Method of manufacturing a heat exchanger

A method is disclosed for manufacturing a tube coil useful as a heat exchanger wherein the tube coil comprises a plurality of slightly spaced, parallel tubes wound onto a supporting core. The tubes are wound at an angle to the radial plane of the support. The winding direction is reversed with respect to the radial plane at an odd number of radial angle positions of the coil and separate tubes of a subsequent winding turn are positioned in the spaces between adjacent tubes of the preceeding winding turn.

The present invention relates to a method for producing a tube coil for use 
in a heat-exchanger system comprising at least one and preferably several 
heat-exchanger units each unit consisting of one or more tubes, preferably 
made of plastic, wound to form a hollow coil. 
At the present time there is an urgent requirement for heat-exchangers for 
the institution of heat transfer between water on the one hand and air on 
the other. Heat-exchangers of this kind are used for example to recover 
heat from the air discharge from dwelling houses and factories. Other 
applications of this kind of heat-exchanger are to heat air in rooms or to 
remove excess heat from rooms. 
A primary object of the invention is therefore to provide a simple and 
efficient method for producing tube coils for use in a heat-exchanger 
system of the convector type. 
The system which incorporates coils made by the method of the present 
invention is useful for heat exchange between air and water and comprises 
at least one heat-exchanger unit, which unit comprises at least one, but 
preferably several tubes which are wound to form a hollow coil and which 
are arranged to conduct water. 
The coil is closed or covered at one end. The other end of the coil, which 
is open, is placed against a base plate having an opening. This opening is 
aligned with the coil core and has a size and a shape corresponding to the 
coil core opening. Moreover the tubes turn of the coil are slightly 
separated in order to permit the air to flow perpendicularly across the 
tube during the passage through the wall of the coil. 
The coil preferably comprises a plurality of tubes, say 20-100 tubes which 
are wound in parallel. 
Moreover the system may comprise a plurality of coils. The coil may have 
conical shape, whereby a plurality of coils can be placed in contact with 
each other (at the base surfaces) thus permitting a very compact 
construction while maintaining the air flow substantially radially to the 
axis of each coil. 
In a preferred embodiment of the invention, the tubes consist of a heat 
resistant plastic such as cross-linked polyethylene. 
Preferably, each coil has a conical or cylindrical central cavity. Fillets 
are inserted at regular angular intervals. For an interval of 90.degree. 
the fillets may have a radial thickness of (.sqroot.2 - 1) times the tube 
diameter. For this reason, the tube may be made by a simple winding 
procedure while still obtaining a substantially square cross section, 
whereby the coils can be closely packed on the base plate. These fillets 
are preferably provided with notches in order to guide the tubes and keep 
them in predetermined mutual distances. 
The array of tubes that is wound to form a coil, may be wound in zig-zag, 
the bends being positioned at predetermined angular intervals. There 
should be an odd number of bends so that it will not be necessary to 
insert spacers between the tube coils, as the tube bends will constitute a 
notched configuration in which the next layer of tubes is guided.

FIG. 1 illustrates a hollow coil 1 of plastic tubing. The top end of the 
coil is closed off by a disc 3 and the central opening in the coil is 
disposed centrally above an opening 4 in a baseplate 5. A distributor pipe 
6 is connected to the external ends of the tubes 2 and a manifold pipe 7 
is connected to the internal ends of the tubes 2. Axial bolts 8 extend 
between the plate 5 and the disc 3 and hold the coil 1 together in this 
way. 
FIG. 2 illustrates a heat-exchanger unit corresponding to that shown in 
FIG. 1, in which, however, the coil 1 has a conical cross-section. In 
addition, the illustrations show how the distributor pipe 6 and the 
manifold pipe 7 are plugged into main lines 10 and 9, respectively. The 
plug-in connection can be of the sliding seal type, thus facilitating 
exchange of a unit 1 should it develop a malfunction. In the plan views of 
FIGS. 3 and 4, it is shown how the area of the plate 5 can best be 
utilized by giving the conical or pyramidal coils a polygonal base surface 
configuration. In FIG. 5 it can be seen how the units 1 can be arranged 
centrally opposite one another with an opening 4 in the plate 5. In this 
embodiment, however, manifold pipe 7 is taken through the coil for 
connection outside the latter to main line 9. In a corresponding way the 
distributor pipe 6 is connected to main line 10 which is arranged at the 
same side of the disc 5 as the corresponding coil 1. In FIGS. 5A and 5B 
tube spreaders 15a and 15b respectively, are shown which are designed to 
be arranged between the turns of the sets of tubes 2 in order to maintain 
the tubes at the desired mutual interval. In FIG. 5C, 5D a pyramid-shaped 
spacer or fillet 15c has been shown which, when the coil is wound on a 
cylindrical cone, 12 is arranged at intervals of 90.degree. in order to 
give the wound core a pyramidal shape with a square base area, thus 
producing the configuration shown in FIG. 3 and FIG. 5E. The fillet 15c 
has a thickness in the radial direction of the coil, of around 
(.sqroot.2-1) times the diameter of the plastic tube. With a coil in 
accordance with the invention, the water flows spiral fashion from the 
centre to the periphery of the coil through several turns of the tube 
located one outside the other. 
At the same time, the air flows radially inward. Alternatively, the two 
flow directions are reversed. As far as the temperature gradient is 
concerned, a "counterflow" arrangement is obtained, i.e. the coldest water 
meets the coldest air and the hottest water the hottest air, in the 
situation where the air is to be cooled. At the same time, a "cross-flow" 
is obtained, i.e. the air flow in a direction at right angles to the tube 
through which the water is passing, so that high heat transfer rates are 
obtained. This yields maximum efficiency. 
These technical principles are of course well-known but in the context of 
the present invention they have proven their efficiency. 
In FIGS. 6 and 7, spacers 11 can be seen which are used in the manufacture 
of a coil in accordance with the invention. If a pair of adjacent spacers 
11 are considered in closer detail, it can be seen that, at sides facing 
one another, the spacers are provided with centrally opposed recesses 
which in combination with the gap between spacers are designed to 
accommodate tubes 2A and 2B. In adjacent gaps designed to take tubes, the 
recesses are radially staggered by a distance corresponding to half the 
pitch of the tube coil. When the tube 2A is introduced into its respective 
recesses, in the manner shown in FIG. 6, the spacers 11 located between 
the windings of the tube 2A are guyed up by tube 2A or in other words 
supported so they do not pivot apart when the windings of tube 2B are 
introduced between the spacers 11 so that the tube 2B cannot be moved 
further down than the position shown in FIG. 6. The tube 2B in turn 
stiffens the spacers so that the next turn of the tube 2A cannot be moved 
further down than the intended recesses. FIG. 7 illustrates how the 
spacers 11 are detachably fixed in a rotatable winding drum 12. Two tubes 
sets 2A and 2B have their ends fixed in a manifold pipe 7 which is 
arranged in a recess in the external surface of the drum. The tube sets 2A 
and 2B extend at an angle to one another so that the set 2A penetrates 
deepest between the spacers 11 and therefore stiffens the latter with the 
result that the tube set 2B cannot penetrate down any further than the 
intended recesses as shown in FIG. 6. The tube sets 2A and 2B pass through 
comb structures 14, the tubes running through the gaps thereof with a 
certain degree of friction so that they are held tensioned in the desired 
alignment during winding. 
In order that the tube turns should maintain a spiral shape during winding 
according to the procedure shown in FIG. 7, and not be deformed into a 
polygonal shape because of stretching of the tube, disc-shaped tube 
spreaders 15 are employed, for example at angular intervals of 45.degree. 
from the spacers 11. When the coil has been completely wound the discs are 
removed. 
FIG. 8 illustrates how a straight, polygonal coil in accordance with the 
invention can be manufactured. The coil is wound on a removable core drum 
12B having, for example, a triangular cross section. The ends of the tube 
2 are directed to a manifold pipe (this has not been shown but can be 
accommodated in the drum 12B in a manner similar to that shown in FIG. 7). 
The tube 2 is unwound from the drums 13c and is guided during the winding 
operation by one or more comb arrangements 14. During winding, the combs 
14 are oscillated axially as shown in FIG. 8, so that the direction of 
winding of the tube changes after passing each edge of the core 12B. The 
underlying layer of tube 2 on the coil consequently, exhibits a recessed 
space between each tube of each individual winding in which, at the 
corners of the drum 12B, the individual windings in the topmost layer are 
laid down thus enabling the pitch of the tube to be maintained and the 
tube secured in position with changes in direction. The spacing effect 
described can of course be obtained by additionally introducing corrugated 
or plastic strips, for example as shown in FIGS. 5A and 5B, at the corners 
of the coil on the drum 12B. FIG. 8A shows how the comb structures 14 
illustrated schematically in FIGS. 7 and 8 appear. The gaps between the 
comb teeth can be narrower than the diameter of tube 2 so that the latter, 
in passing the gap experiences a deformation resistance or friction. 
A drum with a polygonal circumference will have an odd number of corners, 
three or five. The zig-zag wound tube can, therefore reverse its direction 
only above the particular tube turn located closest below it. 
The comb structures 14 shown in FIG. 8A can be displaced simultaneously in 
the same axial direction or they can be displaced synchronously but in 
opposite directions. 
FIG. 9 illustrates how coils in accordance with the invention can be 
assembled to form a heat-exchanger system. The coils 1 are supported by a 
plate 5 and are placed with their base surfaces in contact with one 
another in order to make best use of the available area on the plate 5. 
The coils are covered at the top by a disc 3. If required, the coils 1 can 
be matched conically so that the part removed from the plate 5 to provide 
access for airflow, corresponds to the requisite dimensions of the disc 3. 
The coils 1 each possess a distribution pipe 6 and a manifold pipe 7 which 
are connected to principal lines 10 and 9, respectively by means of 
sliding couplings. The coils 1 are assembled in a casing or housing 21 and 
a fan 20 or the like can be provided in order to produce air flow through 
the heat-exchanger units 1. 
FIGS. 10 and 11 illustrate a variant embodiment of the heat-exchange system 
shown in FIG. 9, in which the baseplate 5A consists of a polygonal 
(octagonal) cylindrical shell which is closed at one end. A fan 20 can be 
provided inside baseplate 5A. The facets of the baseplate are provided 
with openings over which the tube coils 1 are placed. In this manner, a 
large number of standard and easily exchangeable coils can be arranged on 
a common baseplate so that all the coils 1 are easily accessible. 
FIG. 12 illustrates an construction of the coil 1 for use in a 
heat-exchanger system of the kind shown in FIG. 9. In the embodiment shown 
in FIG. 12, the distributor pipe 6 is introduced into the central opening 
of the coil so that the main lines 9 and 10 can be laid adjacent one 
another in order to facilitate assembly and the insertion of the lines 6 
and 7 into lines 9 and 10. 
It will be evident that the coil shown in FIG. 1 can be used for example, 
as a separate air-cooler, in which case the plate 5 consists of a ring 
substantially of the same width as the coil 1, the disc 3 consists of a 
fixed part of a structure such as a roof or a wall in the room where the 
air is to be heated or cooled. 
In manufacturing coils in accordance with the invention it has been found 
highly advantageous if a large number of tubes, say 30 to 100, preferably 
at least 30 to 40, are fixed in a plenum chamber 7 (which may take the 
form of the manifold pipe shown) and the plenum chamber attached to the 
core around which the coil is to be wound. The coil is then rotated the 
desired number of turns during winding of one or more flat tube sets, for 
example 10 to 30 turns, after which the tube set is cased and fixed in a 
plenum chamber 6 (distributor pipe). 
Referring to FIG. 9, it will be clear that the fan 20 can be replaced by a 
flue which is sufficiently high to produce a natural draft through the 
heat-exchanger system. If the tube coils 1 carry hot water whose heat 
content is to be transferred to the air, then water can be tapped off, for 
example from the line 10 to the spray nozzles 22 so that a liquid spray is 
introduced into the airflow to wet the surface of the coils 1. This 
results in a considerable increase in heat transfer coefficient. 
The heat-exchanger described can be matched to differing temperature 
requirements by choosing the least expensive type of plastic which is 
acceptable for the particular temperature, such as, for example 
polyethylene for relatively low temperatures, polybutylene for higher 
temperatures and cross-linked polyethylene for even higher temperatures. 
Furthermore, the tube can be of a kind provided with circumferential 
corrugations.