Abstract:
A heat exchanger for storing or releasing heat including a channel unit in which a heat medium flows; and a heat exchange unit contacted-combined with the channel unit and containing a porous heat transfer member which conducts heat exchange with a thermal storage material.

Description:
This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 10-2001-0089318 filed in Korea on Dec. 31, 2001, which is herein incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a thermal storage/release system, and in particular to a thermal storage/release system for storing or releasing latent heat energy using porous members. 
   2. Description of the Prior Art 
   A latent heat storage system, as one of the heat storage systems, uses latent heat generated according to phase transition (for example water to/from ice) of a thermal storage material, and it can be divided into a type of system for congealing or melting phase transition material used as the thermal storage material around a heat exchanger tube and into a type of system for storing and releasing heat energy generated by the phase transition of thermal storage material contained in a sealed casing. 
   In any system, the 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 the progress of phase transition, and the heat transfer resistance due to the presence of thermal storage material filled between the surfaces is increased. 
   Accordingly, according to the progress of congelation or melting of the thermal storage material, the congelation speed or the melting speed is lowered, and therefore the heat storage and release efficiencies are lowered. 
   SUMMARY OF THE INVENTION 
   In order to solve the above-mentioned problem, it is an object of the present invention to provide a thermal storage/release system that is capable of improving the congelation or melting speed of thermal storage material and improving heat storage and release efficiencies. 
   In order to achieve the above-mentioned object, a thermal storage/release system in accordance with the present invention includes a channel unit through which a heat transfer medium flows; and at least one thermal storage unit including at least one housing having an empty space therein in contact with the channel unit, a thermal storage material contained in the housing to store/release heat energy by a phase transition between a solid state and a liquid state, at least one porous member extending from the channel unit into the housing to exchange heat with the thermal storage material therethrough. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a sectional view illustrating a first embodiment of a thermal storage/release system in accordance with the present invention; 
       FIG. 2  is a sectional view illustrating a modified example of the thermal storage/release system of  FIG. 1 ; 
       FIG. 3  is a sectional view illustrating another modified example of the thermal storage/release system of  FIG. 1 ; 
       FIG. 4  is a sectional view illustrating a second embodiment of the thermal storage/release system in accordance with the present invention; and 
       FIG. 5  is a graph showing the performance of the thermal storage/release system in accordance with the present invention in comparison with a conventional thermal storage system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Hereinafter, the preferred embodiments of a thermal storage/release system in accordance with the present invention will be described in detail with reference to accompanying drawings. 
   As depicted in  FIGS. 1  to  4 , the thermal storage/release system in accordance with the present invention comprises a channel unit  20  in which heat transfer medium flows; and a thermal storage unit  10  including a plurality of housings  13  having an empty space therein contacted-combined with the channel unit  20 , a thermal storage material contained in the housings  13  to store/release heat energy by a phase transition between solid state and liquid state, and a plurality of porous members  1  extending from the channel unit  20  into the housing to exchange heat with the thermal storage material therethrough. 
   As depicted in  FIG. 4 , in the thermal storage/release system in accordance with a first embodiment of the present invention, the channel unit  20  consists of a pipe through which the heat transfer medium flows. And, the thermal storage unit  10  has a housing  13  contacted-combined with the outer surface of the channel unit  20 . The pipe can be formed as a general pipe shape or as a plate shape having regular intervals. 
   The channel unit  20  is connected-installed to a channel pipe (not shown). The heat transfer medium, after 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. The heat transfer medium absorbs or releases heat in the external unit. 
   The porous members  1  is formed in the empty space in the housing  13 . And there is interstitial void volume between the porous members  1 . The thermal storage material—(e.g. water) filled with the housing  13  exchanges heat with the heat transfer medium (e.g. vapor) in the channel unit  20  through the porous members  1  with improved speed and efficiency. 
   In more detail, by using a porous member  1  having a high thermal conductivity and a large interstitial surface area therebetween, the thermal conductance through the thermal storage material (e.g. water) increases enormously, and accordingly the speed of heat exchange can be improved. For high thermal conductance, it is more preferable for the porous member  1  to be made of a foam metal, more specifically, aluminum foam. 
   Though various phase change materials may be used as the thermal storage material, water is most widely used, because it is free of environmental contamination and possesses substantial amount of latent heat in phase transition. 
   In case of water, the volume is largely varied in phase transition between water and ice. In this case, as depicted in  FIGS. 2 and 3 , in the thermal storage/release system in accordance with the first embodiment, the thermal storage unit  10  includes a plurality of porous members  1 , each porous member  1  is combined with the channel unit  20  at a predetermined interval, i.e. intervals portions  12 , and accordingly it is possible to absorb volume variations according to the phase transition of the thermal storage material. 
   In more detail, as depicted in  FIG. 2 , in the thermal storage/release system in accordance with the present invention, when the volume of the thermal storage material is expanded by phase transition (i.e. from liquid phase to solid phase for water), the thermal storage material (e.g. water) is pushed out of the porous member  1 , and accordingly there is little deformation in the porous member  1  due to the volume expansion of the thermal storage material. 
   In particular, because the greater amount of heat exchange occurs at a position abutting the channel unit  20 , as depicted in  FIG. 3 , the further the interval portions  12  extend away from the channel unit  20 , the narrower the width of the interval portions  12  become. That is, the further the porous members  1  extend away from the channel unit  20 , the broader the width of the porous members  1 . Therefore, as the thermal storage material (e.g. water) is far away from the channel unit  20 , the thermal storage material has larger contact surface with the porous member  1  to exchange heat. Accordingly, both the thermal storage material near the channel unit  20  and the thermal storage material far from the channel unit  20  exchange a similar amount of heat energy with the porous member  1  thereby attaining the performance of simultaneous storage/release regardless of the location of the thermal storage material. 
   As depicted in  FIG. 4 , a housing  13  covers the exterior of the thermal storage unit  10  in which the porous member  1  is disposed so as to fill the thermal storage unit  10 . Also, the channel unit  20  is combined with or in contact with the exterior of the housing  13 . 
     FIG. 5  is a graph showing the performance of the thermal storage/release system in accordance with the present invention in comparison with a conventional thermal storage/release system. It shows a thawing thickness and a heat release rate of the thermal storage/release system using porous aluminum having 92% of porosity. 
   The dotted line shows the performance of the conventional thermal storage/release system, and the solid line shows a performance of the thermal storage/release system of present invention in accordance with the present invention. As depicted in  FIG. 5 , the heat release performance of the present invention is exceedingly superior to that of the conventional thermal storage/release system. 
   Herein, the porosity is an important factor. When the porosity is excessively high, the heat transfer rate is low and there is not much difference between the present and the conventional thermal storage/release system in a heat release or heat storage time aspects. On the contrary, when the porosity is very low, the heat storage capacity is lowered due to a decrease in the quantity of the thermal storage material disposed around the porous member. Accordingly, it is preferable for the porous member  1  to have a porosity about 80-95%. 
   In the thermal storage/release system in accordance with the present invention, because the heat resistance between a heat transfer surface and the phase transition boundary surface is greatly reduced due to the high thermal conductance of the porous member  1 , although the interval between the plurality of the porous members  1  is increased and/or the width of the housing  13  including the porous member  1  is increased, it is possible to cause the heat storage and release efficiencies to be higher than those of the conventional thermal storage/release system, and accordingly the thermal storage rate per unit volume of the thermal storage/release system of the present invention can be increased. 
   In addition, in the conventional thermal storage/release system, 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. 
   However, in the thermal storage/release system of the present invention, even when the 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 porous member  1 . 
   In the present invention, the thermal storage/release system is capable of improving the congelation or melting speed of the thermal storage material (e.g. water) and improving heat storage and release efficiencies. In addition, in the design of a thermal storage/release system or in the 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. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.