Patent Application
20050056411
Subject matter disclosed herein relates generally to methods, devices, and/or systems for exchange of heat energy between two fluids and, in particular, a liquid and a gas wherein the gas is an exhaust gas.
Heat exchangers find a variety of uses in engine systems. For example, recent efforts to enhance fuel economy and/or reduce emissions use heat exchangers to cool exhaust gas in exhaust gas recirculation systems. Currently, exhaust gas recirculation (EGR) heat exchangers or coolers are constructed in either shell-tube or bar-plate form. Typically, the shell-tube type of construction provides less heat transfer in a given volume than does the bar-plate. However, bar-plate fabrication can be expensive. Thus, a need exists for heat exchangers that can provide heat transfer equivalent to, or better than, the bar-plate, while reducing the associated fabrication expense. Methods, devices and/or systems capable of reducing construction costs and/or facilitating and/or enhancing transfer of heat energy are described below.
A more complete understanding of the various methods, devices and/or systems described herein, and equivalents thereof, may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:
The connectors 102, 104, 106, 108 have substantially circular flow cross-sections on an upper end and substantially rectangular flow cross-sections on a lower end. The shape of the lower end flow cross-section facilitates connection of the connectors 102, 104, 106, 108 to the fluid apertures 122, 124, 126, 128 of the upper cover plate 132. Of course, the lower end flow cross-sections and the apertures may have other shapes, such as, but not limited to, circular, elliptical, etc. In addition, to facilitate flow of gas or liquid through the stack 120 and/or to enhance heat exchange between a gas and a liquid, the cross-sectional area of the inlet and outlet apertures and/or inlet and outlet connectors may differ. For example, during heat exchange, a gas may lose heat energy and increase in density. Under such circumstances, mass flow rate of the gas will remain constant while the volumetric flow rate decreases due to the increase in density. If the cross-sectional flow area for the gas remains constant, a drop in gas velocity normal to the cross-sectional flow area will occur. Thus, in an effort to maintain gas velocity, a gas outlet connector may have a cross-sectional flow area that is smaller than that of a gas inlet connector. Further, an outlet aperture may have a cross-sectional area that is less than that of an inlet aperture. Yet further, or alternatively, a stack may have a cross-sectional flow area that decreases with respect to the flow path of a gas. An exemplary stack having such characteristics is described below with respect to
In general, the exemplary heat exchange unit 100 is constructed from a heat-resistant material, such as, but not limited to, stainless steel. For example, an exemplary heat exchanger is constructed from materials capable of withstanding temperatures greater than approximately 1000 F (e.g., approximately 538 C). Hence, an exemplary stack plate or cover plate may be constructed from stainless steel having a thickness of approximately 0.012 inch (e.g., approximately 0.3 mm). Further, the stack of heat exchange plates 120 and/or the upper cover plate 132 and/or the lower cover plate 136 (e.g., or a bottom plate) may be subjected to a brazing process that forms appropriate seals between various plates and/or flow partitions, if present. Of course, additional or alternative processes (e.g., welding, chemical adhesion, chemical bonding, etc.) may be used to form or help form seals. Plates may optionally include compression or press-fit seals. Flow partitions may provide a stack and/or cover plates with some additional structural integrity for withstanding brazing and/or fluid flow pressures. An exemplary flow partition, as described in more detail below, may be constructed from stainless steel having a thickness of approximately 0.004 inch (e.g., approximately 0.1 mm) to approximately 0.006 inch (e.g., approximately 0.15 mm).
As shown, the upper cover plate 132 includes a gas inlet aperture 122 and a gas outlet aperture 124 while the lower cover plate 136 includes plug regions 138, 138′, which plug gas flow apertures 186, 186′ of the lower plate 148. Of course, a lower plate optionally omits gas flow apertures which may alleviate the need for a lower cover plate having such plug regions.
According to this arrangement, gas can enter the stack and flow through flow paths defined at least in part by the gas flow partition 168 and then exit the stack while liquid can enter the stack and flow through flow paths defined at least in part by the liquid flow partitions 164, 164′ and then exit the stack. In general, this arrangement is suitable to facilitate transfer of heat energy from a gas to a cooler liquid. For example, gas in the paths defined by the gas flow partition 168 may transfer heat energy to liquid in paths defined by the upper liquid flow partition 164 and/or the lower liquid flow partition 164′. For most applications, a two plate stack having an upper cover plate and a lower cover plate represents a minimum number of stack plates and/or cover plates to achieve acceptable, but perhaps not optimal, heat transfer.
The upper inner surface 174 is suitable for holding a liquid flow partition such as the liquid flow partition 164 of
If the upper plate 144 is connected to the bottom side of an upper cover plate (e.g., the cover plate 132), the raised gas flow apertures 176, 176′ connect to gas flow apertures (e.g., the apertures 122, 124) of the upper cover plate and/or connectors attached thereto in a manner that does not permit gas to flow into the space between and defined by the upper cover plate (e.g., the cover plate 132) and the upper plate 144, which is a liquid flow space. Similarly, if the upper plate 144 is connected to the bottom side of a lower plate (e.g., plate 148), the raised gas flow apertures 176, 176′ connect to the lower plate in a manner that does not permit gas to flow into the space between and defined by the lower plate and the upper plate (e.g., plate 144), which is a liquid flow space.
An exemplary upper plate has the following dimensions: approximately 7.6 cm (e.g., approx. 3 in.) in a widthwise dimension; approximately 15.2 cm (e.g., approx. 6 in.) in a lengthwise dimension; and approximately 0.25 cm (e.g., approx. 0.1 in.) in thickness.
The lower inner surface 184 is suitable for holding a gas flow partition such as the gas flow partition 168 of
If the lower plate 148 is connected to the upper side of an upper plate (e.g., the plate 144), the gas flow apertures 186, 186′ connect with the raised gas flow apertures 176, 176′ in a manner that does not permit gas to flow into the space between and defined by the lower plate 148 and the upper side of the upper plate (e.g., the plate 144), which is a liquid flow space. Similarly, if the lower plate 148 is connected to the bottom side of an upper plate (e.g., plate 144), the raised liquid flow apertures 188, 188′ connect with the liquid flow apertures 178, 178′ of the upper plate in a manner that does not permit liquid to flow into the space between and defined by the lower plate and the bottom side of the upper plate (e.g., plate 144), which is a gas flow space. Further, if the lower plate 148 is connected to the upper side of a lower cover plate (e.g., the cover plate 136), then the gas flow apertures 186, 186′ are plugged by the raised plug regions (e.g., regions 138, 138′) of the lower cover plate (e.g., the cover plate 136), which prevents gas from entering the space between and defined by the lower plate 148 and the upper side of the lower cover plate (e.g., the cover plate 136), which is a liquid flow space.
Overall, each upper plate 148 has a lower inner surface 184 that helps to define a gas flow space wherein the opposing surface (not shown in
An exemplary lower plate has the following dimensions: approximately 7.6 cm (e.g., approx. 3 in.) in a widthwise dimension; approximately 15.2 cm (e.g., approx. 6 in.) in a lengthwise dimension; and approximately 0.25 cm (e.g., approx. 0.1 in.) in thickness.
A lower plate 148 is positioned below the upper plate 144. The two plates meet at a liquid flow aperture at approximately y8. The lower plate 148 has a thickness equal approximately to the difference between y8 and y9, y10 and y11, and y12 and y13. The upper plate 144 optionally includes a lip having a height equal to approximately the difference between y8 and y9. The lip may help to seal the upper plate 144 and the lower plate 148 about the liquid flow aperture.
The lower surface at y6 of the upper plate 144 and the upper surface at y10 of the lower plate 148 define a gas flow space which has a gas flow partition 168 positioned therein. The height of the gas flow space is approximately equal to the difference between y6 and y10. The gas flow partition 168 includes a plurality of vertical partitions that define a plurality of flow paths (e.g., channels, etc.). In general, the vertical partitions are in contact with the upper and lower surfaces that define the gas flow space (e.g., the surfaces at y6 and y10). In this example, the vertical partitions of the gas flow partition 168 are substantially orthogonal to the vertical partitions of the liquid flow partition 164. Gas entering the unit 100 via a gas aperture of the upper cover plate 132 may enter the plurality of flow paths and eventually exit the unit 100. In particular, gas entering the unit 100 may flow through such flow paths and transfer heat energy to a cooler liquid. Further, a gas flow partition may act to increase surface area for transfer of heat energy. Yet further, the aforementioned vertical partitions may include surface indicia to increase surface area and/or to increase turbulence at or near a vertical partition.
An exemplary upper cover plate may have the following dimensions with y3 arbitrarily defined at y=0 mm (e.g., y3=0 mm): y2=1.3 mm; y1=2.3 mm; and y0=3.6 mm. Of course, in another example, y2 may exceed y1, which may act to increase a height or space between adjacent plates. An exemplary upper plate may have the following dimensions with y9 arbitrarily defined at y=0 mm (e.g., y9=0 mm): y8=0.3 mm; y7=0.6 mm; y6=3.5 mm; y5=3.8 mm; y4=4.8 mm; and y3=5.1 mm. An exemplary lower plate may have the following dimensions with y13 arbitrarily defined at y=0 mm (e.g., y13=0 mm): Y12=0.3 mm; y11=2.6 mm; y10=2.9 mm; y9=5.8 mm; and y8=6.1 mm. Given these exemplary dimensions, a liquid space has a height of approximately 2.6 mm and a gas space has a height of approximately 6.4 mm.
The exemplary dimensions allow for an estimation of flow conditions. For example, a liquid flow space may be considered to have a cross-sectional flow area of approximately 0.26 cm by approximately 15.2 cm or approximately 4 cm2, with a corresponding hydraulic diameter of approximately 0.5 cm. Given a single liquid flow space, a liquid flow rate of approximately 160 cm3.s−1 (e.g., about 2.5 gallons per minute) and an area of approximately 4 cm2, an average flow velocity along an x-axis of approximately 40 cm.s−1 results. Assuming a liquid density of approximately 1 g.cm−3 and a viscosity of 0.01 g.cm−1.s−1, a Reynolds number (i.e., density times hydraulic diameter times velocity divided by viscosity) of approximately 2000 results, which is typically indicative of turbulent flow. Of course, various flow dividers, surface indicia, etc., may also be used to promote turbulent flow and thereby increase heat transfer. In general, turbulence is associated with a decrease in boundary layer thickness, which, in turn, is associated typically with an increase in heat transfer. Of course, similar calculations or estimates may be used for multiple plates that create multiple liquid flow spaces. For example, an exemplary heat exchanger having four liquid flow spaces, each having a height of approximately 0.26 cm and a length of approximately 15.2 cm, would have an average Reynolds number of 2000 for a liquid flow rate of about 10 gallons per minute (e.g., approx. 640 cm3.s−1).
As described herein, an exemplary heat exchanger has a cross-sectional area and a number of layered liquid flow spaces selected to maintain a Reynolds number (e.g., typically greater than or equal to approx. 2000) tending toward turbulent flow at a given liquid flow rate. An exemplary heat exchanger optionally operates in a liquid flow rate range from approximately 120 cm3.s−1 (e.g., approx. 2 gallons per minute) to approximately 6500 cm3.s−1 (e.g., approx. 100 gallons per minute), wherein an average Reynolds number of greater than 2000 exists for flow rates greater than approximately 640 cm3.s−1 (e.g., approximately 10 gallons per minute).
With respect to gas flow rate, in one example, gas flow rate is given or provided in units of mass or weight per unit time in a range of approximately 15 g.s−1 (e.g., approximately 2 lb per minute) to approximately 150 g.s−1 (e.g., approximately 20 lb per minute). Of course, other gas flow rates may be used if desired and optionally depend on heat transfer requirements. In addition, various calculations related to gas flow are possible (e.g., Reynolds number, flow per gas space, number of spaces, etc.), which may be compared to conditions and/or requirements for liquid flow rates. Such calculations may help in determining number of spaces and/or various dimensions, etc. While various examples refer to gas and liquid flow spaces, depending on circumstances, such spaces may include more than one phase (e.g., gas, liquid and/or particulate phases) or a liquid space may serve as a gas space and/or a gas space may serve as a liquid space.
The upper surface of the upper plate 144 and the lower surface of the upper cover plate 132 define a liquid flow space which has a liquid flow partition 164 positioned therein. The liquid flow partition 164 includes a plurality of vertical partitions that define a plurality of flow paths (e.g., channels, etc.). Liquid entering the unit 100 via a liquid aperture of the upper cover plate 132 may enter the plurality of flow paths and eventually exit the unit 100. Further, a liquid flow partition may act to increase surface area for transfer of heat energy. Yet further, the aforementioned vertical partitions may include surface indicia to increase surface area and/or to increase turbulence at or near a vertical partition. In general, an increase in turbulence of a flowing liquid at or near a wall (e.g., a vertical partition, a horizontal surface, or other surface) will enhance transfer of heat energy to the liquid.
A lower plate 148 is positioned below the upper plate 144. These two plates meet to form an outer seal at y8 and about liquid flow apertures as discussed above with reference to
As shown, the core 220 includes a stack of individual plates, such as, the plates 244, 248. A cover plate 232 may be considered a housing component and/or a plate of the core 220. For example, placement of the cover plate 232 over the individual plate 244 can form or define a fluid space between the cover plate 232 and the individual plate 244 (e.g., part of a core side fluid space). Such a fluid space can allow for flow of a fluid and exchange of heat energy between the fluid and another fluid (e.g., liquid or gas in a shell side space) wherein transfer of heat energy between the two fluids occurs at least in part via the cover plate 232 and/or the individual plate 244. In some instances, heat transfer may occur via an edge of a plate, for example, where the edge contacts another structure (e.g., the U-shaped housing wall 236, the inlet 212, the outlet 214, etc.).
In the exemplary heat exchanger 200, the housing components (e.g., 236, 212, 214) fit together cooperatively to house the core 220. The inlet header 212 has an inlet orifice 202, an upper edge 216 that conforms to part of the cover plate 232, and a lower edge 218 that conforms to an outer edge 238 of the U-shaped wall 236. Thus, once in place, the inlet header 212 can help form or define a shell side fluid space. In a similar manner, the outlet header 214 can help form or define a shell side fluid space. In the exemplary heat exchanger 200, the cover plate 232 also helps to define a shell side fluid space. Hence, in this example, the cover plate 232 serves as part of the core 220 to define a core side fluid space and as a housing component to define a shell side fluid space. Further, in this example, the cover plate 232 includes a lip 234 that, once in place, forms a seal with the U-shaped wall 236, the inlet header 212 and the outlet header 204. As shown, the lip 234 forms a seal with the U-shaped wall 236 along the lengthwise edges of the cover plate 232 and forms seals with the inlet header 212 and the outlet header 214 along the widthwise edges of the cover plate 232. In this example, the widthwise edges of the cover plate 232 are substantially arcuate and convex while the upper edge 216 of the inlet header 212 and the upper edge of the outlet header 214 are substantially arcuate and concave. Thus, in this example, the widthwise edges of the cover plate 232 are complementary to the upper edges of the headers 214, 216 (e.g., concave-convex, etc.).
In the exemplary heat exchanger 200, the complementary convex-concave edges of the cover plate 232 and headers 214, 216 allow for positioning of the inlet 226 closer to the header inlet 202 and/or for positioning of the outlet 228 closer to the header outlet 204. Further aspects of such positioning are described with reference to
Fluid may flow to and/or from the core 220 via one or more inlets or outlets. The cover plate 232 includes an inlet 226 for receiving an inlet conduit 206 and an outlet 228 for receiving an outlet conduit 208. Of course, the function of the cover plate inlet 226 and outlet 228 may be reversed. Thus, the exemplary heat exchanger 220 may operate in a substantially counter-current or co-current manner, depending on fluid flow into or out of the various inlets and outlets (e.g., 202, 204, 206, 208, 226, 228). Note that in a co-current operation, the inlet conduit 206 and the inlet header 212, as shown, may each receive a respective feeder conduit wherein the feeder conduits travel along parallel paths, for at least a portion of their lengths prior to meeting the inlet conduit 206 and the inlet header 202. Similarly, the outlet conduit 208 and the outlet header 214 may each receive an exit conduit wherein the exit conduits travel along parallel paths for at least a portion of their lengths after meeting the outlet conduit 208 and the outlet header 204. For counter-current operation, such parallel paths for conduits are also possible.
A lower plate 248 includes a lip 249 having a substantially downwardly directed edge 250. The lip 249 may deviate at first in an upward direction. However, as shown, the edge of the lip 250 deviates substantially downwardly, typically to a lowermost position of the lower plate 248. The lower plate 248 also includes a substantially upwardly directed and open shaft 251. In this example, upon proper positioning of the upper plate 244 and the lower plate 248, the open shaft 247 and the open shaft 251 form a sealed shaft. For example, the open shaft 247 may receive the open shaft 251 and/or vice versa. The two shafts 247, 251 may form a compression or press-fit seal and/or form a seal upon brazing or using other seal means (e.g., welding, chemical adhesion, chemical bonding, etc.). Once properly positioned, the upper plate 244 and the lower plate 248 define a fluid space 258, which is typically a shell side fluid space.
Another upper plate 244′ may be positioned with respect to the lower plate 248. In this example, the lip 245′ of the upper plate 244′ forms a seal with the lip 250 of the lower plate 248. Such a seal may be a compression or press-fit seal and/or a seal formed upon brazing or use of other seal means (e.g., welding, chemical adhesion, chemical bonding, etc.). Once properly positioned, the upper plate 244′ and the lower plate 248 define a fluid space 254, which is typically a core side fluid space.
The core 220 may also include a lower core plate, for example, a plate having features of the upper plate 244; however, without the substantially downwardly directed shaft 247. Such a plate may seal a core side fluid space from a shell side fluid space.
In this example, the lengthwise edges of the lip 236 of the cover plate 232 form seals along the lengthwise runs of the U-shaped wall 236, for example, compression or press-fit seals and/or seals formed upon brazing or use of other seal means (e.g., welding, chemical adhesion, chemical bonding, etc.). The foremost section of the lip 236 of the cover plate 232 forms a seal with the inlet header 212 at or near the upper edge 216. Similarly, an aftmost section of the lip 236 of the cover plate 232 forms a seal at or near the upper edge of the outlet header 214. The inlet header 212 also forms a seal with the U-shaped wall 236 at or near the edge of the inlet header 218. In this example, the inlet header has a cross-section that diverges (e.g., increases) in the direction of fluid flow, as illustrated by the diverging wall 213. The diverging cross-section helps to distribute shell side fluid more evenly in the shell (e.g., space defined by the housing).
The exemplary heat exchanger 200 includes a core having the cover plate 232, seven lower plates 248-248′, seven upper plates 244-244′ and one end plate 244″. Various flow partitions are positioned in the eight core side spaces and the seven shell side spaces between the plates. In this example, the core side flow partitions 264 have a lesser height than the shell side flow partitions 268. Of course, other heights, height relationships and/or types of flow partitions are possible. While a shell side space may exist between the end plate 244″ and the U-shaped wall; in general, the end plate 244″ is in intimate contact with the U-shaped wall, or close enough thereto, to avoid channeling of shell side fluid in such a space.
The shaft region for flow of core side fluid has a plurality of shaft wall sections 247-247′ that prevent fluid from entering the shell side of the heat exchanger 200. Note that the core side fluid spaces are accessible via the shaft via regions that bound the wall sections 247-247′.
As already mentioned, the convex-concave relationship between the cover plate 232 and the inlet header 212 may allow for a better distribution of shell side fluid. Further, shell side fluid distribution may be enhanced by positioning the core side fluid flow shaft in line with the inlet 202 of the inlet header 212. In the first instance, the convex widthwise edge of the cover plate and other plates creates a more streamlined core for the flow of shell side fluid. In the second instance, positioning of the core side fluid flow shaft in line with the inlet 202 of the inlet header 212 allows the shaft to obstruct incoming flow and hence prevent or reduce detrimental channeling of shell side fluid. In combination, the convex-concave relationship and the positioning of the shaft in line with the inlet 202 of the inlet header 212, allow shell side fluid to quickly encounter an obstruction and to flow more easily to the shell side space. For example, the convex-concave relationship may allow for a more forward positioning of the core side fluid shaft and for a reduction in eddy formation in shell side fluid, when compared to a heat exchanger core having a flat fore end. Further, the convex shape of the core may allow for increased strength of the shaft and/or the core when compared to a core having a flat fore end of substantially similar materials and construction.
In the exemplary heat exchanger 350, which corresponds approximately to the exemplary heat exchanger 200 of
Although some exemplary methods, devices and systems have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the methods and systems are not limited to the exemplary embodiments disclosed, but are capable of numerous rearrangements, modifications and substitutions without departing from the spirit set forth and defined by the following claims.
