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An apparatus and method for cooling hot fluids, especially exhaust gases, with a multi-pass cooler core. The cooler core is particularly useful for cooling exhaust gases flowing in an exhaust gas recirculation (EGR) system or regime in operative association with an internal combustion engine, such a

An apparatus and method for cooling hot fluids, especially exhaust gases, with a multi-pass cooler core. The cooler core is particularly useful for cooling exhaust gases flowing in an exhaust gas recirculation (EGR) system or regime in operative association with an internal combustion engine, such as a diesel engine. Cooled gases are recirculated to the engine input to help reduce noxious exhaust emissions. The invention utilizes unequal areas-in-flow between the first exhaust pass through the core and the second and subsequent passes through the core. The first pass through the core features an area-in-flow comparatively larger than the area-in-flow of the second pass. The difference in areas-in-flow between passes influences gas velocities to reduce fouling, despite changes in exhaust gas temperature between passes through the core.

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1. A method for making a multi-pass heat exchanger core comprising the steps of:providing at least one coolant plenum for containing flowing coolant; installing adjacent to the at least one coolant plenum as least on first-pass plenum for containing a flowing heated gas and defining a first area-in-

1. A method for making a multi-pass heat exchanger core comprising the steps of:providing at least one coolant plenum for containing flowing coolant; installing adjacent to the at least one coolant plenum as least on first-pass plenum for containing a flowing heated gas and defining a first area-in-flow of the heated gas; and disposing adjacent to the at least one coolant plenum at least one subsequent-pass plenum for containing the heated gas and defining a second area-in-flow of the heated gas; and arranging the plenums so that the contained heated gas flow past a coolant plenum at least twice; wherein the step of defining a first area-in-flow comprises defining a ratio of the first area-in-flow to the second area-in-flow to be between about 1.3 to 1 and about 1.7 to 1.2. The method of claim 1 wherein:the step of providing at least one coolant plenum comprises providing a plurality of coolant plenums; the step of installing at least one first-pass plenum comprises installing a plurality of first-pass plenums, the plurality of first-pass plenums defining a first plurality of exhaust passages to direct exhaust gas flow through the first-pass plenums; the step of disposing at least one subsequent-pass plenum comprises disposing a plurality of subsequent-pass plenums, the plurality of subsequent-pass plenums defining a second plurality of exhaust passages to direct exhaust gas flow through the subsequent-pass plenums; wherein the first plurality of exhaust passages substantially exceed in number the second plurality of exhaust passages; andfurther comprising the step of arranging the first-pass plenums and the subsequent-pass plenums in an alternate manner between cooling plenums, every second plenum being cooling plenum.3. The method of claim 1 comprising the steps of:disposing all the plenums substantially parallel; and separating the first-pass plenums from the subsequent-pass plenums with at least one elongate divider substantially perpendicular to the plenums. 4. A method for making a multi-pass fold-flow exhaust gas recirculation cooler comprising the steps of:providing a plurality of coolant plenums for containing flowing coolant; disposing adjacent to at least one of the coolant plenums a plurality of first-pass plenums, defining a first-area-in-flow, for containing hot exhaust gases; disposing adjacent to at least one of the coolant plenums a plurality of subsequent-pass plenums, definig a second area-in-flow for containing the hot exhaust gases; wherein the total number of first-pass plenums substantially exceeds the total number of subsequent-pass plenums, whereby a ratio of the first area-in-flow to the second area-in-flow is between bout 1.3 to 1 and about 1.7 to 1.5. The method of claim 4 comprising the further steps of:defining a plurality of exhaust passages in each of the first-gas plenums; and defining a plurality of exhaust gas passages in each of the subsequent-pass plenums. 6. A method for making a multi-pass cross-flow heat exchanger core comprising the steps of:providing a plurality of coolant plenums for containing flowing coolant; installing adjacent to at the coolant plenums a plurality of first-pass plenums for containing a flowing heated gas and defining a first area-in-flow of the heated gas; and disposing adjacent to the coolant plenum a plurality of subsequent-pass plenums for containing the heated gas and defining a second area-in-flow of the heated gas; disposing all the plenums substantially parallel; separating the first-pass plenums from the subsequent-pass plenums with at least one elongate divider substantially perpendicular to the plenums; and arranging the plenums so that the contained heated gas flows past a coolant plenum at least twice;wherein the step of defining a first area-in-flow comprises defining a ratio of the first area-in-flow to a subsequent area-in-flow to be between about 1.3 to 1 and about 1.7 to 1. 7. The method of claim 6 wherein the number of first-pass plenums equals the number of subsequent pass plenums, and further wherein the step of defining a ratio of the first area-in-flow to a subsequent area-in-flow comprises providing the subsequent-pass plenums with a selected smaller effective dimension.