FR2648549A1 - Manifold for heat exchanger of the tube-in-tube type - Google Patents

Abstract

The invention relates to a manifold for a heat exchanger of the tube-in-tube type. The manifold is formed in a single piece such that the distribution plate 37 provided at one end is formed integrally with the body of the manifold 36; such a design eliminates the process of brazing the distribution plate 37 in the manifold body 36, which substantially simplifies the assembly process; in order to allow use of thin-walled inner tubes 53 and a distribution plate 37 which is also thin, reinforcing sleeve tubes are arranged around the ends of the inner tubes and are brazed in position in the openings 59 of the distribution plate.

Description

Collector for tube-in-tube heat exchanger
The most common type of heat pump is one in which heat is transmitted from a refrigerant by means of a heat exchanger over which ambient air flows. Such a system is sometimes called an air source heat pump since it is the condition of the ambient air that is used to change the temperature of the refrigerant. Similarly, when there is a source of water, such as a pond or the like, which can be used to act on the condition of a refrigerant, a so-called pump is used. heat from a water source to cool or heat the refrigerant by means of a heat exchanger which is traversed by the water flow.

 Typically, a water-to-refrigerant heat exchanger of this kind is in the form of a so-called tube-in-tube heat exchanger where one or more inner tubes are arranged in an outer tube and where passes the liquid and the refrigerant through the respective outer and inner tubes, or vice versa, so that heat transmission is effected in relation to the radial dimensions of the inner tube (s). To maintain a separation between the liquid and the refrigerant in a system of this kind, it is common to provide a manifold in order to define a common delimitation between the circuits for the flow of the liquid and the coolant and to maintain the ends of the tubes interiors.

 In the past, this has been achieved by using an intermediate plate, separated from the manifold body, so as to function as the separator / distributor between the water and the refrigerant. To fix this intermediate plate inside the collector body, it was first necessary, with certain difficulties, to install it in the desired position, then to fix it in this position. Gas welding or flame brazing have typically been used to braze the plate in position. Either solution tends to heat a large amount of material, thus requiring more solder alloy and larger manifolds to prevent alloy reflux. Thus, when two separate brazed joints are located in close physical proximity to one another, and when they cannot be brazed simultaneously, the brazing of the second joint tends to produce a fusion of the brazing of the first joint. And even when they can be brazed simultaneously, if thin-walled tubes are used, one should avoid prolonged maintenance of the metal at the brazing temperature since this can reduce the resistance of the metal. Since flame brazing requires longer times to maintain the brazing temperature, the inner tubes must generally have relatively thick walls to suitably obtain very reliable joints. Although there is thus a need to involve tubes with relatively thick walls, it is recognized that inner tubes with thin walls are desirable because they improve the heat transfer characteristics, the colts and the weight.

 In addition to the difficulty of brazing thin-walled tubes as described above, it is also recognized that the relative thicknesses of the elements to be brazed (i.e. the thickness of the tubes and the thickness of the plate ) must be comparable. Thus, if the plate is thick and if the tubes are thin, it is very difficult to produce brazed joints which are correct and robust. In addition, if the thickness of the plate is reduced to accommodate the thin wall of the tubes, then the resistance of the thin walled plate to high pressures may not be sufficient to prevent deformation of the plate. , which in turn can cause tube failure.

 Consequently, an object of the present invention is to provide an improved collector structure for a tube-in-tube heat exchanger.

 Another object of the present invention is to allow a reduction in the difficulties of installing the separation / distribution element in a tube-in-tube heat exchanger manifold.

 Yet another object of the present invention is to create a tube-in-tube heat exchanger which can allow the use of inner tubes with relatively thin walls.

 Yet another object of the present invention is to create a tube-in-tube heat exchanger which allows the use of both thin-walled tubes and a relatively thin separating / distributing element without tube failures occurring. during high pressure operation.

 Yet another object of the present invention is to provide a tube-in-tube heat exchanger to prevent tube failure when the separation / distribution member bends under the effect of high pressure.

 Yet another object of the present invention is to create a tube-in-tube heat exchanger manifold which is of economical manufacture and of practical and efficient use.

 According to one aspect of the invention, the collecting element of a tube-in-tube type heat exchanger is formed in one piece which has, at one end, a partition / distribution wall which forms the delimitation between the water and refrigerant.

Since the requirement for brazing of the partition / distribution wall in the manifold is eliminated, it is possible to use inner tubes with relatively thin walls which can be easily brazed in their distribution openings by means of a brazing process by induction. A cap is then placed on the end of the manifold, so as to surround the distribution wall, in order to thus complete the internal flow circuit.

 According to another aspect of the invention, to prevent a failure of thin-walled tubes when a separation / distribution element with a relatively thin wall is deformed under the effect of the high pressures which are exerted on it, a reinforcing sleeve is arranged around each of the tubes in order to prevent them from bending in places close to their ends. The sleeves are brazed by their outer side on the plate and by their inner side on the tubes so as to prevent leaks and increase their reinforcing characteristics.

 To solve the problems defined above, the manifold assembly according to the invention, of the type which connects an external flow circuit with an internal flow circuit in a tube-in-tube type heat exchanger, comprises: a manifold body of tubular shape and having an open end for a fluid connection with a sheath, said sheath and said manifold body defining the outer limit of the external flow circuit and containing at least one inner tube which defines the outer limit of the circuit internal flow: and said manifold body having on one side a connection opening with a first conduit for fluid communication with said sheath by means of said manifold body; this manifold assembly being characterized in that said manifold body further comprises a closed end connected unitarily to define a mutual limit between the external and internal flow circuits, said closed end comprising at least one opening intended to receive said inner tube at less provided so that an open end of said at least one inner tube is fluidly connected with a part of said internal flow circuit on one side of said closed end: and a cap connected to said manifold body at said closed end for further defining said internal flow circuit and comprising an opening for fluid communication with a second circuit.

According to other particularities of the collector assembly according to the invention:
- Said at least one inner tube has a thickness which is less than 0.41 mm.

 - Said closed end is disposed substantially opposite to said open end of said manifold body.

 - Said closed end has a substantially planar shape.

 - The manifold assembly comprises means for sealing the fluid of at least one opening between the outer periphery of said inner tube at least provided and the surrounding structure of said closed end.

 - Said sealing means comprise a brazing material.

 - Said brazing material is deposited by an induction brazing process.

 - Said external flow circuit is traversed by a flow of water and said internal flow circuit is traversed by a flow of refrigerant.

 - The manifold assembly comprises a reinforcing sleeve disposed around said inner tube at least provided near said opening at least provided so as to prevent lateral deformation of said tube.

 - Said reinforcing sleeve enters said opening at least provided.

Other characteristics and advantages of the invention will be highlighted, in the following description, given by way of nonlimiting example with reference to the appended drawings in which:
Figure 1 is a representation of a tube-in-tube heat exchanger manifold corresponding to the prior art;
Figure 2 is a front elevational view of a tube-in-tube heat exchanger according to the present invention;
Figure 3 is a plan view of this heat exchanger;
Figure 4 is a view of an end part of the heat exchanger, showing the collecting element;
Figure 5 is an end view of a manifold element;
Figure 6 is an elevational view of this collecting element;
Figure 7 is a sectional view of the manifold, taken along line 7-7 of Figure 5;
Figure 8 is a schematic representation of the collector element which is shown with dynamic forces acting on it.

Figure 9 is an end view of a modified embodiment of the present invention:
Figure 10 is a side elevational view of the structure of Figure 9;
Figure II is a longitudinal sectional view of a sleeve-shaped part involved in the present invention.

 Now considering FIG. 1, this represents a collecting element 11 usable in a tube-in-tube type heat exchanger according to the prior art. A manifold body 12 of cylindrical shape is brazed by means of a seal 13 on a sheath 14 to contain the flow of external fluid. Several inner tubes 16 with relatively thick walls (that is to say greater than 0.41 mm) are disposed both in the sheath 14 and in the manifold body 12. A tube 17 is brazed in the lateral opening of the body 12 by means of a seal 18 so as to further define the flow path of the external fluid.

 The boundary between the outer fluid and the inner fluid includes a separation / distribution plate 19 which is brazed in position near the end of the manifold body 12. The plate 19, which is relatively thick so as to withstand high pressures which can be exerted on it is brazed by means of a seal 21 which extends over the entire periphery of the plate so as to fix it securely on the internal surface of the collector body 12.

 In the plate 19 are formed several openings 25 intended to receive the ends of the individual lower tubes 16. The tubes 16 are then brazed in the aforementioned openings 25, the brazed joints 22 extending over the entire periphery of the tubes so as to fix them tightly in the openings and to complete the fluid-tight separation between the exterior and interior fluid compartments. The internal fluid compartment is completed by means of a cap 23 which is firmly fixed to one end of the manifold body 12 and which is brazed in position by means of a seal 24.

 It is recognized that a collector assembly of the prior art of this kind is difficult to manufacture and has certain operating deficiencies.

When assembling the different components, brazing is the usual method to ensure their fixing in position. When mounting the plate 19, it is first necessary to place the plate in its desired position and then to maintain it in this position during the brazing performed over its entire circumference. It is preferred, but difficult, to simultaneously braze the individual tubes 16 into the openings 25 in the plate. Alternatively, the tubes can be brazed separately, taking care that the previously brazed joint around the periphery of the plate 19 is not unsoldered in the operation. Finally, when the cap 23 has been placed in position and brazed by means of the seal 24, care must be taken that the seal 24 is spaced from the seal 21 by a sufficient distance so that the brazing of the seal 24 does not produce debrasement of the joint 21. For this reason, it was necessary to provide a considerable overlap between the cap 23 and the end of the manifold body 12, as shown in the Figure.

 Referring now to Figure 2, this shows a pair of manifolds 26 and 27 according to the present invention. The collectors 26 and 27 are fixed to opposite ends of a tube-in-tube type heat exchanger coil which is shaped to a helical shape as indicated. It goes without saying, of course, that the collector structure of the present invention can be applied as well to any other form of tube-in-tube type heat exchanger.

 In operation, a flow of refrigerant (interior fluid) penetrates through the inlet 29 and runs the entire length of the interior tubes 16 while being discharged through the outlet opening 31.

The external flow preferably progresses against the current so that the water penetrates into the opening 32 of the tubing, traverses the entire sheath of the coil 28 and exits through the discharge opening 33 of the tubing. Again, it goes without saying that various other embodiments can be employed while using the collector of the present invention. For example, in a heat pump, it may be more convenient to provide flows in parallel, and not against the current, in one of the modes such as the heating mode. Also, when only one inner tube is used, it may be desirable to pass the water through the inner tube and the coolant through the outer tube.

 Referring now to Figure 4, the present invention is generally designated by 34 as comprising a manifold body 36 in one piece, provided with a distribution plate 37 which is formed unitarily with a cylindrical part of the body of the manifold 36 as shown. Two inner tubes 38 and 39, preferably with relatively thin walls (that is to say less than 0.41 mm), are disposed in the sheath 41 and the manifold body 36 as shown, their ends projecting through 'respective openings 42 and 43 provided in the distribution plate 37. The tubes 38 and 39 are brazed in the openings 42 and 43 in a manner which will be described below.

 The sheath 41 is brazed in the manifold body 36 by means of a seal 44 and the tube 46 is brazed in a lateral opening of the manifold body 36 by means of a seal 47. The cap 48 is brazed on the manifold body 36 by means of a seal 49.

In this regard, it is obvious that, since there is no joint in the interface between the distribution plate 37 and the manifold body 36, the overlap between the cap 48 and the manifold body 36 can be reduced to the minimum so that the seal 49 is relatively close to the periphery of the distribution plate 37, as shown. In this way, a substantial saving of material is achieved.

 The inner tubes 38 and 39 are preferably of the improved type or spiral grooves are formed on the inner side of the tubes in order to improve their heat transmission characteristics. For example, such an improved tube may have a nominal thickness of 0.41 mm but the thickness of the grooves (i.e. the minimum thickness) may be 0.3 mm (i.e. say what corresponds to the American designation "12 wall tube").

 Referring now to Figures 5 to 7, these show a slightly modified version of the manifold body 36, or the openings 51 and 52 are arranged side by side instead of being located one above the other as shown in Figure 4. In either case, the openings 51 and 52 are formed in the same manner by drilling or punching the openings in the distribution plate 37. We see that a slight chamfer is preferably formed at the inner end of the openings to facilitate mounting of the inner tubes in the openings before brazing in their fixing positions.

 The manufacture of the distribution plate 37 as an integral part of the manifold body 36 is carried out by a known process of "pushing back".

The process involves the pushing along the axis of an open cylinder and the gradual folding down of its end, in successive stages, using a pushing mallet which is applied to this end. The end of the folded part finally closes at a central point so that the resulting distribution plate 37 is continuous from one side to the other (possibly with the exception of a very small hole provided in the medium and which can be closed by means of a flow of solder material) and has a thickness which is substantially the same as the thickness of the manifold body 36.

 Since the thickness of the manifold body 36 is relatively thin compared to a distribution plate of the prior art, the thickness of the distribution plate 37 formed unitarily with it is relatively thin (i.e. the two parts have substantially the same thickness).

When the manifold body 36 is relatively small, for example when only two inner tubes are used as shown in Figures 5 to 7, the strength of the plate 37 should be sufficient to withstand high pressures although it is relatively thin . However, when more tubes are used and when the diameter of the plate 37 must therefore be increased, the relatively thin wall of this plate 37 can cause difficulties.

 In this regard, there is shown in Figure 8 a manifold 36 of larger diameter in which are arranged several tubes (for example new), spaced circumferentially and a part of which is indicated at 53 and 54, as well as a tube disposed at center and designated by 55. The thin-walled tubes are brazed in openings made in the distribution plate 37 in the manner described above. When the internal flow circuit is subjected to high pressures, then both the cap 48 and the plate 37 tend to deform to assume a spherical configuration as a whole, as indicated by the dotted lines. When this occurs, tubes 53 and the like tend to curve outward as shown.

 In connection with this phenomenon, it has also been realized that, in the process of brazing the inner tubes in the openings of the distribution plate 37, the tubes are heated near their ends and that the heat is transmitted longitudinally in the tubes over a distance called the "heat affected area".

The copper in the "heat affected area" is annealed in the process and is therefore weakened. When the degree of curvature described above reaches a point where the weakened tube can no longer absorb the stress, the tube bends and breaks as indicated in point 57 in Figure 8. Such a deficiency obviously produces an interruption in the system since integrity between separate internal and external flow circuits is suppressed.

 To solve this problem, a modified version of the present invention is shown in Figures 9 to 11 where several reinforcing sleeves 58 are inserted into the openings 59 of the distribution plate 37. The tubes, 53 and others, are then engaged in the reinforcement sleeves 58 and brazed in position. The reinforcing sleeves are dimensioned so that their outer dimensions establish a relatively tight fitting in the openings 59 of the plate 37 and their internal diameter is chosen so that the tubes, 53 and the like, are loosely mounted but in being relatively well centered in the openings. As shown in Figure 11, the end of the reinforcing sleeve 58 which engages in the opening 59 is preferably chamfered at 61 to facilitate the assembly process. The length of the sleeves is chosen such that reinforcement of the inner tubes is produced at the longitudinal point beyond the weakest point in the heat affected area.

The assembly is preferably carried out in the following manner. The different inner tubes 53 and others protruding from the sheath are grouped together and the manifold body 36 is engaged thereon so that the ends of the tubes protrude through the openings 59 of the distribution plate 37. The sleeves reinforcement 58 are then inserted into the openings 59, in overlapping relationship with the inner tubes, 53 and the like, until the chamfer 61 comes to bear against the external surface of the plate 37. The reinforcement sleeves 58 are then brazed in the openings 59 and the inner tubes, 53 and the like, are brazed in the reinforcement sleeves 58. This is done completely on the outside of the plate 37, where all the elements are easily accessible. All the soldered joints on the plate 37 are produced substantially at the same time by an induction brazing process. A cap 48 is then placed and brazed on the manifold body 36 as shown in Figure 4. The manifold body 36 is also brazed, at its other end, on the sheath as shown in the
Figure 4. The tubing 46 can be brazed into the lateral opening of the manifold body 36 either before or after the operations described above.

Claims (10)

 1. An improved collector assembly of the type which connects an external flow circuit with an internal flow circuit in a heat exchanger of the tube-in-tube type, comprising:  - a manifold body (36) of tubular shape and having an open end for a fluid connection with a sheath (41), said sheath (41) and said manifold body (36) defining the outer limit of the external flow circuit and containing at least one inner tube (38, 39; 53, 54, 55) which defines the outer limit of the internal flow circuit; and  - said manifold body (36) comprising on one side a connection opening with a first conduit for fluid communication with said sheath (41) by means of said manifold body (36), characterized in that:  - said collector body further comprises a closed end (37) connected unitarily to define a mutual limit between the external and internal flow circuits, said closed end (37) comprising at least one opening (42, 43; 51, 52 ) intended to receive said at least provided inner tube (38, 39; 53, 54, 55) so that an open end of said at least provided inner tube (38, 39: 53, 54, 55) is fluidly connected with a part of said internal flow circuit on one side of said closed end (37); and  - A cap (48) connected to said manifold body (36) at said closed end (37) to further define said internal flow circuit and comprising an opening for fluid communication with a second conduit.  2. Improved manifold assembly according to claim 1, characterized in that said at least one inner tube (38, 39; 53, 54, 55) has a thickness which is less than 0.41 mm.  3. Improved manifold assembly according to claim 1, characterized in that said closed end (37) is disposed substantially opposite to said open end of said manifold body (36).  4. Improved manifold assembly according to claim 1, characterized in that said closed end (37) has a substantially planar shape.  5. improved manifold assembly according to claim 1, characterized in that it comprises means for sealing the fluid at least one opening (42, 43; 51, 52) between the outer periphery of said inner tube at least provided (38, 39; 53, 54, 55) and the surrounding structure of said closed end (37).  6. Improved manifold assembly according to claim 5, characterized in that said sealing means comprise a brazing material.  7. Improved collector assembly according to claim 6, characterized in that said solder material is deposited by an induction brazing process.  8. Improved manifold assembly according to claim 1, characterized in that said external flow circuit is traversed by a flow of water and said internal flow circuit is traversed by a flow of refrigerant.  9. Improved manifold assembly according to claim 1, characterized in that it comprises a reinforcing sleeve (58) disposed around said inner tube at least provided (38, 39; 53, 54, 55J near said opening at least provided (42, 43; 51, 52) so as to pocket a lateral deformation of said tube.  10. Improved manifold assembly according to claim 9, characterized in that said reinforcing sleeve (58) enters said opening at least provided l42, 43; 51, 52).