Abstract:
A heat exchanger comprises: flat tubes laminated on each other, an external fluid flowing in a space formed between the flat tubes arranged adjacent to each other; and fins interposed between the flat tubes, the fins being formed into a protruding and recessing shape having a flat plate portion joined to an outer wall face of the tube when viewed in the flow direction of the external fluid and having a vertical plate portion crossing the flat plate portion, wherein heat is exchanged between the external fluid and the internal fluid flowing in the tubes, the flat plate portion including protruding portions arranged so the protruding portions is inclined in the flow direction of the external fluid, protrusions of the protruding portions being increased toward the downstream side of the external fluid, the vertical plate portion being formed so it meanders in the flow direction of the external fluid.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a heat exchanger preferably used for exchanging heat between hot water to be supplied, which flows in tubes, and a combustion gas which flows in a fin region interposed between the tubes. 
   2. Description of the Related Art 
   Concerning the conventional heat exchanger, for example, JP-A-2003-106794 discloses a well known heat exchanger. This heat exchanger exchanges heat between the exhaust gas, which is discharged from an internal combustion engine, and the cooling water. In this heat exchanger, a plurality of wings (louvers, in this document) are provided in the exhaust gas flow direction on the inner wall side of the exhaust gas passage of the wave-shaped fins arranged in the exhaust gas passage. 
   Each wing is formed out of a face, the distance from the inner wall side of which is increased as it comes to the downstream side of the exhaust gas flow, arranged crossing the flow direction of the exhaust gas. 
   Due to the foregoing, vertical vortexes are formed when the exhaust gas moves over the wings. The vertical vortexes are drawn onto the inner wall side on the downstream side by a pressure difference between the side of the wing on the upstream side and the side of the wing on the downstream side. At the same time, the vertical vortexes are accelerated. Further, the exhaust gas passing in a gap, which is formed between the vertical plate section of the fins crossing the inner wall and the wings, is also accelerated by the vertical vortexes. Therefore, the heat transfer coefficient on the exhaust gas side can be enhanced and, further, an unburned substance, such as soot, attached to the fins can be blown away. Accordingly, while the fins are being prevented from clogging, the heat exchanging efficiency can be enhanced. 
   However, when the distribution of the flow velocity was analyzed in detail in the entire fin region in which a plurality of wings were arranged, the following results were obtained. In the heat exchanger of the present invention described later, as shown in  FIG. 8 , on the upstream side of the external fluid (combustion gas), it was possible to confirm the effect of the wings  123 . However, as it came to the downstream side, the external fluid flowed being separated from the wing  123 , and the generation of the vertical vortexes was attenuated and the flow velocity was lowered in the wing portions  123 . Investigations were also made into the heat flux as follows. As shown in  FIG. 9 , the same result as that of the above flow velocity distribution was obtained. That is, it was found that a sufficiently high effect of the wings  123  was not obtained. In this connection,  FIGS. 8A to 8D  are views respectively showing the flow velocity distributions (The flow velocity on the flow-in side is 7 m/s.) in the root portion, the middle portion and the forward end portion of the wings  123  and also showing the flow velocity distribution of the middle portion of the fin  120 .  FIG. 9A  is a view showing a heat flux distribution on the left of the vertical plate portion  122  of the fin  120  in  FIG. 9B ,  FIG. 9B  is a view showing a heat flux distribution on the flat plate portion  121  on the inner wall side of the fin  120 , and  FIG. 9C  is a view showing a heat flux distribution on the right of the vertical plate portion  122  of the fin  120  in  FIG. 9B . 
   SUMMARY OF THE INVENTION 
   The present invention has been achieved in view of the above problems. It is an object of the present invention to provide a heat exchanger capable of enhancing the heat exchanging performance by effectively generating vertical vortexes all over the region from the upstream side to the downstream side of the external fluid. 
   In order to accomplished the above object, the present invention adopts the following technical means. 
   According to a first aspect of the present invention, there is provided a heat exchanger comprising: a plurality of flat tubes ( 110 ) laminated on each other, an external fluid flowing in a space formed between the flat tubes ( 110 ) arranged adjacent to each other; and fins ( 120 ) interposed between the plurality of flat tubes ( 110 ), the fins ( 120 ) being formed into a protruding and recessing shape having a flat plate portion ( 121 ) joined to an outer wall face ( 110   a ) of the tube ( 110 ) when it is viewed in the flow direction of the external fluid and also having a vertical plate portion ( 122 ) crossing the flat plate portion ( 121 ), wherein heat is exchanged between the external fluid and the internal fluid flowing in the tubes ( 110 ), the flat plate portion ( 121 ) including a plurality of protruding portions ( 123 ) arranged so that the protruding portions ( 123 ) can be inclined in the flow direction of the external fluid, protrusions of the protruding portions ( 123 ) themselves being increased toward the downstream side of the external fluid, the vertical plate portion ( 122 ) being formed so that it can meander in the flow direction of the external fluid. 
   Due to the foregoing, vertical vortexes are formed in the external fluid by the protrusions ( 123 ), and the external fluid is accelerated. When the external fluid collides with the meandering vertical plate portion ( 122 ), the flow of the external fluid can be pushed back to the protrusion ( 123 ) side. Therefore, vertical vortexes can be repeatedly formed by the protrusions ( 123 ) all over the region from the upstream side to the downstream side of the external fluid. Accordingly, the heat exchanging performance can be enhanced. 
   In this connection, the second aspect of the present invention is preferably applied to a heat exchanger in which the external fluid is gas of high temperature containing steam, the internal fluid is fluid of low temperature, the temperature of which is lower than that of the gas of high temperature, and the fluid of low temperature is heated by recovering not only sensible heat from the gas of high temperature but also latent heat of condensation. Condensed water generated from the gas of high temperature at the time of heat exchange can be effectively discharged from the fins ( 120 ) by the action of the vertical vortexes (The flow velocity is increased.) generated in the gas of high temperature. Accordingly, it is possible to prevent the heat exchanging performance from deteriorating. 
   Incidentally, the reference numerals in parentheses, to denote the above means, are intended to show the relationship of the specific means which will be described later in an embodiment of the invention. 
   The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view showing a heat exchanger of the first embodiment. 
       FIG. 2  is a plan view showing a heat exchanger of the first embodiment. 
       FIG. 3  is a perspective view showing appearance of an outer fin. 
       FIGS. 4A to 4D  are velocity distribution charts respectively showing a distribution of flow velocity of the combustion gas in the first embodiment. 
       FIGS. 5A to 5C  are heat flux distribution charts respectively showing a distribution of heat fluxes on a fin surface in the first embodiment. 
       FIGS. 6A to 6D  are flow velocity distribution charts respectively showing a distribution of flow velocity of the combustion gas in another embodiment. 
       FIGS. 7A to 7C  are heat flux distribution charts respectively showing a distribution of heat fluxes on a fin surface in another embodiment. 
       FIGS. 8A to 8D  are flow velocity distribution charts respectively showing a distribution of the flow velocity of the combustion gas in the prior art. 
       FIGS. 9A to 9C  are heat flux distribution charts respectively showing a distribution of heat fluxes on a fin surface in the prior art. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   First of all, the first embodiment will be explained below. Referring to  FIGS. 1 to 3 , the first embodiment of the present invention is explained as follows. In this connection,  FIG. 1  is a front view showing a heat exchanger  100 ,  FIG. 2  is a plan view showing the heat exchanger  100 , and  FIG. 3  is a perspective view showing appearance of the outer fin  120 . 
   In the heat exchanger  100  of this embodiment, heat is exchanged between the hot water (corresponding to the internal fluid and the fluid of low temperature of the present invention) to be supplied which is used for a hot water supply unit and the combustion gas containing steam (corresponding to the external fluid and the gas of high temperature). Of course, the temperature of the hot water is lower than that of the combustion gas, and the hot water is heated by the combustion gas. As shown in  FIGS. 1 and 2 , this heat exchanger  100  is of the drawn cup type in which a plurality of flat tubes  110  are laminated on each other together with the outer fins  120 . After all the components have been assembled to each other, the entire body is soldered into one body. 
   The tube  110  is composed of two tube plates  111 ,  112  which are combined with each other. The tube  110  includes: a flat tube portion  110   a  in which a U-shaped water passage is formed; and a set of tank portions  110   b  which are communicated with both end portions of the water passage. The communicating port  110   c  is open to this tank portion  110   b.    
   A winding and fastening portion (not shown) is provided in the periphery of one tube plate  111 . The two tube plates  111 ,  112  are assembled by being wound and fastened in such a manner that the winding and fastening portion of one tube plate  111  is folded back from the inside to the outside of the other tube plate  112  and wound and fastened so that the end portions of the other tube plate  112  can be pinched from both sides, and then the contact face between both members is soldered. 
   The tank portion  110   b  is provided in such a manner that the thickness and width of the tank portion  110   b  are larger than those of the flat tube portion  110   a.  On the outer wall face of the tube plate  111 ,  112  composing the tank portion  110   b,  the flat face  110   d,  which becomes a soldered face, is annularly arranged round the communicating port  110   c.    
   A plurality of tubes  110  are laminated on each other so that the respective tank portions  110   b  can be contacted with each other, and the flat portions  110   d  provided round the communicating port  110   b  are joined to each other. Due to the foregoing, the water passages of the tubes  110  are communicated with each other via the communicating ports  110   c  which are open to the tank portions  110   b.  In this connection, in order to increase the heating surface area, inner fins (not shown) may be inserted into the tubes  110 . 
   Concerning the tube  110  arranged on one end side in the laminating direction, the hot water supply port  130  and the hot water discharge port  140  are joined to the tank portion  110   b.  The reinforcing plates  150  are respectively joined to both end sides of the tube  110  in the laminating direction. 
   Concerning the flat tube portion  110   a,  the thickness and width of which are smaller than those of the tank portion  110   b,  a flat space, the width of which is substantially constant, is formed between the flat tube portions  110   a  which are adjacent to each other. This space is a combustion gas passage  110   f  in which the combustion gas passes. In this combustion gas passage  110   f,  the outer fins (corresponding to the fins described in the present invention)  120  are arranged. 
   As shown in  FIG. 3 , the outer fins (referred to as fins hereinafter)  120  are made in such a manner that a sheet made of metal, the heat transmission property of which is high, is folded and formed into protruding and recessing portions. The fins  120  are arranged so that the combustion gas flows in the protruding and recessing spaces from the upper to the lower portion. These fins  120  are soldered onto the outer wall face  110   e  of the flat tube portion  110   a.  The combustion gas passage  110   f  is divided into a plurality of small passages  110   g  by the fins  120  which are folded into the protruding and recessing shape. 
   In this connection, among the wall faces of the fin  120  folded into the protruding and recessing shape, the wall face, which is arranged in parallel with the outer wall face  110   e  of the tube  110  and soldered to this outer wall face  110   e,  is a flat plate portion  121 . Among the wall faces of the fin  120  folded into the protruding and recessing shape, the side wall face, which crosses the flat plate portion  121 , is a vertical plate portion  122 . 
   In the flat plate portion  121  of the fin  120 , in almost all regions of the fin  120  arranged in the combustion gas passage  110   f,  a plurality of rising pieces (referred to as wings hereinafter)  123  are dispersedly provided at predetermined intervals. 
   In this case, the wing  123  is formed in such a manner that a triangular portion, except for one side of the triangle, is raised from the flat plate portion  121  of the fin  120 . Therefore, the wing  123  composes a protruding portion which protrudes into the combustion gas passage  110   f.  In this connection, the wing  123  is arranged so that the height (the protrusion) from the flat plate portion  121  can be increased toward the downstream side of the combustion gas flow. 
   The wing  123  is arranged so that it can be inclined by a predetermined angle with respect to the direction of the combustion gas flow. Two wings  123 , which continue to each other in the vertical direction of the fin  120 , are raised so that the inclination angles with respect to the direction of the combustion gas flow can be different from each other. In other words, the wings  123  are arranged zigzag in such a manner that the inclination angles are different from each other with respect to the combustion gas flow. In this connection, the height and width of the wing  123  are determined at values so that a wing  123  cannot close each combustion gas passage. 
   Further, the vertical plate section  122  of the fin  120  is formed so that it can meander in the combustion gas flow direction. In this connection, the flat plate portion  121  is formed into a meandering shape in which the flat plate portion  121  is arranged along the vertical plate portion  122 . Generally, the small passage  110   g  is formed into a meandering passage. 
   Next, the operation and the operational effect of this embodiment will be explained below. Hot water to be supplied flows from the hot water supply port  130  of the heat exchanger  100  into the tank portion  110   b  of each tube  110  and flows from one tank portion  110   b  into the water passage, which is formed in the flat tube portion  110   a,  and then flows out from the other tank portion  110   b  passing through the hot water discharge port  140 . On the other hand, as shown in  FIG. 1 , the combustion gas flows from an upper portion of the heat exchanger  100  to a lower portion. In this case, the temperature on the upstream side is approximately 200° C. When the combustion gas passes through the heat exchanger  100 , heat is exchanged between the combustion gas and the hot water to be supplied, so that the hot water to be supplied can be heated. At this time, on the discharge port side of the heat exchanger  100 , the temperature of the combustion gas is lowered to a value (for example, 30 to 50° C.) not higher than the dew point. Therefore, steam contained in the combustion gas is condensed. That is, this heat exchanger  100  can heat the hot water to be supplied when the heat exchanger  100  absorbs not only the sensible heat of the combustion gas but also the latent heat of condensation which is emitted when the combustion gas is condensed. 
   In this case, when the combustion gas flows in the small passage  110   g,  a vertical vortex is formed in the combustion gas by the wing  123  or the combustion gas is accelerated. When the combustion gas collides with the meandering vertical plate portion  122 , the combustion gas can be pushed back toward the wing  123  side. Therefore, all over the entire range from the upstream side to the downstream side of the combustion gas, vertical vortexes can be repeatedly formed by the wings  123 , and the heat exchanging performance can be enhanced. 
   Condensed water generated from the combustion gas at the time of heat exchange can be effectively discharged from the fins  120  by the effects of the vertical vortexes (an increase in the flow velocity) generated in the combustion gas. Accordingly, it is possible to prevent the heat exchanging performance from being deteriorated by the condensed water. 
   In this connection,  FIG. 4  is a view showing a flow velocity distribution of the combustion gas in this embodiment.  FIG. 5  is a view showing a heat flux distribution in this embodiment. The portion to be measured and the condition of the measurement are the same as those of  FIG. 8  and  FIG. 9  (the prior art). In this embodiment, the following was confirmed. As compared with the prior art, by the meandering vertical plate section  122  in addition to the wings  123 , the vertical vortexes were effectively formed even on the downstream side, and the flow velocity and the heat flux were enhanced. 
   In this embodiment, a quantity of heat exchanged in the heat exchanger  100  was confirmed as follows. It was confirmed that the quantity of heat exchanged in the heat exchanger  100  was enhanced by 6% with respect to the prior art. This confirmation was made at the time when the upstream side combustion gas flow rate was 7 m/s. In this connection, it was confirmed that the quantity of heat exchanged in the heat exchanger  100  was enhanced by 8% even in the low flow rate region (the flow rate: 3.5 m/s) of the combustion gas. 
   Finally, another embodiment will be explained below. The direction of the inclination of the wing  123  with respect to the flow direction of the combustion gas may be reverse to that of the first embodiment. In this case, the same effect as that of the first embodiment can be obtained as shown in  FIGS. 6 and 7 . 
   In the embodiment explained above, the fin  120  is formed into a shape which is bent into a rectangular shape as shown in  FIG. 3 . However, as long as the fin  120  has a sufficiently large flat plate portion  121  for forming the wing  123 , any shape of the fin  120  can be employed. A fin, the folded portion of which is formed so that it can have an R-shaped portion, may be employed. 
   On the wall face of the tube  110  opposed to the flat plate portion  121  on which the wing  123  is formed, a protruding and recessing portion, which protrudes into the combustion gas passage  110   f,  may be formed, for example, by means of embossing. 
   The objective heat exchanger is not limited to the above heat exchanger  100  used for hot-water-supply units. The present invention can be applied to radiators and evaporators other than the hot-water-supply units. 
   While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.