Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVEN'rJON
The invention relates to a heat exchanger of the type
having two parallel tubes in contact with each other and in
which a first medium flows through one tube and a second medium
flows through the other tube. The tubes are normally spirally
arranged on a former and a thrid medium may be arranged to flow
through a plurality of ducts formed between first and second
tube spirals constituting an assembly enclosed in a suitable
vessel.
The contact between the tubes normally of metal,
through which the different media flow is used to effect heat
exchange between the two media, possibly with the assistance
of the third medium.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the heat
exchange properties of known heat exchanger of this type. This
is achieved by a special design of the cross section of the tubes
so that the contact surface between two adjacent tubes in an
assembly is increased.
Accordingly, the present invention provides a heat
exchanger assembly, comprising two tubes for carrying respective
fluids between which heat is to be exchanged arranged alternately
in a stack, said tubes having contiguous walls such that heat
~s transferred between sa;d fluids by conduction through said
walls, respective inlets and outlets for said fluids in com-
munication with said tubes, means for limiting the expansion
of said stack due to internal pressure in said tubes, and said
tubes being of non-circular cross section whereby said internal
pressure increases the area of contact and the contact pressure
between said tubes.
Not only does the non-circular shape of -the tubes
increase the contact area, it also gives rise to a high contact
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pressure between the tubes as a result of the action of the medium
within the tube. In a preferred embodiment the tubes are spiral
wound.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail
by way of example only, with reference to the accompanying
drawings, in which:-
Fig. 1 is a rectangular cross section through a tubeof a heat exchanger according to the invention;
Fig. 2 is a cross section through an assembly of two
tube circuits in metallic contact;
Figs. 3A and 3B are enlargements of heat exchanger
tubes in cross-section; and
Fig. 4 is a vertical sectional view through a heat
exchanger having three circuits.
DESCRIPTION OF PREFERRED E~BODIMENT
In its normal unstressed state the heat exchanger tube
shown in Fig. 1 is rectangular as shown in continuous lines,
although other non-circular shapes may be employed. ~hen
2Q internal pressure is applied to the medium in the tube causing it
to flow therethrough, it acts on the walls of the tubes in the
direction of the arrows. This pressure distorts the tube,
owing to its elasticity, into the shape shown by the broken
lines. The loading in this case is similar to that which takes
place in a beam supported at its ends and loaded along its
length. The load will deflect the beam by an amount which
depends on its elasticity. Oth~r non-circular forms of the cross
section will also behave in a similar way. This is ~alid for
tubes with an elliptical cross section as shown in Figs. 2 and
3, the most noticeable deflection occuring on the flatest
portions of the elliptical cross section (Figs. 3A and 3B). In
these Figures also, the continuous lines show the unloaded
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shape and the broken lines show to the loaded shape of the tubes
when internal pressure is applied~
The heat exchanger assembly shown in Fig. 2 comprises
an inlet 1 and an outlet 2 for a first medium and an inlet 3
and an outlet 4 for a second medium. The assembly comprises at
least one layer of parallel spiral wound metal tubes 5,6 which
enclose and conduct the media from the inlets to the outlets
thereof respectively. The tubes are wound on a coil body or
former 7 and form a stack of turns between two end flanges 8,9
in parallel,with the tubes 5,6 of the respective circuits
starting from the inlets 1 and 3 and alternating so that every
second turn in height is associated with one circuit and the
intervening turns with the other circuit. The tubes 5,6 are
pressed against each other and the flanges 8,~compress the as-
sembly in the axial direction. The metallic contact causes
heat conduction from the tube 5 to the tube 6~ This type of
winding of the tubes used in the assembly restricts the e~pansion
of the tubes in the loaded state and ~rin~s about an increase
in the area of contact between the adjacent tubes in the assembly.
This increase in the contact area and the increased pressure
which the tubes exert on each other improve the heat transfer
by the metallic contact between the tubes.
In a variant shown in Fig. 4 the assembly is enclosed
in a vessel 10 (Fig. 4) containing a third meaium which, e.g.,
may be water. It has an end wall 11 at the bottom and another
end wall 12 at the top and is closed to keep the water under
pressure so that it can circulate to radiators or the like. The
assembly is located in the center of the vessel and provided
with inlet and outlet manifolds 13, 14 for a first flow medium,
and inlet and outlet manifolds 15, 16 for a second medium. The
assembly comprises a stack of coiled tubes 17,18 which have
elliptical cross sections. The tubes 17, 18 are arranged
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alternately in the stack. Each tube 17, 18 is wound on itself
and extends from its associated inlet manlold to outlet manifold
to enable the associated medium to flow therebetween. The
third medium flows from a pipe 19 and is heated by the tube 17
enclosing the first medium during passage through the assembly
outwardly in spiral-shaped ducts 20 between the tubes to the
outlet through the pipe 21 extending through the wall of the
vessel 10. The tubes 17, 18 are pressed together in the vessel,
the end walls ll and 12 compressing the assembly in the axial
direction. This causes an increase in the area of contact
between the tubes and also improves the heat transfer when an
internal pressure is applied as hereinbefore described.
Various alternative embodiments of the invention are
of course possible. The tube with for example, elliptical cross-
section can be wound with the long axis of the ellipse either -~
perpendicular to the axial direction of the winding (Fig. 3A) or
parallel thereto (Fig. 3B).
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