CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims priority to German patent application DE 10 2012 102 959.8, entitled "Umgossene Heat-Pipe", and filed on April 4, 2012.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of integrating a heat pipe into a wall made of a diecasting alloy and to a wall made of a diecasting alloy comprising an integrated heat pipe, which may be produced according to the method of the present invention. Further, the present invention relates to a housing comprising a wall of the present invention with an integrated heat pipe.

A heat pipe is to be understood as a hollow body whose interior is filled with a working fluid, which is hermitically sealed, which is often elongated, and which, in operation, extends between a lower heat source to an upper heat sink. In the area of the heat source, the liquid working fluid is evaporated so that evaporation heat is transferred to the working fluid. Together with the vaporous working fluid, the evaporation heat ascends up to the heat sink, and by means of condensation of the working fluid this heat is transferred to the heat sink as condensation heat. The re-liquefied working fluid flows downwards back to the heat source. This operation of a heat pipe allows for transferring larger amounts of heat across smaller differences in temperature between the heat source and the heat sink than could be transferred with solid, liquid or gaseous heat conductors which do not undergo a phase transition and which are not actively circulated in case of liquid or gaseous heat conductors, even if these heat conductors are of a high thermal conductivity. A heat pipe is a purely passively operated heat transfer device without any mechanical components moved for circulating the working fluid.

Various housings, like for example housings of electric and electronic devices, are not only used for protecting their content but also for removing heat generated in their interior. For this purpose, an electronic component which generates much lost heat is sometimes directly coupled to a metal housing to transfer this lost heat to the housing and to dissipate the heat from there into the surroundings of the housing. Under such conditions a situation may quickly occur in which the housing, in the area of the thermal coupling of the component, permanently has a higher temperature than remote from the thermal coupling of the component. One means of counteracting this situation is to provide a heat sink in the area of the thermal coupling by means of forming cooling ribs or the like at the backside of the housing. Often, however, the housing as such would be sufficient as a heat sink, if the lost heat could be distributed over a larger area of the housing, like for example into areas to which no electric or electronic components are coupled. For this purpose, for example, it is of interest to integrate a heat pipe into a wall of a housing, which provides for such a distribution of heat over the extension of the housing.

BACKGROUND ART

A method of integrating a heat pipe into a wall of a radiator is known from US 6,085,830. This document primarily concerns the formation of a heat sink by a diecasting process, wherein cooling rips are arranged as pre-manufactured parts within a diecasting mold prior to casting on liquid diecasting alloy in which the cooling ribs are anchored at one of their ends. US 6,085,830 also describes the manufacture of a heat sink comprising a heat pipe within its basis. According to this method, a hollow body made of copper and having the shape of a truncated square pyramid is arranged within a diecasting mold in such a way that a fill-in nipple extending from the basis of the hollow body in a lateral direction terminates in a recess in the wall of the diecasting mold. Then, the liquid diecasting alloy is casted on the hollow body, and the hollow body is embedded within the diecasting alloy, the fill-in nipple remaining free. After taking the component manufactured in this way out of the diecasting mold, the interior of the hollow body, via the fill-in nipple, is filled with water as a working fluid. Before the interior is hermetically sealed by closing the fill-in nipple, the air remaining above the working fluid is displaced by evaporating a part of the working fluid. For this purpose, the entire component including the molded-in heat pipe has to be heated up. The thermal coupling of the heat source to the heat pipe is provided via a purposefully thin-walled area of the diecasting alloy at the tip of the truncated pyramid.

A further method of integrating a heat pipe into a wall is known from US 6,321 ,452. In this method, a copper pipe is arranged within a groove of a diecasting mold. Then the copper pipe is molded in a diecasting alloy to form a heat sink, wherein at least one open end of the copper pipe extends out of the diecasting alloy of the heat sink. Via this open end, the interior of the copper pipe is later filled with the working fluid of the heat pipe, and after displacing air remaining above the working fluid, the interior is hermetically sealed. For this purpose, the entire component including the molded-in heat pipe has to be heated up.

Further methods of integrating a heat pipe into a wall or a radiator by which a particularly well thermal coupling of the heat pipe to the wall or the radiator is achieved are known from US 2001/0047590 A1 and US 2004/0074633 A1 . Again, the interior of the heat pipe is filled with the working fluid of the heat pipe and hermetically sealed after molding the hollow body of the heat pipe in the diecasting alloy. In this context it is reported in US 2001/0047590 A1 that there is a severe risk of damaging a heat pipe during the step of diecasting as, if its hollow body cracks or breaks, the working fluid emerges and the heat pipe will thus not function properly.

A method of manufacturing a metallic diecasting product into which a hollow body is embedded is known from DE 30 14 456 A1 . Here, a molten metal is injected into a cavity between two metal diecasting mold halves, in which the hollow body is arranged. A pressure- resistant medium is located in the hollow body, and the hollow body is tightly closed prior to injecting the molten metal into the diecasting mold to avoid that the hollow body is compressed due to the high outer pressure of the molten material. The hollow body is closed at an open end which is located outside the cavity formed between the two metallic diecasting mold halves and which is thus not molded-in by means of a sealing plug which is preferably supported in a movable way to provide a constant internal pressure in the hollow body despite the thermal expansion of the pressure-resistant medium. The pressure-resistant medium may be a liquid which is placed into the interior of the hollow body together with a gas. After removing the diecasting product out of the cavity between the diecasting mold halves, and after removing the sealing plug from the hollow body, the pressure-resistant medium is released from the hollow body.

There still is a need for a method of integrating a heat pipe into a wall which is applicable in a cost-efficient way and which allows for a more advanced integration of a heat pipe into a wall made of a diecasting alloy than possible up to now.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a method of integrating a heat pipe into a wall made of a diecasting alloy. The method comprises filling an interior of the hollow body with a working fluid via a filling area of the hollow body and permanently hermetically sealing the interior by sealing the filling area; only afterwards locating the already permanently hermetically sealed hollow body within a cavity of a diecasting mold; and casting liquid diecasting alloy on the sealed hollow body in the cavity to mold the sealed hollow body in the diecasting alloy.

In this context, the expression that the interior of the hollow body is permanently hermetically sealed by sealing the filling area is to be understood such that the interior is permanently hermetically sealed by at least sealing the filling area. Thus, the expression particularly covers the following situations:

(i) Directly after its production, the hollow body of the heat pipe only comprises one opening. This may, for instance, be the case, if the hollow body is a deep-drawn component. Here, the filling area is represented by said one opening, and this one opening has to be permanently hermetically sealed after filling the interior of the hollow body with the working fluid, (ii) Directly after its production, the hollow body of the heat pipe comprises more than one, particularly two openings. Typically, this is the case, if the hollow body is cut to length from a tube shaped stock. Here, one of the two openings is already permanently hermetically sealed prior to filling the interior of the hollow body with the working fluid. The other one of the two openings then is the filling area only sealed after filling the interior with working fluid. In this case (ii) the permanent hermetical sealing of the interior of the hollow body is achieved not exclusively - but also - by permanently hermetically sealing the filling area.

In another embodiment, the present invention relates to a wall made of a diecasting alloy with an integrated heat pipe which is at least partially embedded in the diecasting alloy. The heat pipe comprises a hollow body whose hermetically sealed interior has been filled with a working fluid via a filling area of the hollow body, wherein the filling area is molded in the diecasting alloy.

In a further embodiment, the present invention relates to a housing comprising a wall of the previous embodiment of the present invention.

Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and the detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims. BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views.

Fig. 1 shows a part of a wall with an integrated heat pipe in a plane view.

Fig. 2 is a vertical section through the part of the wall according to Fig. 1.

Fig. 3 shows a part of another wall according to the present invention comprising an integrated heat pipe.

Fig. 4 shows a vertical section through a branch of the heat pipe of the wall according to

Fig. 3.

Fig. 5 illustrates the materials between the interior of the heat pipe and a surface of the wall according to Fig. 3 and 4 in an enlarged view.

Fig. 6 shows an alternative distribution of the materials between the interior of the heat pipe and a surface of the wall; and.

Fig. 7 illustrates the arrangement of a heat pipe within a diecasting tool prior to casting a diecasting alloy on the heat pipe.

DETAILED DESCRIPTION

In a method of integrating a heat pipe into a wall made of a diecasting alloy according to the present invention, at first, an interior of a hollow body of the heat pipe is filled with a working fluid via a filling area and permanently hermetically sealed by also sealing this filling area. This step includes that any air is displaced out of the interior by heating the working fluid and/or applying an underpressure to the working fluid to partially evaporate the working fluid. In this step, only the hollow body with the working fluid arranged therein needs to be heated up and/or subjected to the underpressure. Only the already hermetically sealed hollow body is arranged in a diecasting mold. Afterwards, the liquid or molten diecasting alloy is casted on the hollow body already filled with the working fluid and hermetically sealed. During this step, the typical operational pressure of diecasting of several 10 Megapascal may already be applied when injecting the diecasting alloy, i.e. when the hollow body and the working fluid of the heat pipe located in the hollow body are heated up to the temperature of the liquid diecasting alloy, or only afterwards, when the diecasting alloy has already been injected into the diecasting mold. In any case, it is surprisingly easy to dimension the hollow body and its hermetic seal in such a way that they withstand the maximum pressure difference dropping over them at the maximum temperature at which this maximum pressure difference may occur.

In the method according to the present invention, this maximum pressure difference never exceeds the pressure difference between the internal pressure which arises in the interior of the hollow body at the temperature of the liquid diecasting alloy, on the one hand, and the normal or atmospheric pressure in the surroundings of the diecasting mold, on the other hand. If the hollow body and the hermetic seal of the hollow body withstand this pressure difference at the temperature of the liquid diecasting alloy they will also withstand all pressure differences actually arising in the method according to the present invention.

A suitable dimensioning of the hollow body and the working fluid enclosed in the hollow body is required so that the heat pipe withstands the internal pressure arising when being molded- in. Due to the comparatively high temperature of the diecasting alloy (typically 670°C when employing an aluminum diecasting alloy), the critical point of the working fluid is generally exceeded when the heat pipe is molded-in. As a consequence, the internal pressure of the heat pipe arising at the temperature of the diecasting alloy essentially depends on the kind and the relative amount of the working fluid employed. Here, the ratio of the amount of substance of the working fluid (e. g. expressed as the number of moles of the working fluid, n^) to the interior volume V _h b of the hollow body is particularly relevant. The larger the amount of substance, the larger is the internal pressure arising. With a given interior volume V _hb , the maximum internal pressure arising may thus be adjusted by means of the amount of substance r of the working fluid enclosed in the hollow body. Particularly, the amount of substance r of the working fluid and the wall thickness of the hollow body may be adjusted to each other in a simple way, and the result of this dimensioning may be verified in a simple test. For example, a completely ready-for-use heat pipe may be subjected to the temperature of the diecasting alloy even prior to being molded-in, i.e. as long as it is not yet molded-in, and then checked for the occurrence of any damages. Particularly, a correctly dimensioned heat pipe should not suffer any damages during such a tempering, neither at the wall of the hollow body (like for example by large scale bursts or by incident micro cracks), nor at the seals of the hollow body. Minor deformations of the heat pipe during the test may, however, be tolerated, if they do not cause any leaks of the heat pipe.

With typical boundary conditions (interior volume of the hollow body V _hb = 19.2 ml; working fluid = water; number of moles of the working fluid r = 0.1 18 mol), the internal pressure arising may definitely amount to some 10 MPa (some 100 bar). For example, the internal pressure with water as the working fluid and with a typical processing temperature during diecasting of 670°C is about 42 MPa under the above boundary conditions. The internal pressure is thus, however, not significantly higher than the typical operating pressure in diecasting of 37 MPa to which a not yet hermetically sealed hollow body of a heat pipe is also subjected during diecasting from the outside. In practice, it is thus sufficient to slightly increase the wall thickness of the hollow body above the usual dimensions of integrated heat pipes and to strengthen the hermetic sealing of the hollow body accordingly to be able to execute the method according to the present invention without problems due to the high internal pressure in the interior of the hollow body of the heat pipe which result during diecasting. With a sufficient dimensioning of the wall thickness of the hollow body and the hermetic sealing, there is particularly no danger of damages to the hollow body or its hermetic sealing during diecasting, which endanger the later function of the heat pipe. Due to the method according to the present invention, there is no need to heat up the entire component made by diecasting and comprising the wall with the integrated heat pipe for properly filling the interior of the hollow body of the heat pipe with the working fluid, or to subject the entire component to an underpressure. Thus, in the method according to the present invention, filing the interior of the hollow body with the working fluid is comparatively easy due to the small size and weight of the hollow body to which no diecasting alloy is yet attached. Additionally, the diecasting mold may be of a simple construction, as the hollow body of the heat pipe may be completely located within the diecasting mold, and no fill-in nipple or pipe end has to be led out of the cavity of the diecasting mold to avoid the intrusion of diecasting alloy into the interior of the hollow body.

In the method according to the present invention, the sealed filling area of the hollow body may be molded in the diecasting alloy within the diecasting mold and thus permanently protected against damages. It is not unusual that heat pipes have their sealing area at their lowest or highest point, i.e. there where they are thermally coupled to a heat source or heat sink. This thermal coupling is made easier by molding in the sealed filling area in such a way that a defined contact area for the heat source or heat sink is formed.

In the method of the present invention, typically no portion of the hollow body of the heat pipe extends beyond the cavity of the diecasting mold, because there is no need to avoid that the diecasting alloy gets into the still open interior of the hollow body as this interior has already been hermetically sealed before. To nevertheless position the hollow body within the diecasting mold in a defined way and to thus also define the position of the heat pipe within the wall manufactured within the diecasting mold, the hollow body may be aligned with supporting areas of the diecasting mold within the diecasting mold. In these supporting areas, the hollow body may directly reach up to the surface of the wall manufactured in the diecasting mold. It is, however, also possible to mount supporting elements to the hollow body in a fixed way, via which the hollow body is aligned with the supporting areas in the diecasting mold. The hollow body itself may then, except for the mounting areas of the supporting elements, be completely molded in the diecasting alloy. This complete molding-in of the hollow body, however, is not mandatory. Instead, areas of the hollow body may purposefully remain free at the surface of the wall manufactured in the diecasting mold.

In case of a hollow body having the shape of a pipe section, both of its ends may be molded in the diecasting alloy within the diecasting mold.

If the hollow body is made of a copper alloy and molded in an aluminum diecasting alloy within the diecasting mold, a full surface coupling of the diecasting alloy to the hollow body without inclusion of air is easily ensured as aluminum and copper are very well mixable and as, as a result, the aluminum diecasting alloy wets the hollow body made of the copper alloy well. Due to being made of copper, the hollow body has a better thermal conductivity than any usual diecasting alloy, even than an already well thermally conductive aluminum diecasting alloy. For this reason, a comparatively high wall thickness of the hollow body of the heat pipe is no disadvantage with regard to the thermal coupling of the heat pipe. With a same overall thickness of the material between the interior of the heat pipe and a heat source or heat sink, the thermal coupling is the better, the more of the material between the interior and the heat source or heat sink is copper and the less this material consists of aluminum or any other diecasting alloy. In other embodiments of the present invention, a zinc or magnesium diecasting alloy may be used in combination with a hollow body made of copper. The diecasting alloy may further also be a copper diecasting alloy or a silicone tombac diecasting alloy.

As already supported by data above, water as the working fluid of the heat pipe is not critical in the method according to the present invention as the maximum internal pressure of the heat pipe resulting at the usual temperature of the liquid diecasting alloy does not significantly exceed the operational pressure of diecasting. However, ammonia may also be used as the working fluid, for example. With the same processing temperature and the same ratio of number of moles of the working fluid to the interior volume of the hollow body, the pressure of ammonia is about 10 MPa higher than the pressure of water, but it may thus still be governed by a proper dimensioning of the hollow body and the hermetic sealing of the interior of the heat pipe without problems.

In a wall according to the present invention made of a diecasting alloy with an integrated heat pipe which is at least partially embedded into the diecasting alloy, wherein the heat pipe comprises a hollow body whose hermetically sealed interior has been filled with a working fluid, a sealing area of the hollow body is molded in the diecasting alloy. In case of a pipe section shaped hollow body, typically both of its ends are molded in the diecasting alloy.

The hollow body itself or supporting areas protruding from it may reach up to the surface of the wall. The hollow body preferably consists of a copper alloy, whereas the diecasting alloy typically is an aluminum diecasting alloy. The working fluid of the heat pipe is ammonia or water, for example. With the above indicated ratio of the number of moles of the working fluid water to the interior volume of the hollow body, a wall thickness of a pipe section shaped hollow body with an outer diameter of up to about 13 mm is preferably at least 2.0 mm, even more preferably at least 3.0 mm, wherein it is decisive to which indication of the tenth of millimeter the actual wall thickness is rounded. Further, these dimensions relate to the wall thickness of a pipe section shaped hollow body made of technical copper, to a temperature of the liquid diecasting alloy of 670°C and to an operational pressure of diecasting of 37 MPa. With other materials, other shapes of the hollow body, other working fluids, other ratios of the number of moles of the working fluid to the interior volume of the hollow body or other diecasting parameters, these dimensions have to be adjusted appropriately.

A housing including a wall according to the present invention into which a heat pipe is integrated may particularly be provided for electric or electronic devices, wherein a heat source is thermally coupled to the wall in a lower area of the heat pipe, and wherein a heat sink is formed by the wall in an upper area of the heat pipe or coupled to the wall. Such a pronounced heat sink, however, is no mandatory feature of the housing of the present invention. Instead, it can be sufficient that the heat pipe distributes the heat energy over the area of the housing so that the housing itself serves as a large area heat sink. When the heat energy is distributed over the area of the housing, a given housing area can more efficiently dissipate a given quantity of generated lost heat due to the fact that a significantly larger part of the housing area contributes to the dissipation of said lost heat. This is different to a case, in which the given housing area comprises several hot spots in addition to a comparatively cold remainder of the housing area. In this case only the small sized hot spots of the housing area contribute to the dissipation of the lost heat whereas the colder areas do not (significantly) contribute to said dissipation.

Now referring in greater detail to the drawings, Figs. 1 and 2 show a part of a wall 1 in which a heat pipe 2 is integrated into the wall 1. The heat pipe 2 comprises a pipe section shaped hollow body 3 whose interior 4 is filled with a working fluid 5 and hermetically sealed. The working fluid 5 is a substance, like for example water or ammonia, which is a liquid under normal pressure in the operational temperature range of the heat pipe 2. This liquid 6, however, is only found in the lower area of the hollow body 3, whereas the upper area of the hollow body 3 is filled with vapor 7 of the working fluid 5. In the normal temperature range of the heat pipe 2, the interior 4 is at an underpressure as compared to the normal pressure in the surroundings 8.

The heat pipe 2 is here integrated into the wall 1 in that the hollow body 3 is molded in a diecasting alloy 9. The diecasting alloy 9 makes up the essential structure of the wall 1 and essentially encloses the hollow body 3 in all directions. Particularly, the diecasting alloy 9 is an aluminum diecasting alloy, whereas the hollow body 3 of the heat pipe 2 is normally made of a copper alloy, like for example technical copper. Copper comprises an even better thermal conductivity than aluminum and makes up a metallic continuity with aluminum at its boundary. Due to the good miscibility and the corresponding good wetting properties of both materials with regard to each other, inclusions of air at the boundary which may lead to a deterioration of the heat transfer between the heat pipe 2 and the diecasting alloy 9 are avoided. Not enclosed by the diecasting alloy 9 in all directions are supporting elements 10 which protrude from the hollow body 3 up to the surface 1 1 of the wall 1 and which served for aligning the hollow body 3 within a diecasting form during formation of the wall 1 in the diecasting mold. These supporting elements had been previously connected to the hollow body 3 in a fixed way. The connection between the supporting elements 10 and the hollow body 3 may be either a force-fitting, like for example via a metal spring receiving or at least partially enclosing the hollow body 3, or via metallic continuity, like for example via a soldered connection.

The pipe section shaped hollow body 3 is here enclosed by the diecasting alloy 9 at both of its ends 12. As the interior 4, at least at one of the ends 12 (i. e. in a filling area), is only sealed after being filled with the working fluid 5, this is only achievable in that the interior 4 is already filled with the working fluid 5 and permanently hermetically sealed prior to forming the wall 1 in the diecasting mold. In turn, this means that the hollow body 3 including its hermetic sealing has to be designed such that it both withstands the internal pressure in the interior 4 arising at the temperature of the diecasting due to the working fluid 5 typically being heated beyond its critical point, and the processing pressure of the diecasting.

The heat pipe 2 in the wall 1 is particularly suited for transferring heat from a heat source close to the lower end 12 to a larger area of the wall 1 or to a heat sink formed by the wall 1 or coupled to the wall 1 close to the upper end 12 of the heat pipe 2.

The wall 1 partially depicted in Figs. 3 and 4 also comprises an integrated heat pipe 2. The hollow body 3 of this heat pipe is also of pipe section shape but bent in an U-shape, both of its ends 12 being located at the top of the heat pipe 2. These two ends 12 as well as a lower middle section 14 of the hollow body 3 are also completely molded in the diecasting alloy 9 here. In between, the hollow body 3 is free at the surface 1 1 of the wall 1. These free sections may be used for aligning the hollow body 3 in a diecasting mold used for manufacturing the wall 1. Further, Figs. 3 and 4 show a coupling surface 15 formed above the lower middle section 14 of the hollow body and provided for a heat source not depicted here, and a heat sink 17 made of cooling ribs 16 which protrude from the opposing surface 13 of the wall 1 to dissipate heat into the surroundings 8 which has been removed from the heat source by the heat pipe 2. The cooling rips may either be formed by the diecasting process itself or they may be preformed cooling rips which are inserted in recesses within the diecasting mold and fixed to the wall 1 during the formation of the wall 1 by the diecasting process.

Figs. 5 and 6 illustrate different distributions of materials between the interior 4 of the heat pipe 2, which is only depicted partially here, and the coupling surface 15 for a heat sink and/or a heat source. In Fig. 4 the materials between the interior and the coupling surface 15 consist by one half of copper of the hollow body 3 and by one half of the diecasting alloy 9 of the wall 1. This distribution may be the result of a comparatively high wall thickness of the hollow body 3 which is necessary so that the hollow body 3 withstands the high pressures arising during manufacture of the wall 1. Fig. 6 illustrates a section of a wall 1 with the same overall thickness of the materials between the interior 4 and the coupling surface 15 with a hollow body 3 of copper having a lower wall thickness and a correspondingly higher thickness of the diecasting alloy 9. This ratio of thicknesses may occur when a not yet filled hollow body according to the prior art is molded in the diecasting alloy 9 except for a filling nipple, which thus has not to withstand such high pressures during manufacture of the wall. As a result, the thermal connectivity between the interior 4 and the coupling surface 15 according to Fig. 6 is worse than the corresponding thermal conductivity according to Fig. 5 as the copper of the hollow body 3 has a higher thermal conductivity than the diecasting alloy 9. I.e. the higher wall thickness of the hollow body 3 needed for stabilizing the heat pipe 2 during molding it in the aluminum diecasting alloy is no disadvantage but even results in a better thermal coupling of the coupling surface 15 to the interior 4 of the heat pipe 2.

Fig. 7 illustrates the arrangement of the heat pipe 2, i.e. of the hollow body 3 already filled with working fluid 5 via a filling area (typically located at one of its ends) and permanently hermetically sealed by sealing the filling area, within a diecasting mold 18 comprising two mold halves 19 and 20. Within the cavity 22 of the diecasting mold 18, the hollow body 3 is aligned by means of supporting elements 10 which are fixed to the hollow body 3 and which may engage in corresponding recesses 23 in the mold half 19, and by means of a supporting area 21 of the mold half 20. In this way, the hollow body 3 is arranged in a defined way in the wall 1 formed when liquid diecasting alloy 9 solidifies after being injected into the cavity 22.

With an outer diameter of the pipe section shaped hollow body 3 of 12.7 mm and a maximum processing temperature during diecasting of 670°C and with the further boundary conditions of a hollow body volume V _h b = 19.2 ml and a number of moles of the working fluid r = 0.1 18 mol, an internal pressure of 42 MPa results in case of the working fluid being water. When using technical copper for the hollow body 2 with a strength value of 125 N/mm ² , a security factor of 1.1 as well as a load factor in the area of welded seams of 1 , a wall thickness of the hollow body of 2.0 mm is required to withstand an internal pressure of 42 MPa at the temperature of 670°C. This dimensioning of the wall thickness is only slightly thicker than that one which is required to withstand the operational pressure of diecasting of 37 MPa.

Many variations and modifications may be made to the preferred embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined by the following claims.

LIST OF REFERENCE NUMERALS wall

heat pipe

hollow body

interior

working fluid

liquid

vapor

surroundings

diecasting alloy

supporting element

surface

end

surface

middle section

coupling surface

cooling rib

heat sink

diecasting mold

mold half

mold half

support area

cavity

recess