Heat exchanger and sheet material therefor

A bulkhead is formed of a sheet of material which is preformed so as to have alternatingly opposed S-shaped creases at spaced intervals which define pairs of mutually facing recessed grooves between adjacent creases. Resilient surface area enlarging members are each provided with a pair of lips formed on the opposite edges thereof. Each pair of lips are received within a pair of mutually facing recessed grooves of the bulkhead. The surface area enlarging members can be snapped into or out of operative position with respect to the bulkhead to adjust the surface area of the device.

The invention relates to a heat exchanger as described in the heading of 
claim 1. The surface-area increasing members are fitted in accordance with 
the intended capacity per unit surface area of the heat exchanger. For a 
specific application, the total effective surface area needed in order to 
achieve a desired heat transmission can be determined in advance. This 
kind of accurate advance determination may be laborious or unfeasible, for 
example in the case of small production quantities or in the case of 
certain applications. 
For example, in the case of a heat exchanger for a gas heater, it is not 
really possible to calculate the total surface area required for an 
optimal output. The performance of a gas heater is namely influenced by 
the circumstances under which it operates, in particular by the chimney 
draught. In the case of a poorly-functioning chimney the heat exchanger 
requires a smaller heat-exchanging surface, so that the combustion gas to 
be discharged will still have a sufficiently high temperature to be 
effectively extracted through the chimney. A manufacturer of such a gas 
heater will generally determine the dimensions of the heat exchanger on 
the basis of these relatively unfavourable circumstances. This means that 
in other cases, where a good chimney draught is in fact available, the 
heater delivers a less than optimal output. For an optimal performance it 
is thus desirable that the heat exchanging surface can be adapted to the 
circumstances. 
The invention has for its object to provide a heat exchanger of the kind 
described in the preamble which can also be fabricated efficiently in 
small production quantities and which is in principle suitable for a 
simple adjustment of its total heat exchanging surface area. 
According to the invention this is achieved through the measures claimed in 
the characteristic of claim 1. Through these measures a specific quantity 
of profile members of a desired form can be mounted, according to the 
desired total heat exchange surface area. 
In the cited example of a heat exchanger for a gas heater, the manufacturer 
can design and make the heat exchanger for application with an effective 
chimney. When it becomes apparent during use that the combustion gas is 
not being extracted satisfactorily--something which can easily be 
detected, for example through condensation on external windows-one or more 
profile members can be removed by the user, so that the combustion gas 
leaves the heat exchanger with a higher temperature and can thus be better 
extracted by a non-optimally functioning chimney. 
The fabrication of the heat exchanger according to the invention is simple. 
The bulkhead can be formed as sheet material into the desired shape, 
whereafter the required number of profile members with a suitable length 
can be arranged in the grooves. 
Through the alternatingly opposed S-shaped creases, sideways-recessed 
grooves which face towards each other are formed on both sides of the 
bulkhead. Profile members can therefore be accommodated on both sides of 
the bulkhead. 
When adjustability of the total heat exchanging surface area is not 
necessary or not desired, the embodiment according to claim 5 can be used 
with advantage. In this manner the bulkhead and profile members are joined 
together as an entity, with the concomitant advantage of an improved heat 
transfer at the point of the contact surfaces of the profile members in 
the grooves. 
A further development of the invention is characterized in claim 6. Through 
this, the material can be pressed flat to a uniform thickness and known 
sheet-material working methods such as seam folding can be used. The 
bulkhead of a heat exchanger can thereby be completed fully sealed by a 
folding operation on an end edge transverse to the longitudinal direction 
of the S-creases. 
The invention also relates to and provides a sheet material that is 
intended for the fabrication of a heat exchanger according to the 
invention. This sheet material is characterized in that in cross section 
it displays a profile with alternatingly opposed S-shaped creases spaced 
at intervals. This sheet material can be formed into a required shape 
using normal sheet-material working techniques, whereafter an arbitrary 
heat exchanger can be obtained in a simple way by the addition of profile 
members.

As FIG. 1 shows, a heat exchanger 3 according to the invention is mounted 
on the rear side of a gas heater 1. The combustion gas enters the heat 
exchanger 3 via the inlet 2. In the heat exchanger 3, the hot combustion 
gas imparts a portion of its heat to the surrounding air. The heat 
exchanger 3 comprises a bulkhead 5 bent over into a box form, which 
mutually separates the circulation space for the combustion gas inside the 
heat exchanger 3 on the one hand from the circulation space for the air to 
be heated outside the heat exchanger on the other. As FIGS. 1 and 2 show, 
an inverted U-shaped guide 14 is mounted in the heat exchanger 3. This 
guide ensures that combustion gas entering via the inlet 2 moves downwards 
along the bulkhead to the bottom of the heat exchanger, and then flows 
upwards inside the guide and exits the heat exchanger via an integral 
spout 15 and via the outlet 4 connected to the chimney. The heat exchanger 
is open at the bottom, so that any back pressure resulting for instance 
from a fall wind cannot travel into the heater as far as the burner. The 
construction of the heat exchanger with integral fall wind deflector is 
known per se. 
In accordance with the invention, the bulkhead 5 of the heat exchanger 
according to the invention has a profile with alternatingly opposed 
S-shaped creases spaced at intervals. Three of these creases are 
identified by reference numbers 6, 7 and 8. As can be seen, the S-shaped 
crease 7 is opposite to S-shaped crease 6, and similarly the S-shaped 
crease 8 is opposite to the adjacent S-shaped crease 7. Two opposed 
S-shaped creases, for instance 6 and 7, define sideways-recessed grooves 
which face towards each other. The creases 6 and 7 form such grooves on 
the outside and the creases 7 and 8 form such grooves on the inside of the 
heat exchanger 3. The curved profile members 12 and 13 respectively are 
held in these pairs of grooves. These members are bent from sheet material 
and are provided at their lower ends with projecting lips, which grip in 
opposite grooves. The profiled members 12 and 13 clamp firmly in the 
grooves through their own resilience. The contact pressure caused by the 
spring force affords a good heat-conducting junction between the bulkhead 
and the profile members. It will be apparent that when it is desired to 
reduce the capacity of the heat exchanger, one or more of the profile 
members 12 or possibly 13 may be removed. 
As observed earlier, the heat exchanger according to the invention can be 
simple to manufacture. The bulkhead 5 is folded by use of the normal sheet 
material working techniques into the U-shaped shown. Mounted at the ends 
are the closing side caps 9, which are held by a flange 17 at sides and 
top in the S-crease at the end of the bulkhead 5. The caps 9, and 
similarly the profile members 12 and 13, can optionally be fastened by 
spot welding. 
As shown in FIGS. 1 and 3, the bulkhead made with S-creases according to 
the invention has the further advantage that the mounting brackets 10, 11 
can simply grip therein. A mounting bracket 10 is shown in more detail in 
FIG. 3. This bracket 10 is fabricated from a piece of 
commercially-available half-round section, one end of which is thrust 
between the two S-creases 16. At the other end, the bracket 10 is fastened 
to the carcass of the heater 1. 
The bracket 11 fastens the heat exchanger at the bottom to the heater 1 in 
a similar way, and at the same time fixes the two opposite wall parts of 
the bulkhead 5 at the desired distance from each other. 
The heat exchanger shown in FIGS. 4 and 5 is similarly intended for a 
heater. The heat exchanger 20 comprises a bulkhead 21 which again is 
provided with alternatingly opposed S-shaped creases 29, 30, 31 spaced at 
intervals. A cap 33 is connected to the side and upper edges of the 
bulkhead 21, which cap forms together with the bulkhead 21 a circulation 
space for the combustion gases. On the other side bulkhead 21 is 
connected, along its side edges only, to a cap 24 which together with the 
bulkhead 21 defines a circulation space 25 for the air to be heated. The 
combustion gases are supplied via the intake 32 and are discharged via the 
chimney connection 28. Between the intake and the outlet an extra guide 
plate is also mounted, which partitions a circulation space 27. The 
combustion gases can flow downwards into the space 26 and arrive in the 
space 27 at the bottom of the heat exchanger, where the gas flows upwards 
to the outlet 28. 
In the circulation channel 25, profile members 22 are held repeatedly by 
two adjacent S-shaped grooves. Accommodated in circulation space 26 are 
profile members 23 which grip in mutually facing grooves of S-creases 
which are separated from each other by a distance of three S-creases. As 
is particularly shown in FIG. 5, the lip edges 34 of the profile members 
22 and the lip edges 35 of the profile members 23 are bent back to some 
extent, such that a good clamping contact is achieved in the respective 
grooves of the bulkhead 21. Hence a good heat transmission is assured. 
In general, various measures can be adopted for ensuring good heat 
transmission between the profile members and the bulkhead concerned. In 
many cases the gripping sliding joints shown will be sufficient. In 
special cases a heat-conducting paste can be applied in the grooves. 
Another possibility is that after the mounting of the profile members the 
entire heat exchanger is dipped in a bath of molten metal such as tin or 
zinc. After cooling, this metal bonds the profile members firmly to the 
bulkhead. In that case a perfect sealing is also ensured for any surface 
joint edge transversely of the longitudinal direction of the S-creases. 
For example, in the heat exchanger of FIG. 4 the cap 33 will be surface 
joined along the top edge to the bulkhead 21. A good seal can be obtained 
through use of a seam folded joint of an edge of the cap 33 with the 
bulkhead 21, possibly with the interposition of a gasket material. Instead 
of the use of gasket material, a complete seal can also be ensured in the 
manner described by dipping in a bath of molten metal. 
FIG. 6 shows another embodiment of sheet material that is intended for a 
heat exchanger according to the invention. The sheet material is here an 
extrusion moulding 40 that comprises four S-creases and which is provided 
along one longitudinal edge with a groove 42 and on the other edge with a 
tongue 41 which fits into said groove 42. A random number of extruded 
mouldings 40 can be assembled into a bulkhead of the desired dimensions by 
the sliding into each other of tongues and grooves 41, 42 respectively. 
At the position of the S-creases 43, the wall thickness of the extruded 
moulding is approximately one third of that of the intervening parts 44. 
Thus when the S-creases are pressed flat, the sheet material acquires a 
smooth surface on both sides. In the flattened state, for example, a 
completely sealed seam folded joint can be formed with an adjoining piece 
of sheet material. 
The heat exchanger 45 of FIG. 7 is tube-shaped. The bulkhead 50 itself is 
tube-shaped and has a profile in cross section which again has 
alternatingly opposed S-creases spaced at intervals. Profile members 46 
are gripped firmly on the inside, and profile members 47 on the outside. 
Accommodated in the interior amid the profile members 46 is a tube 49, 
which serves as a flow guide and ensures that the heat exchanging medium 
remains in good contact with the profile members 46 and the bulkhead 50. 
The assembly is held in an external tube 48, which ensures in a similar 
way that the other heat exchanging medium comes into good contact with the 
profile members 47 and the bulkhead 50. 
The variant shown in FIG. 8 again comprises a bulkhead 56 with alternating 
S-creases. The profile members 57, 58 are in this example extruded 
mouldings. 
In the above description, a gas-gas heat exchanger has been assumed in all 
cases. The invention is of course also applicable to liquid-liquid or 
liquid-gas heat exchangers. In the latter case, for example, profile 
members will be arranged only on the gas sides of the bulkhead. An example 
of such an application is a convector of a central heating installation. 
In that case at least one of the layers of the convector is of sheet 
material with S-creases according to the invention. For the adjustment of 
the capacity of the convector, profile members of the desired form can be 
added or removed in the manner described. 
It will be found from the applications described that the sheet material 
according to the invention, which in cross section has a profile with 
alternatingly opposed S-creases spaced at intervals, is very generally 
usable for the fabrication of a heat exchanger.