Patent Publication Number: US-7213639-B2

Title: Heat exchanger exhaust gas recirculation cooler

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a system and a method for a heat exchanger. 
   2. Background Art 
   Heat exchanger assemblies, such as an automobile radiator, an exhaust gas recirculation (EGR) cooler, and the like are typically used to transfer heat from a fluid on one side of a barrier to a fluid on the other side without bringing the fluids into direct contact. Heat exchangers are used with several types of fluids, for example: air-to-air, air-to-water or water-to-water (or exhaust gas, coolant, etc.). 
   However, conventional heat exchangers have a number of deficiencies. The deficiencies of conventional heat exchangers include thermal stress in critical areas at the inlet which can cause fractures and failures of the heat exchanger, local “hot spots” due to stagnant water flow areas by the hot passage, poorly shaped return tank and poor flow distribution, excessive gas pressure loss through the cooler thereby causing poor cooler thermal efficiency, trapped vapor pockets (e.g., bubbles) and film boiling in liquid coolant, poor heat rejection, re-circulation on the inlet side of the header tank and non-uniform gas mass flux to the inlet tubes, re-circulation of coolant in the heat exchanger (in particular, re-circulation of coolant at the turnaround section), and excessive coolant flow short circuit (i.e., coolant that does not flow past the gas flow tubes) velocities (and reduced coolant flow across the gas tubes). 
   Thus, there exists a need and an opportunity for an improved system and an improved method for heat exchangers that addresses some or all of the deficiencies noted above. 
   SUMMARY OF THE INVENTION 
   The present invention generally provides new, improved and innovative techniques for heat exchangers. The present invention generally provides a system and a method for heat exchangers that may reduce or eliminate deficiencies of conventional approaches such as thermal stress in critical areas at the inlet, local “hot spots” due to stagnant water flow areas by the hot passage, poorly shaped return tank and poor flow distribution, excessive gas pressure loss through the cooler, trapped vapor pockets (e.g., bubbles) and film boiling in liquid coolant, poor heat rejection, re-circulation on the inlet side of the header tank and non-uniform gas mass flux to the inlet tubes, re-circulation of coolant in the heat exchanger (in particular, re-circulation of coolant at the turnaround section), excessive coolant flow short circuit velocities, and reduced coolant flow across the gas tubes. 
   According to the present invention, a two-pass, loop flow heat exchanger is provided. The heat exchanger comprises an inlet plenum that receives a fluid to be cooled, a housing, a plurality of inlet flow passages substantially centrally positioned within the housing and having a first end fluidly coupled to the inlet plenum to receive the fluid, a turnaround plenum fluidly coupled to a second end of the inlet flow passages for reversing the flow of the fluid, a plurality of outlet flow passages peripherally positioned within the housing and having a first end fluidly coupled to the turnaround plenum, and an outlet plenum fluidly coupled to a second end of the outlet flow passages to present the fluid. 
   Also according to the present invention, a method of performing a heat exchange operation using a two-pass, loop flow heat exchanger is provided. The method comprises presenting a fluid to be cooled to an inlet plenum, positioning a plurality of inlet flow passages substantially centrally within a housing and fluidly coupling a first end of the inlet flow passages to the inlet plenum to receive the fluid, fluidly coupling a turnaround plenum to a second end of the inlet flow passages for reversing the flow of the fluid, positioning a plurality of outlet flow passages peripherally within the housing, and fluidly coupling a first end of the outlet flow passages to the turnaround plenum, and fluidly coupled an outlet plenum to a second end of the outlet flow passages to present the fluid. 
   The above features, and other features and advantages of the present invention are readily apparent from the following detailed descriptions thereof when taken in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram illustrating a simplified isometric, cutaway view of an example of a heat exchanger of the present invention; 
       FIG. 2  is a top cutaway view of the heat exchanger of  FIG. 1 ; 
       FIG. 3  is a sectional side view of the heat exchanger of  FIG. 1 ; 
       FIG. 4  is a diagram illustrating a top cutaway view of another example of a heat exchanger of the present invention; and 
       FIG. 5  is a sectional side view of the heat exchanger of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
   With reference to the Figures, the preferred embodiments of the present invention will now be described in detail. Generally, the present invention provides an improved system and an improved method for heat exchangers. In one example, the heat exchanger of the present invention may advantageously implemented as an exhaust gas recirculation (EGR) gas cooler. However, the heat exchanger of the present invention may used in connection with any appropriate application to transfer heat from a fluid on one side of a barrier to a fluid on the other side without bringing the fluids into direct contact. Heat exchangers implemented in accordance with the present invention may be used with several types of fluids, for example: air-to-air, air-to-water or water-to-water (or exhaust gas, coolant etc.), fluid to solid or semi-solid, etc. or combination thereof as appropriate to meet the design criteria of a particular application. 
   The present invention generally provides for having a hot fluid (or gas) stream (i.e., the fluid to be cooled via the heat exchange operation performed using the heat exchanger of the present invention) passing through the center of the heat exchanger, and for cooled (or outlet) fluid (e.g., gas) shielding the hot (or inlet) gas from all sides. The inlet and outlet gas paths are generally separated by any appropriate structure to meet the design criteria of a particular application. The shape of the external housing of the heat exchanger of the present invention may be round, square, triangular, oval, “kidney”, etc., i.e., any appropriate shape to meet the design criteria of a particular application. 
   The benefits derived from the present invention do not generally depend on orientation of the heat exchanger. The implementation of a central hot gas passage within a cooled gas passage according to the present invention is generally applicable for all orientations, and for heat exchangers of all types (e.g., air-to-air, air-to-water or water-to-water (or exhaust gas, coolant, semi-solid, etc.)). 
   The present invention generally provides for reduced thermal stress at the inlet for the cooled fluid. The present invention generally provides for reduced thermal differentials between inlet and outlet interfaces, and, therefore, coolant “short circuit” paths (i.e., coolant flow paths around rather than through passages carrying the fluid to be cooled) may have smaller passages than in conventional approaches. As such, the efficiency of the heat exchanger of the present invention may be greater than in conventional approaches. 
   The present invention generally reduces the risk of local “hot spots” due to the elimination of stagnant coolant flow areas by the hot passage on the water (coolant) side. In one example of the present invention, a “piston bowl”, “dog dish”, “donut”, generally annular shaped return tank may provide improved flow distribution via a “flow within flow”. The “flow within flow” heat exchangers of the present invention may be implemented in connection with any appropriate applications, and the benefit may be most advantageously realized when implemented in connection with a very large temperature differential between inlet and outlet sides of the cooled fluid. 
   The present invention generally provides improved heat rejection capacity that may accommodate increased EGR rates. The present invention may minimize gas pressure loss of the cooled fluid through the cooler thereby providing improved cooler thermal efficiency, reduce or prevent trapped vapor pockets (e.g., bubbles) and film boiling in liquid coolant, improve heat rejection, minimize re-circulation on the inlet side of the header tank and thereby provide more uniform gas mass flux to the inlet tubes, minimize re-circulation of coolant in the heat exchanger (in particular, minimize re-circulation of coolant at the turnaround section), reduce coolant flow short circuit (i.e., coolant that does not flow past the gas flow tubes) velocities (and increase coolant flow across the gas tubes) by having a reduced gap between the gas tubes and the coolant jacket when compared to conventional approaches. 
   Referring to  FIG. 1 , a diagram illustrating an isometric, simplified cutaway view of an example of a heat exchanger  100  of the present invention is shown. Referring to  FIG. 2 , is a top cutaway view of the heat exchanger  100  is shown. Referring to  FIG. 3 , a diagram illustrating a sectional view of the heat exchanger  100  taken at the line A—A of  FIG. 2  is shown. 
   Referring generally to  FIGS. 1–3 , the heat exchanger  100  generally comprises a top fluid plenum (e.g., manifold, tank, section, end, cavity, region, area, header tank, etc.)  102 , a bottom fluid plenum (e.g., manifold, tank, section, end, cavity, region, area, turnaround, etc.)  104 , a plurality of hollow passage ways (e.g., tubes, pipes, flow tubes, passages, and the like)  106  (not shown in  FIG. 1  for clarity, shown in  FIGS. 3–5 ) arranged in a substantially parallel, spaced-apart relationship (e.g, orientation, placement, etc.), and a housing  108  for enclosing passage ways  106  and mechanically coupled to and between the sections  102  and  104 . The heat exchanger  100  generally further comprises separator plates (e.g., dividers, walls, bulkheads, etc.)  120  and  122  having holes for receiving and mounting the tubes  106 . 
   The walls  120  and  122 , in connection with the housing  108 , generally form a coolant (or cooling) chamber (i.e., body)  110  having the tubes  106  contained therewithin. The dividers  120  and  122  also generally form a portion of the walls that comprise the plenums  102  and  104 , respectively. The inlet manifold  102  is generally mechanically and hermetically coupled to a first end of the housing  108 . The outlet manifold  104  is generally mechanically and hermetically coupled to a second end of the housing  108 . The heat exchanger  100  is generally implemented as a two-pass, loop flow (e.g., serpentine flow) heat exchanger. 
   In one example, the heat exchanger  100  as illustrated in  FIG. 1  may be advantageously implemented as an EGR gas cooler. While the heat exchanger  100  is described herein in connection with an implementation as an EGR cooler, such description is for clarity of illustration, and not a limitation on the possible implementations and applications of the present invention as understood by one skilled in the art. 
   The top plenum region  102  generally comprises an inlet region (e.g., section, portion, area, sub-manifold, plenum, etc.)  130 , and an outlet region (e.g., section, portion, area, sub-manifold, plenum, etc.)  132 . The regions  130  and  132  may share adjacent wall structures (e.g., sections of the wall  120 ). However, the regions  130  and  132  are separated such that fluid that is introduced into the inlet sub-manifold  130  passes through some of the tubes  106  (e.g., tubes  106   a ), into the plenum  104 , through others of the tubes  106  (e.g., tubes  106   b ), and into the outlet sub-manifold  132 . The inlet plenum  130  is generally not directly fluidly coupled to the outlet plenum  132 . The inlet plenum  130  is generally indirectly fluidly coupled to (i.e., in fluid communication with) the outlet plenum  132  via the tubes  106  and the manifold  104 . 
   The inlet plenum  130  generally includes an inlet (e.g., fitting, coupling, connector, etc.)  140 . The inlet plenum  130  generally receives a fluid (e.g., liquid, gas, semi-solid, vapor, air, exhaust gas, vaporous mixture, etc.) that is to be cooled at the inlet  140 . The outlet plenum  132  generally includes an outlet (e.g., fitting, coupling, connector, etc.)  142 . The outlet plenum  132  generally presents cooled fluid (i.e., the fluid to be cooled after cooling) at the outlet  142 . 
   The inlet portion  130  and the outlet portion  132  are generally shaped substantially as truncated cones having the inlet  140  and the outlet  142 , respectively, at the narrow ends of the cones. The inlet  140  and the outlet  142  are generally oriented (i.e., pointed, positioned, placed, etc.) to provide an efficient (e.g., unobstructed) hook up (i.e., connection, coupling, etc.) to respective connecting members (e.g., hoses, pipes, etc., not shown). 
   The passage ways  106  generally comprise inlet tubes  106   a  that are fluidly coupled to the inlet sub-manifold  130  to receive the fluid that is to be cooled at a first end and fluidly coupled to the plenum  104  at a second end, and outlet tubes  106   b  that are fluidly coupled to the plenum  104  at a first end and to the outlet sub-manifold  132  at a second end that presents the cooled fluid into the sub-manifold  132 . The inlet tubes  106   a  are generally positioned (i.e., displaced, arranged, set, configured, disposed, etc. substantially centrally within the cooling chamber  110  (e.g., away from the housing  108 ). The outlet tubes  106   b  are generally positioned (i.e., displaced, arranged, set, configured, disposed, etc. substantially peripherally within the cooling chamber  110  (e.g., near the housing  108 ). That is, the inlet tubes  106   a  are “inner” passage ways, and the outlet tubes  106   b  are “outer” passage ways for the fluid that is to be cooled. 
   The inlet passages  106   a  and outlet passages  106   b  are generally provided in size or number such that the total cross-sectional area of the inlet of the passages  106   a  to which the fluid to be cooled is presented is essentially (i.e., approximately, substantially, about, etc.) 1.5 times the total cross-sectional area of the inlet of the outlet passages  106   b  to which the fluid to be cooled is presented. The ratio of the total cross-sectional area of the inlet passages  106   a  to the total cross-sectional area of the outlet passages  106   b  may be in a range of 1:1 to 3:1 (i.e., 1 to 1–3 to 1), a preferred range of 1.25:1 to 2:1 (i.e. 1.25 to 1–2 to 1), a most preferred range of 1.35:1 to 1.7:1 (i.e., 1.35 to 1–1.7 to 1). 
   In one example, the passage ways  106  may be implemented as substantially circular tubes (or pipes). In another example (not shown), the passage ways  106  may be implemented as tubes having a substantially oval shape. In yet another example (not shown), the passage ways  106  may be implemented as tubes having a substantially square or rectangular shape. In yet another example (as described in more detail in connection with elements  106 ′ of  FIGS. 4 and 5 ), the passage ways  106  may be implemented as circular tubes (or pipes) having a helical twist (or indentations that provide a helical shape). However, the passage ways  106  may be implemented having any appropriate shape to meet the design criteria of a particular application. 
   The fluid to be cooled generally circulates through heat exchanger  100  in a substantially serpentine (e.g., two-pass) path. The fluid to be cooled generally enters the heat exchanger  100  via the inlet  140 , flows through the plenum  130  into the substantially centrally positioned inlet passage ways  106   a , out of the inlet passage ways  106   a  and into the plenum  104  where the fluid to be cooled reverses flow direction (i.e., the plenum  104  may be configured as a “turn around” for the fluid to be cooled) and enters the outlet passage ways  106   b , through the passage ways  106   b  into the outlet plenum  132 , and the cooled fluid to be cooled is presented by the outlet  142 . 
   In one example, the plenum  104  may be substantially annular (e.g., ring, donut, etc.) shaped with a substantially disc shaped offset (e.g., biased towards the plate  122 ) center section (e.g., portion, region, area, etc.)  160  and an outer ring section (e.g., portion, region, area, etc.)  162 . The center area  160  is generally sized to about the same size as and positioned at the region of the divider  122  where the inlet passages  106   a  are mounted at the plenum  104 , and the outer ring region  162  is generally sized to about the same size as and positioned at the region of the divider  122  where the outlet passages  106   b  are mounted at the plenum  104 . The center area  160  is generally separated from the inlet passages  106   a  at the plate  122  by a thickness C. The outer ring area  162  is generally separated from the outlet passages  106   b  at the plate  122  by a thickness R. The transitions between the regions  160  and  162  are generally gradually tapered such that the flow of the fluid to be cooled through the turnaround  104  is substantially non-turbulent. 
   The ratio of the center  160  thickness C to the ring thickness R may be in a range of 1:1 to 0.1:1 (i.e., 1 to 1–0.1 to 1) (i.e., at one extreme, the thicknesses C and R may be substantially the same and the side of the plenum  104  opposite the divider  122  may be substantially flat, and at the other extreme, the center thickness C may be 1/10 the outer ring thickness R), a preferred range of 0.8:1 to 0.5:1 (i.e., 0.8 to 1–0.5 to 1), and a most preferred range of 0.6:1 to 0.2:1 (i.e., 0.6 to 1–0.2 to 1), and have a nominal value of 0.3:1 (i.e., 0.3 to 1). 
   The heat exchanger  100  generally receives the fluid (e.g., liquid, gas, vapor, etc.,) to be cooled through the inlet fitting  140 . The fluid to be cooled generally circulates through the heat exchanger  100  and a heat exchange operation is generally performed therein. In fluidly coupled combination, the top and bottom fluid manifolds  102  and  104  and passage ways  106  generally provide a continuous flow path for the fluid to be cooled through the heat exchanger  100 . The internally circulated and cooled fluid may be discharged from the heat exchanger  100  through the outlet fitting  142 . In one example (not shown), the heat exchanger  100  may include multiple inlet fittings  140  and/or outlet fittings  142  to meet the design criteria of a particular application. 
   The housing  108  generally comprises an inlet (e.g., fitting, coupling, connector, etc.)  180  and an outlet  182 . In one example, an auxiliary outlet (e.g., a by-pass outlet)  184  may be included on the housing  108 . The inlet  180  generally receives a fluid (e.g., liquid, gas, semi-solid, vapor, air, engine coolant from the outlet side of a radiator, etc., hereinafter referred to as a coolant) that provides transfer of heat away from the fluid to be cooled. The housing  108  generally presents the circulated coolant at the outlet  182 , and alternatively, also at the outlet  184 . The coolant generally enters the cooling chamber  110  via the inlet  180 , circulates around the tubes  106   b  and  106   a , and exits the chamber  110  via the outlet  182 , and alternatively, also at the outlet  184 . 
   In a heat exchanger such as the heat exchanger  100 , there may be a so-called short circuit coolant flow path between the outlet flow tubes  106   b  and the inner surface of the housing  108 . However, in the heat exchanger  100  because mechanical stress at the divider  120  may be reduced when compared to conventional approaches, the so-called short circuit coolant flow path is generally smaller than in conventional approaches. Thus, the efficiency of the heat exchanger of the present invention is generally more efficient than a similarly sized conventional heat exchanger. 
   Extreme thermal gradients (e.g., high temperature differentials or “deltas”) between adjacent elements of the present invention may be reduced or eliminated when compared to conventional approaches because the present invention is implemented having the fluid to be cooled presented centrally within the housing  108 , and thus centrally within the cooling chamber  110 . As such, when compared to conventional approaches mechanical stress at the divider  120  may be reduced, local “hot spots” due to stagnation of coolant flow may be reduced, trapped vapor pockets and film boiling in the coolant may be reduced, and pressure loss of the fluid to be cooled may be reduced. Further, re-circulation of coolant in the heat exchanger  100  (in particular, re-circulation of coolant at the turnaround section  104 ), may be reduced when compared to conventional approaches. 
   The reduction of extreme thermal gradients and mechanical stresses may be beneficially achieved at the interface (i.e., connection, weld, attachment, transition, etc.) of the header plenum  102  and the housing  108 . In one example simulation (an example having a circular housing  108 ), the stress reduction was 76–86% and the temperature reduction was 57–69 deg C. for a heat exchanger of the present invention when compared to a conventional approach. 
   In one example, the housing  108  may have a substantially cylindrical shape with a substantially circular cross-section as illustrated in  FIGS. 1 ,  2  and  4 . In another example (not shown), the housing  108  may have a substantially square cross-section. In yet another example (not shown), the housing  108  may have a substantially triangular cross-section. In another example (not shown), the housing  108  may have a substantially kidney-shaped cross-section. However, the housing  108  may have any appropriate shape to meet the design criteria of a particular application (e.g., a shape to conform to packaging space). In any case, the heat exchanger  100  generally implements a two-pass flow pattern having the inlet of the fluid to be cooled at cooling passages that are substantially centrally located in the housing  108  and outlet of the fluid to be cooled at cooling passages that are substantially peripherially located in the housing  108 . 
   The housing  108  may also have one or more brackets  190  that generally provide a structure to mechanically fasten the heat exchanger  100  at a desired position in connection with the design criteria of a particular application. The brackets  190  are generally produced with an appropriate shape and fixed to the heat exchanger  100  in appropriate locations for the design criteria of the application. 
   Referring to  FIGS. 4 and 5 , diagrams illustrating a heat exchanger  100 ′ is shown. Referring to  FIG. 4 , is a top cutaway view of the heat exchanger  100 ′ is shown. Referring to  FIG. 5 , a diagram illustrating a sectional view of the heat exchanger  100 ′ taken at the line A—A of  FIG. 4  is shown. The heat exchanger  100 ′ may be another example of a heat exchanger according to the present invention. The heat exchanger  100 ′ may be implemented similarly to the heat exchanger  100 . The heat exchanger  100 ′ generally comprises a header plenum  102 ′ having an inlet region  130 ′ with an inlet  140 ′ and an outlet region  132 ′, and flow passages  106 ′. 
   The inlet region  130 ′ may be substantially conically shaped and the inlet  140 ′ may be substantially parallel with the flow tubes  106 ′. The outlet region  132 ′ may be substantially annular (e.g., ring, donut, etc. shaped). The flow tubes  106 ′ may be formed having a substantially helically twisted shape. 
   As is readily apparent from the foregoing description, then, the present invention generally provides an improved apparatus and an improved method for heat exchangers. The improved system and method of the present invention may provide reduced thermal differentials at element interfaces, and improved efficiency when compared to conventional approaches. 
   While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.