Heat transfer device and metod for manufacturing such А heat transfer device

Abstract

A heat transfer device (100) for transferring heat generated by a heat source (150) to a heat sink (160) via a fluid is disclosed. The heat transfer device (100) comprises an evaporation region (100a) configured to evaporate the fluid in the liquid phase and a condensation region (100b) configured to condense the fluid in the vapor phase. Moreover, the heat transfer device (100) comprises a vapor channel (110) extending from the evaporation region (100a) to the condensation region (100b) so that evaporated fluid flows from the evaporation region (100a) to the condensation region (100b) through the vapor channel (110). The heat transfer device (100) further comprises a porous structure (120) at least partially embedding the vapor channel (110) and extending from the condensation region (100b) to the evaporation region (100a) so that condensed fluid flows from the condensation region (100b) to the evaporation region (100a) through the porous structure (120) by action of capillary forces. The cross-section of the vapor channel (110) comprises a first portion (111) having the shape of an isosceles trapezoid.

Description

[0001] HEAT TRANSFER DEVICE AND METHOD FOR MANUFACTURING SUCH A HEAT

[0002] TRANSFER DEVICE

[0003] TECHNICAL FIELD

[0004] Generally, the present invention relates to the field of cooling technology. The present invention relates to a heat transfer device for transferring heat generated by a heat source to a heat sink via a fluid working in evaporating-condensing cycles as well as a method for manufacturing such a heat transfer device.

[0005] BACKGROUND

[0006] A heat source (e.g. an electronic device such as a chip or a circuit) generates heat. The heat may be transferred to a heat sink where the heat can be dissipated to the ambient air. A heat transfer device, for example a heat pipe, comprises an evaporation region and a condensation region, a vapor channel extending between them, and a porous structure surrounding the vapor channel.

[0007] Such a heat transfer device may transfer heat on long distances via a fluid flowing in the vapor phase through the vapor channel, and flowing back to the evaporator in the liquid phase through the porous structure that generates a capillary pressure (and, therefore, is often also referred to as wick structure or simply wick). In order to allow for mass production, the porous structure of a conventional heat pipe is uniformly distributed around the vapor channel.

[0008] WO2020252555A1 discloses a heat transfer device, in particular heat pipe, with an eccentric porous structure due to an eccentric positioning of a pin when sintering the porous structure. The porous structure comprises a sequence of segments, including at least a first segment near the evaporation region with smaller pores size and a second segment near the condensation region with bigger pores size. The eccentric position of the pin results in a local decrease of the wick thickness from the evaporator / condenser side for lowest temperature difference and keeping the wick cross-sectional area for max heat transfer ability (comparing with uniform wick thickness, made by centered pin). However, from a mass production point of view, such a design might face difficulties with pin manufacturing tolerance, caused by accuracy of pin producing and installation.

[0009] Thus, for conventional heat pipes, as disclosed in WO2020252555A1, it can be very difficult to generate a porous structure, e.g. wick with a small thickness on the evaporation / condensation side, mainly due to pin manufacturing tolerance. Moreover, a substantive deformation of the porous structure, e.g. decreasing wick deformation strain during a flattening process may result in a different porosity, permeability as well as random cracking of the porous structure.

[0010] SUMMARY OF THE INVENTION

[0011] It is an objective of the present disclosure to provide an improved heat transfer device for transferring heat generated by a heat source to a heat sink via a fluid working in evaporatingcondensing cycles as well as a method for manufacturing such a heat transfer device.

[0012] The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

[0013] According to a first aspect a heat transfer device, in particular heat pipe, for transferring heat generated by a heat source to a heat sink via a fluid is provided.

[0014] The heat transfer device according to the first aspect comprises an evaporation region configured to evaporate the fluid in the liquid phase and a condensation region configured to condense the fluid in the vapor phase. Moreover, the heat transfer device according to the first aspect comprises a vapor channel extending from the evaporation region to the condensation region so that evaporated fluid flows from the evaporation region to the condensation region through the vapor channel defining a flow direction along the vapor channel. The heat transfer device according to the first aspect further comprises a porous structure, e.g. wick at least partially embedding, e.g. defining the vapor channel and extending from the condensation region to the evaporation region so that condensed fluid flows from the condensation region to the evaporation region through the porous structure by action of capillary forces. The cross-section of the vapor channel substantially transverse to the flow direction along the vapor channel comprises a first portion having the shape of an isosceles trapezoid.

[0015] Accordingly, the heat transfer device according to the first aspect with its special shape of the cross-section of the vapor channel results in a decreased deformation of the porous structure and, thus, provides an increased pin manufacturing tolerance for lower thermal resistance of evaporator / condenser regions, suitable for mass production. For example, a decreased compressive deformation supports a high porosity and therefore a high permeability of the porous wick structure leading to an increase of the maximum heat transfer capability of the heat transfer device, e.g. heat pipe. The decreased stretching avoids cracks in the porous wick structure, which may lead to discontinuity of the liquid flow in the porous wick structure with a resulting degradation of the maximum heat transfer capability of the heat transfer device, e.g. heat pipe.

[0016] The fluid may form an internal working media with two phases (liquid phase, vapor phase). In a particular implementation form, the fluid may be water or any other evaporative liquid. When the heat transfer device is in service the fluid may evaporate as the heat-receiving outer surface receives heat from the heat source, e.g. from an electronic device. Evaporation of the fluid occurs in an evaporation region. The evaporated fluid may flow through the vapor channel and toward the heat-emitting outer surface. The evaporated fluid may condense when the heat-emitting outer surface emits heat and hence dissipate it in the ambient. Condensation of the fluid occurs in a condensation region. The condensed fluid may flow through the porous structure back toward the heat-receiving surface. In an implementation form, the heat transfer device may operate in a so- called anti-gravity configuration, in which the liquid phase flows vertically upwards, hence against the gravity, from the condensation region to the evaporation region. In another implementation form, the heat transfer device may operate in the opposite configuration, the evaporation region being located below the condensation region. In yet another implementation form, the heat transfer device may operate in a horizontal or inclined orientation.

[0017] In a further possible implementation form, the heat transfer device according to the first aspect comprises a preferably metallic housing defining a hermetical case, wherein the housing is configured to accommodate the evaporation region, the condensation region, the vapor channel and the porous structure so that the porous structure at least partially embeds the vapor channel, wherein at least a portion of the housing has the shape of a flattened hollow cylinder. This allows to have an appropriate coupling between the flattened portion of the heat pipe and a flat heat source (for example electronic components of a circuit) or a flat heat sink. Moreover, remaining nonflattened portions of the heat pipe provide aa larger cross section (larger volume) for the vapor and liquid flow due to circular cross section of the housing.

[0018] In a further possible implementation form, the housing defines, e.g. comprises a first wall facing the heat source and / or the heat sink and a second wall opposite to the first wall, wherein a first base, in particular a long base, and a second base, in particular a short base, of the first portion of the cross-section of the vapor channel having the shape of an isosceles trapezoid extend substantially parallel to the first wall and / or the second wall of the housing. Since the bases extend substantially parallel to the first and / or second wall, the thickness of the porous wick structure along the corresponding walls can be maintained constant and therefore allows uniform heat transfer conditions without local overheating or overcooling of surfaces of the heat source or the heat sink, respectively.

[0019] In a further possible implementation form, the first base, in particular long base, of the first portion of the cross-section of the vapor channel is closer to the first wall of the housing than the second base, in particular short base, of the first portion of the cross-section. Due to such an alignment, the evaporated or condensing vapor passes through the first base (outgoing from the porous wick structure in the evaporation region and intruding the porous wick structure in the condensation region) with low flow resistance due to a large surface of the first base.

[0020] In a further possible implementation form, a ratio of a distance B between the second base, in particular short base, of the first portion of the cross-section of the vapor channel and an inner surface of the second wall and a distance A between the first base, in particular long base, of the first portion of the cross-section of the vapor channel and an inner surface of the first wall of the housing has a value between 2 and 10. Therefore, the porous wick structure thickness (distance A) involved in the evaporation or condensation process may be small resulting in a small thermal resistance and a correspondingly small temperature difference.

[0021] In a further possible implementation form, the cross-section of the vapor channel (substantially transverse to the fluid flow direction along the vapor channel) further comprises a second portion, wherein the second portion of the cross-section of the vapor channel has the shape of an isosceles triangle and wherein a base of the second portion of the cross-section of the vapor channel coincides with the second base, in particular short base, of the first portion of the cross-section of the vapor channel. The second portion provides additional space for the vapor flow and, thus, decreases the corresponding flow resistance and leads to an increased maximum heat transfer capability of the heat transfer device, e.g. heat pipe.

[0022] In a further possible implementation form, the comer of the second portion of the cross-section of the vapor channel opposite to the base of the second portion of the cross-section of the vapor channel extends to the inner surface of the second wall of the housing. In other words, in an implementation form the vapor channel may extend to the inner housing. The comer leads to a desired controlled cracking in the middle of the porous wick structure, which helps to release stretching stresses in the regions nearby so that additional cracks are less likely to appear, which would lead to a disruption of the liquid flow continuity. In a further possible implementation form, a further portion of the housing has the shape of a hollow cylinder with a circular cross section, wherein along the further portion of the housing the cross-section of the vapor channel has a further, e.g. third portion having the shape of a circular segment or a further isosceles trapezoid. The further portion provides additional space for the vapor flow and, thus, decreases the corresponding flow resistance and leads to an increased maximum heat transfer capability of the heat transfer device, e.g. the heat pipe.

[0023] In a further possible implementation form, a chord of the further portion of the cross-section of the vapor channel shaped as a circular segment or a base of the further portion of the cross-section of the vapor channel shaped as a further isosceles trapezoid overlaps at least partially with the first base or the second base of the first portion of the cross-section of the vapor channel. Such overlapping is an alternative way of shaping the porous wick structure compared to the compression process of a conventional heat pipe. During overlapping no significant wick compressive deformation appears, therefore porosity and flow resistance aren’t affected, so maximum heat transfer capability of heat pipe is improved.

[0024] In a further possible implementation form, the further portion of the cross-section of the vapor channel shaped as a circular segment or as a further isosceles trapezoid is located closer to a side of the housing facing the heat source and / or the heat sink than the first portion of the cross-section of the vapor channel shaped as an isosceles trapezoid. The further portion of the cross-section provides additional surface for passing of the vapor through the interface between the vapor channel and the porous wick structure thereby decreasing the corresponding flow resistance.

[0025] In a further possible implementation form, the arc of the further portion of the cross-section of the vapor channel shaped as the circular segment is located closer to the side of the housing facing the heat source and / or the heat sink than the chord of the further portion of the cross-section of the vapor channel shaped as the circular segment or wherein a short base of the further portion of the cross-section of the vapor channel shaped as the further isosceles trapezoid is located closer to the side of the housing facing the heat source and / or the heat sink than a long base of the further portion of the cross-section of the vapor channel shaped as the further isosceles trapezoid. This feature allows for a small thickness of the porous wick structure on the side of the housing facing the heat source and / or heat sink. Therefore, the corresponding temperature difference becomes small due to a low thermal resistance of the thin porous wick structure. In a further possible implementation form, the chord of the further portion of the cross-section of the vapor channel shaped as the circular segment extends with both of its ends to an inner surface of the housing or a long base of the further portion of the cross-section of the vapor channel shaped as the further isosceles trapezoid extends with both of its ends to an inner surface of the housing. This feature allows for an additional controlled cracking, which helps releasing compressive stresses induced by the flattening of the porous wick structure.

[0026] In a further possible implementation form, the heat transfer device comprises a further porous structure, wherein the further porous structure is formed as a layer at least partially covering the inner surface of the housing and at least partially embedding the porous structure. This allows to make fabrication procedure of the heat transfer device, e.g. heat pipe more stable. Especially the thickness of the thin layer can be controlled more precisely.

[0027] In a further possible implementation form, a base of the first portion of the cross-section of the vapor channel extends along an inner surface of the further porous structure. The further porous structure provides a thin layer of wick with improved uniformity of thickness near the base of the first portion of the cross-section of the vapor channel.

[0028] According to a second aspect an electronic assembly comprising a heat source, a heat sink, and the heat transfer device according to the first aspect is provided, wherein the evaporation region of the heat transfer device is in thermal contact with the heat source and the condensation region of the heat transfer device is in thermal contact with the heat sink.

[0029] According to a third aspect a method is provided for manufacturing a heat transfer device, in particular a heat transfer device according to the first aspect, for transferring heat generated by a heat source to a heat sink via a fluid. The heat transfer device comprises an evaporation region configured to evaporate the fluid in the liquid phase and a condensation region configured to condense the fluid in the vapor phase. Moreover, the heat transfer device comprises a vapor channel extending from the evaporation region to the condensation region so that evaporated fluid flows from the evaporation region to the condensation region through the vapor channel. The heat transfer device further comprises a porous structure at least partially embedding, e.g. defining the vapor channel and extending from the condensation region to the evaporation region so that condensed fluid flows from the condensation region to the evaporation region through the porous structure by action of capillary forces. The method according to the third aspect comprises sintering the porous structure such that the cross-section of the vapor channel comprises a first portion having the shape of an isosceles trapezoid.

[0030] In an implementation form, the sintering process may comprise: providing an atmosphere containing at least one of nitrogen gas and argon gas and a sintering temperature ranging from 860 degrees Celsius to 890 degrees Celsius. The sintering process may have a duration in the range of 1.2 h to 2.0 h, advantageously in the range of 1.5 h to 2.0 h.

[0031] In an implementation form, the method further comprises: before the sintering process: placing a filling material in a space corresponding to the vapor channel; and after the sintering process: removing the filling material. In an implementation form, the filling material is a core pin.

[0032] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

[0035] Figs. 1 and 2 show a schematic side view as well as cross-sectional views of a conventional heat transfer device;

[0036] Fig. 3 shows cross-sectional views of a conventional heat transfer device manufactured with a noncentral pin position;

[0037] Fig. 4 shows cross-sectional views of a conventional heat transfer device manufactured with a noncentral pin position illustrating pin position tolerances and areas of increased porous structure deformation;

[0038] Fig. 5 shows schematic side views of a heat transfer device according to an embodiment;

[0039] Fig. 6 shows schematic side views of a heat transfer device according to a further embodiment;

[0040] Fig. 7a shows schematic cross-sectional views of a heat transfer device according to an embodiment;

[0041] Fig. 7b shows a more detailed view of one of the cross-sectional views of figure 7a;

[0042] Fig. 8 shows schematic cross-sectional views of a heat transfer device according to an embodiment;

[0043] Fig. 9 shows schematic cross-sectional views of a heat transfer device according to an embodiment; Fig. 10 shows schematic cross-sectional views of a heat transfer device according to an embodiment illustrating the effect of manufacturing intolerances;

[0044] Fig. 11 shows schematic cross-sectional views of a heat transfer device according to an embodiment for addressing the manufacturing intolerances illustrated in figure 10;

[0045] Fig. 12 shows schematic cross-sectional views of a heat transfer device according to an embodiment;

[0046] Fig. 13 shows schematic cross-sectional views of a heat transfer device according to an embodiment;

[0047] Fig. 14 shows schematic cross-sectional views of a heat transfer device according to an embodiment including a further porous structure;

[0048] Fig. 15 shows schematic cross-sectional views of a heat transfer device according to an embodiment including a further porous structure;

[0049] Fig. 16a shows a schematic cross-sectional view of a heat transfer device according to an embodiment;

[0050] Fig. 16b shows schematic cross-sectional views of a heat transfer device according to an embodiment;

[0051] Fig. 17a shows schematic side views of a heat transfer device according to an embodiment;

[0052] Fig. 17b shows a table illustrating the performance of the heat transfer device of figure 17a; and Fig. 18 shows a flow diagram illustrating a method according to an embodiment for manufacturing a heat transfer device according to an embodiment.

[0053] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0054] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] In the following description, reference is made to the accompanying figures, which form part of the disclosure, which illustrate specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0056] For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.

[0057] Figures 1 and 2 show a schematic side view as well as cross-sectional views of a conventional heat transfer device, in particular anti-gravity heat pipe (AGHP), which are designed to transfer large thermal power over a relatively long distance and where the heater side is located higher than the cooler side with respect to the direction of gravity. According to the heat transfer device disclosed in WO2020252555A1 this may be achieved by providing a sequence of porous structure, e.g. powder zones with different pore sizes, optimized for each zone of the heat pipe and considering maximum liquid permeability, as is schematically illustrated in figure 1.

[0058] The conventional design shown in figure 1 can lead to a high temperature difference (dT) for the evaporator and the condenser, defined between the points Th-Tvapl and Tvap2-Tc accordingly. As will be appreciated, the temperature difference dT is caused by the large thickness of the porous structure, e.g. wick, selected for transferring large amounts of heat. To address this issue WO2020252555A1 further suggested a non-central, e.g. eccentric position of the pin for manufacturing, in particular sintering the porous structure, e.g. wick resulting in a non- symmetrical shape of the cross-section of the porous structure. In other words, as illustrated in figure 3, the thickness of the porous structure, for the heat pipe is locally decreased at the heater and cooler sides, so that the temperature difference dT of evaporator and condenser can be decreased.

[0059] However, the conventional design illustrated in figures 2 and 3 might lead to several issues, in particular during the manufacturing process, namely the difficulty to make a thin layer of the porous structure due to axial pin position tolerance and enormous deformation of the porous structure during flattening process. The areas of wick compression illustrated in figure 4 have a lower porosity and correspondingly lower permeability, while the areas of wick stretching may be randomly cracking and corresponding risk of continuity disruption of liquid flow. As the result, such a heat pipe has thermal performance deviation and may lead to a sub-optimal thermal performance.

[0060] As will be described in detail in the following, embodiments disclosed herein address the issues outlined above. Embodiments disclosed herein provide a heat transfer device, e.g. heat pipe with low temperature difference between the evaporator and the condenser and with a decreased deformation of the porous wick structure.

[0061] Figures 5 and 6 show schematic side views of a heat transfer device 100 according embodiments for transferring heat generated by a heat source 150 to a heat sink 160, for instance in the form of a heat radiator 160, via a fluid.

[0062] The heat transfer device 100 comprises an evaporation region 100a in thermal contact with the heat source 150, where the fluid in the liquid phase may evaporate. Moreover, the heat transfer device 100 comprises a condensation region 100b in thermal contact with the heat sink, where the fluid in the vapor phase may condense.

[0063] As illustrated in figures 5 and 6, the heat transfer device 100 may further comprise a housing 130 (herein also referred to as hermetic case 130), wherein the housing is configured to accommodate the evaporation region 100a and the condensation region 100b and to hermetically seal the fluid within the housing 130. As illustrated in figures 5 and 6 and as will be described in more detail below, along its longitudinal axis (which in operation may coincide with the axis along which the gravitational force is acting) the housing 130 may comprise one or more portions having the shape of a flattened hollow cylinder (such as the portions referred to as flat evaporator and flat condenser in figures 5 and 6) and / or one or more portions having the shape of a circular hollow cylinder, e.g. with a circular cross-section (such as the portion referred to as cylindrical central part and cylindrical condenser in figures 5 and 6).

[0064] As illustrated in figures 7a and 7b, the housing 130 may further accommodate a vapor channel 110 and a porous structure 120 of the heat transfer device 100 so that the porous structure 120 at least partially embeds, e.g. surrounds the vapor channel 110. The vapor channel 110 extends from the evaporation region 100a to the condensation region 110b of the heat transfer device 100 so that evaporated fluid may flow from the evaporation region 100a to the condensation region 100b through the vapor channel 110. The porous structure 120, which at least partially embeds the vapor channel 110, extends from the condensation region 100b to the evaporation region 100a of the heat transfer device 100 so that condensed fluid flows from the condensation region 100b to the evaporation region 100a through the porous structure 120 by action of capillary forces. The porous structure 120 may comprise sintered material, e.g. copper, formed of sintered particles, which particles may have an average particle size of about 40 to 500 microns before being sintered.

[0065] As already mentioned above, Figure 7a shows schematic cross-sectional views of the heat transfer device 100 according to an embodiment. For example, the lower left cross-sectional view of figure 7a shows the heat transfer device 100 prior to the sintering stage, where a pin 125 is inserted into the loose porous structure material for defining the porous structure 120 to be sintered, while the lower right cross-sectional view of figure 7a shows the heat transfer device 100 after the sintering stage and after a flattening process of the housing 130 as well as the sintered porous structure 120 contained therein. As will be appreciated, the lower left cross-sectional view of figure 7a corresponds to the cross-sectional view of the heat transfer device 100 after the sintering process (with the pin 125 removed), when no flattening is performed. The upper cross-sectional view of figure 7a illustrates the shape of the pin 125 as well as the deviations thereof from a cylindrical pin. Figure 7b shows a more detailed view of the lower right cross-sectional view of figure 7a showing the heat transfer device 100 after the sintering stage and after the flattening process of the housing 130 as well as the sintered porous structure 120 contained therein.

[0066] As illustrated in figures 7a and 7b, the cross-section of the vapor channel 110 transverse to the flow direction of the fluid through the vapor channel comprises a first portion 111 having the shape of an isosceles trapezoid with a first long base 11 la, an opposite second short base 11 lb as well as legs or lateral sides 111c and 11 Id. In the embodiment shown in figures 7a and 7b, the first long base 11 la as well as the legs or lateral sides 111c and 11 Id of the first portion 111 having the shape of an isosceles trapezoid are defined by the outer surface of the sintered porous structure 120. The at least partially flattened housing 130 defines a first wall 130a facing the heat source 150 or the heat sink 160 and a second wall 130b opposite to the first wall 130a, wherein the long base 11 la and the short base 11 lb of the first portion 111 of the cross-section of the vapor channel 110 extend parallel to the first wall 130a and / or the second wall 130b of the at least partially flattened housing 130. In the embodiment shown in figures 7a and 7b, the long base 11 la of the first portion 111 of the cross-section of the vapor channel 110 is closer to the first wall 130a of the at least partially flattened housing 130 than the second base 11 lb of the first portion 111 of the cross-section.

[0067] In the embodiment shown in figures 7a and 7b, the cross-section of the vapor channel 110 further comprises a second portion 113 having the shape of an isosceles triangle with a base 113a, a comer 113b opposite to the base as well as legs 113c,d. As will be appreciated, the base 113a of the second portion 113 of the cross-section of the vapor channel 110 coincides with the second short base 11 lb of the first portion 111 of the cross-section of the vapor channel 110, while the two legs 113c,d of the second portion 113 of the cross-section of the vapor channel 110 are defined by the outer surface of the sintered porous structure 120.

[0068] In the embodiment shown in figures 7a and 7b, the comer 113b of the second portion 113 of the cross-section of the vapor channel 110 opposite to the base 113a of the second portion 113 of the cross-section of the vapor channel 110 extends to the inner surface of the second wall 130b of the housing 130.

[0069] As will be appreciated, the shape of the first portion 111 and the second portion 113 of the crosssection of the vapor channel 110 results essentially from the shape of the pin 125 illustrated in the lower left cross-sectional view of figure 7a. According to embodiments disclosed herein, the crosssection of the pin 125 has a first “lower” portion having the shape of a circular segment, a second “middle” portion having the shape of an isosceles trapezoid, and a third “top” portion having the shape of an isosceles triangle. In the embodiment shown in figure 7a, a chord of the first portion extends at both ends to the inner surface of the housing thereby defining a pin with a wing-like structure. In comparison with a conventional fully cylindrical pin the pin 125 allows excluding the volume of the porous wick structure 120 from the most deformable regions, e.g. the compression and stretching regions illustrated in figure 4, which significantly decreases the strain of areas of leftover porous wick structure. Moreover, there are three contact sides regions between the pin 125 and the inner wall surface of the housing 130 allowing a self-positioning of the pin 125 and helping to achieve more stable geometry sizes, including the thin layer thickness during mass production. Furthermore, the pointed third portion shape forms the stress-free region for the adiabatic wick side, which significantly decreases the possibility of uncontrolled cracking.

[0070] Figure 8 shows a further embodiment allowing to increase the capillary heat transfer limit by enlarging the thickness of the porous wick structure 120 close to the adiabatic second wall 130b of the housing. In other words, in the embodiment shown in figure 8 the pin 125 as well as the second portion 113 no longer extend to the inner surface of the housing 130. As will be appreciated, during the flattening process the porous wick structure 120 will still experience less deformation due to the wing-shaped portion of the pin 125. The two points of contact provide an improved manufacturing size stability of the thin layer thickness as well as a controlled cracking in the center of adiabatic wick side, thanks to the pointed third portion of the pin 125. As will be appreciated, such a top shape creates a mechanical stress concentrator inside the porous structure 120 during the flattening process and makes crack originate in this area more preferable, compared to the side areas of the adiabatic porous wick structure 120. After appearing, the centered crack may be “relaxing” the porous wick structure 120 stretching stress and prevent other cracks from appearing.

[0071] Figure 9 shows a further embodiment for increasing the cross-sectional area of the porous wick structure 120 for enhancing the capillary heat transfer limit. As will be appreciated, in the embodiment shown in figure 9 the pin 125 comprises the first “lower” portion having the shape of a circular segment, and the second “middle” portion having the shape of an isosceles trapezoid but not the third “top” portion having the shape of an isosceles triangle (present in the embodiments of figures 7a, 7b and 8). Consequently, the cross-section of the vapor channel 110 transverse to the flow direction of the fluid through the vapor channel 110 comprises the first portion 111 having the shape of an isosceles trapezoid with the first long base I l la, the opposite second short base 111b as well as the legs or lateral sides 111c and 11 Id, but not the second portion 113 of the embodiments shown in figures 7a, 7b and 8. In an embodiment, the ratio of the distance B illustrated in figure 9, e.g. the distance between the second short base 11 lb of the first portion 111 of the cross-section of the vapor channel 110 and the inner surface of the second wall 130b of the housing 130, and the distance A illustrated in figure 9, e.g. the distance between the first long base 11 la of the first portion 111 of the cross-section of the vapor channel 110 and the inner surface of the first wall 130a of the housing 130, has a value between 2 and 10.

[0072] Due to technological limitations during flattening process, an axial rotation tolerance may appear, as illustrated in figure 10. As result, the side areas of the porous wick structure 120 may have a less effective mechanical / hydraulic contact between adiabatic and thin wicks. The formed “open side”, during the operation, may be filled by gas phase and affect the max heat transfer limit of the evaporator and increasing the condenser temperature difference by increasing the possibility of flooding. In the following some further embodiments are described addressing the manufacturing issue illustrated in figure 10. In the embodiment shown in figure 11 the pin 125 also has the “wing-shape” described above to solve the mechanical compression problem, but with a shorter chord of the first portion of the pin 125 (which compared with the previous embodiments no longer touches the inner surface of the housing 130). The smaller first portion of the pin 125 forms a gap, which is filled by porous structure material 120 during heat pipe manufacturing.

[0073] Figure 12 shows a further embodiment, which is a variant of the embodiment shown in figure 11. In comparison with the embodiment shown in figure 12, the pin 125 comprises the third pointed “top” portion having the shape of an isosceles triangle. Consequently, the cross-section of the vapor channel 110 transverse to the flow direction of the fluid through the vapor channel 110 comprises in addition to the first portion 111 having the shape of an isosceles trapezoid with the first long base 11 la, the opposite second short base 11 lb as well as the legs or lateral sides 111c and 11 Id, the second portion 113 having the shape of an isosceles triangle (also present in the embodiments shown in figures 7a, 7b and 8). This embodiment allows further improving the capillary transport stability of the porous wick structure 120 due to the pointed top part for adiabatic wick control cracking.

[0074] Figure 13 shows a further embodiment allowing to better control the geometrical stability of the thin layer during manufacturing. In the embodiment shown in figure 13 the heat transfer device 100 comprises a further porous structure 122 formed as a layer at least partially covering the inner surface of the housing 130 and at least partially embedding the porous structure 120. In an embodiment, the porous structure 120 and the further porous structure 122 may have different pore sizes. In the embodiment shown in figure 13, the further porous structure 122 (prior to the flattening process) has the shape of a hollow cylindrical tube with a circular cross section. A further embodiment is shown in figure 14, where the further porous structure 122 only partially covers the inner surface of the housing 130. In both embodiments of figure 13 and figure 14, the long base 11 la of the first portion 111 of the cross-section of the vapor channel 110 extends along an inner surface of the further porous structure 122 covering at least a portion of the inner surface of the housing 130.

[0075] As indicated in figure 14, to enhance the position tolerance for a first cylindrical pin (referred to as Pinl in figure 14) during the formation of the further porous wick structure 122 (referred to as Porous wick 1 in figure 14), the pin shape can have a step. The height of the step is determined by the cylinders shape of sizel and size2, which has a level difference, equal to the thin layer thickness A. The size2 may be equal for the inner wall of the housing 130 and for the outer surface of the Step on Pinl to have good assembly.

[0076] The step width can have various sizes C and for certain cases may be wide enough to provide stable and lowest possible Pinl position tolerance ±X & ±Y. On the other side, the width C should not be too big due to necessity of presence of a good interconnection between the porous structure 120 and the further porous structure 122 for liquid capillary flow and preventing the delamination risk after flattening and axial rotation tolerance influence. In an embodiment, the size C is an angular sector in the range from 10 to 180 degrees.

[0077] As well as the sintered powder wick, all of the described above embodiments may make use of different types of porous structures 120, like mesh, fiber or in combinations with each other. For example, a sintered powder wick structure, as illustrated in the embodiment of figure 15, may be made with a smooth, finned wall or coupled with various randomized roughness with a different average hydraulic pore size. This embodiment may be useful for preventing unexpected wick-wall delamination and cracks.

[0078] Figure 16a shows a further embodiment, which is a variant of the embodiments above, wherein the lower the first “lower” portion of the pin 125 does not have the shape of a circular segment, but the shape of a further isosceles trapezoid. Consequently, in portions of the housing 130, which are not flattened, the cross-section of the vapor channel 110 comprises in addition to the first portion I l l a further portion having the shape of a further isosceles trapezoid 117 with a long base 117a and a short base 117b. In the embodiment shown in figure 16a, the long base 117a of the further isosceles trapezoid 117 coincides with the long base 11 la of the first portion 111 of the cross-section of the vapor channel 110.

[0079] Figure 16b shows another example for the cross-section of a heat transfer device.

[0080] Figure 17a shows schematic side views of the heat transfer device 100 according to an embodiment and figure 17b shows a table illustrating the performance of samples 7 to 12 the heat transfer device 100 of figure 17a in comparison with samples 1 to 6 of conventional heat transfer devices manufactured with a cylindrical pin. Figure 17a also indicated the positions of temperature sensors T0-T4 used for determining the values provided in the table of figure 17b. As will be appreciated, the temperature difference for the heat transfer device 100 according to embodiments disclosed herein between two ends of heat pipe 100 T0-T4, is 7 7.71 °C, for a heating power of 60W in anti- gravity orientation. Comparing with the conventional cylindrical pin, the temperature difference between T0-T4 is in the 1 H15.1°C range.

[0081] Figure 18 shows a flow diagram illustrating steps of a method 1800 for manufacturing the heat transfer device 100 for transferring heat generated by a heat source 150 to a heat sink 160 via a fluid. As already described above, the heat transfer device 100 comprises an evaporation region 100a configured to evaporate the fluid in the liquid phase and a condensation region 100b configured to condense the fluid in the vapor phase. Moreover, the heat transfer device 100 comprises a vapor channel 110 extending from the evaporation region 110a to the condensation region 110b so that evaporated fluid flows from the evaporation region 110a to the condensation region 110b through the vapor channel 110. The heat transfer device 100 further comprises a porous structure 120 at least partially embedding, e.g. defining the vapor channel 110 and extending from the condensation region 110b to the evaporation region 110a so that condensed fluid flows from the condensation region 110b to the evaporation region 110a through the porous structure 120 by action of capillary forces. The method 1800 comprises a step 1801 of sintering the porous structure 120 such that the cross-section of the vapor channel 110 comprises a first portion 111 having the shape of an isosceles trapezoid.

[0082] In an embodiment, the sintering step 1801 may further comprise: providing an atmosphere containing at least one of nitrogen gas and argon gas and a sintering temperature ranging from 860 degrees Celsius to 890 degrees Celsius The sintering step may have a duration in the range of 1.2 h to 2.0 h, advantageously in the range of 1.5 h to 2.0 h.

[0083] In an embodiment, the method 1800 further comprises: before the sintering step 1801: a step of placing a filling material in a space corresponding to the vapor channel 110, and after the sintering step 1801: a step of removing the filling material. In an embodiment, the filling material is a pin.

[0084] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0085] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

[0086] The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

[0087] In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

CLAIMS1. A heat transfer device (100) for transferring heat generated by a heat source ( 150) to a heat sink (160) via a fluid, wherein the heat transfer device (100) comprises: an evaporation region (100a) configured to evaporate the fluid in the liquid phase; a condensation region (100b) configured to condense the fluid in the vapor phase; a vapor channel (110) extending from the evaporation region (100a) to the condensation region (110b) so that evaporated fluid flows from the evaporation region (100a) to the condensation region (100b) through the vapor channel (110); and a porous structure (120) at least partially embedding the vapor channel (110) and extending from the condensation region (100b) to the evaporation region (100a) so that condensed fluid flows from the condensation region (100b) to the evaporation region (100a) through the porous structure (120) by action of capillary forces, wherein the cross-section of the vapor channel (110) comprises a first portion (111) having the shape of an isosceles trapezoid.

2. The heat transfer device ( 100) of claim 1 , wherein the heat transfer device (100) comprises a housing (130), wherein the housing (130) is configured to accommodate the evaporation region (100a), the condensation region (100b), the vapor channel (110) and the porous structure (120) so that the porous structure (120) at least partially embeds the vapor channel (110), wherein at least a portion of the housing (130) has the shape of a flattened hollow cylinder.

3. The heat transfer device (100) of claim 2, wherein the housing (130) defines a first wall (130a) facing the heat source (150) or the heat sink (160) and a second wall (130b) opposite to the first wall (130a) and wherein a first base (11 la,b) and a second base (11 lb, a) of the first portion (111) of the cross-section of the vapor channel (110) extend parallel to the first wall (130a) and / or the second wall (130b) of the housing (130).

4. The heat transfer device ( 100) of claim 3 , wherein the first base ( 111 a,b) of the first portion ( 111 ) of the cross-section of the vapor channel ( 110) is closer to the first wall (130a) of the housing (130) than the second base (11 lb, a) of the first portion (111) of the cross-section.

5. The heat transfer device (100) of claim 4, wherein a ratio of a distance B between the second base (11 lb, a) of the first portion (111) of the cross-section of the vapor channel (110) and an inner surface of the second wall (130b) of the housing (130) and a distance A between the firstbase (11 la,b) of the first portion (111) of the cross-section of the vapor channel (110) and an i surface of the first wall (130a) of the housing (130) has a value between 2 and 10.

6. The heat transfer device (100) of any one of claims 3 to 5, wherein the cross-section of th vapor channel (110) further comprises a second portion (113), wherein the second portion (11; of the cross-section of the vapor channel (110) has the shape of an isosceles triangle and wherei n a base (113a) of the second portion (113) of the cross-section of the vapor channel (110) coincides with the second base (11 lb, a) of the first portion (111) of the cross-section of the vapor channel (HO).

7. The heat transfer device (100) of claim 6, wherein the comer (113b) of the second portic (113) of the cross-section of the vapor channel (110) opposite to the base (113a) of the secor d portion (113) of the cross-section of the vapor channel (110) extends to the inner surface of th i*e second wall (130b) of the housing (130).

8. The heat transfer device (100) of any one of claims 3 to 7, wherein a further portion housing (130) has the shape of a hollow cylinder with a circular cross section and wherein the further portion of the housing (130) the cross-section of the vapor channel (110) has a furth I portion having the shape of a circular segment (115) or a further isosceles trapezoid (117).

9. The heat transfer device (100) of claim 8, wherein a chord (115a) of the further portion of the cross-section of the vapor channel (110) shaped as a circular segment (115) or a base (117 a) of the further portion of the cross-section of the vapor channel (110) shaped as a further isoscel es trapezoid (117) overlaps at least partially with a first base (11 la) or a second base (11 lb) of t ie first portion (111) of the cross-section of the vapor channel (110).

10. The heat transfer device (100) of claim 8 or 9, wherein the further portion of the s- section of the vapor channel (110) shaped as a circular segment (115) or as a further isosce es trapezoid (117) is located closer to a side of the housing (130) facing the heat source (150) or the heat sink (160) than the first portion (111) of the cross-section of the vapor channel (110).

11. The heat transfer device ( 100) of claim 10, wherein the arc ( 115b) of the further portion of the cross-section of the vapor channel (110) shaped as the circular segment (115) is located closer to the side of the housing (130) facing the heat source (150) and / or the heat sink (160) than lhe chord (115a) of the further portion of the cross-section of the vapor channel (110) shaped as lhe 2circular segment ( 115) or wherein a short base (117b) of the further portion of the cross-section the vapor channel (110) shaped as the further isosceles trapezoid (117) is located closer to the of the housing (130) facing the heat source (150) and / or the heat sink (160) than aof the further portion of the cross-section of the vapor channel (110) shaped as thetrapezoid (117).

12. The heat transfer device ( 100) of claim 11 , wherein the chord ( 115a) of the further portic n of the cross-section of the vapor channel (110) shaped as the circular segment (115) extends wf both of its ends to an inner surface of the housing (130) or wherein a long base (117a) of the portion of the cross-section of the vapor channel (110) shaped as the further isoscelesnd(117) extends with both of its ends to an inner surface of the housing (130).

13. The heat transfer device (100) of any one of the preceding claims, wherein the heat transfer device (100) comprises a further porous structure (122), wherein the further porous structure (122) is formed as a layer at least partially covering the inner surface of the housing (130) and at least partially embedding the porous structure (120).

14. The heat transfer device (100) of claim 13, wherein a base (l l la,b) of the first (111) of the cross-section of the vapor channel (110) extends along an inner surface of the :r porous structure (122).

15. An electronic assembly comprising a heat source (150), a heat sink (160), and the heat transfer device (100) of any one of the preceding claims wherein the evaporation region (100a) is in thermal contact with the heat source (150) and the condensation region (100b) is in thermal contact with the heat sink (160).

16. A method (1800) for manufacturing a heat transfer device (100) for transferring heat generated by a heat source (150) to a heat sink (160) via a fluid, wherein the heat transfer device (100) comprises: an evaporation region (100a) configured to evaporate the fluid in the liquid phase; a condensation region (100b) configured to condense the fluid in the vapor phase; a vapor channel (110) extending from the evaporation region (100a) to the condensation regio »ni (100b) so that evaporated fluid flows from the evaporation region (100a) to the condensation region (100b) through the vapor channel (110); anda porous structure (120) at least partially embedding the vapor channel (110) and extending ft the condensation region (100b) to the evaporation region (100a) so that condensed fluid flo wrs from the condensation region (100b) to the evaporation region (100a) through the porous struct ne (120) by action of capillary forces, wherein the method (1800) comprises sintering (1801) the porous structure (120) such that :he cross-section of the vapor channel (120) comprises a first portion (111) having the shape of an isosceles trapezoid.

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