Piping arrangement and heating and / or cooling appliance

Abstract

The invention relates to a piping arrangement for flowing fluid, wherein the piping arrangement comprises a first piping element and a second piping element, wherein the first piping element and the second piping element are connected or connectable to each other so as to be arranged relative to each other such that the first and second piping elements overlap in an overlap region, wherein the overlap region comprises an adhesive region in which adhesive is arranged in at least a part of a gap (8) between the first and second piping element to adhere the first and second piping elements to each other and an alignment region, which is configured to coaxially align the first and second piping element relative to each other.

Description

[0001] Piping arrangement and heating and / or cooling appliance

[0002] The invention concerns a piping arrangement, a heating and / or cooling appliance comprising said piping arrangement and a method for forming such a piping arrangement.

[0003] Piping arrangements are, at a joint connecting first and second piping elements, often brazed. However, brazed joints may be perceived as insufficient in terms of reliability, repeatability and / or may imply design constraints. The quality of a brazed joint may depend on the worker actually carrying out brazing, e.g., the experience, and the conditions, such as possible access, space for tools and / or positioning of parts. For example, it is conceivable that a system turns out to be less compact due to limitations as to the compactness imposed by brazing. This may lead to risks associated with brazed joints / connections, e.g., occurrence of leaks.

[0004] A specific application, to which the present disclosure is not limited, may be flammable refrigerant, which creates additional risk. For maintenance purposes, it is often required to disassemble / reassemble the piping connection when an element of the circuit needs to be replaced. There may remain a small amount of refrigerant in the circuit, even if a vacuum draw is achieved. In this case, with flammable refrigerant as propane, there is a safety risk for the installer when brazing-debrazing, as it is done with a flame on the circuit.

[0005] Thus, the object is to provide a piping arrangement in which the piping elements are joined in simple and reliable way independent of the refrigerant flowing through the piping arrangement.

[0006] The object is solved by a piping arrangement for flowing fluid, wherein the piping arrangement comprises a first piping element and a second piping element, wherein the first piping element and the second piping element are connected or connectable to each other so as to be arranged or arrangeable relative to each other such that the first and second piping elements overlap in an overlap region, wherein the overlap region comprises an adhesive region in which adhesive is arranged or arrangeable in at least a part of a gap between the first and second piping element to adhere the first and second piping elements to each other and an alignment region, which is configured to coaxially align the first and second piping element relative to each other.

[0007] Another object of the invention is to provide a method for forming a piping arrangement in which the piping elements are joined in simple and reliable way independent of the refrigerant flowing through the piping arrangement.

[0008] The object is solved by a method for forming a piping arrangement, the method comprising arranging the first piping element and the second piping element relative to each other such that the first and second piping elements overlap in an overlap region, coaxially aligning the first piping element and the second piping element relative to each other in an alignment region of the overlap region and supplying adhesive into a gap between the first and second piping element to adhere the first and second piping elements to each other.

[0009] According to the invention it is realized that a simple connection between two piping elements can be realized by using adhesive to connect the two piping elements. Further, it is realized that the two piping elements have to be coaxially aligned to each other so that a cross section area of the gap between the first and second piping element does not change significantly in tangential direction of the piping arrangement. Such a gap enables that the same amount or basically the amount of adhesive arranged along the tangential direction of the gap does not change or does not significantly change. This is advantageous for sealing purposes as it is explained below more in detail. The tangential direction of the gap corresponds to a tangential direction around the central axis of the piping arrangement.

[0010] The overlap region is a region in which a piping element portion of the first piping element or the second piping element surrounds or, prior to assembly, is arranged to surround a piping element portion ofthe other pipingelement. The piping element portion can, in particular fully, surround the other piping element portion in tangential direction of the piping element. The tangential direction of the piping element corresponds to a tangential direction around the central axis of the piping element. The overlap region is defined by the piping elements after the piping element is inserted in the other element along the central axis. In the following it is described that the first piping element is moved relative to the second piping element. However, it is possible that only the second piping element is moved relative to the first piping element or that both piping elements are moved relative to each other.

[0011] The overlap region comprises the adhesive region and the alignment region. The alignment region is the region in which the two piping elements are arranged to be coaxially aligned to each other. Specifically, the two piping elements are arranged such that their piping element axis are coaxially to each other. The central axis of the piping arrangement comprises the two piping element axis, when the piping elements are coaxially aligned to each other, and thus corresponds to a common central axis of the two piping elements.

[0012] In the alignment region the two piping elements can be moved relative to each other wherein the alignment region ensures that the piping elements remain coaxially aligned during the movement. Outside the alignment region the piping elements might also be coaxially aligned whereas the piping elements can be moved relative to each such that the piping elements are not coaxially aligned anymore. The piping elements are outside the alignment region when an aligning portion of the first piping element and a counter-aligning portion of the second piping element do not contact each other.

[0013] In the sense of the application the piping elements are aligned if the piping element axis are arranged coaxial to each other. In that case the piping elements can move only along one direction relative to each other as long as adhesive is not supplied to the gap or the adhesive is not cured. Specifically, the aligned piping elements can only move along the central axis relative to each other.

[0014] The adhesive region is the region in which adhesive is arranged to be supplied when assembling the first and second piping elements together. The adhesive region comprises the gap between the first piping element and the second piping element. The gap extends in radial direction and in axial direction, wherein radial and axial direction refer to the central axis of the piping arrangement. In an embodiment in which adhesive is "arrangeable" in at least a part of a gap a not assembled piping arrangement is meant, which comprises the first and second piping element that are configured to be used together to form the assembled piping arrangement by supplying adhesive into the gap.

[0015] The two piping elements are connected or are connectable to each other. After the connection of the two piping elements, the piping elements cannot move relative to each other. The two piping elements are connected by means of the adhesive with each other.

[0016] "Flowing fluid" means that a gas or liquid flows inside the piping arrangement, in particular the first and second piping element. The gas or liquid can be a refrigerant, in particular a flammable refrigerant, such as propane. After the piping elements are connected to each other, they cannot move relative to each other.

[0017] According to an embodiment the adhesive that is arranged or arrangeable in the adhesive region can be configured such to seal the first piping element and the second piping element. In that case the adhesive fulfills two functions, namely to connect the two piping elements and to seal them. The sealing function is possible as the two piping elements are coaxially aligned to each other. This ensures that the gap has a constant or basically constant cross-section area along the tangential direction. That means, the cross-section area of the gap does not change or basically does not change in a plane that is perpendicular to the central axis. Therefore, the same or basically the same amount of adhesive can be supplied to each gap portion along the tangential direction. The cross-section area of the gap can change along the central axis. That means, the cross-section area of the gap can change in planes that are perpendicular to the central axis and that are arranged offset to each other along the central axis. This results in that the amount of adhesive changes along the central axis.

[0018] Such an adhesive distribution differs from known pipe arrangements in which the piping elements are not aligned. In said solutions the adhesive amount differs along the tangential direction or along the central axis resulting in that some gap portions do not comprise sufficient adhesive to seal the piping elements. This results because in the known solutions the piping elements can come into contact at some areas along the tangential direction of the gap during assembling of the piping elements. The adhesive supplied into the gap cannot flow in said contact regions so that no adhesive is arranged in the contact region. Further, the gap between the piping elements can be small so that only a small amount of adhesive can fill said gap. In both cases, the adhesive does not seal well the piping elements. However, if flammable refrigerant is used, due to safety reasons it has to be ensured that the adhesive seals the piping elements along the complete tangential direction. The aligning region can be arranged next to the adhesive region along the common central axis. Both regions can be arranged directly next to each other. That means, there are no other regions between the adhesive region and the alignment region along the central axis. In the end a compact piping arrangement is realized.

[0019] The first piping element can comprise an aligning part and the second piping element can comprise a counter-aligning part, wherein the first and second piping elements are coaxially aligned when the aligning part and the counter-aligning part contact each other. Thus, the two piping elements can be easily coaxially aligned by ensuring that the aligning part of the first piping element contacts the counter-aligning part of the second piping element. As long as the aligning and counter-aligning part are in contact with each other, the two piping elements can only be moved in one dimension relative to each other. Specifically, the two piping elements can be moved along the central axis relative to each other. The movement is only possible as long no adhesive is supplied into the gap, or, if the adhesive is to be cured, as long as it has not been cured. In the end the two piping elements can be coupled and coaxially aligned in an easy manner.

[0020] The aligning part can be arranged at an end of the first piping element. Further, the aligning part can comprise a greater diameter than the remaining part of the first piping element. Thus, a simple shaped first piping element is provided.

[0021] The centering part can have tighter dimensional tolerance than the remaining part of the first piping element and / or the counter-aligning part can have a tighter dimensional tolerance than the remaining part of the second pipe. The tighter dimensional tolerance enables that the first piping element and the second piping element can be very precisely aligned to each other. As discussed above this has the advantage that the cross-section area of the gap around the tangential direction does not or only slightly changes. This ensures that sufficient adhesive can be supplied into each portion of the gap to seal the piping elements and / or that the adhesive is evenly or basically evenly distributed around the tangential direction of the piping arrangement.

[0022] The "dimensional tolerance" refers to the diameter of the aligning part and the counter-centering part. Specifically, the dimensional tolerance refers to the outer diameter of the first piping element, in particular the aligning part, and to the inner diameter of the second piping element, in particular the counter-aligning part.

[0023] The inner diameter of the counter-aligning part can be different than an inner diameter of a remaining part of the second piping element. Specifically, the inner diameter of the counter-aligning part can have a smaller diameter than the remaining part of the second pipe. Thus, the first piping element can be easily moved through the adhesive region before it is aligned in the aligning part. This is possible as the outer diameter of the aligning part is smaller than the inner diameter of the remaining part so that the aligning part does not contact the remaining part.

[0024] The cross section of the gap can change, in particular increase, starting from the aligning part in a direction pointing to an insertion opening of the second piping element. In other words, the gap increases along the central axis starting from the counter-aligning part towards the insertion opening of the second piping element through which the first piping element is inserted into the second piping element. An increasing gap volume along the central axis has the advantage that sufficient adhesive can be supplied into the gap to fixedly connect the first and second pipe to each other and to, in particular better, seal the first and second piping element.

[0025] A part of the second piping element, which forms of the adhesive region, can have a conical shape or can be arranged offset from the counter-centering part of the second piping element, in particular in radial direction. Arranging offset from the counter-centering part of the second piping element means that the part of the second piping element is widened, in particular in radial direction relative to the central axis, with respect to the counter-centering part.

[0026] In the case that the part of the second piping element is arranged offset from the counter-centering part, the part of the second piping element can have a cylindrical shape. Such a shape of the part of the second piping element results in that the first piping element, in particularthe aligning part does not contact the part of the second piping element that forms the adhesive region. Further, such a shape of the second piping element ensures that the first piping element can be easily inserted into the second piping element. That means that the first piping element and the second pipe does not have to be coaxially aligned when the aligning part of the first piping element and the counter-aligning part of the second piping element are not in contact. This is for example the case when the first piping element is inserted into the second piping element but the aligning part of the first piping element is not arranged in the alignment region and thus not in contact with the counter-aligning part. The piping elements coaxially align by moving the first and second piping elements relative to each other. The part of the second piping element can be, in particular directly, arranged next to the counter-aligning part of the second piping element.

[0027] The first piping element and the second piping element can be configured such that, when no adhesive is arranged yet in the gap, the first piping element and the second piping element can move along, in particular merely, one dimension relative to each other when the aligning part and the counter- aligning part are in contact with each other. The first pipping element can be moved along the central axis until it abuts against a part of the second element and thus no movement along the central axis is possible anymore.

[0028] Further the first piping element and the second piping element can move along at least two dimensions relative to each other when the aligning part and the counter- aligning part are not in contact with each other. This is the case when the aligning part moves through the adhesive region of the piping arrangement. At the end a pipe arrangement is provided in which the insertion of the first piping element into the second piping element and the coaxially alignment can be easily achieved by moving the first and / or second pipping element relative to each other. If both pipping elements are moved, the movement direction of the first pipping element along the central axis is contrary to the movement direction of the second pipping element.

[0029] According to an embodiment the adhesive region can be free of friction or form fit elements for connecting the first and second piping elements. The connection of the first and second element can be only ensured by the adhesive. Thus, the first and second element can be easily connected to each other. Thus, no further mechanical means for pressing the piping elements and / or heating of the piping elements is necessary. Thus, piping element through which flammable refrigerant flows can be easily connected to each other.

[0030] As discussed above, the cross section area of the gap along the tangential direction of the first and / or second piping element is constant or is within a predetermined range. In said case the adhesive can seal the first and second piping element well. The adhesive can be arranged in the gap along the tangential direction of the first and / or second piping element so that the adhesive connects the piping elements, in particular complete, along the tangential direction. Further, the adhesive connects the piping elements to each other along the central axis.

[0031] According to an aspect of the invention the piping arrangement is used for flowing flammable fluid, in particular flammable refrigerant flowing in a heating and / or cooling appliance.

[0032] According to another aspect of the invention a heating and / or cooling appliance, in particular heat pump, comprises an inventive piping arrangement. The heating and / or cooling appliance comprises a refrigerant circulating in a circuit of the heating and / or cooling appliance, wherein the refrigerant is a flammable refrigerant, such as R290, or mildly-flammable such as R32 or R454C. Alternatively, the refrigerant can be R744.

[0033] A heating and / or cooling system can comprise an inventive piping arrangement. The heating and / or cooling system can comprise at least one heating and / or cooling appliance, in particular heat pump. Further the heating and / or cooling system can comprise at least one consumer, in particular a radiator, an underfloor heating appliance, etc.), which is connected to the heating and / or cooling appliance.

[0034] In the following the forming process of the pipe arrangement is explained more in detail. The pipe arrangement can be formed duringthe manufacturing process of the heating and / or cooling appliance. Alternatively, it is possible that the pipe arrangement is formed by an installer. This can be necessary if the installer needs to maintenance some parts of the heating and / or cooling appliance.

[0035] The piping elements can be arranged such that they overlap by inserting the first piping element in an inner space of the second piping element. Thereto, the first piping element is moved such that the aligning part passes through the insertion opening of the second piping element. Specifically, the first piping element can be moved along the central axis through the adhesive region. For coaxially aligning it might be necessary that the first piping element and / or the second piping element are moved in radial direction. By moving in radial direction, the piping elements can be arranged in radial direction relative to each other such that the first piping element can be further moved into the aligning region in which the piping elements are aligned to each other.

[0036] The adhesive can be supplied into the adhesive region, in particular the gap, through the insertion opening. Thus, the adhesive and the first piping element are inserted into the second piping element through the same insertion opening. This results in a compact piping arrangement.

[0037] After the first piping element is coaxially aligned with the second piping element the first piping element is further moved along the central axis until it abuts against the second piping element. Thereafter, the adhesive is supplied to the gap of the adhesive region.

[0038] According to an aspect the piping arrangement comprises at least first (i.e. inner) and second (i.e. outer) piping elements fluidly coupled to each other at the piping overlap (section / region), in which overlap the first and second piping elements at least partially overlap in a flow direction of the fluid flow (i.e. axially) and are arranged such that the gap at the piping overlap in a direction perpendicular to the flow direction (i.e. transverse direction) is formed between an outer side of the first piping element and an inner side of the second piping element.

[0039] A size of the gap seen in a cross-sectional view perpendicular to the flow direction corresponds to the difference between the outer diameter of the first piping element and the inner diameter of second piping element at the piping overlap, wherein the gap and the overlap define a gap volume between the first and second piping elements. The adhesive region is provided at the piping overlap and at least partially fills the gap volume with adhesive, wherein the first and second piping elements adhere to each other by means of the adhesive, and the adhesive region is at least in parts in (direct) contact with the outer side of the first piping element and the inner side of the second piping element. The size of the gap is less than 0.5 mm, optionally less than 0.2 mm, and the piping overlap is, seen in the flow direction, at least 4 mm, and the gap volume is between 0.001 to 0.20 ml, preferably between 0.001 to 0.10 ml. Adhering two parts together by means of the adhesive may mean to hold the parts together and also to create a seal between the parts, in particular a high performance sealing.

[0040] An idea underlying the present invention is joining of piping elements by means of an overlap and adhesive between the piping elements. The overlap may be seen as a male / female connection, wherein the first, inner piping element represents the male part, and the second, outer piping element represent the female part. It was found that the minimum piping overlap as mentioned above, the maximum size of a gap between the piping elements as mentioned above, and the specific gap volume as mentioned above which may at least in parts be filled by adhesive, altogether provide for an appropriate connection of the piping elements. For example, a larger gap size may not offer sufficient mechanical resistance, sufficient sealing and the adhesive may flow inside the inner pipe and create a clogging or a reduction in the cross-sectional area of the fluid flow, resulting in reduced heat pump performance or even failure; a shorter piping overlap may reduce the mechanical stability; and the gap volume as claimed provides for an appropriate interrelation / interplay of the gap size and the overlap.

[0041] The invention offers various improved embodiments in terms of reliability, repeatability and / or safety, and versatility, practicability and / or handling. Specifically, at least in some embodiments, flexibility regarding relative positions of the female and male parts may be achieved, e.g. including the possibility to make the assembly, i.e. manufacture, horizontal. In particular, safety may be increased, e.g. reduced risk of burn of fluid of high pressure - in particular compared to brazing. Alternatively or additionally, the time to realize the piping arrangement may be relatively short, at least compared to alternative joining types. Less skilled workers may be able to carry out manufacture of the piping arrangement of the invention. Possibly, manufacturing of a piping arrangement of the invention may more easily be automatized. Also benefits in terms of costs of the material (as glue / adhesive is typically less expensive than silver, nuts, crimp etc..) and / or costs of the process (no need for heating) may be achieved for an embodiment of the invention. Alternatively or additionally, a piping arrangement according to an embodiment of the invention may be multimaterial in that at most a few constraints apply, as a piping arrangement of an embodiment of the present invention may be more flexible regarding the materials of the piping elements. No deformation of a piping element may be necessary when joining, which may reduce stress exerted on the joined parts. As no flame is needed for manufacture, compared to brazing, the risk associated with the use of flammable fluid to be flown through the piping arrangement of an embodiment of the invention may be reduced. Further, when brazing, there may be thermal conduction between the junction connection and the pipe and components around (high thermal conductivity of e.g. copper tubes). This may cause the surrounding components to heat up, which can lead to failure. It also may mean that designers have to move components further apart to avoid overheating, which may increase material consumption and reduces system compactness. More specifically, when brazing, one has to protect components around or move. This may be specifically important where there are two or more joints very close (on a T-connection, for example). Due to the thermal conduction when brazing one connection, a neighboured connection may be degraded or unbrazed.

[0042] The overlap may be seen as a joint, in particular an axial overlap, wherein the axis corresponds to the flow direction of the fluid flow. The overlap, i.e. the joint, may allow for coupling of a first tube and a second tube; or of a tube and an inlet / outlet of a fluid circuit, e.g. fluid piping. In other words, the adhesive may be used to directly connect a piping element to an element of the fluid circuit, e.g. the refrigeration circuit.

[0043] The piping overlap may be seen as joining ends / terminations of piping elements. The piping elements are at least close to the respective end / termination of the respective piping element dimensioned such that the piping overlap in terms mentioned above is realized in the piping arrangement. It is not excluded that the piping elements have, outside the piping overlap, e.g. inner / outer diameters different to the dimensions at the piping overlap.

[0044] For the (axial) overlap to be formed, the outer shape, e.g. diameter of the first (i.e. inner) piping element is smaller than the inner shape, e.g. diameter of the second (i.e. outer) piping element, at least at the overlap. Accordingly, the first piping element at least partially overlaps (and e.g. is surrounded by) the second piping element.

[0045] Optionally, at least the outer side of the first piping element and the inner side of the second piping element have a circular cross-section. However, other geometries are also possible, preferably matching geometries to the effect that the joined sides of the elements conform to each other.

[0046] The adhesive may also be referred to as glue. The adhesive / glue may provide for molecular binding of the adjacent piping elements. Optionally, glue extends in and along the gap volume by means of capillarity. Glue may be added around the entire overlap, or just a part of it. Thermal or chemical activation (with an additional chemical compound / additive) activation of the adhesive is possible, but not necessary. For example, an activator based on copper crystals to facilitate the polymerisation of the adhesive may be used. This may depend on the specific adhesive used.

[0047] A step of cleaning may be carried out on the piping elements. It may be decided whether or not cleaning is necessary, and on appropriate means for cleaning. This may have an impact on the mechanical strength, displacement capacity and / or coverage of the adhesive. The adhesive may be seen as sandwiched between the first and second piping elements. The adhesive may be seen as the only link / connection between the first and second piping elements.

[0048] The gap between the first and second piping elements perpendicular to the axial direction (i.e. the direction of the fluid flow) is represented by a cavity between the first and second piping elements (which cavity is at least partially filled by adhesive). In other words, the gap between the first and second piping elements may be seen as relating to a radial distance between the first and second piping elements. It is noted that the gap is seen as the total gap between the first and second piping elements.

[0049] The gap may be measured along a line crossingthe center of the first piping element. The sum of two gap portions on opposite sides of the first piping element, when seen in a cross-sectional view perpendicular to the flow direction (F), yield the (total) gap size. The gap G = G1 + G2 may be defined as G = D2 - D1, wherein D1 is the outer diameter of first piping element and D2 is the inner diameter of second piping element. Optionally, a difference between outer diameter of the first, inner tube and an inner diameter of second, outer tube is less than 0.2 mm.

[0050] The gap volume may be represented by a hollow cylinder, i.e. a cylindrical cavity between the first and second piping elements. The wall thickness of such virtual cylinder corresponds to the gap size, and the length of such virtual cylinder corresponds to the overlap length.

[0051] The adhesive volume may be between 0.002 ml to 0.06 ml, in particular between 0.005 ml to 0.03 ml. The adhesive does not need to fill the gap in its entirety, but may only partially fill the gap volume. In some embodiments, the adhesive volume may exceed the gap volume, namely when adhesive is also present outside the overlap. E.g. adhesive is intentionally or unintentionally also at the outside of the first piping element.

[0052] Piping elements may be made of metal. For example, aluminum, e.g. instead of copper, may be used. In general, for a piping arrangement including first / second piping elements, the following combinations of materials are typical: copper / copper, copper / brass, copper / aluminum, cop per / stain less steel, aluminum / aluminum. However, further materials and / or combinations are possible.

[0053] Piping elements may be realized as a tube, hose, pipe, connector, adaptor etc. Example combinations of piping elements as a first piping element with a second piping element may be as follows: a tube with a tube, a tube with refrigerant components, a tube with hydraulic components, a tube with hydraulic / refrigerant modules, a tube with electronic components (sensor for pressure or temperature, switch etc..). Various combinations are first and second elements are possible.

[0054] The first piping element may be regarded as a male part, wherein the second piping element may be regarded as a female part.

[0055] It is not excluded that more than two piping elements may be joined at the overlap.

[0056] In some embodiments of the invention, no intermediate layer between the first and second piping elements is provided. In this case, the first and second piping elements are directly joined by means of adhesive.

[0057] As mentioned above, the piping arrangement is free of welding and / or brazing lines for connecting the piping elements to each other. Put differently, a piping arrangement of at least some embodiments of the invention has been manufactured without welding and / or brazing. Optionally, the piping overlap length is, seen in the flow direction, at least 5 mm or at least 10 mm, optionally less than 30 mm long. Put differently, optionally, the gap length (i.e. the piping overlap) is of the same length.

[0058] Optionally, the adhesive region is formed by a coherent (e.g. undisjointed or continuous) adhesive volume. This may mean that the adhesive region is continuous, e.g. without separations or interruptions. In other words, the adhesive region may be free of adhesive-free sub-regions. In other words, the adhesive may be present all around, and there must be no discontinuities, e.g. in the periphery. This may define the adhesive region irrespective of the application of the adhesive, e.g. droplets of the adhesive may be applied during manufacture.

[0059] Optionally, the adhesive has a specific viscosity at 25°C between 3 and 600 -10'3Pa-s (cP). Examples of suitable adhesives contain anaerobic acrylic and / or the basis Urethanmethacrylate. The adhesive may be configured to activate when there is no more oxygen applied. Additionally or alternatively, the adhesive may activate when in contact with particular material, such as copper or other metals. Additionally or alternatively, the relative density (at 23°C) may be 1 .1 .

[0060] The shear strength according to IS10123 test conditions may be 10 to 6 N / mm2.

[0061] The adhesive may be UV fluorescent (e.g. for controlling the presence of adhesive).

[0062] An example adhesive is Loctite 648, Loctite 209 or Loctite 603 from Henkel.

[0063] Optionally, the overlap is free of friction or form fit elements. For example, a piping arrangement of an embodiment of the invention is free of additional securing elements, in particular mechanical joining elements. More specifically, the piping arrangement of an embodiment of the invention is free from form and / or fiction fitting means, such as a ring, e.g. a crimping means. A piping arrangement of an embodiment of the invention may be based on only molecular bonding between the first and second piping elements by way of adhesive between the first and second elements.

[0064] The first and second piping elements are substantially concentric at least at the piping overlap. In other words, the first and second piping elements are coaxial in that the first and second piping elements share, at least at the piping overlap, a common center. In a cross-sectional view perpendicular to the axial direction, the first and second piping elements may be concentrically arranged.

[0065] Optionally, an outer diameter of the first and / or second piping elements is less than 23 mm, in particular less than 16 mm, optionally between 5 and 16 mm. Specifically, the outer diameter of the first piping elements may be between 5 and 16 mm, and the inner diameter of the second piping element may be between 5 and 16 mm, wherein the outer diameter of the first piping element is smaller than the inner diameter of the second piping element.

[0066] Optionally, the wall thickness of the first and / or second piping elements is at least 0.6 mm, at least at the overlap. Optionally, piping elements having such wall thickness are refrigerant piping pipes for flowing refrigerant. Hydraulic pipes for flowing water-based fluid may have a smaller wall thickness.

[0067] The overlap is realized along the entire perimeter (e.g. diameter) of at least the outer side of the first piping element and the inner side of the second piping element. This may be seen as a circumferential overlap. Preferably, the second piping element completely surrounds the first piping element. Hence, it is preferred that the female part completely surrounds the male part, at least at the overlap / joint. Optionally, at least one of the first and second piping elements, optionally both, are made of copper. According to EN 14276-2 or EN 12735-2, e.g. Cu-DHP (no. CW027: Cu > 99,9 mass%, Phosphor 0,015 - 0,04 mass%) may be used as copper.

[0068] Optionally, one of the first and second piping elements is made of copper (e.g. Cu- DHP, and the other one of the first and second piping elements is made of aluminum or brass or plastic or steel or stainless steel.

[0069] Optionally, the piping arrangement is configured to comply with at least one of the following the requirements, more optionally with all of the flowing requirements: a burst pressure of at least 9-103kPa, preferably at least 13.5-103kPa, even preferably at least 16-103kPa; an operational pressure of at least 2-103kPa, preferably 4.5-103kPa, a leakage rate of less than 1 -10-3Pa-m3-s'1Helium at 3 -103kPa at 293 K, more preferably less than 1 -1 O’6Pa-m3-s'1Helium at 3-103kPa at 293 K and even more preferably less than 1 -1 O'8Pa-m3-s'1Helium at 3 -103kPa at 293K. The burst pressure may be defined as a pressure at which no breakage occurs, but deformation is acceptable. The operational pressure may be defined as a pressure at which no deformation occurs. This may allow for appropriate sealing efficiency. This may fulfill the standards EN 378-2; EN 6033-2-40; and EN ISO 14903 and / or safety / leakage requirements.

[0070] Optionally, at least the outer side of the first piping element comprises at least partially at the piping overlap an indentation, such that the dimension of the outer side of the first piping element is reduced. The indentation is a cross-sectional indentation / reduction in that the outer diameter of the first piping element is reduced. This may be seen as a reduction of the outer dimension of first piping element, i.e. to reduce outer cross-section. Outside the indentation, the first piping element may have another size / diameter than at the indentation. For example, the first and second piping elements may have the same diameter except for at the overlap region, where the indentation is realized by means of a reduced diameter of the first piping element.

[0071] Additionally or alternatively, at least the inner side of the second piping element comprises at least partially at the piping overlap a widening, such that the dimension of the inner side of the second piping element is increased. The widening is a cross- sectional widening in that the inner diameter of the second piping element is widened. This increase of the inner dimension of the second piping element may be seen as an increase of the inner cross-section. Outside the widening, the second piping element may have another size / diameter than at the widening. For example, the first and second piping elements may have the same diameter except for at the overlap region, where the widening is realized by means of an enlarged diameter of the second piping element.

[0072] The invention is also directed to the use of the piping arrangement of the invention in a fluid circuit of a heating and / or cooling system, optionally a heat pump system, wherein refrigerant fluid is flown through the first and second piping elements and the piping overlap.

[0073] Optionally, during use, a flammable refrigerant (e.g. propane) is flown through the piping arrangement. Compared to the use of brazing (involving flames) the use of adhesive is particularly expedient.

[0074] When a refrigerant is used as fluid, the fluid circuit may be flown at 10 to 42 bar. In a hydraulic circuit, fluid (e.g. water-based) may be flown at a lower pressure, e.g. at 3 to 7 bar.

[0075] The invention is also directed to a heating and / or cooling system, optionally comprising a heat pump unit as heating and / or cooling appliance. Specifically, the system of the invention comprises at least one of a refrigerant circuit and a hydraulic circuit for heating or cooling a building. The system comprises a piping arrangement of any the invention.

[0076] The invention, in general, refers to any kind of heat pump system, including at least one ground source (water)- and / or air source-heat pump unit. The heat pump units may be indoor or outdoor units. A heat pump unit of the heat pump system may be a split unit or a monobloc unit. The heat pump system may be configured to heat and / or cool air or water (of a closed loop or of an open loop, such as domestic hot water).

[0077] In addition or alternatively to the described manufacturing method above, as an example, the following steps may be performed during manufacture of a piping arrangement of an embodiment of the invention:

[0078] 1 ) Fitting two piping elements together. At least a section of one of the two piping elements, called the female part, surrounds at least a section of the other one of the two piping elements, called the male part. The fitting can comprise the step to coaxially align the piping elements to each other.

[0079] 2) Glue / adhesive is added at the entrance to the fitting / overlap between the two pining elements. The glue moves by capillarity between the two piping elements and fills the gap between the piping elements at least partially. The adhesive may be added around the whole of the joint / overlap or just part of it. The assembly may be carried out horizontally, vertically or freely. If one piping element is above the piping element, it is preferable to use the female part below the male part.

[0080] 3) Waiting for a defined time for polymerization of the adhesive, if necessary. Optionally, testing for sufficient performance before handling or filling with fluid (e.g. pressure or leakage test). In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

[0081] Fig. 1 shows a cross section of a piping arrangement of an embodiment of the invention,

[0082] Fig. 2 shows a cross section of a piping arrangement of an embodiment of the invention,

[0083] Fig. 3 shows a cross section of a piping arrangement of an embodiment of the invention,

[0084] Fig. 4 schematically shows in Fig. 4(a) a plan view of a piping arrangement of an embodiment of the invention; in Fig. 4(b) a cross-sectional view in the axial direction of a piping arrangement of an embodiment of the invention; in Fig. 4(c) a cross-sectional view perpendicular to the axial direction of a piping arrangement of an embodiment of the invention,

[0085] Fig. 5 schematically shows in each of Fig. 5(a) to 5(d) planar views of a piping arrangement of an embodiment of the invention,

[0086] Fig. 6 schematically shows a perspective view of a piping arrangement of an embodiment of the invention.

[0087] Fig. 1 shows a cross section of a piping arrangement 1 of an embodiment of the invention. The piping arrangement 1 is shown when assembled and comprising a first piping element 4 and a second piping 5 that are connected to each other. Both piping elements 4, 5 are connected to each other such so as to be arranged relative to each other such that the first and second piping elements 4, 5 overlap in an overlap region 3. Specifically, a part of the first piping element 4 is arranged in an inner space of the second piping element 5. The second piping element 5, in particular fully, surrounds the first piping element 4 in tangential direction of the first piping element 4 and / or of the second piping element 5. The overlap region 3 comprises an adhesive region 7 and an alignment region 11 which are arranged adjacent along the central axis M. In the adhesive region 7 adhesive 12 is arranged in at least a part of a gap 8 between the first and second piping element 4, 5 to adhere the first and second piping elements 4, 5 to each other. The gap 8 is arranged between the first and second piping element in a radial direction R of the piping arrangement 1. The gap 8 is delimited by the alignment region 11 at one end and is open at the other end. Adhesive 12 is supplied into the gap 8 via said opening. The open end of the second piping element 5 comprises an insertion opening 15 through which the first piping element 4 is inserted into the second piping element 5. Thus, the adhesive and the first piping element 4 are inserted through the same insertion opening into the second piping element 5.

[0088] The overlap region 3 is arranged at an end of the second piping element 5 that comprises an insertion opening 15 through which the first piping element 4 is inserted into the second piping element 5. The part of the second piping element 4 forming the overlap region comprises a greater inner diameter D01 , D02b than an inner diameter D2a of the remaining portion of the second piping element 5 that extends from the part of the second piping element 5 in a direction away from the insertion opening 15.

[0089] The alignment region 11 is configured such to coaxially align the first and second piping element 4, 5 relative to each other. The first piping element 4 comprises an aligning part 13. The aligning part 13 is arranged at an end of the first piping element 4 and has a greater diameter than the remaining part of the first piping element 4. Further, the aligning part 13 has a tighter dimensional tolerance then the remaining part of the first piping element 4. The aligning part 13 has a cylindrical shape.

[0090] The second piping element 5 comprises a counter-aligning part 14. In the alignment region 11 the aligning part 13 of the first piping element 4 and the counter-aligning part 14 contact each other. The counter-aligning part 14 has an inner diameter D01 which is smaller than the inner diameter D2a of the remaining part of the second piping element 5. Further, the counter-aligning part 14 has a tighter dimensional tolerance than the remaining part of the second piping element 5. The counteraligning part 14 has a cylindrical shape.

[0091] The alignment region 11 ensures that a central axis of the first piping element 4 is coaxially to a central axis of the second piping element 5. The central axis M comprises the central axis of the first and second piping element 4, 5. In a plane that is perpendicular to the central axis M, the gap 8 comprises a cross-section area that is constant or basically constant along the tangential direction of the piping arrangement 1. Said constant cross-section is a result of the coaxial arrangement of the first and second piping element 4, 5.

[0092] For connecting the first piping element 4 and the second piping element 5 together, the first piping element 4 is inserted through the insertion opening 15 into the second piping element 5. The first piping element 4 is translatory moved until the first piping element 4 reaches the aligning region 11 . In the aligning region 11 the first piping element 4 and / or the second piping element 5 are aligned in radial direction R so that the first piping element 4 and the second piping element 5 are aligned. The piping elements 4, 5 are aligned such that the first piping element 4 can be further translatory moved into the aligning region 11 until the aligning part 13 abuts against a part of the second piping element 5. In other words, the first piping element 4 can move in two or three dimensions relative to the second piping element 5 when the first piping element is not partially arranged in the aligning region. Afterwards, adhesive is added into the gap 8 between the first and second piping element 4, 5 to connect them with each other. In the connection process explained above, the first piping element is moved. However, it is also possible that only the second piping element is moved of that the first and second piping element is moved. Fig. 2 shows a cross section of a piping arrangement 1 of an embodiment of the invention. The piping arrangement 1 shown in fig. 2 differs from the piping arrangement shown in fig. 1 in that the first piping element 4 does not comprise an aligning part 13 that has a greater diameter than the remaining part of the first piping element 4. However, the aligning part 13 is arranged at the end of the first piping element 4 and / comprises a tighter dimensional tolerance than the remaining part of the first piping element 4.

[0093] The second piping element 5 differs from the second piping element shown in fig. 2 in that the part of the second piping element that forms the adhesive region 7 has a conical shape. Thus, the gap 8 increases starting from the aligning region 11 towards the insertion opening 15 of the piping arrangement 1 .

[0094] Fig. 3 shows a cross section of a piping arrangement 1 of an embodiment of the invention. The piping arrangement 1 shown in fig. 3 differs from the piping arrangement shown in fig. 2 in the shape of the second piping element 5 in the overlap region 3. In contrary to the embodiment shown in fig. 2, the part of the second piping element 5 forming the adhesive region 7 does not have a conical shape but a cylindrical shape. However, the part of the second piping element 5 is widened in radial direction R with respect to the counter-aligning part 14 of the second piping element 5.

[0095] Each of Fig. 4(a) to 4(c) schematically shows a piping arrangement 6 according to an embodiment of the invention for flowing fluid (not shown) inside the piping arrangement 6, wherein Fig. 4(a) is a plan view, Fig. 4(b) is a cross-sectional view in the axial direction (which corresponds to the flow direction F), and Fig. 4(c) is a cross- sectional view perpendicular to the axial direction (i.e. in a transverse direction, perpendicular to the flow direction F). For the sake of simplicity, the alignment region is not shown in Fig. 4(a) to 4(c). However, the embodiment shown in Fig. 4(a) to 4(c) comprises the alignment region. The piping arrangement 6 may be part of a fluid circuit of a heating and / or cooling system, e.g. a heat pump system (not shown) and / or a heating and / or a cooling appliance (not shown). The piping arrangement 6 may more specifically contain / flow refrigerant as fluid (if part of a refrigerant circuit), or alternatively water-based fluid (if part of a hydraulic circuit). If the piping arrangement 6 is used in a refrigerant circuit, the refrigerant may be flammable.

[0096] Turning to Fig. 4(a), the piping arrangement 6 comprises first 4 and second 5 piping elements, partially overlapping in the flow direction F to form a piping overlap (section) 3. The overlap (section) 3 may be regarded as a joint joining the first 4 and second 5 piping elements. The piping overlap 3 is, seen in the flow direction F, at least 4 mm, or at least 5 mm or at least 10 mm, optionally less than 30 mm.

[0097] The first piping element 4 is an inner piping element and is located, in the overlap 3, inside the second piping element 5, which is an outer piping element. The first piping element 4 has a smaller outer diameter D1 than the inner diameter D2 of the second piping element 5. The piping elements 4, 5 are, in the embodiment of Fig. 1, cylindrical (having an axis running in the flow direction F) and each represent tubes. The outer diameter D1 of the first 4 and / or the inner diameter D2 of the second 5 piping elements is less than 16 mm, optionally between 5 and 16 mm, wherein the D2>D1 .

[0098] Fig. 4(b) schematically shows that a (circumferential) gap / clearance 8 is formed between an outer side 1 of the first piping element 4 and an inner side 2 of the second piping element 5. A size of the gap 8 seen in a cross-sectional view perpendicular to the flow direction F corresponds to the difference between the outer diameter D1 of the first piping element 4 and the inner diameter D2 of second piping element 5 at the piping overlap 3, wherein the gap 8 and the overlap 3 define a gap volume V between the first and second piping elements 4, 5. The size of the gap 8 is less than 0.5 mm, optionally less than 0.2 mm and the gap volume V is between 0.001 to 0.20 ml.

[0099] An adhesive region 7 at the piping overlap at least partially fills the gap volume Vwith adhesive, wherein the first and second piping elements 4, 5 adhere to each other due to the adhesive. The adhesive joins the first 4 and second 5 piping elements based on molecular forces. The gap 8 is at least partially filled with adhesive forming an adhesive region 7. The adhesive region 7 is at least in parts in direct contact with the outer side 1 of the first piping element 4 and the inner side 2 of the second piping element 5.

[0100] A wall thickness W1 of the first piping element 4 is at least 0.6 mm, at least at the overlap 3. A wall thickness W2 of the second piping element 5 is at least 0.6 mm, at least at the overlap 3. The wall thickness may be different outside the overlap 3.

[0101] Fig. 4(b) and 4(c) indicate that the adhesive region 7 is formed by a coherent adhesive volume. This means that the adhesive region 7 is not interrupted and is free of isolated "adhesive islands". Rather, the adhesive substantially forms a hollow cylinder.

[0102] The adhesive has a specific viscosity at 25°C between 3 and 600-1 O'3Pa-s (cP). For the embodiments of Fig. 1 -6, the adhesive Henkel, Loctite 648, is an option.

[0103] Fig. 4 to 6 show that the overlap 3 is free of friction or form fit elements. Specifically, no crimping means may be needed in a piping arrangement 6 of an embodiment of the invention.

[0104] Fig. 4(a) to (c) show that the first 4 and second piping elements 5 are substantially concentric at least at the piping overlap 3. Fig. 4(c) shows that the overlap 3 is realized along the entire perimeter of at least the outer side 1 of the first piping element 4 and the inner side 2 of the second piping element 5. Hence, the adhesive region 7 and the second piping element 5 completely surround the first piping element 4 at the overlap 3, wherein the first piping element

[0105] 4 and the second piping element 5 sandwich the adhesive region 7.

[0106] The gap 8 is defined by the total gap width G representing a wall thickness of the clearance-cylinder between the first 4 and second 5 piping elements related to the diameters, as well as the length 0 of the overlap 3. The volume V of the gap 8 is defined by V = TT X ((0.5 x D2)2- (0.5 x D1 ))2x O = 0.25 x TT X O x (D22-D12).

[0107] In case of the concentric arrangement shown in Fig.4, the gap size G consists of gaps (parts) G1 and G2 which are of the same size at both sides of the first piping element 4. If the tubes 4, 5 are not concentric, there may be a gap only at one side, e.g. G=G1 , G2=0.

[0108] Fig. 5 shows various geometries of first 4 and second 5 piping elements at the overlap 3. Fig. 5(a) shows that the first 4 and second 5 piping elements may have a uniform, continuous geometrical shape, such as a cylinder.

[0109] Alternatively, the diameter of the first 4 and / or second 5 piping elements at the overlap 3 may differ from the remaining respective diameter: Fig. 5(b) reflects that the second piping element 5 may comprise at least partially at the piping overlap 3 a widening 9, e.g. such that the dimension of the inner side 2 of the second piping element 5 is increased. In this case, the diameter / geometry of the first 4 and second

[0110] 5 piping elements may, outside / except for the overlap 3, be substantially identical.

[0111] Fig. 5(c) reflects that the first piping element 4 may comprise at least partially at the piping overlap 3 an indentation 10, e.g., such that the dimension of the outer side 1 of the first piping element 4 is decreased. In this case, the diameter / geometry of the first 4 and second 5 piping elements may, outside / except for the overlap 3, be substantially identical.

[0112] Fig. 5(d) reflects that the first piping element 4 may comprise at least partially at the piping overlap 3 an indentation 10, and that the second piping element 5 may comprise at least partially at the piping overlap 3 a widening 9. The indentation 10 and the widening 9 are dimensioned such that the outer diameter D1 of the first piping element 4 is smaller than the inner diameter D2 of the second piping element

[0113] 5 at the overlap 3.

[0114] Fig. 6 shows a piping arrangement 6 of an embodiment of the invention, wherein the first piping element 4 is a tube, and the second piping element 5 is a multiple pipes connector. Although an outer side of the connector 5 is not cylindrical, the inner side 2 (not visible in Fig. 6) is cylindrical, so as to match the outer side 1 of the tube 4. In this example, the first piping element 4 is made of copper, and the second piping element 5 is made of brass.

[0115] Any of the embodiments shown in the figures comply with at least one of the following the requirements, in line with the applicable standards: burst pressure of at least 9-103kPa, preferably at least 13.5-103kPa, more preferably at least 16-103kPa; an operational pressure of at least 2-103kPa, preferably 4.5-103kPa, a leakage rate of less than 1 -10’3Pa-m3-s’1Helium at 3-103kPa at 293 K, more preferably less than 1 -1 O’

[0116] 6Pa-m3-s’1Helium at 3-103kPa at 293 K and even more preferably less than 1 -1 O’8Pa-m3-s’1Helium at 3 -103kPa at 293 K. However, these requirements may not in all applications of a piping arrangement 6 of an embodiment of the invention need to be complied with.

[0117] The detailed description of the invention is provided with respect to the embodiments depicted in the drawings. Obvious variations and alternatives may occur to the skilled person, based on the summary of the invention. These variations and alternatives are part of the invention in so far they are covered by the appended claims.

[0118] REFERENCE SIGNS

[0119] 1 Outer side of first piping element

[0120] 2 Inner side of second piping element

[0121] 3 Overlap region

[0122] 4 First piping element

[0123] 5 Second piping element

[0124] 6 Piping arrangement

[0125] 7 Adhesive region

[0126] 8 Gap

[0127] 9 Cross-sectional widening

[0128] 10 Cross-sectional indentation

[0129] 11 Aligning region

[0130] 12 Adhesive

[0131] 13 aligning part

[0132] 14 Counter- aligning part

[0133] 15 Insertion opening

[0134] D1 Outer diameter of first piping element

[0135] D2 Inner diameter of second piping element

[0136] W1 Wall thickness of first piping element

[0137] W2 Wall thickness of second piping element

[0138] G1, G2 Width of gap part

[0139] D01 Inner diameter of counter-centering part

[0140] D2a Inner diameter of remaining part of second piping element

[0141] D2b Inner diameter of a further remaining part of second piping element

[0142] F Flow direction

[0143] G Total width of gap

[0144] M Central axis

[0145] 0 Length of overlap

[0146] R Radial direction

Claims

CLAIMS1 . Piping arrangement (6) for flowing fluid, wherein the piping arrangement (6) comprises a first piping element (4) and a second piping element (5), wherein the first piping element (4) and the second piping element (5) are connected or connectable to each other so as to be arranged relative to each other such that the first and second piping elements (4, 5) overlap in an overlap region (3), wherein the overlap region (3) comprises an adhesive region (7) in which adhesive (12) is arranged or arrangeable in at least a part of a gap (8) between the first and second piping element (4, 5) to adhere the first and second piping elements (4, 5) to each other and an alignment region (11 ), which is configured to coaxially align the first and second piping element (4, 5) relative to each other.

2. Piping arrangement (6) according to claim 1 , characterized in that the adhesive (5) arranged or arrangeable in the adhesive region (7) is configured to seal the first piping element (4) and the second piping element (5).

3. Piping arrangement (1 ) according to claim 1 or 2, characterized in that the aligning region (11 ) is arranged next to the adhesive region (7) along a central axis (M) of the piping arrangement (6).

4. Piping arrangement (6) according to at least one of the claims 1 to 3, characterized in that the first piping element (4) comprises an aligning part (13) and that the second piping element (5) comprises a counter-aligning part (14), wherein the first and second piping elements (4, 5) are coaxially aligned when the aligning part (6) and the counter-aligning part (14) contact each other.

5. Piping arrangement (6) according to claim 4, characterized in thata. the aligning part (6) is arranged at an end of the first piping element (2) and / or b. the aligning part (6) comprises a greater diameter than the remaining part of the first piping element (2).

6. Piping arrangement (6) according to claim 4 or 5, characterized in that the aligning part (13) has a tighter dimensional tolerance than the remaining part of the first piping element (4) and / or the counter-aligning part (14) has a tighter dimensional tolerance than the remaining part of the second piping element (5).

7. Piping arrangement (1 ) according to at least one of the claims 4 to 6, characterized in that a. an inner diameter (D01 ) of the counter-aligning part (14) is different than an inner diameter (D02) of a remaining part of the second piping element (5) and / or in that b. a cross section of the gap (8) changes, in particular increases, in a direction (A) pointing to an insertion opening of the second piping element (6).

8. Piping arrangement (1 ) according to at least one of the claims 1 to 7 characterized in that a part of the second piping element (5), which forms the adhesive region (7), has a conical shape or is widened with respect to the countercentering part (14) of the second piping element (6), in particular in radial direction (R).

9. Piping arrangement (6) according to at least one claim 4 to 8, characterized in that the first piping element (4) and the second piping element (5) are configured such that, when no adhesive (12) is arranged in the gap (8), the first piping element (4) and the second piping element (5) can move along one dimension relative to each other when the aligning part (13) and the counter- aligning part (14) are in contactwith each other and can move along at least two dimensions when the aligning part (13) and the counter-aligning part (14) are not in contact with each other.

10. Piping arrangement (6) according to at least one claim 1 to 9, characterized in that the adhesive region (11 ) is free of friction or forms fit elements for connecting the first and second piping elements (4, 5).

11. Piping arrangement (6) according to at least one of the claims 1 to 10, characterized in that a cross section area of the gap (8) along a tangential direction of the first and / or second piping element (4, 5) is constant or is within a predetermined range.

12. Piping arrangement (6) according to at least one of the claims 1 to 11 , characterized in that the adhesive (12) is arranged or arrangeable in the gap (8) such that the adhesive (12) adheres the first and second piping elements to each other along a tangential direction of the first and / or second piping element (4, 5).

13. Heating and / or cooling appliance, in particular heat pump, with a piping arrangement (6) according to at least one of the claims 1 to 12.

14. Heating and / or cooling appliance according to claim 13, characterized in that the heating and / or cooling appliance comprises a refrigerant circulating in a circuit of the heating and / or cooling appliance, wherein the refrigerant is a flammable refrigerant.

15. Method for forming a piping arrangement (6), in particular a piping arrangement according to at least one of the claims 1 to 12, the method comprising arranging the first piping element (4) and the second piping element (5) relative to each other such that the first and second piping elements (4, 5) overlap in an overlap region (3),coaxially aligning the first piping element (4) and the second piping element(5) relative to each other in an alignment region (11 ) of the overlap region (3) and supplying adhesive (12) into a gap (8) between the first and second piping element (4, 5) to adhere the first and second piping elements (4, 5) to each other.

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