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
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
  • F28F13/02—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by influencing fluid boundary
• • 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
  • F28D21/0005—Recuperative heat exchangers the heat being recuperated from exhaust gases for domestic or space-heating systems
  • F28D21/0007—Water heaters
• • 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
  • F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
  • F28D7/16—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation
  • F28D7/1684—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation the conduits having a non-circular cross-section
• • 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

Definitions

• the invention relates to a heat exchanger comprising at least one first duct for a first medium and at least one second duct for a second medium in heat-exchanging contact therewith via at least one wall.
• a heat exchanger is generally known.
• the invention has for its object to provide a heat exchanger with an increased efficiency.
• Such an improved heat exchanger can take a more compact form compared to : known heat exchangers and still have the same heat transfer capacity.
• this is achieved in a heat exchanger as described above in that the dimensions of at least the first duct in the flow direction of the first medium and perpendicularly thereof are chosen such that boundary layers formed along the walls of the duct and developing in the flow direction meet each other substantially at a downstream end of the duct.
• the dimensions of the first duct of the heat exchanger according to the invention preferably substantially satisfy the relation:
• V flow velocity of the first medium
• v kinematic viscosity of the first medium
• the heat exchanger is advantageously provided with a plurality of first ducts placed in series as seen in the flow direction, wherein means are in each case present between successive ducts for enhancing the heat transfer inside the first medium.
• the transfer-enhancing means can herein comprise a space with an enlarged cross-section compared to the first ducts.
• the length of the first ducts can be kept relatively short.
• the invention also relates to a heating system incorporating a heat exchanger of the above described type.
• Fig. 1 shows a partly broken-away perspective view of a heat exchanger according to the invention
• Fig. 2 is a schematic cross-sectional view of a duct showing the development of the boundary layers and the associated velocity curves, and
• Fig. 3 shows a diagram in which, for a number of different media, the optimum length of an exchanger duct is plotted as a function of the flow velocity.
• a heat exchanger 1 (fig. 1) according to the invention comprises a number of first ducts 2 for a first medium, for instance flue gas from a burner 7, and a number of second ducts 4 for a second medium which is in heat-exchanging contact with the first medium, for instance water intended for radiators of a heating system (not shown here) .
• Ducts 2 and 4 are physically separated from each other by walls 5 which are readily permeable to heat and are for instance manufactured from a metal.
• the first ducts 2 are connected on one side to a space 6 in which a burner 7 Is arranged, and on the other side to an outlet 8.
• Ducts 4 are included in a closed circuit of the heating system and connected to an inlet 9 and an outlet 10.
• first ducts 2 in the flow direction of the medium (arrow F) and perpendicularly thereof are chosen such that the boundary layers 11 formed along walls 5 of these ducts 2 just make mutual contact at the end of each duct 2.
• Optimum benefit is in this way gained from the transport of the medium transversely of its main flow direction during the creation and development of boundary layers 11.
• Means are herein preferably present at the end of each duct 2 for enhancing the heat transfer inside the medium, for instance in the form of a part 12 with enlarged cross-section. In the shown embodiment this part 12 forms a bend between two successive ducts 2 as seen in the flow direction. Owing to the enlarged cross- section of part 12 and the flow phenomena resulting therefrom, additional movement components are introduced into the flow which enhance the heat transfer.
• the boundary layers 11 (fig. 2) thus develop along walls 5 of each duct 2 from the inflow side, whereby the effective surface area of each duct 2 becomes increasingly smaller.
• the medium flowing therethrough is hereby urged toward the middle of duct 2, and this forced transport transversely of flow direction F causes a heat transport in the same direction, whereby the efficiency of heat exchanger 1 is greatly increased.
• the velocity curve in transverse direction of duct 2 herein changes from a completely uniform velocity over the whole surface into a parabolic velocity distribution with a low speed (practically zero) along walls 5 and a higher speed in the middle of duct 2.
• This Reynolds number is herein defined as:
• R x p * V * x / , wherein p and ⁇ represent the density and the dynamic viscosity of the medium, and V represents the flow velocity thereof.
• each boundary layer 11 along two opposite walls 5 of each duct 2 make mutual contact when the thickness ⁇ of each boundary layer 11 amounts to half the distance D between these walls 5.
• the Reynolds number For the distance x from the inflow side where this occurs there applies: or, by substituting the value of the Reynolds number, :
• This distance x therefore forms in principle the optimal length of duct 2 with an eye to the heat transfer inside one of the media themselves.
• the length of duct 2 must also be sufficient to enable the intended heat transfer between the two media flowing through the exchanger.
• the choice of the length of duct 2 will therefore often have to be slightly larger in practice than would follow from the above relation. This length may not however become so great as to result in the danger of transition of the flow from laminar to turbulent, since the flow losses in heat exchanger 1 would thereby increase greatly.
• the duct length wherein the boundary layers 11 just make mutual contact is shown (fig. 3) as a function of the undisturbed flow velocity of the medium for a number of different media.
• D hydr flow surface area divided by circumference
• fig. 3 The duct length wherein the boundary layers 11 just make mutual contact, expressed as multiple of the hydraulic cross-section D hydr (flow surface area divided by circumference) of duct 2, is shown (fig. 3) as a function of the undisturbed flow velocity of the medium for a number of different media.
• the progression of the relevant curves is found to depend on the nature of the medium, wherein the kinematic viscosity determines the gradient of the curves.
• gases such as flue gases and thermal oil
• a relatively short length of the ducts 2 is found to be ideal over a wide range of flow velocities.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Geometry (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Yarns And Mechanical Finishing Of Yarns Or Ropes (AREA)
• Central Heating Systems (AREA)
• Steam Or Hot-Water Central Heating Systems (AREA)
• Compression-Type Refrigeration Machines With Reversible Cycles (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=19772024

Family Applications (1)

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• 2000
  • 2000-09-05 NL NL1016104A patent/NL1016104C1/nl not_active IP Right Cessation
• 2001
  • 2001-09-05 WO PCT/NL2001/000658 patent/WO2002021063A2/en active IP Right Grant
  • 2001-09-05 DE DE60119348T patent/DE60119348T2/de not_active Expired - Lifetime
  • 2001-09-05 AU AU2001296088A patent/AU2001296088A1/en not_active Abandoned
  • 2001-09-05 EP EP01976933A patent/EP1317648B1/de not_active Expired - Lifetime
  • 2001-09-05 AT AT01976933T patent/ATE325324T1/de active

Non-Patent Citations (1)

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