Abstract:
The present invention relates to a heat exchanger comprising: a burner for combusting a mixture of air and fuel; and a heat exchange unit in which heat is exchanged between combustion gas caused by the combustion of the burner and a heating medium, wherein the heat exchange unit includes a plurality of unit plates stacked on each other, and a sensible-heat exchange unit and a latent-heat exchange unit coaxially disposed around the burner are integrally formed with the unit plates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of International Application No. PCT/KR2015/002456 filed on Mar. 13, 2015, which claims priority to Korean Application No. 10-2014-0031442 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 having a simplified structure and also improving heat transfer efficiency between a heating medium and combustion gas by stacking a unit plate manufactured in a constant pattern to integrally form a sensible-heat exchange unit and a latent-heat exchange unit which are arranged at the circumference of a burner in a coaxial structure. 
       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 Registered Patent 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 Registered Patent 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 supplied 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 has 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 a 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 reducing the number of components configuring the heat exchanger and simplifying a coupling structure by stacking a unit plate to integrally configure a sensible heat exchanger and a latent heat exchanger, and also integrally configuring a heating medium passage, a combustion gas passage, and an outer wall structure sealing outer lateral surfaces of the heating medium passage and the combustion gas passage. 
         [0014]    Another 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 at maximum 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. 
         [0015]    Still another object of the present disclosure is to provide a heat exchanger capable of more improving thermal efficiency by collecting combustion heat of combustion gas into a heating medium at maximum, wherein the combustion gas is discharged through a discharge passage of the combustion gas. 
         [0016]    To realize the above described objects, a heat exchanger of the present disclosure includes a burner  200  configured to burn a mixture of air and fuel, and a heat exchange unit  300  configured to exchange heat between combustion gas generated by combustion of the burner  200  and a heating medium, wherein the heat exchange unit  300  is configured by stacking a plurality of unit plates, and a sensible-heat exchange unit  300 - 1  and a latent-heat exchange unit  300 - 2  are arranged at a circumference of the burner  200  in a coaxial structure to be integrally formed at the plurality of unit plates being stacked. 
         [0017]    A first heating medium passage P 1  and a first combustion gas passage P 2  are separately and alternately formed to be adjacent to each other at the sensible-heat exchange unit  300 - 1 , a second heating medium passage P 3  and a second combustion gas passage P 4  are separately and alternately formed to be adjacent to each other at the latent-heat exchange unit  300 - 2 , and a combustion gas discharge passage P 5  is formed at an edge of each of the plurality of unit plates to discharge combustion gas passed the first combustion gas passage P 2  and the second combustion gas passage P 4 . 
         [0018]    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 first passage forming protruding portion D 1  and a second passage forming protruding portion D 3  formed to be spaced apart from each other to an inward side and an outward side at a region between the edge of the first plane portion A 1  and the first through hole B 1  and having an upwardly convex shape, 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  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 and coupled to a first flange portion C 1  of a unit plate being located below the second plate, and a first passage forming depressed portion D 2  and a second passage forming depressed portion D 4  arranged to be spaced apart from each other to an inward side and an outward side at a region between the edge of the second plane portion A 2  and the second through hole B 2  and formed to be concave downward, wherein the first passage forming depressed portion D 2  may form the first heating medium passage P 1  between the first passage forming protruding portion D 1  and the first passage forming depressed portion D 2 , and the second passage forming depressed portion D 4  may form the second heating medium passage P 3  between the passage forming protruding portion D 3  and the second passage forming depressed portion D 4 . 
         [0019]    The first flange portion C 1  may be formed to be higher than a protruding height of each of the first passage forming protruding portion D 1  and the second passage forming protruding portion D 3 , the second flange portion C 2  may be formed to be deeper than a depressed depth of each of the first passage forming depressed portion D 2  and the second passage forming depressed portion D 4 , and thus a longitudinally separated space may be provided between a lower end of a first passage forming depressed portion D 2  of a unit plate being located at an upper side among unit plates being longitudinally located to be adjacent to each other, and an upper end of a first passage forming protruding portion D 1  of a unit plate being located at a lower side thereamong, thereby forming the first combustion gas passage 
         [0020]    P 2 , and a longitudinally separated space may be provided between a lower end of a second passage forming depressed portion D 4  of the unit plate being located at the upper side, and an upper end of a second passage forming protruding portion D 3  of the unit plate being located at the lower side, thereby forming the second combustion gas passage P 4 . 
         [0021]    A plurality of first gap maintaining protruding portions E 1  may be formed to protrude at the same height as that of the first flange portion C 1  at the first passage forming protruding portion D 1 , a plurality of second gap maintaining protruding portions E 3  may be formed to protrude at the same height as that of the first flange portion C 1  at the second passage forming protruding portion D 3 , a plurality of first gap maintaining depressed portions E 2  may be formed to be depressed at the same depth as that of the second flange portion C 2  at the first passage forming depressed portion D 2 , and a plurality of second gap maintaining depressed portions E 4  may be formed to be depressed at the same depth as that of the second flange portion C 2  at the second passage forming depressed portion D 4 . 
         [0022]    A first 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 5 , and a second combustion gas outlet F 2  may be formed at a position on the edge of the second plane portion A 2 , wherein the position longitudinally may correspond to the first combustion gas outlet F 1 , and thus combustion gas, which passed the first combustion gas passage P 2  and the second combustion gas passage P 4 , may sequentially pass the first combustion gas outlet F 1  and the second combustion gas outlet F 2  which are formed at each of the plurality of unit plates being longitudinally stacked, thereby being discharged. 
         [0023]    A turbulent flow forming portion G having an irregular shape on a surface thereof may be formed at the first passage forming protruding portion D 1 , the first passage forming depressed portion D 2 , the second passage forming protruding portion D 3 , and the second passage forming depressed portion D 4 , wherein a protruding upper end and a depressed lower end of the turbulent flow forming portion G may be formed to come into contact with each other inside the first heating medium passage P 1  and the second heating medium passage P 3 . As one embodiment, the first passage forming protruding portion D 1  may be formed to be entirely communicated along a circumferential direction of the first plate, the first passage forming depressed portion D 2  may be formed to be entirely communicated along a circumferential direction of the second plate, and a through hole may be formed at the first gap maintaining protruding portion E 1  and the first gap maintaining depressed portion E 2  so as to connect a first heating medium passage P 1  of the unit plate being located at the upper side to that of the unit plate being located at the lower side, wherein the through hole may be located to reverse a direction of the first heating medium passage P 1  in the unit plate being located at the upper side against that of the first heating medium passage P 1  in the unit plate being located at the lower side. 
         [0024]    In this case, a heating medium, which flowed in through a through hole formed at one side of a first plate configuring a unit plate being located at an upper side among unit plates that are longitudinally located to be adjacent to each other, may be branched off to both directions to flow along the first heating medium passage P 1 , and then may pass a through hole formed at a second plate being located at an opposite side against the first plate and a through hole formed at a first plate configuring a unit plate being located at a lower side, thereby flowing in a first heating medium passage P 1  of the unit plate being located at the lower side. 
         [0025]    As another embodiment, the first passage forming protruding portion D 1  may be formed to be partially communicated along a circumferential direction of the first plate, the first passage forming depressed portion D 2  may be formed to be partially communicated along a circumferential direction of the second plate, and a through hole may be formed at the first gap maintaining protruding portion E 1  and the first gap maintaining depressed portion E 2  so as to connect a first heating medium passage P 1  of the unit plate being located at the upper side to that of the unit plate being located at the lower side, wherein the through hole may be located so as to reverse a direction of the first heating medium passage P 1  in the unit plate being located at the upper side against that of the first heating medium passage P 1  of the unit plate being located at the lower side. 
         [0026]    A heating medium, which flowed in through a through hole formed at one side of a first plate configuring a unit plate located at an upper side among unit plates being longitudinally located to be adjacent to each other, may flow in one direction along the first heating medium passage P 1 , and then may pass a through hole formed at a second plate being located at an opposite side against the first plate and a through hole formed at a first plate configuring a unit plate being located at a lower side thereamong, thereby flowing in a first heating medium passage P 1  of the unit plate being located at the lower side. 
         [0027]    In the above described embodiments, multiple first heating medium passages P 1  may be configured in parallel with each other by stacking the unit plate. 
         [0028]    A heating medium inflow pipe  410  may be connected to a lower part of the latent-heat exchange unit  300 - 2 , wherein a heating medium may flow in the second heating medium passage P 3 , a passage connecting portion E may be provided at an upper part of each of the latent-heat exchange unit  300 - 2  and the sensible-heat exchange unit  300 - 1  and may be communicated with an upper part of the second heating medium passage P 3  and an upper part of the first heating medium passage P 1 , thereby guiding a heating medium passed the second heating medium passage P 3  to flow in the first heating medium passage P 1 , and a heating medium discharge pipe  420  may be connected to a lower part of the sensible-heat exchange unit  300 - 1  to discharge the heating medium passed the first heating medium passage P 1 . 
         [0029]    An upper duct  100  may be provided at an upper part of the heat exchange unit  300 , wherein combustion gas, which is passing the combustion gas discharge passage P 5  to flow upward, may be discharged through the upper duct  100 , and a lower duct  400  may be provided at a lower part of the heat exchange unit  300 , wherein a condensed water guide portion  401  may be formed at the lower duct  400  to guide condensed water of water vapor, which is contained in the combustion gas passing the combustion gas discharge passage P 5 , to a condensed water discharge pipe. 
         [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 first 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, the number of components of the heat exchanger may be reduced and a structure thereof may be simplified by integrally forming a sensible-heat exchange unit and a latent-heat exchange unit which are arranged to surround a burner in a coaxial structure inside unit plates being stacked in a multiple stage, and also configuring a heating medium passage, a combustion gas passage, and a combustion gas discharge passage together therewith. 
         [0033]    Also, a heat transfer area between a heating medium and combustion gas may be secured to be large by forming a heating medium passage to alternately change a flow channel through which the heating medium flows inside unit plates being stacked in a multiple stage to provide the flow channel of the heating medium to be long at maximum in a restricted space, and also thermal efficiency may be maximized by promoting generation of a turbulent flow in the flow of the heating medium and the combustion gas. 
         [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. 
         [0037]    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 form being overheated and more improving thermal efficiency. 
         [0038]    Furthermore, heat insulation efficiency between a sensible-heat exchange unit and a latent-heat exchange unit 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 unit and the latent-heat exchange unit. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0039]    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; 
           [0040]      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; 
           [0041]      FIG. 4  is an exploded perspective view of the heat exchanger according to one embodiment of the present disclosure; 
           [0042]      FIG. 5  is a plan view of the heat exchanger according to one embodiment of the present disclosure; 
           [0043]      FIG. 6  is a bottom view of the heat exchanger according to one embodiment of the present disclosure; 
           [0044]      FIG. 7  is a perspective view taken along line A-A of  FIG. 5 ; 
           [0045]      FIG. 8  is a dissected perspective view of a part of a unit plate; 
           [0046]      FIG. 9  is a cross-sectional view taken along line A-A of  FIG. 5 ; 
           [0047]      FIG. 10  is a cross-sectional view taken along line B-B of  FIG. 5 ; 
           [0048]      FIG. 11  is a cross-sectional view taken along line C-C of  FIG. 6 ; 
           [0049]      FIG. 12  is a cross-sectional view taken along line D-D of  FIG. 6 ; 
           [0050]      FIG. 13  is a diagram for describing a flow channel of a heating medium at the heat exchanger according to one embodiment of the present disclosure; 
           [0051]      FIG. 14  is a perspective view of a stacked structure of a unit plate according to another embodiment of the present disclosure; 
           [0052]      FIG. 15  is an exploded perspective view of  FIG. 14 ; 
           [0053]      FIG. 16  is a diagram for describing a flow channel of a heating medium at the unit plate shown in  FIG. 14 ; 
           [0054]      FIG. 17  is a perspective view of a stacked structure of a unit plate according to still another embodiment of the present disclosure; and 
           [0055]      FIGS. 18A and 18B  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 
       [0056]    Hereinafter, a configuration and an action with respect to a preferred embodiment of the present disclosure will be described in detail as follows with reference to the accompanying drawings. 
         [0057]    With reference to  FIGS. 2 to 5 , a heat exchanger according to the present disclosure includes an upper duct  100  at which a mixture inflow unit  110  and a flue  120  are formed, wherein a mixture of air and fuel flows in the mixture inflow unit  110  and the flue  120  discharges combustion gas; a burner  200  for burning the mixture flowing therein through the mixture inflow unit  110 ; a heat exchange unit  300  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 ,  390 , and  390 - 1  which are longitudinally stacked; and a lower duct  400  coupled to a lower part of the heat exchange unit  300 . 
         [0058]    The mixture inflow unit  110  is configured to include a mixture inflow pipe  111  and a support panel  112  supporting the burner  200  and blocking a leakage of combustion gas. 
         [0059]    The burner  200  burns a mixture of air and fuel flowing therein through the mixture inflow unit  110  to generate combustion gas of high temperature. The burner  200  is configured to be fixed to the support panel  112  to generate flame in a downward direction. 
         [0060]    As shown in  FIG. 7 , the heat exchange unit  300  is configured with a sensible-heat exchange unit  300 - 1  for absorbing sensible heat of combustion gas generated by combustion of the burner  200 , and a latent-heat exchange unit  300 - 2  for absorbing latent heat generated while water vapor contained in combustion gas, which has undergone heat exchange at the sensible-heat exchange unit  300 - 1 , is condensed. According to the present disclosure, the sensible-heat exchange unit  300 - 1  and the latent-heat exchange unit  300 - 2 , which have a coaxial structure centering on the burner  200 , are integrally configured at the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1  which are stacked in a multiple stage. 
         [0061]    In other words, the sensible-heat exchange unit  300 - 1  is located at an inside of each of the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1 , and the latent-heat exchange unit  300 - 2  is integrally formed at a position spaced apart from the sensible-heat exchange unit  300 - 1  to an outward side thereof. 
         [0062]    The lower duct  400  is connected to a heating medium inflow pipe  410  through which a heating medium flows in the latent-heat exchange unit  300 - 2 , and a condensed water discharge pipe  430  discharging condensed water from which water vapor contained in combustion gas passing the latent-heat exchange unit  300 - 2  is condensed to fall. 
         [0063]    Also, the lower duct  400  includes a condensed water guide portion  401  of a depressed shape for guiding falling condensed water to flow toward the condensed water discharge pipe  430 , and a flange portion  402  formed at an outer circumference of the condensed water guide portion  401  and coupled to a flange portion C 2  that is formed at a unit plate  390   a  being located at a lower-most position. 
         [0064]    Hereinafter, a configuration and an action of each of the sensible-heat exchange unit  300 - 1  and the latent-heat exchange unit  300 - 2  configuring the heat exchange unit  300 , which are a characteristic configuration of the present disclosure, will be described. 
         [0065]    The present disclosure is characterized in that the sensible-heat exchange unit  300 - 1  and the latent-heat exchange unit  300 - 2  are integrally formed at a plurality of unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1  configuring the heat exchange unit  300  and being longitudinally stacked, and also heating medium passages P 1  and P 3 , combustion gas passages P 2  and P 4  and a combustion gas discharge passage P 5  are formed together at the plurality of unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1 . 
         [0066]    With reference to  FIGS. 4, 7, 8, and 13 , the heat exchange unit  300  is configured with the plurality of unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1  being longitudinally stacked and having a similar pattern to each other. 
         [0067]    The unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1  are configured with first plates  310   a,    320   a,    330   a,    340   a,    350   a,    360   a,    370   a,    380   a,    390   a,  and  390   a - 1  (hereinafter, referred to as a ‘first plate’) which are located at upper parts of the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1 , and second plates  310   b,    320   b,    330   b,    340   b,    350   b,    360   b,    370   b,    380   b,    390   b,  and  390   b - 1  (hereinafter, referred to as a ‘second plate’) which are coupled to lower parts of the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1 . 
         [0068]    The first plate is configured to 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  extending 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 first passage forming protruding portion D 1  and a second passage forming protruding portion D 3 , which have an upwardly convex shape, arranged to be spaced apart to an inward side and an outward side at a region between the edge of the first plane portion A 1  and the first through hole B 1 . 
         [0069]    The second plate is configured to 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 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 ; and a first passage forming depressed portion D 2  and a second passage forming depressed portion D 4 , which are formed in a downwardly concave shape, arranged to be spaced apart to an inward side and an outward side at a region between the edge of the second plane portion A 2  and the second through hole B 2 , wherein the first passage forming depressed portion D 2  forms a first heating medium passage P 1  between the first passage forming protruding portion D 1  and the first passage forming depressed portion D 2 , and the second passage forming depressed portion D 4  forms a second heating medium passage P 3  between the second passage forming protruding portion D 3  and the second passage forming depressed portion D 4 . 
         [0070]    The first flange portion C 1  is formed to be higher than a protruding height of each of the first passage forming protruding portion D 1  and the second passage forming protruding portion D 3 , and the second flange portion C 2  is formed to be deeper than a depressed depth of each of the first passage forming depressed portion D 2  and the second passage forming depressed portion D 4 . 
         [0071]    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 first passage forming depressed portion D 2  of a unit plate located at an upper side thereamong and an upper end of a first passage forming protruding portion D 1  of a unit plate located at a lower side thereamong, thereby forming a first combustion gas passage P 2 , and a longitudinally separated space is provided between a lower end of a second passage forming depressed portion D 4  of a unit plate located at an upper side thereamong and an upper end of a second passage forming protruding portion D 3  of a unit plate located at a lower side thereamong, thereby forming a second combustion gas passage P 4 . 
         [0072]    And, a plurality of first 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 at the first passage forming protruding portion D 1 , a plurality of second gap maintaining protruding portions E 3 , each of which protrudes at the same height as that of the first flange portion C 1 , are formed at the second passage forming protruding portion D 3 , a plurality of first 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 first passage forming depressed portion D 2 , and a plurality of second gap maintaining depressed portions E 4 , each of which is depressed at the same depth as that of the second flange portion C 2 , are formed at the second passage forming depressed portion D 4 . 
         [0073]    Therefore, among unit plates being longitudinally stacked to be adjacent to each other, a second flange portion C 2  formed at a unit plate being located at an upper side thereamong is coupled to a first flange portion C 1  formed at a unit plate being located at a lower side thereamong, a lower end of a first gap maintaining depressed portion E 2  formed at the unit plate being located at the upper side comes into contact with an upper end of a first gap maintaining protruding portion E 1  formed at the unit plate being located at the lower side, and a lower end of a second gap maintaining depressed portion E 4  formed at the unit plate being located at the upper side comes into supporting contact with an upper end of a second gap maintaining protruding portion E 3  formed at the unit plate being located at the lower side. 
         [0074]    A first combustion gas outlet F 1  is formed at the edge of the first plane portion A 1  to provide the combustion gas discharge passage P 5 , and a second combustion gas outlet F 2  is formed at a position, which longitudinally corresponds to the first combustion gas outlet F 1 , on the edge of the second plane portion A 2 , and thus combustion gas, which passed the first combustion gas passage P 2  and the second combustion gas passage P 4 , sequentially passes the first combustion gas outlet F 1  and the second combustion gas outlet F 2  which are formed at each of the unit plates being longitudinally arranged, thereby being discharged. 
         [0075]    As described above, because the second flange portion C 2  of the upper side and the first flange portion C 1  of the lower side are coupled to each other, the first gap maintaining depressed portion E 2  and the second gap maintaining depressed portion E 4  of the unit plate being located at the upper side come into supporting contact with the first gap maintaining protruding portion E 1  and the second gap maintaining protruding portion E 3  of the unit plate being located at the lower side, respectively, and the first combustion gas outlet F 1  and the second combustion gas outlet F 2 , which are longitudinally communicated with each other, are formed at the edges of the first plate and the second plate, the first heating medium passage P 1  and the first combustion gas passage P 2  which configure the sensible-heat exchange unit  300 - 1 , the second heating medium passage P 3  and the second combustion gas passage P 4  which configure the latent-heat exchange unit  300 - 2 , and the combustion gas discharge passage P 5 , through which combustion gas passed the latent-heat exchange unit  300 - 2  is discharged toward the flue  120  of the upper duct  100 , may be integrally formed and also bond strength may be improved. 
         [0076]    Also, one among the passage forming protruding portions D 1  and D 3  and the passage forming depressed portions D 2  and D 4 , or all 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 each of the passage forming protruding portions D 1  and D 3  and the passage forming depressed portions D 2  and D 4 , 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. 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 the flow of a heating medium passing each of the heating medium passages P 1  and P 3  and the flow of combustion gas passing each of the combustion gas passages P 2  and P 2 . 
         [0077]    Further, when the turbulent flow forming portion G is formed at the passage forming protruding portions D 1  and D 3  of the first plate in an downward depressed shape and at the passage forming depressed portions D 2  and D 4  of the second plate in an upward protruding shape, thereby being configured to 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 inside the heating medium passages P 1  and P 3 , bond strength between the passage forming protruding portions D 1  and D 3  and the passage forming depressed portions D 2  and D 4  may be increased, thereby preventing the passage forming protruding portions D 1  and D 3  and the passage forming depressed portions D 2  and D 4  from being deformed and damaged due to pressure of the heating medium passing each of the heating medium passages P 1  and P 3 . 
         [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. With reference to  FIGS. 5 and 7 to 9 , a longitudinal flow of combustion gas generated by combustion of the burner  200  is blocked by the support panel  112  being located over the burner  200  and the unit plate  390 - 1  being located therebelow, and thus the combustion gas flows in a radially outward direction centering on the burner  200  to pass the first combustion gas passage P 2  of the sensible-heat exchange unit  300 - 1  and the second combustion gas passage P 4  of the latent-heat exchange unit  300 - 2 . While passing the first and second combustion gas passages P 2  and P 4 , the combustion gas transfers heat to a heating medium passing each of the first heating medium passage P 1  of the sensible-heat exchange unit  300 - 1  and the second heating medium passage P 3  of the latent-heat exchange unit  300 - 2 . 
         [0081]    In the course of passing the combustion gas passages P 2  and P 4 , 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 each of the passage forming protruding portions D 1  and D 3  and the passage forming depressed portions D 2  and D 4  so that heat transfer efficiency between the combustion gas and the heating medium may be increased. 
         [0082]    The combustion gas, which passed the second combustion gas passage P 4 , sequentially passes the combustion gas discharge passage P 5  and moves upward to be discharged to an outside through the flue  120  provided at the upper duct  100 , wherein the combustion gas discharge passage P 5  is 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 ,  390 , and  390 - 1  being longitudinally stacked. 
         [0083]    At this point, while the combustion gas is passing the combustion gas discharge passage P 5 , heat transferred to an outer wall of the combustion gas discharge passage P 5  is retransferred to the heating medium passing each of the heating medium passages P 1  and P 3  via the plane portions A 1  and A 2 , the passage forming protruding portions D 1  and D 3 , and the passage forming depressed portions D 2  and D 4  by a conducting method, and thus a heat loss may be minimized to more improve thermal efficiency. 
         [0084]    A flow channel of a heating medium is configured such that the heating medium flows in the first heating medium passage P 1  of the latent-heat exchange unit  300 - 2  through the heating medium inflow pipe  410  connected to a lower part of the latent-heat exchange unit  300 - 2  to move upward, and the heating medium moved to an upper side of the first heating medium passage P 1  flows in an upper side of the second heating medium passage P 3  of the sensible-heat exchange unit  300 - 1  to move downward, thereby being discharged through a heating medium discharge pipe  420  connected to a lower part of the sensible-heat exchange unit  300 - 1 , wherein the second heating medium passage P 3  is communicated through an inner space S of a passage connecting portion E formed at the first plate  310   a  of the unit plate  310  being located at an upper-most position. 
         [0085]    With reference to  FIGS. 6 and 11 to 13 , a flow channel of a heating medium will be described. 
         [0086]    Firstly, a flow channel of a heating medium of the latent-heat exchange unit  300 - 2  will be described. 
         [0087]    In the unit plates  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370 ,  380 ,  390 , and  390 - 1 , the second gap maintaining protruding portion E 3  and the second gap maintaining depressed portion E 4  are formed at four corners of each of the second passage forming protruding portion D 3  and the second passage forming depressed portion D 4 , respectively, and through holes  311 ,  321 ,  322 ,  324 ,  325 ,  331 ,  332 ,  335 ,  336 ,  341 ,  342 ,  344 ,  345 ,  351 ,  352 ,  355 ,  356 ,  361 ,  362 ,  364 ,  365 ,  371 ,  372 ,  375 ,  376 ,  381 ,  382 ,  384 ,  385 ,  391 ,  392 ,  395 ,  396 ,  391   a,    392   a,    392   b,  and  391   b,  some of which longitudinally correspond to each other, are formed at the second gap maintaining protruding portion E 3  and the second gap maintaining depressed portion E 4  which are diagonally opposite to each other. 
         [0088]    Consequently, a heating medium flowing in through the heating medium inflow pipe  410  flows in the second heating medium passage P 3  through the through hole  391   b  of the unit plate  390 - 1  being located at the lower-most position of the latent-heat exchange unit  300 - 2 , passes the through hole  311  formed at the unit plate  310  being located at the upper-most position thereof via each of the second heating medium passages P 3  of the unit plates being located from a lower position to an upper position of the latent-heat exchange unit  300 - 2 , and then moves to the upper side of the first heating medium passage P 1  of the sensible-heat exchange unit  300 - 1  through a through hole  312  formed at the unit plate  310  according to a switching of a passage by the passage connecting portion E. 
         [0089]    In this case, the heating medium may flow in and out the second heating medium passage P 3  formed inside the latent-heat exchange unit  300 - 2  through the through holes being formed diagonally opposite to each other to flow in both directions, and thus the flow channel of the heating medium may be formed to be long so that collection efficiency of latent heat may be increased. 
         [0090]    Next, one embodiment of a flow channel of a heating medium in the sensible-heat exchange unit  300 - 1  will be described. 
         [0091]    The present disclosure is configured such that a heating medium, which flowed in a through hole formed at one side of a first plate configuring a unit plate being located at an upper side among unit plates that are longitudinally located to be adjacent to each other, is branched off to both directions to flow along the first heating medium passage P 1 , and then passes a through hole formed at a second plate being located at an opposite side against the first plate and a through hole formed at a first plate configuring a unit plate being located at a lower side thereamong, thereby flowing in a first heating medium passage P 1  of the unit plate being located at the lower side. 
         [0092]    In a configuration for the purpose of implementing the described above, the first passage forming protruding portion D 1  is formed to be entirely communicated along a circumferential direction of the first plate, the first passage forming depressed portion D 2  is formed to be entirely communicated along a circumferential direction of the second plate, and a through hole is formed at the first gap maintaining protruding portion E 1  and the first gap maintaining depressed portion E 2  so as to connect a first heating medium passage P 1  of a unit plate located at the upper side to that of a unit plate located at the lower side, wherein the through hole is located so as to reverse a direction of the first heating medium passage P 1  at the unit plate located at the upper side against that of the first heating medium passage P 1  at the unit plate located at the lower side. 
         [0093]    Hereinafter, a flow channel of a heating medium in the sensible-heat exchange unit  300 - 1  will be described in more detail with reference to  FIGS. 4, 12 , and  13 . 
         [0094]    A heating medium, which flowed in first heating medium passages P 1  inside unit plates  320  and  330  being located at a lower side through a through hole  312  of a unit plate  310  located at an upper-most position and through holes  323 ,  327 , and  334  located below the through hole  312 , flows in an arrow direction toward through holes  326 ,  333 , and  337  being located diagonally opposite the through holes  323 ,  327 , and  334 . 
         [0095]    And, the heating medium, which flowed in first heating medium passages P 1  inside unit plates  340  and  350  being located at the lower side through the through hole  337  of the unit plate  330  and through holes  343 ,  346 , and  353  being located below the through hole  337 , flows toward through holes  347 ,  354 , and  357  being located diagonally opposite the through holes  343 ,  346 , and  353 . 
         [0096]    Thereafter, the heating medium, which flowed in first heating medium passages P 1  inside unit plates  360  and  370  being located at the lower side through the through hole  357  of the unit plate  350  and through holes  363 ,  367 , and  374  being located below the through hole  357 , flows toward through holes  326 ,  373 , and  377  being located diagonally opposite the through holes  363 ,  367 , and  374 . 
         [0097]    Afterward, the heating medium, which flowed in first heating medium passages P 1  inside unit plates  380  and  390  being located at the lower side through the through hole  377  of the unit plate  370  and through holes  383 ,  386 , and  393  being located below the through hole  377 , flows toward through holes  387 ,  394 , and  397  being located diagonally opposite the through holes  383 ,  386 , and  393 . 
         [0098]    And then, the heating medium, flowed inside a unit plate  390 - 1  through the through hole  397  of the unit plate  390  and a through hole  393   a  being located below the through hole  397 , is discharged to the heating medium discharge pipe  420  through a through hole  392   b  being located diagonally opposite the through hole  393   a.    
         [0099]    As described above, in the sensible-heat exchange unit  300 - 1 , the passage of the heating medium may be alternately changed in a direction from a lower left end to an upper right end and vice versa in the unit plates being located at the upper and lower sides, respectively. Consequently, the passage of the heating medium may be formed to be long so that heat transfer efficiency between the combustion gas and the heating medium may be increased. 
         [0100]    Hereinafter, another embodiment of a flow channel of a heating medium will be described with reference to  FIGS. 14 to 16 . Unit plates  510 ,  520 ,  530 , and  540  according to the present embodiment may replace the above described unit plates configuring the heat exchange unit  300  described above, and therefore, a structure of each of the unit plates  510 ,  520 ,  530 , and  540  configuring a single set and a flow channel of a heating medium inside the structure thereof will be described below. 
         [0101]    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 first plate configuring a unit plate being located at an upper side among unit plates being longitudinally located to be adjacent to each other, flows in one direction along the first heating medium passage P 1 , and then passes a through hole formed at a second plate being located at an opposite side against the first plate and a through hole formed at a first plate configuring a unit plate located at a lower side thereamong to flow in a first heating medium passage P 1  of the unit plate located at the lower side. 
         [0102]    In a configuration for the purpose of implementing the described above, the first passage forming protruding portion D 1  is formed to be partially communicated along a circumferential direction of the first plate, the first passage forming depressed portion D 2  is formed to be partially communicated along a circumferential direction of the second plate, and a through hole is formed at the first gap maintaining protruding portion E 1  and the first gap maintaining depressed portion E 2  so as to connect a first heating medium passage P 1  of a unit plate being located at the upper side to that of a unit plate being located at the lower side, wherein the through hole is located so as to reverse a direction of the first heating medium passage P 1  at the unit plate being located at the upper side against that of the first heating medium passage P 1  at the unit plate being located at the lower side. 
         [0103]    With reference to  FIGS. 15 and 16 , a latent-heat exchange unit has a structure similar to that of the above described implementation, and through holes  511 ,  512 ,  514 ,  515 ,  521 ,  522 ,  525 ,  526 ,  531 ,  532 ,  534 ,  535 ,  541 ,  542 ,  545 , and  546 , some of which longitudinally correspond to each other, are formed at a second gap maintaining protruding portion E 3  and a second gap maintaining depressed portion E 4 , which are located diagonally opposite to each other, of first plates  510   a,    520   a,    530   a,  and  540   a  and second plates  510   b,    520   b,    530   b,  and  540   b  of the unit plates  510 ,  520 ,  530 , and  540 . Therefore, a heating medium may flow in and out a second heating medium passage P 3  formed inside the latent-heat exchange unit through the through holes being formed diagonally opposite to each other to flow in both directions, and thus a flow channel of the heating medium may be formed to be long so that collection efficiency of latent heat may be increased. 
         [0104]    Next, a flow channel of a heating medium in a sensible-heat exchange unit will be described. 
         [0105]    A heating medium, which flowed in a first heating medium passage P 1  through a through hole  513  of the unit plate  510  being located at an upper side, flows in a counterclockwise direction when viewed from the top plane to a through hole  517 , and then flows in a first heating medium passage P 1  of the unit plate  520  through a through hole  516  and a through hole  524  being located therebelow. 
         [0106]    The heating medium, which flowed in the first heating medium passage P 1  of the unit plate  520 , flows in a counterclockwise direction when viewed from the top plane to a through hole  533  of the unit plate  530  being located below the unit plate  520 , and then flows in a first heating medium passage P 1  of the unit plate  530  through the through hole  533 . 
         [0107]    The heating medium, which flowed in the first heating medium passage P 1  of the unit plate  530 , flows in a clockwise direction toward a through hole  543  of the unit plate  540  being located below the unit plate  530 , and then flows in the unit plate  540  through the through hole  543 . Similarly, the heating medium also flows in the clockwise direction inside the unit plate  540 . 
         [0108]    In the present embodiment as described above, a flow direction of the heating medium may be configured to alternately change from the counterclockwise direction to the clockwise direction and vice versa in one unit plate being placed at the upper side and the other unit plate being located below the one unit plate being placed at the upper side, and thus the passage of the heating medium may be formed to be long so that thermal efficiency may be increased. 
         [0109]    The unit plates  510 ,  520 ,  530 , and  540  exemplified and described in the present embodiment may be stacked in a plurality of unit sets to configure the heat exchange unit  300 . 
         [0110]    Although the above described embodiments have exemplified the unit plates which configure the heat exchange unit  300  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  FIG. 17 , unit plates  610 ,  620 ,  630 , and  640  may be arranged and configured in a circular shape. The flow channels of the heating medium and the combustion gas in the unit plates  610 ,  620 ,  630 , and  640  shown in  FIG. 17  may be applicable the same as those of the above described embodiments, and thus a description thereof will be omitted. 
         [0111]    Meanwhile, as shown in  FIG. 18 , a heating medium connecting passage P may be additionally formed and configured at a lateral circumferential surface of an upper part of the burner  200 , wherein the heating medium connecting passage P is connected to the first heating medium passage P 1  being located at the upper part, thereby allowing a heating medium to pass the heating medium connecting passage P. 
         [0112]    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. 
         [0113]    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.