Patent Publication Number: US-10760834-B2

Title: Evaporator in a refrigerant circuit D

Description:
FIELD 
     The invention relates to an evaporator in a refrigerant circuit, which evaporator can be used, for example, in a vehicle air conditioning system. 
     BACKGROUND 
     In a closed refrigerant circuit of this type, a compressor, a condenser and an expansion member are connected in addition to the evaporator. During air conditioning operation, the vaporous refrigerant which comes from the evaporator is compressed in the compressor and is conducted into the condenser. The condenser can be arranged by way of example in the front end of the vehicle and can be flowed through by the air stream, as a result of which the refrigerant which is situated in the condenser condenses into its liquid phase, to be precise with the dissipation of thermal energy to the air stream which is flowing through. The refrigerant which is then liquid is expanded in the downstream expansion member to form a two-phase liquid/vapour mixture which is fed to a separator. A phase separation takes place in the separator, in the case of which phase separation the liquid phase is separated from the vapour phase of the refrigerant. The vapour phase is conducted via a bypass line directly to the evaporator outlet. The liquid phase which is separated from the vapour phase is conducted through the heat exchanger tubes of the evaporator. During air conditioning operation, the evaporator (for example, a cross-counterflow heat exchanger) is flowed through by way of an air flow to be cooled which is guided into the vehicle interior compartment. The refrigerant liquid phase in the evaporator is therefore evaporated into the vapour phase with absorption of thermal energy from the air flow, while the air flow is cooled at the same time. 
     WO 2015/073106 A1 has disclosed an evaporator of the generic type which has a bottom-side inlet chamber which is connected in flow terms via evaporator tubes to an evaporator outlet side. A separator for a phase separation is integrated into the evaporator inlet chamber. The evaporator tubes are realised in each case as a flat tube with a plurality of micro-channels, through which the refrigerant is guided. 
     In WO 2015/073106 A1, the phase separation takes place in the separator by way of the use of centrifugal force. To this end, the two-phase liquid/vapour mixture is introduced into the evaporator inlet chamber in a vortex flow along the inner wall of a distributor tube. As a result, the vapour phase collects radially within the vortex flow, and the said vapour phase is fed to a bypass line. In contrast, the liquid phase collects radially on the outside at the vortex flow which is guided along the distributor tube inner wall. The use of centrifugal force is complicated in terms of process technology. In addition, a structurally complicated separator geometry is required. 
     U.S. Pat. No. 7,832,231B2 has disclosed an evaporator, the evaporator tubes of which are likewise realised as flat tubes with micro-channels. The evaporator has an upper-side (in the evaporator height direction) inlet chamber, into which a separator for a phase separation is integrated. EP 2 159 514 A2 has disclosed an evaporator, the evaporator tubes of which are likewise configured as flat tubes, into which in each case a plurality of micro-channels are integrated. Further evaporators are known from WO 2006/083442 A2 and from US 2015/0345843 A1. 
     SUMMARY 
     It is the object of the invention to provide an evaporator with a separator which is integrated into it, which evaporator operates simply in terms of process technology and is of structurally simple configuration. 
     In order to configure the separator, the micro-channels of the at least one evaporator flat tube can be divided into at least one vapour phase micro-channel which forms the bypass line and into at least one liquid phase micro-channel, into which the liquid phase which is collected in the inlet chamber flows. 
     In one technical implementation, the inlet chamber can be configured by way of a chamber bottom and side walls which are raised from it in the evaporator height direction and terminate at an upper chamber top wall. The evaporator flat tube can protrude downwards through the chamber top wall into the inlet chamber. 
     Here, the orifice openings of the micro-channels are spaced apart from the chamber bottom by a free spacing. In the case of an evaporator of this type, the liquid phase collects on the chamber bottom of the inlet chamber with a filling level. According to the invention, the free spacing between the orifice openings of the micro-channels and the chamber bottom is selected in such a way that the liquid phase micro-channel is dipped with its orifice opening into the liquid phase which is collected in the inlet chamber. In contrast, the vapour phase micro-channel is positioned with its orifice opening above the liquid phase level in the inlet chamber by a height offset. 
     The free spacing of the orifice opening of the vapour phase micro-channel from the chamber bottom can preferably be greater than the free spacing of the orifice opening of the liquid phase micro-channel. 
     In one specific design variant, the evaporator flat tube can have a right-angled flat profile cross section, to be precise with narrow sides and flat sides which lie opposite one another in each case. The micro-channels are arranged between the flat tube narrow sides in an aligned manner at least in one row behind one another in a parallel arrangement. 
     In the case of a flat tube construction of this type, the orifice openings of the micro-channels are configured on a flat tube end side which is, in particular, planar and faces the chamber bottom. With regard to a properly operating separator, it is preferred if the flat tube end side lies, in particular completely, in an oblique plane. The said oblique plane defines an oblique angle with a horizontal plane, as a result of which different free spacings result between the orifice openings of the micro-channels and the chamber bottom. 
     The evaporator can preferably be of plate-shaped configuration, to be precise with an inlet chamber which is elongate in an evaporator transverse direction. In this case, a plurality of evaporator flat tubes can be arranged behind one another and at a spacing from one another in the evaporator transverse direction in an aligned manner in a parallel arrangement. Intermediate spaces, through which air flows, are formed between the evaporator flat tubes, through which intermediate spaces the air flow to be cooled is guided during air conditioning operation. In the region of their orifice openings, all of the evaporator flat tubes can preferably have in each case identical separator geometries which are specified above. 
     In order to increase the degree of efficiency, the separator can have a distributor tube which extends within the inlet chamber in the evaporator transverse direction. The distributor tube can have a reduced cross section in comparison with the inlet chamber. During air conditioning operation, the two-phase liquid/vapour mixture flows via the distributor tube into the inlet chamber. The distributor tube can have at least one discharge opening which is assigned a deflector wall. During air conditioning operation, a refrigerant jet can therefore exit from the discharge opening and come into contact with the deflector wall, at which a phase separation takes place. 
     In one preferred design variant, the discharge opening can be configured on the outer circumference of the distributor tube and/or can be oriented upwards in the evaporator height direction. In this case, the chamber top wall can act in a structurally simple manner as a deflector wall, with which the refrigerant jet comes into contact. 
     With respect to a proper phase separation, it is advantageous if the distributor tube discharge opening is offset from the orifice openings of the evaporator flat tubes in the evaporator transverse direction by a transverse offset. In this case, the distributor tube discharge opening is directed directly onto the chamber top wall (which acts as a deflector wall), the refrigerant jet which exits being guided past the orifice openings of the micro-channels. 
     By way of the component geometry which is described in the following text, a pocket-shaped phase separation space can be provided, with the aid of which the phase separation in the separator is increased further. The evaporator flat tubes can thus protrude in each case with a tube projection from the chamber top wall downwards into the inlet chamber. The mutually facing flat sides of the tube projections, the chamber top wall and the chamber side walls which lie opposite one another in the evaporator depth direction delimit the pocket-shaped phase separation space. The refrigerant jet which exits from the distributor tube discharge opening is sprayed into the phase separation space. 
     With regard to perfect functionality of the separator, it is advantageous if the distributor tube protrudes beyond the liquid phase level in the inlet chamber at least with its discharge opening and is not dipped completely into the liquid phase which collects in the inlet chamber. In this case, the distributor tube can be positioned at least with its discharge opening in an inner corner region which is defined between the refrigerant liquid phase level and the flat tube end sides. 
     The evaporator can be configured as a cross-counterflow heat exchanger. Accordingly, as a first flat tube, the evaporator flat tube can be a constituent part of a first evaporator tube set. In the first evaporator tube set, the refrigerant is guided counter to gravity as far as into an upper deflecting chamber. From the upper deflecting chamber, the refrigerant is guided back further via at least one second flat tube which is a constituent part of a second evaporator tube set in the direction of gravity into a bottom-side outlet chamber. The bottom-side outlet chamber can be attached in flow terms to a suction side of the compressor. 
     The outlet chamber and the inlet chamber can preferably be arranged in a common bottom-side distributor housing of the evaporator. In the case of flow guidance of this type, the first flat tube (which leads to the deflecting chamber) and the second flat tube (which leads to the outlet chamber) can be arranged behind one another in an aligned manner in an evaporator depth direction. Here, the first and second flat tubes are positioned in such a way that their flat sides lie in each case in vertical planes which are defined between the evaporator depth direction and the evaporator height direction. In one technical realisation, the first flat tubes in the first evaporator tube set and the second flat tubes in the second evaporator tube set can be provided in identical numbers. 
     In the following text, a preferred geometry of the evaporator flat tube will be described, in the case of which preferred geometry the flat tube narrow sides are spaced apart from one another over a flat tube width. The flat tube flat sides are spaced apart from one another over a flat tube thickness. With regard to a perfect functionality of the separator and to a high degree of efficiency of the evaporator, it is preferred if the number of micro-channels in the first flat tube (assigned to the first evaporator tube set) is greater than in the second flat tube (assigned to the second evaporator tube set). As an alternative and/or in addition, the flat tube width of the first flat tube can be greater than the flat tube width of the second flat tube. As an alternative and/or in addition, the flat tube thickness of the first flat tube can be smaller than the flat tube thickness of the second flat tube. 
     Each micro-channel of the first/second flat tube has a micro-channel flow cross section. The micro-channel flow cross sections of all the micro-channels of the first/second flat tube can preferably be of identical configuration. 
     It is preferred if the micro-channels of the first flat tube provide an overall flow cross section which is greater than an overall flow cross section which is provided by the micro-channels of the second flat tube. In one specific design variant, the number of micro-channels in the first flat tube can lie, for example, at  29 . The number of micro-channels in the second flat tube can lie at  19 . The flat tube width of the first flat tube can be 20 to 30 mm, preferably 25 to 27 mm, by way of example, whereas the flat tube width of the second flat tube can be 10 to 20 mm, preferably 15 to 18 mm. In addition, the flat tube thickness of the first flat tube can possibly lie at 1.2 to 1.3 mm, preferably 1.25 to 1.28 mm, whereas the flat tube thickness of the second flat tube can lie at 1.3 to 1.4 mm, preferably 1.35 to 1.38 mm. 
     On account of the phase separation which takes place in the separator, the pressure loss in the evaporator is reduced considerably during air conditioning operation. Consequently, the flow cross section which is provided by the micro-channels can preferably be reduced. A reduction of this type of the micro-channel flow cross section is accompanied by only a slightly increased evaporator pressure loss. 
     During air conditioning operation, the liquid phase which collects in the inlet chamber flows into the liquid phase micro-channel, and said liquid phase can evaporate into a vapour bubble at least partially in the further flow path through the liquid phase micro-channel. This results in the problem that the pressure loss rises in the liquid phase micro-channel, and the vapour bubble which forms is possibly pressed back into the inlet chamber in the opposite direction to the flow. A vapour return flow of this type impairs the degree of efficiency of the evaporator. 
     Against this background, a vapour return flow preventer is configured in the region of the orifice opening of the liquid phase micro-channel. The vapour return flow of the vapour bubble which is formed in the liquid phase micro-channel back into the inlet chamber can be prevented by way of the vapour return flow preventer. 
     In one embodiment which is simple in terms of production technology, the vapour return flow preventer is a restricting orifice, by means of which the flow cross section of the orifice opening is reduced in comparison with the remaining micro-channel flow cross section. In order to reliably prevent a vapour return flow, it is preferred if the flow cross section is reduced at the micro-channel orifice opening by up to from 50% to 75%. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, one exemplary embodiment of the invention is described using the appended figures, in which: 
         FIG. 1  shows a block circuit diagram of a refrigerant circuit of a vehicle air conditioning system; 
         FIG. 2  shows a roughly diagrammatic perspective part view of the evaporator which is connected into the refrigerant circuit; 
         FIG. 3  shows details of a side sectional view of the evaporator; 
         FIG. 4  shows details of a side sectional view of the evaporator; 
         FIG. 5  shows a detailed view of the evaporator; 
         FIG. 6  shows another detailed view of the evaporator; and 
         FIG. 7  shows another detailed view of the evaporator; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a closed refrigerant circuit for, for example, a vehicle air conditioning system. An evaporator  1 , a compressor  3 , a condenser  5  and an expansion member  7  are connected into the refrigerant circuit. A separator  9  is connected between the expansion member  7  and the evaporator  1 , in which separator  9  a phase separation takes place. During air conditioning operation, a vaporous refrigerant which comes from the evaporator  1  is compressed in the compressor  3  and is conducted into the condenser  5 . The condenser  5  can be arranged by way of example in the front end of the vehicle and can be flowed through by the air stream. As a result, the refrigerant condenses into its liquid phase with the dissipation of thermal energy. The liquid refrigerant is expanded in the expansion member  7  which is connected downstream in flow terms to form a two-phase liquid/vapour mixture  10  ( FIG. 7 ) which is fed to the separator  9 . In the separator  9 , the liquid phase  11  of the refrigerant is separated from its vapour phase  13 . The liquid phase  11  is fed via a low-pressure line  15  ( FIG. 1 or 2 ) to the evaporator  1 , whereas the vapour phase  13  is guided via a bypass line  17  to the outlet side  22  ( FIG. 3 ) of the evaporator  1 . During air conditioning operation, the evaporator  1  is flowed through by an air flow L which is guided into the vehicle interior compartment and provides thermal energy while being cooled, by means of which thermal energy the refrigerant liquid phase  11  evaporates into the vapour phase  13  in the evaporator  1 . The vapour phase  13  which is produced in the evaporator  1  is conducted via the evaporator outlet  22  to the suction side of the compressor  3 . 
       FIG. 2  indicates the evaporator  1  structurally in a perspective illustration to the extent that it is required for understanding the invention. Accordingly, the evaporator  1  has a bottom-side distributor housing  19  which is divided in  FIG. 3  into an inlet chamber  21  and into an outlet chamber  23  which are separated from one another in a fluid-tight manner via a dividing wall  25 . The separator  9  which will be described later is integrated into the evaporator inlet chamber  21 , into which separator  9  the refrigerant which is expanded to a low pressure in the expansion member  7  is introduced as a two-phase liquid/vapour mixture  10  ( FIG. 7 ) and is separated into the vapour phase  13  and into the liquid phase  11  which is separate therefrom. 
     In  FIG. 2 , the evaporator  1  has a first evaporator tube set  29 , in which the refrigerant which is collected in the bottom-side inlet chamber  21  is conducted in an evaporator height direction z (that is to say, counter to the direction of gravity) as far as into an upper-side deflecting chamber  31  which is indicated in  FIG. 3 . In the deflecting chamber  31 , the refrigerant flow path K is deflected, as shown by way of an arrow in  FIG. 3 . The refrigerant is returned from the upper-side deflecting chamber  31  via a second evaporator tube set  33  ( FIG. 2 ) into the bottom-side outlet chamber  23  ( FIG. 3 ). The outlet chamber  23  is flow-connected via the evaporator outlet side  22  to the suction side of the compressor  3 . 
     The evaporator  1  which is shown in the figures is realised as a cross-counterflow evaporator. Accordingly, the air flow L which is to be cooled and is guided into the vehicle interior compartment is guided in a crossflow first of all through the second evaporator tube set  33  and then through the first evaporator tube set  29 . 
     In accordance with  FIG. 2 , the bottom-side distributor housing  19  of the evaporator  1  is of elongate configuration in an evaporator transverse direction y. A plurality of first flat tubes  35  which are constituent parts of the first evaporator tube set  29  are arranged behind one another and at a spacing in the evaporator transverse direction y in an aligned manner in a parallel arrangement, to be precise with the formation of intermediate spaces  37 , through which air flows. In  FIG. 2 , the second evaporator tube set  33  has second flat tubes  39 . Each of the second flat tubes  39  is arranged in alignment behind a corresponding first flat tube  35  in each case in an evaporator depth direction x. The number of first flat tubes  35  in the first evaporator tube set  29  and the number of second flat tubes  39  in the second evaporator tube set  33  are identical. 
       FIGS. 5 and 6  in each case show a first flat tube  35  and a second flat tube  39  in cross section. Accordingly, the two flat tubes  35 ,  39  in each case have a number of micro-channels  41 . In  FIGS. 5 and 6 , the flat tubes  35 ,  39  are configured with a right-angled flat profile cross section, to be precise with narrow sides  43  and flat sides  45  which lie opposite one another in each case. The narrow sides  43  of the flat tubes  35 ,  39  are spaced apart from one another over a flat tube width b 1 , b 2 , whereas the flat tube flat sides  45  are spaced apart from one another over a flat tube thickness d 1 , d 2 . The micro-channels  41  extend in the respective flat tube  35 ,  39  between the flat tube narrow sides  43  which lie opposite one another, to be precise behind one another in an aligned manner in one row and in a parallel arrangement. 
     As is apparent from  FIG. 3 , the inlet chamber  21  is delimited in a fluid-tight manner by a chamber bottom  47 , side walls and dividing walls  49 ,  25  which are raised from it in the evaporator height direction z, and a chamber top wall  51 . The first evaporator flat tubes  35  protrude downwards through the chamber top wall  51  into the inlet chamber  21 , to be precise in each case with a tube projection  53  ( FIG. 2 ). The bottom-side orifice openings  55  of the micro-channels  41  of the first flat tubes  35  are spaced apart from the chamber bottom  47  over free spacings a ( FIG. 3 ). 
     In the following text, the construction and the method of operation of the separator  9  will be described using  FIG. 3 . Accordingly, the orifice openings  55  of the micro-channels  41  of the first flat tube  35  which is shown are configured in a planar, obliquely set flat tube end side  57  which lies completely in an oblique plane. The said oblique plane defines an oblique angle α with a horizontal plane. 
     This results in a wedge-shaped separator geometry, in the case of which an inner micro-channel  41  which faces the dividing wall  25  is spaced apart from the chamber bottom  47  at a minimum spacing a min  ( FIG. 4 ), and an outer micro-channel  41  in the evaporator depth direction x is spaced apart from the chamber bottom  47  at a maximum spacing a max  ( FIG. 4 ). 
     The above-described separator geometry is designed in such a way that, in every operating situation, the filling level f ( FIG. 3 ) of the liquid phase  11  which is collected in the inlet chamber  21  is greater than the minimum spacing a min . Consequently, during air conditioning operation, the micro-channels  41  of the flat tube  35  are divided into at least one vapour phase micro-channel  41   a  which is flowed through exclusively by the vapour phase  13 , and into at least one liquid phase micro-channel  41   b , into which exclusively the liquid phase  11  flows. That filling level f of the liquid phase  11  which is shown in  FIG. 3  results by way of example in the seven partially shown vapour phase micro-channels  41   a . The latter are positioned above the liquid phase level  65  and therefore form the bypass line  17 . In addition, the six partially shown liquid phase micro-channels  41   b  result in  FIG. 3 . Exclusively the liquid phase  11  flows into the liquid phase micro-channels  41   b . The obliquely positioned flat tube end side  57  therefore dips partially into the liquid phase  11  which is collected in the inlet chamber  21 , and partially protrudes beyond the liquid phase level  65  of the liquid phase  11 . 
     In addition, the separator  9  has a distributor tube  59 . The distributor tube  59  extends in the inlet chamber  21  in the evaporator transverse direction y and is configured with a reduced cross section in comparison with the inlet chamber  21 . The distributor tube  59  has discharge openings  61  which are arranged behind one another on the outer circumference in each case at a spacing and are oriented upwards in the evaporator height direction z, to be precise in the direction of the chamber top wall  51 . Via the distributor tube  59 , the two-phase liquid/vapour mixture  10  flows into the inlet chamber  21 , to be precise via the discharge openings  61 . A refrigerant jet  62  (indicated by way of an arrow in  FIG. 4 ) exits in each case from the discharge openings  61 . The refrigerant jet  62  comes into contact with the chamber top wall  51  which acts as a deflector wall. A phase separation takes place in the case of the contact of the refrigerant jet  62  with the chamber top wall  51 . In order to further assist the said phase separation, the discharge openings  61  are arranged offset by a transverse offset Δy ( FIG. 4 ) with respect to the first flat tubes  35  as viewed in the evaporator transverse direction y. This ensures that the refrigerant jets  62  which exit come directly into contact with the chamber top wall  51  and are conducted past the orifice openings  55  of the micro-channels  41  of the first flat tubes  35 . 
     In order to further increase the phase separation, each refrigerant jet  62  is assigned a pocket-shaped phase separation space  63  which is open towards the bottom and into which the refrigerant jet  62  is sprayed. The phase separation space  63  is delimited by the mutually facing flat sides  45  of the tube projections  53  of the first flat tubes  35 , by the chamber top wall  51  and by the side wall  49  and the dividing wall  25 . 
     In order not to impair the functional capability of the separator  9 , the distributor tube  59  is to be positioned in the inlet chamber  21  in such a way that at least its discharge openings  61  protrude beyond the liquid phase level  65 , as shown in  FIG. 3 or 7 . Accordingly, the distributor tube  59  is positioned at least with its discharge openings  61  in an inner corner region. The latter is defined between the liquid phase level  65  and the obliquely set flat tube end side  57 . 
       FIG. 5  shows one of the first flat tubes  35  in cross section. Accordingly, the first flat tube  35  has a total of 20 to 38, for example 29, micro-channels  41 , the flat tube width b 1  being 27 mm and the flat tube thickness d 1  lying at 1.28 mm. In contrast to this,  FIG. 6  shows one of the second flat tubes  39  in cross section. Accordingly, the number of micro-channels  41  in the second flat tube  39  lies at 10 to 28, for example 19, whereas the flat tube width b 2  lies at 18 mm, and the flat tube thickness d 2  is 1.35 mm. 
     On account of the highly efficient phase separation which takes place in the separator  9 , the flow cross section which is provided by the micro-channels  41  can be reduced substantially in comparison with the prior art. The micro-channel cross section q 1  in the first flat tube  35  thus lies at (0.5 to 0.6 mm, preferably 0.55 to 0.57 mm)×(0.6 to 0.8 mm, preferably 0.7 to 0.75 mm), all of the micro-channels  41  in the first flat tube  35  having substantially identical micro-channel cross sections q 1 . In the second flat tube  39 , the micro-channel cross section q 2  lies at (0.6 to 0.8 mm, preferably 0.7 to 0.75 mm)×(0.5 to 0.65 mm, preferably 0.55 to 0.6 mm), all of the micro-channels  41  in the second flat tube  35  having substantially identical micro-channel cross sections q 2 . 
     As is further apparent from  FIG. 7 , during air conditioning operation, the liquid phase  11  which is collected in the inlet chamber  21  flows into the liquid phase micro-channels  41   b . In the further flow path towards the top, the liquid phase  11  which has flowed in can evaporate at least partially into a vapour bubble  68 . In a case of this type, there is the risk that the vapour bubble  68  is returned into the inlet chamber  21  counter to the refrigerant flow direction. In order to prevent a vapour return flow of this type into the inlet chamber  21 , restricting orifices  67  ( FIG. 7 ) are configured in the region of the orifice openings  55  of the micro-channels  41  of the respective first flat tube  35 . The said restricting orifices  67  act as vapour return flow preventers which prevent a return flow of the vapour bubbles  68  which are formed in the liquid phase micro-channels  41   b  into the inlet chamber  21 . Here, the flow cross section at the restricting orifices  67  is reduced by approximately from 50% to 75% in comparison with the remaining micro-channel flow cross section.