Abstract:
A heat exchanger comprising a mixture inflow unit into which a mixture of air and fuel is introduced, a burner for combusting the mixture introduced through the mixture inflow unit, a heat exchange unit that is disposed around the burner, and a combustion gas discharge unit for discharging the combustion gas having passed through the heat exchange unit is provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of International Application No. PCT/KR2015/002458 filed on Mar. 13, 2015, which claims priority to Korean Application No. 10-2014-0031440 filed on Mar. 18, 2014. The applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a heat exchanger provided in a boiler for heating or hot water, and more particularly, to a heat exchanger improving heat transfer efficiency between a heating medium and combustion gas, and also having a simplified structure by stacking a unit plate manufactured in a constant pattern to integrally form a heating medium passage, a combustion gas passage, and a combustion gas discharge passage. 
       BACKGROUND ART 
       [0003]    A boiler for heating or hot water is a device for applying heat to heating water or direct water (hereinafter, referred to as a ‘heating medium’) by a heat source to heat a desired zone or supply hot water, and is configured to include a burner for burning a mixture of gas and air, and a heat exchanger for transferring combustion heat of combustion gas to the heating medium. 
         [0004]    A boiler produced in the early days employed a heat exchanger of heating a heating medium using only sensible heat generated upon combustion of a burner, whereas a boiler produced recently is a condensing boiler designed to improve thermal efficiency, which is provided with a sensible heat exchanger for absorbing sensible heat of combustion gas generated in a combustion chamber and a latent heat exchanger for absorbing latent heat generated upon condensation of water vapor that is contained in the combustion gas undergone heat exchange in the sensible heat exchanger. Such a condensing boiler is commercialized in an oil boiler as well as a gas boiler to thereby contribute much to an increase of boiler efficiency and fuel expenses reduction. 
         [0005]    As described above, a conventional heat exchanger of a condensing type configured with a sensible heat exchanger and a latent heat exchanger has a structure in which an air blower, a fuel supply nozzle, and a burner are typically installed at an upper part of a housing, and the sensible heat exchanger and the latent heat exchanger, in which heat exchange fins are coupled to an outside of a heat exchange pipe, are sequentially installed inside the housing below the burner. 
         [0006]    However, such a heat exchanger of a condensing type has a problem in that a dimension of the heat exchanger should be increased due to the structure in which the air blower is located at the upper part of the housing and the sensible heat exchanger and the latent heat exchanger are longitudinally located inside the housing. 
         [0007]    As the prior art for addressing such a problem, minimizing the dimension and improving heat exchange efficiency, a heat exchanger is disclosed in Korean Patent Registered Nos. 10-1321708, 10-0581578, and 10-0813807, wherein the heat exchanger is configured with a burner located at a center thereof and a heat exchange pipe wound on a circumference of the burner in a coil shape. 
         [0008]      FIG. 1  shows a cross-sectional view of a heat exchanger of a condensing boiler disclosed in Korean Patent Registered No. 10-0813807. A heat exchanger  40  shown in  FIG. 1  is configured to include a burner  10  installed to discharge downward combustion gas, a heat exchange pipe  20  wound on a circumference of the burner  10  in a coil shape so as to heat water suppled inside the heat exchanger  40  to a desired temperature by heat generated at the burner  10  to thereby provide the heated water as heating water or hot water, and a partition wall  30  installed at a lower side of the heat exchange pipe  20  in a horizontal direction to form a passage of combustion gas. As shown in  FIG. 1 , the heat exchange pipe  20  is arranged to have an inclined surface  21  that is inclined from an outside of a body to an inside thereof by a predetermined angle to be directed to a central direction of the burner  10 , and one end of a connecting pipe  33  is connected to and installed at a body of the partition wall  30 , which forms a communication hole  32  thereinside, thereby connecting one side of the heat exchange pipe  20  to the other side thereof through the other end of the connecting pipe  33 . 
         [0009]    However, the heat exchanger disclosed in the prior art documents has a disadvantage in which a torsional phenomenon occurs while the heat exchange pipe is helically processed to cause a difficulty in processing an entire surface of the heat exchange pipe in a uniform shape. 
         [0010]    Also, when a heat exchange pipe is undergone a bending process, damage may occur upon the bending process due to a difference of a strain rate between an inside surface of the heat exchange pipe toward a center of a burner and an outside surface thereof opposite the inside surface, and thus the heat exchange pipe exchanging heat with combustion gas may have a limitation to be formed in a wider width. As a result, there is a structural limitation in which a sufficient area for processing an irregular shape promoting a turbulent flow on a surface of a heat exchange pipe is not secured as a configuration for more improving heat transfer efficiency between a heating medium and combustion gas. 
         [0011]    In addition, the conventional heat exchanger has problems in that an installation structure of the heat exchanger is complicated because a housing H is separately provided as a configuration for tightly sealing an outer circumference of the heat exchange pipe  20  being helically wound, and a heat source of combustion gas is not fully transferred to a heating medium flowing inside the heat exchange pipe  20  because heat transferred to the housing H is directly radiated and dissipated to an outside thereof, wherein the heat is transferred to the housing H while the combustion gas generated by combustion of the burner  10  passes a longitudinally separated space of the heat exchange pipe  20  to flow through a space between the heat exchange pipe  20  and an inner wall of the housing H. 
         [0012]    Additionally, the conventional heat exchanger has problems in that heat generated by the combustion of the burner  10  is transferred to a plate  11  for fixing the burner  10  to thereby cause an overheating, and also an insulating material or a heat dissipation fin at an outside of the plate  11  should be additionally provided in order to prevent such an overheating such that a complicated structure and a heat loss are induced. 
       SUMMARY 
       [0013]    To address the above described problems, an object of the present disclosure is to provide a heat exchanger capable of securing a large heat transfer area between a heating medium and combustion gas by forming a flow channel of the heating medium to be long in a restricted space, and also maximizing thermal efficiency by promoting generation of a turbulent flow in the flow of the heating medium and the combustion gas. 
         [0014]    Another object of the present disclosure is to provide a heat exchanger capable of reducing the number of components configuring the heat exchanger and simplifying a coupling structure, by integrally configuring a heating medium passage, a combustion gas passage, and an outer wall structure for tightly sealing outside surfaces of the heating medium passage and the combustion gas passage. 
         [0015]    Still another object of the present disclosure is to provide a heat exchanger capable of more improving thermal efficiency by maximizing a collection of combustion heat of combustion gas into a heating medium, wherein the combustion heat is discharged through a combustion gas discharge passage. 
         [0016]    To realize the above described objects, a heat exchanger of the present disclosure includes a mixture inflow unit  100  in which a mixture of air and fuel flows; a burner  200  configured to burn the mixture flowing in through the mixture inflow unit  100 ; heat exchange units  300  and  400  provided at a circumference of the burner  200 , configured to exchange heat between combustion gas generated by combustion of the burner  200  and a heating medium, and configured with a plurality of unit plates being longitudinally stacked; and a combustion gas discharge unit  500  configured to discharge combustion gas that passed the heat exchange units  300  and  400 , wherein, in an inside of each of the plurality of unit plates that are stacked to configure the heat exchange units  300  and  400 , a heating medium passage P 1  and a combustion gas passage P 2  are separated from each other and longitudinally and alternately formed to be adjacent to each other, and a combustion gas discharge passage P 3  is formed to connect the combustion gas passage P 2  to the combustion gas discharge unit  500 . 
         [0017]    In this case, each of the plurality of unit plates may be configured with a first plate and a second plate which are longitudinally stacked, the first plate may include a first plane portion A 1  in which a first through hole B 1  is formed at a central part thereof; a first flange portion C 1  formed to extend from an edge of the first plane portion A 1  to an upper side thereof to be bended to an outward side thereof; and a passage forming protruding portion D 1  formed to be convex upward at a region between the edge of the first plane portion A 1  and the first through hole B 1 , and the second plate may include a second plane portion A 2  in which a second through hole B 2  of a shape corresponding to that of the first through hole B 1  is formed at a central part of the second plane portion A 2 , and having an upper surface coming into tight contact with a bottom surface of the first plane portion A 1 ; a second flange portion C 2  formed to extend from an edge of the second plane portion A 2  to a lower side thereof to be bended to an outward side thereof, and coupled to a flange portion C 1  of a unit plate being located below the second plate; and a passage forming depressed portion D 2  formed to be concave downward at a region between the edge of the second plane portion A 2  and the second through hole B 2 , thereby forming the heating medium passage P 1  between the passage forming protruding portion D 1  and the passage forming depressed portion D 2 . 
         [0018]    The first flange portion C 1  may be formed to be higher than a protruding height of the passage forming protruding portion D 1 , and the second flange portion C 2  may be formed to be deeper than a depressed depth of the passage forming depressed portion D 2 , and thus a longitudinally separated space, which forms the combustion gas passage P 2 , may be provided between a lower end of a passage forming depressed portion D 2  of a unit plate being located at an upper group among unit plates that are longitudinally located to be adjacent to each other, and an upper end of a passage forming protruding portion D 1  of a unit plate being located at a lower group thereamong. 
         [0019]    A plurality of gap maintaining protruding portions E 1 , each of which protrudes at the same height as that of the first flange portion C 1 , may be formed to be spaced apart from each other at the passage forming protruding portion D 1  in a circumferential direction, and a plurality of gap maintaining depressed portions E 2 , each of which is depressed at the same depth as that of the second flange portion C 2 , may be formed to be spaced apart from each other at the passage forming depressed portion D 2  in the circumferential direction, and thus a lower end of each of the plurality of gap maintaining depressed portions E 2  of a unit plate being located at the upper group among the unit plates being longitudinally located to be adjacent to each other, and an upper end of each of the plurality of gap maintaining protruding portions E 1  of a unit plate being located at the lower group thereamong may come into contact with each other. 
         [0020]    A combustion gas outlet F 1  may be formed at the edge of the first plane portion A 1  to provide the combustion gas discharge passage P 3 , and a combustion gas outlet F 2  may be formed at a position, which longitudinally corresponds to the combustion gas outlet F 1 , on the edge of the second plane portion A 2 , and thus combustion gas, which passed the combustion gas passage P 2 , may sequentially pass the combustion gas outlets F 1  and F 2  which are formed at each of the unit plates being longitudinally arranged, thereby flowing toward the combustion gas discharge unit  500 . 
         [0021]    A turbulent flow forming portion G having an irregular shape may be formed at the passage forming protruding portion D 1  or the passage forming depressed portion D 2 . 
         [0022]    In this case, a protruding upper end and a depressed lower end of the turbulent flow forming portion G may come into contact with each other inside the heating medium passage P 1  and the combustion gas passage P 2 . 
         [0023]    As one embodiment, the passage forming protruding portion D 1  may be formed to be communicated with an entire section at a region between the edge of the first plane portion A 1  and the first through hole B 1  along the circumferential direction, the passage forming depressed portion D 2  may be formed to be communicated with an entire section at a region between the edge of the second plane portion A 2  and the second through hole B 2  along the circumferential direction, and a through hole may be formed at each of the plurality of gap maintaining protruding portions E 1  and each of the plurality of gap maintaining depressed portions E 2  so as to connect a heating medium passage P 1  of the unit plate located at the lower group to a heating medium passage P 1  of the unit plate located at the upper group, wherein the through hole may be located so as to reverse a direction of the heating medium passage P 1  of the unit plate located at the lower group against that of the heating medium passage P 1  of the unit plate located at the upper group. 
         [0024]    A heating medium, which flows in through a through hole formed at one side of a second plate configuring the unit plate located at the lower group among the unit plates being longitudinally located to be adjacent to each other, may be branched off to both directions to flow along the heating medium passage P 1 , and then pass a through hole formed at a first plate being located at an opposite side against the second plate and a through hole formed at a second plate configuring a unit plate being located at the upper group, thereby flowing in a heating medium passage P 1  of the unit plate being located at the upper group. 
         [0025]    As another embodiment, the passage forming protruding portion D 1  may be formed to be communicated with some section at a region between the edge of the first plane portion A 1  and the first through hole B 1  along the circumferential direction, the passage forming depressed portion D 2  may be formed to be communicated with some section at a region between the edge of the second plane portion A 2  and the second through hole B 2  along the circumferential direction, and a through hole may be formed at each of the plurality of gap maintaining protruding portions E 1  and each of the plurality of gap maintaining depressed portions E 2  so as to connect a heating medium passage P 1  of the unit plate located at the lower group to a heating medium passage P 1  of the unit plate located at the upper group, wherein the through hole may be located so as to reverse a direction of the heating medium passage P 1  of the unit plate located at the lower group against that of the heating medium passage P 1  of the unit plate located at the upper group. 
         [0026]    A heating medium, which flows in through a through hole formed at one side of a second plate configuring the unit plate located at the lower group among the unit plates being longitudinally located to be adjacent to each other, may flow in one direction along the heating medium passage P 1 , and then pass a through hole formed at a first plate being located at an opposite side against the second plate and a through hole formed at a second plate configuring a unit plate being located at the upper group, thereby flowing in a heating medium passage P 1  of the unit plate being located at the upper group. 
         [0027]    In the above described embodiments, multiple heating medium passages P 1  may be configured in parallel with each other by stacking the unit plate. 
         [0028]    The heat exchange units  300  and  400  may be configured with a sensible-heat exchange unit  300  configured to absorb sensible heat of the combustion gas generated by the combustion of the burner  200 , and a latent-heat exchange unit  400  configured to absorb latent heat of water vapor contained in the combustion gas being undergone heat exchange in the sensible-heat exchange unit  300 , and a heat isolator  390  may be provided between the sensible-heat exchange unit  300  and the latent-heat exchange unit  400  to spatially separate the sensible-heat exchange unit  300  and the latent-heat exchange unit  400  from each other, and thus the combustion gas generated by the combustion of the burner  200  may pass the combustion gas passage P 2  of the sensible-heat exchange unit  300  to flow in a radially outward direction, and then pass the combustion gas passage P 2  of the latent-heat exchange unit  400  after passing the combustion gas discharge passage P 3  to flow in a radially inward direction, thereby being discharged to the combustion gas discharge unit  500 . 
         [0029]    The heat isolator  390  may include a heating medium filled between an upper cover panel  390   a  and a lower cover panel  390   b  which are longitudinally stacked; and an insulating material  390   c  stacked on the upper cover panel  390   a.    
         [0030]    The unit plate may be arranged to surround the circumference of the burner  200  in a polygonal shape, a circular shape, or an oval shape. 
         [0031]    A heating medium connecting passage P may be formed at a lateral circumferential surface of an upper part of the burner  200 , wherein the heating medium connecting passage P may be connected to a heating medium passage P 1  located at the upper part of the burner  200 , thereby allowing the heating medium to pass the heating medium connecting passage P. 
         [0032]    In accordance with the heat exchanger of the present disclosure, thermal efficiency may be maximized by stacking a plurality of unit plates manufactured in a similar pattern to form a heating medium passage and a combustion gas passage which are separately and alternately arranged to be adjacent to each other in an inner space of the stacked unit plates, forming a flow channel of the heating medium to be long at maximum length in a restricted space, and configuring a turbulent flow forming portion, which promotes generation of a turbulent flow in the flow of the heating medium and the combustion gas, to be formed at a large area on a surface of each of the unit plates. 
         [0033]    Also, in accordance with the present disclosure, a heating medium passage, a combustion gas passage, and the structure of an outer wall for tightly sealing outside surfaces of the heating medium passage and the combustion gas passage, through which combustion gas passes, are integrally formed inside a heat exchanger that is configured by stacking a plurality of unit plates, such that the number of components configuring the heat exchanger may be reduced to simplify an installation structure, and also heat of combustion gas transferred to the outer wall in the integral structure is retransferred to a heating medium by a conducting method, thereby more improving thermal efficiency. 
         [0034]    In addition, a plurality of unit plates are multiply stacked to configure multiple heating medium passages in parallel with each other such that a pressure loss may be minimized, a separate connection component may not be needed, and a part for connecting the heating medium passages to each other may be used as a heat exchange area. 
         [0035]    Additionally, deformation of a unit plate due to a pressure of a heating medium may be prevented and pressure resistance performance of the unit plate may be improved by contacting and welding a shape for forming a turbulent flow to an inside of each of a heating medium passage and a combustion gas passage. 
         [0036]    Further, a heating medium passage and a combustion gas passage are configured to connect to a unit plate, respectively, so that heat exchange may be performed through an entire unit plate, thereby more improving thermal efficiency. Moreover, a passage through which a heating medium passes may be formed at a lateral surface of an upper part of a burner, thereby preventing a burner support plate from being overheated and more improving thermal efficiency. 
         [0037]    Furthermore, heat insulation efficiency between a sensible heat exchange portion and a latent heat exchange portion may be increased by allowing a heating medium to pass a space between plates configuring a heat isolator that is located between the sensible heat exchange portion and the latent heat exchange portion. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0038]      FIG. 1  is a cross-sectional view of a heat exchanger in which a heat exchange pipe is helically installed at a circumference of a conventional burner. 
           [0039]      FIGS. 2 and 3  are perspective views of a heat exchanger according to one embodiment of the present disclosure when viewed from upper and lower sides, respectively. 
           [0040]      FIG. 4  is a right lateral view of the heat exchanger according to one embodiment of the present disclosure. 
           [0041]      FIG. 5  is an exploded perspective view of the heat exchanger according to one embodiment of the present disclosure. 
           [0042]      FIG. 6  is a plan view of the heat exchanger according to one embodiment of the present disclosure. 
           [0043]      FIG. 7  is a bottom view of the heat exchanger according to one embodiment of the present disclosure. 
           [0044]      FIG. 8  is a perspective view taken along line A-A of  FIG. 6 . 
           [0045]      FIG. 9  is a perspective view enlarging a part of a unit plate shown in  FIG. 8 . 
           [0046]      FIG. 10  is a cross-sectional view taken along line A-A of  FIG. 6 . 
           [0047]      FIG. 11  is a cross-sectional view taken along line B-B of  FIG. 6 . 
           [0048]      FIG. 12  is a cross-sectional view taken along line C-C of  FIG. 7 . 
           [0049]      FIG. 13  is a diagram for describing a passage of a heating medium at a latent-heat exchange unit of the heat exchanger according to one embodiment of the present disclosure. 
           [0050]      FIG. 14  is a diagram for describing a passage of a heating medium at a sensible-heat exchange unit of the heat exchanger according to one embodiment of the present disclosure. 
           [0051]      FIG. 15  is a perspective view of a stacked structure of unit plates according to another embodiment of the present disclosure. 
           [0052]      FIG. 16  is an exploded perspective view of  FIG. 15 . 
           [0053]      FIG. 17  is a diagram for describing a passage of a heating medium at the unit plate shown in  FIG. 15 . 
           [0054]      FIGS. 18A and 18B  are an exploded perspective view and a coupled perspective view of one embodiment of a heat isolator provided at a boundary between a sensible-heat exchange unit and a latent-heat exchange unit, respectively. 
           [0055]      FIG. 19  is a perspective view of a stacked structure of unit plates according to still another embodiment of the present disclosure. 
           [0056]      FIGS. 20A and 20B  are a perspective view and a partially dissected perspective view of an embodiment in which a passage of a heating medium is additionally formed at an upper part of a burner, respectively. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    Hereinafter, a configuration and an action with respect to an embodiment of the present disclosure will be described in detail as follows with reference to the accompanying drawings. 
         [0058]    With reference to  FIGS. 2 to 5 , a heat exchanger  1  according to the present disclosure is configured to include a mixture inflow unit  100  in which a mixture of air and fuel flows; a burner  200  for burning the mixture flowing in through the mixture inflow unit  100 ; heat exchange units  300  and  400  provided at a circumference of the burner  200  to exchange heat between combustion gas generated by combustion of the burner  200  and a heating medium and configured with a plurality of unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  410 ,  420 ,  430 , and  440  which are longitudinally stacked; and a combustion gas discharge unit  500  through which the combustion gas passed the heat exchangers  300  and  400  is discharged. 
         [0059]    The mixture inflow unit  100  is configured to include an upper cover plate  110  at which a through hole  111  is formed at one side of the upper cover plate  110 , wherein a heating medium discharge pipe  112  passes through the through hole  111 , and a mixture inflow pipe  120  passing through a center of the upper cover plate  110  to allow the mixture to flow in the mixture inflow pipe  120 . 
         [0060]    The burner  200  burns the mixture of the air and the fuel flowing therein through the mixture inflow unit  100 , to thereby generate combustion gas of high temperature. The burner  200  is configured to be fixed to a burner support plate  210  to generate flame in a downward direction. The burner support plate  210  is configured with a plane portion A in which a through hole B is formed at a central part thereof, wherein the burner  200  passes through the through hole B; a flange portion C extending from an edge of the plane portion A to a downward side thereof to be bended to an outward side thereof; and a depressed portion D having a downwardly concave shape at a region between the edge of the plane portion A and the through hole B. 
         [0061]    The heat exchange units  300  and  400  may be configured with a sensible-heat exchange unit  300  for absorbing sensible heat of combustion gas generated by combustion of the burner  200 , and a latent-heat exchange unit  400  for absorbing latent heat generated while water vapor contained in combustion gas, which is undergone heat exchange at the sensible heat exchangers  300 , is condensed. 
         [0062]    The combustion gas discharge unit  500  is configured with a lower cover plate  510  covering a lower part of the latent-heat exchange unit  400 , an exhaust gas discharge pipe  520  communicating with a lower side of a through hole B formed at a center of the lower cover plate  510  and connected to a condensed water discharge pipe  513  at a lower end of the exhaust gas discharge pipe  520 , and a flue  530  connected to one side of the exhaust gas discharge pipe  520  to extend to an upward side. 
         [0063]    The lower cover plate  510  includes a plane portion A at which the through hole B is formed at a central part thereof, a flange portion C extending from an edge of the plane portion A to an upward side thereof to be bended to an outward side thereof, a passage forming protruding portion D 1  having an upwardly convex shape at a region between the edge of the plane portion A and the through hole B, and a plurality of gap maintaining protruding portions E 1  protruding at the same height as that of the flange portion C on corners of the passage forming protruding portion D 1 , and a through hole  511  through which a heating medium inflow pipe  512  passes is formed at the gap maintaining protruding portions E 1 , which is located at one side of the lower cover plate  510 . 
         [0064]    Hereinafter, a configuration and an action of each of the sensible-heat exchange unit  300  and the latent-heat exchange unit  400  configuring the heat exchange units  300  and  400  which are a characteristic configuration of the present disclosure will be described. 
         [0065]    The present disclosure is characterized in that a heating medium passage P 1 , a combustion gas passage P 2 , and a combustion gas discharge passage P 3  are integrally formed inside the plurality of unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  410 ,  420 ,  430 , and  440  which configure the heat exchange units  300  and  400  and are longitudinally stacked. 
         [0066]    With reference to  FIGS. 5, 8, 9, 13, and 14 , the sensible-heat exchange unit  300  is configured with the plurality of unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 , and  380  which are longitudinally stacked, and the latent-heat exchange unit  400  is configured with the plurality of unit plates  410 ,  420 ,  430 , and  440  which are longitudinally stacked. And, a heat isolator  390  is provided between the sensible-heat exchange unit  300  and the latent-heat exchange unit  400  so as to spatially separate the sensible-heat exchange unit  300  from the latent-heat exchange unit  400  and to prevent sensible heat generated at the sensible-heat exchange unit  300  from being directly transferred to the latent-heat exchange unit  400 . 
         [0067]    The unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 , and  380 , which configure the sensible-heat exchange unit  300 , are configured with first plates  310   a ,  320   a ,  330   a ,  340   a ,  350   a ,  360   a ,  370   a , and  380   a  located at upper parts of the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 , and  380 , and second plates  310   b ,  320   b ,  330   b ,  340   b ,  350   b ,  360   b ,  370   b , and  380   b  coupled to lower parts of the first plates  310   a ,  320   a ,  330   a ,  340   a ,  350   a ,  360   a ,  370   a , and  380   a.    
         [0068]    The unit plates  410 ,  420 ,  430 , and  440 , which configure the latent-heat exchange unit  400 , are configured with first plates  410   a ,  420   a ,  430   a , and  440   a  located at upper parts of the unit plates  410 ,  420 ,  430 , and  440 , and second plates  410   b ,  420   b ,  430   b , and  440   b  coupled to lower parts of the first plates  410   a ,  420   a ,  430   a , and  440   a  so that they have a stacked structure of a similar shape to that of the sensible-heat exchange unit  300 . 
         [0069]    Hereinafter, the first plates  310   a ,  320   a ,  330   a ,  340   a ,  350   a ,  360   a ,  370   a , and  380   a  configuring the sensible-heat exchange unit  300 , and the first plates  410   a ,  420   a ,  430   a , and  440   a  configuring the latent-heat exchange unit  400  are configured in a similar shape pattern so that they will be referred to as a ‘first plate,’ and also the second plates  310   b ,  320   b ,  330   b ,  340   b ,  350   b ,  360   b ,  370   b , and  380   b  configuring the sensible-heat exchange unit  300 , and the second plates  410   b ,  420   b ,  430   b , and  440   b  configuring the latent-heat exchange unit  400  are configured in a similar shape pattern so that they will be referred to as a ‘second plate,’ and then a configuration of each of them will be described. 
         [0070]    The first plate includes a first plane portion A 1  in which a first through hole B 1  is formed at a central part thereof, a first flange portion C 1  extending from an edge of the first plane portion A 1  to an upper side thereof to be bended to an outward side thereof, a passage forming protruding portion D 1  formed to be convex upward at a region between the edge of the first plane portion A 1  and the first through hole B 1 , and a combustion gas outlet F 1  longitudinally passing through the edge of the first plane portion A 1  to provide a combustion gas discharge passage P 3 . 
         [0071]    The second plate includes a second plane portion A 2  in which a second through hole B 2  of a shape corresponding to that of the first through hole B 1  is formed at a center of the second plane portion A 2 , and having an upper surface coming into tight contact with a bottom surface of the plane portion A 1 ; a second flange portion C 2  extending from an edge of the second plane portion A 2  to a lower side thereof to be bended to an outward side thereof and coupled to a first flange portion C 1  of a unit plate being located below the second flange portion C 2 ; a passage forming depressed portion D 2  formed to be concave downward at a region between the edge of the second plane portion A 2  and the second through hole B 2 , thereby forming the heating medium passage P 1  between the passage forming protruding portion D 1  and the passage forming depressed portion D 2 ; and a combustion gas outlet F 2  longitudinally passing through the edge of the second plane portion A 2  to provide the combustion gas discharge passage P 3 . 
         [0072]    The first flange portion C 1  is formed to be higher than a protruding height of the passage forming protruding portion D 1 , and the second flange portion C 2  is formed to be deeper than a depressed depth of the passage forming depressed portion D 2 . Consequently, among unit plates being longitudinally stacked to be adjacent to each other, a longitudinally separated space is provided between a lower end of a passage forming depressed portion D 2  of a unit plate located at an upper side thereamong and an upper end of a passage forming protruding portion D 1  of a unit plate located at a lower side thereamong, thereby forming the combustion gas passage P 2 . 
         [0073]    And, a plurality of gap maintaining protruding portions E 1 , each of which protrudes at the same height as that of the first flange portion C 1 , are formed to be spaced apart from each other in a circumferential direction at the passage forming protruding portion D 1 , and a plurality of gap maintaining depressed portions E 2 , each of which is depressed at the same depth as that of the second flange portion C 2 , are formed at the passage forming depressed portion D 2 . Therefore, among the unit plates being longitudinally stacked to be adjacent to each other, a second flange portion C 2  formed at a unit plate located at an upper side thereamong is coupled to a first flange portion C 1  formed at a unit plate located at a lower side thereamong, and a lower end of a gap maintaining depressed portion E 2  formed at the unit plate located at the upper side and an upper end of a gap maintaining protruding portion E 1  formed at the unit plate located at the lower side come into contact with and are supported by each other. 
         [0074]    As described above, because the second flange portion C 2  at the upper side and the first flange portion C 1  at the lower side are coupled to each other, the gap maintaining depressed portion E 2  at the upper side and the gap maintaining protruding portion E 1  at the lower side come into contact with each other to be supported, and the combustion gas outlets F 1  and F 2  being longitudinally communicated are formed at the edge of each of the first plate and the second plate, the heating medium passage P 1 , the combustion gas passage P 2 , and the combustion gas discharge passage P 3  are integrally formed inside the unit plates being longitudinally stacked to be adjacent to each other when the unit plates are stacked, and also bond strength between the unit plates may be improved. 
         [0075]    Also, one of the passage forming protruding portion D 1  and the passage forming depressed portion D 2 , or both of them may be configured to include a turbulent flow forming portion G of an irregular shape. The turbulent flow forming portion G may be configured in an outward protruding shape or an inward depressed shape on a surface of the passage forming protruding portion D 1  and the passage forming depressed portion D 2 , and such a shape may be configured in a variety of shapes including an embossed shape, an oval shape, a rib shape inclined to one side, or the like. 
         [0076]    According to the configuration of the turbulent flow forming portion G, heat exchange efficiency may be improved by promoting generation of a turbulent flow in a flow of a heating medium passing the heating medium passage P 1  and a flow of combustion gas passing the combustion gas passage P 2 . 
         [0077]    Further, when the turbulent flow forming portion G is formed at the passage forming protruding portion D 1  of the first plate in an downward depressed shape and at the passage forming depressed portion D 2  of the second plate in an upward protruding shape, to thereby contact a lower end of the downward depressed segment of the turbulent flow forming portion G to an upper end of the upward protruding segment thereof, bond strength between the passage forming protruding portion D 1  and the passage forming depressed portion D 2  may be increased, thereby preventing the passage forming protruding portion D 1  and the passage forming depressed portion D 2  from being deformed and damaged due to pressure of the heating medium passing the heating medium passage P 1 . 
         [0078]    In a helical heat exchange pipe structure according to the related art, deformation and damage problems of a pipe are caused by a bending process of the pipe so that there is a limitation to a structure in which it may be very difficult to secure a sufficient area on a surface of a heat exchange pipe so as to form an irregular shape promoting a turbulent flow thereon. On the other hand, according to the present disclosure, a heat exchanger is configured by stacking unit plates so that there is an advantage in which a space for forming the turbulent flow forming portion G may be secured to be large. 
         [0079]    Hereinafter, flow channels of combustion gas and a heating medium in the heat exchanger according to the present disclosure will be described. 
         [0080]    Firstly, a flow channel of combustion gas will be described. 
         [0081]    With reference to  FIGS. 6 and 8 to 11 , a longitudinal flow of combustion gas generated by combustion of the burner  200  is blocked by the upper cover plate  110  and the heat isolator  390 , and thus the combustion gas flows in a radially outward direction centering on the burner  200  to pass the combustion gas passage P 2  formed at each of the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 , and  380  configuring the sensible-heat exchange unit  300 . While passing the combustion gas passage P 2 , the combustion gas transfers heat to a heating medium passing the heating medium passage P 1  of the sensible-heat exchange unit  300 . 
         [0082]    In the course of passing the combustion gas passage P 2 , generation of a turbulent flow is concurrently promoted in the flow of the combustion gas and the heating medium by the turbulent flow forming portion G formed at the passage forming protruding portion D 1  and the passage forming depressed portion D 2  so that heat transfer efficiency between the combustion gas and the heating medium may be increased. 
         [0083]    The combustion gas, which passed the combustion gas passage P 2 , sequentially passes the combustion gas discharge passages P 3  to move downward, wherein the combustion gas discharge passages P 3  are longitudinally communicated by the combustion gas outlets F 1  and F 2  formed at each of the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  410 ,  420 ,  430 , and  440  being longitudinally stacked. At this point, while the combustion gas is passing the combustion gas discharge passage P 3 , heat transferred to an outer wall of the combustion gas discharge passage P 3  is retransferred to the heating medium passing the heating medium passage P 1  via the plane portions A 1  and A 2 , the passage forming protruding portion D 1 , and the passage forming depressed portion D 2  by a conducting method, and thus a heat loss may be minimized to more improve thermal efficiency. 
         [0084]    Thereafter, a downward flow of the combustion gas entering the combustion gas discharge passage P 3  of the latent-heat exchange unit  400  is blocked by the lower cover plate  510  and the combustion gas passes the combustion gas passage P 2 , which is formed at each of the unit plates  410 ,  420 ,  430 , and  440  configuring the latent-heat exchange unit  400 , to flow inside the latent-heat exchange unit  400 . In the course of the above described process, latent heat of condensed water contained in water vapor of the combustion gas is transferred to the heating medium passing the heating medium passage P 1  of the latent-heat exchange unit  400 , thereby preheating the heating medium. Also, while the combustion gas is passing the combustion gas passage P 2  of the latent-heat exchange unit  400 , generation of a turbulent flow is promoted in the flow of the combustion gas and the heating medium by the turbulent flow forming portion G formed at the passage forming protruding portion D 1  and the passage forming depressed portion D 2  so that a collection rate of the latent heat may be increased. 
         [0085]    The combustion gas, which passed the combustion gas passage P 2  of the latent-heat exchange unit  400 , is discharged upward through the exhaust gas discharge pipe  520  and the flue  530 , and the condensed water is discharged downward through the condensed water discharge pipe  513  connected to the lower part of the exhaust gas discharge pipe  520 . 
         [0086]    Hereinafter, a flow channel of a heating medium will be described. 
         [0087]    A flow channel of a heating medium is configured such that the heating medium flows in the latent-heat exchange unit  400  through the heating medium inflow pipe  512  connected to the lower part thereof, and absorbs latent heat and sensible heat by sequentially passing the latent-heat exchange unit  400  and the sensible-heat exchange unit  300 , and are discharged through a heating medium discharge pipe  112  connected to an upper part of the sensible-heat exchange unit  300 . 
         [0088]    Firstly, with reference to  FIGS. 5, 7, 12, 13, and 14 , one embodiment of a flow channel of a heating medium will be described. 
         [0089]    A flow channel of a heating medium according to one embodiment is configured such that the heating medium, which flows in through a through hole formed at one side of a second plate configuring a unit plate located at a lower side of unit plates being longitudinally located to be adjacent to each other, is branched off to both sides to flow along a heating medium passage P 1  and then passes a through hole formed a first plate located at an opposite side against the second plate and a through hole formed at a second plate configuring a unit plate being located over the first plate, and flows in a heating medium passage P 1  being located at the unit plate over the first plate. 
         [0090]    In a configuration for the purpose of implementing the described above, the passage forming protruding portion D 1  is formed to be communicated with an entire section at a region between the edge of the first plane portion A 1  and the first through hole B 1  along a circumferential direction, the passage forming depressed portion D 2  is formed to be communicated with an entire section at a region between the edge of the second plane portion A 2  and the second through hole B 2  along the circumferential direction, and a through hole is formed at the gap maintaining protruding portion E 1  and the gap maintaining depressed portion E 2  so as to connect a heating medium passage P 1  of a unit plate being located at the lower side to that of a unit plate being located at the upper side, wherein the through hole is located so as to reverse a direction of the heating medium passage P 1  at the unit plate being located at the lower side against that of the heating medium passage P 1  at the unit plate being located at the upper side. 
         [0091]    Hereinafter, a flow channel of a heating medium in the heat exchange units  300  and  400  will be described in more detail with reference to  FIGS. 5, 13, and 14 . 
         [0092]    Firstly, with reference to  FIGS. 5 and 13 , a flow channel of a heating medium in the latent-heat exchange unit  400  will be described. As arrows shown in  FIG. 13 , a heating medium, which flowed in through the heating medium inflow pipe  512 , flows in a heating medium passage P 1  inside the unit plate  440  through a through hole  443  formed at the second plate  440   b  of the unit plate  440  that is located at a lower-most position of the latent-heat exchange unit  400 . 
         [0093]    Some of the heating medium, which flows in the heating medium passage P 1  inside the unit plate  440 , flows in a heating medium passage P 1  inside the unit plate  430  through a through hole  441  formed at the first plate  440   a  and a through hole  432  formed at the second plate  430   b  of the unit plate  430  being stacked over the first plate  440   a , and the remaining of the heating medium is branched off to both sides centering on the through hole  443  to flow in a direction toward a through hole  442  formed at the first plate  440   a  being located at an opposite side against the second plate  440   b  and then flows in the heating medium passage P 1  inside the unit plate  430  through a through hole  433  formed at the second plate  430   b  of the unit plate  430  being stacked over the first plate  440   a.    
         [0094]    The heating medium, which flowed in through the through hole  432  of the unit plate  430 , is branched off to both sides to flow in a direction toward a through hole  431  formed at the first plate  430   a  being located at an opposite side against the second plate  430   b , and then flows in a heating medium passage P 1  of the unit plate  420  through a through hole  423  formed at the second plate  420   b  of the unit plate  420  being stacked over the first plate  430   a.    
         [0095]    Some of the heating medium, which flowed in the heating medium passage P 1  of the unit plate  420 , flows in a heating medium passage P 1  inside the unit plate  410  through a through hole  422  formed at the first plate  420   a  and a through hole  413  formed at the second plate  410   b  of the unit plate  410  being stacked over the first plate  420   a , and the remaining of the heating medium is branched off to both sides centering on the through hole  423  to flow in a direction toward a through hole  421  formed at the first plate  420   a  being located an opposite side against the second plate  420   b , and then flows in the heating medium passage P 1  inside the unit plate  410  through a through hole  412  formed at the second plate  410   b  of the unit plate  410  being stacked over the first plate  420   a.    
         [0096]    The heating medium, which flowed in the heating medium passage P 1  inside the unit plate  410  through the through hole  413  formed at the second plate  410   b , is branched off to both sides to flow toward a through hole  411  formed at the first plate  410   a  being located at an opposite side against the second plate  410   b , and then passes a through hole  392  formed at a lower cover panel  390   b  and a through hole  391  formed at an upper cover panel  390   a  to flow to the sensible-heat exchange unit  300 , wherein the lower cover panel  390   b  and the upper cover panel  390   a  configure the heat isolator  390 . Meanwhile, the heating medium is filled between the upper cover panel  390   a  and the lower cover panel  390   b , thereby preventing combustion heat of the sensible-heat exchange unit  300  from being transferred to the latent-heat exchange unit  400 . 
         [0097]    As described above, the passage of the heating medium is branched off to both sides at an upper left end of each of the unit plates  440  and  430  located at a lower stacked group of the latent-heat exchange unit  400  so that the heating medium flows in a direction toward a lower right end thereof, whereas the passage of the heating medium is branched off to both sides at a lower right end of each of the unit plates  420  and  410  being located at an upper stacked group of the latent-heat exchange unit  400  so that the heating medium flows in a direction toward an upper left end thereof, and thus a direction of the passage of the heating medium may be changed to form the passage of the heating medium to be long. 
         [0098]    Next, a flow channel of a heating medium in the sensible-heat exchange unit  300  will be described with reference to  FIGS. 5 and 14 . As arrows shown in  FIG. 14 , a heating medium, which passed the through hole  391  formed at the upper cover panel  390   a  of the heat isolator  390 , flows in a heating medium passage P 1  inside the unit plate  380  through a through hole  383  formed at the second plate  380   b  of the unit plate  380  that is located at a lower-most position of the sensible-heat exchange unit  300 . 
         [0099]    Some of the heating medium, which flowed in the heating medium passage P 1  inside the unit plate  380 , flows in a heating medium passage P 1  inside the unit plate  370  through a though hole  381  formed at the first plate  380   a  and a through hole  372  formed at the second plate  370   b  of the unit plate  370  being stacked over the first plate  380   a , and the remaining of the heating medium is branched off to both sides centering on the through hole  383  to flow in a direction toward a through hole  382  formed at the first plate  380   a  being located at an opposite side against the second plate  380   b  and then flows in the heating medium passage P 1  inside the unit plate  370  through a through hole  373  formed at the second plate  370   b  of the unit plate  370  being stacked over the first plate  380   a.    
         [0100]    The heating medium, which flowed in through the through hole  372  of the unit plate  370 , is branched off to both sides to flow in a direction toward a through hole  371  formed at the first plate  370   a  being located at an opposite side against the second plate  370   b , and then flows in a heating medium passage P 1  of the unit plate  360  through a through hole  363  formed at the second plate  360   b  of the unit plate  360  being stacked over the first plate  370   a.    
         [0101]    Some of the heating medium, which flowed in the heating medium passage P 1  of the unit plate  360 , flows in a heating medium passage P 1  inside the unit plate  350  through a through hole  362  formed at the first plate  360   a  and a through hole  353  formed at the second plate  350   b  of the unit plate  350  being stacked over the first plate  360   a , and the remaining of the heating medium is branched off to both sides centering on the through hole  363  to flow in a direction toward a through hole  361  formed at the first plate  360   a  being located at an opposite side against the second plate  360   b , and then flows in the heating medium passage P 1  inside the unit plate  350  through a through hole  352  formed at the second plate  350   b  of the unit plate  350  being stacked over the first plate  360   a.    
         [0102]    The heating medium, which flowed in through the through hole  353  of the unit plate  350 , is branched off to both sides to flow in a direction toward a through hole  351  formed at the first plate  350   a  being located at an opposite side against the second plate  350   b , and then flows in a heating medium passage P 1  of the unit plate  340  through a through hole  343  formed at the second plate  340   b  of the unit plate  340  being stacked over the first plate  350   a.    
         [0103]    Some of the heating medium, which flowed in the heating medium passage P 1  of the unit plate  340 , flows in a heating medium passage P 1  inside the unit plate  330  through a through hole  341  formed at the first plate  340   a  and a through hole  332  formed at the second plate  330   b  of the unit plate  330  being stacked over the first plate  340   a , and the remaining of the heating medium is branched off to both sides centering on the through hole  343  to flow in a direction toward a through hole  342  formed at the first plate  340   a  being located at an opposite side against the second plate  340   b , and then flows in the heating medium passage P 1  inside the unit plate  330  through a through hole  333  formed at the second plate  330   b  of the unit plate  330  being stacked over the first plate  340   a.    
         [0104]    The heating medium, which flowed in through the through hole  332  of the unit plate  330 , is branched off to both sides to flow in a direction toward a through hole  331  formed at the first plate  330   a  being located at an opposite side against the second plate  330   b , and then flows in a heating medium passage P 1  inside the unit plate  320  through a through hole  323  formed at the second plate  320   b  of the unit plate  320  being stacked over the first plate  330   a.    
         [0105]    Some of the heating medium, which flowed in the heating medium passage P 1  inside the unit plate  320 , flows in a heating medium passage P 1  inside the unit plate  310  through a through hole  322  formed at the first plate  320   a  and a through hole  313  formed at the second plate  310   b  of the unit plate  310  being stacked over the first plate  320   a , and the remaining of the heating medium is branched off to both sides centering on the through hole  323  to flow in a direction toward a through hole  321  formed at the first plate  320   a  being located at an opposite side against the second plate  320   b , and then flows in the heating medium passage P 1  inside the unit plate  310  through a through hole  312  formed at the second plate  310   b  of the unit plate  310  being stacked over the first plate  320   a.    
         [0106]    The heating medium, which flowed in the heating medium passage P 1  inside the unit plate  310 , is branched off to both sides centering on the through hole  313  to flow toward a through hole  311  formed at the first plate  310   a  being located at an opposite side against the second plate  310   b , and then is discharged through the heating medium discharge pipe  112 . 
         [0107]    As described above, the passage of the heating medium is branched off to both sides at the upper left end of each of the unit plates  380  and  370  located at lower-most positions in the sensible-heat exchange unit  300  so that the heating medium flows in a direction toward the lower right end of each of the unit plates  380  and  370 . And, the passage of the heating medium is branched off to both sides at the lower right end of each of the unit plates  360  and  350  located over the unit plates  380  and  370  so that the heating medium flows in a direction toward the upper left end of each of the unit plates  360  and  350 . In addition, the passage of the heating medium is branched off to both sides at the upper left end of each of the unit plates  340  and  330  being located over the unit plates  360  and  350  so that the heating medium flows in a direction toward the lower right end of each of the unit plates  340  and  330 . Further, the passage of the heating medium is branched off to both sides at the lower right end of each of the unit plates  320  and  310  being located over the unit plates  340  and  330  so that the heating medium flows in a direction toward the upper left end of each of the unit plates  320  and  310 . As a result, the direction of the passage may be alternately changed to form a passage of the heating medium to be long. 
         [0108]    Hereinafter, another embodiment of a flow channel of a heating medium will be described with reference to  FIGS. 15 to 17 . Unit plates  450 ,  460 ,  470 , and  480  according to the present embodiment may replace the above described unit plates configuring the sensible-heat exchange unit  300  and the latent-heat exchange unit  400 , and therefore, a structure of each of the unit plates  450 ,  460 ,  470 , and  480  configuring a single set and a flow channel of a heating medium inside the structure thereof may be described below. 
         [0109]    A flow channel of a heating medium according to the present embodiment is configured such that the heating medium, which flowed in through a through hole formed at one side of a second plate configuring one unit plate being located at a lower side among unit plates being longitudinally located to be adjacent to each other, flows in one direction along a heating medium passage P 1  and then passes a through hole formed at a first plate being located at an opposite side against the second plate and a through hole formed at a second plate configuring another unit plate being located at an upper side thereamong to flow in a heating medium passage P 1  of the other unit plate being located at the upper side. 
         [0110]    In a configuration for the purpose of implementing the described above, the passage forming protruding portion D 1  is formed to be communicated with some section at a region between the edge of the first plane portion A 1  and the first through hole B 1  along a circumferential direction, the passage forming depressed portion D 2  is formed to be communicated with some section at a region between the edge of the second plane portion A 2  and the second through hole B 2  along the circumferential direction, and a through hole is formed at the gap maintaining protruding portion E 1  and the gap maintaining depressed portion E 2  so as to connect a heating medium passage P 1  of a unit plate being located at the lower side to a heating medium passage P 1  of a unit plate being located at the upper side, wherein the through hole is located so as to reverse a direction of the heating medium passage P 1  at the unit plate being located at the lower side against that of the heating medium passage P 1  at the unit plate being located at the upper side. 
         [0111]    With reference to  FIGS. 16 and 17 , some of a heating medium, which flowed in a heating medium passage P 1  of the unit plate  480  through a through hole  483  formed at a second plate  480   b  of the unit plate  480  being located at a lower-most position, flows in a heating medium passage P 1  inside the unit plate  470  through a through hole  482  formed at a first plate  480   a  and a through hole  473  formed at a second plate  470   b  of the unit plate  470  being stacked over the first plate  480   a , and the remaining of the heating medium flows in one direction (a counterclockwise direction when viewed from the top plane) centering on the through hole  483  along the heating medium passage P 1 , and then flows in the heating medium passage P 1  inside the unit plate  470  through a through hole  481  formed at the first plate  480   a  being located at an opposite side against the second plate  480   b  and a through hole  472  formed at the second plate  470   b  of the unit plate  470  being stacked over the first plate  480   a.    
         [0112]    The heating medium, which flowed in the heating medium passage P 1  inside the unit plate  470 , flows in one direction (a counterclockwise direction when viewed from the top plane) centering on the through hole  473  along the heating medium passage P 1 , and then flows in a heating medium passage P 1  inside the unit plate  460  through a through hole  471  formed at a first plate  470   a  being located at an opposite side against the second plate  470   b  and a through hole  463  formed at a second plate  460   b  of the unit plate  460  being stacked over the first plate  470   a.    
         [0113]    Some of the heating medium, which flowed in the heating medium passage P 1  inside the unit plate  460  through the through hole  463 , flows in a heating medium passage P 1  inside the unit plate  450  through a through hole  461  formed at a first plate  460   a  and a through hole  452  formed at a second plate  450   b  of the unit plate  450  being stacked over the first plate  460   a , and the remaining of the heating medium flows in another direction (a clockwise direction when viewed from the top plane) centering on the through hole  463  along the heating medium passage P 1 , and then flows in the heating medium passage P 1  inside the unit plate  450  through a through hole  462  formed at the first plate  460   a  being located at an opposite side against the second plate  460   b  and a through hole  453  formed at the second plate  450   b  of the unit plate  450  being stacked over the first plate  460   a.    
         [0114]    The heating medium, which flowed in the heating medium passage P 1  of the unit plate  450 , flows in another direction (a clockwise direction viewed from the top plane) centering on the through hole  452  along the heating medium passage P 1 , and then flows in a heating medium passage of a unit plate (not shown) being located over a first plate  450   a  through a though hole  451  formed at the first plate  450   a  being located at an opposite side against the second plate  450   b.    
         [0115]    As described above, according to the present embodiment, the unit plates  480  and  470  being located at a lower group are configured to direct the heating medium to flow in one direction (the counterclockwise direction when viewed from the top plane) along the heating medium passage P 1 , whereas the unit plates  460  and  450  being located at an upper group are configured to direct the heating medium to flow in another direction (the clockwise direction when viewed from the top plane) along the heating medium passage P 1 , thereby alternately changing the flow direction of the heating medium to form the passage to be long. And, the unit plates  450 ,  460 ,  470 , and  480 , which have been described as an example in the present embodiment, may be stacked in a plurality of unit sets to configure the heat exchange units  300  and  400 . 
         [0116]    Meanwhile, as shown in  FIG. 18 , the heat isolator  390  may be configured to prevent combustion heat generated at the sensible-heat exchange unit  300  from being transferred to the latent-heat exchange unit  400  by filling a heating medium between the upper cover panel  390   a  and the lower cover panel  390   b  which are longitudinally stacked, and stacking an insulating material  390   c  on the upper cover panel  390   a . In this case, the heating medium filled between the upper cover panel  390   a  and the lower cover panel  390   b  may serve to perform an insulation function so that the insulating material  390   c  may be selectively used as necessary. 
         [0117]    Although the above described embodiments have exemplified the unit plates which configure the heat exchange units  300  and  400  and are formed to surround the burner  200  in a quadrangular shape, the unit plates may be configured in a polygonal shape including a pentagonal shape and the like in addition to the quadrangular shape, and an oval shape. Further, as shown in  FIGS. 19 and 20 , unit plates  610 ,  620 ,  630 ,  640 , and  650  may be arranged and configured in a circular shape. 
         [0118]    Meanwhile, as shown in  FIG. 20 , a heating medium connecting passage P may be additionally formed and configured at a lateral circumference of an upper part of the burner  200 , wherein the heating medium connecting passage P is connected to the heating medium passage P 1  located at the upper part of the burner  200 , thereby allowing a heating medium to pass the heating medium connecting passage P. 
         [0119]    With a configuration of the heating medium connecting passage P, it may prevent a burner supporting plate from being overheated by combustion heat transferred through the upper part of the burner  200 , and the combustion heat of combustion gas may be absorbed by the heating medium passing the heating medium connecting passage P such that insulation and thermal efficiency may be more improved. 
         [0120]    In the above described embodiments, although the heat exchange units  300  and  400  have been described as an example of a condensing type heat exchanger that is configured with the sensible-heat exchange unit  300  and the latent-heat exchange unit  400 , it should be understood that the heat exchanger of the present disclosure may be applicable to a general heat exchanger in which heat exchange is performed using only combustion sensible heat as well as a condensing type heat exchanger. 
         [0121]    As described above, the present disclosure is not limited to the described embodiments, and it should be construed that modifications can be apparently devised by those skilled in the art without departing from the technical spirit of this disclosure defined by the appended claims, and also such modifications will fall within the scope of this disclosure.