Heat exchanger rotor and a method of manufacturing such a rotor

The invention provides a regenerative heat exchanger rotor with an outer casing which comprises a plurality of layers of a helically wound strip orientated so that its width direction is radial with respect to the rotor, a core on which the strip is wound and which is permeable for the medium with which the rotor is to be used, said strip having channels therein to allow the radial passage of the current of the medium. A further strip on the rotor is free of channels and is also wound on the permeable core helically so as to be associated with the channeled strip so that the layers or turns of the unchanneled strip (20) alternate with those of the channeled one with each layer or turn of the channeled strip being followed by one layer or turn of the unchanneled one. This arrangement makes possible an extraordinarily satisfactory efficiency as regards flow and heat transfer. This advantage is combined with the advantage of the possibility of very simple and cost-effective production.

BACKGROUND OF THE INVENTION 
The present invention relates to hollow cylindrical rotors for regenerative 
heat exchangers and more particularly to such a rotor comprising an outer 
casing which comprises a plurality of layers of a helically wound strip 
orientated so that its width direction is radial with respect to the 
rotor, a core on which the strip is wound and which is permeable for the 
medium with which the rotor is to be used, said strip having channels 
therein to allow the radial passage of the current of the medium. 
Such a rotor has been proposed in the German Pat. No. 3,308,445 with the 
aim of providing a heat exchanger which on the one hand had a high flow 
and thermal efficiency and on the other hand was able to be simply 
produced. In order to achieve this object the strip was so designed that 
the recesses or grooves therein only extended over a fraction of its 
height and formed the channels in the individual layers of the strip, 
which were placed in sealing contact with each other so that flow in the 
circumferential direction was prevented. For shaping the strip while being 
wound on a drum it was run between embossing rolls with complementary 
outer faces, the shaped or embossed strip then being continuously wound 
onto a core taking care to see that the channels of the consecutive layers 
were precisely aligned in relation to each other in order to ensure the 
passage of the flow of medium therebetween. However such a structure could 
only be produced by a machine moving in steps and with a high degree of 
accuracy. If the required degree of precision was not kept to while 
winding the strip on the core the resulting structure would interfere with 
the flow of the medium. 
SHORT SUMMARY OF THE PRESENT INVENTION 
One object of the present invention is to provide for a further 
simplification of the production of such a rotor. 
A further aim of the invention is to accelerate the production process 
while at the same time ensuring an evenly proceeding thermal transfer at a 
particularly high rate. 
In order to achieve these or other objects appearing from the present 
specification and claims, a further strip is provided on the rotor which 
is free of channels and is also wound on the permeable core helically so 
as to be associated with the channeled strip so that the layers or turns 
of the unchanneled strip alternate with those of the channeled one with 
each layer or turn of the channeled strip being followed by one layer or 
turn of the unchanneled one. In this respect the arrangement may for 
instance be such that the consecutive layers of the two strips are 
arranged parallel or approximately so in relation to each other. It is an 
advantage if the channeled strip has a corrugated or zig-zag form with an 
amplitude of the corrugations therein equal to between 1 and 5 mm and 
preferably to approximately 2 mm, while the channel to channel pitch may 
be between 2 and 8 mm and more especially amounts to approximately 5 mm. 
On the other hand the layers of the unchanneled strip may be comprised in 
a single plane. It is convenient if the unchanneled strip has axial holes 
therein for the passage of the medium. In this respect the unchanneled 
strip may have a structure resembling that of expanded metal lathing, 
while the channels of the channeled strip extend in a radial direction 
from the outside to the inside, that is to say towards the longitudinal 
center axis of the core with a taper so that the strip is compacted at the 
radially inner side thereof. 
The arrangement in accordance with the invention involves two advantages, 
namely that the thermal efficiency and the flow efficiency are 
extraordinarily high and that this advantage is combined with a further 
simplification and cheapening of the production process. The thermal 
efficiency is improved because of the fact that it is now possible to 
utilize the thinnest possible sheet metal for the two strips and to have a 
very fine corrugated channeling of the channeled strip, there a very large 
surface area available for the heat exchanger. It is possible to see 
further advantages in the fact that the flow through the rotor will be 
practically completely smooth or free of turbulence while production is 
simple. More especially, a satisfactory continuous method of production 
may be employed without absolute accuracy on fitting the consecutive 
layers together being of primary importance. In this respect the 
unchanneled strip serves to more or less direct the flow and to avoid 
turbulence and other irregularities in the flow, although owing to the 
small amplitude or height of the channels it is now no longer significant 
whether the consecutive layers are in communication with each other to 
some extent or not. Furthermore, if the heat exchanger is used for clean 
air, the channels may be small or very small while the medium with which 
the heat exchanger is used is contaminated, it is preferred to provide 
large channels. 
Production may for instance be further simplified if the channels in the 
channeled strip are produced with the aid of cooperating conical embossing 
rolls which in the embossing station are in engagement with each other and 
run against each other so that the strip to be channeled, as for instance 
aluminum sheet strip, may be drawn through the nip between the rolls 
continuously, while the plain or unchanneled strip may be slotted by, for 
instance, stamping, and being subjected to tension in the length direction 
of the strip so that the slots assume a rhombic form. The primary purpose 
of the slots is to prepare and adapt the unchanneled strip so that it may 
be readily wound about the core. However apart for the provision of slots, 
this aim may be achieved in some different way, for instance by using 
rolls to extend the strip at its upper radially outer edge while in at the 
lower, inner edge the strip is compressed. It is preferred to produce the 
channeled and the unchanneled strips in separate stations so as to be 
ready for winding and then to wind them onto the core continuously which 
is placed on a mandril rotating about an axis perpendicular to the axis of 
rotation of the embossing roll, the core then also being moved along the 
axis of this mandril. It will be clear that production only demands a few 
simple operations without any additional measures being needed to achieve 
an excessive degree of accuracy. 
The invention will now be described in more detail with reference to the 
accompanying drawings.

DETAILED ACCOUNT OF THE INVENTION 
FIG. 1 shows the rotor in accordance with the invention which has been 
generally referenced 1 and which forms part of a heat exchanger generally 
referenced 2 and which is shown with part of its housing broken away. Two 
flows of mediums or fluids move through the rotor 1 in the direction 
indicated by the arrows 3, each of the two flows of medium passing in a 
generally radial direction through the casing 4 of the rotor 1. The 
interior of the rotor 1 is divided up by a partition 5 into two chambers 
6, one for each of the two flows. The partition 5 is stationarily arranged 
in the interior of the rotor 1 and constitutes a part of the housing in 
which the rotor 1 rotates about its longitudinal axis as marked by the 
arrow 7. The housing of the heat exchanger 2 further includes partitions 8 
which adjoin the outer casing of the rotor 1 and separate the inlet parts 
9 and the outlet parts 10 of the two flows from each other. The inlet and 
outlet parts for the one and the other flow are spaced about the 
circumference of the rotor 1 by 90.degree. and the inlet and outlet parts 
for the two flows are opposite to each other on the periphery of the rotor 
so that the outlet part 10 for the flow 3a is diametrally opposite to the 
outlet part 10 of the flow 3b while the inlet part 9 of the flow 3a is 
diametrally opposite to the inlet part 9 for the flow 3b. With this 
arrangement it will thus be seen that the flows pass in opposite 
directions through the rotor 1, this being an advantage as regards the 
efficiency of heat exchange. In the inlet part 9 there is a respective 
flow through the casing 4 from the outside in an inward direction and in 
the outlet part 10 there is a flow from the inside in an outward 
direction. Where the rotor has the flows passing through it the rotor 1 is 
heated, since heat is abstracted from the flow which was hotter in the 
first place. Owing to the rotation of the rotor 1 in the direction of the 
arrow 7 the heated part of the rotor 1 is moved into the flow of the 
other, originally colder flow, which takes up heat here and at the same 
time cools down the rotor 1. When further rotation takes place the cold 
part of the rotor casing 4 moves back in the hot flow and the heat 
transfer operation is accordingly repeated. 
The rotor 1 has the configuration of a hollow, circularly cylindrical heat 
exchanger roller whose casing contains a number of layers of a strip 15 
which is placed on edge so as to be radially aligned and which has 
channels 16 made in it which assure the radial passage of the flow in 
question as marked by the arrows 3. This strip 15 provided with the 
channels 16 is helically wound on a core 17 which is permeable for the 
flows, i.e. it allows the flows to move through it. The core may be in the 
form of a perforated metal cylinder with a large free cross sectional area 
or it may be in the form of a piece of piping with openings through its 
wall. The core 17 thus serves as a support for the coils of the strip 15 
and thus as a carrying support of the rotor 1 in the housing of the heat 
exchanger 2 while its internal surface simultaneously serves as a smooth 
running surface for the partition 5 so that the latter may be placed with 
a very small clearance between it and the internal casing surface of the 
core 17. The core 17 may also be made of a stiff wire fabric but a cage 
structure of the core 17 would also be possible in the case of which there 
would be a large number of bars arranged parallel to each other on the 
outer surface of the cylinder, such bars then being supported relatively 
at their ends. The openings in the wire fabric or the spaces between the 
bars would then form the opening or passage for the flows, which move 
through them with a low degree of resistance. Such a design of the heat 
exchanger roll or drum has been proposed in the German Pat. No. 3,308,445. 
In accordance with the present invention the channeled strip 15 is placed 
adjacent to a second strip 10 which is also helically wound on the 
permeable core 17 and which is not channeled. The individual layers or 
turns of this strip 20 alternate with the layers of the channeled, or more 
specifically corrugated, strip 15 in such a manner that each layer of the 
channeled strip 15 is followed by a layer or turn of the unchanneled strip 
20 and vice versa. In this design the consecutive layers of the two strips 
15 and 20 are placed so as to be parallel, or approximately so, to each 
other. This arrangement is shown in detail in FIGS. 2a and 2b, from which 
it will be seen that the layer or turn 15a of the channeled strip is 
followed by the layer 20a thereunder of the unchanneled strip 20, which is 
then followed by the layer 15b of the channeled strip 15 which rests on 
the layer 20b of the unchanneled strip 20. It is best for the alternating 
layers ot be in contact with each other. The primary purpose of the layers 
of the unchanneled strip is to direct and guide the flow of the medium 
serving for heat exchange without fitting the individual layers exactly 
together. 
As will be more especially seen from FIGS. 3 and 4, the channeled strip 15 
has a corrugated or zig-zag structure, and it will be especially be 
apparent from FIG. 3 that there are waves 18a and troughs 18b coming 
thereafter which rest on the unchanneled strip. The height a of the 
corrugated structure is between 1 and 5 mm and preferably amounts to 
approximately 2 mm, while the corrugation pitch b amounts to between 2 and 
8 mm, or more especially approximately 5 mm. Lastly it is to be noted that 
the channeling of the channeled strip 15 tapers radially inwards (see 
arrow 19 in FIG. 4) from the outside 19a to the inside 19b towards the 
longitudinal center axis of the core so that at the radially inner side 
the strip is compacted or more puckered than at the outer edge. The 
channels in the channeled strip 15 are produced by cooperating conical 
embossing rolls whose peripheries are in engagement with each other in the 
embossing station where they are located. The strip to be furnished with 
channels, as for example in the form of aluminum sheet is drawn through 
the nip of the embossing rolls continuously. The corrugations or channels 
may be made small in size if the heat exchanger is to be used in 
conjunction with clean air and if the flow is dirty air they will have to 
be made with a suitably larger size. 
As will be seen from the drawing the individual layers of the unchanneled 
strip 20 are comprised in a plane so that the troughs of the corrugated 
structure of the channeled strip are well able to engage this flat, even 
unchanneled strip. The unchanneled strip 20 has axially directed openings 
21 so that this unchanneled strip 20 has the form of expanded metal as 
will be more especially seen from FIG. 5a of the drawing. This unchanneled 
strip, consisting for example of aluminum, is provided with slots by 
stamping for instance and then stretched by a tensile force acting in the 
length direction as indicated by the arrows 22 so that the slots assume a 
rhombic shape. This makes it possible for the strip to be readily wound 
onto the cylindrical core without any further preparation. Dependent on 
specific requirements referring now to FIGS. 7 and 8, the slots 21a or 21b 
may be placed with a large distance between them (as a wide mesh structure 
or expanded metal lathing) or quite close to each other respectively. 
Owing to the design of the two strips as described it is possible to employ 
very thin sheet metal for the production of the strips and furthermore the 
channels may be very small in size so that--owing also to the large heat 
transfer surface as well--there is a highly satisfactory heat transfer 
action and there are also advantages as regards the flow since the radial 
flow through the heat exchanger roller is more or less completely free of 
any disturbance or turbulence. 
The production of the novel heat exchanger roll is simple and low in price. 
Firstly the channeled and the unchanneled strips are produced in a 
finished condition at separate stations, that is to say a station for 
stamping and stretching in the case of the unchanneled strip and 
channeling by suitable embossing rolls in the case of the channeled strip 
and the two strips are continuously wound onto the core in the form of 
helices after the ends of the strips have been anchored to the core. In 
lieu of a stretched openwork structure, which primarily serves to 
facilitate winding of the respective strip on the core, the strip may be 
produced in a helical form by extending the outer edge of the strip by 
rolling and compressing the inner edge part thereof. The strip may be 
wound on the core in such a compact array that, as has already been 
described, the corrugation troughs 18b of the channeled strip 15 rest on 
the plane of the following layer of the unchanneled strip 20 and the layer 
of this unchanneled strip 20 for its part rest on the waves 18a of the 
corrugated structure of the following layer of the channeled strip. 
In this respect it is possible for the ends of the core to have covers 
which extend past the outer surface of the core and contain the strips 
between them, the strips best being clamped between the covers and being 
wound compactly between the same so that they are retained by their 
inherent elasticity.