Patent Publication Number: US-8985192-B2

Title: Plate fin heat exchanger

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a so-called plate fin heat exchanger which is internally provided with fin plates. 
     2. Description of the Related Art 
     As the plate fin heat exchanger (hereinafter also simply referred to as “heat exchanger”), the one described in Japanese Patent Application Laid-Open No. 7-167580 is conventionally known. This heat exchanger includes a heat exchange part including plural flow passages for carrying first fluid and flow passages for carrying second fluid alternately arranged within a casing. Concretely, as shown in  FIGS. 4A and 4B , a heat exchange part  100  includes a plurality of partition plates  102  placed in parallel at intervals; corrugated plate-like fin plates  104  each of which is placed between the partition plates  102 ; and sealing members  106  placed on both sides of the fin plates  104  in their width direction so as to sandwich them, the sealing members  106  sealing the space between the partition plates  102  along the fin plate  104  to form a flow passage r together with the partition plates  102  therein. In order to transfer the heat of a fluid flowing in the flow passage r with the fin plate  104  placed therein to a pair of partition plates  102  with the fin plate  104  therebetween, the plate fin  104  connects the pair of partition plates  102  at specific positions arranged at intervals between one sealing member  106  and the other sealing member  106  (refer to  FIG. 4B ). In the thus-constituted heat exchange part  100 , a number of flow passages r are arranged in layers. 
     In this heat exchanger, each of two kinds of fluids (e.g., high-temperature fluid and low-temperature fluid) are alternately flowed in each of plural layers of flow passages r arranged in the heat exchange part  100  in order to perform heat exchange between the two kinds of fluids flowing in adjacent flow passages through the partition plate  102 . At that time, the fin plate  104  transfers the heat of the fluid flowing between the pair of partition plates  102  with the fin plate  104  therebetween to the pair of partition plates  102 , whereby the efficiency of the heat exchange is improved. The thus-constituted heat exchanger is used as heat exchangers for various purposes such as an air separator which requires compactness since it has a relatively simple structure and a high overall heat transfer coefficient. 
     Protection parts  110  each provided with an internal space r 1  are generally disposed on both outsides of the above-mentioned heat exchange part  100  respectively in the arrangement direction of the flow passages r of the heat exchange part  100  (in the vertical direction in  FIG. 4B ). The protection part  110  is a member provided to protect the flow passage r for carrying the fluid from damage attributed to a contact of the heat exchange part  100  with other members, etc. at the time of the installation or transfer, etc. of the heat exchanger. Namely, even if the heat exchange part  100  is contacted with other members and the outer surface of the heat exchange part  100  dents, the dent occurs only within the range of the protection part  110 , and therefore the deformation resulting from the dent is not generated on the partition plates  102  constituting the flow passages r, etc. which are inside the protection part  110 . The protection part  110  has the same structure as each flow passage r of the heat exchange part  100 . 
     In the above-mentioned heat exchange part  100 , since the sealing member  106  generally has higher rigidity than the fin plate  104 , and the fin plate  104  generally has more excellent heat transfer performance than the sealing member  106 , the following property to thermal change is higher in the fin plate  104  than in the sealing member  106 . Therefore, if the temperature of the fluid flowing in each flow passage r in the heat exchange part  100  suddenly changes, the fin plate  104  deforms more largely than the sealing member  106  in each flow passage r based on this temperature change. Such a difference in the temperature change-based deformation amount between the sealing member  106  and the fin plate  104  causes a stress (thermal stress) based on this difference in deformation amount in a specific site of the heat exchange part  100 . Concretely, although the sealing member  106  does not expand so much by a sudden temperature change of the fluid (e.g., 50° C./min, etc.), the fin plate  104  is apt to expand more largely than the sealing member  106 . At that time, as shown in  FIG. 5 , although the space between a pair of partition plates  102  with the flow passage r therebetween is not changed largely in the vicinity of a site where the highly rigid sealing member  106  is disposed, the space is expanded by the expansion of the fin plate  104  in a site distant from the sealing member  106  or in the width-directional center site of the flow passage r. Such deformation of the partition plates  102  causes the deformation-attributed stress (thermal stress) in a specific site of the partition plates  102 . This thermal stress generally generates, upon a sudden change in flow rate or temperature in the heat exchange part  100 , due to the difference in the deformation amount based on the change in temperature or the like of each member, and such thermal stress attributed to the difference in deformation amount of each member is similarly caused in the specific site not only by the change in temperature or the like of the high-temperature fluid but also by the change in temperature or the like of the low-temperature fluid. 
     In general, since a number of (e.g., several hundreds) flow passages r are arranged in layers in the heat exchange part  100 , the deformation amount from the initial position of the partition plate  102  separating the flow passages r from each other is increased from the center toward the outer side (the upper side and lower side in  FIG. 5 ) in the arrangement direction of the flow passages r. This is attributed to that the deformation amount in each layer (each flow passage) is added from the center toward the outer side as shown in  FIG. 5 . 
     Therefore, as in the case where the heat exchanger is used in a chemical plant, for example, the deformation is repeated at each time of sudden change in temperature of the fluid performing the heat exchange or start-stop during the entire period of use, and as a result, the fatigue based on the thermal stress is accumulated most in a specific position of the partition plate  102  which receives the largest deformation amount and separates the protection part  110  from the flow passage r on the inside of the protection part  110 , whereby the probability of damage such as hole or cracking in the partition plate  102  becomes high. 
     If damage such as hole occurs in the partition plate  102  at this position, the fluid flowing in the flow passage r flows into the internal space r 1  of the protection part  110 . Since the fluid in high-pressure state flows in the flow passage r of the heat exchange part  100  in operation, continuous outflow of the fluid from the flow passage r into the internal space r 1  of the protection part  110  can lead to leak of the fluid from the internal space r 1  of the protection part  110  to the outside of the heat exchanger due to the gradual increase of pressure within the protection part  110 . 
     Thus, for preventing such leak of the fluid out of the heat exchanger, it has been considered to enhance the rigidity of the fin plate  104  or to suppress the deformation amount of the partition plate  102  between the flow passages r by inserting a reinforcing member into each of the flow passages r to suppress the deformation amount of the partition plate  102  and thereby the accumulation of fatigue. 
     However, when the rigidity of the fin plate  104  is enhanced in this way, the heat conductivity of the fin plate  104  is reduced, whereby the heat exchange efficiency of the heat exchange part  100  is deteriorated, resulting in deterioration of performance of the heat exchanger. The use of the reinforcing member involves a problem such as increase in size or weight of the device. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned problems, the present invention thus has an object to provide a plate fin heat exchanger, capable of preventing the external leak of fluids performing heat exchange while suppressing the deterioration of performance or the increase in size or weight. 
     The present invention provides a plate fin heat exchanger configured to perform heat exchange between plural fluids, comprising: a heat exchange part main body including layers of flow passages for carrying each of the plural fluids arranged with partition walls each of which is arranged between each of two adjacent said flow passages respectively; heat transfer members each of which is disposed within each of said flow passages of said heat exchange part main body respectively, each of said heat transfer member connecting said partition walls opposed across each of said flow passages to transfer the heat of the fluid flowing in each of said flow passages to said opposed partition walls; sensing parts connected to both outer sides of said heat exchange part main body in the arrangement direction of said flow passages respectively, each of said sensing parts including a plurality of sealed spaces arranged in the arrangement direction of said flow passages, and a sensor wall disposed to separate an outermost sealed space of said plural sealed spaces from a sealed space on the inner side of said outermost sealed space; and a detection means for detecting damage of said sensor wall. 
     According to this configuration, by placing the sensor wall which is free from external leak of fluid even in the event of damage such as hole or cracking in a position where the fatigue by the thermal stress based on the heat of the fluid is accumulated more than in each partition wall of the heat exchange part, accumulation of the thermal stress-based fatigue in each partition wall can be detected by causing the sensor wall to be damaged by the thermal stress prior to each partition wall and detecting this, and repair or the like can be performed before each partition wall is actually damaged by the accumulation of fatigue to cause the external leak of the fluid. Further, by providing the detection means for detecting damage of the sensor wall, the fatigue by the thermal stress based on the heat of the fluid, which is accumulated in each partition wall, can be detected without external leak of the fluid. 
     Concretely, when a sudden change in temperature or flow rate of fluid occurs, the space between the partition walls opposed across each flow passage is expanded by the thermal expansion of the heat transfer member to deform each partition wall. The deformation amount from the initial position in the outer partition wall in the arrangement direction of the flow passages is larger than that in the central partition wall. This is attributed to that the deformation is repeated in such a manner that a partition wall closer to the center deforms, and a partition wall on the outer side of this deformed partition wall further deforms by the thermal expansion of the heat transfer member disposed between the partition wall and the partition wall closer to the center. Accordingly, the sensing part is provided on the further outer side of the outermost flow passage in the arrangement direction of the flow passages, a plurality of sealed spaces arranged in the same direction as the flow passages is provided in the sensing part, and the sensor wall is provided in a position to separate the sealed spaces from each other, whereby the sensor wall is deformed most seriously based on the thermal stress. Therefore, the sudden change in temperature or the like of the fluid or the start-stop of the heat exchanger is repeated, and the deformation and return to initial position based on the heat of the fluid are consequently repeated, and as a result, the accumulation of the thermal stress-based fatigue is largest in the sensor wall. Thus, by placing the sensor wall in the position with the largest accumulation of the thermal stress-based fatigue in a manner such that no external leak of fluid is generated even if the sensor wall is damaged, and detecting damage such as hole generated in this sensor wall, the accumulation of the thermal stress-based fatigue in each partition wall can be detected before the partition wall is actually damaged. 
     In the plate fin heat exchanger according to the present invention, the detection means preferably includes a pressurizing means for pressurizing the inside of one of the two sealed spaces with the sensor wall therebetween, and a pressure measuring means for measuring pressure in the other sealed space. 
     According to this structure, it is possible to accurately detect the presence of even initial damage, or minute hole or cracking generated in the sensor wall by maintaining the pressure in the one sealed space by the pressurizing means and measuring the pressure in the other sealed space by the pressure measuring means while. 
     Concretely, by maintaining the pressure in the one sealed space at constant level by the pressurizing means, in case of the generation of damage such as hole in the sensor wall, the fluid (e.g., nitrogen gas, etc.) in one sealed space leaks from the one sealed space to the other sealed space through the hole or the like, and the pressure in the other sealed space rises. Therefore, this pressure is measured by the pressure measuring means, whereby the presence of damage of the sensor wall can be detected. 
     Preferably, the heat exchange part main body includes an outside partition wall which separates an outermost flow passage of the flow passages in the arrangement direction of the flow passages from the outside, and each of the sensing parts is connected to the heat exchange part main body so that an innermost sealed space of the sealed spaces in the arrangement direction of the flow passages is adjacent to the outermost flow passage of the heat exchange part main body with the outside partition wall therebetween, and has strength enough to endure a situation such that the pressure within each of the sealed spaces is equal to the pressure within each of the flow passages with the fluid flowing therein of the heat exchange part main body. 
     According to this structure, even if the outside partition wall between the heat exchange part main body and the sensing part is damaged during operation of the heat exchanger, and the fluid flows into the sealed space of the sensing part through the damaged part, breakage of the sensing part by the pressure of this fluid can be prevented. Further, since the fluid leaked into the sealed space is confined within the sealed space, the fluid can be prevented from further leaking to the outside. 
     The heat exchanger preferably includes a fluid detection means for detecting the presence of the fluid in the innermost sealed space of the sealed spaces in the arrangement direction of the flow passages. 
     According to this structure, even if the fluid flows from the outermost flow passage in the arrangement direction of the flow passages of the heat exchange part into the innermost sealed space of the sensing part during the operation of the heat exchanger, the fluid detection means detects this outflow, whereby the outflow of the fluid from the flow passage can be easily and surely detected. Further, since the fluid leaked to the innermost sealed space is confined within the sealed space, the fluid can be prevented from further leaking to the outside. 
     Each of the sensing parts preferably has two of the sealed spaces. By providing two sealed spaces in each sensing part, the fatigue by the thermal stress based on the heat of the fluid, which is accumulated in each partition wall, can be detected without external leak of the fluid while suppressing the increase in size and weight of the heat exchanger. 
     According to the present invention, it is possible to provide a plate fin heat exchanger capable of preventing external leak of fluid performing the heat exchange while suppressing deterioration of performance or increase in size and weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural view of a plate fin heat exchanger according to one preferred embodiment of the present invention; 
         FIG. 2  is a partially enlarged perspective view with partial cutaway of a heat exchange part in the plate fin heat exchanger; 
         FIG. 3  is a cross-sectional schematic view of the heat exchange part and sensing parts; 
         FIG. 4  illustrate a heat exchange part in a conventional heat exchanger, wherein  FIG. 4A  is an exploded perspective view thereof and  FIG. 4B  is a front view thereof; and 
         FIG. 5  is a typical view showing a thermally expanded state of the conventional heat exchange part. 
     
    
    
     PREFERRED EMBODIMENTS OF THE PRESENT INVENTION 
     One preferred embodiment of the present invention will be described in reference to the accompanying drawings. 
     A plate fin heat exchanger (hereinafter also simply referred to as “heat exchanger”) according to the present invention is adapted to perform heat exchange between a first fluid and a second fluid both flowing therein. More specifically, as shown in  FIGS. 1 to 3 , a heat exchanger  1  includes a vertical box-shaped casing  2 ; and a heat exchange part  3  provided within the center of the casing  2 , in which a first flow passage  30   a  for carrying a first fluid F 1  and a second flow passage  30   b  for carrying a second fluid F 2  are alternately arranged. 
     The casing  2  includes a bottom header  21  and a top header  22  for the first fluid provided at the bottom and at the top thereof respectively. The casing  2  further includes an upside header  23  and a downside header  24  for the second fluid provided at an upside and a downside portions thereof respectively. A first fluid inlet pipe  21   a  for taking in the first fluid F 1  into the heat exchanger  1  is connected to the bottom header  21 , and a first fluid outlet pipe  22   a  for discharging the first fluid F 1  out of the heat exchanger  1  is connected to the top header  22 . A second fluid inlet pipe  23   a  for taking in the second fluid F 2  into the heat exchanger  1  is connected to the upside header  23 , and a second fluid outlet pipe  24   a  for discharging the second fluid F 2  out of the heat exchanger  1  is connected to the downside header  24 . 
     A heat exchange part  3  is disposed at a vertically central portion within the casing  2 , and an upper distribution part  25  and a lower distribution part  26  are disposed over and below the heat exchange part  3  respectively. The upper distribution part  25  is an area for guiding the second fluid F 2  taken into the upside header  23  from the second fluid inlet pipe  23   a  to each second flow passage  30   b  of the heat exchange part  3  and also guiding the first fluid F 1  passed through each first flow passage  30   a  of the heat exchange part  3  to the top header  22 . On the other hand, the lower distribution part  26  is an area for guiding the first fluid F 1  taken into the bottom header  21  from the first fluid inlet pipe  21   a  to each first flow passage  30   a  of the heat exchange part  3  and also guiding the second fluid F 2  passed through each second flow passage  30   b  of the heat exchange part  3  to the downside header  24 . 
     According to such a structure, the first fluid F 1  supplied to the heat exchanger  1  is taken from the first fluid inlet pipe  21   a  into each first flow passage  30   a  of the heat exchange part  3  successively through the bottom header  21  and the lower distribution part  26 , passed through each first flow passage  30   a , and then discharged from the first fluid outlet pipe  22   a  successively through the upper distribution part  25  and the top header  22 . On the other hand, the second fluid F 2  supplied to the heat exchanger  1  is taken from the second fluid inlet pipe  23   a  into each second flow passage  30   b  of the heat exchange part  3  successively through the upside header  23  and the upper distribution part  25 , passed through each second flow passage  30   b , and then discharged from the second fluid outlet pipe  24   a  successively through the lower distribution part  26  and the downside header  24 . 
     The heat exchange part  3  includes a heat exchange part main body  31  in which a number of flow passages  30  (the first flow passages  30   a  and the second flow passages  30   b ) are arranged in layers by alternately placing the first flow passages  30   a  and the second flow passages  30   b ; and a fin plate (heat transfer member)  32  arranged within each of the flow passages  30 . The heat exchange part main body  31  includes a plurality of partition plates (partition walls)  33 , and a side bar  34  connecting the partition plates  33  to each other. The partition plate  33  is a plate-like member capable of transferring heat between one surface and the other surface thereof, and in this embodiment, a rectangular plate-like member formed of aluminum alloy such as A3003 is adopted. The plurality of partition plates  33  are disposed at intervals and parallel to each other. As materials of the partition plate  33 , an aluminum alloy such as A3003 is used in this embodiment as an example, and titanium, copper, stainless steel or the like may be used. 
     The side bar  34  is a member which connects opposed partition plates  33  of the plurality of partition plates  33  disposed at intervals, and forms the flow passage  30  between the opposed partition plates  33  by sealing the space between the partition plates  33 . The side bars  34  are disposed along both sides of the space between each two of the partition plates  33 , and extend vertically along the sides of the partition plates  33  while sealing the space between each of the adjacent two of the partition plates  33 . As materials of the side bar  34 , an aluminum alloy such as A3003 is used in this embodiment as an example, and titanium, copper, stainless steel or the like may be used. 
     By disposing the partition plates  33  and the side bars  34  in this manner, the flow passage  30  enclosed by a pair of partition plates  33  and a pair of side bars  34  disposed between these partition plates  33  is formed between each two of the partition plates  33 . Accordingly, in the heat exchange part  3 , a number of flow passages  30  are arranged in layers (refer to  FIG. 3 ). The passages  30  include the first flow passages  30   a  for carrying the first fluid F 1  and the second flow passages  30   b  for carrying the second fluid F 2 . The first flow passage  30   a  and the second flow passage  30   b  have the same structure. In this embodiment, since each of the first fluid F 1  and the second fluid F 2  are alternately flowed through each of the number of flow passages  30  arranged in layers, the first flow passages  30   a  and second flow passages  30   b  are alternately arranged in the heat exchange part  3 . 
     The fin plate  32  is a member disposed within each flow passage  30  to connect the partition plates  33  opposed across the flow passage  30  and to transfer the heat of the fluid F 1  or F 2  flowing in the flow passage  30  to the opposed partition plates  33 . Namely, the fin plate  32  is a member for improving the heat exchange efficiency of the heat exchange part  3  by ensuring, within each flow passage  30 , the contact area with the fluid flowing in the flow passage  30 . Concretely, the fin plate  32  is a sheet member repetitively protruded and recessed in the width direction of the flow passage  30  (the direction of arrow α in  FIG. 2 ) so as to alternately contact with the partition plates  33  opposed across the fin plate  32 , in other words, a corrugated plate-like member. The thus-constituted fin plate  32  is larger in thermal expansion coefficient than the side bar  34 . This difference in thermal expansion coefficient is resulted from the difference in heat capacity or rigidity of each member based on shape, size or the like. As materials of the fin plate  32 , an aluminum alloy such as A3003 is used in this embodiment as an example, and titanium, copper, stainless steel or the like may be used. 
     Sensing parts  35  are connected respectively to both outer sides in the arrangement direction of the flow passages  30  (in the vertical direction in  FIG. 3 ) of the thus-constituted heat exchange part  3 . In other words, the sensing parts  35  are connected to the heat exchange part  3  so as to sandwich the heat exchange part  3  from both the outer sides in the arrangement direction of the flow passages  30 . Each of the sensing parts  35  includes a sensor plate (sensor wall)  36  which is more easily damaged by the thermal stress based on the heat of the fluid flowing in the flow passage  30  than each partition plate  33  of the heat exchange part  3 . Concretely, each sensing part  35  internally has a plurality of (two in this embodiment) sealed spaces  30   c  arranged in the arrangement direction of the flow passages  30 , and the sensor plate  36  is disposed so as to separate the outermost sealed space  30   c  in the arrangement direction of the plurality of sealed spaces  30   c  from the sealed space  30   c  on the inner side thereof. 
     In this embodiment, the sensing part  35  is formed integrally with the heat exchange part  3 . Concretely, the sensing part  35  is formed by placing a plurality of (two in this embodiment) partition plates  33  along each both of the outer sides of the heat exchange part  3  in the arrangement direction of the flow passages  30  in parallel and at intervals, and sealing the entire circumference of the space between each two of the partition plates  33  including the same fin plate  32   a  as in the heat exchange part  3  therein with side bars  34   a . In the sensing part  35 , the sealed space  30   c  is formed between a pair of partition plates  33  by sealing the entire circumference of the pair of partition plates  33  with the side bars  34   a . The second outermost partition plate  33  in the arrangement direction of the flow passages  30  constitutes the sensor plate  36 . Namely, since the degree of accumulation of the fatigue by the thermal stress based on the heat of the fluid F 1  or F 2  is differed among the plurality of partition plates  33  arranged in parallel depending on the arrangement position thereof, and the accumulation of the fatigue is largest in the second outermost partition plate  33  in this embodiment, the partition plate  33  of this position is taken as the sensor plate  36 . This is attributed to that the deformation amount from the initial position of the partition plate  33  based on the difference in thermal expansion coefficient between the fin plate  32  and the side bar  34  is increased toward the outer side in the arrangement direction of the flow passages  30 . 
     In this embodiment, the same plate is used for the partition plate  33  of the sensing part  35  and the partition plate  33  of the heat exchange part  3 , and the same plate is used for the fin plate  32   a  of the sensing part  35  and the fin plate  32  of the heat exchange part  3 . The side bar  34   a  of the sensing part  35  and the side bar  34  of the heat exchange part  3  are formed of the same material. Therefore, the sensing part  35  has strength enough to endure a situation such that the pressure in the sealed space  30   c  is equal to the pressure in the flow passage  30  with the high pressure fluid F 1  or F 2  in the heat exchange part  3  flowing therein. 
     An outside sheet  37  for protecting the heat exchange part  3  and the sensing part  35  is provided on the outside of the sensing part  35 . 
     A detection means  50  for detecting damage of the sensor plate  36  is provided for each sensing part  35  constituted as above. The detection means  50  includes a pressure measuring means  51 , a pressurizing means  52 , and a gas leak check means (fluid detection means)  53 . As the pressure measuring means  51  for measuring pressure within each sealed space  30   c , a pressure gauge is used in this embodiment. The pressurizing means  52  for pressurizing the inside of each sealed space  30   c  is configured to pressurize the inside of the sealed space  30   c  by feeding nitrogen gas into the sealed space  30   c  in this embodiment. The gas leak check means  53  checks the presence of the fluid F 1  or F 2  in each sealed space  30   c.    
     Concretely, pipes  55  connecting with the respective sealed spaces  30   c  are connected to each sensing part  35 , and each of the pipes  55  is branched to three branch pipes (a first branch pipe  55   a , a second branch pipe  55   b , and a third branch pipe  55   c ). The branch pipes  55   a  to  55   c  are provided with valves  56   a  to  56   c  respectively, the pressure measuring means  51  is connected to the first branch pipe  55   a , the gas leak check means  53  is connected to the second branch pipe  55   b , and the pressurizing means  52  is connected to the third branch pipe  55   c . The pipe  55  communicating with the outer sealed space  30   c  in the arrangement direction of the flow passages  30  is communicated with the pipe  55  communicating with the sealed space  30   c  on the inner side thereof through a connecting pipe  57 , and the connecting pipe  57  is provided with a valve  58 . 
     In the heat exchanger  1  constituted as above, heat exchange is performed between the first fluid F 1  (natural gas based on methane of 40° C. in this embodiment) and the second fluid F 2  (natural gas based on methane of −40° C. in this embodiment) by starting the heat exchanger  1 , taking the first fluid F 1  from the first fluid inlet pipe  21   a  into the heat exchanger  1 , and also taking the second fluid F 2  from the second fluid inlet pipe  23   a  into the heat exchanger  1 . Specific fluids and temperature used in the heat exchange through the heat exchanger  1  are never limited to the above-mentioned gases or temperatures. 
     Concretely, upon start-up of the heat exchanger  1 , the first fluid F 1  guided from the first fluid inlet pipe  21   a  into the heat exchange part  3  through the bottom header  21  and the lower distribution part  26 , and the second fluid F 2  guided from the second fluid inlet pipe  23   a  into the heat exchange part  3  through the upside header  23  and the upper distribution part  25  flow in mutually opposed directions through each partition plate  33  (upwardly for the first fluid F 1  and downwardly for the second fluid F 2  in  FIG. 1 ) in the heat exchange part  3 . The first fluid F 1  and the second fluid F 2  flow in the respective flow passages  30  of the heat exchange part  3  in this way, whereby the first fluid F 1  and the second fluid F 2  perform heat exchange through the partition plate  33  and the fin plate  32  disposed within each flow passage  30  and in contact with the partition plate  33 . 
     After operation of the heat exchanger  1  for a predetermined time, the supply of the first fluid F 1  and second fluid F 2  is stopped, and the heat exchanger  1  is also stopped. The heat exchanger  1  repeats start and stop in this way. 
     A sudden change in temperature or flow rate often occurs in the first fluid F 1  or the second fluid F 2  flowing in each flow passage  30  of the heat exchange part  3  during operation of the heat exchanger  1 . This sudden change in temperature or flow rate can occur at times other than the start or stop of the heat exchanger  1 . In such a case, the partition plate  33 , the fin plate  32  and the side bar  34  which are in contact with the first fluid F 1  or second fluid F 2  suddenly changed in temperature or flow rate are thermally expanded. The deformation amount based on the thermal expansion is differed among the partition plate  33 , the fin plate  32  and the side bar  34  since each member has a different coefficient of thermal expansion. Concretely, since the fin plate  32  is larger in the coefficient of thermal expansion than the side bar  34  as described above, the partition plates  33  with each flow passage  30  therebetween are deformed by the fin plate  32  arranged therebetween. In more detail, the side bar  34  does not expand so much by the heat of the fluid F 1  or F 2 , while the fin plate  32  is apt to expand more than the side bar  34  by the heat of the fluid F 1  or F 2 . Therefore, the space between a pair of partition plates  33  with each flow passage  30  therebetween is not so much changed by the thermal expansion of the fin plate  32  at the sides of the partition plate  33  where the side bars  34  are disposed, but the space is broadened at an area distant from the side bars  34 , or at the center in the width direction of the flow passages  30 . Upon such deformation of the partition plate  33 , a stress (thermal stress) resulting from the deformation is caused at a specific site (concretely, in the vicinity of the side bars  34 ) of the partition plate  33 . 
     Since a number of (e.g., several hundreds) flow passages  30  are arranged in layers in the heat exchange part  3  in this embodiment, the deformation amount from the initial position of the partition plate  33  separating the flow passages  30  from each other increases from the center part toward the outer side (the upper side or lower side in  FIG. 3 ) (e.g., refer to  FIG. 5 ). This is attributed to that the deformation amount in each flow passage  30  is added from the center part toward the outer side. Namely, the deformation is repeated in such a manner that a partition plate  33  on the center side is deformed, and a partition plate  33  on the outer side of this deformed partition plate  33  is further deformed by the thermal expansion of the fin plate  32  disposed between the partition plate  33  and the partition plate  33  on the center side. Accordingly, the outer partition plate  33  in the arrangement direction of the flow passages  30  has the larger deformation amount. 
     The partition plate  33  returns from the deformed state to a flat state (initial position) when the distribution of the fluids F 1  and F 2  within the flow passages  30  is stopped, for example, by stop of the heat exchanger  1 , since the thermally-expanded fin plate  32  contracts to its original state. 
     In this way, the above-mentioned expansion and contraction are repeated at such sudden changes in temperature or flow rate of the fluid F 1  or F 2  distributed within the heat change part  3  as the repeated start and stop during the entire period of use of the heat exchanger  1 . And as a result, at the outer partition plate  33  with the largest deformation amount, more fatigue based on the thermal stress is accumulated in the above specific site, whereby the probability of damage such as hole or cracking in the partition plate  33  becomes high. 
     In the heat exchanger  1  of this embodiment, therefore, the sensing part  35  provided with the sensor plate  36  is provided on each outer side of the heat exchange part  3 , and the detection means  50  for detecting damage of the sensor plate  36  is provided to detect the damage, whereby the fatigue by the thermal stress based on the heat of the fluid, which is accumulated in each partition plate  33 , can be detected without external leak of the fluid F 1  or F 2 . 
     Namely, the sensor plate  36  which is free from external leak of the fluid F 1  or F 2  even at the occurrence of hole or cracking etc. is disposed in a position where the fatigue by the thermal stress based on the heat of the first fluid F 1  is accumulated more than in each partition plate  33  of the heat exchange part  3  (or an outside position in the arrangement direction), whereby the accumulation of the fatigue based on thermal stress in each partition plate  33  can be detected by causing the sensor plate  36  to be damaged by the thermal stress prior to each partition plate  33 , and detecting this, and repair or the like can be performed before each partition plate  33  is actually damaged by the accumulation of the fatigue to cause the external leak of the fluid F 1  or F 2 . 
     The damage detection of the sensor plate  36  is performed as described below. 
     The valve  56   a  of the first branch pipe  55   a  of the pipe  55  communicating with the sealed space  30   c  on the outer side in the arrangement direction of the flow passages  30  is opened, and the valve  56   c  of the third branch pipe  55   c  of the pipe  55  communicating with the closed space  30   c  on the inner side of the sealed space  30   c  is opened. In this state, the pressure in the outer sealed space  30   c  is measured by the pressure measuring means  51  connected to this outer sealed space  30   c  while pressurizing the inner sealed space  30   c  by injecting nitrogen gas thereto by the pressurizing means  52  connected to this inner sealed space  30   c . Since the pressure in the outer sealed space  30   c  rises if damage such as hole or cracking occurs in the sensor plate  36  separating the outer sealed space  30   c  from the inner sealed space  30   c , the damage can be detected. Namely, if the damage such as hole occurs in the sensor plate  36 , the pressure within the outer sealed space  30   c  rises since the nitrogen gas filled in the inner closed space  30   c  leaks from the inner sealed space  30   c  to the outer sealed space  30   c  through the hole or the like. Therefore, this change in pressure is detected by the pressure measuring means  51  connected to the outer sealed spaced  30   c , whereby the presence of the damage of the sensor plate  36  can be detected. 
     Such damage detection of the sensor plate  36  may be regularly or periodically performed. The damage detection of the sensor plate  36  can be performed otherwise by measuring the pressure in the inner sealed space while maintaining the pressure in the outer sealed space  30   c  by pressurization. 
     The valve  56   b  of the second branch pipe  55   b  communicating with the inner sealed space  30   c  in the arrangement direction of the flow passages  30  is opened during operation of the heat exchanger  1 , whereby damage of the partition plate  33  separating the inner sealed space  30   c  from the flow passage  30  of the heat exchange part  3  can be detected. Concretely, if damage such as hole occurs in this partition plate  33 , the fluid F 1  or F 2  flows from the flow passage  30  into the inner sealed space  30   c  through the hole or the like. Therefore, the damage of the partition plate  33  can be detected based on leak of the fluid F 1  or F 2  by analyzing the component of the gas in the inner sealed space  30   c  by the gas leak check means  53  connected to the inner sealed space  30   c.    
     Further, the valve  56   b  of the second branch pipe  55   b  communicating with the outer sealed space  30   c  is opened, whereby damage of the partition plate  33  separating the inner sealed space  30   c  from the outer sealed space  30   c  (the sensor plate  36 ) can be also detected in addition to damage of the partition plate  33  separating the flow passage  30  from the inner sealed space  30   c . Namely, the fluid F 1  or F 2  reaches from the heat exchange part  3  to the outer sealed space  30   c  only when both the partition plates  33  are damaged. Therefore, the damage of both the partition plates  33  can be detected by analyzing the gas in the outer sealed space  30   c  to check whether the component of the fluid F 1  or F 2  is contained therein. 
     Further, the valve  56   a  of the first branch pipe  55   a  communicating with the inner sealed space  30   c  is opened during operation of the heat exchanger  1 , whereby the presence of damage of the partition plate  33  separating the flow passage  30  of the heat exchange part  3  from the inner sealed space  30   c  of the sensing part  35  can be detected. Concretely, if damage occurs in this partition plate  33 , the fluid F 1  or F 2  flows into the inner sealed space  30   c , and the pressure in the inner sealed space  30   c  rises. Therefore, this pressure rise is detected by the pressure measuring means  51  connected to the inner sealed space  30   c , whereby the occurrence of the damage of the partition plate  33  can be detected. 
     The plate fin heat exchanger  1  of the present invention is never limited to the above-mentioned embodiment, and various changes or modifications can be performed without departing from the gist of the present invention. 
     Although two sealed spaces  30   c  are provided within each sensing part  35  in the above-mentioned embodiment, three or more sealed spaces may be provided without limitation. However, by providing two sealed spaces  30   c  in each sensing part  35 , the fatigue by the thermal stress based on the heat of the fluid F 1 , which is accumulated in each partition plate  33 , can be detected without external leak of the fluid F 1  or F 2  while suppressing the increase in size and weight of the heat exchanger  1 . 
     In the detection means  50  in this embodiment, the pressure measuring means  51 , the pressurizing means  52  and the gas leak check means  53  are connected to each sealed space  30   c  of the sensing part  35  through the pipe  55 . However, the connection is not limited to this embodiment. In the detection means  50 , at least the pressurizing means  52  is connected to one of the two sealed spaces  30   c  with the sensor plate  36  therebetween to pressurize the inside of the one sealed space  30   c , and at least the pressure measuring means  51  is connected to the other sealed space  30   c  to measure the pressure in the other sealed space  30   c.    
     The detection means  50  may not include the gas leak check means  53 . Namely, the gas leak check means  53  may be provided independently from the detection means  50 . In this case, the gas leak detection means  53  may be connected to the innermost sealed space  30   c  in the arrangement direction of the flow passages  30 . By connecting the gas leak check means  53  in this way, even if damage such as hole occurs in the partition plate  33  between the heat exchange part  3  and the detection part  35  at the start (during operation) of the heat exchanger  1  to cause outflow of the fluid F 1  or F 2  into the sealed space  30   c  of the sensing part  35  through the damaged portion, the gas leak check means  53  can detect this. Therefore, the outflow of the fluid F 1  or F 2  from the flow passage  30  can be easily and surely detected. Further, since the fluid leaked into the sealed space  30   c  is confined within the sealed space  30   c , the fluid can be prevented from leaking to the outside. Further, since the sensing part  35  has the strength equal to that of the heat exchange part  3 , it is possible to prevent the damage or the like of the sensing part  35  by the pressure of the fluid F 1  or F 2  leaked from the flow passage  30  of the heat exchange part  3  to the sealed space  30   c  of the sensing part  35 . 
     The heat exchange part  3  in this embodiment is configured so that two kinds of fluids F 1  and F 2  perform heat exchange while flowing in opposite directions. The heat exchange part  3  may be configured also so that the two kinds of fluids F 1  and F 2  flow in the same direction, or flow while crossing each other. In the heat exchanger part  3 , flow passages of F 1  and flow passages of F 2  may be arranged not alternatively. Namely, there are no limitations in arrangement of the flow passages of the two kinds of fluid. Further, the heat exchange part  3  may be configured also so that heat exchange is performed between three or more kinds of fluid. Also in this case, there are no limitations in arrangement of the flow passages of the three or more kinds of fluid. In any of the heat exchange part  3  explained above, the fatigue based on the thermal stress is likely to accumulate in the outer partition plate  33  in the arrangement direction of the flow passages  30  due to the thermal expansion, when a number of flow passages  30  are arranged in layers, and the fin plate  32  is disposed in each flow passage  30 . Therefore, by providing the sensing part  35  and the detection means  50  therein, the same effect as in this embodiment can be attained, or the fatigue by the thermal stress based on the heat of the fluid, which is accumulated in each partition wall, can be detected without external leak of the fluid.