The invention relates to a heat exchanger comprising:

- an outer conduit;

- an inner conduit extending in longitudinal direction through the outer conduit, wherein both ends of the outer conduit are sealed to the outer surface of the inner conduit and wherein an inlet opening and outlet opening are arranged in the wall of the outer conduit to supply a fluid to and discharge the fluid from the space between the outer conduit and inner conduit; and a groove arranged in the outer wall of the inner conduit, wherein the groove extends at least from the inlet opening to the outlet opening and comprises a linear part extending in substantially axial direction of the inner conduit.

Such a heat exchanger is known from US 2006/0096314. The described internal heat exchanger is used for air-conditioning systems for automotive applications.

WO 2010124871 discloses another heat exchanger for air-conditioning application, which is bent into a U-shape or another shape because of space restrictions typically present in the engine compartment of a car. The bending of the heat exchanger is also required to obtain sufficient cooling capacity within the restricted space, as well as it will provide an improved robustness to the heat exchanger when bent.

The heat exchanger is described, prior to being bent into a U-shape or other shape, to have two concentric tubes, an inner tube and an outer tube. The inner tube originally is cylindrical, i.e. has a circular cross section. During production, a part of the inner tube is deformed to have an elliptical cross section (i.e. an oval cross section) or a cross section which is substantially elliptical but with flattened sides. This elliptical cross section is applied to the inner tube by clamping portions of the inner tube sequentially. In doing so, a part of the wall of the inner tube will be closer to the centre point of the inner tube (corresponding to a short axis of the ellipse with a length smaller than the radius) and a part of the wall will be further away from the centre point of the inner tube (corresponding to a long axis of the ellipse with a length larger than the radius). Then the clamp is removed and the inner tube is advanced a distance along its longitudinal axis. The inner tube is also rotated by a fixed angle. Then it is clamped again to give a second portion the elliptical cross section. By repeating this process over a part of the length of the inner tube, that part of the inner tube is provided with a helical shape composed out of oval cross-section parts. When fitted in the outer tube, there are two channels defined between the outer surface of the inner tube and the inner surface of the outer tube. The combination is then bent into shape.

During bending of the heat exchanger with the inner tube mounted in the outer tube, the inner tube and the outer tube may bend differently. Because the inner tube is less supported during bending, it will have the tendency to collapse sooner. As a result, the inner conduit will get in to contact with the inner wall of the outer conduit over a substantial length. The direct contact of the inner conduit with the outer conduit will restrict the channels, which were defined by the oval cross-section parts and are now collapsed by the bending of the heat exchanger. Moreover, the bending of the inner conduit is uncontrolled such that a large production variance occurs, which makes that the efficiency of the heat exchanger has a large variance as the total surface area of the cross section varies. The total surface area determines the flow velocity and the heat transfer coefficient. It is an object of the invention to provide a heat exchanger according to the preamble, in which the above mentioned disadvantages are reduced.

This object is achieved with a heat exchanger, which is characterized by the features of claim 1.

Because a groove is arranged in the outer wall of the inner conduit, the overall cross-sectional shape of the inner conduit is not changed, while a defined channel is provided with the groove.

The groove comprises a linear part extending in substantially axial direction of the inner conduit. With a linear part of the groove, the retention time of the fluid in the heat exchanger can be minimized. Furthermore, a linear part of the groove also provides a defined bending axis for the conduit. The bending axis of the conduit will be perpendicular to the linear part. During design of the heat exchanger, this groove shape can be used to define a bending axis and to better predict any deformation of the inner tube.

A part of the outer conduit and inner conduit is bent into a curve and the linear part of the groove is positioned within the curve.

In yet another embodiment of the heat exchanger according to the invention the linear part of the groove is directed towards the outside of the curve. The groove defines the path of the fluid through the space between the outer conduit and the inner conduit. By having the linear part of the groove directed towards the outside of the curve, it is ensured that the fluid flow will not be restricted even if any unpredicted deformation of the inner conduit would occur.

When the heat exchanger is bent, the inner conduit will bent along with the outer conduit and the inner conduit may deform. However, even if the inner conduit is deformed such that it is in contact with the inner wall of the outer conduit, there still will be the groove running from the inlet opening to the outlet opening and thus the passage will not be restricted due to deformation of the inner tube.

Also, the path along which the fluid will flow is still defined, after bending and possible deformation of the inner conduit, due to the presence of the groove in the outer wall of the inner conduit.

An additional advantage of having a defined flow path, is that the space between the inner conduit and the outer conduit can be minimised and any unpredicted deformations do not have to be taken into account. Minimising the space will reduce the required amount of cooling fluid for a cooling system, which reduces the costs.

In a preferred embodiment of the heat exchanger according to the invention the groove is arranged in the outer wall by deformation of the wall of the inner conduit, such that the inner wall protrudes into the inner conduit.

By deforming the wall of the inner conduit to shape a groove, the conduit is provided with a strengthening rib. This strengthening rib will influence the inner conduit during bending of the heat exchanger, such that the deformation of the inner conduit can be predicted better.

In another embodiment of the heat exchanger according to the invention at least part of the groove spirals around the circumference of the inner conduit. By setting the pitch of the spiral, one can design the retention time of the fluid inside the heat exchanger and design the amount of heat exchange.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a schematic view of a cooling system with an embodiment of the heat exchanger according to the invention.

Figure 2 shows the heat exchanger of figure 1 in perspective view with cut away portions.

Figure 3 shows the inner conduit of the heat exchanger of figures 1 and 2 in perspective view. Figure 4 shows a cross-sectional view along the line IV-IV in figure 2.

Figure 1 shows a schematic view of a typical cooling system with a heat exchanger 1 according to the invention. The cooling system has a compressor 2, a condenser 3, a restriction 4 and an evaporator 5 all connected by conduits. The low pressure conduit 6 running from the evaporator 5 to the compressor 2 is in heat exchanging contact at the heat exchanger 1 with the high pressure conduit running from the condenser 3 to the restriction 4. This heat exchange improves the cooling efficiency of the cooling system.

Figure 2 shows the heat exchanger 1 of figure 1 in perspective view with cut away portions and in more detail.

The heat exchanger 1 has an outer conduit 8, being part of the high pressure conduit 7, and an inner conduit 9, being part of the low pressure conduit 6. The inner conduit 9 extends in longitudinal direction through the outer conduit 8. The outer conduit 8 is sealed at both ends 10, 11 to the inner conduit 9. The high pressure conduit 7 is connected at both ends 10, 11 via an inlet opening 12 and an outlet opening 13.

The inner conduit 9 (see also figure 3) is provided with a groove 14 in the outer wall. In this embodiment the inner conduit 9 has a spiral groove part 15 and two linear groove parts 16, 17. The spiral groove part 15 and linear groove parts are positioned such that after bending the inner conduit 9 and outer conduit 8, the spiral groove part 15 is positioned at a straight portion of the heat exchanger, while the linear grooves 16, 17 are positioned at the curves in the heat exchanger 1. The groove 14 ensures that although the inner conduit 9 is in contact with the outer conduit 8, there will always be a predictable flow path for the cooling fluid of the cooling system 1.

Figure 4 shows a cross-sectional view along the line IV-IV in figure 2. From this figure it is clear that although the inner conduit 9 is over the major part in direct contact with the inner wall of the outer conduit 8, the groove 14 still provides a passage.