WO2003036212A1

WO2003036212A1 - Heat exchanger, especially for the cooling of gases in an exhaust gas recycling system

Info

Publication number: WO2003036212A1
Application number: PCT/IB2002/004429
Authority: WO
Inventors: José Luis GARCIA BERNAD; Carlos Perez Caseiras; Stephan Geissler; Joachim Kautz
Original assignee: Valeo Termico, S.A.; Hde Metallwerk Gmbh
Priority date: 2001-10-26
Filing date: 2002-10-25
Publication date: 2003-05-01
Also published as: ES2199036B1; ES2199036A1

Abstract

Heat exchanger which presents a plurality of parallel tubes (10) for the flow of gas, each one provided with helicoidal corrugations (11); said tubes (10) having an exterior diameter of between 7.5 mm and 10.5 mm, and the helicoidal corrugations (11) forming an angle (α) of between 5° and 25°C with a plane perpendicular to the axis of the tube (10).

Description

HEAT EXCHANGER, ESPECIALLY FOR

THE COOLING OF GASES IN AN EXHAUST

GAS RECYCLING SYSTEM

This invention relates to a heat exchanger, especially for the cooling of gases in an exhaust gas recycling system, which presents a plurality of parallel tubes for the flow of gas, each one provided with helicoidal corrugations.

BACKGROUND OF THE INVENTION

In some heat exchangers for the cooling of gases, for example those used in systems for the recirculation of exhaust gases towards the inlet manifold of an internal- combustion engine (systems denominated "Exhaust Gas Recycling" or EGR) , the gases circulate through a bundle of parallel tubes housed in a casing, and during this circulation they are cooled by heat exchange with a cooling fluid which is made to circulate inside the casing, on the outside of the gas-passage ducts.

In some exchangers of this type, the tubes have been made corrugated instead of smooth, in order to improve the thermal efficiency of the apparatus. Several corrugation shapes have been tested, and some exchangers have been developed recently which have helicoidal corrugations running the length of the tubes. These helicoidal corrugations have a spiral angle of about 30°, that is, the spiral is inclined by some 30° with respect to a plane perpendicular to the axis of the tube, in order to prevent high pressure drops in the flow of the gases.

These solutions are limited to adding corrugations to the known exchanger tubes, without substantially modifying other characteristics thereof, and they have some disadvantages: indeed, although these exchangers have good thermal efficiency, the pressure drop of the gases in the tubes is higher than with smooth tubes, and the cost of the apparatuses remains high.

DESCRIPTION OF THE INVENTION

One objective of this invention is to resolve the disadvantages mentioned by developing a heat exchanger whose thermal efficiency and performance are similar to those of existing exchangers, both with smooth and corrugated tubes, but which are of lower cost.

In accordance with this objective, the heat exchanger of this invention is characterised in that said tubes have an exterior diameter of between 7.5 mm and 10.5 mm, and in that the helicoidal corrugations form an angle of between 5° and 25° with a plane perpendicular to the axis of the tube.

The smaller spiral-turn angle of the corrugations in comparison with other exchangers permits the thermal efficiency of each tube to be increased, so that it is possible to use fewer tubes in the exchanger, with the consequent reduction of cost, without loss of power; the larger tube diameter reduces gas-pressure drops.

In conclusion, the exchanger in accordance with the invention permits the same thermal efficiency and performance as the known exchangers, but at lower cost.

Preferably, the tubes have a diameter of between 8 mm and 9 mm and the helicoidal corrugations form an angle of between 10° and 15° with the plane perpendicular to the axis of the tube.

In one embodiment, each tube has a single helicoidal corrugation.

In one embodiment, the tubes have a smooth zone at the ends; in this case, preferably, the smooth zone at each end of the tubes is less than 10 mm in length. In one embodiment of the exchanger with a casing approximately 45 mm in diameter, the tubes number between eleven and fifteen; in an embodiment with a casing approximately 54 mm in diameter, the tubes number between eighteen and twenty-two.

These exchangers have significantly fewer tubes than similar exchangers of the prior art, for which reason their cost is clearly lower.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of all that has been set out herein, some drawings are attached which show schematically and solely by way of non-restrictive example a practical case of embodiment. In said drawings:

Figure 1 is a section view of a heat exchanger in accordance with one embodiment of the invention; and

Figure 2 is an elevation view of a detail of one of the tubes of the exchanger of Figure 1.

DESCRIPTION OF A PREFERRED EMBODIMENT

Figure 1 shows a view of a heat exchanger of the type used in EGR (Exhaust Gas Recycling) systems in which the exhaust gases of an internal-combustion engine are recirculated towards the intake manifold; the exchanger is used to cool the gases before mixing them with the intake air and the fuel. In the exchanger, the gases circulate through the interior of a bundle of tubes 10 running parallel to each other and housed in a casing 20, and during this circulation they are cooled by heat exchange with a cooling fluid which is made to circulate inside the casing 20 on the outside of the tubes 10. As the figure shows, this embodiment uses only thirteen tubes 10 in the casing 20, which has here a diameter of 45 mm, which is one of the standard measurements used in exchangers for EGR. This number of tubes is much lower that that habitually used in these exchangers, which means that there is a considerable saving of materials. In accordance with the invention, the tubes 10 have an exterior diameter of between 7.5 mm and

10.5 mm, preferably between 8 mm and 9 mm. Figure 2 shows an end of one of the tubes 10 in longitudinal elevation.

The tube presents ^' a helicoidal corrugation 11 which runs most of the length of the tube; this corrugation affects the wall of the tube in such a way that it projects towards the interior of the tube, affecting the flow of gas through its interior. There is a smooth section 12 at both ends of the tube.

In accordance with the invention, the spiral angle α of the corrugation, that is, the angle the corrugation forms with a plane perpendicular to the axis of the tube, is between 5° and 25°, preferably between 10° and 15°.

This angle is quite small; in other words, the corrugation 11 runs transversally to the flow of the gas, and this improves the thermal efficiency by increasing the turbulence in the gas and the average distance it travels in the tube; as a result, it increases the time the gas remains inside the tube.

The larger diameter of the tubes compared with known exchangers, which usually have tubes with a diameter of about 7 mm, more than compensates for the greater pressure drop caused inside the tubes 10 by the corrugation 11, as will be explained below.

Other parameters of the tubes, such as the depth, width or shape of the helicoidal corrugation, have less influence on the performance of the exchanger, so that the protection of the patent is not limited by these parameters. By way of example, the corrugation can have a depth of between 0.5 mm and 1 mm approximately, and a width of some 2 mm. Set out below are the results of thermal efficiency and pressure-drop tests carried out with heat exchangers in accordance with the invention and with exchangers of conventional type.

The exchangers used for these tests had the following characteristics:

For both exchangers, three tests were carried out with different flows of gas, and the thermal efficiency was measured, represented by the power P200 (power in kW which is exchanged with a thermal gradient of 200°, for example with a cooling water intake temperature of 100°C and a gas intake temperature of 300°C) , and the pressure drop ΔP of the gas between intake and exit, in mbar.

The results obtained were as follows:

A comparison of the second and fourth columns of the table shows that the power of the exchanger of the invention was similar to that of the exchanger of the state of the art; the third and fifth columns of the table show that the exchanger of the invention has the further advantage of a lower pressure drop of the gases for any flow of gas .

In spite of these excellent performance figures, the exchanger in accordance with the invention has a cost significantly lower than that of the known exchangers, due to the lower number of tubes of the exchanger; in this case, thirteen tubes instead of nineteen.

Although one specific embodiment of this invention has been described and shown, it will be obvious that an expert in the subject would be able to make variants and changes, or replace details with others that are technically equivalent, without departing from the scope of protection defined in the attached claims. For example, although reference has been made in this specification to an exchanger with a 45 mm casing, the invention is equally applicable to exchangers of other sizes, as long as the characteristics of the tubes and corrugations are as specified in Claim 1 attached. The main design characteristic which would vary from one embodiment to another would be the number of tubes of the exchanger; for example, with a casing of 54 mm diameter, an exchanger in accordance with the invention can have twenty tubes. Furthermore, although- emphasis has been laid on the application of an exchanger in accordance with the invention to EGR systems, other applications are also possible.

Claims

1. Heat exchanger, especially for the cooling of gases in an exhaust gas recycling system, which presents a plurality of parallel tubes (10) for the flow of gas, each one provided with helicoidal corrugations (11) , characterised in that said tubes (10) have an exterior diameter of between 7.5 mm and 10.5 mm, and in that the helicoidal corrugations (11) form an angle of between 5° and 25° with a plane perpendicular to the axis of the tube.

2. Heat exchanger as claimed in Claim 1, characterised in that the tubes (10) have a diameter of between 8 mm and 9 mm.

3. Heat exchanger as claimed in Claims 1 or 2, characterised in that the helicoidal corrugations (11) form an angle of between 10° and 15° with the plane perpendicular to the axis of the tube (10) .

4. Heat exchanger as claimed in any of Claims 1 to 3, characterised in that each tube (10) has a single helicoidal corrugation (11) .

5. Heat exchanger as claimed in any of the previous claims, characterised in that the tubes (10) have a smooth zone (12) at the ends.

6. Heat exchanger as claimed in Claim 5, characterised in that the smooth zone (12) at each end of the tubes (10) is less than 10 mm in length.

7. Heat exchanger as claimed in any of Claims 1 to 6, characterised in that it includes tubes (10) numbering between eleven and fifteen, housed in a casing (20) of approximately 45 mm in diameter.

8. Heat exchanger as claimed in any of Claims 1 to 6, characterised in that it includes tubes (10) numbering between eighteen and twenty-two, housed in a casing (20) of approximately 54 mm in diameter.