Abstract:
A heat exchanger serves to cool a cooling medium, which in turn is intended to cool an electronic component ( 76 ). The heat exchanger has an inflow ( 64 ) for delivery of hot coolant, and an outflow ( 68 ) for discharge of coolant cooled in the heat exchanger. An equalizing vessel ( 30 ) is joined to the heat exchanger to form one module. The vessel serves to equalize changes in coolant volume. The equalizing vessel ( 30 ) is closed off by a flexible membrane ( 54 ) which follows such changes in volume. The equalizing vessel ( 30 ) is implemented as a component of the coolant circuit. One part of the equalizing vessel is implemented as a component of the inflow ( 64 ) and another part as a component of the outflow ( 68 ), which parts are in liquid communication with one another via a switchback path through passages ( 22 ) within the heat exchanger ( 20 ) that is implemented in double-flow fashion.

Description:
CROSS-REFERENCE 
       [0001]    This application is a section 371 of PCT/EP05/014 154, filed 31 Dec. 2005, published 24 Aug. 2006 as WO-2006-087031-A. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a heat exchanger for cooling a cooling medium, in particular in an electrical/electronic device. 
       BACKGROUND 
       [0003]    In a closed cooling system filled with a coolant, temperature changes as well as permeation, for example through tube walls, result in a change in the volume of the coolant. Some compensation or equalization for this coolant volume change, that ensures that no, or only small, pressure changes occur in the system, must be found. 
         [0004]    Such changes in volume can be buffered by means of a so-called equalizing vessel. This causes additional costs, however, and also increases the risk of cooling medium leaking out. 
         [0005]    An important problem in the context of heat exchangers for electronic devices is that their exact operating orientation is not known, a priori. This is true not least for transportation to the customer, since such cooling systems are already filled with cooling medium at the manufacturer&#39;s premises, and the orientation they will assume during transport cannot be predicted. The same is true for utilization in vehicles of all kinds (aircraft, ships, land vehicles, vehicles in a weightless state). Operating reliability must therefore be guaranteed in all conceivable operating orientations. If liquid were to mix with gas in the cooling circuit, reliable operation of a circulating pump would then no longer be guaranteed, with the result that cooling performance might rapidly decrease. This would then very quickly cause the electronic component being cooled either to switch itself off, or to be destroyed by the increase in temperature. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the invention to make available a novel heat exchanger. 
         [0007]    According to the invention, this object is achieved by forming a two-part equalizing vessel, incorporating a flexible membrane which dynamically adapts to changes in coolant volume, as part of a heat exchanger, one part being implemented as part of the inflow and one part being implemented as part of the outflow of the heat exchanger. 
         [0008]    A compact and economical arrangement is thereby achieved. The risk that cooling medium may leak out and cause damage to the electronics is reduced. The at least one flexible membrane or diaphragm also causes the internal volume of the cooling circuit to be adapted automatically to the variable volume of the cooling medium that is present in the cooling circuit, so that the creation of gas bubbles in the cooling medium is prevented, regardless of the operating orientation of the heat exchanger. This makes possible reliable cooling even after the heat exchanger has temporarily assumed an unusual operating orientation, e.g. during transport. 
         [0009]    A particularly preferred embodiment of such a heat exchanger is to join a heat exchanger to an equalizing vessel in a single module, incorporating a coolant filter at an interface therebetween. It prevents, at very low cost, problems and damage due to contaminants in the cooling medium. 
         [0010]    The preferred refinement, according to which the filter is a plastic part directly attached to a housing of the equalizing vessel, yields a compact, robust, and cost-saving design. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0011]    Further details and advantageous refinements of the invention are evident from the exemplifying embodiments, in no way to be understood as limitations of the invention, that are described below and depicted in the drawings. 
           [0012]      FIG. 1  is a schematic depiction showing, by way of example, a heat exchanger according to the invention and its arrangement in a cooling circuit; 
           [0013]      FIG. 2  is an enlarged depiction of detail II of  FIG. 1 ; 
           [0014]      FIG. 3  is an enlarged depiction of detail III of  FIG. 1 ; 
           [0015]      FIG. 4  is an enlarged depiction of detail IV of  FIG. 1 ; 
           [0016]      FIG. 5  is a three-dimensional depiction, shown partially in section, of an exemplifying embodiment according to the invention; 
           [0017]      FIG. 6  is a depiction analogous to  FIG. 5 , viewed in the direction of arrow VI of  FIG. 5 ; 
           [0018]      FIG. 7  is a three-dimensional depiction of the membrane used in the heat exchanger according to  FIGS. 1 to 6  and of the spring element joined to it; and 
           [0019]      FIG. 8  shows a second exemplifying embodiment of the invention; 
           [0020]      FIG. 9  is an overview of a second exemplifying embodiment of the invention; 
           [0021]      FIG. 10  is a section viewed along line X-X of  FIG. 11 ; 
           [0022]      FIG. 11  is a top view looking in the direction of arrow XI of  FIG. 10 ; 
           [0023]      FIG. 12  is an enlarged depiction of detail XII of  FIG. 10 ; 
           [0024]      FIG. 13  is a three-dimensional depiction of a heat exchanger  130 ′ that is equipped with an integrated large-area filter; 
           [0025]      FIG. 14  is an enlarged depiction of detail XIV of  FIG. 13 ; 
           [0026]      FIG. 15  is a section through the upper part of heat exchanger  120 ′ depicted in  FIG. 13 ; 
           [0027]      FIG. 16  is a section analogous to  FIG. 15 ; in this variant, filter  170  is arranged and mounted differently than in  FIG. 15 ; and 
           [0028]      FIG. 17  is a sectioned detail depiction of the filter and the seal from  FIG. 16 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  schematically shows a heat exchanger  20 . The latter has, in known fashion, flat cooling tubes  22  through which a cooling medium  24  flows during operation, and which are joined in thermally conductive fashion to cooling plates  26  arranged in a zigzag shape. 
         [0030]    The spaces between the flat tubes  22  are closed off at the top in liquid-tight fashion by closure panels  28 , thus creating an upper tank  30  that is subdivided by a vertical partition  32  into an inflow-side chamber  34  and an outflow-side chamber  36 . 
         [0031]    The spaces between tubes  22  are likewise closed off at the bottom in liquid-tight fashion by closure panels  38 , so that a lower tank  40  is formed there. 
         [0032]    Upper tank  30  is joined in liquid-tight fashion to heat exchanger  20  by means of a crimped join  44 . It has an upper wall  46  ( FIG. 3 ) that is implemented here integrally with partition  32 . Apertures are located in said wall, namely an aperture  48  above outflow-side space  36  and an aperture  50  above inflow-side space  34 . 
         [0033]    These apertures  48 ,  50  are hermetically closed off in liquid-tight fashion on their upper sides by a flexible membrane  54  on which rests a flat spring arrangement  56  made of non-corroding spring steel. This spring arrangement  56  is joined to membrane  54 , for example, by vulcanization. For this purpose, spring arrangement  56  can also be vulcanized into membrane  54  in order to protect it particularly well from corrosion. 
         [0034]    Diaphragm  54  and spring arrangement  56  are retained in fluid-tight fashion at their outer rim by the rim  58  of a cover  60 . They are likewise retained at the center by a strut  61  of cover  60  (cf.  FIG. 3 ). Air or an inert gas, e.g. nitrogen, is present in space  62  between cover  60  and membrane  54 . 
         [0035]    Upper tank  30  has an inflow  64 , and through the latter cooling medium (hereinafter “coolant” for short)  24  flows in the direction of an arrow  66  to inflow-side chamber  34 . From there, it flows downward through passages or tubes  22  located there to lower tank  40 , and from the latter through the left-hand (in  FIG. 1 ) tubes  22  upward to outflow-side chamber  36 , i.e. the flow follows a switchback or two-direction-flow path. The flow direction can, of course, be the reverse in some cases. 
         [0036]    From there the cooling medium flows through an outflow  68 , in the direction of an arrow  70 , to a heat sink  74  that is joined in thermally conductive fashion to an electronic component  76  that is arranged on a circuit board  78  and is supplied with current through the latter. 
         [0037]    The cooling medium is heated in heat sink  74 , and the heated cooling medium is delivered back to inflow  66  by means of a circulating pump  82  driven by an electric motor  80 . 
         [0038]    Heat exchanger  20  is cooled by air by means of a fan  84 , this being indicated only very schematically. 
         [0039]      FIGS. 5 to 7  show the construction of spring arrangement  56 . The latter is formed by the fact that a left-hand spiral-shaped aperture  90  and a right-hand spiral aperture  92  are incorporated into a thin sheet of spring steel, thereby creating at the left a larger spiral spring  94  that is associated with larger chamber  36 , and at the right a smaller spiral spring  96  that is associated with smaller chamber  34 . 
         [0040]    Chambers  34 ,  36  are filled with cooling medium  24  up to membrane  54 . When said medium expands, membrane  54  bulges upward above apertures  48 ,  50 ; springs  94 ,  96  prevent membrane  54  from protruding and being damaged at individual locations. 
         [0041]    When cooling medium  24  contracts, membrane  54  bulges downward through apertures  48 ,  50 ; here again, springs  94 ,  96  ensure uniform deflection. 
         [0042]    A reliably functioning equalizing vessel  30  is thereby obtained with little complexity. 
         [0043]    In  FIG. 7  the deflections described are depicted symbolically by arrows  100 ,  102  (upward) and  104 ,  106  (downward). 
         [0044]      FIG. 8  shows an equalizing vessel  110  that has only a single connector  112  through which coolant flows in or out during operation. Vessel  110  has at the bottom a cup  114  at whose upper end is provided an outwardly projecting flange  116  in which an annular groove  118  is located. Engaging into the latter is a sealing bead  120  belonging to an elastic membrane  121 , which bead is pressed sealingly into annular groove  118  by a cover  122 . The mounting of cover  122  on cup  114  is not depicted because it is known. 
         [0045]    Elastic membrane  121  is pressed downward at its center, in the manner shown, by a plunger  126  acted upon by a spring  124 . Plunger  126  projects at the top through an opening  128  in cover  122  and is equipped there with a scale  130  for pressure indication. This plunger  126  facilitates venting, e.g. after a repair. Here as well, the space beneath membrane  121  is filled completely with coolant, i.e. with no air bubbles. 
         [0046]      FIGS. 9 to 12  show a second, preferred exemplifying embodiment of the invention. Parts identical or functioning identically to those in  FIGS. 1 to 8  are usually labeled with the same reference characters as therein, and are not described again. 
         [0047]      FIG. 9  is an overview image analogous to  FIG. 1 . The heated cooling fluid from heat absorber  74  is delivered via a conduit  66  to inflow  64  of heat exchanger  120 , where it is cooled. From outflow  68 , it flows via a conduit  70  to a unit  140 . The latter contains a circulating pump for the cooling fluid (analogous to pump  82  of  FIG. 1 ) and a fan (analogous to fan  84  of  FIG. 1 ) to generate cooling air for heat exchanger  120 . In contrast to  FIG. 1 , the fan and the circulating pump are driven by the same electric motor (cf. e.g. the Assignee&#39;s WO2004/031588A1, ANGELIS et al., whose U.S. phase is U.S. Ser. No. 10/527,471, published as US-2006-032 625-A. 
         [0048]    Cooling channels  22 , cooling plates  26 , etc. are configured in the same way as in the first exemplifying embodiment according to  FIGS. 1 to 8 . 
         [0049]    As shown particularly well by  FIG. 12 , heat exchanger tank  130  is manufactured from a thermoplastic by injection molding. 
         [0050]    This tank  130  has an inwardly projecting flange  48 , and in a second injection-molding step a flexible membrane  154  made of TPE (thermoplastic elastomer) is molded, as a soft component, onto the upper side of this flange  48 . This method is also referred to as two-component injection molding. The seam is labeled  155 . 
         [0051]    Thermoplastic silicone elastomers that are made up of a two-phase block copolymer (polydimethylsiloxane/urea copolymer) are preferably suitable for membrane  154 . A TPE-A (polyether block amide) can also be used if applicable. 
         [0052]    Because the strength of the join between the thermoplastic material of tank  130  and the molded-on TPE of membrane  154  is not very high in the region of joining seam  156 , cover  60  is used as additional security; this has a downwardly projecting portion  158 ′ that rests with pressure on the welded-on rim of membrane  154  in region  156 , i.e. along the entire periphery of membrane  154 . 
         [0053]    For this purpose, outer rim  158  of cover  60  is joined to upper rim  160  of tank  130 , e.g. by laser welding, adhesive bonding, bolting, or by way of a latching join.  FIG. 12  shows a join by means of a notch  166  and a projecting rim  168 , which are joined by laser welding. Laser welding results, in space  162  between cover  60  and membrane  154 , in an enclosed air cushion that braces membrane  154  toward the top and thereby relieves mechanical stress. 
         [0054]    If too much oxygen diffuses into the cooling system through the plastic walls, it oxidizes the corrosion inhibitors contained in the coolant and gas bubbles may form; this can result in malfunctions in the cooling system and in some cases even a failure of the cooling system. If too much coolant diffuses outward through the plastic walls, at some time during the required service life (often approx. 60,000 hours) there will be too little coolant remaining in the system for it to continue functioning, and a failure then likewise occurs. 
         [0055]    These requirements, in addition to the temperature and strength demands, limit the suitable materials. 
         [0056]    Appropriate basic materials (hard components) for tank  130  are: polyphenylene oxide (PPO), glass-fiber reinforced; optionally also polypropylene (PP), likewise glass-fiber reinforced. Particularly suitable on the basis of present knowledge, in view of the requirement of very low permeability for water, glycol, or another coolant outward from the cooling circuit on the one hand, and for oxygen from outside into the coolant on the other hand, is polyphenylene sulfide (PPS), glass-fiber reinforced; or PA-HTN, a temperature-stabilized polyamide, likewise glass-fiber reinforced. 
         [0057]    PA is very well suited for laser welding, PPS somewhat less so. PA is therefore preferred when suitable, including for price reasons. 
         [0058]    What is achieved by means of the invention is that heat exchanger  120  can simultaneously also work as an equalizing vessel to allow the equalization of changes in the volume of cooling liquid; such changes are inevitable during extended operation, and can also occur as a result of temperature fluctuations. 
         [0059]      FIG. 13  shows a heat exchanger  120 ′ having an integrated filter  170 . According to  FIG. 14 , this filter  170  has filter openings  172  that, for example, can be larger on inflow side  36  (on the right in  FIG. 13 ) than on outflow side  34 , in order to achieve firstly coarse filtration and then fine filtration. The portion of filter  170  that performs the coarse filtration could also be referred to as a sieve. 
         [0060]    Filter  170  can be made of metal or plastic, and according to  FIG. 15  is mounted on the lower side of vessel  130 ′, e.g. using the two-component injection molding method. 
         [0061]      FIG. 16  shows an alternative in which filter  170  is joined to seal  44   a  to form one module. This can be achieved, for example, by vulcanization. Alternatively, and particularly economically, it is possible e.g. to injection-embed filter  170  in TPE using the injection molding method. In both cases, assembly is simplified, and a very robust heat exchanger is obtained. 
         [0062]    In the region of inflow  36 , filter  170  filters cooling medium that flows via inlet  64  into vessel  130 ′ and from there downward into flat tubes  22  of heat exchanger  20 . Coarse dirt is thereby held back on the right side of filter  170 . 
         [0063]    The cooling medium then flows through the left half of flat tubes  22  from bottom to top, being filtered by the left half of filter  170  so that coolant, which has been filtered twice, flows through outflow  68  to pump  140  ( FIG. 9 ). 
         [0064]    This is important because pump  140  is very sensitive to contaminants in the coolant, and therefore must be particularly well protected, since contaminants could cause pump  140  to seize. 
         [0065]    From pump  140 , the coolant flows (according to  FIG. 9 ) to heat absorber  74  and from there back to inlet  64 . 
         [0066]    The result of the large filter area, in the context of this innovative arrangement, is that the pressure drop at filter  170  becomes very low. 
         [0067]    When a heat absorber that has been machined in chip-removing fashion is used, the machining chips that are created cannot be completely removed without reducing the efficiency of heat absorber  74 . 
         [0068]    In heat exchanger  20  as well, residual chips and dirt particles cannot be avoided during the manufacturing process, but at best can be reduced by soldering it under vacuum and then thoroughly rinsing and cleaning it. 
         [0069]    The entry of dirt into the coolant circuit, during filling with coolant and subsequent testing, likewise cannot be entirely avoided. 
         [0070]    The consequence is that chips and dirt might clog the small-scale structures in the heat absorber and thereby reduce efficiency. The danger also always exists that dirt particles may get into a narrow gap in pump  140  and thus cause blockage of the pump. 
         [0071]    Such problems are eliminated by the invention. It is particularly advantageous that the invention yields a large filter area, and an additional filter housing can thus be eliminated. In the liquid circuit, chips and dirt particles that become detached in the heat absorber and heat exchanger are reliably held back on the outflow side at filter  170  before they flow into pump  140 . The large filter area, relative to the amount of dirt that occurs, prevents clogging of the filter and an excessive pressure drop in the cooling medium in the circuit. 
         [0072]    The invention therefore eliminates the need to provide a separate filter housing along with hose connections, thus reducing costs. In addition, no space is required for a separate filter housing and the requisite hose connections, enabling a compact design. Lastly, with the filter arranged as depicted (i.e. in the heat exchanger tank), chips that become detached from heat absorber  74  and heat exchanger  20  cannot get into pump  140 , since the latter is arranged in the flow direction after heat exchanger  20  and before heat absorber  74 . At no other location in the overall system, moreover, could the filter area be made so large without substantial additional cost. Clogging of the small-scale structures of heat absorber  74  is therefore prevented or greatly reduced in simple fashion, as is blockage of circulating pump  140 . 
         [0073]    An equalization vessel that is separate from the heat exchanger could of course also be manufactured using the same principle, for example if the volume of the heat exchanger is limited for space reasons. In other ways as well, many variants and modifications are possible within the scope of the present invention. 
         [0074]      FIG. 17  is a sectioned detail depiction of filter  170  and seal  44   a  of  FIG. 16 . Upon installation of filter  170  into heat exchanger  20 , seal  44   a  is preferably deformed in order to produce a good seal (cf.  FIG. 16 ).