Abstract:
A vapor chamber, comprising a lower shell and an upper shell, wherein at least one gas-tight and liquid-tight intermediate area is formed between lower shell and upper shell, in which area a fluid working medium is accommodated and a porous material that interacts with the fluid is arranged; the porous material is in contact, at least in some areas, with the upper shell and/or the lower shell, but does not completely fill the at least one intermediate area, forming at least one cavity-like vapor gap. The upper shell of the vapor chamber has on its top side a plurality of indentations which are distributed over the surface thereof, extend towards the lower shell and act as sample receptacles, into which samples to be temperature-controlled can be introduced from the top using the vapor chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation under 35 U.S.C. §120 of International Application PCT/EP2012/004857, filed Nov. 23, 2012, which claims priority to DE Application 10 2011 119 174.0 filed Nov. 23, 2011, the contents of each of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a vapor chamber comprising a lower shell and an upper shell, wherein at least one gas-tight and liquid-tight intermediate space is formed between lower shell and upper shell, in which space a fluid working medium is received and a porous material cooperating with the fluid working medium is disposed, wherein the porous material contacts the upper shell and/or the lower shell at least in some zones, albeit without completely filling the at least one intermediate space but instead forming at least one cavity-like vapor gap. 
       BACKGROUND 
       [0003]    Such vapor chambers, which are constructed in the manner of a so-called heat pipe, which usually has an expansive and flat shape, and which depend on the functional principle thereof, are sufficiently familiar from the prior art, for example from WO 2005/114084 A1, and are known to have very good thermal conductivity. Furthermore, FIG. 7 of U.S. Pat. No. 36,890,189 also shows a vapor chamber of the type mentioned in the introduction, in which chamber the lower and upper shells are each designed as plate-shaped members, wherein upper and lower shell are joined to one another in gas-tight and liquid-tight relationship via bars with rectangular cross section disposed along the rims to form the intermediate space necessary for a vapor chamber. 
         [0004]    Any temperature difference existing between the lower and upper shells of a vapor chamber is equalized by the fact that the fluid working medium evaporates, for example in the zone of the hotter lower shell, whereupon the vapor—because of a pressure gradient that develops—migrates through the vapor gap (which is a vapor duct passing suitably in the vapor chamber) toward the cooler upper shell, where is recondenses. The porous material inside the vapor chamber functions to receive and transport the condensed and therefore liquid phase of the working medium, thus conveying it inside the intermediate space between upper and lower shell by capillary forces back toward the hotter side of the vapor chamber, where the working medium—provided an equilibrium condition has not yet developed due to temperature equalization—can then evaporate once again. Under these conditions, the porous material advantageously constitutes a communication, passing in the interior of the vapor chamber, between upper and lower shells, thus ensuring effective transport of the liquid phase of the working medium between the two mutually facing (inner) sides of the upper and lower shells. 
         [0005]    The latent heat absorbed or released in a continuous process by the working medium during the phase transitions in question and the transport of the vapor and liquid phases of the working medium that takes place through the vapor gap and the porous medium provide for very rapid equalization of any temperature difference existing between upper and lower shell, and so, for example in the case of active heating of the lower shell, which may be achieved by a heating means fastened to the underside thereof, very rapid heating of the upper shell takes place. It is further advantageous in this context that—even if the lower shell is being heated only at points or at several places/zones under certain circumstances—the homogeneity of the temperature distribution achieved on the upper shell is completely acceptable for most applications. 
         [0006]    Furthermore, heat may also be removed very effectively from the upper or lower shell (or from a component thermally coupled therewith) by means of a vapor chamber, by coupling the respective other shell thermally with a suitable heat sink. 
         [0007]    The working zone of a vapor chamber is predetermined by the properties of the working medium contained therein (e.g. water) and by the pressure prevailing in the vapor chamber, and can therefore be adjusted, for example, by suitable choice of the (at least one) working medium. 
         [0008]    Vapor chambers—which are heat pipes of flat shape—of the class in question are frequently used in cooperation with suitable heating and/or cooling means for the most uniform possible thermal regulation of shaped blocks in (direct or indirect) contact with the heat pipe—for example in the form of depressions provided on the top side thereof—which blocks in turn have a multiplicity of receptacles for samples therein to be exposed to a certain temperature. 
         [0009]    In particular, vapor chambers of the class in question are used in so-called thermal cyclers, in which a temperature variation suitable for running the polymerase chain reaction (PCR) must be imposed several times cyclically in connection with simultaneous thermal regulation of a multiplicity of (biological) samples, for example for the purpose of DNA amplification. It is self evident that particularly precise thermal regulation of the various samples is just as desirable as the fastest possible completion of the temperature cycle, in which it is of substantial importance that the various samples be exposed to various temperatures (for a time period predetermined respectively for each) in chronological succession. A typical cycle involves heating of the samples to approximately 95° C. at first (for the process step known as denaturing; melting), subsequent cooling to approximately 55° C. (for the process step known as primer hybridization) and reheating to approximately 72° C. (for the process step known as elongation), whereupon the cycle begins anew by further heating back to 95° C. These temperature levels—for all samples to be thermally regulated simultaneously—are supposed to be maintained as exactly as possible, and the heating and cooling processes required between the temperature levels are supposed to take place as rapidly as possible. 
         [0010]    The thermal cyclers known heretofore from the prior art, such as described, for example, in EP 1710017 A1, WO 01/24930 A1 or WO 2004/105947 A1, typically comprise a sandwich structure of a heat sink, at least one vapor chamber (“thermal base”, “heat pipe”) of the class in question, a heating and if necessary cooling means (e.g. designed as at least one Peltier or PTC element), which if necessary consists of several elements and which may be disposed above or below the vapor chamber, and a sample receiving block in direct thermal contact with the heating means and/or the vapor chamber (“thermal block” or “sample block” or “test tube receiving block”), with a multiplicity of depressions disposed on the top surface thereof, into which depressions the samples to be exposed to a particular temperature variation may be introduced—if necessary inside suitable sample containers—for the purpose of thermal regulation thereof. Each depression functions as a receptacle for a sample to be thermally regulated therein and is advantageously configured such that a sample container—usually made of a thin plastic—to be inserted therein from above and containing the sample to be thermally regulated, can be introduced for the purpose of good heat transmission in surface-to-surface contact with the depression functioning as the sample receptacle. 
         [0011]    In this connection, the sample receiving block, which for its part is thermally regulated by means of the at least one vapor chamber, is usually constructed of solid silver (or aluminum), which besides the large weight of such a shaped block and a relatively high heat capacity, which in particular opposes fast temperature changes, is associated with a not inconsiderable outlay of materials and costs. Furthermore, it then proves to be particularly difficult to achieve good temperature uniformity in the various sample receptacles (depressions), especially in the zone of the depressions disposed along the rim or in a corner zone of the sample receiving block. 
         [0012]    To improve the homogeneity of the temperature established in the individual sample receptacles, it has therefore been proposed in this regard, in WO 01/24930 A1, that instead of using a separate vapor chamber or heat pipe (“temperature equalizing plate”) underneath the test tube receiving block—which consisted there of several segments—individual tubular heat pipes be integrated in the various segments of the test tube receiving block in such a way that they are oriented in the direction between each two rows of test tube holders. Even in this case, the test tube receiving block has a relatively high heat capacity because of its otherwise monolithic construction. 
         [0013]    And, finally, U.S. Pat. No. 5,161,609 A also discloses various exemplary embodiments of a vapor chamber of the type mentioned in the introduction, functioning on the “heat pipe” principle and intended for use in a thermal cycler, wherein the said vapor chamber, by virtue of the imposed geometry of the enclosure receiving the fluid working medium and containing an inner coating of porous material, serves simultaneously to receive the samples to be thermally regulated or to receive sample containers to be thermally regulated. 
         [0014]    In a first configuration of the vapor chamber described in U.S. Pat. No. 5,161,609 A, cylindrical passages for the purpose of receiving a multiplicity of sample containers to be thermally regulated are provided through the vapor chamber, each open on the top and bottom sides of the vapor chamber and surrounded by a vapor gap. This vapor chamber is heated or cooled along its rim encircling it laterally by a heating/cooling source, is provided on the top and bottom sides with thermal insulation and is covered with a cap. In a second configuration of the vapor chamber described in U.S. Pat. No. 5,161,609 A, a multiplicity of depressions functioning as sample receptacles is provided on the top side, but in this respect no more detailed information is disclosed about the internal structure of the vapor chamber. This vapor chamber is also in contact along its rim encircling it laterally with a heating/cooling source, while a heating or cooling cap covering the vapor chamber is also provided on the top side. 
         [0015]    In neither of the two alternative embodiments explained in the foregoing is it described how the inner walls of the vapor chamber are coated with the porous material. Furthermore, it must be pointed out that the working fluid for thermal regulation of the sample receptacles that are not disposed along the rim must travel relatively long transport paths e.g. when it is condensed for the purpose of heating a sample in the zone of the through passages or depressions and is returned through the porous material back to the heated rim. 
       SUMMARY 
       [0016]    Against this background, it is the object of the present invention to provide a vapor chamber of the type mentioned in the introduction, which in particular is suitable for use in highly efficient thermal cyclers (or in other instruments for thermal regulation of samples) equipped with heating/cooling means that heat or cool the vapor chamber on the bottom side and thus permits particularly fast temperature changes in connection with thermal regulation of samples to be thermally regulated using the vapor chamber. Another object is that a multiplicity of samples can be thermally regulated simultaneously by means of an inventive vapor chamber, specifically with improved homogeneity of the temperature acting on the individual samples. 
         [0017]    This object is achieved with an inventive vapor chamber which—beside the features already mentioned in the introduction—is characterized among other aspects by the fact that the upper shell of the vapor chamber is provided on the top side with a multiplicity of depressions, distributed over its surface, extending toward the lower shell and functioning as sample receptacles, in which samples to be thermally regulated using the vapor chamber can be introduced from above, wherein at least one vapor gap bounded at least partly by the porous material extends three-dimensionally in such a way that, inside the intermediate space disposed between upper and lower shell, it surrounds at least part of the lateral periphery of one or more depressions of the upper shell. 
         [0018]    Furthermore, it is provided according to the invention that at least some of the depressions, preferably all depressions, formed on the upper shell and extending toward the lower shell contact the lower shell with their bottom end, that at least some of the depressions contacting the lower shell are joined at their bottom end to the lower shell, that each depression of the upper shell is contacted inside the intermediate space with the porous material and that the porous material adjoining the depressions inside the intermediate space contacts the porous material adjoining the lower shell in the zone of the respective depressions. 
         [0019]    The inventive vapor chamber is therefore characterized by the fact among others that it has on the top side a multiplicity of sample receptacles, which are formed by depressions in the upper shell bounding the intermediate space for the (at least one) fluid working medium. 
         [0020]    Thus the depressions in a substantially monolithic component, which will be thermally regulated by means of at least one vapor chamber or heat pipe, do not function as the receptacles for the samples to be thermally regulated, but instead the vapor chamber itself becomes the sample receiving block, by the fact that the upper shell bounding the intermediate space for the working medium is provided on the top side with suitable depressions that function as sample receptacles. In comparison with a sample receiving block consisting of solid silver, as is currently used in highly efficient thermal cyclers, considerably better thermal conductivity ([W/mK]) (by up to a factor of 7) can be achieved in this way, so that heating and cooling processes taking place in connection with thermal regulation of the multiplicity of sample receptacles can be achieved considerably faster. 
         [0021]    The fact that at least one vapor gap in the present case, i.e. the at least one vapor gap formed inside the intermediate space, is oriented three-dimensionally in such a way that, inside the intermediate space, it surrounds—at least part of—the lateral periphery of one or more depressions of the upper shell, then makes it possible simultaneously to achieve a temperature homogeneity that is improved compared with the prior art, i.e. the difference between the temperatures in the various sample receptacles is always particularly small, especially when such sample receptacles that otherwise could not normally be thermally regulated sufficiently rapidly or effectively, especially the sample receptacles disposed along the rim or in a corner zone, are each surrounded either separately and/or in blocks by the (at least one) vapor gap, wherein it is obviously of particular advantage within the scope of the present invention when a single uninterrupted vapor gap (respectively) then surrounds the entire periphery of each of one or more depressions. 
         [0022]    In this connection, a vapor gap must be understood as that volume inside the intermediate space disposed between upper and lower shells in which the vapor phase of the working medium is being transported inside the inventive vapor chamber. Where “at least one” vapor gap is mentioned in the present context, it obviously includes the possibility that a single continuous vapor gap does not necessarily have to pass through the entire vapor chamber over its entire expansive extent in the present case, but instead that a multiplicity of vapor gaps may also be provided, wherein they are separated from one another by, for example, the porous material functioning for transport of the liquid phase and/or by at least one element of the lower and/or upper shell subdividing the intermediate space. 
         [0023]    The porous material used in an inventive vapor chamber may in principle be any material whatsoever which—by virtue of its porosity—is suitable for receiving and for transport of the liquid phase of the working medium by exerting a capillary action on the liquid phase of the working medium (e.g. water). 
         [0024]    The circumstance that the vapor chamber in the present case itself becomes the sample receiving block due to suitable depressions on its top side also proves to be extremely advantageous because herewith the weight and the heat capacity of a sample receiving block used, for example, in thermal cyclers, can be significantly reduced compared with monolithically constructed sample receiving blocks from the already known prior art, in which case—besides the improved performance with respect to heat transport to the individual depressions/sample receptacles—massive cost savings are simultaneously achieved because of the reduced outlay of material. 
         [0025]    By the fact that, according to the invention, every depression of the upper shell is contacted with the porous material inside the intermediate space, the porous material resting directly against the depressions may in particular also contribute to conductive heat transport in the vapor chamber based on the heat pipe principle. 
         [0026]    Moreover, it is provided within the scope of the invention that at least some of the depressions formed on the upper shell and extending toward the lower shell, especially all depressions, contact the lower shell with their bottom end, wherein at least some (or again, preferably all) of the depressions contacting the lower shell are bonded at their bottom end to the lower shell, especially by brazing. On the one hand, the mechanical stability of an inventive vapor chamber can be improved herewith, since in this way the depressions forming the sample receptacles create—at least partly—a mechanical support or joint between upper shell and lower shell. On the other hand, the thermal conductivity between lower and upper shell is simultaneously also improved hereby, especially in the zone of the depressions forming the sample receptacles, especially when, as is provided according to the invention, the porous material adjoining the lower shell also comes into contact in the zone of the respective depressions with the porous material adjoining the depressions inside the intermediate space, which then also improves the conductive heat transport inside the vapor chamber. Consequently, working fluid condensed in the zone of the depressions, i.e. inside the upper shell, may be conveyed through the porous material directly and via a short path back to the heated lower shell. Analogously, during cooling of the lower shell, the working medium of the vapor chamber condensed there can be conveyed via the shortest path to the zone of the porous material provided inside the intermediate space at the respective depressions. 
         [0027]    The depressions, forming the sample receptacles, in the upper shell of an inventive vapor chamber are advantageously distributed in a regular pattern over the surface of the upper shell and particularly preferably are matched in number and geometry to the number and geometry of the cavities (English: “wells”) of commercial microtiter plates, as are used in connection with industrial processing of (biological) samples, so that a microtiter plate may be mounted on the top side of the vapor chamber in such a way that the individual cavities (filled from above with, for example, liquid samples and projecting freely downward) of the microtiter plate each reach into a depression of the upper shell with the best possible (surface-to-surface) contact with the respective side wall of the depression. As an example, especially 24, 48 or 96 depressions are therefore advantageously provided in an appropriate regular distribution in the upper shell, thus permitting the largest possible number of samples to be thermally regulated simultaneously and at defined temperatures by means of the inventive vapor chamber. 
         [0028]    Where it is stated in connection with the present invention that the vapor chamber has a lower shell and an upper shell, the vocabulary chosen for this purpose is intended not to describe any specific geometry of the components in question but instead to impart the impression that the inventive vapor chamber has at least two parts (which could also be referred to as an upper part and a lower part), between which the gas-tight and liquid-tight intermediate space for receiving the working medium and the porous material is formed. Obviously the upper and lower shells (or upper part and lower part) do not necessarily have to be constituted by two separate components, but instead—for example by using suitable forming processes—may also be constructed in one piece under certain circumstances, although a gas-tight and liquid-tight intermediate space must always be formed between the upper and lower parts bounding the vapor chamber at the top and bottom respectively. Preferably, however, at least the lower shell or the upper shell is actually also configured as a shell with a peripheral rim formed on it, whereby the lateral boundary of the vapor chamber can be formed simply by the rim in question of the lower or upper shell. 
         [0029]    In a first preferred improvement of the present invention, it is provided that at least one vapor gap, which encircles the lateral outer periphery of all depressions and for this purpose is formed inside the intermediate space between the lateral boundary of the vapor chamber and the depressions disposed along the rim, is provided between upper and lower shell in an inventive vapor chamber. Obviously it is then advantageously possible to provide in particular that the depressions along the rim (on their respective side facing the intermediate space) are in (at least partial) contact with the porous material disposed inside the intermediate space or are coated therewith, so that particularly effective heat transport is achieved (even) in this zone. 
         [0030]    Such a vapor gap encircling all depressions or sample receptacles all together permits—in a vapor chamber geometry that can be easily constructed by appropriate geometry of the upper and lower shells (as well as of the porous material)—even the depressions disposed along the rim and in the corner zone of the upper shell to benefit in their entirety from the excellent thermal conductivity of a vapor chamber and thus to be heated and/or cooled uniformly and quickly. 
         [0031]    Furthermore, it is advantageously provided in a particular configuration of the present invention that the entire periphery of each depression is surrounded by at least one vapor gap, permitting the excellent thermal conductivity of a heat pipe to be fully utilized in the zone of each depression functioning as a sample receptacle, with the consequence of particularly good temperature homogeneity over all sample receptacles. If such a vapor gap extending through the entire vapor chamber and simultaneously encircling the entire lateral periphery of each depression is provided on the whole in the vapor chamber, virtually the best possible temperature homogeneity can be achieved for the purpose of thermal regulation of all sample receptacles (or of the samples disposed therein). 
         [0032]    Particularly preferably, it may be further provided in the scope of the present invention that the porous material is formed by at least two layers of porous material, of which a first material layer is formed inside the intermediate space on the upper shell and a second material layer is formed inside the intermediate space on the lower shell, wherein the first and second material layers are in contact with one another in some zones but are spaced apart from one another in other zones in order to form the at least one vapor gap. 
         [0033]    The porous material used in a heat pipe or the two aforesaid porous material layers may consist, for example, of a material that at first is substantially powdery with spherical and/or rod-like material constituents (e.g. of copper) with identical or different dimensions, which—e.g. as constituents of a liquid or pasty molding compound—are first applied in suitable layer thickness onto the respective inside of the lower and upper shells and then baked there to a certain extent by the action of appropriately high temperatures (in a kind of sintering process), whereupon on the one hand it solidifies—with formation of the desired porous structure—and on the other hand adheres or bonds metallurgically to the lower or upper shell, which advantageously are joined together only in a later process step. Practical experience has shown that, when two material layers of porous material formed on the upper and lower shells in the foregoing sense are used and must subsequently be in contact with one another in some zones, especially in the zone of the depressions, when the upper and lower shells are joined together, problems of thermal conductivity may develop unless demanding manufacturing tolerances are met. On the one hand, undesired gaps may appear between the material layers formed on the upper and lower shells, thus impairing or preventing liquid transport by capillary action in the zone of the gap. On the other hand, it is possible under certain circumstances for the porous material to become compacted in the zone of contact of the two material layers, thus also greatly impairing the capillary transport of liquid between the two material layers. 
         [0034]    It is therefore provided in a preferred improvement of the present invention that the contact between the porous material adjoining the depressions inside the intermediate space and the porous material adjoining the lower shell is established by forming the porous material on the upper and lower shells as an inner coating that on the whole is continuous throughout the vapor chamber. In such a continuous inner coating (inside the intermediate space) of the vapor chamber, the contact between the porous materials provided inside the upper and lower shells is therefore established by the fact that a continuous and uninterrupted layer of porous material connects the upper and lower shell, especially in the zone of the depressions. As an example, this may be achieved by flooding the intermediate space between the upper and lower shells (which have already been joined together) with a liquid of suitable viscosity containing the porous material, in such a way that the porous material settles in the desired layer thickness on the upper and lower shells, whereupon—after removal of excess liquid if necessary—it can be “hard sintered” onto the upper and lower shells by appropriate heat treatment. 
         [0035]    Furthermore, it may be provided in the scope of the invention that the porous material is produced from an initially pasty molding compound at least in some zones, especially in that zone in which the porous material adjoining the depressions inside the intermediate space is in contact with the material adjoining the lower shell in the zone of the respective depressions, which compound was applied before assembly on appropriate zones of the upper and lower shells and was solidified by heat treatment at appropriately high temperature (with evaporation of liquid ingredients) after assembly of the upper and lower shells. In this connection, either the entire porous material suitably covering and joining the upper and lower shells in the intermediate space may be produced using a pasty molding compound in the sense mentioned in the foregoing, or on the other hand the use of a pasty molding compound in the sense mentioned in the foregoing only in some zones may in particular offer the ability to join material layers of porous material produced in other ways and already formed on the lower and/or upper shell, without forming gaps or compacted zones. 
         [0036]    Yet another preferred improvement of the invention provides that the porous material is formed at least partly by at least one prefabricated shaped part of porous material, which is fitted onto at least one depression of the upper shell from below before assembly of upper and lower shells and which is configured such that the shaped part contacts the at least one depression and the lower shell inside the intermediate space after assembly of the upper and lower shells. 
         [0037]    In this connection, for example, it is possible to provide an individual shaped part of porous material, which part is fitted onto all depressions of the upper shell and which—in the zone of the respective depression—joins each depression and the lower shell. Furthermore, it is also possible if necessary to provide a separate shaped part for each depression (or respectively a group of depressions), which part is fitted onto the depression (or the group of depressions) in question in the sense mentioned in the foregoing. In this case, zones that may not have been contacted by the shaped parts, including zones of the lower and/or upper shell or intermediate zones that may be present within the shaped parts, may then be filled with further porous material, for example, again using a pasty molding compound in the sense mentioned in the foregoing. 
         [0038]    Furthermore, within the scope of the present invention it is possible in particularly preferred manner to provide that the porous material contacting the upper and lower shells inside the intermediate space has varying layer thickness and/or varying porosity and/or varying pore diameters. 
         [0039]    Since the layer thickness of the porous material has an influence on its absorption capacity and the evaporation rate imposed in a specific zone, it is therefore possible, by varying the layer thickness of the porous material, to optimize specific zones of the lower and/or upper shell for evaporation or liquid working medium or for absorption of condensed working medium. Furthermore, by specific variation of the porosity or of the pore diameter of the porous material—which has been applied, for example, by various pasty molding compounds—it is possible to adapt the capillary forces developing in this way selectively to the desired liquid transport in the porous layer. 
         [0040]    Since it is possible within the scope of the present invention to provide not only cooling on the bottom side but also heating of the lower shell of the vapor chamber, it is particularly advantageous when the variation mentioned in the foregoing of the layer thickness and/or of the porosity of the porous material takes into consideration the desired heat transport in both directions, by creating in the porous material—in the zone of each depression, for example, or distributed in alternating manner over the vapor chamber—a first fluid path with improved properties for liquid transport from the upper to the lower shell and a second fluid path with improved properties for liquid transport from the lower to the upper shell and/or with correspondingly improved evaporation rates at the lower and upper shells respectively. 
         [0041]    The upper shell and/or the lower shell of an inventive vapor chamber may in principle be made of any suitable material whatsoever with comparatively good thermal conductivity as well as sufficiently simple processability (e.g. of silver), although—for cost reasons also—they are preferably made of copper or aluminum. 
         [0042]    Preferably the upper and lower shell of an inventive vapor chamber are joined to one another in gas-tight and liquid-tight relationship along a peripheral rim—advantageously running in one plane—especially by welding and/or brazing. 
         [0043]    It proves to be further particularly advantageous when the upper and/or lower shell—with the exception of webs that may be provided for stiffening purposes—have a layer thickness of smaller than or equal to 2 mm, even more preferably of smaller than or equal to 1 mm. Preferably the wall thickness can be made as thin as possible for this purpose, although in view of the pressure conditions prevailing inside the vapor chamber it is obviously imperative to ensure that the mechanical stability is still adequate. Such thin layer thicknesses in turn favor even more improved heat transport as well as a particularly low heat capacity and also a particularly low weight of an inventive vapor chamber, which is also a worthwhile objective in view of constructional aspects. 
         [0044]    An upper shell with depressions suitable for the present purpose may be made, for example, by deep drawing from a suitable metal sheet. Furthermore, electrogalvanic manufacturing techniques, especially that known as “electroforming”, are suitable for making an upper shell of suitable geometry, especially when this—as is particularly advantageous—is supposed to have a very small layer thickness of much thinner than 1 mm. 
         [0045]    Especially the depressions of the upper shell functioning as sample receptacles may be configured particularly preferably with thin walls (advantageously &lt;1 mm, even more advantageously &lt;5 mm), since this permits—because of the correspondingly smaller mass of the wall bounding the depression—a smaller specific heat capacity in the immediate vicinity of the sample receptacle to be thermally regulated, whereby faster temperature changes are possible. 
         [0046]    Moreover, it may be advantageously provided within the scope of the present invention that the vapor chamber has at least one temperature and/or pressure sensor reaching into the vapor gap. 
         [0047]    A temperature sensor reaching into the vapor gap proves to be advantageous in particular when its measured value of temperature is compared, by means of a suitable monitoring and comparison unit (e.g. continuously or at predetermined intervals), with that of a second temperature sensor, which is disposed, for example, on the bottom side of the vapor chamber (i.e., in contact with the lower shell). 
         [0048]    This means that the two temperature values measured in this way by temperature sensors disposed at various positions are in fixed relationship to one another, and so—if a deviation occurs in this respect—a malfunction of the vapor chamber can be detected reliably and quickly. Such a malfunction, which obviously means that proper thermal regulation then no longer exists and that destruction of possibly irretrievable samples may be expected under certain circumstances, can be caused, for example, by a leak in the gas-tightness of the intermediate space, which in turn may lead to a change in the pressure conditions prevailing in the vapor chamber, ranging from subtle to loss of function. 
         [0049]    In the constructional respect, it proves to be particularly advantageous in an inventive vapor chamber when at least one threaded blind hole is formed on the bottom side of the lower shell—for example in a zone with extra reinforcement for the purpose—in order that the vapor chamber can be joined on its bottom side to an adjacent component by means of a screw connection. 
         [0050]    And, finally, the present invention relates not only to a vapor chamber as such, which in principle could be used in the most diverse devices—including, for example, an incubator—but especially also to a thermal cycler, which—for thermal regulation of samples with predefined temperature cycles—comprises at least one heat sink, (at least) one preferably electrical heating means (e.g. as a kind of PTC element) and a vapor chamber of the inventive type as described in the foregoing. Obviously all already mentioned aspects are applicable analogously for this purpose, and so reference thereto is made in order to avoid repetitions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0051]    Hereinafter an exemplary embodiment of the present invention will be described in more detail on the basis of the drawing, wherein 
           [0052]      FIG. 1  shows an exploded diagram of an exemplary embodiment of an inventive vapor chamber together with a microtiter plate that can be inserted therein, 
           [0053]      FIG. 2  shows a perspective—partly cutaway—diagram of the vapor chamber from  FIG. 1 , 
           [0054]      FIG. 3  shows a cross-sectional diagram through the vapor chamber from  FIGS. 1 and 2  with microtiter plate inserted therein through the offset section line III-III from  FIG. 2 , 
           [0055]      FIG. 4  shows a perspective view of an exemplary embodiment of the main components of an inventive thermal cycler, 
           [0056]      FIG. 5  shows a diagram for comparison of the temperature homogeneity of an inventive vapor chamber with that of a sample receiving block constructed from solid silver, and 
           [0057]      FIGS. 6-10  show various diagrams of further exemplary embodiments of inventive vapor chambers for use in an inventive thermal cycler, wherein heating and cooling of the vapor chamber take place on the bottom side. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]      FIGS. 1 to 3  show an exemplary embodiment of an inventive vapor chamber  1  in various views, wherein the perspective exploded diagram of  FIG. 1  and the sectional diagram of  FIG. 3  additionally illustrate a microtiter plate  2  that can be inserted or has been inserted therein. 
         [0059]    Vapor chamber  1  comprises a lower shell  3 , made from copper in the present case, as well as an upper shell  4  made from the same material, wherein upper shell  4  has on the top side a multiplicity, in the present case 96 in total, of depressions  6 , distributed over its surface  5  and extending toward lower shell  3 . These depressions  6  function as sample receptacles, in which samples  7  (see  FIG. 3 ) to be thermally regulated—using vapor chamber  1 —may be introduced either indirectly or directly. In this connection, however, lower shell  3  and upper shell  4  may also be made of other suitable materials, such as from aluminum or from silver. 
         [0060]    In the present case, (liquid) samples  7  to be thermally regulated are received in individual cavities or sample containers  8  of microtiter plate  2 , for which purpose sample  7  in question has been filled through an opening  9  accessible from above into the respective sample container  8 . Samples  7 , in sample containers  8  projecting downward from microtiter plate  2 , are introduced into depression  6  assigned respectively to sample  7  in question by mounting microtiter plate  2  in correct orientation on upper shell  4 , which is adapted to its geometry. Thus sample containers  8  of microtiter plate  2 , via their respective outer sides, are in surface-to-surface contact with the side wall of depression  6 , in order to ensure good heat transmission. 
         [0061]    Along a rim  10 —which completely encircles vapor chamber  1 —upper shell  4  and lower shell  3  are joined to one another in gas-tight and liquid-tight relationship, which may be achieved, for example, by a suitable welded and/or brazed joint. Inside intermediate space  11  formed between upper shell  4  and lower shell  3  there is received a fluid working medium (not illustrated) and there is disposed—in the form of layers on upper and lower shells  3 ,  4 —a porous material  12 ,  13 , which cooperates with the fluid working medium in the sense that it is able to absorb the liquid phase of the working medium and to transport it by the effect of capillary forces. The fluid working medium may be introduced into intermediate space  11 , for example through an appropriately sealable access opening in the upper or lower shell. 
         [0062]    Between the porous material  12 ,  13  covering lower and upper shells  3 ,  4  inside the intermediate space, there is formed in the present case a vapor gap  14 , which passes through the entire vapor chamber  1  and in the present case extends between the two porous material layers  12 ,  13 , while at the same time, among other features—according to dashed line  14 ′ illustrated in FIG.  1 —it surrounds the entire lateral periphery of all depressions  6  of upper shell  4  all together, specifically between the lateral boundary of vapor chamber  1  and depressions  6  disposed along the rim. At the same time, furthermore, the entire periphery of each depression  6  is also separately surrounded by vapor gap  14 , as indicated by the two dashed lines  14 ″ in  FIG. 2 . 
         [0063]    In the presence of active heating of lower shell  3 , the liquid phase of the working medium absorbed in the layer of porous material  12  adjoining it penetrates into vapor gap  14  while absorbing latent heat, and there it is transported toward cooler upper shell  4  or toward depressions  6  formed therein as a result of a suitably developing pressure gradient. In this respect, it is of advantage for the desired temperature homogeneity in the zone of the various depressions  6  that vapor gap  14  extends three-dimensionally and continuously over the entire cross-sectional area of vapor chamber  1  and in doing encircles depressions  6 , wherewith the vapor phase is also able to migrate transversally or laterally around depressions  6 . The working medium is then able to recondense in the zone of the upper shell while releasing latent heat. 
         [0064]    There it is absorbed by porous material  13  disposed on the upper shell. Because of the capillary forces of porous material  12 ,  13  and of the communication between porous material  12 ,  13  disposed on the upper and lower shells, which communication exists at least in some zones—but in the present case in particular also encircling each depression  6 —the condensed liquid phase of the working medium is then conveyed back to the zone of porous material  12  on the lower shell, where it is able to evaporate again as long as temperature equalization has not yet been established. 
         [0065]    By the fact that each depression  6  inside the intermediate space is completely surrounded in the present case by the at least one vapor gap  14  of vapor chamber  1 , particularly effective heating of the individual depressions  6  functioning as sample receptacles—and thus of samples  7  received therein—can be achieved. 
         [0066]    Especially in  FIGS. 2 and 3 , it can be readily seen in the present exemplary embodiment of the invention that all depressions  6  of upper shell  4  are in contact in the zone of their bottom end  15  with lower shell  3 , in which case the layer of porous material  12  disposed on the lower shell in this zone is discontinuous. Some or all depressions  6  may be joined there to lower shell  3 , especially by metallurgical techniques, in order to increase the mechanical stability of vapor chamber  1 —and to improve the heat transport. 
         [0067]    A multiplicity of webs  16 —distributed over lower shell  3  in a square pattern—which add to the existing layer thickness of lower shell  3 , which may be smaller than 2 mm or even smaller than 1 mm, is disposed on lower shell  3 , thus providing mechanical reinforcement for the structure of lower shell  3 . 
         [0068]    Furthermore, lower shell  3  has on its bottom side a multiplicity of threaded blind holes  17 , of which one is visible in the sectional diagram of  FIG. 3  and which serve for mounting vapor chamber  1  in fixed position on an adjacent component, such as a heating and cooling element. In this zone, lower shell  3  also has suitable reinforcement  18 . 
         [0069]    The right bottom part of the section through vapor chamber  1  illustrated in  FIG. 3  further shows two bores  19 ,  20 —which are accessible from outside for introduction of a temperature sensor—of which one bore  19  is disposed close to the bottom while the other bore  20  is positioned somewhat higher in vapor chamber  1 , where it extends into or adjoins vapor gap  14  present in intermediate space  11 . By means of temperature sensors (not illustrated) disposed therein and a suitable electronic system, as has already been explained hereinabove, the correct functioning of vapor chamber  1  can be monitored, in order that the thermal regulation of vapor chamber  1  can be turned off—automatically if necessary—in sufficient time to prevent destruction of samples  7  in the event of a malfunction. 
         [0070]      FIG. 4  shows a perspective view—partly cut away for better illustration of the components used therein—of an exemplary embodiment of an inventive thermal cycler  21 , which in the present case has a layered structure with thermal coupling of the mutually adjacent components, which from bottom to top are:
       a heat sink  22  of appropriately large dimensions,   a first flat vapor chamber  23  (without depressions for sample receptacles on the top side),   a multiplicity of heating/cooling elements  24   a ,  24   b ,  24   c  (e.g. Peltier elements) and   a second vapor chamber  25  of inventive design, disposed above heating/cooling elements  24   a ,  24   b ,  24   c , with depressions  6  formed on its top side for receiving the samples to be thermally regulated by means of thermal cycler  21 .       
 
         [0075]    Heat sink  22  has a lamellar structure  26  on its bottom side, thus achieving high cooling capacity by providing a particularly large surface area for effective heat exchange with a cooling fluid (such as air) flowing between the lamellas. 
         [0076]    Lower vapor chamber  23 , which in the present case is mounted by means of several screw connections  27  between a mounting plate  28  and the top side of heat sink  22 , establishes excellent thermal contact between heat sink  22  and heating/cooling means  24   a ,  24   b ,  24   c —which are disposed in a recess of mounting plate  28 —especially because they present a larger contact face for dissipation of heat to heat sink  22  than would otherwise be the case compared with the much smaller area of heating/cooling elements  24   a ,  24   b ,  24   c . For the purpose of screwing lower vapor chamber  23  together with heat sink  22  and mounting plate  28 , through bores, such as described, for example, in WO 2005/114084 A1, are provided for screw-connection purposes in the vapor chamber. 
         [0077]    Ultimately, however, it must be pointed out that lower vapor chamber  23  indeed improves the thermal contact between heating/cooling elements  24   a ,  24   b ,  24   c , but does not necessarily have to be present and—if somewhat slower cooling of samples is acceptable under certain conditions—could even be completely omitted, and so in the present case it is merely provided as an option in the sense of a preferred alternative embodiment of an inventive thermal cycler. 
         [0078]    In the present case, six heating and cooling elements  24   a ,  24   b ,  24   c  (e.g. Peltier elements) in total, each of flat construction, are disposed in two adjacent rows of three units each between heat sink  22  or lower vapor chamber  23  and the upper (inventive) vapor chamber, which elements—depending on electrical circuitry—function for heating or cooling of the bottom side of upper vapor chamber  25  or of the samples appropriately introduced into their depressions  6 . 
         [0079]    The upper vapor chamber is almost identical to that of  FIGS. 1 to 3 , and so its mode of operation and the features relevant thereto can be understood by referring to the foregoing explanations. In this respect, it must be pointed out that the only difference compared with the exemplary embodiment shown in  FIGS. 1 to 3  is that upper vapor chamber  25  in  FIG. 4  has a thicker walled upper shell  4 , although even here at least the wall thickness of depressions  6  reaching into the intermediate space between upper shell  4  and lower shell  3  and functioning as sample receptacles still has sufficiently thin structure—with a wall thickness of preferably smaller than or equal to 2 mm or even more preferably smaller than or equal to 1 mm. 
         [0080]    And finally  FIG. 5  shows a diagram with measured values of comparative measurements to illustrate the clearly improved temperature homogeneity or uniformity of an inventive vapor chamber compared with the prior art. 
         [0081]    For this purpose a typical PCR cycle—using various measuring setups explained respectively hereinafter—was carried out with temperature levels held for 10 seconds at +95° C., at +55° C. and at +72° C. respectively. 
         [0082]    The first-mentioned temperature level at +95° C. was approached by appropriate control of the heating/cooling means at a rate of temperature rise of +3° C./s (or 3 K/s) and then held for 10 seconds. Immediately thereafter the temperature in the sample receptacles was lowered to +55° C. at a rate of −1.5 K/s and also held at this temperature level for 10 seconds, whereupon a new phase of heating at a rate of +3 K/s took place to +72° C., and the temperature was then held at this level for 10 seconds. At the same time, the temperature established in a total of eight different sample receptacles of the respective sample receiving block, each of which had 96 sample receptacles, was monitored by means of suitable temperature sensors. The positions of the sample receptacles monitored by means of the temperature sensors can be seen in the schematic diagram shown at the top right of  FIG. 5 , the said schematic diagram representing an overhead view of the respective sample receiving block. The monitored sample receptacles are indicated therein by solid black circles. 
         [0083]    Four of the monitored sample receptacles therefore corresponded to the sample receptacles disposed at the corners of the sample receiving block. Two further sample receptacles were disposed at approximately the midpoints of the rim. And the last two monitored sample receptacles were disposed approximately at the respective middle of the left and right halves of the given layout of 96 sample receptacles in total. 
         [0084]    At each temperature level, the measurements were made three times in rapid succession in the last part of the 10-second holding time, the temperature in all monitored sample receptacles being determined simultaneously, and then the difference—considering all measurements in the various sample receptacles—obtained between the maximum value and the minimum value—defined as uniformity (the English term) in the present case—of the temperatures measured in this way was calculated and plotted on the y-axis of the bar diagram in  FIG. 5 . 
         [0085]    The measurements were made in one case on an inventive thermal cycler of the type shown in  FIG. 4  (“96 well 3D-VCM”) and in the other case on a layout known from the prior art, in which—compared with the layout of FIG.  4 —upper vapor chamber  25  was replaced by a sample receiving block of solid silver (“96 well Silvermount”), which also has 96 sample receptacles, which in turn was mounted on its bottom side on a flat heat pipe, which established the thermal contact with the underlying heating and cooling elements. 
         [0086]    The measurements show that the maximum temperature difference between the measured temperatures in the various sample receptacles are always much smaller in an inventive layout (i.e. at all three established temperature levels) than is the case in the layout known from the prior art. It was only 0.25 K for the 95° C. temperature plateau (compared with 0.49 Kelvin for the layout used in the prior art), only 0.13 K for the 55° C. temperature plateau (compared with 0.26 K for the layout used in the prior art) and only 0.23 K for the 72° C. temperature plateau (compared with 0.31 K for the layout used in the prior art). Within the scope of the present invention, therefore—besides the advantages explained in detail hereinabove—it is found that the homogeneity of the temperature is also clearly improved during simultaneous thermal regulation of a plurality of samples. 
         [0087]    For demonstration of several variants for introducing porous material into the vapor chamber,  FIGS. 6 to 10  show several diagrams of further exemplary embodiments of inventive vapor chambers  1  for use in an inventive thermal cycler with heating/cooling means that heat or cool vapor chamber  1  at its bottom side. 
         [0088]    Each of these  FIGS. 6 to 9  shows two diagrams, one above the other, wherein the upper diagram shows a section through an inventive vapor chamber  1  before its final assembly and the lower diagram shows a section through the finished vapor chamber  1 . 
         [0089]    In this connection,  FIG. 6  relates to an alternative embodiment of the invention in which—see the upper diagram—a material layer  13 ,  12  of porous material was applied inside the intermediate space on both upper shell  4  and lower shell  3  respectively before assembly of the vapor chamber and was already solidified beforehand by heat treatment (in a kind of sintering process), as described hereinabove. By design, however, material layer  13 , which is provided on the upper shell and which also covers the surface of depressions  6  inside the intermediate space, does not extend so far along depression  6  toward their bottom end that it would come into contact with material layer  12  on the lower shell during assembly of vapor chamber  1 . 
         [0090]    On the other hand, porous material  30 , in that zone in which it adjoins both depressions  6  and lower shell  3  inside the intermediate space, is made in the present case from an originally pasty molding compound  29 , which is applied as a bead in the zone of the lateral ends of depressions  6  pointing toward the lower shell before assembly of upper and lower shells  4 ,  3  and is solidified by heat treatment at appropriately high temperature after assembly of upper and lower shells  4 ,  3 . 
         [0091]    The lower diagram of FIG.  6 —especially the enlarged detail presented therein—clearly shows how the originally pasty molding compound  29  has solidified in that zone in which porous material  13 ,  30  adjoining depressions  6  inside the intermediate space is in contact with porous material  12  adjoining lower shell  3  and how it has joined together with the respective adjoining material layers  12 ,  13 , so that, in the zone of the respective depressions  6 , direct transport of the liquid phase of the working medium of the vapor chamber can take place between porous material  12 ,  13 ,  30  provided on the lower shell and upper shell. 
         [0092]      FIG. 7  shows a further exemplary embodiment of an inventive vapor chamber, in which (see the upper diagram) both upper shell  4  (and its depressions  6 ) and lower shell  3  were coated inside the intermediate space with a pasty molding compound  29  containing the porous material before assembly of the vapor chamber, so that—during assembly of upper and lower shell—the two layers of pasty molding compound  29  come into contact with one another in some zones and, after a subsequent heat treatment in the sense already explained, an inner coating of porous material  30  (see the lower diagram from  FIG. 7 ) can form continuously on the whole in vapor chamber  1 . 
         [0093]      FIG. 8  shows a further exemplary embodiment, in which upper and lower shells  4 ,  3  themselves do not have any peripheral rim sealing the vapor chamber. Therefore, as can be seen in the upper diagram of  FIG. 8 , upper shell  4  is joined together with lower shell  3  in such a way that the surfaces of upper and lower shells  4 ,  3  inside the intermediate space are still always accessible from the outside and can be coated with a pasty molding compound  29  containing the porous material. Thereafter vapor chamber  1  can be sealed with a separate, peripheral boundary  31 . Once again, a solidified layer of porous material  30  can then be produced from pasty molding compound  29  by suitable heat treatment, as is shown in the lower diagram of  FIG. 8 . 
         [0094]    The exemplary embodiment illustrated in  FIG. 9  relates to the use of prefabricated shaped parts  32  that is possible within the scope of the invention, which parts are configured such that they can be fitted from below onto depressions  6  of upper shell  4  before assembly of upper and lower shells  4 ,  3 , such that each shaped part  32  contacts at least depression  6  and lower shell  3  inside the intermediate space after assembly of the upper and lower shells. 
         [0095]    For completeness, it must be mentioned that the bottom end  15  of each depression  6  in the exemplary embodiment according to  FIG. 9 , i.e. that side of the wall forming the bottom of the respective depression  6  which points toward the lower shell, also contacts the lower shell and, after assembly of the vapor chamber, is advantageously bonded metallurgically with the lower shell. 
         [0096]    Finally,  FIG. 10  shows a last exemplary embodiment of an inventive vapor chamber in which upper and lower shells  4 ,  3 —which are not yet covered with porous material—are joined together first, while an opening  33 , through which the porous material can be introduced into intermediate space  11  and which can be sealed in fluid-tight relationship with a cap  34 , is disposed on the rim. A liquid of suitable viscosity, containing the porous material, can then be introduced through this opening  33  into intermediate space  11  in such a way that the porous material settles in the desired layer thickness on the upper and lower shells, whereupon—after removal of any excess liquid if necessary—it can be “hard baked” onto the upper and lower shells by appropriate heat treatment.