Heat exchanger

[0001] 1. Field of the Invention

[0002] The present invention relates to a heat exchanger, and in particular to a heat exchanger for storing or releasing heat.

[0003] 2. Description of the Prior Art

[0004] A latent heat storage system as one of a heat storage system uses latent heat generated according to phase transition (for example water to/from ice) of thermal storage material, and it can be divided into a type for congealing or melting phase transition material used as thermal storage material around a heat exchanger tube and a type for storing and releasing heat generated by phase transition of thermal storage material contained in a sealed casing.

[0005] In any type, a distance between a heat transfer surface (tube wall surface or surface of the sealed casing) and a phase transition boundary surface is increased according to progress of phase transition, and heat transfer resistance due to the thermal storage material filled between the surfaces is increased.

[0006] Accordingly, according to progress of congelation or melting of the thermal storage material, a congelation speed or a melting speed is lowered, and therefore heat storage and release efficiencies are lowered.

[0007] In order to solve the above-mentioned problem, it is an object of the present invention to provide a heat exchanger that is capable of improving congelation or melting speed of thermal storage material and bettering heat storage and release efficiencies.

[0008] In order to achieve the above-mentioned object, a heat exchanger in accordance with the present invention includes a channel unit in which heat transfer medium flows; and a heat exchange unit contacted-combined with the channel unit and having porous heat transfer member so as to perform heat exchange with thermal storage material therein.

[0009] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[0010] In the drawings:

[0011] FIG. 1 is a sectional view illustrating a first embodiment of a heat exchanger in accordance with the present invention;

[0012] FIG. 2 is a sectional view illustrating a modified example of the heat exchanger in FIG. 1;

[0013] FIG. 3 is a sectional view illustrating another modified example of the heat exchanger in FIG. 1;

[0014] FIG. 4 is a sectional view illustrating a second embodiment of a heat exchanger in accordance with the present invention; and

[0015] FIG. 5 is a graph showing a performance of the heat exchanger in accordance with the present invention in comparison with that of the conventional heat exchanger.

[0016] Hereinafter, the preferred embodiments of a heat exchanger in accordance with the present invention will be described in detail with reference to accompanying drawings.

[0017] As depicted in FIGS. 1 to 4, the heat exchanger in accordance with the present invention includes a channel unit 20 in which heat transfer medium flows; and a heat exchange unit 10 contacted-combined with the channel unit 20, having porous heat transfer member 11 and performing heat exchange with thermal storage material.

[0018] As depicted in FIG. 1, in the heat exchanger in accordance with the first embodiment of the present invention, the channel unit 20 consists of a pipe in which the heat transfer medium flows. And, the heat exchange unit 10 is contacted-combined with the outer surface of the channel unit 20. The pipe can be formed as a general pipe shape or a plate shape having a regular interval.

[0019] The channel unit 20 is connected-installed to a channel pipe (not shown), the heat transfer medium completing the heat exchange while passing through the channel unit 20 is transferred to an external heat exchange unit (not shown) through the channel pipe. And, the heat transfer medium absorbs or releases heat in the external unit.

[0020] The heat transfer member 11 is made of porous material with the interstitial void volume filled with thermal storage material, it performs heat exchange with the heat transfer medium flowing in the channel unit 20, performs heat exchange with thermal storage material contacted thereto and stores/releases heat in/to the thermal storage material.

[0021] In more detail, by using the porous heat transfer member 11 having high thermal conductivity and large interstitial surface area, the thermal conductance through the thermal storage material increases enormously, and accordingly a heat exchange speed can be improved. For high thermal conductance, it is more preferable for the heat transfer member 11 to be made of foam metal, more specifically, aluminum foam.

[0022] Though various phase change materials may be used as thermal storage material, water is most widely used, because it is free of environmental contamination and has lots of latent heat in phase transition.

[0023] In case of water, a volume is largely varied in phase transition between water and ice. In this case, as depicted in FIGS. 2 and 3, in the heat exchanger in accordance with the first embodiment, the heat exchange unit 10 may be made to include plural heat transfer members 11, each heat transfer member 11 is combined with the channel unit 20 with a certain interval, i.e. interval portions 12, and accordingly it is possible to absorb volume variation according to phase transition of thermal storage material.

[0024] In more detail, as depicted in FIG. 2, in the heat exchanger in accordance with the present invention, when volume of the thermal storage material is expanded by phase transition, the thermal storage material is pushed out of the heat transfer member 11, and accordingly there is little deformation in the heat transfer member 11 due to the volume expansion of the thermal storage material.

[0025] In particular, because the more heat exchange occurs at a position abutting on the channel unit 20, as depicted in FIG. 3, the more the interval portions 12 get away from the channel unit 20, the narrower widths of the interval portions 12 are.

[0026] In the meantime, as depicted in FIG. 4, a heat storage casing 13 covers the exterior of the heat exchange unit 10 in which the heat transfer member 11 is disposed so as to fill the heat exchange unit 10, and the channel unit 20 is combined with the exterior of the heat storage casing 13.

[0027] FIG. 5 is a graph showing a performance of the heat exchanger in accordance with the present invention in comparison with that of the conventional heat exchanger. It shows a thawing thickness and a heat release rate of a heat exchanger using porous aluminum having 92% of porosity as a thermal storage member.

[0028] A dotted line shows a performance of the conventional heat exchanger, and a solid line shows a performance of the heat exchanger in accordance with the present invention. As depicted in FIG. 5, a heat release performance of the heat exchanger in accordance with the present invention is exceedingly superior to that of the conventional heat exchanger.

[0029] Herein, the porosity is an important factor. When the porosity is excessively high, a heat transfer rate is low and there is no such difference between the present and the conventional heat exchangers in a heat release or heat storage time aspects. On the contrary, when the porosity is very low, a heat storage capacity is lowered due to the decrease in a quantity of thermal storage material filled in the porous material. Accordingly, it is preferable for porous material to have porosity about 8095%.

[0030] In the heat exchanger in accordance with the present invention, because heat resistance between a heat transfer surface and a phase transition boundary surface is greatly reduced due to the high thermal conductance of porous material, although an interval between plural pipes is increased in a channel unit or a width of a heat storage casing including a heat transfer member is increased, it is possible to have the heat storage and release efficiencies higher than those of the conventional heat exchanger, and accordingly a heat storage rate per unit volume of a heat exchanger can be increased.

[0031] In addition, in the conventional heat exchanger, because the heat discharge rate is greatly reduced with the progress of heat release, it may be impossible to supply the heat release quantity corresponding to an instant large heat load even though the stored heat capacity is sufficient, and accordingly an excessively large storage unit has to be installed or simultaneous operation of both the storage unit and the refrigerator has to be applied.

[0032] However, in the heat exchanger in accordance with the present invention, even when heat load varies largely with time, it is possible to supply the heat release quantity corresponding to a heat load due to the quick congealing and melting capability resulting from the high thermal conductance of the heat exchange unit.

[0033] In the present invention, a heat exchanger is capable of improving a congelation or melting speed of a thermal storage material and bettering heat storage and release efficiencies. In addition, in design of a thermal storage system or in determination of the operation method, there is no need to consider the restrictions from the heat storage/discharge rate decreasing with the progress of the storage/discharge process.