AN ANNULAR HEAT EXCHANGER

ECHANGEUR DE CHALEUR ANNULAIRE

English Abstract

An annular heat exchanger comprising at least two circumferentially enclosed tube profiles (1, 2) arranged inside each other for media flow and having a thermal conductive structure (3) arranged inside. The thermal conductive structure (3) comprises a helically tightly wound pair of bands (4, 5) lying on each other, the first band (4) being smooth, the other band (5) being corrugated transversally to the winding direction to create flow channels (6).

French Abstract

L'invention concerne un échangeur de chaleur annulaire comportant au moins deux profilés de tube (1, 2) entourés de manière circonférentielle agencés à l'intérieur l'un de l'autre pour un écoulement de milieu et ayant une structure thermoconductrice (3) agencée à l'intérieur. La structure thermoconductrice (3) comporte une paire de bandes enroulées de manière serrée et hélicoïdale (4, 5) reposant l'une sur l'autre, la première bande (4) étant lisse, l'autre bande (5) étant ondulée dans le sens transversal par rapport à la direction de l'enroulement pour créer des canaux d'écoulement (6).

Claims

7
CLAIMS
1. An annular heat exchanger comprising at least two circumferentially
enclosed
tube profiles arranged inside each other for media flow, each of the tube
profiles
having a thermal conductive structure arranged inside, wherein the thermal
conductive structure comprises a helically tightly wound pair of bands lying
on
each other, the pair of bands including a first band and a second band, the
first
band being smooth, the second band being corrugated transversally to a winding
direction to create flow channels.
2. The annular heat exchanger according to claim 1, wherein the tube profiles
have a circular, oval or rectangular cross-section.
3. The annular heat exchanger according to claim 1 or 2, wherein the
thermal
conductive structure completely fills the tube profiles.

Description

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An annular heat exchanger
Technical Field
The invention relates to an annular heat exchanger comprising at least two
circumferentially enclosed tube profiles arranged inside each other for media
flow
and having a thermal conductive structure arranged inside.
Prior Art
Heat exchangers comprised of at least two tubes for media flow arranged inside
each other are sometimes referred to as "tube-in-tube" exchangers. The tube in
"tube-in-tube" exchangers has two principal functions ¨ it separates the media
and
at the same time serves as a heat-exchange surface. Thermal convection from
the
media to the heat exchanger material is decisive for the exchange of heat,
while
thermal conduction is present to a minimal extent, just by the tube wall.
Increasing the heat exchange surface increases the output of the heat
exchanger.
In the "tube-in-tube" exchanger the tube length needs to be increased to
increase
the heat-exchange surface. As the tube separates the media at the same time,
the
entire heat exchange surface must have such a wall thickness to withstand the
pressures of the media and their pressure difference. This makes the weight
and
size of such exchangers very large.
The heat exchange surface can be increased by finning. The fins are part of
the
tube and have a thickness on the order of mm. In this case, both thermal
convection and thermal conduction are partly present, but thermal convection
is
still decisive.
Finning (increasing of the heat exchange surface) is used unilaterally ¨
inside or
outside.
To achieve maximum output with a minimum exchanger weight, there is an effort

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to reduce the thickness of the wall separating the media, which is restricted
by
technological limits especially if media having high or different pressures
are
concerned. In addition, these thin walls need to be joined in a way ¨ e.g. by
soldering or welding in the case of plate exchangers. This has certain
technological limits as well.
A tube for exchangers, filled with a heat-exchange surface having the shape of
fins
is known from the patent US6533030.
Further, heat exchangers are known that are filled with a honeycomb-shaped
structure. The Japanese patents JPH02150691 and JPS62288495 can be
mentioned as an example.
Further, rotary regenerative heat exchangers made e.g. by the company KASST
is are known, which use the condenser principle, which means that they are
cyclically charged and after the charged part of the heat exchange surface is
turned to a place with a lower temperature they are discharged again. This is
quite
a different functional principle from that of "tube-in-tube" exchangers from
the
technical point of view.
The object of the invention is to adapt known "tube-in-tube" exchangers to
achieve
a considerable weight reduction and an increase of the exchanger output.
Disclosure of Invention
The said object is achieved through an annular heat exchanger comprising at
least
two circumferentially enclosed tube profiles arranged inside each other for
media
flow and having a thermal conductive structure arranged inside according to
the
invention, the principle of which is that the thermal conductive structure
comprises
a helically tightly wound pair of bands lying on each other, the first band
being
smooth, the other band being corrugated transversally to the winding direction
to
create flow channels.

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An advantage of the invention is that the individual thermal conductive
structures
are separated from each other by the respective tube profiles which work as a
heat exchange surface in standard exchangers, but in the inventive exchanger
they predominantly act as media separators. The tube profiles do not primarily
form a heat exchange surface, but a piece of the exchanger that separates the
media so the tube profiles can be sized to the respective pressure difference
and
the exchanger according to the invention can be used for almost any media
pressure difference. Since the thermal conductive structure can have a
thickness
of tens of micrometers regardless of the media pressures while the thickness
of
Da the wall and possible fins in finned tubes of known exchangers is on the
orders of
millimeters, i.e. 2 orders thicker, the weight of the exchanger according to
the
invention is considerably lower at the same output.
The tube profiles can have in principle any cross-section, especially
circular, oval,
is or rectangular.
The thermal conductive structure preferably fills the tube profiles
completely.
Brief Description of Drawings
Fig. 1 schematically shows a cross-section of the first example of an annular
heat
exchanger according to the invention. Fig. 2 shows a detail of the design of
the
thermal conductive structure in the area of the inner profile. Figs. 3, 4, 5
and 6
show other embodiments of annular heat exchanger according to the invention.
Description of preferred embodiments
An embodiment of an annular heat exchanger according to Fig. 1 comprises three
concentrically arranged tube profiles for media flow, namely the outer profile
1,
inner profile 2 and central profile 7. In this embodiment, the tube profiles
1, 2, 7
consist of tubes with a circular cross-section The intermediate spaces between
these profiles 1, 2, 7 are completely filled with a thermal conductive
structure 3
that is composed of a helically tightly wound pair of bands 4, 5 of aluminum
sheet

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with the thickness of 0,05mm, lying on each other. The first band 4 is smooth
while
the other band 5 is corrugated transversally to the winding direction to
produce
flow channels 6 (see Fig. 2).
The embodiment of an annular heat exchanger according to Fig. 3 only differs
from the embodiment of Fig. 1 in that it does not have a central profile 7 and
that
the entire inner profile 2 is completely filled by the thermal conductive
structure 3.
The embodiment of an annular heat exchanger in accordance to Fig. 4 comprises
lo several central profiles 7. In such a case, there may be two media, or the
exchanger can be designed for heat exchange between more media.
Figs. 5 and 6 show examples of exchangers whose tube profiles 1, 2 have a
rectangular cross-section. A skilled person will find it obvious that the
profiles 1, 2,
7 can virtually have any cross-section with enclosed circumference.
The annular heat exchanger according to the present invention can be connected
as a counter-current or co-current exchanger with any number of inserted
profiles
1, 2, 7. The exchanger can also be used for liquid/liquid media, but its
benefits are
maximally manifested when used for gas/gas and gas/liquid media and in
applications with a high pressure difference at the hot and cold side (steam
generators, recuperators of combustion turbines, condensers, evaporators).
The function of an annular heat exchanger according to the present invention
will
be described using the embodiment shown in Fig. 1 and 2. The other
embodiments work in an analogous way.
Hot medium is supplied to the space between the inner profile 2 and the
central
profile 7 where the medium transfers heat by convection into the thermal
conductive structure 3. The thermal conductive structure 3 conducts this heat
to
the tube that forms the inner profile 2 and subsequently the heat is conducted
to
the thermal conductive structure 3 that fills the space between the inner
profile 2
and the outer profile 1. In this space, the thermal conductive structure 3
transfers

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heat by convection into the colder medium that flows in this space. The motion
of
heat is indicated with arrows in Fig. 2.
Thus, the annular heat exchanger according to the present invention is based
on
5 combined heat exchange when thermal convection has the same importance as
thermal conduction. Its heat transfer surface is maximized by insertion of the
thermal conductive structure 3 described above. Heat transfer into this
thermal
conductive structure 3 and the subsequent thermal conduction by this thermal
conductive structure 3 to the separating wall of the respective profile 1, 2,
7 are
o equally used for the heat exchange. Thus, thermal conduction by the thermal
conductive structure 3 is applied to a considerably higher extent, being
equally
important as thermal convection in the exchanger based on the present
invention.
Individual thermal conductive structures 3 are separated from each other by
the
respective tube profiles 1, 2, 7, which work as a heat exchange surface in
standard exchangers, but in the inventive exchanger they predominantly act as
media separators.
As the media are separated by the tube profiles 1, 2, 7 that are designed for
the
respective pressure difference, the exchanger based on the present invention
can
be used for virtually any pressure difference of media. Thus, the tube
profiles 1, 2,
7 do not primarily form a heat-exchange surface, but a media-separating part
of
the exchanger. Since the thermal conductive structure can have a thickness of
tens of micrometers regardless of the media pressures while the thickness of
the
wall and possible fins in finned tubes of known exchangers is on the orders of
millimeters, i.e. 2 orders thicker, the weight of the exchanger according to
the
invention is considerably lower at the same output.
A comparison calculation utilizing a numerical model in the ANSYS CFD program
was used to compare the heat output transferred by a 50-mm aluminum tube with
the diameter of 20 mm in four versions, simulating 4 different types of
exchangers:
- smooth tube
- standard finned tube

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- finned tube according to the patent US6533030
- exchanger in accordance with the invention
Calculation conditions: a tube heated from the outside to the constant
temperature
of 100 C; air entering the tube having the temperature of 20 C and flow speed
of
31.87 m/s.
An ideal exchanger having 100 % efficiency would have the output of 604 W.
Using the numerical model, the following values were calculated:
Smooth tube ¨ 32 W (5 % of the ideal exchanger)
Standard finned tube ¨ 146 W (24 % of the ideal exchanger)
Finned tube according to the patent US6533030 ¨ 252 W (42 % of the ideal
exchanger)
Exchanger in accordance with the invention ¨ 375 W (62 % of the ideal
exchanger)
From the above it is obvious that the inventive exchanger has by far the
highest
output.
List of reference signs:
1 outer profile
2 inner profile
3 thermal conductive structure
4 first band
5 second band
6 flow channel
7 central profile

Representative Drawing