EP0122667A1

EP0122667A1 - Heat exchanger and central heating boiler comprising such a heat exchanger

Info

Publication number: EP0122667A1
Application number: EP84200489A
Authority: EP
Inventors: Petrus Johannus Remmen
Original assignee: AWB Apparatenfabriek Warmtebouw BV
Current assignee: AWB Apparatenfabriek Warmtebouw BV
Priority date: 1983-04-15
Filing date: 1984-04-05
Publication date: 1984-10-24
Also published as: DK190984D0; DK190984A; KR840008498A; NL8301329A

Abstract

The heat exchanger (3) comprises a tube for separating the space forthe heating fluid from the spaceforthefluidto be heated.

The separating tube is composed of section-staves (17) welded together, one leg or flange of said staves extending in the circumferential wall of said tube and the other leg or web of said staves pointing inwards and forming fins for the improvement of the heat transfer.

Further improvement of the heat transfer being obtained by lips (14) which are locally forced out of said fins and bent out of the plane of the latter.

Description

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.
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.
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.
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.
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.
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 Fi^gs.1 and 2.

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.
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.
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.
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.
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.

Claims

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.