Heat exchanger

1. An exhaust gas recirculation system with a heat exchanger for an internal combustion engine comprising:

an exhaust conduit for containing flowing heated exhaust in fluidic contact with the exhaust manifold of an internal combustion engine and the intake manifold of the internal combustion engine;

a recirculating liquid coolant conduit; and

a heat exchanger disposed alone the exhaust conduit, the heat exchanger comprising:

at least one exhaust plenum for containing flowing heated exhaust having at least one inlet receiving flowing heated exhaust and at least one outlet for discharging flowing heated exhaust, said inlet(s) spaced from said outlet(s); and

at least one elongated coolant plenum for containing flowing liquid coolant, the coolant plenum contacting the exhaust plenum and having at least one first zone adjacent to the at least one inlet of the exhaust plenum and at least one second zone adjacent to the at least one outlet of the exhaust plenum, wherein the number of coolant plenum(s) is the same in the first zone and the second zone, the first zone comprising an area-in-flow less than an area-in-flow of the second zone, whereby the liquid coolant has a higher velocity in the second zone than in the first zone.

2. The apparatus according to claim 1 , comprising a plurality of exhaust plenums and a plurality of coolant plenums, wherein the exhaust plenums are arranged in an alternating manner between cooling plenums, every second plenum being a cooling plenum.

3. The apparatus according to claim 1 , wherein the first zone comprises more than one first pass coolant plenum and the second zone comprises the same number of subsequent pass coolant plenums.

4. The apparatus according to claim 1 , wherein the at least one coolant plenum has a defined length, with the direction of flow along said length, a defined width, and a height, with the height of the first zone less than the height of said second zone.

5. A heat exchanger for an exhaust gas recirculation system of an internal combustion engine comprising:

at least one exhaust plenum for containing flowing heated exhaust having at least one inlet receiving flowing heated exhaust and at least one outlet for discharging flowing heated exhaust, said inlet(s) spaced from said outlet(s), with said inlet(s) in fluidic contact with an exhaust manifold of an internal combustion engine and with said outlet(s) in fluidic contact with an intake manifold of the internal combustion engine; and

at least one coolant plenum for containing flowing liquid coolant, the coolant plenum making at least two passes contacting the exhaust plenum, the first coolant pass adjacent to the at least one inlet of the exhaust plenum and at least one subsequent coolant pass adjacent to the at least one outlet of the exhaust plenum, wherein the area-in-flow of at least a portion of the first coolant pass is less than the area-in-flow of any subsequent coolant pass, said liquid coolant having a higher velocity in the at least a portion of the first coolant pass than in any subsequent coolant pass, and wherein the number of coolant plenums in the first pass is equal to the number of coolant plenums in the second pass.

6. The apparatus according to claim 5 , comprising a plurality of exhaust plenums and a plurality of coolant plenums, wherein said exhaust plenums are arranged in an alternating manner between cooling plenums, every second plenum being a cooling plenum.

7. The apparatus according to claim 5 , wherein the ratio of the area-in-flow of the first coolant pass to the area-in-flow of at least one subsequent coolant pass is less than 1:1.

8. The apparatus according to claim 7 , wherein the ratio is between about 1:1.3 and about 1:2.

9. The apparatus according to claim 5 , wherein the at least one coolant plenum has a defined length, with the direction of flow along said length, a defined width, and a height, with the height of the first coolant pass less than the height of at least one subsequent coolant pass.

10. The apparatus according to claim 5 , wherein the at least one exhaust plenum makes at least two passes contacting the at least one coolant plenum, wherein a first exhaust pass comprises the at least one inlet receiving flowing heated exhaust and a subsequent exhaust pass comprises the at least one outlet for discharging flowing heated exhaust, and wherein that portion of the first coolant pass adjacent to the first exhaust pass has an area-in-flow less than the area-in-flow of at least one subsequent coolant pass.

11. The apparatus according to claim 10 , wherein the area-in-flow of that portion of the first coolant pass adjacent to the first exhaust pass is less than the area-in-flow of any subsequent coolant pass.

12. A heat exchanger for an exhaust gas recirculation system of an internal combustion engine comprising:

at least one exhaust plenum for containing flowing heated exhaust having at least one inlet receiving flowing heated exhaust and at least one outlet for discharging flowing heated exhaust, said inlet(s) spaced from said outlet(s), with said inlet(s) in fluidic contact with an exhaust manifold of an internal combustion engine and with said outlet(s) in fluidic contact with an intake manifold of the internal combustion engine;

at least one coolant plenum for containing flowing liquid coolant, the coolant plenum contacting the exhaust plenum and having at least one first zone adjacent to the at least one inlet of the exhaust plenum and at least one second zone adjacent to the at least one outlet of the exhaust plenum; and

the first zone comprising an area-in-flow less than an area-in-flow of the second zone whereby flowing coolant adjacent the exhaust plenum in the first zone has a greater velocity than the velocity of flowing coolant adjacent the exhaust plenum in the second zone.