, for example, 16 mm at a width B of the rib 3 of 26 mm. The length L1 of the long main axis HA1 is 55 mm.

The winglets 6b are as punched out 11 from the rib 3 self-educated. Based on the triangular punched out 11 it can be seen that the winglets 6b are formed as isosceles triangles. The winglets 6b are each perpendicular to the ribs 3 issued. All winglets 6b point in the same direction. In this case, they point out of the picture plane. The winglets 6b are in the corner E not only at a distance from the long side 7 and the transverse side 8th but also at the distance A from the elliptical tube 2 , They are located in a range of 40% to 60% of the distance A from the corner 9 to the pipe 2 is measured. This distance A is the smallest distance to be measured between the tube 2 and the corner 9 , Preferably, the winglets are located 6b at an angle W in a range of 20 ° to 45 ° to the longitudinal side 7 , In particular, the angle is 30 °.

11 shows a single tube 2 with the ribs arranged on it 3 as well as the individual winglets 6b formed as isosceles triangles. The winglets 6b have a height H of 70% to 95% of the rib distance A1 and in particular a height H of 80% to 90% of the rib distance A1.

The base of the winglets 6b that is, those areas along which the winglets 6b have been folded and issued, each has a length of 6 mm ( 10 and 12 ). The winglets designed as an isosceles triangle 6b may in this case have a height H of, for example, 2 mm. It is therefore a symmetrical punching structure.

12 shows a perspective view of a rib 3 with the said, as isosceles triangles trained winglets 6b as well as with a collar 10 over which the ribs 3 with the pipe 2 stay in contact. The collar 10 is slightly higher than the winglets 6b , The collar 10 serves as a spacer between two adjacent ribs 3 ,

While in the 10 and 12 shown ribs no additional turbulators 13 own, illustrate the 13 to 15 an alternative embodiment in which not only additional turbulators 13 are provided, but in which also the shape of the winglets has been changed. The winglets 6a are trapezoidal ( 15 ). Your base 12 is wider than its top 14 , The ratio between the base and length L3 of the base 12 and the height H is in a range of about 1: 5. The ratio of the top 14 to the base 12 is about 3: 5, especially if the angle W1 of the flanks 15 of the winglet 6a is in a range of 30 ° to 60 °, in particular 45 °.

13 shows that the winglets 6a compared to the embodiment of 10 also from punched out 11 the ribs 3 are formed, so that according to the size of the winglets 6a trapezoidal cutouts 11 located in the corners E. The turbulators 13 are also punched out 16 formed and in the direction of the winglets perpendicular to the plane of the ribs 3 issued items. The punched holes are almost square. Accordingly, the turbulators 13 also square. The turbulators 13 are much smaller than the winglets 6a , Their height is not greater than that of the winglets 6a , Three turbulators each 13 are at a distance to the long sides 7 educated. Just like the winglets 6a are the punched out areas 11 closer to the long sides 7 , The winglets 6a or turbulators 13 are thus closer to the tube than on the long side 7 or the transverse side 8th , The in 13 drawn distance A2 between the transverse side 8th and the punching 11 is greater than the width of the punched hole 11 , especially twice as big. The distance A3 is about as long as the length L3 of the base 12 the winglets 6a ,

14 shows in the perspective view of the exhibited winglets 6a as well as the three turbulators 13 along each longitudinal side 7 , 14 further shows a collar 10 over which the ribs 3 with the pipe not shown in contact.

The heat exchanger according to the invention 1 possesses excellent k-values, which point to a synergetic effect of the in particular triangular or trapezoidal winglets 6a . 6b , the gap 5 between adjacent ribs 3 and on by the displacement or displacement of the rows of tubes R1, R2 or tubes 2 is due. This connection is based on the 16 be clarified.

16 shows on the horizontal axis, the flow velocity v and on the vertical axis on the one hand, the heat transfer coefficient k and the pressure loss .DELTA.p. The lower curves K1, K2, K3 in the image plane represent three different embodiments of heat exchangers. For these curves K1, K2, K3, which show the respective pressure loss Δp, the three upper curves K1 ', K2', K3 'correspond to the respective heat transfer coefficients k.

When viewed, the gap between adjacent finned tubes is 0.67 mm. This standard design usually provides for the staggered arrangement of the tubes, since, viewed in terms of heat and flow, it represents the most energetically favorable variant overall. In addition to the staggered arrangement, the pushed arrangement should be considered, as it achieves the highest heat transfer coefficients at a constant flow velocity, but also the highest pressure losses.

The curve K1 shows the standard of a staggered arrangement with very small gap width. The curve K2 stands for the pushed arrangement with a small gap width and finally the curve K3 for the pushed arrangement with increased transverse distribution or increased gap width.

Starting point of the consideration is the state of the art, which is symbolized by the curve K1. At point I, there is a pressure loss Δp1 at flow velocity v1. In point II is the k value k1. With constant flow velocity v1, it can be seen that the pressure losses increase very sharply in the pushed arrangement according to the dot-dash line K2, but the k value is also improved compared to the standard.

Noteworthy, however, line K3 (pushed arrangement with increased gap width). At constant inflow velocity v1, it can be seen that the pressure loss Δp at constant flow velocity v1 falls compared to the standard (curve K1), while at the same time the k value at constant flow velocity v1 is improved compared to the standard (curve K1 '). Conversely, this means that the flow velocity v1 can be achieved with lower energy input due to lower pressure losses and at the same time more heat can be transferred (higher k value). The variant according to the curves K3, K3 'is therefore to be preferred.

Since the electrical energy to be expended is proportional to the volume flow and proportional to the pressure loss Δp, the saved electrical energy can be used to increase the flow velocity. Keeping the electrical energy constant, the pressure loss reduction can be invested in increasing the viewing speed or volume flow increase. This increases the flow velocity from v1 to v2. At curve K3 you are now in point III. That is, at a flow velocity v2, the pressure loss Δp2 is lower than at the point I. At the same time, it follows from the point IV on the curve K3 'that the k value k2 has been substantially increased.

From this ratio it can be seen that under the condition of the same electrical drive energy can be significantly increased by significantly reducing the air-side pressure drop of the air mass flow. Assuming constant heat output, this means that the air outlet temperature from the heat exchanger becomes smaller as the air mass flow increases. Thus, however, also increases the decisive for the heat exchange driving temperature difference Δθm. This saving makes it possible to reduce the heat exchanger surface with the same heat exchanger performance.

Overall, with constant heat output by improving the k-value and the average temperature difference Δθm, the exchange surface of the heat exchanger can be reduced. This allows cheaper construction methods. Of course, the cost-effective design can also be used to reduce the power required for operation electrical power, if this should be the goal of the design of the heat exchanger.

LIST OF REFERENCE NUMBERS

1

heat exchangers

2

pipe

3

rib

4

view plane

5

gap

6a

winglet

6b

winglet

7

long side

8th

transverse side

9

corner

10

collar

11

punching

12

Base

13

turbulators

14

top

15

flank

16

outs

A

distance

A1

distance

A2

distance

A3

distance

B

average width

e

corner

H

height

HA1

long main axis 1 from 2

HA2

short main axis of 2

k

k-value (heat transfer coefficient)

L

length

L1

Length of HA1

L2

Length of HA2

L3

length of 12

P

flow direction

v.

flow

R1

line 1

R2

line 2

S

average gap width

.DELTA.T

Temperature difference of the cooling air

v

flow rate

v1

flow rate

v2

flow rate

W

angle

W1

angle

Δθm

mean temperature difference (cooling air product)

Ap

pressure difference

VQ

transverse offset

TQ

Cross pitch

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

• EP 2379977 B1 [0002]

Claims (13)

Heat exchanger ( 1 ) comprising crude ( 2 ) with outer ribs ( 3 ) and having the following characteristics: 1.1. Several rows (R1, R2) of the tubes ( 2 ) are arranged one behind the other in the direction of flow (P); 1.2. The rows (R1, R2) are transverse to the direction of flow (P); 1.3. The pipes ( 2 ) of successive rows (R1, R2) are offset by a transverse offset (VQ) parallel to the previous row (R1, R2), the transverse offset (VQ) being unequal to a transverse pitch (TQ) transverse to the direction of flow (P), or 1.4. The tubes adjacent within a row (R1, R2) ( 2 ) are offset from one another by a longitudinal offset (VL) running in the direction of flow (P), the longitudinal offset (VL) being smaller than a longitudinal pitch (TL) of the tubes (FIG. 2 ) successive rows (R1, R2); 1.5. The transverse separation distance (TQ) of the pipes ( 2 ) of a row (R1, R2) is larger than the one across the plane ( 4 ) of the row (R1, R2) measured average width (B) of the ribs ( 3 ), so that its gap ( 5 ) between the ribs ( 3 ) of adjacent pipes ( 2 ) is present at 0.1 to 0.5 times the mean width (B); 1.6. The square ribs ( 3 ) have winglets ( 6a . 6b ). Heat exchanger according to claim 1, characterized in that the ribs ( 3 ) are rectangular or square. Heat exchanger according to claim 1, characterized in that the ribs ( 3 ) are trapezoidal. Heat exchanger according to claim 1, characterized in that the ratio of length (L) to average width (B) of a rib ( 3 ) is in a range of 1: 1 to 3: 1. Heat exchanger according to claim 1 to 4, characterized in that the winglets ( 6b ) are quadrangular. Heat exchanger according to one of claims 1 to 4, characterized in that the winglets ( 6a ) are triangular. Heat exchanger according to claim 6, characterized in that the winglets ( 6a ) are formed as isosceles triangles. Heat exchanger according to one of claims 1 to 7, characterized in that the winglets ( 6a . 6b ) have a height (H) that is 70% to 100% of the rib distance (A1) of a pipe ( 2 ) is. Heat exchanger according to one of claims 1 to 8, characterized in that in each case a winglet ( 6a . 6b ) in the corner region (E) of a rib ( 3 ) at a distance (A2) from long sides ( 7 ) and transverse sides ( 8th ) of the ribs ( 3 ) is arranged. Heat exchanger according to claim 9, characterized in that the winglets ( 6 ) in a range of 40% to 60% of the distance (A) from the corner ( 9 ) of a rib ( 3 ) to the pipe ( 2 ) are arranged. Heat exchanger according to one of claims 1 to 10, characterized in that the winglets ( 6 ) One Base ( 12 ), which they use with the ribs ( 3 ) and which at an angle of 20 ° q to 50 ° to the longitudinal side ( 7 ) of the ribs ( 3 ) runs. Heat exchanger according to one of claims 1 to 11, characterized in that the middle Spaltbereite (S) of a gap ( 5 ) between the ribs ( 3 ) a row (R1, R2) 15% to 30% of the average width (B) of the ribs ( 3 ) is. Heat exchanger according to one of claims 1 to 12, characterized in that the tubes ( 2 ) are elliptical in cross-section, the average width (B) of the rib ( 3 ) equal to twice +/- 10% of the length (L2) of the shorter major axis (HA2) of the ellipse.

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