EP0769669A1

EP0769669A1 - Heat exchanger

Info

Publication number: EP0769669A1
Application number: EP95202797A
Authority: EP
Inventors: Bjorn Vestergaard
Original assignee: Norsk Hydro Technology BV; Norsk Hydro Elektrisk Kvaelstof AS
Current assignee: Yara Technology BV; Norsk Hydro Elektrisk Kvaelstof AS
Priority date: 1995-10-17
Filing date: 1995-10-17
Publication date: 1997-04-23
Also published as: AU7293796A; WO1997014927A1

Abstract

A heat exchanger consists of a number of strips stacked adjacent one another in parallel relationship to provide air passages, and at least one flat tube for carrying a fluid. Each tube passes through holes in the strips and is fitted in the holes in heat exchange relationship with the strips, and is zigzag folded so as to have a number of rectilinear sections interconnected by bent portions.

Description

The invention relates to a heat exchanger including a number of strips stacked adjacent one another in parallel relationship to provide air passages, and at least one flat tube for carrying a fluid, said tube or tubes passing through holes in the strips and being fitted in the holes in heat exchange relationship with the strips.
Such a heat exchanger is known from US - A - 4 428 419.
In this known heat exchanger a number of flat tubes is passing through a number of holes provided in the strips. Each tube being fitted within one hole and being completely surrounded by the edges of that hole.
As such the tubes can be used for a fluid flow passing in parallel through all the tubes at the same time. Otherwise it is possible to make the right connections between the ends of the individual tubes in order to provide one or more flows in series.
As such the heat exchanger is simply to manufacture and to assemble. However each end of each tube, independent of the flow system to be used, has to be provided with a coupling system in order to provide the tube with an inlet and an outlet for a fluid. This is a labour intensive product which is highly susceptible for leakages.
It is therefore an object of the invention to provide an heat exchanger of the above mentioned type, which is cheap to manufacture and to assemble, and with a high efficiency of heat exchanger.
This object is achieved in that each tube is zigzag folded so as to have a number of rectilinear sections interconnected by bent portions.
By providing such tubes composed of rectilinear and bent portions the assembling time may be heavily reduced while maintaining a low risk of leakage.
In one embodiment of the invention each strip is provided with holes with such dimension that each opening fits around two sections of the same tube.
In this way assembling is easy as the tube may be inserted in the hole by introducing the bent portion interconnecting the two sections into the hole. Otherwise the contact area between the strips and the tube is still high in order to have a good heat exchanger contact.
In another embodiment of the invention each strip is provided with elongated holes with such dimension that each hole fits around one section of the tube. In this case each elongated hole has a slot-like shape with an open end at one end of the strip.
In this way each tube comprising rectilinear sections and bent portions can easily be fitted to the strips by inserting the same through the open ends of the slot-like holes.
Other advantages and characteristics of the invention will become clear from the following description, reference being made to the annexed drawings.
In the drawings there is :

Fig. 1: a front view, partly in cross-section of a heat exchanger according to the invention,
Fig. 2: a side view of the heat exchanger of Fig. 1,
Fig. 3: a cross-section, on enlarged scale, according to the line III-III in Fig. 2,
Fig. 4: a perspective view of the heat exchanger of Fig. 1 before assembling,
Fig. 5: a cross-section, as in Fig. 3 of a modified embodiment of the heat exchanger according to the invention.

As shown in Fig.'s 1 and 2 the heat exchanger 1 comprises a number of strips 2, which in the embodiment shown each consists of a rectangular plate made of a material with good heat conducting properties such as aluminium or aluminium alloys. The strips 2 are positioned in a parallel way with respect to each other thereby forming a cooling pack.
Each strip 2 is provided with a number of openings or holes 3 which in the embodiment shown have an elongated form, and are open ended to one side so as to firm cut-outs in the strip 2, as shown in Figs 1 and 3.
A flat tube 4 is inserted in the openings 3 of the cooling pack, the flat tube 4 being bent in a serpentine way and as such is composed of a number of rectilinear sections 5 and bent portions 6. The flat tube is preferably of the type obtained by multiple port extrusion, i.e. a flat tube having a number of parallel internal flowing channels 10 (see Fig. 3); for a fluid (liquid or gas) separated by innerwalls 11, the outer walls of such tube being formed by two parallel flat walls 13 and 14 interconnected by two semi-circular sections 15 and 16 and the already mentioned inner walls 11. Such a tube may be produced by a single step extrusion process by using especially adapted extrusion dies. The main advantage of such flat tubes is that the heat exchange surface is much greater compared with traditional round tubes, so that heat exchangers based upon this type of tubes are more effective.
However it is also possible to use flat tubes of the type described US-A-5 058 266. Flat tubes obtained by other type of processes are applicable as well.
The height of the flat tube 4, i.e. the smallest dimension of the tube is somewhat bigger than the smallest dimension (i.e. the height) of the opening 3.
The way in which the heat exchanger according to Fig. 1 and 2 is obtained is shown in Fig. 4. A piece of flat tube 4 is folded in a serpentine shape i.e. a construction comprising a number of rectilinear portions 5 interconnected by bent portion 6.
In the embodiment shown the rectilinear portions are parallel to each other and the distance between the facing outer walls of two adjacent rectilinear portions is equal to the smallest distance between two adjacent openings 3 in the strips 2. Having formed the tube 4 in such a configuration the heat exchanger of Figs 1 and 2 can easily be obtained by laterally inserting the preshaped tube 4 into the openings 3 of a stack of strips 2. As a result of the chosen dimensions the tube will automatically fit in the openings 3 and there will be a good heat transfer contact between the wall of the tube 4 and the individual strips 2.
Although the heat exchanger of the embodiment shown has parallel rectilinear sections of tubes it is possible, according to the invention, to use non-parallel rectilinear sections. In this case the strips are to be provided with openings which are not located on the same place in each strip, but the position of the opening is gradually changing from one strip to another. It is even possible to have a tube with not completely rectilinear sections, but with e.g. ondulated sections between two bent portions 6. Basically it is even possible to have random configuration, provided the openings 3 in the strips are made accordingly.
In fig. 5 there is shown a modified embodiment of the invention. Each strip 3 is provided with a number of substantially rectangular openings 24 with four rounded corners 25. One dimension of the opening 24 corresponds to the width of the flat tube 4 to be used in connection with this strip 2. The other dimension is substantially bigger than the height of the tube 5. In fact that dimension is substantially equal to the distance between two non-facing walls of two adjacent rectilinear portions of the tube as shown in Fig. 4. The heat exchanger is obtained in that the tube is shaped in accordance with Fig. 4. Thereupon the tube 4 is with the bent portion 6 first introduced in the openings 24 of the stack of strips 3. In this way a heat exchanger almost identical to the heat exchanger shown in the figures 1 and 2 can be obtained.
It is obvious that by the invention there is obtained a heat exchanger with flat tubes which can easily be assembled and constructed and wherein only very few connections have to be made. Other embodiments are possible especially with respect to the shape of the strips and the internal construction of the tubes and the invention is only restricted by the scope of the claims.

Claims

A heat exchanger including a number of strips stacked adjacent one another in parallel relationship to provide air passages, and at least one flat tube for carrying a fluid, said tube or tubes passing through holes in the strips and being fitted in the holes in heat exchange relationship with the strips,
characterised in that
each flat tube is zigzag folded so as to have a number of rectilinear sections interconnected by bent portions.
Heat exchanger according to claim 1,
characterised in that
each strip is provided with holes with such dimensions that each hole fits around two sections of the same tube.
Heat exchanger according to claim 1,
characterised in that
each strip is provided with elongated holes with such dimension that each hole fits around one section of a tube.
Heat exchanger according to claim 3,
characterised in that
each elongated hole has a slot-like shape having an open end at one edge of the strip.
Heat exchanger including a number of identical strips stacked adjacent one another in parallel relationship to provide air passages, each strip being provided with a number of elongated slots having an open end at one edge of the strip, and at least one flat tube for carrying a fluid, said tube being composed of a number of rectilinear sections interconnected by bent portions, each tube being fitted in a set of openings provided in the strips.
Heat exchanger according to any one of the preceeding claims,
characterised in that
the rectilinear sections are parallel to each other.
Heat exchanger according to any one of the preceeding claims,
characterised in that
the flat tube is extruded, drawn as welded tube.