Technical field
[0001] The invention relates to a fin for a boiler tube arrangement comprising a number
of boiler tubes extending along each other, which fin is arranged to extend perpendicular
to a length of the boiler tubes. The invention also relates to an assembly comprising
two such fins and a boiler tube arrangement including a first boiler tube.
Background art
[0002] Boilers are well-known and used in many different heat exchange applications, for
example in waste heat recovery applications. A known waste heat recovery boiler, used
after e.g. a diesel engine to recover heat from the exhaust gases from the diesel
engine, comprises a closed vessel and a number of tubes extending along each other
inside the vessel. A medium, such as water, is fed through the tubes, and exhaust
gas from the diesel engine is fed through the vessel and thus around the tubes, whereby
heat is transferred from the exhaust gas to the medium inside the tubes. To increase
the heat transfer efficiency of the boiler, the tubes may be provided with surface
enlarging elements in the form of fins attached to the tubes. Typically, the fins
are formed as rectangular plates provided with voids for receiving the tubes. Even
if such fins are widely used and fill their desired purpose, there is still room for
improvements.
Summary
[0003] An object of the present invention is to provide a fin for a boiler tube arrangement
which is improved as compared to prior art fins. The basic concept of the invention
is to provide a fin with a unique, advantageous shape enabling all parts of the fin
to contribute considerably to increased heat transfer efficiency, and enabling manufacturing
of fins with little waste or scrap. Another object of the present invention is to
provide an improved assembly comprising such fins and a boiler tube arrangement. The
fin and the assembly for achieving the objects above are defined in the appended claims
and discussed below.
[0004] A fin according to the present invention is for a boiler tube arrangement comprising
a number of boiler tubes extending along each other. A longitudinal center axis of
the fin is arranged to extend perpendicular to a length of the boiler tubes, and the
fin comprises an inner edge and an outer edge. The fin is characterized in that a
contour of the inner edge is essentially identical to a contour of the outer edge,
each of the contours of the inner and outer edges defining a number of ridges and
a number of valleys. The ridges and valleys are alternately arranged and connected
to each other at transitions being half way between a highest point and a lowest point
of the connected ridge and valley, respectively. The valleys defined by the inner
edge are each arranged to receive, and only partly enclose, a respective one of the
boiler tubes.
[0005] The expressions "ridges" and "valleys" are used herein to specify the shape of the
fin with reference to longitudinal axes of the fin extending between the ridges and
valleys of the inner and outer edges when the fin has a certain orientation. Naturally,
if the fin is turned up-side-down, the valleys are in fact ridges, while the ridges,
in fact, are valleys. However, throughout the text, what is defined as a valley and
a ridge of the fin when this has said certain orientation will be referred to as a
valley and a ridge irrespective of the orientation of the fin.
[0006] The number of boiler tubes of the boiler tube arrangement can be one or more. Further,
the number of valleys defined by each of the inner and outer edges can be one or more.
Similarly, the number of ridges defined by each of the inner and outer edges can be
one or more.
[0007] As mentioned above the fin has an extension perpendicular to a length of the boiler
tubes. Naturally, the fin could be arranged to extend obliquely to the length of the
boiler tubes, i.e. to have an extension both perpendicular to, and along, the length
of the boiler tubes.
[0008] Because of the essentially identical inner and outer fin edges, the ridges defined
by the inner fin edge fit into, and fill out, the ridges defined by the outer fin
edge, while the valleys defined by the outer fin edge fits into, and fill out, the
valleys defined by the inner fin edge. In other words, two similar fins fit into each
other when the inner edge of one of the fins faces the outer edge of the other one
of the fins. Thus, a plurality of fins according to the present invention can be manufactured
in a very material efficient way by being cut out of a sheet, typically a metal sheet,
with minimal waste. By essentially identical is meant that the inner and outer edges
need not be 100% identical but similar enough such as to enable fin interfitting.
Thus, for example, an inner fin edge having a small recess or similar is essentially
identical with an outer fin edge lacking such a recess.
[0009] Portions of the fin more distant to the tube will contribute less to the heat transfer
than portions of the fin more closer to the tube. Because of the fin according to
the invention having a wave shape instead of the conventional shape of a rectangle
provided with a tube receiving void, the extension of the fin may be adapted to a
distance from the tube such that all portions of the fin may contribute considerably
to the heat transfer. Consequently, the fin can be made less material consuming, and
thus lighter, and more compact, and it may still contribute considerably to the heat
transfer.
[0010] The valleys may be non-uniform with, i.e. have a different shape than, the ridges.
In other words, the valleys may be received in, but will not fill out, the ridges,
and vice versa. Consequently, two similar fins do not fit into each other when the
outer edge of one of the fins faces the outer edge of the other one of the fins, or
the inner edge of one of the fins faces the inner edge of the other one of the fins.
Instead, a distance between the two fins will be varying. This may be advantageous
as regards heat transfer efficiency, as will be further discussed below.
[0011] Below, the shape of the fin is discussed with reference primarily to the inner fin
edge. However, since the contours of the inner and outer fin edges are essentially
identical, the below discussion is at least in part applicable also as regards the
outer fin edge.
[0012] The fin may be such that a first one of the valleys defined by the contour of the
inner edge, which first valley has a bottom, is arranged between two of the ridges
defined by the contour of the inner edge. Further, a second one of the ridges defined
by the contour of the inner edge, which second ridge has a top, may be arranged between
two of the valleys defined by the contour of the inner edge. Such an embodiment means
that the number of valleys, just like the number of ridges, defined by the inner fin
edge is at least two.
[0013] A contour of the first valley may be shorter than a contour of the second ridge.
This is a straight-forward way of achieving the above mentioned nonuniformity between
the valleys and the ridges.
[0014] The fin may be such that the first valley has a symmetry axis extending perpendicular
to the longitudinal center axis of the fin. Further, also the second ridge may have
a symmetry axis extending perpendicular to the longitudinal center axis of the fin.
This may facilitate and provide for an optimized fitting of the respective boiler
tube in the first valley.
[0015] The fin may be such that the bottom of the first valley and the top of the second
ridge are plane and defined by respective straight portions of the inner edge. These
straight portions may, or may not, extend parallel to the longitudinal center axis
of the fin. Thereby, if the boiler tubes have a circular cross section, as is conventional,
areas of no contact between the fin and the boiler tube(s) may be guaranteed. This
may be advantageous as regards cleaning and also heat transfer efficiency, as will
be further discussed below.
[0016] A flank connecting the bottom of the first valley and the top of the second ridge
may be defined by an at least partly straight portion of the inner edge. This flank
forms part of both the first valley and the second ridge. Thereby, if the boiler tubes
have a circular cross section, as is conventional, areas of no contact between the
fin and the boiler tube(s) may be guaranteed. This may be advantageous as regards
cleaning and also heat transfer efficiency, as will be further discussed below.
[0017] An assembly according to the present invention comprises a boiler tube arrangement
including a first boiler tube and first and second fins of the type described above.
The first and second fins extend perpendicular to a longitudinal center axis of the
first boiler tube on opposite sides of the first boiler tube. The inner edge of each
of the first and second fins faces, and only partly encloses, the first boiler tube.
The first boiler tube is received in a respective one of the valleys defined by the
inner edges of the first and second fins.
[0018] Naturally, the first fin and/or the second fin could extend obliquely to the longitudinal
center axis of the first boiler tube, i.e. they could have an extension both perpendicular
to, and along, the length of the first boiler tube.
[0019] Thus, the inner edges of the first and second fins face each other and enclose together,
at least partly, the first boiler tube. The outer edge of one or both of the first
and second fins may be arranged to face the outer edge of another adjacent fin, as
in the below described embodiment.
[0020] The assembly may be such that the boiler tube arrangement further includes a third
boiler tube extending along the first boiler tube and third and fourth fins of the
types described above. The third and fourth fins may extend perpendicular to a longitudinal
center axis of the third boiler tube on opposite sides of the third boiler tube. The
inner edge of each of the third and fourth fins may face, and only partly enclose,
the third boiler tube, and the third boiler tube may be received in a respective one
of the valleys defined by the inner edges of the third and fourth fins. Further, one
of the valleys defined by the outer edge of the third fin may be received in one of
the ridges defined by the outer edge of the second fin, and one of the valleys defined
by the outer edge of the second fin may be received in one of the ridges defined by
the outer edge of the third fin.
[0021] Thus, the wave shape of the fins enables a staggered arrangement of the boiler tubes
and a compact assembly since adjacent pairs of fins may be received in each other.
The conventional rectangular fins do not enable such a compact assembly.
[0022] The assembly may be such that the second fin partly enclosing the first boiler tube
and the third fin partly enclosing the third boiler tube are separated from each other.
Thereby, a medium flow between the second and third fins, resulting in increased flow
turbulence and thus improved heat transfer, is enabled. Further, such a separation
may facilitate cleaning of the fins, e.g. removal of soot deposits from the fins originating
from exhaust gas.
[0023] Depending on the design of the second and third fins, the distance between them may
vary or be constant along their lengths. According to one embodiment of the invention,
a distance between the outer edge of the second fin and the outer edge of the third
fin is varying along the outer edges of the second and third fins. Such a distance
variation may be achieved with second and third fins as described above, i.e. second
and third fins the valleys and ridges of which are non-uniform with each other. The
distance variation between the second and third fins may result in an increased flow
turbulence and thus improved heat transfer.
[0024] The assembly may be such that the first and seconds fins enclosing the first boiler
tube are separated from each other by a predetermined distance. Thereby, the first
boiler tube is not completely enclosed by the first and second fins. This enables
a medium flow between the first and second fins, resulting in increased flow turbulence
and thus improved heat transfer. Further, this may facilitate cleaning of the fins
and the first boiler tube.
[0025] According to one embodiment of the assembly, an outer contour of the first boiler
tube at the first and second fins, and a space for receiving the first boiler tube
between the first and second fins, defined by the inner edges of the first and second
fins, are non-uniform, i.e. have different shapes. Thereby, areas of no contact between
the first and second fins and the first boiler tube may be guaranteed which may result
in increased flow turbulence and thus improved heat transfer, and facilitate cleaning.
For example, such nonuniformity may be obtained, as mentioned above, by the first
boiler tube having a circular outer contour or cross section, and the space for receiving
the first boiler tube being at least partly delimited by straight portions of the
inner fin edges.
[0026] The first and second fins may engage with the first boiler tube in engagement points
which are separated from each other. Thereby, areas of no contact between the first
and second fins and the first boiler tube may be guaranteed which may result in increased
flow turbulence and thus improved heat transfer, and facilitate cleaning.
[0027] Of course, the advantages associated with the different embodiments of the fins discussed
above are advantageous also for an assembly comprising the fins.
[0028] Still other objectives, features, aspects and advantages of the invention will appear
from the following detailed description as well as from the drawings.
Brief description of the drawings
[0029] The invention will now be described in more detail with reference to the appended
schematic drawings, in which
Fig. 1 is a top view of a metal sheet for producing fins,
Fig. 2 is a top view of a fin, and
Fig. 3 is a top view of an assembly.
Detailed description
[0030] In Fig. 1 a metal sheet 2 is shown from which four identical fins 4 can be obtained
by cutting the sheet along lines 6. The fins obtained are wave-shaped, more particularly,
they have a wave-shaped inner edge 8 and a wave-shaped outer edge 10, which inner
and outer edges have identical contours. One of the fins is shown separately in Fig.
2 from which it is clear that the inner edge 8 of each fin 4 defines a first valley
12, a second valley 14, a first ridge 16, a second ridge 18 and a third ridge 20.
The first valley 12 is arranged between the first and second ridges 16 and 18, the
second valley 14 is arranged between the second and third ridges 18 and 20 and the
second ridge 18 is arranged between the first and second valleys 12 and 14. A transition
P between a ridge and an adjacent valley is half way between a highest point H of
the ridge and a lowest point L of the valley. The first and second valleys 12 and
14 are identical and the first and third ridges 16 and 20 are identical to a respective
part of the second ridge 18.
[0031] Similarly, the outer edge 10 of each fin 4 defines a first valley 22, a second valley
24, a first ridge 26, a second ridge 28 and a third ridge 30. The first valley 22
is arranged between the first and second ridges 26 and 28, the second valley 24 is
arranged between the second and third ridges 28 and 30 and the second ridge 28 is
arranged between the first and second valleys 22 and 24. A transition P' between a
ridge and an adjacent valley is half way between a highest point H' of the ridge and
a lowest point L' of the valley. The first and second valleys 22 and 24 are identical
and the first and third ridges 26 and 30 are identical to a respective part of the
second ridge 28. Accordingly, since the valleys and ridges of the inner and outer
fin edges 8 and 10 are equally deep and high, respectively, the transitions P for
the inner edge 8 are arranged along an imaginary straight line I and the transitions
P' for the outer edge 10 are arranged along an imaginary straight line I'. A longitudinal
center axis C of the fin is arranged half way between the imaginary straight lines
I and I'.
[0032] The first valleys 12, 22 and the second valleys 14, 24 each has a symmetry axis S
extending perpendicular to the longitudinal center axis C of the fin 4. Similarly,
the second ridges 18 and 28 each has a symmetry axis R extending perpendicular to
the longitudinal center axis C of the fin 4. Further, the first valleys 12, 22 and
the second valleys 14, 24 each have a plane bottom B and B', respectively, extending
parallel to the longitudinal center axis C of the fin. Similarly, the first ridges
16, 26, the second ridges 18, 28 and the third ridges 20, 30 each has a plane top
T and T', respectively, extending parallel to the longitudinal center axis C of the
fin. Moreover, flanks F and F' connecting the tops and bottoms of the ridges and valleys
of the inner and outer fin edges each comprises a straight portion.
[0033] As is clear from the figures, the shape of the valleys 12, 14, 22 and 24 is different
from the shape of the ridges 16, 18, 20, 26, 28 and 30 in that the ridges are less
"sharp" or less "acute" than the valleys, and a contour of the ridges is longer than
a contour of the valleys. Accordingly, as an example, an area A1 delimited by the
imaginary straight line I' and the contour of the first valley 22 is smaller than
an area A2 delimited by the imaginary straight line I' and the contour of the second
ridge 28.
[0034] With reference to Fig. 1, the lines 6 each defines the inner edge 8 of one fin 4
and the outer edge 10 of an adjacent fin 4. Since the inner and outer edges 8 and
10 have identical contours, the fins 4 fit perfectly into each other when the inner
edge 8 of one fin faces the outer edge 10 of an adjacent fin, the valleys 22 and 24
defined by the outer edge of said adjacent fin are received in the valleys 12 and
14, respectively, defined by the inner edge of said one fin, and the ridges 16, 18
and 20 defined by the inner edge of said one fin are received in the ridges 26, 28
and 30, respectively, defined by the outer edge of said adjacent fin. Thus, the fins
4 can be cut out of the sheet 2 with a minimum of waste material.
[0035] In Fig. 3 an assembly 32 is shown which comprises a boiler tube arrangement of a
number of parallel boiler tubes and the same number of fins 4 of the above described
type. The assembly 32 is comprised in a waste heat recovery boiler (not illustrated
in its entirety) of the initially described type, whereby water is fed inside the
boiler tubes and exhaust gas is fed outside the boiler tubes to transfer heat from
the exhaust gas to the water. The boiler tubes are pairwise arranged between two opposing
ones of the fins. Thus, first and second boiler tubes 34 and 36, which are separated
from each other in an x dimension by a certain distance, are arranged between first
and second fins 4a and 4b, and third and fourth boiler tubes 38 and 40, which are
separated from each other in the x dimension by said certain distance, are arranged
between third and fourth fins 4c and 4d.
[0036] The first and second fins 4a and 4b are thus arranged, aligned with each other in
dimensions z and y, on opposite sides of the first and second boiler tubes 34 and
36, with their respective longitudinal center axes C (Fig. 2) extending parallel to
each other and perpendicular to longitudinal center axes A of the first and second
boiler tubes. Further, the first and second fins 4a and 4b are separated from each
other by a predetermined distance in a y dimension and so arranged that their inner
edges 8 face each other. The first boiler tube 34 is received in a space defined by
the first valley 12 of the first fin 4a and the second valley 14 of the second fin
4b, while the second boiler tube 36 is received in a space defined by the second valley
14 of the first fin 4a and the first valley 12 of the second fin 4b. Thus, the first
and second boiler tubes 34 and 36 are partly enclosed by the first and second fins
4a and 4b. Arranged like this, the first and second boiler tubes are welded to the
inner edges of the first and second fins 4a and 4b in welding points 42, here six
per boiler tube, distributed around the first and second boiler tubes.
[0037] Similarly, the third and fourth fins 4c and 4d are arranged, aligned with each other
in dimensions z and y, on opposite sides of the third and fourth boiler tubes 38 and
40, with their respective longitudinal center axes C extending parallel to each other
and perpendicular to longitudinal center axes A of the third and fourth boiler tubes.
Further, the third and fourth fins 4c and 4d are separated from each other by a predetermined
distance in the y dimension and so arranged that their inner edges 8 face each other.
The third boiler tube 38 is received in a space defined by the first valley 12 of
the third fin 4c and the second valley 14 of the fourth fin 4d, while the fourth boiler
tube 40 is received in a space defined by the second valley 14 of the third fin 4c
and the first valley 12 of the fourth fin 4d. Thus, the third and fourth boiler tubes
38 and 40 are partly enclosed by the third and fourth fins 4c and 4d. Arranged like
this, the third and fourth boiler tubes are welded to the inner edges of the third
and fourth fins 4c and 4d in welding points 42, here six per boiler tube, distributed
around the third and fourth boiler tubes.
[0038] As is clear form Fig. 3, the first, second, third and fourth boiler tubes 34, 36,
38 and 40 all have the same round shape or contour, i.e. the same circular cross section.
Further, the spaces formed by the first, second, third and fourth fins 4a, 4b, 4c
and 4d for receiving the boiler tubes all have, because of the partly straight portions
of the inner edges defining the valleys, the same edgy shape. Because of this difference
in shape, the boiler tubes will not contact the respective fins all around their outer
surface. Instead, the boiler tubes will be separated from the respective fins in areas
44, 46 between the welding points, wherein each of the areas 44 is formed between
one of the fins and one of the boiler tubes while each of the areas 46 is formed between
the fins of one of the fin pairs and one of the boiler tubes. This fin-boiler tube
separation results in an increased exhaust gas flow turbulence around the boiler tubes
and the fins, and thus an increased heat transfer from the exhaust gas to the water
fed through the boiler tubes.
[0039] The first, second, third and fourth fins 4a, 4b, 4c and 4d are so arranged that their
longitudinal center axes C extend parallel to each other. Further, the fin pairs 4a
+ 4b and 4c + 4d are aligned with each other in the z dimension and the outer edge
10 of the second fin 4b faces the outer edge 10 of the third fin 4c. The third and
fourth boiler tubes 38 and 40 are displaced from the first and second boiler tubes
34 and 36 in the x dimension such that the fourth boiler tube 40 is arranged halfway
between the first and second boiler tubes 34 and 36, and the first boiler tube 34
is arranged halfway between the third and fourth boiler tubes 38 and 40. Accordingly,
the fin pairs 4a + 4b and 4c + 4d have a staggered arrangement. Herein, by staggered
arrangement is meant that the fin pairs are not aligned with each other, but rather
displaced, in the y dimension. More particularly, the first valley 22 defined by the
outer edge of the third fin 4c is received in the third ridge 30 defined by the outer
edge of the second fin 4b, the first valley 24 defined by the outer edge of the second
fin 4b is received in the second ridge 28 defined by the outer edge of the third fin
4c, the second valley 24 defined by the outer edge of the third fin 4c is received
in the second ridge 28 defined by the outer edge of the second fin 4b and the first
valley 22 defined by the outer edge of the second fin 4b is received in the third
ridge 30 defined by the outer edge of the third fin 4c.
[0040] Thus, the valleys of the second fin are received in the ridges of the third fin while
the valleys of the third fin are received in the ridges of the second fin. The second
and third fins 4b and 4c are arranged separated from each other. Since the ridges
and valleys have different shapes, the distance between the second and third fins,
and more particularly the outer edges thereof, varies along the longitudinal center
axis C of the second and third fins. This varying distance results in an increased
exhaust gas flow turbulence around the boiler tubes and fins, and thus an increased
heat transfer from the exhaust gas to the water fed through the boiler tubes.
[0041] The rest of the assembly is configured in a way corresponding to the above described
why a description thereof is unnecessary.
[0042] The above described embodiment of the present invention should only be seen as an
example. A person skilled in the art realizes that the embodiment discussed can be
varied and combined in a number of ways without deviating from the inventive conception.
[0043] For example, the fins and the assembly according to the present invention can be
used in other types of boilers than waste heat recovery boilers, and for heating,
evaporating or superheating other media than water by means of another heat source
than exhaust gas. For example, the fins and the assembly according to the present
invention can be used in connection with gas turbines or combustion units such as
burners.
[0044] The distance between the fins 4b and 4c in Fig. 3 may be in the range of 1-20 mm,
but other distances are naturally conceivable. The distance may inter alia be dependent
upon the dimensions of the fins and the boiler tubes.
[0045] In the above described embodiment of the inventive assembly, the boilers are attached
to the fins by welding. Of course, other attachment methods, such as brazing or gluing
are possible. Further, the number of welding points between the fins and the boiler
tubes need not be six per boiler tube like above but could be less or more than six.
Also, the welding need not be made in points but could be made along lines extending
partly or all the way around the boiler tubes. Furthermore, as an alternative, the
fins of each pair could be attached to each other and the boiler tubes fixed to the
fins by friction only.
[0046] The above described fins are each provided with two valleys and three ridges along
each of the inner and other edges. Naturally, the number of ridges and valleys could
be less or more than three and two, respectively. As an example, the inner and outer
edges of each fin could define two ridges only and one valley arranged between the
ridges. A pair of such fins could be arranged to enclose one boiler tube only.
[0047] All the fins of the assembly need not look the same. Not even the fins of one and
the same pair need to look the same. Further, the number of fins cooperating to enclose
one or more boiler tubes could be more than two. As an example, a fin configured according
to the figures, i.e. arranged to partly enclose two boiler tubes, could be arranged
to cooperate with two fins arranged to partly enclose a respective one of the two
boiler tubes.
[0048] The valleys defined by the inner fin edge need not be identical, just like the valleys
defined by the outer fin edge. Further, the inner and outer edges of the fins need
not comprise straight portions but could be curved through-out. Also, the boiler tubes
could have another cross-section than that illustrated in the figures.
[0049] In the above described embodiment the ridges are less "sharp" than the valleys and
a contour of the ridges is longer than the contour of the valleys. Naturally, the
fin could be designed in alternative ways, for example with valleys being less "sharp"
than the ridges and a contour of the valleys being longer than a contour of the ridges.
[0050] The fins and boiler tubes could be made of any suitable material, such as carbon
steel, stainless steel or aluminum. Further, the fins need not be solid but could
comprise apertures to further increase the flow turbulence.
[0051] The fins of a pair need not be aligned in the y and z dimensions. As an example,
the fins of a pair may be displaced in relation to each other so as to not be aligned
in the y dimension and/or the z dimension. The same displacement possibilities as
regards the z dimension exist between the pairs of fins.
[0052] In the above described embodiment, each of the boiler tubes is enclosed by the first
valley defined by the inner edge of one fin and the second valley defined by the inner
edge of another fin. Naturally, depending on how the two fins are oriented, each of
the boiler tubes could instead be enclosed by the first valleys defined by the inner
edges of the two fins, or the second valleys defined by the inner edges of the two
fins.
[0053] It should be stressed that a description of details not relevant to the present invention
has been omitted and that the figures are just schematic and not drawn according to
scale. It should also be said that some of the figures have been more simplified than
others. Therefore, some components may be illustrated in one figure but left out in
another figure. Finally, as used herein, when one component is said to be connected
to another component, the connection may be direct as well as indirect.
1. A fin (4, 4a, 4b, 4c, 4d) for a boiler tube arrangement comprising a number of boiler
tubes (34, 36, 38, 40) extending along each other, wherein a longitudinal center axis
(C) of the fin is arranged to extend perpendicular to a length of the boiler tubes,
and wherein the fin comprises an inner edge (8) and an outer edge (10), characterized in that a contour of the inner edge is essentially identical to a contour of the outer edge,
each of the contours of the inner and outer edges defining a number of ridges (16,
18, 20, 26, 28, 30) and a number of valleys (12, 14, 22, 24), which ridges and valleys
are alternately arranged and connected to each other at transitions (P, P') being
half way between a highest point (H, H') and a lowest point (L, L') of the connected
ridge and valley, respectively, the valleys defined by the inner edge each being arranged
to receive, and only partly enclose, a respective one of the boiler tubes.
2. A fin (4, 4a, 4b, 4c, 4d) according to claim 1, wherein the valleys (12, 14, 22, 24)
are non-uniform with the ridges (16, 18, 20, 26, 28, 30).
3. A fin (4, 4a, 4b, 4c, 4d) according to any of the preceding claims, wherein a first
one of the valleys (12) defined by the contour of the inner edge (8), and having a
bottom (B), is arranged between two of the ridges (16, 18) defined by the contour
of the inner edge, and a second one of the ridges (18) defined by the contour of the
inner edge, and having a top (T), is arranged between two of the valleys (12, 14)
defined by the contour of the inner edge.
4. A fin (4, 4a, 4b, 4c, 4d) according to claim 3, wherein a contour of the first valley
(12) is shorter than a contour of the second ridge (18).
5. A fin (4, 4a, 4b, 4c, 4d) according to any of claims 3-4, wherein the first valley
(12) has a symmetry axis (S) extending perpendicular to the longitudinal center axis
(C) of the fin.
6. A fin (4, 4a, 4b, 4c, 4d) according to any of claims 3-5, wherein the second ridge
(18) has a symmetry axis (S) extending perpendicular to the longitudinal center axis
(C) of the fin.
7. A fin (4, 4a, 4b, 4c, 4d) according to any of the claims 3-6, wherein the bottom (B)
of the first valley (12) and the top (T) of the second ridge (18) are plane and defined
by respective straight portions of the inner edge (8).
8. A fin (4, 4a, 4b, 4c, 4d) according to any of claims 3-7, wherein a flank (F) connecting
the bottom (B) of the first valley (12) and the top (T) of the second ridge (18) is
defined by an at least partly straight portion of the inner edge (8).
9. An assembly (32) comprising a boiler tube arrangement including a first boiler tube
(34) and first and second fins (4a, 4b) according to any of the preceding claims,
wherein the first and second fins extend perpendicular to a longitudinal center axis
(A) of the first boiler tube on opposite sides of the first boiler tube, the inner
edge (8) of each of the first and second fins facing, and only partly enclosing, the
first boiler tube, the first boiler tube being received in a respective one of the
valleys (12, 14) defined by the inner edges of the first and second fins.
10. An assembly (32) according to claim 9, wherein the boiler tube arrangement further
includes a third boiler tube (38) extending along the first boiler tube (34) and third
and fourth fins (4c, 4d) according to any of claims 1-8, wherein the third and fourth
fins and extend perpendicular to a longitudinal center axis (A) of the third boiler
tube on opposite sides of the third boiler tube, the inner edge (8) of each of the
third and fourth fins facing, and only partly enclosing, the third boiler tube, the
third boiler tube being received in a respective one of the valleys (12, 14) defined
by the inner edges of the third and fourth fins, wherein one of the valleys (22, 24)
defined by the outer edge (10) of the third fin (4c) is received in one of the ridges
(26, 28, 30) defined by the outer edge (10) of the second fin (4b), and one of the
valleys (22, 24) defined by the outer edge of the second fin is received in one of
the ridges (26, 28, 30) defined by the outer edge of the third fin.
11. An assembly (32) according to claim 10, wherein the second and third fins (4b, 4c)
are separated from each other.
12. An assembly (32) according to any of claims 10 or 11, wherein a distance between the
outer edge (10) of the second fin (4b) and the outer edge (10) of the third fin (4c)
is varying along the outer edges of the second and third fins.
13. An assembly (32) according to any of claims 9-12, wherein the first and second fins
(4a, 4b) are separated from each other by a predetermined distance.
14. An assembly (32) according to any of claims 9-13, wherein an outer contour of the
first boiler tube (34) at the first and second fins (4a, 4b), and a space for receiving
the first boiler tube between the first and second fins, are non-uniform.
15. An assembly (32) according to any of claims 9-14, wherein the first and second fins
(4a, 4b) engage with the first boiler tube (34) in engagement points (42) which are
separated from each other.