Patent Publication Number: US-2023136711-A1

Title: Fin Structure and Heat Exchanger

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a U.S. National Stage Application of International Patent Application No. PCT/CN2021/079352, filed on Mar. 5, 2021, which claims priority to Chinese Patent Application No. 202010588660.1 filed on Jun. 24, 2020, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present application relates to the technical field of refrigeration devices, and in particular, to a fin structure and a heat exchanger. 
     Description of Related Art 
     In prior art, fin tube heat exchangers are widely used in chemical, ventilation, heating, air conditioning, refrigeration and other industries due to characteristics such as simple manufacture and strong applicability, and how to maximally transfer heat and utilize thermal energy (enhancing heat transfer) has always been the focus of research in the industry. 
     Fin structures of the fin tube heat exchanger mainly include straight fins, corrugated fins and corresponding slotted (windowed) structures, etc. For the traditional straight fins and corrugated fins, the leeward side of a heat exchange tube often has poor heat exchange, and the corresponding slotted structures increase the contact area on an air side, and at the same time, the structure irregularity disturbs a flow field, which enhances the mixing between fluids and delays flow separation of a boundary layer, thereby enhancing the overall heat exchange performance. However, since the slotted structure usually decreases a flow gap and increases a flow resistance of the fin, the fin is easily blocked by frost under wet conditions, the service life of the fin is shortened, and at the same time, the effective heat exchange area is reduced, which affects an actual heat exchange effect of the fin. Comprehensively considering a resistance, the heat transfer performance and processability, the corrugated fins are in a form that is more suitable for industrial applications. However, with further improved requirements on heat dissipation of the heat exchangers, it is difficult for the traditional corrugated fins to meet the performance requirements of high-efficiency heat exchangers. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present application provide a fin structure and a heat exchanger, so as to improve a heat exchange effect of the fin and enhance a heat exchange performance of the heat exchanger. 
     In order to achieve the above purpose, the present application provides a fin structure, including: a fin base, wherein the fin base is provided with a tube hole for a heat exchange tube passing though, and the fin base is a corrugated fin; and a plurality of convex parts, wherein the convex part is disposed on the fin base, and the plurality of convex parts surround an outer circumference of the tube hole. 
     Further, the fin base includes a plurality of first plates and a plurality of second plates, the second plate is connected between two first plates, and a corresponding node length L1 of the first plate is greater than a corresponding node length L2 of the second plate. 
     Further, there are two second plates between two first plates, and the two second plates are disposed adjacently. 
     Further, a ratio h1/S of a corrugation height h1 of the fin base to a fin spacing S is 0.58˜0.62, and L1/L2 is 1.5˜1.7. 
     Further, the plurality of convex parts include: an annular convex part, the annular convex part being convexly disposed on the first plate; and a lateral convex part, the lateral convex part being convexly disposed on the second plate. 
     Further, the annular convex part is an annular convex structure, a plurality of the annular convex parts are disposed, and the plurality of the annular convex parts are symmetrically distributed on the outer circumference of the tube hole. 
     Further, the lateral convex part is a boss, a plurality of the lateral convex parts are disposed, and the plurality of the lateral convex parts are symmetrically distributed on the outer circumference of the tube hole. 
     Further, a ratio h3/S of a raised height h3 of the annular convex part to the fin spacing S is 0.35˜0.4. 
     Further, a ratio h2/S of a raised height h2 of the lateral convex part to the fin spacing S is 0.35˜0.4. 
     Further, the fin base is provided with an annular groove, wherein the tube hole is located in the annular groove, the annular groove and the tube hole are concentrically disposed, an outer circumference of the annular groove is connected to the first plate and the second plate, and the convex parts are all located outside the annular groove. 
     Further, there are two second plates between two first plates, the two second plates are disposed adjacently, and a wave trough line is formed on which the two second plates intersect; and two arc-shaped surfaces symmetrical with respect to the tube hole are formed at joints between the annular groove and the two first plates, and four planes symmetrical with respect to the tube hole are formed at joints between the annular groove and the two second plates. 
     Further, a groove bottom of the annular groove is tangent to the wave trough line in a vertical incoming flow direction; and an included angle θ between a generatrix of the arc-shaped surface and a central axis of the heat exchange tube is 45°. 
     Further, a ratio d1/D of a diameter d1 of the groove bottom of the annular groove to an outer diameter D of the heat exchange tube is 1.6˜1.7. 
     Further, the two first plates are symmetrically disposed with respect to the tube hole, and the two second plates are symmetrically disposed with respect to the tube hole. 
     Further, a ratio D1/D of an inner diameter D1 of the tube hole to an outer diameter D of the heat exchange tube is 1.025˜1.035. 
     According to another aspect of the present application, a heat exchanger is provided, the heat exchanger including the above fin structure. 
     The structure of the corrugated fin is improved in the present application by disposing the plurality of convex parts on the outer circumference of the tube hole. The convex parts play a role of enhancing airflow disturbance nearby the tube hole (installed heat exchanger), so that a flow rate of a local area is increased, a mixing of cold and hot fluids is enhanced, and an effective heat exchange area of the fin is increased, thereby enhancing a heat exchange performance of a heat exchanger. Compared with the windowed fin, the fin structure according to the present application is less likely to form frost on a fin surface under wet conditions, thereby effectively reducing the occurrence of blockage of a flow channel. Compared with the ordinary corrugated fins, the fin structure according to the present application effectively increases the heat exchange area, thereby further improving the heat exchange effect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic plan view of a fin structure according to an embodiment of the present application: 
         FIG.  2    is a schematic three-dimensional structural diagram of a fin structure according to an embodiment of the present application; 
         FIG.  3    is an A-A sectional view of the fin structure of  FIG.  1   ; 
         FIG.  4    is a B-B sectional view of the fin structure of  FIG.  1   ; 
         FIG.  5    is a data comparison diagram of a change condition of a heat exchange amount Q with an inlet wind speed; 
         FIG.  6    is a data comparison diagram of a change condition of a Nusselt number Nu with the inlet wind speed: 
         FIG.  7    is a data comparison diagram of a change condition of a thermal resistance R with the inlet wind speed; 
         FIG.  8    is a schematic comparison diagram of flow field characteristics in a flow channel when the inlet wind speed is 2 m/s; 
         FIG.  9    is a schematic comparison diagram of flow field characteristics in a flow channel when the inlet wind speed is 4 m/s; and 
         FIG.  10    is a schematic comparison diagram of flow field characteristics in a flow channel when the inlet wind speed is 6 m/s. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The present application will be described in further detail below in combination with the accompanying drawings and specific embodiments, which are not intended to limit the present application. 
     Referring to  FIG.  1    to  FIG.  4   , according to embodiments of the present application, a fin structure is provided. The fin structure includes a fin base  10  and a plurality of convex parts  30 . The fin base  10  is provided with a tube hole  20  for a heat exchange tube passing through, and the fin base  10  is a corrugated fin. The convex part is disposed on the fin base  10 , and the plurality of convex parts  30  surround an outer circumference of the tube hole  20 . 
     The structure of the corrugated fin is improved in the present application by disposing the plurality of convex parts  30  on the outer circumference of the tube hole. The convex parts  30  play a role of enhancing airflow disturbance nearby the tube hole (installed heat exchanger), so that a flow rate of a local area is increased, a mixing of cold and hot fluids is enhanced, and an effective heat exchange area of the fin is increased, thereby enhancing a heat exchange performance of a heat exchanger. Compared with the windowed fin, the fin structure according to the present application is less likely to form frost on a fin surface under wet conditions, thereby effectively reducing the occurrence of blockage of a flow channel. Compared with the ordinary corrugated fins, the fin structure according to the present application effectively increases the heat exchange area, thereby further improving the heat exchange effect. 
     In combination with  FIG.  1    and  FIG.  2   , the fin base  10  includes a plurality of first plates  11  and a plurality of second plates  12 , the second plate  12  is connected between two first plates  11 , and a corresponding node length L1 of the first plate  11  is greater than a corresponding node length L2 of the second plate  12 . That is to say, a surface of the fin base  10  is divided into large plates and a small plate, which are the first plates and the second plate respectively and expanded in an M shape along an airflow direction. The “plurality” herein refers to two or more. 
     There are two second plates  12  between two first plates  11 , and the two second plates  12  are disposed adjacent to each other. In some embodiments, the two first plates  11  are disposed symmetrically with respect to the tube hole  20 , the two second plates  12  are disposed symmetrically with respect to the tube hole  20 , and a wave trough line is formed on which the two second plates  12  intersect. To the fin base  10  of the present embodiment, such structural arrangement of the first plates  11  and the second plates  12  makes the whole fin surface is expanded in the M shape along the airflow direction. 
     In some embodiments, a ratio h1/S of a corrugation height h1 of the fin base  10  to a fin spacing S is 0.58˜0.62, and L1/L2 is 1.5˜1.7. Based on such relationship between the corrugation height and the fin spacing, as well as such relationship between the corresponding node length L1 of the first plate  11  and the corresponding node length L2 of the second plate  12 , a heat exchange capacity of the fin itself is improved. 
     Referring to  FIG.  2   , the plurality of convex parts  30  include an annular convex part  31  and a lateral convex part  32 . The annular convex part  31  is convexly disposed on the first plate  11 ; the lateral convex part  32  is convexly disposed on the second plate  12 . The annular convex part  31  and the lateral convex part  32  both enhance fluid disturbance, and they are disposed on different plates, thereby delaying a phenomenon of flow separation of a boundary layer and improving the heat exchange performance of the fin. 
     The annular convex part  31  is an annular convex structure, a plurality of the annular convex parts  31  are disposed, and the plurality of the annular convex parts  31  are symmetrically distributed on the outer circumference of the tube hole  20 . In the present embodiment, the plurality of the annular convex parts  31  are four segments of annular convex parts symmetrically disposed on the first plates  11 . 
     The lateral convex part  32  is a boss, a plurality of the lateral convex parts  32  are disposed, and the plurality of the lateral convex parts  32  are symmetrically distributed on the outer circumference of the tube hole  20 . The plurality of the lateral convex parts  32  are four segments of square bosses symmetrically disposed on the second plates  12 . The lateral convex parts  32  have a shape of a rectangular block. Due to the arrangement of the lateral convex parts  32  and the annular convex parts  31 , the airflow disturbance nearby the heat exchange tube is enhanced, so that the flow rate in the local area is improved, the mixing of hot and cold fluids is enhanced, and a thickness of the boundary layer is reduced, thereby significantly reducing a wake area behind the tube, and increasing the effective heat exchange area of the fin. 
     In order to consider a balanced relationship between the airflow and a height of the annular convex part  31 , a ratio h3/S of a raised height h3 of the annular convex part  31  to the fin spacing S is 0.35˜0.4. 
     In order to consider a balanced relationship between the airflow and a height of the lateral convex part  32 , a ratio h2/S of a raised height h2 of the lateral convex part  32  to the fin spacing S is 0.35˜0.4. 
     In some embodiments, the fin base  10  is provided with an annular groove  40 , the tube hole  20  is located in the annular groove  40 , the annular groove  40  and the tube hole  20  are disposed concentrically, an outer circumference of the annular groove  40  is connected to the first plate  11  and the second plate  12 , and the convex parts  30  are all located outside the annular groove  40 . The structural arrangement of the annular groove  40  is convenient for stamping and forming of the peripheral lateral convex parts  32  and annular convex parts  31 , which improves process practicality. Due to the structure of the annular groove  40 , the processing difficulty is simplified, the processing cost of the fin structure is reduced, and a very high industrial value is achieved. 
     There are two second plates  12  between two first plates  11 , the two second plates  12  are disposed adjacent to each other, and a wave trough line  13  is formed on which the two second plates  12  intersect. An arc-shaped surface  41  is formed at a joint between the annular groove  40  and each first plate  11 . Two planes  42  are formed at joints between the annular groove  40  and each second plate  12 . The two arc-shaped surfaces formed at the joints between the annular groove  40  and two first plates  1  are symmetrical with respect to the tube hole  20 . The four planes  42  formed at the joints between the annular groove  40  and two second plates  12  are symmetrical with respect to the tube hole  20 . The groove bottom  43  of the annular groove  40  is a circular surface, and is tangent to the wave trough line  13  in a vertical incoming flow direction. An included angle θ between a generatrix of the arc-shaped surface  41  and a central axis of the heat exchange tube is 45°. 
     A ratio d1/D of a diameter d1 of the groove bottom  43  of the annular groove  40  to an outer diameter D of the heat exchange tube is 1.6˜1.7. A ratio D1/D of an inner diameter D1 of the tube hole  20  to the outer diameter D of the heat exchange tube is 1.025˜1.035. 
     The present application also provides an embodiment of a heat exchanger, and the heat exchanger includes the fin structure of the above embodiments. 
     The present embodiments are verified by ANSYS Fluent simulation. During the simulation, an inlet air flow rate is 2 m/s, 3 m/s, 4 m/s, 5 m/s and 6 m/s respectively, an air inlet temperature is 35° C., a tube wall temperature is 50.62° C., change conditions of a heat exchange amount Q, a Nusselt number Nu and a thermal resistance R as well as flow field characteristics in a flow channel before and after the lateral convex parts  32  and the annular convex parts  31  are disposed in the case of the same flow are compared, wherein the heat exchange amount Q, Nusselt number Nu, and thermal resistance R are defined as follows: 
         Q=mC   p ( T   out   −T   in ) 
     m is a mass flow, and its unit is kg/s; Cp is a constant pressure specific heat capacity, and its unit is j/(kg·K); T out  is an outlet average temperature of an air flow channel, and its unit is K; and T in  is an inlet average temperature of the air flow channel, and its unit is K. 
     
       
         
           
             Nu 
             = 
             
               
                 𝒽 
                 ⁢ 
                 
                   D 
                   e 
                 
               
               λ 
             
           
         
       
     
     h is a convective heat transfer coefficient, and its unit is w/(m 2 ·K); De is an equivalent diameter of an air flow surface, and its unit is m; and λ is an air thermal conductivity coefficient, and its unit is w/(m·K). 
     
       
         
           
             𝒽 
             = 
             
               Q 
               
                 S 
                 ⁢ 
                 Δ 
                 ⁢ 
                 
                   T 
                   m 
                 
               
             
           
         
       
     
     S is a heat transfer surface area of the fin, and its unit is m 2 ; and ΔTm is a logarithmic average temperature difference and its unit is K. 
     
       
         
           
             
               Δ 
               ⁢ 
               
                 T 
                 m 
               
             
             = 
             
               
                 
                   Δ 
                   ⁢ 
                   
                     T 
                     max 
                   
                 
                 - 
                 
                   Δ 
                   ⁢ 
                   
                     T 
                     min 
                   
                 
               
               
                 ln 
                 ⁢ 
                 
                   
                     Δ 
                     ⁢ 
                     
                       T 
                       max 
                     
                   
                   
                     Δ 
                     ⁢ 
                     
                       T 
                       min 
                     
                   
                 
               
             
           
         
       
       
         
           
             
               Δ 
               ⁢ 
               
                 T 
                 max 
               
             
             = 
             
               
                 T 
                 wall 
               
               - 
               
                 T 
                 in 
               
             
           
         
       
       
         
           
             
               Δ 
               ⁢ 
               
                 T 
                 min 
               
             
             = 
             
               
                 T 
                 wall 
               
               - 
               
                 T 
                 out 
               
             
           
         
       
     
     Twall is an average temperature of the fin surface and its unit is K. 
     
       
         
           
             R 
             = 
             
               
                 Δ 
                 ⁢ 
                 
                   T 
                   m 
                 
               
               Q 
             
           
         
       
     
     The heat exchange amount Q, Nusselt number Nu, and thermal resistance R may all be calculated by extracting simulation data, and the larger the heat exchange amount Q and the Nusselt number Nu are, or the smaller the thermal resistance R is, the better the heat exchange performance is. 
     The change condition of the heat exchange amount Q with an inlet wind speed is shown by  FIG.  5   . As the inlet wind speed increases, the increase of the heat exchange amount is improved. At 6 m/s, the increase of the heat exchange amount is the largest compared with the original fin and is 4.37%. The new fin in  FIG.  5    refers to the fin structure according to the present application, and the original fin refers to a fin structure of the prior art. 
     The change condition of the Nusselt number Nu with the inlet wind speed is shown by  FIG.  6   . As the inlet wind speed increases, the Nusselt number gradually increases. At 2 m/s, the increase of the Nusselt number is the largest compared with the original fin and is 11.16%. The new fin in  FIG.  6    refers to the fin structure according to the present application, and the original fin refers to the fin structure of the prior art. 
     The change condition of the thermal resistance R with the inlet wind speed is shown by  FIG.  7   . As the inlet wind speed increases, the thermal resistance gradually decreases. At 2 m/s, the decrease of the thermal resistance is the largest compared with the original fin, and is 14.52%. The new fin in  FIG.  7    refers to the fin structure according to the present application, and the original fin refers to the fin structure of the prior art. 
     The present application also provides comparison conditions of the flow field characteristics in the flow channel before and after the lateral convex parts  32  and the annular convex parts  31  are disposed when the inlet wind speed is 2 m/s, 4 m/s and 6 m/s, as shown in  FIGS.  8 - 10   .  FIG.  8    shows the comparison condition of the flow field characteristics in the flow channel when the inlet wind speed is 2 m/s;  FIG.  9    shows the comparison condition of the flow field characteristics in the flow channel when the inlet wind speed is 4 m/s; and  FIG.  10    shows the comparison condition of the flow field characteristics in the flow channel when the inlet wind speed is 6 m/s. 
     At different inlet wind speeds, the comparison between the fin structure of the prior art and the fin structure of the present application shows the same difference in the flow field characteristics, which mainly reflects that due to the arrangement of the lateral convex parts  32  and the annular convex parts  31 , the airflow disturbance nearby the heat exchange tube is enhanced, so that the flow rate in the local area is increased, the mixing of cold and hot fluids is enhanced, and the thickness of the boundary layer is reduced, which significantly reduces a wake area behind the tube, and increases the effective heat exchange area of the fin, thereby enhancing the heat exchange performance of the heat exchanger. 
     It should be noted that the terms used herein are merely for the purpose of describing specific embodiments, and are not intended to limit exemplary embodiments according to the present application. As used herein, unless the context clearly indicates, otherwise, the singular is intended to include the plural. In addition, it should also be understood that when the term “containing” and/or “including” is used in the description, it indicates the existence of features, steps, works, devices, components and/or combinations thereof. 
     It should be noted that the terms “first”, “second”, etc., in the description, claims and the above drawings of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It is to be understood that the data used as such can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in sequences other than those illustrated or described herein. 
     Of course, the above are the preferred embodiments of the present application. It should be pointed out that for those skilled in the art, without departing from basic principles of the present application, several improvements and modifications can also be made, and these improvements and modifications are also regarded as the protection scope of the present application.