Low-enthalpy heat exchanger

Abstract

Low-enthalpy heat exchanger, comprising a plastic coil tube (1) housed in a channel machined into a structure of regular cells, and a bottom skin (7) and a top skin (8) forming a sandwich-like configuration. The exchanger includes a binder mass (3) poured into the channel, enveloping the tube (1) and bonding it to the structure of regular cells. The tube (1) has an external diameter D of between 6 and 13 mm and a maximum thickness of 1.5 mm, and the structure comprises open regular cells (5) next to the coil tube (1), forming fins (6) adjacent to said tube (1). The machined channel has a depth equal to at least the external diameter D of the tube (1) and a width of D, and the binder mass (3) has a thermal conductivity lower than 2.2 W / mK and a fluidity higher than 150 mm according to European Standard EN 445 test.

Description

[0001] DESCRIPTION

[0002] Low enthalpy heat exchanger

[0003] Field of invention

[0004] The present invention belongs to the technical field of low-enthalpy thermal systems and high-performance energy solutions. Specifically, it relates to heat exchangers designed for applications operating under low-enthalpy conditions, such as heating and cooling buildings, data centers, electronic systems, and other applications.

[0005] Background of the invention

[0006] Currently, various systems exist for capturing and utilizing thermal energy for heating and cooling applications in buildings and other systems. In order to reduce negative environmental impacts (e.g., CO2 emissions), measures and guidelines are being established to reduce energy consumption to near zero.

[0007] Specifically, in the construction sector, one of the approaches taken has been the application of high levels of insulation to the entire building envelope, simultaneously eliminating thermal bridges and optimizing solar and internal heat gains, and also implementing highly efficient mechanical ventilation with heat recovery. These are known as passive buildings.

[0008] Furthermore, active systems are being developed, such as state-of-the-art solar thermal and photovoltaic collectors and sensible and latent thermal energy storage, which can meet energy demand even under the most adverse weather conditions. In these cases, the thermal demand must be met with renewable resources generated on or near the building itself.

[0009] New developments in heat transfer, particularly low-enthalpy technologies, allow for the highly efficient capture of ambient thermal energy. This is achieved by increasing the efficiency of heat pumps and transforming any low-enthalpy resource into a valuable energy source. Furthermore, any structural mass or liquid reservoir can be transformed into efficient sensible or latent thermal storage systems that operate with small temperature differentials. This simplifies the loading of these systems and minimizes heat loss, as the temperature difference with the environment is kept to a minimum.

[0010] EP3453985B1, the holder of which is the applicant for this application, shows a bioclimatic building with at least one solar energy collection system and a thermal distribution and emission system consisting of at least one tubular coil for a heat transfer fluid within a concrete layer composed of a mixture of cementitious binders and aggregates containing a silicon carbide composition with a grain size greater than 1 millimeter in at least 30% of the total volume of concrete, and where the total volume of the composition including silicon carbide is at least 45% of the total volume of concrete. The result is a radiative model with low enthalpy and high efficiency in the capture, emission, and distribution of heat, providing a self-sufficient and energy-positive building virtually every day of the year.However, these buildings present several drawbacks, such as the high cost of the systems used (due to the high cost of SiC and the complexity of its installation) and the high CO2 emissions in the materials used (embedded CO2), which hinder the widespread deployment of this solution and its large-scale use, thus preventing its potential contribution to the decarbonization of buildings and cities worldwide. Furthermore, its high weight per square meter makes it difficult to use in building renovations to make them energy positive.

[0011] Furthermore, a major drawback of current heat exchange systems using metal tube coils is their limited durability outdoors, as they are not resistant to freezing. Additionally, the small contact surface between the tubes and fins creates a bottleneck that limits the efficiency of heat transfer between the tube and the surrounding air. These fins have a limited contact surface because welding and stamping the metal are expensive. Their manufacturing process makes them costly, which limits their sizing and necessitates large temperature differentials between the heat transfer fluid and the air, thus preventing low enthalpy. This problem could be solved by using cast sections to form the duct and integrated fins to achieve the highest possible radial flow, but this is a complex and very expensive solution with limited outdoor applications.The system described in PCT / ES2022 / 070321 overcomes the drawbacks of the previous system by using a heat exchanger with at least one coiled tube for a heat transfer fluid housed within a periodic cell structure. The walls of this structure have very high thermal conductivity, and the enclosure elements form a sandwich-like configuration. The coiled tube is made of low-cost, high-resilience thermoformable plastic, which improves resilience by absorbing, through elastic deformation, the expansion caused by the freezing of the heat transfer fluid. This heat exchanger also has a binding mass that surrounds the coiled tube and is in contact with the periodic cells, containing aggregates of high thermal conductivity.This binding agent creates a uniformly distributed radial heat flow, enabling efficient heat exchange across the entire perimeter surface of the coiled tube, resulting in a completely uniform temperature throughout its mass. Specifically, the binding agent can be cement, resin, or a combination of both. Furthermore, the aggregates included in the binding agent can be silicon carbide (SiC), metals, graphite, graphene, or combinations thereof. The high thermal conductivity of the binding agent counteracts the low thermal conductivity of the plastic used in the coiled tube wall, thus generating a uniform radial flow. This allows the heat exchanger to operate with small temperature differentials and low enthalpy, despite the plastic being a poor thermal conductor.

[0012] Figure 1 schematically shows a cross-sectional plan view of the heat exchanger of PCT / ES2022 / 070321, illustrating its main elements and features. It clearly shows that the cells neither touch nor guide the tube, merely providing a continuous channel that is easily filled with any binding agent.

[0013] Figure 2 schematically shows a side-sectional view of the same heat exchanger from PCT / ES2022 / 070321. This section is essentially uniform throughout the channel formed within the periodic cell structure to house the tube. The bonding mass surrounds the tube without restriction, but the periodic cells result in a reduced heat exchange surface area and long heat flow lines, leading to increased heat dissipation and hindering efficient heat transfer.

[0014] Various approaches related to low-enthalpy management focus on optimizing heat transfer efficiency (ΔQ / ΔT) by maximizing heat conduction through increased heat exchange surface area (ΔA) and ensuring a high heat exchange coefficient (ΔU). This has been achieved using a binding mixture composed of high thermal conductivity aggregates. This approach significantly reduces the temperature differential (ΔT) between the two media compared to traditional heat exchangers. Although traditional heat exchangers also utilize high thermal conductivity materials to achieve a high heat exchange coefficient (ΔU), the high cost of these materials limits the total heat exchange surface area (ΔA). Consequently, traditional systems are forced to operate with larger temperature differentials to maintain performance.The low-enthalpy solutions described above have focused on using large surfaces with high thermal conductivity for heat exchange, employing a binder mass with high thermal conductivity, as detailed in the aforementioned documents. The thermal conductivity of a heterogeneous binder mass is determined by the conductivity of its constituent elements. When a mass is composed of a large proportion of high-conductivity particles, the overall thermal conductivity will be relatively high. This results from the combined effect of the properties and distribution of the individual particles within the binder mass.As defined in EP 3453985, it is also important to have a high proportion of large conductive particles in the binding material to maximize total thermal conduction over internal thermal convection and radiation occurring at each particle boundary. Heat exchangers of the type described in PCT / ES2022 / 070321, which employ a plastic coiled tube and periodic cells with a highly conductive binding mass surrounding both, have proven to be optimal low-enthalpy heat exchangers. These heat exchangers can be manufactured on an industrial scale to provide low-enthalpy solutions for a wide range of potential applications.

[0015] So far, these exceptional results are achieved because the heat transfer rate "U" is high due to the high thermal conductivity of the binding mass between the plate containing the periodic cells and the plastic tube.

[0016] Having demonstrated through real-world projects that this low-enthalpy concept and technology can dramatically improve the efficiency of thermal processes and facilitate the decarbonization of buildings, it is now essential to further reduce its economic cost and embodied CO2 emissions while maintaining its current efficiency. This will enable a massive expansion of the technology and eliminate the initial investment barrier that has limited its adoption. High-conductivity binders are composed of special synthetic metals or minerals, which not only have a high economic cost but also contain a significant amount of embodied CO2.

[0017] Therefore, it is desirable to have a heat exchange system based on an efficient low-enthalpy heat exchange that avoids these drawbacks of high cost and environmental footprint of previous state-of-the-art systems.

[0018] Description of the invention

[0019] The present invention solves existing problems in the prior art by means of a low-enthalpy heat exchanger, equipped with at least one plastic coil tube for the internal circulation of a heat transfer fluid. This coil tube is housed in a machined channel within a structure of periodic cells for internal air circulation. These periodic cells are oriented perpendicular to the coil tube, the walls of the periodic cells have a thermal conductivity greater than 100 W / mK, and the cross-section of the periodic cells is circumscribed within a circle of diameter B. The heat exchanger has closing means comprising a lower skin or bottom plate and an upper skin or top plate, forming a sandwich-type configuration that houses the periodic cell structure, which in turn houses the coil tube.Additionally, the heat exchanger has a binding mass that surrounds the coil tube, coming into contact with said coil tube and joining it to the periodic cell structure, the binding mass having a low thermal conductivity, i.e., less than 2.2 W / mK.

[0020] Therefore, the present invention provides a new range of low enthalpy heat exchangers capable of transferring heat with a result similar to that obtained so far (with a transfer rate of at least 13 W / m³). 2K), but in this case using a specific low thermal conductivity binder (with a coefficient below 2.2 W / mK), instead of the high thermal conductivity binders described in EP 3453985 and PCT / ES2022 / 070321. The result is a more affordable, low-enthalpy heat exchanger with reduced embodied CO2. The subsequent widespread use of these efficient, low-cost heat exchangers will contribute to the elimination of fossil fuels in building heating and cooling, as well as in other applications mentioned above.These low-enthalpy heat exchangers will further improve heat exchange performance, as it will be economically viable to deploy a larger heat exchange surface, thereby reducing temperature differentials and consequently improving the efficiency of heat pumps within the same budget constraints.

[0021] However, since the binder now has low thermal conductivity, the current heat transfer rate between the tube and the sandwich plate containing the periodic cells would be reduced. This line of reasoning appears inherently problematic unless a set of measures and a specific configuration can be identified to compensate for the loss of thermal conductivity in the binder.

[0022] To provide the same rate of heat transfer under low enthalpy conditions, with a more sustainable binding mass, i.e., one having low thermal conductivity, the following characteristics must be present in the heat exchanger of the invention:

[0023] As stated above, a coil tube made of plastic should be used because it remains essential to provide the required strength needed in low enthalpy applications, protecting the tube from failure due to corrosion and elastically absorbing internal solid expansion in case the heat transfer fluid freezes.

[0024] Furthermore, the dimensional stability of the plastic tube is also essential to prevent the formation of stresses that cause the failure of the binding mass that thermally bonds the tube and the periodic cells.

[0025] Furthermore, the coiled tube has an outer diameter of between 6 and 13 mm and a maximum thickness of 1.5 mm. The 13 mm value is key to ensuring turbulent flow inside the tube under low-enthalpy heat transfer conditions, which occur primarily between -15°C (minimum for heat absorption) and 30°C (maximum for heat release). This ensures that the flow is noise-free at heat transfer fluid velocities below 0.5 m / s. Turbulent flow must be guaranteed, as it provides heat transfer factors exceeding 2000 W / m². 2 K, instead of heat transfer factors below 500 W / m 2K, which provides laminar flow. Traditional heating systems and solar collectors easily achieve turbulent flow with larger diameters at these low fluid velocities, for minimal noise generation, since their heat transfer fluid typically operates at temperatures above 50°C. The outer diameter D must be greater than 6 mm because otherwise there would be too much pressure drop, the flow would be reduced, and heat transfer would be negatively affected. Therefore, these parameters maximize convective heat transfer inside the coil tube.

[0026] Once the heat transfer by convection has been maximized, it is essential to eliminate any restrictive factors that limit the heat transfer between the coil tube and the emitting surface of the skin or plate through the periodic cells, in order to maintain the heat transfer potential of the plate or skin to the surrounding environment.

[0027] According to the present invention, the periodic cell structure includes, in a differentiated manner, closed periodic cells and open periodic cells. The open periodic cells result from the periodic cell structure being machined to accommodate the coiled tube. Thus, these open periodic cells are located adjacent to the coiled tube once it is inserted, and the walls of these open periodic cells form fins adjacent to the coiled tube.

[0028] The main body of this low-enthalpy heat exchanger is a sandwich structure formed by the periodic cell structure and two metal sheets, which are the lower and upper plates or skins. The total thickness of this main body results from the entire sandwich structure, where the periodic cell structure described above has a thickness at least equal to the outer diameter D of the coil tube (to accommodate it properly), and the two metal sheets have a maximum thickness of 1.5 mm each. This could result in a total thickness of at least D+3 mm.

[0029] This sandwich, formed by the two plates enclosing the periodic cell structure, is machined from one end to the other to create a channel that will house the serpentine tube. The machining is performed with a special tool that allows the top skin or upper plate to be machined to a specific width and the periodic cell structure to a different one. The top plate or upper skin is machined to a width that allows the binding agent to be poured into all the machined periodic cells, but no more, and is less than three times the diameter B when the periodic cell structure is machined symmetrically in its center. The periodic cell structure is machined to a depth that allows the channel to house the serpentine tube, with a depth at least equal to the outer diameter D of the serpentine tube, and a width of D.

[0030] Therefore, unlike the heat exchanger of PCT / ES2022 / 070321, in the heat exchanger of the present invention, the coiled tube is guided without any gap by the tips of the machined faces, which act as fins, of the open periodic cells. This improves the assembly that guides and secures the coiled tube in the machined channel. This configuration provides the technical effect of maximizing the heat exchange ratio during operation because it increases the heat transfer surface area and reduces the conduction paths between the coiled tube and the open machined periodic cells. Thus, the shortest conduction path in the binder mass is reduced to approximately less than half the diameter B when the periodic cell structure is machined symmetrically at its center.

[0031] According to a preferred embodiment, the diameter B of the circumference enclosing the cross-section of the periodic cells is between 6 and 10 mm. This is because, once convective heat transfer within the tube has been maximized, it is essential to eliminate any restrictive factors that limit heat transfer between the tube and the emitting surface of the plate in order to maintain the plate's heat transfer potential to the surrounding environment. Therefore, the periodic cells must be enclosed within a circumference of diameter B that provides a sufficiently high fin density to the coiled tube, increasing the surface area and resulting in a higher ratio between the "exchange surface area" and the "heat transfer fluid volume." This diameter B must be between 6 and 10 mm.It must be less than 10 mm to shorten the flow paths between the outer surface of the coiled tube and the fins provided by the periodic cell and to increase the heat exchange surface area. It must be greater than 6 mm to allow filling with the binder mass according to some particular embodiments of the invention. Whereas the shortest flow path in the binder mass is reduced to approximately less than half the diameter B when the periodic cell structure is machined symmetrically at its center, as indicated above, in this embodiment the longest flow paths would be between 3 and 5 mm.

[0032] Furthermore, in PCT / ES2022 / 070321, the channel depth extends to the bottom plate. However, in this invention, the machining depth must be at least the outer diameter D of the serpentine tube, and considering that, as explained above, the main body has a total thickness resulting from the entire sandwich (periodic cell structure plus the thickness of the bottom and top skins). According to a particular embodiment of the invention, the machined channel inside the periodic cell structure does not reach the bottom skin, such that open periodic cells remain adjacent to the bottom skin, the walls of these open periodic cells forming fins adjacent to the serpentine tube below it.Therefore, these small fins remaining at the bottom not only provide a larger heat exchange surface and shorter conduction lines at the bottom of the heat exchanger, improving the overall heat exchange ratio, but also ensure that the binder is firmly bonded to the bottom skin via these open periodic cell fins, thus ensuring the binder's resilience and durability, as well as its thermal performance. In the heat exchanger of PCT / ES2022 / 070321, where machining extends to the bottom skin, even though the high-conductivity binder fills the space under the coiled tube, an air layer can easily form with the bottom skin during manufacturing, transport, installation, or over time, reducing heat transfer efficiency.To achieve these residual fins below the serpentine tube, the machining tool can have a tapered or curved end.

[0033] Once all the geometric characteristics and the configuration of the serpentine tube and the mechanized structure of periodic cells of the invention have been defined, the serpentine tube must be joined to the periodic cells by pouring the binding mass.

[0034] According to the invention, the bonding compound has a flowability greater than 150 mm as determined by the European standard EN 445. This allows it to completely envelop the coiled tube, creating a continuous bond with the open periodic cells and the bottom plate, without leaving gaps or air bubbles. This high flowability of the bonding compound provides a technical advantage over prior art heat exchanger bonding compounds, as explained below:

[0035] When a high-conductivity binder, such as those described in EP 3453985 and PCT / ES2022 / 070321, is poured within the configuration and geometric constraints of the present invention, it has been observed that the binder does not completely fill the 360° around the coiled tube, leaving gaps and air bubbles between the tube, the periodic cells, and the sandwich plates. When a high-conductivity binder is used with the specific configuration and geometric constraints of the present invention, as described above—that is, with an outer diameter of the coiled tube between 6 and 13 mm, and a binder that envelops the coiled tube in channels with a width D and a depth at least equal to the outer diameter of the coiled tube—the efficiency is observed to drop to less than 8 W / m². 2K. It was expected that the performance would improve, or at least remain the same, because the heat exchange surface area had increased and the heat flow lines had shortened. However, the performance actually decreased because the bonding mass only adheres to the top of the tube, failing to fully connect the tube to the periodic cells, as the bonding mass does not flow sufficiently to surround the entire tube.

[0036] This is because the heat exchanger of PCT / ES2022 / 070321 is characterized by having a considerable flow surface area that allows the binder mass to flow inside between the coiled tube and the machined periodic cells. This flow surface area can be up to x nB 2 where N is the number of machined cells and B is the diameter of the circumference that circumscribes the periodic cell.

[0037] However, in the present invention the flow surface has been limited to the free machined surface of each machined cell, making the flow surface

[0038] TIB less than —. This means that the aggregates forming the binder mass do not have enough space to flow when the binder mass is poured, causing enormous internal shear in the flowing mass that prevents it from filling the channel. Furthermore, the significant increase in fin surface area causes even greater shear against these fins, reducing the penetration of the binder mass, which would create voids and air bubbles that would decrease the system's heat transfer.

[0039] Experimental results have revealed that in a configuration that includes a plastic tube with a conductivity of less than 0.5 W / mK and a structure of periodic cells of high conductivity bonded to the serpentine tube with a binding mass, it is even more important to provide a complete bond rather than using a high conductivity binding mass.

[0040] Once high heat transfer develops in the coiled tube as a result of turbulent flow, the flow lines must be radial. Otherwise, the heat transfer potential developed inside the tube is lost, forcing the flow lines to inefficiently travel around the entire perimeter of the tube's low thermal conductivity until the bonding mass allows for dissipation. If, instead of using a plastic tube, a high thermal conductivity metal coiled tube were used, the unbonded tube's thickness perimeter would be able to transfer the full heat potential of the turbulent flow inside, even when the high-conductivity bonding mass only covers 50% of the tube's 360° outer circumference.

[0041] Once the conductivity flow lines have been shortened according to the geometric definition and configuration of the present invention, as indicated above, the only way to maintain a high heat transfer rate, above the value of 13 W / m 2 K, is to provide a complete bond between the plastic coil tube and the high-conductivity periodic cell structure in the sandwich-type structure, since the turbulent flow heat exchange is dissipated radially along the 360° of the tube surface, potentially taking the shortest path to the periodic cell sandwich. In this case, a much more important characteristic than the thermal conductivity of the binder mass has been found to be its high fluidity, exceeding 150 mm during pouring and casting (measured by the flow test described in the European standard EN 445).

[0042] It has been observed that high conductivity binders, which have low fluidity, higher embedded CO2 and are more expensive, fail to adequately fill the gap between the coil tube and the open periodic cells according to the configuration and geometric constraints of the present invention, as shown above, leaving gaps of up to 50% of the radial surface of the tube, which prevents it from developing its full heat transfer potential towards the periodic cells.

[0043] However, it has been shown that a standard mortar-type binder with a heat transfer coefficient of 2.2 W / mK (composed mainly of natural substances such as silica or alumina) is even more efficient than a high-conductivity binder if its fluidity exceeds 150 mm according to the European standard EN 445 test. This ensures that the voids are completely filled and, therefore, there are no air bubbles between the tube and the periodic cell structure. The high fluidity reduces internal shear within the binder and shear against the fins of the periodic cells. This allows for achieving and even improving heat transfer efficiency once the binder solidifies, reducing costs and embodied CO2, since these standard conductivity but high-fluidity binders can be obtained without using metallic or synthetic materials.

[0044] Preferably, the binding mass can be silica, alumina, cement (including traditional cements and geopolymers), self-leveling mortar, self-compacting concrete, or a combination thereof.

[0045] Furthermore, and according to particular embodiments of the invention, the binding mass may include different additives such as modified polymers, fiberglass, chemical bonding agents or a combination thereof, to increase the adhesion and anchoring capacity of the binding mass.

[0046] With respect to different particular embodiments of the invention, the periodic cells include holes in their walls. These transverse holes connect certain periodic cells with other adjacent periodic cells, allowing the binding mass to flow from one to another upon injection.

[0047] Specifically, these holes have a diameter of less than 10 mm. This small hole size ensures efficient flow of the binder mass with a fluidity greater than 150 mm, while preserving the structural integrity of the periodic cells, avoiding large openings that could weaken the cell walls and compromise the overall stability of the sandwich structure.

[0048] According to one particular embodiment, the lower and upper skins are plates with high thermal conductivity, i.e., a thermal conductivity greater than 25 W / mK. According to an alternative embodiment of the invention, one of the lower or upper skins may be replaced by a plate with low thermal conductivity, i.e., a thermal conductivity less than 1 W / mK, to optimize heat transfer to the opposite plate of the heat exchanger. This plate with low thermal conductivity has high flexural strength, configured to ensure the stability and durability of the heat exchanger.

[0049] Any version of the low-enthalpy heat exchanger described above can be used as a cooling cover or housing for electrical and electronic devices requiring cooling. This cooling cover or housing could provide both convective and radiative cooling to the device, but this transfer can be further enhanced by using thermal bridges between the most powerful emitting parts of the electrical or electronic device requiring heat dissipation and the cooling cover provided by the low-enthalpy heat exchanger.

[0050] Therefore, according to this particular embodiment as a cooling cover, the low-enthalpy heat exchanger of the invention may have thermal bridges, which include a first end located on the outer surface of the lower skin of the enclosure means and a second end configured to be located on a heat-emitting element that needs greater heat dissipation because it is the main heat source or requires precise temperature control.

[0051] These thermal bridges can be solid or hollow, and can be rigid or flexible, or an assembly of different blocks in contact made of highly conductive material whose cross-section mirrors the emitting surface of the part of the electrical device requiring additional cooling. This creates a bridge between the emitting part and the cooling cap, transferring the heat released by the emitting part to the cooling cap via thermal conduction. The free surfaces not in contact with either the emitting part or the cooling cap can be insulated to prevent heat loss to the surrounding air.

[0052] Hollow thermal bridges contain a dielectric fluid and may include a turbine to enhance heat transfer by creating an internal flow. In these hollow thermal bridges, the first end, located on the outer surface of the lower skin of the low-enthalpy heat exchanger acting as a cooling device, and the second end, positioned on the emitter element, can be metal blocks joined together with a hollow cavity between them. These metal blocks may have fins to increase heat transfer with the dielectric fluid. The metal block positioned on the emitter element has a cross-section similar to the emitter portion of the electrical device, and the first end, located on the outer surface of the heat exchanger, may have a wider metal contact piece.The emitting part of the electrical device heats the second end of the thermal bridge, which heats the dielectric fluid inside. This, in turn, enhances heat transfer through the movement of the fluid via natural convection towards the first end in direct contact with the lower skin of the heat exchanger. This natural convection movement can also be forced using an internal turbine, as previously described.

[0053] Preferably, the hollow thermal bridge filled with the dielectric fluid may include an elastic membrane that seals the dielectric fluid to prevent leakage, provided that the ends are in contact with the emitting part and the cooling cap, and allowing some relative movement to permit removal of the heat exchanger, as long as the contact of all elements has sufficient pressure to provide good thermal contact. This hollow embodiment may also contain some air, thus allowing displacement of the blocks that pressurize the dielectric fluid.

[0054] Brief description of the drawings

[0055] Next, in order to facilitate the understanding of the present invention, and by way of illustrative but not limiting example, an embodiment thereof will be described with reference to a series of figures.

[0056] Figure 1 shows a schematic plan view of a heat exchanger according to the prior art PCT / ES2022 / 070321, illustrating its main components and features. Figure 2 shows a schematic side view of the heat exchanger in Figure 1.

[0057] Figure 3 shows a view of a periodic cell structure of the present invention machined to accommodate the serpentine tube. This configuration includes closed periodic cells and open periodic cells that provide fins. The figure also highlights the relevant dimensions and arrangement, including the minimum required channel depth and the spacing between the periodic cells before adding the binder mass.

[0058] Figure 4, similar to Figure 3, illustrates the coiled tube inserted in place. The figure highlights the narrow channels between the coiled tube and the machined fins of the periodic cells, before the binding agent is poured. This configuration ensures close contact between the coiled tube and the fins, optimizing heat transfer efficiency once the binding agent is applied.

[0059] Figure 5, similar to Figures 3 and 4, shows the configuration immediately after pouring the binding agent. The binding agent completely envelops the serpentine tube and fills the narrow channels between the tube and the fins of the periodic cells, ensuring a complete bond between the serpentine tube and the surrounding structure, without leaving gaps or air bubbles.

[0060] Figure 6 schematically shows a plan view of a particular embodiment of the heat exchanger of the present invention. It illustrates the primary components, including the coiled tube and the periodic cells, showing how the coiled tube is housed within the periodic cell structure to facilitate efficient heat transfer.

[0061] Figure 7 schematically shows the side section view B indicated in Figure 6, showing its main elements and characteristics.

[0062] Figure 8 schematically shows the side section view C indicated in Figure 6, showing its main elements and characteristics.

[0063] Figure 9 schematically shows the side section view D indicated in Figure 6, showing its main elements and characteristics.

[0064] Figure 10 schematically shows the plan view of a particular embodiment of the heat exchanger of the present invention showing holes in the walls of the periodic cells.

[0065] Figure 11 schematically shows a side section of a particular embodiment of the heat exchanger of the invention that includes a solid thermal bridge adapted to a powerful emitting part of an electrical device.

[0066] Figure 12 schematically shows a side section of a particular embodiment of the heat exchanger of the invention that includes a hollow thermal bridge adapted to a powerful emitting part of an electrical device.

[0067] These figures refer to a set of elements which are:

[0068] 1. serpentine tube

[0069] 2. heat transfer fluid

[0070] 3. binding mass

[0071] 4. closed periodic cells

[0072] 5. Open periodic cells

[0073] 6. Open periodic cell fins

[0074] 7. lower plate or skin of the enclosure means

[0075] 8. top plate or skin of the enclosure means

[0076] 9. holes in periodic cells

[0077] 10. Thermal bridges

[0078] 11. emitting element

[0079] 12. electrical appliance

[0080] 13. dielectric fluid

[0081] 14. turbine

[0082] 15. Metal blocks of thermal bridges

[0083] 16. elastic sealing element

[0084] D. outer diameter of the coil tube

[0085] B. Diameter of the circumference that circumscribes the cross-section of the periodic cells. Detailed description of the invention

[0086] The object of the present invention is a low enthalpy heat exchanger.

[0087] As shown in the figures, the heat exchanger has at least one coiled tube 1, made of plastic, for the internal circulation of a heat transfer fluid 2. The coiled tube 1 is housed in a machined channel inside a periodic cell structure for internal air circulation. These periodic cells are oriented perpendicular to the coiled tube 1, the walls of the periodic cells have a thermal conductivity greater than 100 W / mK, and the cross-section of the periodic cells is circumscribed within a circle of diameter B. The heat exchanger has enclosure means that include a lower skin 7 and an upper skin 8, forming a sandwich-type configuration that houses the periodic cell structure, which in turn houses the coiled tube 1.Furthermore, the heat exchanger has a binding mass 3, which envelops the coil tube 1, bringing it into contact with said coil tube 1 and joining it to the periodic cell structure, the binding mass 3 having a low thermal conductivity, i.e., the thermal conductivity is less than 2.2 W / mK.

[0088] As shown in Figure 3, the coil tube 1 has an outer diameter D between 6 and 13 mm, and a maximum thickness of 1.5 mm. In accordance with this geometric constraint, turbulent flow is ensured inside the coil tube 1, which provides high heat transfer factors and reduces pressure drop, as previously mentioned.

[0089] Furthermore, the periodic cell structure includes, in a differentiated manner, closed periodic cells 4 and open periodic cells 5, which are the result of the periodic cell structure having been machined to introduce the serpentine tube 1. As shown in Figure 4, these open periodic cells 5 are located next to the serpentine tube 12 once it has been introduced, and the walls of said open periodic cells 5 provide fins 6 adjacent to said serpentine tube 1.

[0090] Figures 3, 4, and 5 schematically illustrate different stages in the manufacture of a low-enthalpy heat exchanger according to the present invention. Figure 3 shows a periodic cell structure 4, 5 that has been machined to provide a channel for the insertion of the coil tube 1. This machining of the periodic cell structure 4, 5 creates open periodic cells 5 that provide fins 6 to guide and bring into contact the bonding mass 3 and the coil tube 1. Figure 4 shows the periodic cell structure 4, 5 after the coil tube 1 has been inserted into the machined channel. Figure 5 shows the final configuration of the heat exchanger after the bonding mass 3 has been poured and solidified, providing an integral structure that completely surrounds the coil tube 1 without gaps or bubbles, fully bonding the coil tube 1 to the open periodic cells 5 and the lower skin 7.

[0091] As previously stated, the main body of this low-enthalpy heat exchanger comprises the sandwich structure formed by the periodic cell structure 4.5 along with two metal sheets, which are the lower 7 and upper s plates or skins. Thus, this main body has a total thickness resulting from the entire sandwich structure, with the periodic cell structure 4.5 having a thickness that is at least the outer diameter D of the coil tube, and the two metal sheets having a maximum thickness of 1.5 mm each. This makes the total thickness of the main body at least D+3 mm.

[0092] This sandwich, formed by the two plates 7, 8 which contain the periodic cell structure 4, 5 between them, is machined from one end to the other to form a channel to house the serpentine tube 1. The machining is performed with a special tool that allows the upper skin 8, or top plate, to be machined to a specific width, while the periodic cell structure 4 is machined to a different width. The upper plate or top skin 8 is machined to a width that allows the binding agent 3 to be poured into all the machined periodic cells 5, but no more; this width is less than three times the diameter B when the periodic cell structure is machined symmetrically at its center.And the closed periodic cell structure 4 is machined to obtain open periodic cells 5 with a depth that allows making the channel to accommodate the serpentine tube 1, so that it has a depth of at least the outside diameter D of the serpentine tube, and a width of D.

[0093] Therefore, in the heat exchanger of the present invention, the coiled tube 1 will be guided without any gap by the tips of the machined faces of the open periodic cells 5, which act as fins 6. This will improve the assembly, guidance, and securing of the coiled tube 1 in the machined channel. As previously stated, this configuration provides the technical effect of maximizing the heat exchange ratio during operation, as it increases the heat transfer surface area and reduces the conduction paths between the coiled tube 1 and the machined open periodic cells 5. Thus, the shortest conduction path in the binder mass is reduced to approximately less than half the diameter B when the periodic cell structure is machined symmetrically at its center.

[0094] Preferably, the diameter B of the circumference enclosing the cross-section of the periodic cells 4, 5 is between 6 and 10 mm. This will maximize convective heat transfer within the tube. This diameter B must be less than 10 mm to shorten the flow paths between the outer surface of the coil tube 1 and the fins 6 provided by the open periodic cells 5, thereby increasing the heat exchange surface area. It must be greater than 6 mm to allow filling with the binder mass 3 according to certain embodiments of the invention. Since the shortest flow path in the binder mass 3 is reduced to approximately less than half the diameter B when the periodic cell structure is symmetrically machined at its center, as described above, in this embodiment the longest flow paths would be between 3 and 5 mm.

[0095] According to a particular embodiment of the invention, the machined channel inside the periodic cell structure does not reach the lower skin 7, so that the open periodic cells 5 remain adjacent to the lower skin 7, the walls of said open periodic cells 5 providing fins 6 adjacent to the coil tube 1 below said coil tube 1. Therefore, these fins remaining at the bottom provide not only a wider heat exchange surface and shorter conduction lines at the bottom of the heat exchanger, which improves the overall heat exchange ratio, but also ensure that the binding mass 3 is firmly fixed to the lower skin 7 through these fins 6 of the open periodic cells 5, thereby ensuring the resilience of its thermal performance.

[0096] Figure 4 shows the narrow channels provided between the coiled tube 1 and the fins 6 provided by the machined periodic cells 6 before the binding mass 3 is poured. According to the present invention, Figure 6 shows a plan view of a particular embodiment of the heat exchanger, showing its main elements. Figure 6 clearly shows how the coiled tube 1 is guided by the fins 6 provided by the open periodic cells 5, which provides a much larger heat exchange surface, but also creates narrow, open individual cells for the fluid, with limited space for the binding mass 3.

[0097] Figure 7 shows section B of the heat exchanger in Figure 6, where there is more space between the coil tube 1 and the open periodic cells 5 to allow the flow of the binder mass 3 to fill the entire space. At the bottom, below the coil tube 1, there is a fin 6 formed by an open periodic cell 5, which is bonded by the binder mass 3, providing anchorage for the binder mass 3 to the bottom plate or skin 7.

[0098] Figure 8 shows section C of the heat exchanger in Figure 6, the area where the fins 6 provided by the open periodic cells 5 contact and guide the coil tube 1. These fins 6 are encased in the bonding mass 3 that penetrates from the lateral space provided in section B of the heat exchanger. Unlike section B, the lower area under the coil tube 1 is free of fins 6, allowing the bonding mass 3 to encase the lower fins 6 that appear in section B or section C.

[0099] Figure 9 shows section D of Figure 6 of the heat exchanger, a middle zone between sections B and C, in which the space between the coil tube 1 and the fins 6 provided by the lateral open periodic cells 5 narrows and two fins 6 are placed at the bottom below the coil tube 1 provided by the open periodic cells 5 to provide full anchorage to the bottom plate or skin 7. This small volume is filled by wrapping the machined fins 6 with the binding mass 3 using the side and bottom channels provided in sections B and D shown in the previous figures.

[0100] These three sections B, C, and D show that all the volumes between the coil tube 3 and the open periodic cells 5 and the lower skin 7 are properly filled by the bonding mass 3, shortening the heat transfer paths and ensuring efficient heat transfer. Furthermore, the bonding mass 3 has a flowability greater than 150 mm according to the European standard EN 445 test, providing an integral structure that completely surrounds the coil tube 1 without gaps or bubbles, fully bonding the coil tube 1 to the open periodic cells 5 and the lower skin 7, as explained above.

[0101] Preferably, the binding mass 3 can be made of silica, alumina, cement (including traditional cements and geopolymers), self-leveling mortar, self-compacting concrete, or a combination thereof.

[0102] Furthermore, and according to particular embodiments of the invention, the binding mass 3 may include different additives such as modified polymers, fiberglass, chemical bonding agents or a combination thereof, to increase the adhesion and anchoring capacity of the binding mass 3.

[0103] According to another preferred embodiment, the cross-section of the periodic cells 4, 5 is circumscribed within a circle having a diameter B between 6 and 10 mm.

[0104] With respect to different particular embodiments of the invention, the periodic cells 4, 5 include holes 9 in their walls. These transverse holes 9 connect the periodic cells 4, 5 with other adjacent periodic cells 4, 5, allowing the binder mass 3 to flow from one to another upon injection. Figure 10 shows the holes 9 that allow the binder mass 3 to penetrate neighboring periodic cells 4, 5, further ensuring contact with all periodic cells 4, 5 and thus improving their resilience and heat transfer efficiency.

[0105] In particular, these nine holes have a diameter of less than 10 mm. This small hole size allows for efficient flow of the binder mass (flowability >150 mm) while maintaining the structural integrity of the periodic cells, avoiding large openings that could weaken the cell walls and compromise the stability of the sandwich structure.

[0106] According to one particular embodiment, the lower skin 7 and the upper skin 8 are plates having high thermal conductivity, i.e., a thermal conductivity greater than 25 W / mK. According to an alternative embodiment of the invention, one of the lower skin 7 and the upper skin 8 can be replaced by a plate of low thermal conductivity, i.e., a thermal conductivity less than 1 W / mK, to optimize heat transfer to the opposite plate of the heat exchanger, and this plate of low thermal conductivity having high flexural strength, configured to ensure the stability and durability of the exchanger.

[0107] According to particular embodiments, the low enthalpy heat exchanger of the invention may have thermal bridges 10, which include a first end located on the outer surface of the lower skin 7 of the enclosure means and a second end configured to be located on an emitting element 11 that requires heat dissipation.

[0108] These thermal bridges 10 can be solid or, alternatively, hollow.

[0109] Figure 11 schematically shows a side section of a particular embodiment of a solid thermal bridge 10 between a powerful emitting element 11 of an electrical device 12 and the low enthalpy heat exchanger acting as a cooling cap.

[0110] Hollow thermal bridges 10 include a dielectric fluid 13 inside, and in particular may include a turbine 14.

[0111] With regard to these hollow thermal bridges 10, the first end located on the outer surface of the lower skin 7 and the second end configured to be located in the emitting element 11 can be metal blocks 15 joined together with a hollow cavity between them. Figure 12 schematically shows a side section of a particular embodiment of a hollow thermal bridge 10 formed by the assembly of two metal blocks 15 joined with an elastic sealing element 16.

Claims

CLAIMS 1. Low enthalpy heat exchanger, comprising - at least one plastic coiled tube (1), configured for the internal circulation of a heat transfer fluid (2), said coiled tube (1) housed in a machined channel inside - a periodic cell structure configured for internal air circulation, the periodic cells oriented perpendicular to the coil tube (1), the walls of the periodic cells (4) having a thermal conductivity greater than 100 W / mK, and a cross-section circumscribed by a diameter B, - enclosure means including a lower skin (7) and an upper skin (8), forming a sandwich-type configuration that houses the periodic cell structure, which in turn houses the serpentine tube (1), and - a binding mass (3) poured into the machined channel surrounding the serpentine tube (1), which comes into contact with said serpentine tube (1) and fixes it to the periodic cell structure, characterized in that - the serpentine tube (1) has an outer diameter D between 6 and 13 mm, and a maximum thickness of 1.5 mm, - the structure of periodic cells includes - closed periodic cells (4) and - open periodic cells (5) adjacent to the serpentine tube (1), the walls of said open periodic cells (5) provide fins (6) adjacent to said serpentine tube (1), the machined channel inside the periodic cell structure (4,5) has a depth of at least the outer diameter D of the serpentine tube (1) and a width of the outer diameter D, the binding mass (3) has a thermal conductivity of less than 2.2 W / mK, and a flowability greater than 150 mm according to the test of European standard EN 445, providing an integral structure that completely surrounds the serpentine tube (1) without gaps or bubbles, completely bonding the serpentine tube (1) to the open periodic cells (5) and to the lower skin (7).

2. Low-enthalpy heat exchanger according to claim 1, wherein the channel machined inside the periodic cell structure does not reach the lower skin (7), leaving open periodic cells (5) adjacent to the lower skin (7), the walls of said open periodic cells (5) provide fins (6) adjacent to the serpentine tube (1) below said serpentine tube (1).

3. Low enthalpy heat exchanger, according to any of the preceding claims, wherein the periodic cells (4,5) include holes (9) in the walls configured to allow the binding mass (3) to flow between adjacent periodic cells (4,5), ensuring complete coverage and improved heat transfer.

4. Low enthalpy heat exchanger, according to claim 3, wherein the holes (9) have a diameter of less than 10 mm.

5. Low enthalpy heat exchanger, according to any of the preceding claims, wherein the diameter B of the circumference circumscribing the cross-section of the periodic cells (4,5) is between 6 and 10 mm.

6. Low enthalpy heat exchanger, according to any of the preceding claims, wherein the binding mass (3) is selected from silica, alumina, traditional cements and geopolymers, self-leveling mortar, self-compacting concrete, or a combination thereof.

7. Low enthalpy heat exchanger, according to claim 6, wherein the binding mass (3) includes additives selected from modified polymers, glass fiber, chemical bonding agents or a combination thereof, configured to increase the adhesion and anchoring capacity of the binding mass (3).

8. Low enthalpy heat exchanger, according to any of the preceding claims, wherein both the lower skin (7) and an upper skin (8) are plates having a thermal conductivity greater than 25 W / mK.

9. Low enthalpy heat exchanger, according to any of claims 1 to 7, wherein one of the lower skins (7) and one upper skin (8) is a plate having a thermal conductivity of less than 1 W / mK.

10. Low enthalpy heat exchanger, according to any of the claims 11. Low-enthalpy heat exchanger according to claim 10, wherein the thermal bridges (10) are solid.

12. Low enthalpy heat exchanger, according to claim 10, wherein the thermal bridges (10) are hollow and include a dielectric fluid (13) inside.

13. Low enthalpy heat exchanger, according to claim 12, wherein the thermal bridges (10) include a turbine (14) inside.

14. Low enthalpy heat exchanger, according to any of claims 12 to 13, wherein the first end located on the outer surface of the lower skin (7) of the enclosure means and the second end configured to be located in the emitting element (11) are metal blocks joined together with a hollow cavity between them.

Images