Abstract:
An internal heat exchanger unit for use in refrigerant circuits of automotive air conditioning systems. The internal heat exchanger includes a casing within which is located an accumulator, spaced thereapart so as to define a gap between the two components. Located within the gap is a coil-shaped fin tube. The fins of the fin tube include bend end portions at spaced apart locations about the fins, and the bent end portions defining an outer dimension of the fins that substantially corresponds to the gap width.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an internal heat exchanger with a calibrated coil-shaped fin tube, which together with a refrigerant accumulator, forms a unit used in refrigeration circuits of the air conditioning of automotive vehicles.  
         [0003]     The combined accumulator with internal heat exchanger combines the functionalities of both components in one unit, a combined component. The combined component is used preferably in mobile R744-refrigeration plants. Compared to the single components, the compact combined component adapts better to the limited space in the engine compartment. It is also advantageous as to costs for the general system of the mobile refrigeration plant.  
         [0004]     2. Related Technology  
         [0005]     In a refrigeration machine or heat pump, the accumulator is arranged downstream of the evaporator and is intended to take refrigerant filling quantities varying due to varying operation conditions, thereby holding out a refrigerant reserve in order to make up for leakage losses occurring over the maintenance interval. The internal heat exchanger has the function to transfer heat within the system for overcooling from the high from the high-pressure side to the low-pressure side, which thereby is heated.  
         [0006]     The combination of collector and internal heat exchanger can be configured as to containers arranged concentrically. The inner container functions as refrigerant collector. In the annular gap between the inner container and the outer container, there is the internal heat exchanger.  
         [0007]     The state-of-the-art knows varied combinations of internal heat exchangers and accumulators.  
         [0008]     From DE 311 19 440 A1, an internal heat exchanger and accumulator is known where the refrigerant collects in the accumulator at low pressure and is then thermally contacted with high-pressure flow. The heat exchanger coil containing the high-pressure flow consists of coil-shaped bundles of smooth pipes. On the inner side of the coil bundle, the refrigerant passes through the pipe coil of the internal heat exchanger at high pressure, and on the outer side, the refrigerant vapor flows around the pipe coil at low pressure. It applies as a matter of principle that, in the refrigerant circuit, both sides are admitted with equal mass flows. For thermodynamic reasons, the low pressure side is considerably more problematic than the high-pressure side as to the pressure loss and heat transmission. The transport quantities of carbon dioxide (and density as well) on the low-pressure side result in a larger heat transmission area and a larger flow cross-section. The disadvantage of this internal heat exchanger with a high-pressure pipe is that the refrigerant circulating countercurrently produces pressure losses on the low-pressure side that are too high and the available heat exchanger surface is too small. The design structure with several parallel pipes causes that the low-pressure side flows cross-countercurrently relative to the high-pressure side. The pressure loss on the low-pressure side clearly decreases while the heat exchanger area clearly increases. However, manufacture of an internal heat exchanger with bundled smooth pipes is expensive and the produced heat transmission packets are difficult to reproduce as to the exact determination of the gaps decisive for the flow cross-sectional area.  
         [0009]     DE 101 61 886 A1 describes an internal heat exchanger where, in the space between the walls of an inner and an outer container, a helical pipeline (a coil-shaped internal heat exchanger) is provided. A first fluid passes through the helical pipeline while a second fluid passes through two gaps between the walls and the helical pipeline. The gap widths are chosen to reduce the pressure drop without impairing the heat exchanger capacity, or to maximize heat transmission, respectively.  
         [0010]     DE 35 43 230 A1 also describes a coil-shaped pipeline functioning as heat exchanger. A refrigeration unit is disclosed where a liquid refrigerant receiver, a drawn-in vapor refrigerant collector and a refrigerant heat exchanger are integrated to form a unit. The integrated unit is limited by an approximately cylindrical outer casing which forms the drawn-in vapor refrigerant collector, and is provided with a refrigerant vapor inlet and a refrigerant vapor outlet. Further, the integrated unit includes as inner casing, also approximately cylindrical, which is located within the upper part of the outer casing forming an annular space between itself and the outer casing. The inner casing serves a liquid refrigerant receiver having a liquid refrigerant inlet to be connected to the condenser outlet thereof and another outlet located within the inner casing. Further, the integrated unit includes a heat exchanger coil, which is located in the annular space between the inner and outer casings, on the inlet side connected to the outlet of the liquid refrigerant receiver and on the outlet side leading to an outlet to be connected to the evaporator inlet.  
         [0011]     Common to all the solutions described above is that the warmer high-pressure refrigerant passes the pipe coils on the inner side and the colder low-pressure refrigerant flows around the pipe coils on the outer side. Mass flow is equal on both sides so that a considerably bigger volume flow results for the low-pressure side. On the low-pressure side, however, the pressure loss must be kept comparatively low for thermodynamic reasons, which requires relatively wide cross-sections. At the same time, because of the low density and the concomitant low heat transmission capacity of the refrigerant, a large exchange area must be provided.  
         [0012]     Requirements like that are best met by a coil-shaped fin tube seen in DE 35 43 230 A1. As with all above mentioned solutions, the refrigerant collector and the internal heat exchanger are combined by two concentric containers, whereby the coil-shaped fin tube which functions as the internal heat exchanger is placed between the inner and the outer container. This construction, however, has some design disadvantages.  
         [0013]     If the fin heads do not bear against the outer wall of the inner container and the inner wall of the outer container, one, or two, respectively, annular gaps without exchanger area are formed, starting from the internal heat exchanger. Then, low-pressure bypass flows will pass through these annular gaps, significantly impairing the efficiency of the internal heat exchanger.  
         [0014]     If the fin heads do not bear against the annular gap surfaces, then under normal vehicle vibration conditions the tube coil starts to vibrate, continuously beating against the container walls, which leads to considerable noise development.  
         [0015]     If the fin tubes themselves and the tube coils are manufactured true to size in order to avoid annular gaps between the fin heads and the coil walls, at a very great expense, considerable problems are created particularly in series production when the components are assembled. Assembling under the condition of such a little allowance between the tube coils and annular gaps is additionally made even more difficult in that the tube coils with the fines get caught on each other when they are axially assembled. Adapting the coil diameter, for example, by manually rotating the tube coil during the assembling process gets nearly impossible.  
         [0016]     DE 195 46 489 A1 discloses a heat exchanger with a fin tube where, in the contact areas, in order to avoid that two coil flights situated adjacent each other will engage into each other, the fins of at least one coil flight are rectangularly bent at approximately half their radial extension.  
         [0017]     Naturally, the fin heads are pointed relatively sharply. Whether there is a gap or not between the fin heads and the container walls, due to the natural vehicle vibrations, the fins can produce notches in the container walls. The notches may possible lead to failure of the component.  
       SUMMARY OF THE INVENTION  
       [0018]     An objective of the invention is to provide an internal heat exchanger with accumulator for refrigerant circuits, whereby the above mentioned disadvantages of the state-of-the-art the heat exchangers are eliminated, which is configured to be easily and cost-effectively manufactured, which provides a large heat transmission area for the low-pressure flow, which creates less flow losses of the low-pressure flow, and which avoid bypass flows  
         [0019]     In achieving the above, the invention provides an internal heat exchanger with a calibrated coil-shaped fin tube. Together with an accumulator the heat exchanger forms a unit and is used in refrigerant circuits of, particularly, motor vehicle air conditioning units. The internal heat exchanger includes a casing with a top cover plate and a bottom cover plate. Within the casing there is provided an accumulator for the low pressure liquid refrigerant. A coil-shaped fin tube, through which passes high pressure refrigerant, is located in an annular gap (with gap width x) between the accumulator and the casing. The fins are annular and radially arranged on the fin tube so that the refrigerant vapor is readable at low pressure between the fins of the fin tube cross-countercurrently and, possibly, cocurrently to the high pressure refrigerant. According the invention, the fins are calibrated to adopt the dimensions of the annular gap by bending the fins at their distal ends. The coil-shaped fin tube is integrated into the annular gap such that fin heads bear against the inner and outer containers, that means bearing surfaces of the fin heads form in the radial direction.  
         [0020]     More specifically, the fins are bent-off at their distal end by a defined length, length z, whereby the bent length z of the fin is smaller than or equal to the distance between adjacent fins. Further, the surfaces of the fin heads in the region of contact with the walls of the casing or accumulator are larger.  
         [0021]     The internal heat exchanger according to the invention is advantageous in that the fabrication and manufacture processes can be handled better and carried out more effectively, compared with the use of several smooth tubes that must be formed to establish a heat transmission bundle.  
         [0022]     The present invention also results in a significantly reduced pressure loss. The fins of the fin tube serve to maintain the distance between the tube and the accumulator, as well as between the tube and the casing. Refrigerant vapor flows between the fins into the so formed channels. Based on the dedicated establishing of the fin height the gap and, hence, the volume flow or the flow pressure loss, respectively, become calibratable. This results in a reproducible design of the gap width.  
         [0023]     The internal heat exchanger according to the invention can be manufactured at a lower price, as compared to an internal heat exchanger formed of a bundle of smooth tubes. In addition, the internal heat exchanger according to the invention allows a higher efficiency of heat transmission to be reached.  
         [0024]     The concept of the invention consists in that the fin tube coil is calibrated by bending the ends of the fins so as to take the dimensions of the annular gap in order to avoid bypass flows and enlarge the surfaces of the fin heads in contact with the walls defining the annular gap.  
         [0025]     Calibration of the inner and outer diameters of fin tube coils by partially bending the fin heads in radial coil direction results in that the fin tube can itself be manufactured to relatively large tolerances. The resulting accuracy of fit prevents bypass flow around the fin tube coil from developing, so that material expenditure for the internal heat exchanger is reduced because the same heat capacity is reached by less heat transmission surface. In addition, the resulting accuracy of fit prevents the fin tube coil from vibrating, hence from developing undesirable noise.  
         [0026]     Further, the bending of the fins results in the ends of the fins bearing flat against the outer wall, i.e., the wall of the casing, and/or the internal wall of the annular gap, i.e., the wall of the accumulator. This avoids damage (in form of notches) to the container walls due to vehicle vibrations.  
         [0027]     In another advantageous embodiment, the fin heads are partially bent-off not only in the radial direction, but also in the axial direction. As such, bearing surfaces form between individual coils on which the coils can slide relative to one another, without hooking together. The internal heat exchanger is preferably configured as fin tube coil with fin heads bent-off in four locations. In such a construction, the fin heads are bent on opposing sides in the radial and axial directions.  
         [0028]     The bending of the fin heads in the axial direction of the fin tube coil results in individual coils bear against the bent surfaces of adjacent coils and do not hook together. Assembling of the component is made possible also with fin tube coils made true to size. Another advantage consists in that therefore, the height of the fin tube coil is exactly defined and not dependent on the degree of hooking. Homogeneous distribution of the individual coils over the height of the fin tube coil is ensured.  
         [0029]     In yet another embodiment of the invention, annulus-shaped fins are arranged concentric on the fin tube. In a preferred embodiment, the annulus-shaped fins are dimensioned such that between the end of the fins and the casing (and/or the accumulator), a gap of 5% maximum relative to the gap width x is established. The preferred height h of the annulus-shaped fins is 5% to 30% of the gap width value x.  
         [0030]     The annulus-shaped fins are arranged at a distance t to each other. By this, for the dimensional ratio between the distance t and the fin height h a value from a range of one to four is chosen. Preferably, the bent-off length z is at least half the length L 1 , whereby the length L 1  is the distance between two neighboring fin surfaces.  
         [0031]     In an alternative embodiment, an internal heat exchanger with coil-shaped fin tubes, together with an accumulator, forms a unit. The internal heat exchanger has a top cover plate and a bottom cover plate. An accumulator is located in the casing for the liquid refrigerant at low pressure. The coil-shaped fin tube, in which passed the high pressure refrigerant, is located in the gap between the accumulator and the casing.  
         [0032]     The fins are arranged radially on the fin tube so that the refrigerant vapor is readable, at low pressure, between the fins of the fin tube cross-countercurrently and, possibly, cocurrently to the refrigerant at high pressure. As opposed to the solution previously described the fins are formed by upsetting so that bearing surfaces in radial direction develop.  
         [0033]     According to one advantageous embodiment, the inner surface of the casing is equipped with an insulating layer. When the inner cylinder is configured as high-pressure profile, also the inner side of the internal cylinder may also be equipped with an insulating layer. Another embodiment consists in the outer surface of the accumulator being equipped with an insulating layer. Preferably both the top and bottom cover plates of the casing are provided with connections for the refrigerant at low and high pressure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after review of the following description, with reference to the drawings, in which:  
         [0035]      FIG. 1  shows an internal heat exchanger with an accumulator, in cross-sectional view;  
         [0036]      FIG. 2  is a cross-sectional view, generally taken along line  2 - 2  in  FIG. 1  showing the fin tube coil in it assembled position;  
         [0037]      FIG. 3   a  is a prior art construction of two neighboring fins during axial assembling;  
         [0038]      FIG. 3   b  illustrates two neighboring fins and tubes according the present invention fins during axial assembling;  
         [0039]      FIGS. 4   a  and  4   b  are end and side views, respectively, of a portion of a fin tube with bent-off fins;  
         [0040]      FIGS. 5   a  and  5   b  are end and side views, respectively, of a portion of a fin tube with upset fins. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     In  FIG. 1  an internal heat exchanger  100  with a coil-shaped fin tube is shown; the heat exchanger  100 , together with an accumulator  10  forming a unit. The internal heat exchanger  100  includes a casing  2 , which is preferably cylindrical, particularly circular-cylindrical. The casing  2  is limited by a top cover plate  4  and a bottom cover plate  6 . Integrated into the top cover plate  4  is a low-pressure inlet  12  and a high-pressure outlet  20 . Integrated into the bottom cover plate  6  is a low-pressure outlet  16  and a high-pressure inlet  18 . The accumulator  10  is provided concentrically in the interior of the heat exchanger  100  and is in the form of a cylinder. A side wall  11  of the accumulator  10  is closed at the bottom by a bottom cover plate  13  and at the top by a top cover plate  15 . In the top cover plate  15 , there is provided an opening for the low-pressure inlet  12  next to an opening configured as overflow  14 . The refrigerant, at high pressure, passes through the coil-shaped fin tube  8 , which extends from the bottom cover plate  6  and is arranged in the gap (with gap width x) between the accumulator  10  and the casing  2 , coiling coaxially along the side wall  11  of the accumulator  10 , from bottom to top, and exits the internal heat exchanger  100  via the high-pressure outlet  20  through the top cover plate  4 .  
         [0042]     According to this embodiment to  FIG. 1 , the inner surface of the cylindrical casing  2  is provided with an insulating layer  22 . According to another embodiment, the outer surface of the side wall  11  of the accumulator  10  may also be provided with an insulating layer  24 .  
         [0043]     As seen in  FIG. 2 , a single calibrated fin tube coil  26  of the coil-shaped fin tube  8 , which according to the invention is calibrated by bending of the ends or heads of the fins  28  located on the tubes  29 . The bent length z of the fin&#39;s ends can be set unproblematically so that the inner diameter d and the outer diameter D of the fin tube coil  26  can be fitted exactly to the inner and outer diameters defining the annular gap between the casing  2  and the accumulator  10 . Such calibrating of the fin tube coil  26  makes the bent fin heads  30  bear against the limiting side wall  11  of the accumulator  10  and the limiting side wall  32  of the casing  2   r . Therefore, annular gaps for low-pressure side bypass flows in the internal heat exchanger are avoided. Bearing of the bent fin heads  30  also prevents the calibrated tube coil  26  from vibrating, caused by the usual vehicle vibrations, and avoids disturbing noise.  
         [0044]     The bent fin heads  30  enlarge the bearing areas on the limiting side walls  11 ,  32  so that no notches, due to the ends, fins are created in the side walls  11 ,  32 .  
         [0045]     In  FIGS. 3   a  and  3   b , two neighboring fin tube coils are shown during axial assembling of the component into the annular gap.  
         [0046]     In  FIG. 3   a , the hooking of the tube coils into each other is observed in a known assembly, inevitably caused during axial assembly of the component. Adjusting the coil diameter by, for example, manual action becomes impossible due to the coil&#39;s hooking together. If fin tube coils that are manufactured true to size are used, assembling the components may become impossible.  
         [0047]     In  FIG. 3   b , the bent fin heads  30  are bent generally in the axial direction of the tubes  29 . Therefore, bearing surfaces  36  are formed between adjacent ones of the single fin tube coils  26  on which the fin tube coils  26  can axially, transversely and radially slide relative to each other without hooking together. Adaptation of the diameter of the fin tube coil  26  during assembly is no problem for the fins  28  with the fin heads  30  bent in axial direction of the tubes  29 , also when manufactured true to size.  
         [0048]     In  FIGS. 4   a  and  4   b , end and side views of a portions of the coil-shaped fin tube  8  is shown, where the bent fin heads  30  are bent at four bending points  38 , at 90° intervals, and provided with a length z. The heads  30  are bent at both axial and radial locations, relative to longitudinal axis of the heat exchanger  100 . The fins  28  are arranged concentric to the tube  29  so that the values of the fin height h are equal on both sides of the tube  29 . The tube  29  itself has a wall with the wall thickness s, as well as an inner diameter d 1  and an outer diameter d 2 . The complete coil-shaped fin tube  8  has a clear diameter d 3 . The cross-sectional area passed by the high-pressure refrigerant follows from the channel formed by two neighboring fins  14 . The fins  14  are arranged on the tube  29  with a distance whereby L 1  is the distance of neighboring opposing fin surfaces, and L 2  is the fin  28  thickness.  
         [0049]     An alternative forming measure to provide bearing surfaces in radial direction is upsetting of the ends of the fins  40 . A detailed view of a coil-shaped fin tube  8  with fins  40  upset at the fin heads  42  is shown in  FIG. 5   b .  FIG. 5   a  illustrates the fins  29  before the heads  42  have been subjected to upsetting. As seen therein, the cross-section of the fins  40  is such that the fin heads  42  form a general T-shaped configuration.  
         [0050]     Of course, the invention is not limited to the embodiments described and of which only one is illustrated in the accompanying drawings. Modifications are possible, particularly from the point of view of the composition of the various elements and by substitution of technical equivalents, without thereby departing from the scope of protection of the invention.