Heat exchanger tube

A heat exchanger tube is constituted by a flat tube body 14 shaped like a plurality of cylindrical tubes arranged mutually proximally in a plane and connected together at mutually proximate portions of the tubes as communicating portions 13. Cylindrical portions 15 corresponding to the cylindrical tubes of the flat tube body 14 have inner peripheries formed with swirling-flow-forming protrusions 16 directed along spiral trajectories coaxial with central axes O of the cylindrical portions 15 so that the respective cylindrical portions 15 may have individual swirling flows of the exhaust gas 10.

TECHNICAL FIELD

The present invention relates to a heat exchanger tube usable for a heat exchanger of, for example, an EGR cooler.

BACKGROUND ART

Conventionally known is an EGR device for recirculation of a part of exhaust gas from, for example, a vehicle engine to the engine to suppress generation of nitrogen oxides. Some EGR devices are equipped with, midway of an exhaust gas recirculation line to the engine, an EGR cooler for cooling of the exhaust gas since cooling the exhaust gas to be recirculated to the engine will drop a temperature of and reduce a volume of the exhaust gas to lower a combustion temperature in the engine without substantial decrease in output of the engine, thereby effectively suppressing generation of nitrogen oxides.

FIG. 1is a sectional view showing an example of the EGR cooler in which reference numeral1denotes a cylindrical shell with axially opposite ends to which plates2are respectively fixed to close the ends of the shell1. Penetratingly fixed to the respective plates2are opposite ends of a number of tubes3extending axially in the shell1.

Cooling water inlet and outlet pipes4and5A are attached from outside to the shell1near one and the other ends of the shell1, respectively, so that cooling water9is fed through the inlet pipe4into the shell1, flows outside of the tubes3and is discharged outside of the shell1through the outlet pipe5.

The respective plates2have, on their sides away from the shell1, bowl-shaped hoods6fixed to the plates2so as to enclose end surfaces of the plates2. The one and the other hoods6provide central exhaust-gas inlet and outlet7and8, respectively, so that exhaust gas10from the engine enters through the inlet7into the one hood6, is cooled during passage through the number of tubes3by heat exchange with cooling water9flowing outside of the tubes3and is discharged into the other hood6and recirculated through the outlet8to the engine.

In the figure, reference numeral11denotes a bypass outlet pipe, arranged at a position diametrically opposed to the cooling water inlet pipe4, through which a part of the cooling water9is withdrawn to prevent the cooling water9from stagnating at the position diametrically opposed to the cooling water inlet pipe4.

Such conventional EGR cooler has poor heat exchange efficiency since the exhaust gas10may flow straight in the tubes3and insufficiently contact inner peripheries of the tubes3. Thus, it has been proposed that inner peripheries of the tubes3are formed with spiral protrusions12(the tubes3are concaved into spiral grooves on outer peripheries thereof to thereby provide the spiral protrusions12as inverse formations on the inner peripheries) to causes the exhaust gas10flowing through the tubes3to whirl, thereby increasing contact frequency and contact distance of the exhaust gas10to the inner peripheries of the tubes3to enhance the heat exchange efficiency of the EGR cooler (see, for example, Patent Literatures 1 and 2).

As prior art literatures pertinent to the invention, there already exist, for example, the following Patent Literatures 1 and 2.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problems

In order to comply with further possible tightening of exhaust gas regulation in future, it has been demanded to increase, more than ever, an amount of the exhaust gas10to be recirculated to enhance an EGR ratio. However, in the above-mentioned structure with tubes3arranged in parallel with one another and accommodated in the shell1, heat quantity exchanged per unit volume is so little that the EGR cooler as a whole becomes extremely large-sized, disadvantageously resulting in hardness in mounting of the same to a vehicle.

Thus, as shown inFIG. 3, flattening of the tube3is devised so as to enhance heat quantity exchanged per unit volume, which is however found out to have extremely lowered effect of causing the exhaust gas10to swirl by the spiral protrusions12, adversely resulting in deteriorated heat exchange performance.

The invention was made in view of the above and has its object to provide a heat exchanger tube which can cause exhaust gas to swirl to thereby realize high heat exchange efficiency competing to the prior art and can substantially enhance heat quantity exchanged per unit volume to an extent unattainable in the prior art.

Solution to Problems

The invention is directed to a heat exchanger tube, characterized in that it comprises a flat tube body shaped like a plurality of cylindrical tubes arranged mutually proximately in a plane and connected together at mutually proximate portions thereof as communicating portions, cylindrical portions corresponding to said cylindrical tubes of said flat tube body having inner peripheries formed with swirling-flow-forming protrusions along spiral trajectories coaxial with central axes of said cylindrical portions so that swirling flows of heat medium may be individually formed in said respective cylindrical portions.

With the heat exchanger tube being thus constituted, the flows of the heat medium through the respective cylindrical portions of the flat tube body are guided in directions along the spiral trajectories by the swirling-flow-forming protrusions on the inner peripheries of said respective cylindrical portions, so that the swirling flows of the heat medium are individually formed in the respective cylindrical portions. As a result, contact frequency and contact distance of the heat medium to the inner peripheries of said respective cylindrical portions are increased to enhance the heat exchange efficiency. Moreover, the fact that the respective cylindrical portions are mutually in communication through the communicating portions ensures a sufficient flow-path cross-sectional area for passage of the heat medium, so that heat quantity exchanged per unit volume is enhanced and pressure loss is decreased.

It is preferable in the invention that neighboring cylindrical portions are shaped to have the swirling-flow-forming protrusions directed along mutually reversed spiral trajectories, which makes the swirling flows, at the communicating portions of the neighboring cylindrical portions, orientated in one and the same direction and mutually accelerated, so that, despite of the communication portions between the cylindrical portions, formation as swirling flows of the heat medium can be further ensured.

Advantageous Effects of Invention

According to the above-mentioned heat exchanger tube of the invention, various excellent effects can be obtained as mentioned below.

(I) While the heat medium is caused to swirl to thereby realize high heat exchange efficiency competing to the prior art, heat quantity exchanged per unit volume can be substantially enhanced to an extent unattainable in the prior art. In an application to a heat exchanger of, for example, an EGR cooler, the heat exchanger as a whole can be made compact in size to enhance mountability to, for example, a vehicle.

(II) When neighboring cylindrical portions are shaped to have the swirling-flow-forming protrusions directed along mutually reversed spiral trajectories, the swirling flows at the communicating portions of the neighboring cylindrical portions can be orientated in one and the same direction and mutually accelerated, which further ensures formation of the swirling flows in the respective cylindrical portions.

DESCRIPTION OF EMBODIMENT

An embodiment of the invention will be described in conjunction with the drawings.

FIGS. 4 and 5show the embodiment of a heat exchanger tube according to the invention, which is applied to an EGR cooler as is the case in the above-mentioned prior art. In the figures, parts similar to those inFIGS. 1-3are represented by the same reference numerals.

As shown inFIG. 4, the embodiment of the heat exchanger tube comprises a flat tube body14shaped like a plurality of cylindrical tubes arranged mutually proximally in a plane and connected together at mutually proximal portions thereof as communicating portions13. Cylindrical portions15corresponding to the cylindrical tubes of the flat tube body14have inner peripheries formed with swirling-flow-forming protrusions16along spiral trajectories coaxial with central axes O of the cylindrical portions15(the respective cylindrical portions15are concaved into grooves on outer peripheries thereof to thereby provide swirling-flow-forming protrusions16as inverse formations) so that swirling flows of the exhaust gas10may be individually formed in respective cylindrical portions15.

Specifically, as shown inFIG. 5, despite of the communicating portions13between the respective cylindrical portions15, the exhaust gas10flowing through the respective cylindrical portions15is caused to swirl by properly tuning, for example, pitch L between central axes of the respective cylindrical portions15, vertical gap C of the communicating portions13and raised height H of the swirling-flow-forming protrusions16.

Especially in the embodiment, neighboring cylindrical portions15are shaped to have the swirling-flow-forming protrusions16directed along mutually reversed spiral trajectories (see appearances of the respective cylindrical portions15inFIG. 4) such that the swirling flows are orientated in one and the same direction at the communicating portions13of the neighboring cylindrical portions15, which is a contrivance for prevention of mutual counteraction of the swirling flows (see directions of the swirling flows of the exhaust gas10shown by arrows inFIG. 5).

The flat tube body14may be produced by, for example, producing a pair of halved parts constituting upper and lower portions of the flat tube body through press working or the like, placing the halved parts one above the other and welding the parts at opposite ends thereof. Upon such press working, the respective cylindrical portions15may be concaved into grooves on outer peripheries thereof for prominence of the swirling-flow-forming protrusions16on the inner peripheries as inverse formations.

In such production of the flat tube body14, various production methods may be, of course, utilized which have been already practiced for existing heat exchangers such as radiators and intercoolers. For example, parts to be joined may be formed to have overlap portions at which the parts are joined together through brazing; alternatively, a lower structure with an upper structure laid out sideways thereof may be pressed as a single piece, the upper structure being folded back on the lower structure and joined together through welding or brazing.

When sides or a side of the flat tube body14is to be utilized for joining, to form the swirling-flow-forming protrusions16(grooving on the outer periphery: seeFIG. 4) on the sides or side may be partly omitted in view of easiness in a joining work. It has been affirmed by the inventors that the partial omission of the swirling-flow-forming protrusions16on the sides or side does not greatly affect the formation of the swirling flows.

Then, with the heat exchanger tube thus constituted, the flows of the exhaust gas10through the respective cylindrical portions15of the flat tube body14are guided in directions along the spiral trajectories by the swirling-flow-forming protrusions16on the inner peripheries of the respective cylindrical portions15, so that the swirling flows of the exhaust gas10are individually formed in the respective cylindrical portions15. As a result, the contact frequency and the contact distance of the exhaust gas10to the inner peripheries of the respective cylindrical portions15are increased to enhance the heat exchange efficiency. Moreover, the fact that the respective cylindrical portions15are mutually in communication through the communicating portions13ensures a sufficient flow-path cross-sectional area for passage of the exhaust gas10, so that heat quantity exchanged per unit volume is enhanced and pressure loss is decreased.

In the embodiment, neighboring cylindrical portions15are shaped to have the swirling-flow-forming protrusions16directed along mutually reversed spiral trajectories, which makes the swirling flows, at the communicating portions13of the neighboring cylindrical portions15, orientated in one and the same direction and mutually accelerated, so that, despite of the communicating portions13between the respective cylindrical portion15, formation of the exhaust gas10as swirling flows can be further ensured.

Thus, according to the above-mentioned embodiment, while the exhaust gas10is caused to swirl to thereby realize high heat exchange efficiency competing to the prior art, heat quantity exchanged per unit volume can be substantially enhanced to an extent unattainable in the prior art. For example, in an application to an EGR cooler as shown inFIG. 6, accommodated in the shell1with rectangular cross-section are the flat tube bodies14as mentioned in the above in a plurality of rows (two rows in the example illustrated) and in a multistage (nine stages in the example illustrated), so that the EGR cooler as a whole can be made compact in size to enhance mountability to a vehicle while an amount of the exhaust gas10to be recirculated can be increased more than ever to enhance the EGR ratio.

Especially in the embodiment, neighboring cylindrical portion15are shaped to have the swirling-flow-forming protrusions16directed along mutually reversed spiral trajectories, which makes the swirling flows, at the communicating portions13of the neighboring cylindrical portions15, orientated in one and the same direction and mutually accelerated, so that formation of the swirling flows in the respective cylindrical portions15can be further ensured.

It is to be understood that a heat exchanger tube according to the invention is not limited to the above embodiment and that various changes and modifications may be made without departing from the scope of the invention. For example, the invention may be applied to any heat exchanger other than that for an EGR cooler.

REFERENCE SIGNS LIST