The present invention relates to a counterflow heat exchanger.

More specifically, the present invention relates to a heat exchanger of the counterflow type, and even more specifically to a counterflow heat exchanger of the high heat capacity type per volume unit and with a particular efficiency in ensuring a low T value DT (thermal delta) between the flows without needing to resort to a turbulent type motion.

As known, the heat capacity per volume unit of a heat exchanger depends on various factors, such as the size of the heat exchange surfaces, the thermal conductivity of the material forming the diaphragm separating the two flows and the thickness thereof, the thermal conductivity of the fluids, the thickness thereof, and the nature of the motion. The flow inside a heat exchanger, which pursues very low DT (thermal delta) values between the flows, is typically characterized by a turbulent motion, which allows a significant increase in the global heat exchange coefficient (the larger it is, the greater the turbulence) and this is by virtue of the fact that the resistance substantially loses importance to the conduction of the heat, determined by the thickness of the fluid in the conduit, which is, instead, a determining factor when operating in a situation of laminar motion.

The positive effect on the heat exchange coefficient due to the turbulence is greater the more the turbulence is induced, which in turn is higher, the greater the pressure differential used to produce it and therefore so is the required pumping energy.

In order to obtain high heat capacity values with a heat exchanger with turbulent motion, in the light of the above, a high energy pumping cost is required, as well as great mechanical resistance of the equipment used, and this represents a significant drawback related to the fact that a technical solution of this kind is very costly.

Such drawback can be overcome by using a laminar motion instead of a turbulent motion.

However, the solution of a heat exchanger in laminar motion also has some important drawbacks linked to the fact that such types of exchangers require large heat exchange surfaces per volume unit, large passage sections for the fluid against moderate lengths of the conduits in order to obtain a reduction in the speed and load loss of the fluid and thin thicknesses, both for the diaphragms separating the flows and for the conduits, into which said flows flow, however, having all these features at the same time is problematic; for example, as known, the supply of thin thicknesses is very problematic with reference to the management of the flow and it is even more so in the case of thin thicknesses belonging to high sections; wide and thin surfaces subjected to different pressures are also difficult to manage.

It is the object of the present invention to obviate the drawbacks disclosed above.

More specifically, it is an object of the present invention to provide a counterflow heat exchanger adapted to allow obtaining high heat capacity values with a laminar-type flow motion.

It is a further object of the present invention to provide a heat exchanger adapted to ensure modest load loss values in the pumping operation and therefore adapted to ensure low energy consumption.

It is a further object of the present invention to provide a heat exchanger adapted to overcome the problems of the laminar motion and, in particular, linked to the need to have large heat exchange surfaces per volume unit, large passage sections for the fluid against moderate lengths of the conduits in order to obtain a reduction in speed and load loss of the fluid and thin thicknesses, both for the diaphragms separating the flows, which must be able to withstand the deformations induced by the pressure differences varying in the paths thereof, and for the conduits into which said flows flow.

It is a further object of the present invention to provide users with a counterflow heat exchanger adapted to ensure high efficiency and versatility and such as to be easily and economically manufactured and managed, with modulable sizes and flexible in complying with the different project requirements .

These and other objects are achieved by the invention having the features outlined in claim 1.

According to the invention, there is provided a heat exchanger of the counterflow type with high heat capacity per volume unit, and with a modular, laminar-type flow motion with each module comprising an extruded bundle of channels, the end part of which is subjected to plasticization/cementation to strengthen it over the length of 1-2 cm, and make it capable of being combined with a first head consisting of a plurality of overlapping channels and a second head, or end head, provided with openings in the direction of the longitudinal extension of the module, which openings are functional for introducing a flow and releasing a counterflow, the first head abutting at one end of the extruded bundle of channels and the second head, or end head, abutting on said first head.

Advantageous embodiments of the invention become apparent from the dependent claims.

The constructional and functional features of the counterflow heat exchanger of the present invention can be better understood from the following detailed description, in which reference is made to the appended drawings, which show a preferred and non-limiting embodiment, and in which: figure 1 diagrammatically shows a partial axonometric view of a section of the end part of an extruded bundle, the main component of the counterflow exchanger of the invention; figures 2 to 5B diagrammatically show exemplary embodiments of components of the heat exchanger of the invention; figures 6A to 6F diagrammatically show further exemplary embodiment of components of the heat exchanger of the invention; figures 7A and 7B and 8A and 8B diagrammatically show filling features of the channels, forming inner components of the heat exchanger of the invention; figures 9, 10 and 11 and figures 12, 13 and 14 show further examples of components or structural elements of the heat exchanger of the invention.

The aforesaid figures show a preferred and non-limiting embodiment and constructional configuration variants for the counterflow heat exchanger with laminar motion, which uses section bars made of extruded plastic (for example, made of polycarbonate) defining a bundle of tubular elements or channels, in which special profiles or fillings are inserted (with the aim of improving the global heat exchange coefficient), with said elements in a modular and modulable structure in terms of size of the section in order to obtain global sections, even large ones, formed by a plurality of bundles of channels (so as to also obtain a single block of high dimensions).

The use of profiles made of extruded plastic (of extruded polycarbonate also referred to as corrugated plastic) is particularly suitable for manufacturing heat exchangers, operating in a laminar manner and, therefore, with low differentials of applied pressure.

Furthermore, the use of extruded plastic profiles with a plurality of channels, allows achieving highly reduced thicknesses of the diaphragms separating the channels and this allows counterbalancing the low thermal conductivity of the plastic (with reference to the previous description).

In fact, such section bars made of extruded plastic have, by virtue of the thick weave, which characterizes them (by way of example, a "Sabic" section bar with a polycarbonate diaphragm thickness of 0.034mm and with bundles of channels with a section of 10mm in width and 2.5mm in height) a good resistance to the different/varying pressures exerted by the two counterflows along the path thereof, with said resistance to the pressure, which is further increased by means of adding filling profiles in the stated channels.

With reference to figure 1 a module of the exchanger of the invention is schematized, globally indicated with 10, which is defined by an extruded bundle of channels 12 combined with heads 13 and 14, which allow obtaining a supply and outflow of the channels in a centralized and axial manner.

More specifically, there is provided an extruded bundle 12 of tubular elements or channels with a plasticized head and small openings for each channel, a first head 13 made of a plurality of overlapping channels 13' and a second head, or end head (the front head) 14, provided with openings 14' and 14'' in the direction of the longitudinal extension of the module and, functional for introducing a flow and releasing a counterflow, respectively.

The channels forming the extruded bundle 12 are numerous and produced with very thin walls and they can be plasticized/cemented in the end parts, e.g. with thermo setting resins (e.g. epoxy resins, so as to allow avoiding fragility and breaking of the/in the thin diaphragms defining the channels and so as to safely allow the coupling operations with the heads, which are assigned with providing the distribution of the supply and the collection of the drainage. Furthermore, seals 15 can be present between the extruded bundle 12 and the first head 13 and between the first head 13 and the second head, or end head 14.

In particular, the channels can be rectangular with a chessboard-like supply of the hot and cold flows, rectangular with an in-line supply of the hot and cold flows or square with a chessboard-like supply of the hot and cold flows.

With reference to figure 2, one end of the extruded bundle of channels 12 is shown, which has already undergone the operation of plasticization/cementation of a short end stretch and the opening of passages 20 and 20' through the plasticized/cemented section; the channels are arranged in a chessboard pattern and the first channels 16 intended to convey hot flows, the second channels 17 intended to convey the cold flows and the third channels 18 serving the function of allowing a constraint between the extruded bundle and the heads, defining plasticized free compartments or spaces, which are useful for securing the heads and/or shielding an insertion of caps or closing sheets (not shown) of the channels present in the first and second heads 13 and 14 described above (this is to avoid the presence of inconvenient protrusions); the first and second channels 16 and 17 are arranged mutually adjacent to define a chessboard like configuration, while the third channels 18 are arranged along the periphery of the group defined by the first and second channels 16 and 17.

It should be noted that the shape and arrangement of the third channels 18 can vary as a function of the specific aims and, for example, the configuration in figure 2, is suitable for avoiding the protrusion of caps (as better defined below).

Each first 16 and second 17 channel comprises a hole 20' and 20, respectively, which crosses a filling, e.g. thermoplastic present in the end part of the single channel and allows the fluids to enter and exit into/from said channels.

Figure 3 diagrammatically shows a first face 13B of the first head 13 (or intermediate head), which adheres to one end of the extruded bundle of channels 12 (with or without the presence of optional seals 15, which, if present, would have the same holes shown below for said first head), said first head comprises a piece/portion of extruded profile with a plurality of mutually overlapping channels 13' and each comprising a plurality of holes 22 and 22' through which a fraction of hot and cold flow passes, respectively, with said holes corresponding and in contact with the holes 20 and 20' of the described extruded bundle of channels 12.

Furthermore, said first head 13 is closed at the side by means of opposite caps 24.

Figure 4 diagrammatically shows a second face 13C of the first head 13 and, more specifically, the face opposite to the first face, which is adapted to interface with the second head 14, or end head.

For each channel 13', said second face 13C comprises holes 25, which are different to those described with reference to the first face 13B and this is because such holes serve the function of being interfaced with the second head 14 or end head.

Figure 5A shows a first face 14B of the second head 14, or end head, made up as an essential part, of two pieces of extruded channel, set side by side and, more specifically, the face adapted to be interfaced with the first head (with the second face 13C of the first head 13) and figure 5B a second face 14C opposite to said first face 14B.

The first face 14B of the second head 14 comprises holes 26 for being interfaced with the holes of the first head 13, while the second face 14C comprises the holes 14' and 14'' for the two hot and cold flows entering and exiting into/from the described channels. Closing caps 28 are arranged at the top and at the bottom for closing the channels.

By operating with square channels with a chessboard-like arrangement, considering the fact that in such configuration the channels have particularly reduced sizes (less than one centimeter per side), it is advisable to add a further and third head in order to facilitate the centering operations. Figures 6A to 6F illustrate such situation with figures 6A and 6D schematizing the inner face and the outer face, respectively, of the outer head 14, (i.e. the outermost one with respect to the extruded bundle of channels), figures 6B and 6E, which schematize an intermediate head, which comprises an inner face and an outer face, respectively (said last one, which abuts with the inner face of the outer head) and figures 6C and 6F schematize a third head, or inner head 15 and an inner face, which abuts with the extruded bundle of channels and an outer face, which abuts with the inner face of the intermediate head, respectively, which is in the intermediate position between said second head, or outer head and said third head, or inner head.

With the type of structure described, it is also possible to similarly assemble several bundles of extruded channels to form a single large structure and this is considering a configuration, such as that described above to unite the supply of the various channels forming a single extruded bundle; thus, it will also be possible to obtain blocks with significantly sized sections, formed by multiple extruded bundles.

Multiple extruded modules can also be assembled to define a single bundle with a single supply and a single drainage for each hot and cold flow, replicating a head, which is conceptually identical to the second head 14.

Figures 9 to 11 and 12 to 14 schematize continuous filling examples (also preferably obtainable by extrusion) and the positioning thereof when used for square channels (figures 9 to 11 - indicated with reference numeral 40) and rectangular channels (figures 12 to 14 - indicated with reference numeral 42).

Figures 9 and 12 show the illustrative sections of a group 50 and 50' of new hot and cold channels with fillings 40 (42) placed in the center of the channels, which only leave a thin thickness free for the fluid to pass in contact with the periphery of the channel.

In further detail, figures 10 and 13 show the position of the fillings and centering legs/ribs 40' (42') and how they clearly support and contrast the deformation, which the thin diaphragm forming the wall of the channel might undergo as a result of the pressure differences present in the channels between the two counterflows.

In particular, figures 10 and 11 show two complementary illustrative images/views of fillings for square channels, while figures 13 and 14 show those for fillings of rectangular channels.

In particular, the configurations in figures 11 and 14 show the fillings 40 and 42 provided with centering and support legs or ribs 41' and 42', respectively, which are externally protruding with respect to the periphery of the filling and notches 41'' and 42'' on said legs, which are functional for using heat exchangers involving the possibility of scale deposit (e.g. calcium salts); this is to allow a rebalancing of the flows in the single channel if the deposit of any scale is concentrated in one or more single points.

If a scale deposit were predictable, by means of a filling produced with plastic material loaded with salts having a composition similar to that expected to be deposited, it would be possible to favor the deposit of said scale/salts far from the heat exchange surface and therefore on the filling; in fact, considering the smaller amount of activation energy and therefore the smaller saline concentration required for the crystallization in the presence of an initiator, the saline deposit might be favored in zones of choice, i.e. on the inserts 40 and 42 and not on the exchange surface consisting of the polycarbonate (furthermore, the salts usually have very little grip on the polycarbonate) making the need less frequent, e.g. for acid washes to remove them.

Paradoxically, in the initial phase, the deposit of salts on the filling would initially have a positive effect on the global heat exchange coefficient, both reducing the thickness of the slit and slowing down the speed of the fluid in the hottest/coldest zone; in this case, it would be convenient to paint the outermost portions of the ribs/legs of the fillings to avoid scale deposits close to the diaphragms operating the heat exchanges.

In the presence of a substantially laminar motion, non- continuous fillings can be used, but provided with "L" - shaped flaps, which are spaced apart from one another, protruding from a central support "T" of the type exemplified in figures 7A, 7B, 8A and 8B; if the motion is sufficiently laminar, the effect shown, for example, in figure 8B may occur, in which the distance between the end of the flaps "L" of the filling "T" and the wall of the channel "K" determines the thickness of the flow, but then, in the intermediate zone between two flaps "L", the formation of a secondary circular flow is determined, which, by reducing the friction on the inner part of the main flow, results in a partial acceleration thereof and, therefore, in the thinning thereof, resulting in an improvement in the heat exchange coefficient. Such fillings are also particularly useful if the deposit of saline scale is possible, as there is much more space and, therefore, fewer cleaning operations may be required.

As can be seen from the description, the advantages of the configuration of the counterflow heat exchanger of the invention, presented below, are clear.

The insertion of inserts into the channels forming the extruded bundle (as described above) implies a drawback related to a greater load loss, (but which is acceptable and manageable by virtue of the laminar motion and the previous considerations of limited length of the channels and laminar motion), but implies an advantage linked to the fact of significantly improving the heat exchange coefficient per device cubic meter (heat capacity), which is determined by virtue of a great reduction in the thickness/distance determined between the hottest and coldest point of the section and the fact that the introduction of an insert in the presence of a laminar motion determines a slowing down of the speed of the fluid in the hottest/coldest zone and this results in an improved operating DT, about double that resulting from the average difference in temperature of the two counterflows.

The fillings of the channels have the effect of reducing the thickness of the passage of the fluids and thus the distance between the hottest point and the coldest point of the fluids in the two flows in the various sections of the heat exchanger and they thus determine a corresponding improvement in the global heat exchange coefficient per device cubic meter, i.e. of the heat capacity thereof; in fact, the amount of heat transferred is inversely proportionate to such distance.

The thermal delta (DT) value sought with a counterflow heat exchanger is that indicated by the DT, which is between the temperatures of the two inlet and outlet flows, in particular, when such DT is in the presence of a laminar motion, is however different from the DT, which contributes to determining the size of the heat exchanges, i.e. the maximum DT present in the sections; in fact, in the presence of a laminar motion, the speed profile of the fluids in a conduit is parabolic and this results in the speed of the fluids being maximum in the middle of the conduit, which position, in the absence of a filling, is also the position having the greatest temperature differential in the sections. Besides reducing the thickness of the passage, the presence of a filling also moves the maximum speed point in the thickness of the fluid at a smaller distance, about half that in which there is the greatest temperature differential in the section.

Therefore, the result of the presence of a filling is that of allowing a more advantageous ratio between the DT sought between the temperatures of the two inlet and outlet flows and the maximum DT present in the sections (with the same DT entering and exiting between the two flows, the DT contributing to determining the size of the heat exchanges in the presence of a filling advantageously reaches a value about double the DT measured of the inlet and outlet flows). The size of the reduction of the free passage thicknesses obtained by using fillings in the channels can reach very high values, which would normally not be attainable with the known extrusion techniques; distances of a few tenths of a millimeter between the hottest point and the coldest point of the fluids of the two flows are obtainable, resulting in huge advantages in terms of global heat exchange coefficient, as evidenced in Tab. A below shows the values measured for the different operating configurations of the heat exchanger of the invention and, more specifically, for the case of channels with a rectangular profile with filling and a chessboard-like arrangement, channels with a square profile, with filling and a chessboard-like arrangement and channels with a rectangular profile, without filling and with a chessboard-like arrangement. By means of the fillings, the highly reduced distances of the passages for the fluid are made compatible with a correct and efficient supply and drainage.

With the same structure of the bundle of extruded section bars and supply and drainage heads, it is possible to obtain several different heat exchanger variants simply by changing the filling profile and this represents a significant financial and operating advantage since the dies to produce the fillings are a much smaller investment than that for producing the extruded bundles.

The fillings can be produced with materials having a different composition to those forming the extruded bundle of channels.

One particular case is, for example, manufacturing them with loaded plastic, as described, with various additives (e.g. calcium salts) for favoring the preferential depositing of scale thereon (organic and inorganic fouling) and instead preserving the efficiency of the diaphragms of the channels in the heat exchanges; in the case in question, the deposit of fouling doesn't compromise the heat efficiency (which, instead, initially increases as the free thicknesses are reduced) and greater time intervals are allowed for cleaning/descaling operations; in these cases, the centering legs of the fillings are usefully coated/treated to avoid scale deposits close to the diaphragms operating the heat exchanges.

As described (with reference to figures 7A, 7B, 8A and 8B) the fillings can take varying shapes and, in the presence of laminar motion, the narrowing of the fluid passage may also be discontinuous without compromising the distance between the hottest point and the coldest point of the fluids of the two flows, but also favoring a further reduction in the thickness between the hottest point and the coldest point of the fluids of the two flows, and therefore, improving the efficiency; these configurations also allow a greater capacity for accumulating scale or fouling and thus a further extension of time intervals for the cleaning/descaling operations .

The presence of the descriptions of centering legs/ribs in the fillings also forms a mechanical support for the diaphragm, which separates the two counterflow fluids, which must fall as little as possible although there are pressure differentials, which vary along the path thereof; the presence of fillings thus allows using thinner thicknesses for such diaphragms and therefore reducing the heat resistance component due thereto in the global heat exchange coefficient .

Furthermore, in the angular position of the filling (see figures 11 and 14) the centering ribs/legs determine a slowing down of the flow in the corners where there would otherwise be a passage for the fluids having a greater width and therefore with a relatively greater flow than that, which would be had in the other parts; considering the fact that from the point of view of the heat exchanges, the angular zone is a particularly disadvantaged zone, slowing down the flow in such position contributes to improving the overall efficiency of the exchanger.

Moreover, there is a further advantage, which combines the use of extruded channels and filling profiles and that is to selectively vary the length of the paths, obtaining a valuable project flexibility and execution.

Although the invention has been described above with particular reference to an embodiment thereof, given by way of non-limiting example, several modifications and variations will be apparent to those skilled in the art in light of the above description. Therefore, the present invention aims to encompass all modifications and variants falling within the scope of the following claims.