TECHNICAL FIELD

The present invention relates to a heat exchanger having a core of a header plateless type, which is optimal for EGR coolers in which mainly exhaust gas is cooled with cooling water, or exhaust heat recovery devices in which heat of exhaust gas is recovered in cooling water.

In a core of this header plateless type, flat tubes whose open ends are swelled in a thickness direction are used and stacked at the swelling portion to make a header plate needless.

BACKGROUND ART

In Patent Literature 1 below, a header plateless type heat exchanger has been proposed.

In this heat exchanger core15a, as shown inFIGS. 5, 6 and 7, a flat tube16athat forms the core is composed by fitting a pair of plates formed in a groove shape so that respective bottoms of grooves face each other, swelling portions16bare formed at both ends on open sides, stacking is performed at the swelling portions16b, and respective plates are brazed and fixed integrally. Further, as shown inFIG. 6, a crossing angle θ between respective plates is formed in an acute angle.

CITATION LIST

Patent Literature

PTL 1: Japanese Patent Laid-Open No. 2016-183833

SUMMARY OF INVENTION

Technical Problem

In the conventional header plateless type heat exchanger, there is such a risk that temperatures in respective flat tubes become high at an inlet portion of exhaust gas to deteriorate the heat exchanger due to a heat cycle that is generated repeatedly.

This is due to the fact that a header plateless type heat exchanger has such a disadvantage, although it results in an advantage of a simple structure, which cooling performance at the apical portion of respective flat tubes is worse as compared with a heat exchanger with a header plate and the portion reaches a high temperature.

Thus, this invention is directed to provide a heat exchanger that can descend as far as possible the temperature at an apical portion of a flat tube, while having the advantage of header plateless.

Solution to Problem

The present invention according to claim1is a header plateless type heat exchanger, the heat exchanger having a flat tube7that has a pair of plates5,6each including a pair of side walls1on both sides raised up to be formed in a groove-like shape wholly and swelling portions4with narrow width formed outside in a thickness direction at edges on both open sides of a groove bottom3orthogonal to the side wall1, and these plates5,6fitted while facing each other in an opposite direction; and

a heat exchanger core15in which plural flat tubes7are stacked each other at swelling portions4and respective plates5,6are brazed and joined each other, in which

a first fluid10flows from each front edge of the swelling portions4of flat tubes7into the inside thereof, and a second fluid11circulates on the outside thereof,

wherein a recessed groove portion4cthat is recessed inward with narrow width is formed on an outer face side of each of plates5,6, in parallel to the swelling portion4and in the approximately same length, and a projecting part that is inverse to the same is formed on an inner face side thereof.

The present invention according to claim2is the header plateless type heat exchanger according to claim1, wherein each width of the swelling portions4of the respective plates5,6is formed so as to be width wide portions4bwith wide width at both end portions in a longitudinal direction of the swelling portions4and to be width narrow portions4awith narrow width in intermediate portions other than those, and, at the both end portions, the brazed and joined portions in a flat triangle or a curved plane, whose portion lying nearer to the side wall1is wider, are included.

Advantageous Effects of Invention

The present invention according to claim1is one in which the recessed groove portion4crecessed inward with narrow width is formed on the outer face side of each of plates5,6, in parallel to the swelling portion4and in the approximately same length. Accordingly, a flow rate of cooling water flowing through the vicinity of the swelling portion4, that is, the recessed groove portion4c, increases.

Moreover, in contrast to the fact that the crossing angle θ on the outer face side of the stacked portion in the flat tube16aof a conventional type shown inFIG. 6is formed in an acute angle, in the instance of the flat tube7of the present invention, expansion resulted from the formation of the recessed groove portion4calso causes increase in the flow rate of cooling water in the vicinity of the swelling portion4. From these results, cooling of an apical portion of the flat tube7is promoted and temperature rise in the apical portion is suppressed to prevent degradation of the heat exchanger due to a heat cycle.

Furthermore, since the recessed groove portion4cfunctions as a reinforcing rib against bending in the longitudinal direction of the swelling portion4, it becomes capable to reduce the width of the swelling portion4and, as the result, distance from the cooling water to the front edge of the flat tube7becomes shorter. This also promotes cooling of the apical portion and suppresses temperature rise at the apical portion, and therefore degradation of the heat exchanger due to a heat cycle is prevented.

Moreover, the recessed groove portion4cfunctions as a component of elastic deformation for expansion and contraction in an axis direction of the flat tube7to absorb difference in thermal expansion in the direction, and therefore degradation of the heat exchanger due to a heat cycle is also prevented.

In the present invention according to claim2, the width wide portion4b, which is wider, is formed at each of both end portions in the longitudinal direction of the swelling portion4, and the width narrow portion4a, which is narrower, is formed in the intermediate portion other than these. Therefore, a cooling effect is improved in sites with large temperature rise due to exhaust gas (intermediate portions in the longitudinal direction of the swelling portion4).

Furthermore, the width wide portion4bof the swelling portion4is formed in a flat triangle or in a curved plane whose portion lying nearer to side walls1,2is wider. Consequently, concentration of thermal stress near a side wall is released so as to additionally prevent degradation of the heat exchanger due to a heat cycle.

