[0001] The invention relates to a heat exchanger comprising a tube meant for the transfer
of heat and separating the through-flow space for the heating fluid from the one for
the fluid to be heated, said tube consisting of metal staves which are welded to one
another and have each an L-, a U-, a Z-, a T-, an I-shaped or other transverse section,
of each one of said staves a leg or a flange extending in the circumferential wall
of the separating tube and being welded with a free longitudinal edge to a corner
edge which extends also in said wall or to an other free longitudinal edge,which extends
in said wall,of the respective adjacent stave and the other leg or the web without
or with a second flange forming a longitudinal fin which projects into the separating
tube, and also to a central heating boiler comprising such a heat exchanger.
[0002] The heat exchanger described hereabove and the central heating boiler provided therewith
are disclosed in the French patent specification 1.250.235. The invention has the
object to increase the ability of the separating tube to transfer heat, so that when
the capacity of the heat exchanger remains unchanged less staves are required in the
separating tube, whereby the diameter of said tube, consequently, also that of a central
heating boiler provided therewith may be reduced.
[0003] According to the invention this is achieved in that locally lips are forced out of
said fin and said lips remain with one edge connected with said fin and are bent out
of the plane thereof. These lips have the effect that they break the boundary layer
of the fluid flowing in the separating tube along the surface of the staves, consequently,
cause turbulence in said fluid, whereby per unit of time more fluid comes directly
into contact with the staves of the separating tube and more heat is delivered or
taken up. Moreover, the heat transferring area of the separating tube is enlarged
by the area of the narrow sides of the lips and those of the holes formed in the staves,
said latter areas being determined by the thickness of the metal of the longitudinal
fins and also assist the heat transfer. Furthermore, due to the smaller diameters
a considerable saving of material is possible.
[0004] It has appeared that to obtain a substantially optimal result it mostly suffices
if the longitudinal fins of the staves only comprise lips bent out of their planes
in a portion of their length adjoining the exhaust end of the tube.
[0005] A central heating boiler comprising a heat exchanger according to the invention,
a water jacket provided round the separating tube consisting of staves and forming
part of the heat exchanger and a gas or oil burner located in front of one end of
said tube, the flue gas from said burner flowing through the separating tube, has
the advantage that, due to the small diameter of the separating tube, the radial dimension
of the water jacket must be chosen greater than usual to satisfy the required water
volume in the boiler. This results in that the annular end walls obtain without special
measures radial dimensions which are so large as to enable said end walls to take
up the thermal stresses which occur in a boiler provided with a separating tube which
consists of staves and, as a consequence thereof, has become very rigid.
[0006] The invention will be further elucidated with the aid of the drawing. In the drawing:
Fig.1 shows a longitudinal section of a central heating boiler provided with a heat
exchanger comprising a separating tube according to the invention;
Fig.2 illustrates a transverse section taken on the line II-II in Fig.1;
Fig.3 is on a larger scale and in perspective a stave of the separating wall of the
boiler shown in Figs.1 and 2; and
Fig.4 shows on a larger scale a transverse section of a portion of the separating
tube illustrated in Figs.1 and 2.
[0007] The central heating boiler shown in Figs.1 and 2 comprises a furnace 1, a gas or
oil burner 2 located therein, a heat exchanger 3 and a flue gas collecting space 4,
which is bounded by a detachable cap 5 provided with an opening 6 adapted to be connected
to a chimney.
[0008] The heat exchanger consists of a separating tube formed of staves 7 which are welded
to one another and have an L- or angle-shaped transverse profile (see Figs.2,3 and
4), said separating tube being provided between the flue gas passage 8 which extends
between the furnace 1 and the flue gas collecting space 4 and a water jacket 9 which
is bounded on the outer circumference by a straight cylindrical tube 10, at the upper
end by a flat ring 11 and at the lower end by a wall 12 surrounding the furnace 1.
[0009] The staves 7 with their L- or angle-shaped transverse profile have legs which are
welded to one another at 13 and extend in the peripheral wall of the separating tube
and other legs which form inwards pointing fins. It appears from Figs.2,3 and 4 that
lips 14 are locally forced out of each one of these fins, said lips remaining each
connected with one edge with the respective fin and being bent out of the plane thereof.
These fins break the boundary layer of the flue gas flowing along the staves 7, whereby
more flue gas flowing through the separating tube directly contact the staves and
due to that a better heat transfer is obtained. Also the heat transferring area of
the separating wall is enlarged by the narrow sides 15 of the lips 14 and the narrow
sides 16 of the openings formed in the fins by the forced out lips and this improves
the heat transfer too.
[0010] It is observed that the ability of the separating tube to transfer heat is so much
better than that of the known separating tubes consisting of staves that for the same
capacity the diameter of said separating tube can be considerably reduced. This results
in that the water jacket of, for instance, the boiler shown in Figs.1 and 2 must be
chosen somewhat more spacious in order that the water jacket of the boiler will have
a sufficient volume. The result thereof is that the radial dimensions of the water
jacket 9 and those of the end wall 11 may be made so large, as to enable said end
wall and its welds to take up without further measures the thermal stresses causes
by welding together the separating tube consisting of stiff staves 7 one one hand
and the remaining parts 10,11,12 of the heat exchanger consisting of thin sheet steel
on the other hand. Furthermore, it often suffices when the lips 14 are located only
in the second half of the length of the staves seen in the direction of flow.
[0011] Although the drawing only shows an embodiment provided with a fin-tube composed of
L-shaped staves with lips forced out of the fins, these lips may be used as well in
fin-tubes, of which the staves have an other transverse section, say a U-, a Z-, a
T-, an I-shaped or still an other transverse section.
1. A heat exchanger comprising a tube meant for the transfer of heat and separating
the through-flow space for the heating fluid from the one for the fluid to be heated,
said tube consisting of metal staves which are welded to one another and have each
an L-, a U-, a Z-, a T-, an I-shaped or other transverse section, of each one of said
staves a leg or a flange extending in the circumferential wall of the separating tube
and being welded with a free longitudinal edge to a corner edge which extends also
in said wall or to an other free longitudinal edge which extends in said wall of the
respective adjacent stave and the other leg or the web without or with a second flange
forming a longitudinal fin which projects into the separating tube, characterized
in that locally lips are forced out of said fin and said lips remain with one edge
connected with said fin and are bent out of the plane thereof.
2. A heat exchanger according to claim 1., characterized in that the longitudinal
fins of the stave. only comprise lips bent out of their planes in a portion of their
length adjoining the exhaust end of the tube.
3. A central heating boiler comprising a heat exchanger according to claim 1 or 2,
a water jacket provided round the separating tube consisting of staves and forming
part of the heat exchanger and a gas or oil burner located in front of one end of
said tube, the flue gas from said burner flowing through the separating tube.