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
  • F28F13/06—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media
  • F28F13/12—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by affecting the pattern of flow of the heat-exchange media by creating turbulence, e.g. by stirring, by increasing the force of circulation
• • 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
  • F28D7/02—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 helically coiled
  • F28D7/024—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 helically coiled the conduits of only one medium being helically coiled tubes, the coils having a cylindrical configuration
• • 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

Definitions

• Heat exchanger device and method of transferring heat are provided.
• the present invention refers to heat exchangers and in particular to heat exchangers in low temperature systems where heat is to be transferred from a fluid in a circulatory system to a fluid in another system.
• An example of use of such systems is between a solar collector circuit and an accumulator tank.
• a problem in connection with fluid operated solar collector systems is in a simple and non-expensive way to be able to separate the circulatory system of the solar collector from a fluid operated energy storage system without any considerable part of the supplied energy being lost.
• This problem is solved by a heat exchanger according to the invention being provided between the systems.
• the heat exchanger structure according to the invention is particularly intended to optimize the heat transfer for use in which
• the fluid is pumped on the primary side, i.e. that a relatively large pressure drop is accepted and is utilized for a good heat transfer
• the fluid on the secondary side flows through the heat exchanger by means of self-circulation, i. e. that the struc ⁇ ture is optimized in order to obtain a large heat transfer coefficient at the outside despite an extremely low pressure drop,
• FIG. 1 diagrammatically illustrates an energy storage tank with two alternative locations of a heat exchanger according to the invention
• FIG. 2 diagrammatically illustrates production of a capillary tube intended to be included in a heat- exchanger according to the invention
• Figures 3 and 4 diagrammatically illustrate the structural design of the heat exchanger.
• FIG. 1 shows a typical mode of application for the heat exchanger according to the invention in the solar heating technique.
• the contents of an accumulator tank 1 is heated by heat exchange from the solar collector fluid.
• the heat exchanger should either be in the tank (2a) built in or connected for self-circulation outside the tank
• the heat exchanger performs a temperature raise of the cold water at the bottom of the tank from for example 30 °C up to 60 to 70 °C at through flow. This is performed at a loga ⁇ rithmic temperature difference between primary and secondary side of only about 5 degrees.
• Such a heat exchanger promotes the stratification of the tank, enables low values of flows in the solar collector circuit and totally leads to a system with higher performance. This can be accomplished by lower material consumption in the form of thinner tubes in the solar circuit and much less material in the heat exchanger which makes the system much more cost-effective.
• the heat exchanger is constructed from capillary tubes connected in parallel.
• a substantially laminar flow in the tubes is obtained, whereby the the heat transfer between the fluid that is pumped through the tubes and the surrounding fluid is considerably improved with respect to tubes of thicker dimensions.
• the heat exchanger will be particularly well dimensioned at an inner diameter of 1 - 2 mm, preferably 1.5 mm and a wall thickness less than 0.5 mm, preferably about 0.25 mm.
• the length of each tube should be one metre or more and the number of tubes depends on the power that is to be transmitted.
• the sizes are based on tubes of copper and pumping of water with antifreeze in the primary circuit.
• the capillary tubes can be arranged in various ways in order to obtain a good heat exchange, whereby in itself prior known arrangements may be used.
• the capillary tubes 8 on the outside are provided with a sparsely wound on wire 9, see figure 2.
• the wire 9, which preferably is constituted by a smooth wire of copper, in the completed heat exchanger serves the function that it partly creates a defined distance between concentric helices of capillary tubes provided with the wire, and partly enhances the heat transfer on the outside by using flange effect and eddy forming of the wire.
• the capillary tubes 8 can also be wound by a wire of other metal or by a wire consisting of several entwined thinner wires. Normally the wound on wire has only to be fixed to the capillary tube at the ends thereof but it is also possible to fix the wire at evenly spaced intervals or along the entire length thereof. Suitable means for this may be soldering, bonding, immersing in liquid tin or the like. As the heat exchanger is constructed from helically wound capillary tubes all or only a part of the capillary tubes can be wound with wire. It is also possible to use capillary tubes without a wound on wire for a heat exchanger according to the invention, whereby other means may be arranged to keep appropriate distance between the tube helices.
• a number of capillary tubes are first cut to mainly equal length. All capillary tubes will be connected in parallel and they have to be approximately of equal length in order to obtain the same pressure drop and by this, the same temperature drop at flowing through at the inside.
• the capillary tubes then are formed to helices with various diameters in such a way that the pitch angle for each helix is alike. Thereby is achieved that the various helices obtain mainly the same length.
• a different number of capillaries is provided in respective helix in such a way that the number capillaries is generally proportional to the diameter.
• the helix 12 with the smallest diameter contains two capillary tubes 12a and 12b wound in helix with the diameter 20 mm whereby the number of turns per tube becomes about 40 and the length of the helix about 400 mm.
• the next helix 13 with the diameter 30 mm contains three capillary tubes (13a-13c) forming about 27 turns each in order to attain the same length.
• the third turn 14 with 40 mm diameter contains four capillary tubes
• the surrounding tube 10 extends longer than the very heat exchanger part 2 with the capillary tubes to improve the self circulation.
• the tube 10 shall also be able to accommodate couplings (not shown) between the capillary tubes and the external solar collector circuit, which can be realized in an arbitrary way which allows mainly uniform tube lengths and minor obstruction in the self circulatory circuit.
• Coupling to the ends of the capillary tubes can preferably be performed by following method: All tubes are brought together into a cover, after which the cover is filled with solder. Thereafter the cover is cut off so that all tube openings appear in the section surface, which then simply can be coupled to inflow and drain respectively. This procedure has proved to be a cost-effective method to join the tubes, without which a heat exchanger with many capillary tubes according to the invention could not have been produced without problems.
• each cutaway tube end should obtain an elongated curved elliptical shape along the helix.
• the heat exchanger 2 In order to allow self circulation in the secondary circuit the heat exchanger 2 needs also to be dimensioned such, that the secondary fluid flow is not obstructed too much by the package of helically wound capillary tubes. This is achieved thereby that the fluid volume surrounding the capillary tubes in the heat exchanger part 2 relates to the fluid volume inside the capillary tubes as at least 2:1 and preferably more than 5:1. There is of course also an upper limit above which the heat transfer is deteriorated.
• the flow direction of the fluid in the self circulatory circuit is in the main perpendicular to the capillary tubes, whereby the specific heat transfer capability is enhanced.
• a combination of heat transfer from a tube in undisturbed fluid and superponated active flow is utilized and is determined by the density difference between cold and hot water at inlet and outlet respectively secondary side of the heat exchanger as well as the total height of the tube 10.
• the pressure drop on the self-circulatory side can be within the interval 30 - 100 Pa.
• the internal pressure loss by pumping should be at least about 100 times larger, preferably about 1000 times larger or more, and can be within the interval of about 10 - 100 kPa.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Heat-Pump Type And Storage Water Heaters (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20388645

Family Applications (1)

Country Status (6)

Cited By (1)

Citations (10)

• 1993
  • 1993-01-23 SE SE9300209A patent/SE9300209L/sv not_active Application Discontinuation
• 1994
  • 1994-01-24 EP EP94905894A patent/EP0680594B1/en not_active Expired - Lifetime
  • 1994-01-24 WO PCT/SE1994/000048 patent/WO1994017355A1/en active IP Right Grant
  • 1994-01-24 DE DE69426016T patent/DE69426016T2/de not_active Expired - Fee Related
  • 1994-01-24 AU AU59819/94A patent/AU5981994A/en not_active Abandoned
  • 1994-01-24 AT AT94905894T patent/ATE196686T1/de not_active IP Right Cessation

Patent Citations (10)

Non-Patent Citations (1)

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