Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F1/00—Tubular elements; Assemblies of tubular elements
  • F28F1/02—Tubular elements of cross-section which is non-circular
  • F28F1/04—Tubular elements of cross-section which is non-circular polygonal, e.g. rectangular
  • F28F1/045—Tubular elements of cross-section which is non-circular polygonal, e.g. rectangular with assemblies of stacked elements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
  • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
  • F02M26/22—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with coolers in the recirculation passage
  • F02M26/29—Constructional details of the coolers, e.g. pipes, plates, ribs, insulation or materials
  • F02M26/32—Liquid-cooled heat exchangers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
  • F02M26/50—Arrangements or methods for preventing or reducing deposits, corrosion or wear caused by impurities
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
  • F28D9/0031—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other
  • F28D9/0043—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other the plates having openings therein for circulation of at least one heat-exchange medium from one conduit to another
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
  • F28D9/0031—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other
  • F28D9/0043—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other the plates having openings therein for circulation of at least one heat-exchange medium from one conduit to another
  • F28D9/0056—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by paired plates touching each other the plates having openings therein for circulation of at least one heat-exchange medium from one conduit to another with U-flow or serpentine-flow inside conduits; with centrally arranged openings on the plates
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
  • F28D21/0001—Recuperative heat exchangers
  • F28D21/0003—Recuperative heat exchangers the heat being recuperated from exhaust gases
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2250/00—Arrangements for modifying the flow of the heat exchange media, e.g. flow guiding means; Particular flow patterns
  • F28F2250/10—Particular pattern of flow of the heat exchange media
  • F28F2250/102—Particular pattern of flow of the heat exchange media with change of flow direction

Definitions

• the invention relates to a heat exchanger for recirculated exhaust gases from an internal combustion engine, in particular from a motor vehicle.
• the heat exchangers used for this purpose generally consist of an elongated cylindrical casing of small cross section, an inlet manifold box and an outlet manifold box.
• the manifolds are connected to longitudinal tubes internal to the casing in which the exhaust gases circulate.
• the coolant which is generally formed from a mixture of glycol and water from the engine cooling circuit, flows against the current in the crankcase around the tubes.
• Inlet and outlet pipes are connected to each end of the housing for the inlet and outlet of the coolant.
• heat exchangers comprising a multiplicity of pairs of plates of cooling arranged parallel to each other inside a housing in the form of a rectangular parallelepiped.
• the space between the plates of a pair of plates forms a tube or channel in which the exhaust gases circulate, while the coolant circulates between the pairs of plates.
• exchangers are not suitable for certain modes of operation of the engines, in particular during cold starts when the temperature of the coolant is between 0 ° and 60 ° C and / or when a low temperature cooling loop is used. to cool the heat exchanger.
• One of the aims of the invention is to improve the efficiency of a heat exchanger for recirculated exhaust gases in which the fouling of the gas passages is minimized, in particular in the context of operation. at low coolant temperature.
• This object is achieved, in accordance with the invention, by causing the gases to travel a shorter distance and by increasing the gas passage sections in the heat exchanger.
• the invention relates to a heat exchanger for recirculated exhaust gases from an internal combustion engine, in which the exhaust gases circulate inside a bundle cooled by a coolant.
• blind is to be taken here in the broad sense as designating a set of passages, such as, for example, tubes, pairs of plates, channels, etc. They may in particular be parallel channels of substantially identical lengths.
• the effective length EF of the beam is determined as a function of the performance required and of the cross section S of passage of the gases in the beam so that the ratio EF / S between the effective length EF of the beam and the cross section S of gas passage in the beam is between a maximum value EF / S max and a minimum value EF / S min for which fouling of the beam, for example gas passage channels, is minimal.
• the effective length EF of the beam is between a maximum value EFmax for which a risk of condensation of the gases and therefore of fouling can take place and a minimum value EFmin leading to too large an effective section, at speeds of gas too weak and degraded performance.
• the beam is formed of channels and the ratios EF / S max and EF / S min are determined as a function of the length of the channels according to a law which varies linearly as a function of the effective length EF of the beam channels.
• the cross section of the gas passage beam can be arbitrary, in particular rectangular, square or circular.
• 1 exchanger comprises on the one hand, a first passage formed of a multiplicity of pairs of plates each formed of two parallel plates between which circulates a cooling fluid, the pairs of plates being stacked one above the others and on the other hand, a second passage formed by the beam and through which the exhaust gases circulate, the second passage being formed by rows of parallel channels, each row being sandwiched between the pairs of first pass plates.
• Each pair of plates is advantageously in the form of a rectangular parallelepiped and consists of a bottom plate with raised edge and a plate forming a cover above the bottom plate.
• the coolant circulates between these two plates between an inlet orifice and an outlet orifice connected respectively to an inlet manifold and to an outlet manifold through corresponding orifices located opposite each other. plates.
• the path advantageously follows a broken line in the form of a lace or zigzag.
• the path followed by the coolant in each of the pairs of plates is in the form of a zigzag with a U-shaped circulation.
• the parallel branches of the U forming the two half-paths are oriented in a direction which is perpendicular to the longitudinal direction of the channels of the second passage, making a counter-current circulation between the gases and the coolant.
• the path followed by the coolant in each pair of plates is advantageously delimited between the bottom plate and the cover by ribs and the raised edge of the bottom plate.
• the channels of the second passage can be formed by tubes with rectangular, triangular or circular section, but they can also be produced by means of successive folds of a single metal strip.
• the heat exchanger has minimum fouling for an effective length EF value between 4 and 12cm.
• the main advantage of the invention is that it makes it possible to significantly reduce the length of the gas passage beams, while reducing the formation of condensation products at low operating temperatures.
• Fouling tests on heat exchangers having the characteristics shown above show that even with cold water coolant around 30 ° C, these exchangers do not clog more than hot water exchangers, while the condensation temperature is reached for more 50% of the time and the gas temperature is below about 60 ° C for 35% of the time. This is due in particular to their short effective length EF.
• the condensation products of the exhaust gases circulate by mixing with the particles on a smaller part of the exchanger, which reduces the fouling of the exchanger at the outlet.
• FIGS. 1, 2 and 3 are respectively sectional, perspective and exploded views of a heat exchanger according to the invention
• FIG. 4 is a graph determining the ratio to be given between the effective length and the effective surface area of the heat exchanger to effectively reduce both the pressure drop of the gases and the risk of fouling due to condensation
• Figures 5 and 6 are graphs of comparison of thermal characteristics between a long type heat exchanger of the prior art and a short type exchanger according to the invention.
• FIG. 7 is a graph showing the influence of the effective length EF on the fouling rate of heat exchangers according to the invention.
• the heat exchanger which is shown in Figures 1, 2 and 3 comprises on the one hand, a first passage 1 comprising a multiplicity of pairs of parallel cooling plates li forming a bundle, juxtaposed one above the other and each composed of two parallel plates lai, Ibi and on the other hand, a second passage 2 formed of a bundle composed of rows of parallel channels 2j of substantially identical lengths, through which exhaust gases circulate.
• a heat engine in particular from a motor vehicle, and are intended to be recirculated (or recycled) by re-injecting them into the engine.
• first passage 1 circulates a cooling fluid, for example a mixture of water and glycol, between an inlet manifold 3 and an outlet manifold 4.
• a cooling fluid for example a mixture of water and glycol
• This is usually the fluid which is also used for cooling the engine. , but it can also be cooler fluid from a low temperature loop.
• Each of the rows of parallel channels 2j of the second passage is sandwiched between two pairs of successive cooling plates li and li + 1 of the first passage 1.
• the engine exhaust gases circulate inside the parallel channels 2j of the second passage 2 and are cooled by the coolant which circulates against that of the gases inside the pairs of parallel plates li of the first passage , as shown by the arrows in Figure 2.
• the channels 2j of the second passage 2 can be formed by tubes of rectangular, triangular or circular section, but they can also be produced in successive alternating folds of a single metal strip.
• each pair of li plates is in the form of a rectangular parallelepiped and consists of a base plate Ibi with raised edge 5 and a plate lai forming a cover covering the base plate. Between these two plates circulates the coolant between an inlet orifice 6 and an outlet orifice 7 connected respectively to the inlet manifold 3 and to the outlet manifold 4 through corresponding orifices located opposite the other plates.
• the path followed by the coolant is in the form of a zigzag and is composed of two U-shaped half-paths.
• the two half-paths are delimited by an axial rib 8 directed along l 'longitudinal axis XX' of the bottom plate Ibi and by two longitudinal ribs 9, 10 parallel to the axial rib 8 and located on either side thereof.
• the ribs 8 and 9 delimit with the raised edge 5 of the bottom plate Ibi the two parallel branches of the first U and the ribs 8 and 10 delimit with the raised edge 5 of the bottom plate Ibi the two parallel branches of the second U.
• the U are joined head to tail to each other by two adjacent branches having the axial rib 8 in common.
• the parallel branches of the U forming the two half-paths are oriented in a direction which is perpendicular to the longitudinal direction of the channels of the second passage 2.
• the ends of the two adjacent branches having the axial rib 8 in common communicate with each other and the ends of the two remaining branches are respectively connected to the inlet 6 and outlet 7 ports of the coolant.
• the casing 11 is open on its two opposite faces which are opposite respectively with the inlet and the outlet of the gases of the second bundle 2.
• the effective length EF of the channels is determined as a function of the effective section S of passage of the gases in the beam so that for each length of channel, between a minimum value EFmin and a maximum value EFmax, the ratio EF / S between the effective length and the surface S is between a maximum value EF / S max and a minimum value EF / S min for which the fouling of the tubes is minimal.
• the effective length represents the total exchange length of the exchanger in the direction of passage of the gases. For a parallel tube exchanger, it represents approximately the length of a tube.
• the cross section is the total section of the exchanger which is crossed by the gases.
• a tube exchanger it represents the section of a tube multiplied by the number of tubes.
• Figures 1 to 3 which is that of a plate heat exchanger, it is calculated by the number of gas blades multiplied by the width OA of the bundle and the height of the gas blade.
• the ratios EF / S max and EF / S min are determined according to a law which varies linearly as a function of the effective length EF of the beam channels.
• Line A represents the variations of the max EF / S ratio and line B represents the variations of the min. These two lines pass approximately through the origin of the EF / S and EF axes.
• the hatched range, between these two lines and limited on the abscissa between the two values EFmax and EFmin, is that in which the ratio EF / S must be found to obtain optimal operation of the exchanger.
• the effective length EFmax the effective length is too large and runs a risk of increased condensation and at a difference in gas pressure between the outlet and the inlet of the exchanger too large.
• the lengths subject to condensation are respectively for the least severe point of 315mm for the long type exchanger and 56mm for the type exchanger short. It can therefore be seen that the length subjected to condensation is more than 5 times greater on a long type heat exchanger.
• the influence of the effective length EF on the fouling rate can be represented using a bundle of curves, each curve being representative of the evolution of a fouling rate corresponding to a ratio Constant EF / S. These curves all have a minimum of fouling when the effective length EF is between 4 and 12 cm, whatever the ratio EF / S.
• Figure 7 only two curves C and D are shown. They show the evolution of the fouling rate for two values kl and k2 of the EF / S ratio.
• the fouling rate is calculated according to the performance of the exchanger relative to that which it provides when it is not fouled according to the relationship:
• the invention is not limited to the embodiment described above, it also applies to the production of exchangers having gas passage sections of any shape and in particular circular as is generally the case for exchangers comprising a cylindrical casing.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Geometry (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Exhaust-Gas Circulating Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2004
  • 2004-05-18 FR FR0405420A patent/FR2870590B1/fr not_active Expired - Lifetime
• 2005
  • 2005-05-17 WO PCT/FR2005/001223 patent/WO2005124254A1/fr not_active Application Discontinuation
  • 2005-05-17 EP EP05771201A patent/EP1747417A1/de not_active Withdrawn

Non-Patent Citations (1)

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