US20110139417A1 - Method for making brazed aluminum heat exchanger and apparatus - Google Patents

Method for making brazed aluminum heat exchanger and apparatus Download PDF

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Publication number
US20110139417A1
US20110139417A1 US12/639,980 US63998009A US2011139417A1 US 20110139417 A1 US20110139417 A1 US 20110139417A1 US 63998009 A US63998009 A US 63998009A US 2011139417 A1 US2011139417 A1 US 2011139417A1
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boiling
metal
cooling
heat exchanger
layer
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US12/639,980
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Thomas J. Godry
Patrick S. O'Neill
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Honeywell UOP LLC
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UOP LLC
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Assigned to UOP LLC reassignment UOP LLC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: O'NEILL, PATRICK S, GODRY, THOMAS J
Priority to FR1060106A priority patent/FR2953919A1/fr
Publication of US20110139417A1 publication Critical patent/US20110139417A1/en
Abandoned legal-status Critical Current

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    • 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
    • F28D9/0062—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 spaced plates with inserted elements
    • F28D9/0068—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 spaced plates with inserted elements with means for changing flow direction of one heat exchange medium, e.g. using deflecting zones
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04412—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F25J5/002—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F25J5/002—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger
    • F25J5/005—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger in a reboiler-condenser, e.g. within a column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/18—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
    • F28F13/185—Heat-exchange surfaces provided with microstructures or with porous coatings
    • F28F13/187—Heat-exchange surfaces provided with microstructures or with porous coatings especially adapted for evaporator surfaces or condenser surfaces, e.g. with nucleation sites
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
    • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
    • F28F21/081—Heat exchange elements made from metals or metal alloys
    • F28F21/084—Heat exchange elements made from metals or metal alloys from aluminium or aluminium alloys
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/40—Air or oxygen enriched air, i.e. generally less than 30mol% of O2
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/20—Particular dimensions; Small scale or microdevices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/42—Modularity, pre-fabrication of modules, assembling and erection, horizontal layout, i.e. plot plan, and vertical arrangement of parts of the cryogenic unit, e.g. of the cold box
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/44—Particular materials used, e.g. copper, steel or alloys thereof or surface treatments used, e.g. enhanced surface
    • 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
    • F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0033—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for cryogenic applications

Definitions

  • This invention relates to an improved method for making a metal heat exchanger with high heat transfer efficiency. Specifically, this invention relates to the use of High Flux-coated aluminum sheets in the fabrication of a brazed heat exchanger.
  • EBL enhanced boiling layers
  • a common heat exchanger used in cryogenic, refinery and chemical applications is the plate-fin brazed aluminum heat exchanger fabricated by disposing corrugated aluminum sheets between aluminum parting sheets or walls to form a plurality of fluid passages.
  • the sheets are either clad with an aluminum brazing layer or a layer of brazing foil is inserted between the surfaces to be bonded.
  • the brazing foil or cladding melts and forms a metallurgical bond with the adjacent sheets.
  • the resulting heat exchanger contains numerous passages consisting of alternate layers of closely spaced fins.
  • a typical arrangement has alternate layers of passages each containing fins with a density of 6 to 10 fins/cm (15 to 25 fins/inch), and a fin height of 0.5 to 1 cm (0.2 to 0.4 inch).
  • a first series of alternating passages carry vapor for condensing, while a second series of alternating passages carry a liquid for boiling.
  • Typical brazed aluminum heat exchangers must be able to withstand 2068 to 2758 kPa (300 to 400 psia).
  • brazed aluminum heat exchangers In US 2004/0251008, the development of brazed aluminum heat exchangers was described. However, since that time the inventors herein have discovered that these prior art brazed aluminum heat exchangers suffer from poor mechanical properties following the initial brazing process. Previous to the present invention, it has been found necessary to provide extensive mechanical support in the open passages of the brazed aluminum heat exchangers in order to prevent excessive sagging or creep of the EBL-coated sheets during the brazing process employed to join the components of the heat exchanger together.
  • An enhanced boiling layer (EBL) is provided on the walls of the boiling passages.
  • the melting temperature of the brazing material is lower than the melting temperature of the metal particles in the enhanced boiling layer.
  • the metal in the enhanced boiling layer and/or the brazing layer is an alloy of a first metal and a second metal which alloy has a lower melting temperature than that of the first metal.
  • Different second metals can be used in the EBL and in the brazing material so long as the second metal provides an alloy with a lower melting temperature.
  • the concentration of the second metal in the brazing material is greater than in the EBL.
  • the condensing passages contain fins to facilitate heat transfer.
  • brazable aluminum alloys lose most of their strength properties (tensile, hardness, etc) when heated above 1000° F.; however, permanent deflection (sag) tests conducted on 25 mm ⁇ 152 mm ( 1 ′′ ⁇ 6′′) coated strips of 0370/0373 alloys of H18 temper that had been heated to 1085° F. showed that the center line deflections were only about 60% of the value of comparable deflections on coated samples of Aluminum Alloy 3003-H14 material after furnacing. Partial retention of hardness at brazing temperature would mean that less passage support would be required in the subsequent brazing of heat exchangers using these alloys.
  • the 037x alloys would be expected to age harden with time, but we discovered that age hardening, and reformation of the Mg2-Si phase did not compromise the future coating strength, porosity, or adhesion of the EBL particles to themselves or to the base metal.
  • FIG. 1 is a perspective view of three heat exchangers.
  • FIG. 2 is a perspective view of the core of a heat exchanger in FIG. 1 with layers broken away to reveal internals.
  • FIG. 3 is a perspective view of the core of the heat exchanger in FIG. 1 but taken from a different perspective than FIG. 2 .
  • Our methods can be used to construct any configuration of heat exchanger by brazing including shell and tube but may be most appropriately applied to plate exchangers.
  • the boiling and cooling passages of the heat exchangers may be oriented to provide cross flow, counter-current flow or cocurrent flow.
  • the heat exchanger may be applied in the context of cryogenic air separation, hydrocarbon processing or any other process that relies on boiling to effect heat exchange.
  • Several types of metals can be used for construction of heat exchangers.
  • Aluminum is the most widely used metal for brazed heat exchangers. Aluminum is suitable for cryogenic applications because it resists embrittlement at lower temperatures. Steel or copper may be used for heating or cooling fluids that may be corrosive to aluminum.
  • our structures will be described with respect to a counter current, aluminum, plate heat exchanger useful in the context of cryogenic air separation.
  • FIG. 1 shows a train of typical plate heat exchangers 10 used in cryogenic air separation.
  • the heat exchangers 10 have alternating boiling passages 12 and cooling passages 14 provided in a core 20 .
  • a liquid such as liquid oxygen is delivered by conduits 16 to manifolds 18 and distributed to the boiling passages 12 . Delivery of liquid to the boiling passages 12 by means other than the conduits 16 or the manifolds 18 underneath the core 20 is contemplated such as by thermosiphoning at the bottom of the boiling passages 12 .
  • liquid may be delivered to the boiling passages 12 from the side or from the top of the core 20 , perhaps through a distribution network that may comprise distributor fins.
  • Gaseous oxygen from the boiling passages 12 are collected such as by headers 22 and removed through a conduit 24 . Collection of gases from the boiling passages 12 by means other than the conduits 24 or the headers 22 above the core 20 is contemplated such as may be provided in a thermosiphoning arrangement. Moreover, gases may be collected from the boiling passages 12 from the side or from the top of the core 20 , perhaps through a collection network that may comprise collection fins.
  • a fluid such as gaseous nitrogen is delivered by conduits 26 to manifolds 28 and distributed to the cooling passages 14 . Delivery by means other than by the conduits 26 or the manifolds 28 is also contemplated.
  • a liquid or gas can be cooled in the cooling passages 14 .
  • a gas if a gas is delivered to the cooling passages 14 , it may be cooled to such extent to effect a phase change with or without temperature change depending on the needs of the process.
  • Heat conducted across the walls between the cooling passages 14 and the boiling passages 12 to support the boiling in the boiling passages 12 cools the fluid in the cooling passages 14 , thereby condensing the nitrogen gas in the case of air separation.
  • Fluid such as liquefied nitrogen from the cooling passages 14 is collected such as by headers 30 and removed through conduits 32 . Collection of cooled fluid from the cooling passages 14 by means other than the headers 30 and the conduits 32 is contemplated.
  • the delivery and collection manifolds and conduits shown in the embodiment in FIG. 1 may be modified and remain within the scope of our disclosure.
  • FIG. 2 shows the core 20 of one of the heat exchangers 10 with parts broken away to reveal internals.
  • a cap sheet 40 is disposed on both ends of the core 20 to define the last channel on each end. Part of the cap sheet 40 illustrated in FIG. 2 is broken away to reveal the boiling passage 12 .
  • Vertical spacer bars or spacer members 42 are disposed between opposing edges of the cap sheet 40 and a metal wall 44 with a boiling side 44 a covered with an enhanced boiling layer (EBL) 46 .
  • the EBL 46 comprises thermoconductive particles bonded to the boiling side 44 a and to each other to form a texture of pores in which nucleate boiling sites are provided.
  • the thermoconductive particles are metal particles in an embodiment.
  • the boiling passage 12 is defined by an inner surface of the cap sheet 40 , inner edges of the vertical spacer bars 42 and the boiling side of the metal wall 44 .
  • Outer vertical margins 48 of the boiling side 44 a are devoid of the EBL 46 to provide a bonding surface. Vapor leaves the boiling passages 12 through boiling outlets 49 , which may be collected by the boiling headers 22 , shown in the embodiment of FIG. 1 .
  • the boiling passages 12 may contain fins to further facilitate heat transfer. Behind the broken away metal wall 44 and the vertical spacer bars 42 is the cooling passage 14 including primary fins 52 comprising a corrugated sheet of a primary fin stock 54 .
  • the primary fins 52 extend laterally between inner edges of the vertical spacer bars 42 at opposite ends of the cooling passage 14 .
  • Distributor fins 56 comprising a distributor fin stock 58 or being integral with the primary fin stock 54 are disposed in an inclined configuration to evenly distribute cooling fluid from cooling inlets 50 along the tops of the channels provided by the primary fins 52 .
  • cooling fluid is received into cooling inlets 50 which may come from the cooling manifold 28 as shown in the embodiment of FIG. 1 .
  • Another type of distribution configuration with or without fins may be used to distribute cooling fluid.
  • the cooling inlets 50 may be considered the tops of the channels provided by the primary fins 52 .
  • Cooling outlets 64 which may be defined by collection fins 66 allow cooled fluid to exit the core 20 .
  • cooling fluid exits through cooling outlets 64 which may enter into the cooling header 30 in the embodiment of FIG. 1 .
  • Horizontal spacer bars 60 seal the top and the bottom of the cooling passages 14 .
  • the spacer bars 42 , 60 and the fins 52 , 56 , 66 space a cooling side 44 b (the opposite side) of the metal wall 44 from the cooling side 44 b of the adjacent metal wall 44 .
  • no horizontal spacer bars 60 are provided in the boiling passages 12 to permit entry and exit of fluid to and from the boiling passages 12 , respectively.
  • the vertical spacer bars 42 are sandwiched between opposite ends of each pair of the adjacent metal walls 44 , while the horizontal spacer bars 60 are sandwiched only between the adjacent cooling sides 44 b .
  • the fins 52 , 56 , 66 are arranged and bonded appropriately to withstand operating pressure, it is contemplated that spacer bars 42 , 60 can be omitted between the cooling sides 44 b in the cooling passage 14 .
  • the fins 52 , 56 , 66 would provide the spacing function.
  • the walls 44 have an alternating orientation.
  • the cooling side 44 b of the metal wall 44 is always facing the cooling side 44 b of an adjacent wall, and the boiling side 44 a of a wall is always facing the boiling side 44 a of the adjacent metal wall 44 . It is also contemplated in embodiments that the cooling passages 14 include no fins and that the boiling passages 12 be equipped with fins.
  • FIG. 3 shows the core 20 of FIG. 2 but from a perspective that shows the bottom of the core 20 . All elements in FIG. 2 that are visible in FIG. 3 are referenced with numerals. Additionally, boiling inlets 51 to the boiling passages 12 are shown. In an embodiment, the boiling inlets 51 may receive boiling liquid from boiling manifolds 18 ( FIG. 1 ). Moreover, the bottom of the cap sheet 40 and the first metal wall 44 are broken away to reveal collection fins 66 from a third fin stock 68 . The collection fins 66 comprising the third fin stock 68 or being integral with the primary fin stock 54 are disposed in an inclined configuration to evenly collect cooling fluid from cooling outlets 64 along the bottoms of the channels provided by the primary fins 52 .
  • cooling outlets 64 may be considered the bottoms of the channels provided by the primary fins 52 .
  • the cooling outlets 64 may be considered the bottoms of the channels provided by the primary fins 52 .
  • only one set of the collection fins 66 is shown in FIG. 3 .
  • the EBL is added to the boiling side by any of the methods known in the art, such as by applying a slurry, flame spraying, plasma spraying or by electrodeposition. However, it is critical that the subsequent brazing step not diminish the heat exchange efficiency of the EBL once applied.
  • the melting point of the EBL is higher than the melting point of the brazing metal.
  • the relative melting points of the brazing metal and EBL may be obtained by alloying a second metal with a first metal that has the effect of providing a melting point of the alloy that is lower than the melting point of the first metal.
  • the concentration of the second metal may be higher in the brazing metal than in the EBL material, so that the EBL has a higher melting point that can withstand the brazing step without loss of structural integrity.
  • brazed aluminum heat exchangers aluminum is the first metal and silicon, manganese, magnesium or alloys thereof may be the second metal.
  • nickel may be the first metal and phosphorous may be the second metal.
  • copper may be the first metal and phosphorous may be the second metal.
  • brazing occurs at about 100° C. (180° F.) below the melting temperature of copper or at about 960° C. (1760° F.).
  • brazing occurs at about 49° to 54° C. (120° to 130° F.) below its melting temperature of about 649° C. (1200° F.).
  • nickel is the first metal, the brazing step in the furnace will take place at a temperature of about 1037° C. (1900° F.) which is 38° C. (100° F.) below the melting temperature of steel. At these temperatures, the second metal lowers the melting point of the alloy with the first metal.
  • the liquefied brazing metal flows and diffuses into the base metal and forms a metallurgical bond.
  • the EBL once applied will be able to withstand the subsequent lower temperature brazing heat treatment.
  • sintering may be used to form the EBL instead of brazing.
  • the metal is heated to the point of molecular agitation and diffuses over a relatively long period of time into an adjacent metal to form metallurgical bonds.
  • Sintering may be used to provide the EBL with brazing at a lower temperature to bond the components of the heat exchanger together.
  • the first step of applying the EBL is applying a polymer binder to the boiling side of the metal wall.
  • a metal powder which may comprise the first metal and the second metal are then sprinkled onto the plastic binder.
  • the metal wall with metal powder bound by the plastic thereto is blanketed with an inert atmosphere such as nitrogen and the temperature is raised to a brazing temperature for sufficient time to effect metallurgical bonds between the metal powder particles to each other and to the boiling side of the metal wall.
  • the plastic binder decomposes under heat and evaporates.
  • the circulating inert gas diminishes formation of an oxide film and also purges the decomposition gases from the binder material.
  • the bonded metal powder forms a highly porous, three-dimensional matrix that provides the EBL with nucleate boiling sites.
  • Appropriate plastic binders include polyisobutylene, polymethylcellulose having a viscosity of at least 4000 cps and sold commercially as METHOCEL and polystyrene having a molecular weight of 90,000.
  • the binder may be dissolved in an appropriate solvent such as kerosene or carbon tetrachloride for polyisobutylene and polymethylcellulose binders and xylene or toluene for polystyrene binder.
  • the boiling side should be cleaned to be free of grease, oil or oxide to obtain proper bonding of the EBL thereto. Before applying the plastic solution, the boiling side may be flushed with the plastic solution to facilitate wetting, thereby obtaining a more even distribution of plastic binder.
  • the plastic solution may be applied to the boiling side in a way that will achieve a uniform layer such as by spraying, dipping, brushing or paint rolling. After application, the layer is air dried either during or after the application of the metal powder to evaporate away most of the solvent. A solid, self-supporting layer of metal powder and binder is left in place on the metal wall by the binder.
  • the metal powder comprising the first and second metal are mixed with a flux.
  • the flux melts and draws oxides from the metal which could inhibit the bonding of the metal particles to each other and to the boiling side.
  • the flux may be a mineral salt such as commercially available potassium aluminum fluoride, which is a mixture of KAlF 4 and KAlF 6 . Other fluxes may be suitable.
  • the core 20 of the heat exchanger 10 is assembled by stacking layers of components. If the brazing of the core 20 will not be performed in a vacuum furnace, each component should be coated with flux before stacking
  • a suitable way to coat components with flux components is to mix the flux with denatured alcohol in 1:1 volumetric ratio and brush or spray the flux solution onto the component before stacking. The order of stacking will be described with the side shown in FIGS. 2 and 3 on the bottom.
  • the cap sheet 40 is placed on the bottom of a stacking surface with the outer surface of the cap sheet 40 down.
  • a layer of brazing foil is layered at least on the two vertical margins 48 of an inner surface of the cap sheet 40 or perhaps over the whole inner surface of the cap sheet 40 .
  • the vertical spacer bars 42 are stacked on the vertical margins 48 of the inner surface of the cap sheet 40 .
  • the brazing foil may be provided only at the vertical margins 48 of the cap sheet 40 because only the vertical spacer bars 42 will be brazed to the inner surface of the cap sheet 40 that is defining the boiling passage 12 in this case.
  • no horizontal spacer bars 60 are stacked in the boiling passage 12 .
  • the horizontal spacer bars 60 should be stacked on and brazed to the cap sheet 40 .
  • a layer of brazing foil is stacked on top of the vertical spacer bars 42 . Strips of the brazing foil may be placed just over the vertical spacer bars 42 .
  • the metal wall 44 with the EBL 46 on the boiling side 44 a facing downwardly toward the cap sheet 40 and the cooling side 44 b facing upwardly is stacked on top of the vertical spacer bars 42 .
  • the vertical margins 48 of the boiling side 44 a which are devoid of the EBL 46 will rest on the brazing foil on top of the vertical spacer bars 42 .
  • a layer of brazing foil is laid on top of the cooling side 44 b of the metal wall 44 .
  • the primary fin stock 54 comprising the primary fins 52 , the distributor fin stock 58 comprising the distributor fins 56 , the collection fin stock 68 comprising the collection fins 66 and the horizontal spacer bars 60 and the vertical spacer bars 42 are all stacked on top of the layer of brazing foil laid on top of the cooling side 44 b of the metal wall 44 .
  • a layer of brazing foil is laid upon the primary fin stock 54 , the distributor fin stock 58 , the collection fin stock 68 comprising the collection fins 66 and the spacer bars 42 , 60 .
  • another metal wall 44 with the cooling side 44 b facing downwardly and the boiling side 44 a facing upwardly is laid upon the layer of brazing foil.
  • strips of brazing foil are laid down just in the vertical margins 48 of the boiling side 44 a outside of the EBL 46 .
  • the vertical spacer bars 42 are laid down on top of the strips of brazing foil in the vertical margins 48 .
  • Strips of brazing foil are laid on top of the vertical spacer bars 42 .
  • An additional metal wall 44 with the boiling side 44 a facing downwardly is stacked on top with the vertical margins 48 mating with the strips of brazing material on top of the vertical spacer bars 42 .
  • the rest of the core 20 of the heat exchanger 10 is stacked as previously described until the cap sheet 40 is stacked on the top of the stack.
  • both sides of the primary fin stock 54 , the spacer bars 42 , 60 and/or the cooling side 44 b of the metal wall 44 may be integrally clad with a layer of brazing material. This would obviate the need for adding layers of brazing foil in the stack constituting the core 20 . However, if just the fin stock 54 , 58 , 68 and/or the spacer bars 42 , 60 can be obtained with brazed material clad on both sides, the use of brazing foil may be obviated.
  • the core 20 After the core 20 is fully stacked it is inserted into a furnace with an atmosphere of inert gas and heated so that the center 20 of the core attains an elevated temperature. After remaining at the elevated temperature for a period of time, it is allowed to cool.
  • the elevated temperature is above the melting temperature of the brazing material and below the melting temperature of the EBL 46 material upon application and the melting temperature of the base metal. In an embodiment, the elevated temperature may be below the melting temperature of the EBL 46 material after application.
  • Aluminum Alloy 4047 may be used for the brazing material in which case the elevated brazing temperature would be approximately 607° to about 618° C. (1125° to 1145° F.).
  • Aluminum alloy designations given herein will be pursuant to the convention of alloys used by those of ordinary skill in the art of aluminum brazing.
  • the brazing material melts and forms a metallurgical bond with adjacent metal members to provide a robust metal heat exchanger core.
  • the EBL 46 maintains its highly porous structural integrity. Residues of flux on the surface of the core 20 may remain but will typically wash out without affecting operation.
  • the manifolds 18 , 28 and the headers 22 , 30 are welded to the core 20 as shown in the embodiment in FIG. 1 .
  • the conduits 16 , 24 , 26 , 32 are all affixed to the appropriate manifold 18 , 28 or the header 22 , 30 .
  • Other delivery, distribution, collection and recovery equipment than shown in the embodiment of FIG. 1 may be used.
  • one or both of the brazing steps may take place in a vacuum oven. Flux becomes unnecessary and a lower temperature is typically used for brazing. However, in the vacuum brazing process, it takes longer for the core to reach the brazing temperature, after which, cooling is allowed. If the stacked core is brazed in a vacuum environment, Aluminum Alloy 4104 may be used for brazing material in which case the elevated brazing temperature would be approximately 582° to about 593° C. (1080° to 1100° F.).
  • the sheets be made from a harder tempered alloy of aluminum, such as Aloca's 037x family of high strength aluminum alloys or other alloys that have significantly greater tensile and yield strength than the Aluminum Alloy 3003-H14 alloy used in the prior art.
  • the alloy that is used needs to provide superior post-brazed mechanical properties and in some cases may also provide age-hardenable properties.
  • the use of these alloys provide improved creep resistance when subjected to a second brazing cycle.
  • these alloys have been selected to successfully allow adhering of a High Flux coating to these sheets during the initial brazing process. These sheets will have improved flatness retention during handling and assembly as well as reduced tendency to sag or creep during the brazing together of the components.
  • Some of the alloys that were found useful contain about 0.15% to about 0.35% titanium.
  • brazing material whether it be powder, foil or cladding may comprise a eutectic alloy of at least about 80 wt-% aluminum and about 10 to about 15 wt-% silicon.
  • the eutectic alloy comprises about 11 to about 13 wt-% silicon and at least about 85 wt-% aluminum.
  • the brazing eutectic alloy may be Aluminum Alloy 4047 and comprise about 12 wt-% silicon and about 88 wt-% aluminum.
  • Aluminum Alloy 3003 which comprises a highly proportioned aluminum alloy of as low as about 98 wt-% aluminum and as high as about 2 wt-% manganese. Small amounts of magnesium and iron may also be present in Aluminum Alloy 3003.
  • highly proportioned means greater than 90 wt-%.
  • Other components comprising substantially pure aluminum or highly proportioned aluminum alloys may be suitable. In vacuum brazing applications, about 1 to 2 wt-% of magnesium may be provided in the highly proportioned aluminum alloy.
  • the material comprising the EBL may comprise about 0.5 to about 1.5 wt-% silicon and at least about 95 wt-% substantially pure aluminum or highly proportioned aluminum alloy.
  • the EBL may comprise about 5 to about 11 wt-% brazing material and at least about 85 wt-% substantially pure aluminum or highly proportioned aluminum alloy.
  • the EBL comprises at least about 90 wt-% pure or highly proportioned aluminum and a eutectic alloy including about 11 to about 13 wt-% silicon and at least about 85 wt-% aluminum.
  • the eutectic alloy in powder form is mixed with powdered substantially pure or highly proportioned aluminum.
  • a flux comprising about 5 to about 10 wt-% of a powdered mineral salt should be included in the EBL material upon application.
  • the brazing eutectic alloy powder melts and wets the solid, unmelted substantially aluminum powder, thereby forming an alloy.
  • the resulting alloy in the EBL melts at a higher temperature than the brazing eutectic alloy by virtue of the lower concentration of the silicon metal in the aluminum alloy.
  • the EBL is then able to withstand brazing temperatures associated with bonding the stacked heat exchanger core that are perilously close to the temperature at which the EBL material was initially brazed without loss of performance.
  • pure Aluminum Alloy 3003 powder may be sintered at about 1185° F. (641° C.).
  • Brazing foil comprising the eutectic of silicon and aluminum mentioned above may be used to bond the core together at a brazing temperature of about 604° to 613° C. (1120° to 1135° F.) under a controlled inert atmosphere and a brazing temperature of about 566° to 596° C. (1050° to 1105° F.) in a vacuum environment.
  • a family of proprietary Al alloys (the 037x family) was tested for potential use in the application herein.
  • the increasing amount of Mg results in the increasing degree of post-braze age-hardening that occurs with these alloys, such that the yield strength and tensile strength increase over time at room temperature or at an accelerated rate at an elevated temperature.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Pressure Welding/Diffusion-Bonding (AREA)
  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
US12/639,980 2009-12-16 2009-12-16 Method for making brazed aluminum heat exchanger and apparatus Abandoned US20110139417A1 (en)

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FR1060106A FR2953919A1 (fr) 2009-12-16 2010-12-06 Echangeur de chaleur en aluminium brase

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FR2995671A1 (fr) * 2012-09-19 2014-03-21 Air Liquide Ensemble d'echangeurs de chaleur et unite de separation comprenant un tel ensemble d'echangeurs de chaleur
US8991480B2 (en) 2010-12-15 2015-03-31 Uop Llc Fabrication method for making brazed heat exchanger with enhanced parting sheets
JP2015522782A (ja) * 2012-04-23 2015-08-06 ルマス テクノロジー インコーポレイテッド コア交換用のコールドボックス設計

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Publication number Priority date Publication date Assignee Title
US8991480B2 (en) 2010-12-15 2015-03-31 Uop Llc Fabrication method for making brazed heat exchanger with enhanced parting sheets
JP2015522782A (ja) * 2012-04-23 2015-08-06 ルマス テクノロジー インコーポレイテッド コア交換用のコールドボックス設計
FR2995671A1 (fr) * 2012-09-19 2014-03-21 Air Liquide Ensemble d'echangeurs de chaleur et unite de separation comprenant un tel ensemble d'echangeurs de chaleur
WO2014044979A3 (fr) * 2012-09-19 2016-01-07 L'air Liquide,Société Anonyme Pour L'Étude Et L'exploitation Des Procédés Georges Claude Ensemble d'échangeurs de chaleur
JP2016506487A (ja) * 2012-09-19 2016-03-03 レール・リキード−ソシエテ・アノニム・プール・レテュード・エ・レクスプロワタシオン・デ・プロセデ・ジョルジュ・クロード 熱交換器アセンブリ
US10330391B2 (en) 2012-09-19 2019-06-25 L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Heat exchanger assembly

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