GB2391931A

GB2391931A - Heat exchanger for gas

Info

Publication number: GB2391931A
Application number: GB0320641A
Authority: GB
Inventors: Bernad Jose Luis Garcia
Original assignee: Valeo Termico SA
Current assignee: Valeo Termico SA
Priority date: 2001-03-01
Filing date: 2002-02-26
Publication date: 2004-02-18
Also published as: ES2198179B1; WO2002090860A1; GB0320641D0; ES2198179A1

Abstract

The invention concerns a heat exchanger comprising a plurality of parallel conduits (2) wherein circulate the gases to be cooled and an intake manifold (5) interposed between a gas intake pipe (4) and the intake of said conduits (2). The invention is characterised in that a perforated and substantially flat diffusing element (6, 6') is placed in the intake manifold (5) and arranged substantially perpendicular to the flow direction of the gases to be cooled. The diffusing element can be either a plate, or a grid. The diffusing element provides the apparatus with better efficiency without any increase in price or dimensions.

Description

no 02/oso860 2391931 The present invention relates to a heat exchanger for

gases, of the type comprising a number of ducts mounted in parallel, through which the gases for cooling circulate, and an inlet header box inserted between the 5 gas inlet pipe and the entry to these ducts.

For certain heat exchangers suited to the cooling of gases, for example those used in exhaust gas recirculation systems for combustion engines, the two 10 mediums across which heat is exchanged are separated by a wall.

More particularly, the gases circulate via a series of parallel tubes or ducts, which, during this 15 circulation, are cooled by exchange of heat with a coolant which circulates outside the ducts through which the gases pass.

It is known practice for these exchanges to be produced 20 in several configurations: for example, they may be in the form of a bundle of tubes which are arranged inside casing through which the coolant is circulated, or alternatively they may be produced as a series of parallel plates which constitute the heat-exchange 25 surfaces, so that the exhaust gases and the coolant circulate alternately through the ducts formed between two plates.

The gases supplied to the tube bundle or the ducts of 30 the exchanger arrive via an inlet pipe; given that the diameter of the inlet pipe is smaller than the diameter of the casing and of the tube bundle of the exchanger, there is an inlet header box inserted between the two, and this widens progressively.

The distance between the gas inlet pipe and the bundle of tubes is generally small so as to prevent the exchanger from occupying an excessive amount of space;

- 2 - the result of this is that the distribution of the gases is not uniform between all the tubes of the bundle of the exchanger and that a significant proportion of these gases passes through the tubes 5 situated at the center of the bundle and only a small amount of the gases passes through the tubes nearer the periphery. This non-uniform distribution of the gaseous fluid is 10 clearly to the detriment of the power and thermal efficiency of the exchanger.

Some solutions attempting to increase the efficiency of such exchangers have already been developed, some 15 including deflectors having the shape of a bell situated in the inlet header box of the exchanger, and which tend to direct the fluid toward the periphery of the bundle of tubes of the exchanger.

20 These systems do actually improve the efficiency of the exchanger but increase its cost because of the difficulty there is in producing the deflectors and incorporating them into the exchanger.

25 The object of the present invention is to provide a solution to the disadvantages mentioned hereinabove by proposing a heat exchanger that has the same dimensions as a conventional exchanger but offers improved power and improved thermal efficiency, with, at the same 30 time, a lower cost.

The heat exchanger according to the invention is characterized in that a diffuser element is placed, for example fixed, in the inlet header box.

According to the invention, the diffuser element may be perforated.

In a preferred embodiment, the diffuser element is roughly flat.

Advantageously, the diffuser element is arranged more 5 or less at right angles to the direction in which the gases for cooling flow.

By virtue of the presence of the flattened perforated diffuser element, the distribution of gas in the ducts 10 of the exchanger becomes uniform, thus leading to better efficiency of the apparatus; at the same time, in practical terms, incorporating this element into an exchanger of conventional type is very easy because of its configuration, and does not give rise to any 15 significant increase in cost.

Another advantage that needs to be emphasized is that the dimensions of the exchanger do not change, that is to say that a better distribution of the fluid is 20 arrived at without having to resort to longer inlet header boxes that take up more space.

For this reason, this exchanger is particularly well suited to the cooling of the exhaust gases in vehicles 25 equipped with an EGR (exhaust gas recirculation) system. In a first embodiment, such a diffuser comprises a plate equipped with a number of orifices.

The orifices in the plate may be either circular or polygonal shape, and their size may range from 1 to 20 mm.

35 In a second embodiment, this diffuser comprises a grating; this grating will preferably be produced from a 0.2 to 3 mm wire with a grating pitch of between 1 and 10 mm.

- 4 In order to allow a better understanding of that which has just been explained, figures are attached to give a schematic and illustrative example of one practical embodiment. In these figures: figure 1 schematically depicts the inlet side of a heat exchanger of a tube bundle according to the invention; and 10 figures 2 and 3 depict two other embodiments of the diffuser of the exchanger.

The exchanger of figure 1 consists of a casing 1 comprising a bundle of parallel tubes 2, intended for 15 the passage of the gases that are to be cooled. Inside the casing 1, on the outside of the tubes 2, there flows a coolant from the inlet 3 to an outlet (not depicted). 20 The gases that are to be cooled enter the exchanger via an inlet pipe 4 and via an inlet header box 5, which widens progressively. In the embodiment depicted, the casing 1 is cylindrical and the inlet header box 5 therefore has a frustoconical shape.

According to the invention, in the inlet header box 5, a flat and perforated diffuser element is placed in the exchanger, and this, in figures 1 and 2, consists in a plate 6 equipped with a number of circular orifices 7 30 distributed uniformly.

The flow of gas circulating via the inlet pipe 4 is deflected by the plate 6, this having the effect of distributing it in all directions so that a greater 35 proportion of fluids reaches the tubes situated nearest the periphery of the bundle.

The perforated plate 6 may be placed anywhere in the inlet header box 5, that is to say closer to or further

away from the entry of the tubes 2; there may be between 1 and 200 orifices 7 in the plate 6, all dependent upon the size of the exchanger, and each of them may have a diameter of between 1 and 20 mm, 5 preferably between 6 and 8 mm. The orifices 7 may be distributed in various ways across the plate 6, and may have the shape of a polygon rather than that of a circle. It is also possible to combine orifices of different shapes in one and the same plate, for example 10 in order to give a larger passage cross section in some zones rather than in others.

The thickness of the plate can vary between 0.5 mm and 3 mm approximately.

In another embodiment, the diffuser 6 could consist of a grating 6', as depicted in figure 3, instead of the perforated plate. The grating 6' may be made of steel wire 8 the diameter of which is between 0.2 mm and 6 mm 20 and have a grating pitch of between 1 and 10 mm; the pitch of the grating is defined as the distance from one wire to another, that is to say of the size of each of the holes in the grating.

25 The grating 6' has the same function as the plate 6: it distributes the gas flow to ensure that it reaches all the tubes of the bundle in the same proportion.

The diffuser, whether it is a perforated plate 6 or a 30 grating 6', is fixed to the inlet header box 5, preferably by a few spots of welding, although it is possible to bond it in place using an appropriate adhesive or to weld it via an addition of weld material. In certain canes, it may be possible to 35 manufacture the inlet header box 5 directly with the diffuser 6, 6', for example by molding.

In order to determine the behavior of the exchangers according to the invention and the influence of the

- 6 - diffuser, a series of tests was carried out with an exchanger of the same type as the one depicted in figure 1.

5 The power of this apparatus was tested without the diffuser, with a perforated plate and with a grating.

For the various diffuser configurations, the increase in power and the pressure drop of the gases were compared against this same exchanger without the 10 diffuser.

The test was carried out on an exchanger with a shell ring diameter of 54 mm (casing diameter), a diffuser made of stainless steel 45 mm in diameter and 1 mm 15 thick, placed 8 mm from the entry to the tube bundle.

The results of the test are summarized in the table that follows.

Type of and shape Diameter Power Pressure diffuser of orifices drop orifices PLATE 6 mm + 6% + 17% circular PLATE 13 8.5 mm + 4% + 20% circular PLATE 14 8.5 mm + 3% + 23% I circular PLATE 31 6 mm + 6% + 18% hexagonal GRATING Pitch: 2.17 mm + 3% + 2% Wire 0: 0.6 mm 20 As can be seen, in all cases, the introduction of a

diffuser according to the invention allows an increase in the power of the exchanger, and what is more, the grating is particularly suited to minimizing the pressure drop of the gases.

- 7 - Although one particular embodiment of the present invention is described and depicted, it is obvious that those skilled in the art may introduce alternatives or modifications into it, or replace certain details with 5 other technical equivalents without however departing 1 from the overall scope of the invention as claimed. 3

Claims

- 8 - CLAIMS

1. A heat exchanger for gases, comprising a number of parallel ducts (2) through which gases for cooling 5 circulate and an inlet header box (5) inserted between a gas inlet pipe (4) and the entry to said ducts (2), characterized in that a diffuser element (6, 6') is placed in the inlet header box (5).

10

2. The heat exchanger as claimed in claim l, characterized in that the diffuser element is perforated.

3. The heat exchanger as claimed in one of claims 1 15 and 2, characterized in that the diffuser element is roughly flat.

4. The heat exchanger as claimed in one of claims 1 to 3, characterized in that the diffuser element is 20 arranged more or less at right angles to the direction in which the gases for cooling flow.

5. The heat exchanger as claimed in one of claims 1 to 4, characterized in that the diffuser element 25 comprises a plate (6) with an number of orifices (7).

6. The heat exchanger as claimed in claim 5, characterized in that the orifices (7) in the plate (6) are circular or polygonal, with a size ranging between 30 1 and 20 mm.

7. The heat exchanger as claimed in one of claims 1 to 4, characterized in that the diffuser element comprises a grating (6).

8. The heat exchanger as claimed in claim 7, characterized in that the grating 6' is formed from a

- 9 - wire ( 8) of a diameter of O.2 to 3 mm, and in that the pitch of the grating is between 1 and 10 mm.