Patent Publication Number: US-2023143388-A1

Title: Heat exchanger system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/DK2021/050111, having a filing date of Apr. 15, 2021, which is based DK Application No. PA 2020 70232, having a filing date of Apr. 15, 2020, the entire contents both of which are hereby incorporated by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The following relates to a heat exchanger system comprising at least one compressor, at least one condenser, at least one pressure reduction means such as an expansion valve, at least one evaporator, at least one heat exchanger for heating the suction gas between the evaporator and the compressor inlet, which heat exchanger is heated by the refrigerant. 
     BACKGROUND 
     U.S. Pat. No. 6,523,365 B2 discloses an accumulator with an internal heat exchanger for use in an air conditioning or refrigeration system having a compressor, a condenser, an expansion device, and an evaporator. In operation, the accumulator is placed in the system so high pressure, high temperature refrigerant flowing from the condenser and low pressure, low temperature refrigerant flowing from the evaporator simultaneously enters and flows through the heat exchanger disposed in the accumulator, whereby the low pressure, low temperature refrigerant absorbs heat and thereby cools the high pressure, high temperature refrigerant. In one embodiment, the heat exchanger comprises a tube having at least one high temperature channel and one low temperature channel extending through the interior of the tube. In a second embodiment, the heat exchanger comprises a single spirally wound coaxial tube having an outer tube and an inner tube positioned within the outer tube. In a third embodiment, the heat exchanger comprises a plurality of coaxial tubes, each coaxial tube having an outer tube and an inner tube positioned in the outer tube wherein the inner tubes are fluidly connected. 
     SUMMARY 
     An aspect relates to achieving dry suction gas from a flooded evaporator. 
     It is a further aspect of the invention to achieve heat exchange with a minimum flow restriction. It is a further aspect of the invention to achieve evaporation of liquid contained in the suction gas. 
     The aspects can be fulfilled by a system as disclosed in the opening paragraph and by a heat exchanger comprising a circulating path for the suction gas and for the refrigerant liquid. 
     A heat exchanger for heating suction gas, the heat exchanger is heated by the refrigerant liquid, characterised in that the heat exchanger comprises a circulating path for the suction gas and for the refrigerant liquid, wherein the circulating path is formed with a surface between the suction gas and the refrigerant liquid, such that the circulation of the suction gas will force liquid particles in the suction gas to be forced outside in the circulating path and in that way come in direct thermal contact with the surface that separates the suction gas from the refrigerant liquid. 
     A heat exchanger is used to transfer heat for example between suction gas and liquid. Heat exchanger can be used in both cooling and heating processes. The liquids and/or gasses are separated by a surface. The surface may be provided with a smooth surface or a ruffled surface, depending on the purpose of the surface. 
     A heat exchanger for heating suction gas, wherein the heat exchanger also is capable of producing dry suction gas. The dry suction gas is a gas wherein the liquid particles are reduced to a minimum, the liquid particles are substantially removed from the suction gas. The suction gas is for example heated such that the liquid particles in the suction gas may be reduced or removed from the suction gas. The heat exchanger heating suction gas may be arranged between the evaporator and the compressor inlet. The heat exchanger is heated by the refrigerant liquid. The heat exchanger comprises a circulating path for the suction gas and a circulating path for the refrigerant liquid. The suction gas circulating path and the circulating path for the refrigerant liquid are formed with a surface between the suction gas and the refrigerant liquid. The circulation of the suction gas is forcing liquid particles in the suction gas towards the surface. In that way the liquid particles come in direct thermal contact with the surface that separates the suction gas from the refrigerant liquid. 
     A heat exchanger for heating suction gas and providing dry gas. Hereby it can be achieved that the circulating path forms a highly effective heat exchanger. Of course, the circulating path must be formed so that there is a separation between the suction gas and the refrigerant liquid. The circulating path can be achieved with a very large heat-transmitting surface. The circulation of the suction gas will force liquid particles in the suction gas to be forced outside in the circulating path and in that way come in direct thermal contact with the surface that separates the suction gas from the refrigerant liquid. Hereby it can be achieved that all liquid particles contained in the suction gas will be evaporated during the passage of the circulating path. By this highly effective evaporation of liquid particles in the suction gas, it is possible to use flooded evaporators, which can be totally flooded because afterwards the suction gas is leaving the evaporator. The rest of the liquid that is contained in the suction gas will afterwards be evaporated in the heat exchanger. In that way, the pending patent application discloses a system where evaporators can be used one hundred percent, because they can be totally flooded. In prior art cooling systems flooded evaporators are only flooded up to max 80-90% in systems operating with piston compressors. 
     In an embodiment of the invention, the heat exchanger comprises an inner tube and a directing plate winded around the inner tube, wherein the suction gas is forced to circulate along the directing plate around the inner tube, and in that way come in direct thermal contact with the surface that separates the suction gas from the refrigerant liquid. 
     In an embodiment of the invention, the circulating path can be formed in a tank by a number of directing plates for generating a circulating path. The tank further comprises a heat exchanger formed as a plate heat exchanger. Hereby it can be achieved that the directing plates forces the suction gas to circulate inside a heat exchanger. The circulation of the suction gas forces liquid particles in the suction gas into contact with the heat exchanger. 
     In an embodiment for the invention, the circulating path can be formed in a tank, which tank comprises a hollow screw. The hollow screw comprises a surface which may be an uneven surface. Inside the hollow screw is the refrigerant liquid adapted to circulate, outside the hollow screw is the suction gas adapted to circulate. Hereby it can be achieved that the hollow screw has a very large surface. The screw can be formed so that the suction gas is entering the screw in the top and the suctions gas has to follow the screw with several turns into the bottom of a tank. The suction gas will therefore follow the circulating path defined by the screw. Inside the screw is the warm refrigeration liquid circulating, which is coming directly from the condenser. All liquid particles that will come in touch with the hollow screw will be heated and in that way there will be performed evaporation. Because the hollow screw is extremely long, it is possible to evaporate liquid particles up to more than 10% in the suction gas. Hereby it is achieved that evaporators can be totally flooded and in that way evaporators can be very effective. 
     In an embodiment of the invention, the directing plate is in a predefined distance to the threaded surface that separates the suction gas from the refrigerant liquid. 
     Hereby it can be achieved that the circulating path forms a highly effective heat exchanger. The circulation of the suction gas forces the liquid particles in the suction gas towards the threaded surface, wherein the liquid particles come in direct thermal contact with the threaded surface and thereby are separated from the suction gas. Because the hollow screw is extremely long, it is possible to provide efficient evaporation of liquid particles from the suction gas, and thereby provide a dry suction gas. 
     The surface may be provided with substantially circular recesses and/or protrusions. The recesses and/or protrusions may be formed as a thread on the surface between the suction gas and the refrigerant liquid. 
     The heat exchanger may comprise at least one directing plate winded around the inner tube. The suction gas is forced to circulate along the winded directing plate or plates. In that way will the liquid particles come in direct thermal contact with the surface and be separated from the suction gas. 
     The heat exchanger may comprise at least two directing plates. The first winded directing plate may be arranged in a top section of the heat exchanger and forms the circulating path just after the inlet. A second winded directing plate may be arranged in the middle section of the heat exchanger. The second winded directing plate may be an extension of the first winded directing plate, wherein the slope of the first winded directing plate differs from the second winded directing plate. This will provide a relatively low-pressured suction gas in the inlet, and a relatively low-pressured suction gas in the outlet. In the middle part of the circulation path, the pressure is higher than at the inlet and the outlet. In that way will the thermal contact be more efficient when the liquid particles are forced towards the threaded surface. The heat exchange has therefore a minimum flow restriction. Hereby it is achieved that the heat exchanger can handle the suction gas and, in that way, provide an evaporation which increases the efficiency of the heat exchanger. 
     The hollow screw may comprise a winded tube which is arranged adjacent to the inner side of the tank forming a spiral or a coil-like tubing for the refrigerant liquid. The surface is the surfaces formed by the winded tube. The outer surface of the winded tube has a similar function, wherein the refrigerant liquid heats the suction gas, and thereby extract/evaporate the liquid particles form the suction gas, providing a dry suction gas in the process. 
     In an embodiment of the invention, a pitch of the directing plate is larger than the pitch of the threaded crest on the threaded surface. 
     A pitch may for example be measured between threaded crests on the threaded surface. If the distance between the two threaded crests is increased, the slope of the thread is also increased, and vice versa. The slope of the directing plate may be larger than the slope of the threaded crest on the threaded surface. The directing plate is therefore arranged next to/adjacent to the surface. A contact point is the point where the directing plate is nearest the surface. The directing plate with a predefined distance between the threaded surface and the directing plate, increasing the efficiency of the evaporating process. 
     In an embodiment for the invention the tank can comprise an inlet for the refrigerant liquid and an outlet for the refrigerant liquid, which tank comprises an inlet for the suction gas and an outlet for the suction gas. Hereby it can be achieved that the tank containing the hollow screw is connected to the evaporator for inlet of suction gas and connected to the suction side of the compressor at the outlet of the suction gas. Further, the tank is connected to the condenser and refrigerant liquid is sent from the tank through an expansion valve to the evaporator. 
     In an embodiment for the invention the tank can comprise an oil outlet. Hereby it can be achieved that oil drops that is collected in the suction gas flows into the tank and circulates outside the hollow screw, where the oil drops will flow at the outside of the screw and probably these oil particles will follow the screw downwards and end in the bottom of the tank. From the bottom of the tank, oil can in different way be transported back to the compressor, where oil is needed for lubrication. Some cooling systems will include a pump that can perform the transport of the oil back to the compressor. In large evaporator systems, where for example screw compressors are used, oil separation and return of oil is very important. 
     The aspect can also be fulfilled by a method for operating a heat exchange system as previous disclosed, where the compressor generates pressure in a refrigerant gas, which gas is condensed in a condenser to a refrigerant liquid, which liquid is sent to at least one evaporator through a pressure reduction means such as an expansion valve, where a heat exchanger for heating the suction gas is placed between the evaporator and the compressor inlet, which heat exchanger is heated by the refrigerant liquid, where the heat exchanger forces the suction gas into a circulating path for the suction gas, and the heat exchanger forces the refrigerant liquid to heat the suction gas. 
     Hereby it can be achieved that a highly effective evaporation of liquid gas particles contained in the suction gas will be evaporated. By use of a highly effective heat exchanger, it is possible to use a totally to flood evaporators. Even if there are several percentages of liquid particles in the suction gas, these liquid particles will be evaporated in the circulating path for the suction gas. The gas is circulating easily, but liquid particles will be forced in contact with the walls, and if the walls are in contact with the liquid refrigerant, a slight heating is performed which will evaporate the liquid particles in the suction gas. 
     In an embodiment for the invention the suction gas can be forced into the circulating path at the outside of a hollow screw, and inside the hollow screw the refrigerant liquid can be forced to circulate. Hereby it can be achieved that the hollow screw can be formed with a very large surface. The suction gas will follow the circulating path defined by the screw. Inside the screw warm refrigerant liquid can be circulating, which is coming directly from the condenser. All liquid particles that will come in touch with the hollow screw will be heated and in that way there will be performed evaporation. Because the hollow screw is extremely long, it is possible to evaporate liquid particles up to more than 10% in the suction gas. Hereby it is achieved that evaporators can be totally flooded and in that way be very effective. 
     A heat exchanger is a part of a system used to transfer heat for example between suction gas and liquid. The heat exchanger and the heat exchanging system can be used in both cooling and heating processes. The cooling or heating processes may depend on the predefined inlet temperature of the liquid and/or the predefined outlet temperature of the liquid. The cooling or heating processes may also depend on the predefined inlet temperature of the suction or discharge gas and/or the predefined outlet temperature of the suction or discharge gas. The liquids and/or gasses are separated by a surface. 
     The invention has now been explained with reference to a few embodiments which have only been discussed in order to illustrate the many possibilities and varying design possibilities achievable with the heat exchanger and a heat exchange system according to the present invention. 
     The invention achieves to provide a solution for a heat exchanger and a heat exchange system, which produce dry suction gas from a flooded evaporator. The invention also achieves to provide a solution for a heat exchanger having a minimum flow restriction. The invention furthermore achieves to provide an evaporation of liquid contained in the suction gas. 
    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein: 
         FIG.  1    shows a heat exchanger system; 
         FIG.  2    shows a sectional view of a small section of the tank; 
         FIG.  3   a    shows a possible embodiment for a cooling system; 
         FIG.  3   b    shows a possible embodiment for a heat exchanger system; 
         FIG.  4    shows a sectional view of a section of a tank; 
         FIG.  5    shows a sectional view of a section of a tank comprising a circulating path; 
         FIG.  6    shows a sectional view of a section of a tank with a large hollow screw; and 
         FIG.  7    shows a sectional view of a section of a tank with two winded directing plates. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of the invention are explained in the following detailed description. It is to be understood that the invention is not limited in its scope to the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. 
       FIG.  1    shows a heat exchanger in a cooling system as disclosed in U.S. Pat. No. 6,523,365 B2.  FIG.  1    shows a heat exchanger in a cooling system  2  with a compressor  4 , which compressor has an inlet  5 . The outlet from the compressor leads to a condenser  8 , from which condenser refrigerant liquid is sent to a heat exchanger  18  placed in a tank  24 . From the tank  24  refrigerant liquid  10  is sent through tubes to a pressure reduction means  14 , probably formed as an expansion valve  16 . From the expansion valve  16 , refrigerant liquid is sent to at least one evaporator  12 . From the evaporator  12 , the suction gas  20  is sent to the heat exchanger  18 . From the heat exchanger  18 , the suction gas is sent to the compressor inlet  5 . 
     If the system is a heating system, the heating system would depend on the predefined inlet temperature of a discharge gas and/or the predefined outlet temperature of the discharge gas. The heating system would also depend on the predefined inlet temperature of the liquid and/or the predefined outlet temperature of the liquid in the heat exchanger. The main issue is the system comprising a heat exchanger which heats or cools the gas or liquid inside the heat exchanger  18  with a liquid. The heat exchanger comprises a circulating path for the gas and for the liquid, both in a cooling system and in a heating system. The circulating path is also formed with a surface between the gas and the liquid, such that the gas is in direct thermal contact with the surface that separates the gas with the liquid. 
       FIG.  2    shows a sectional view of a small section of the tank  24 . The sectional view is only to show the principles.  FIG.  2    shows an inlet  10  for refrigerant liquid to a tube  32  to the inner  28  of the hollow screw  26 . An outlet  34  shows that the refrigerant liquid is sent further in the system. Outside  30  the hollow screw  26 , the suction gas is circulating, which has an inlet  36  and an outlet  38 . The suction gas is forced to circulate along the hollow screw downwards. The tank can comprise an oil outlet  40 . 
       FIGS.  3   a  and  3   b    are partly overlapping and disclose a possible embodiment for a heat exchanger system  102 . The figures show a compressor module  104  with a compressor inlet line  105 . The compressor module  104  has a pressure outlet  107 , which is connected to a condenser  108 . The condenser  108  is connected to a tank  124  via a pressure line  132 , where the refrigerant liquid  110  is passing a circulating path inside the tank  124 . The refrigerant liquid  110  leaves the tank  124  to a line  134 , and the refrigerant liquid  110  is sent to an expansion valve  116 , before the expanded refrigerant is sent to the evaporator  112 . From the evaporator  112  the suction gas  120  is sent to a pressure line  136  into the tank  124  and into a circulating path  122  placed inside the tank  124 . In the tank  124  the suction gas is slightly heated by the refrigerant liquid  110  that is passing through the line  132  to the line  134 . The suction gas  120  is leaving the tank by a connection  138 , where the suction gas  105  is sent into the compressor. The tank  124  comprises an oil outlet  140  connected to an oil valve  142 . Further is indicated an oil valve  144  connected to the evaporator  112 . The two oil lines are connected to a valve lock  146 . The outlet from the valve lock  146  goes into an oil ejector  150 , where the line  152  is connecting into the oil sump  181 . The oil ejector  150  is further connected to a line  148 , which is directly connected to the pressure line internally in the compressor module  104 . The evaporator  112  comprises an evaporator customer outlet  160 . Further, the evaporator  112  is connected to an evaporator customer inlet  162 . The condenser  108  comprises a cooling media inlet  164  and a cooling media outlet  166 . The cooling media inlet  164  is connected to a magnetic valve  168  and further to a cooling media pump  170 . Further, line  172  is connecting the cooling media to the compressor  104 , first to pass through an oil cooler  180 . Further, the cooling media is sent into the compressor pump device  184  and to the electrical motor  186 , from which electrical motor  186  the cooling media in a line  174  return to the cooling media outlet  166 . Internally in the compressor block  104 , a pressure sensor  188  and a temperature sensor  190  are further indicated. Further are indicated an oil sump  181  and an oil line  182  towards the compressor head covers  184 . Further, at the pressure outlet of the compressor is indicated a pressure sensor  192 , a temperature sensor  194 , and a pressure switch  196 . 
     In operation a system as disclosed in  FIGS.  3   a  and  3   b   , there will of course be an electronic control system, which at least are connected to the different sensors and also send control signals to all the different electronic valves. The electronic device comprises a variable frequency drive  187  in order to generate variable frequencies to the motor. In that way, the motor and also the compressor will be able to operate with different capacity. This can be very important if the load of the heat exchanger system varies. The evaporator outlet  160  could in fact be connected to a plurality of cooling devices, for example in a supermarket. Because the evaporator is formed as a heat exchanger, the media flowing in the connection  160  could be quite different from the refrigerant operating in the heat exchanger system. Probably, the media in the line  160  could be carbon dioxide, which could be used as cooling media in for example a supermarket or in a production of for example meat. Other possibilities to send to the heat exchanger in the evaporator could be a brine, which is a salt contained in water, which can be a highly effective cooling media, for example inside the building. 
       FIG.  4    shows a sectional view of a section of a tank  24 . The heat exchanger  18  forms a plate heat exchanger with refrigerant liquid flowing inside the volume  26 . The suction gas  20  is circulating around the inner tube  38  and the gas is forced to circulate by directing plates  23 . The inner tube  38  and the directing plate or plates  23  may be formed as an auger. The directing plate  23  is winded around the inner tube  38 , and thereby providing a circulating path  22  for the suction gas. 
     The suction gas is forced to circulate along the directing plate  23  around the inner tube  38 , and in that way comes in direct thermal contact with the surface that separates the suction gas from the refrigerant liquid. 
     In operation the suction gas in the tank  24  will be let in at the top ( FIG.  2   ) and the inlet can be placed tangential to the wall of the tank  24 , whereby a circulating starts. The circulation is further achieved by directing plates  23 . The circulation of the suction gas  20  results in that all liquid particles such as non-evaporated drops of refrigerant or drops of oil are forced into the heat exchanger  18 . In the heat exchanger  18  the temperature of the refrigerant liquid  10  will start evaporation of the liquid drops of refrigerant. The tank is so effective that flooded evaporators can be full flooded because this system can accept up to 10% liquid in the suction gas. 
     The suction gas is forced to circulate along the directing plate  23  around the inner tube  38 , and in that way come in direct thermal contact with the surface that separates the suction gas from the refrigerant liquid. The surface as a function as a large heating plate. 
     A refrigerant could be ammonia, but other media could also be used, for example carbon dioxide. 
       FIG.  5    shows a sectional view of a section of a tank comprising a circulating path. The heat exchanger  18  is formed in or as a tank  24 . The heat exchanger comprises a top section  50 , a bottom section  48  and a middle section  49 . The inlet  36  for the suction gas  20  is arranged in the top section  50  of the tank. The hollow screw  26  is arranged in the middle section  49  of the tank  24 . The hollow screw comprises a surface between the suction gas  20  and the refrigerant liquid  10 . An oil outlet  40 , not showed in the  FIG.  5   , may be arranged in the bottom section  48  of the tank  24 . 
     The heat exchanger heats the suction gas  20  inside the heat exchanger  18  with the refrigerant liquid  10 . The heat exchanger  18  comprises a circulating path  22  for the suction gas  20  and for the refrigerant liquid  10 . The heating suction gas is heated by the refrigerant liquid  10 . The heat exchanger  18  comprises a circulating path  22  for the suction gas  20  and for the refrigerant liquid  10 . 
     The heat exchanger  18  comprises an inner tube  37 . The circulating path  22  is formed around the inner tube  37 . The inner tube  37  is hollow, such that the inner tube  37  can be used as an outlet  38  for the suction gas  20 . 
     The circulating path is formed with a surface between the suction gas and the refrigerant liquid. The surface  42  is a threaded surface. The circulation of the suction gas  20  will force liquid particles in the suction gas outside in the circulating path  22 . In that way the liquid particles will come in direct thermal contact with the threaded surface that separates the suction gas  20  from the refrigerant liquid  10 . The treaded surface will lead the liquid particles to the bottom of the heat exchanger  18 , e.g., using gravity. The liquid particles may then be removed from the heat exchanger  18 . The suction gas leaving through the outlet  38  in inner tube  27 , will be dry suction gas. 
     The heat exchanger comprises a directing plate  23  winded around the inner tube  37 . The suction gas is forced to circulate along the winded directing plate  23  around the inner tube  37 , and in that way comes in direct thermal contact with the surface  42  that separates the suction gas  20  with the refrigerant liquid  10 . The refrigerant liquid  10  is flowing in the inside  28  of the hollow screw  26 , between the back wall  44  and the threaded surface  42 . A pitch of the directing plate  23  is defined by two overlaying points  23 ,  23 ″ of the directing plate  23 . A contact point  45  is a predefined distance between the threaded surface  42  and the directing plate  23 . 
       FIG.  6    shows a sectional view of a section of a tank with a large hollow screw. The heat exchanger  18  comprises a top section  50 , a bottom section  48  and a middle section  49 . The inlet  32  for the refrigerant liquid  20  is arranged in the top section  50  of the heat exchanger  18 . The hollow screw  26  is arranged in the middle section  49  of the heat exchanger  18 . The outlet  34  for the refrigerant liquid  10  is arranged at the bottom section  48  of the heat exchanger  18 . The refrigerant liquid  10  flows from the inlet  32  through the inside  28  of the hollow screw  26 , and out of the heat exchanger  18  through the outlet  34  in the bottom section  48 . 
     The directing plate  23  is in a predefined distance to the threaded surface  42 , that separates the suction gas  20  with the refrigerant liquid  10 . The directing plate  23  has a slope different from the threaded surface  42 . A predefined distance is arranged between the directing plates  23  and the threaded surface  42 . 
     A pitch of the threaded crest  46  is measured between two adjacent threaded crests  46 . The pitch of the directing plate  23  is larger than the pitch of the threaded crest  46  on the threaded surface  42 . The inside  28  of the hollow screw  26  is determined by the distance between threaded crests  46  and threaded root  47 , and pitch of the threaded crest  46  and the width of the threaded crests  46  between the threaded roots  47 . The amount of refrigerant liquid  10  flowing through the hollow screw  26  is determined by the volume of the inside  28  and the pressure applied to the refrigerant liquid  10  during the cooling process. 
       FIG.  7    shows a sectional view of a section of a tank with two winded directing plates. Hereby it can be achieved that the circulating path forms a highly effective heat exchanger. The circulation of the suction gas  20  will force liquid particles in the suction gas  20  to the outside of the circulating path. The liquid particles will be captured between the threaded crests  46  and the threaded root  47 , when the liquid particles come in direct thermal contact with the threaded surface and thereby are separated from the suction gas. All liquid particles that will come in touch with the hollow screw will be heated, and in that way, there will be performed evaporation. Because the hollow screw is extremely long, it is possible to evaporate liquid particles from the suction gas and thereby provide a dry suction gas. Hereby it is achieved that evaporators can be totally flooded and in that way be very effective. 
     A first winded directing plate  23   a  is arranged in the top section  50  of the heat exchanger  18 , such that the circulating path  22  is formed just after the inlet  36 . A second winded directing plate  23   b  is arranged in the middle section  49  of the heat exchanger  18 . The second winded directing plate  23   b  may be an extension of the first winded directing plate  23   a.  The slope of the first winded directing plate  23   a  differs from the second winded directing plate  23   b.  This will provide a relatively lower pressure of the suction gas in the inlet and a relatively lower pressure of the suction gas in the outlet than the pressure in the middle part of the circulation path. When increasing the pressure in the circulation path at the second winded directing plate  23   b,  the liquid particles in the suction gas will be forced towards the threaded surface in a more efficient manner, due to the increased pressure in the circulating path. In that way will the thermal contact be more efficient when the liquid particles are forced towards the threaded surface. Hereby it is achieved that the heat exchanger can handle the suction gas and, in that way, provide an evaporation which can be very effective. 
     Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
     For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module. 
     LIST OF REFERENCE SIGNS 
     
         
         Heat exchanger system ( 2 ) 
         Compressor ( 4 ) 
         Compressor inlet ( 5 ) 
         Condenser ( 8 ) 
         Refrigerant liquid ( 10 ) 
         Evaporator ( 12 ) 
         Pressure reduction means ( 14 ) 
         Expansion valve ( 16 ) 
         Heat exchanger ( 18 ) 
         Suction gas ( 20 ) 
         Circulating path ( 22 ) 
         Directing plates ( 23 ) 
         Formed in a tank ( 24 ) 
         Hollow screw ( 26 ) 
         Inside ( 28 ) the hollow screw ( 26 ) 
         Outside ( 30 ) the hollow screw ( 26 ) 
         Inlet ( 32 ) for the refrigerant liquid ( 10 ) 
         Outlet ( 34 ) for the refrigerant liquid ( 10 ) 
         Inner tube ( 37 ) 
         Inlet ( 36 ) for the suction gas ( 20 ) 
         Outlet ( 38 ) for the suction gas ( 20 ) 
         Oil outlet ( 40 ) 
         Threaded surface ( 42 ) Back wall ( 44 ) of the hollow screw ( 26 ) 
         Contact point ( 45 ) 
         Threaded crest ( 46 ) 
         Threaded root ( 47 ) 
         Bottom section ( 48 ) 
         Middle section ( 49 ) 
         Top section ( 50 ) 
         Heat exchanger system ( 102 ) 
         Compressor ( 104 ) 
         Compressor inlet ( 105 ) 
         Compressor outlet ( 107 ) 
         Condenser ( 108 ) 
         Evaporator ( 112 ) 
         Expansion valve ( 116 ) 
         Suction gas ( 120 ) 
         Circulating path ( 122 ) 
         Formed in a tank ( 124 ) 
         Inlet ( 132 ) for the refrigerant liquid ( 10 ) 
         Outlet ( 134 ) for the refrigerant liquid ( 10 ) 
         Inlet ( 136 ) for the suction gas ( 20 ) 
         Outlet ( 138 ) for the suction gas ( 20 ) 
         Oil outlet ( 140 ) 
         Oil valve ( 142 ) 
         Oil valve ( 144 ) 
         Oil valve block ( 146 ) 
         Line for pressured gas ( 148 ) 
         Oil ejector ( 150 ) 
         Oil return line ( 152 ) 
         Evaporator customer outlet ( 160 ) 
         Evaporator customer inlet ( 162 ) 
         Cooling media inlet ( 164 ) 
         Cooling media outlet ( 166 ) 
         Magnetic valve ( 168 ) 
         Coiling media pump ( 170 ) 
         Cooling media compressor inlet ( 172 ) 
         Cooling media compressor outlet ( 174 ) 
         Oil cooler ( 180 ) 
         Oil sump ( 181 ) 
         Compressor oil inlet ( 182 ) 
         Compressor head covers ( 184 ) 
         Electro motor ( 186 ) 
         Variable frequency drive ( 187 ) 
         Pressure sensor ( 188 ) 
         Temperature sensor ( 190 ) 
         Pressure sensor ( 192 ) 
         Temperature sensor ( 194 ) 
         Pressure switch ( 196 )