Patent Publication Number: US-2020284530-A1

Title: Plate-fin heat exchanger core and fin structure thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority under 35 USC 119 to Chinese patent application 201910174617.8, filed Mar. 8, 2019, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to the technical field of plate-fin heat exchangers, and in particular, to a plate-fin heat exchanger core. 
     BACKGROUND 
     According to the statistics, in the world&#39;s primary energy consumption, energy passing through heat exchangers accounts for about 80%. Therefore, it is of great significance to improve the comprehensive heat transfer efficiency of heat exchangers for energy conservation. Compared with other heat exchangers, plate-fin heat exchangers have compact and firm structure, high heat transfer efficiency, light weight, high flexibility and high adaptability. Their heat transfer coefficient is 5-8 times higher than that of shell-and-tube heat exchangers, weight is 80% lower than that of shell-and-tube heat exchangers, and heat transfer area density is 6-10 times that of shell-and-tube heat exchangers. Plate-fin heat exchangers are widely used in petrochemical, aerospace, military, shipbuilding, refrigeration and other fields, and have achieved significant economic benefits in utilizing thermal energy, recovering waste heat, saving raw materials and reducing costs, etc. 
     The plate-fin heat exchanger is composed of heat exchange fin, partition plate, sealing strip, distributing fin, end plate, header and fluid inlet and outlet nozzles. The plate-fin heat exchanger core includes partition plate, fin and sealing strip. The fins are supported by the partition plates, and adjacent partition plates are sealed by the sealing strip. The repeating units are stacked and connected by diffusion welding or brazing into a whole. A major part of heat transfer between the hot and cold fluids in the channel is completed through the fin structure between the partition plates, while a minor part is completed through the partition plates. Since the fins cannot directly exchange heat, they are called “the secondary surfaces”. The fins have various structural forms such as offset strip fins, wavy fins, straight fins, porous fins, louvered fins and pin fins. The plate-fin heat exchanger can improve heat transfer by means of increasing the heat exchange area and turbulence intensity. 
     Scholars at home and abroad have carried out research on the plate-fin heat exchangers. Some scholars have proposed a plate-fin structure (CN207163297) and a fin-tube structure (CN207763553U) with a dimple/protrusion structure. The dimple/protrusion fin structure is used to increase the heat exchange area and form a turbulent effect, so as to generate vortexes and secondary flow and make the flow boundary layer develop continuously. In this way, the dimple/protrusion fin structure achieves the purpose of enhancing heat transfer. However, a recirculation zone is formed behind the turbulence, which locally weakens the heat transfer at the rear side of protrusion and inner front side of the dimple and significantly increases the flow resistance. Some scholars have proposed a porous plate-fin structure (CN104390508). When the fluid flows near the pore, lateral mixing occurs to thin the boundary layer. The flow resistance of the porous plate-fin increases as the porous rate increases with ignorable change in heat transfer However, due to the large number of pores, the heat exchange area is reduced, and the comprehensive heat transfer performance is not significantly improved. In addition, the pore structure weakens the strength of the plate-fin heat exchanger and reduces the pressure resistance of the plate-fin structure. 
     In summary, it is urgent to optimize the structure design of the plate-fin heat exchanger. The optimization is significant for improving the comprehensive heat transfer efficiency of the plate-fin heat exchanger, reducing the flow resistance of the plate-fin heat exchanger, achieving energy saving and reducing consumption, and reducing enterprise production costs. 
     SUMMARY 
     In order to solve the problems existing in the prior art, an objective of the present invention is to provide a plate-fin heat exchanger core and a fin structure thereof. The present invention further improves the compactness and comprehensive heat transfer efficiency of the plate-fin heat exchanger. 
     In accordance with one aspect of the inventive concepts, provided is a fin structure, where the fin is provided with a plurality of dimples/protrusions; the dimple/protrusion is provided with a perforated hole to form a perforated dimple/protrusion. 
     Further, a hole on the perforated dimple and the perforated protrusion can be located at a center of the corresponding perforated dimple/perforated protrusion. 
     Further, a hole on the perforated dimple and the perforated protrusion can have an offset from the center of the corresponding perforated dimple/perforated protrusion. 
     Further, an offset hole on the perforated protrusion can be located on an inflowing leeward side and an offset hole on the perforated dimple can be located on an inflowing side. 
     Further, the hole on the perforated dimple/protrusion can be circular. 
     Further, the fin can be a straight, wavy or offset strip fin. 
     In accordance with one aspect of the inventive concepts, provided is a plate-fin heat exchanger core. The heat exchanger core includes a plurality of partition plates and a fin, where the fin is supported and fixed between two adjacent partition plates; the two adjacent partition plates are sealed to form a fluid channel unit; the fluid channel unit forms a plurality of heat exchange channels for a medium to flow between the adjacent partition plates. 
     Further, the plate-fin heat exchanger core can include a plurality of fluid channel units stacked and fixed together. 
     Further, adjacent fluid channel units can share one partition plate. 
     Further, the perforated dimple and the perforated protrusion are staggered on both sides in the heat exchange channel; the two sides of the fin channel have a perforated protrusion structure, a perforated dimple structure, or a perforated dimple/protrusion mixed structure. 
     The plate-fin heat exchanger core can be composed of a partition plate, a perforated dimple/protrusion fin and a sealing strip. Adjacent fins can be supported by the partition plate, and adjacent partition plates can be sealed with the sealing strip to form an impervious fluid channel. The fluid channel can realize the flow of different fluid and the flow of downflow, counterflow, cross flow of different fin layers. 
     In various embodiments, the fin structure of the plate-fin heat exchanger core mainly combines the structural characteristics of porous and dimple/protrusion fins. In various embodiments, different positions of the hole on the perforated dimple/protrusion structure are punched. In various embodiments, the hole includes non-offset hole and offset hole. In various embodiments, the hole offset is located on an inflowing leeward side of the perforated protrusion structure and on a windward side of the perforated dimple structure. 
     In various embodiments, the perforated dimple/protrusion structure of the fin is staggered on both sides in the channel. In various embodiments, the two sides of the fin channel have perforated protrusion structure, perforated dimple structure, or perforated dimple/protrusion mixed structure. The versatile fin can also be combined with other types of fins. 
     In various embodiments, the fin of the plate-fin heat exchanger is mainly formed by punching on a rectangular plate to form a perforated dimple/protrusion structure and rolling. 
     In various embodiments, the perforated dimple/protrusion fin structure is “the secondary surface”, which increases a heat exchange area, enhances fluid turbulence, destroys a boundary layer, effectively reduces flow resistance, and has a significantly enhanced heat transfer. 
     In various embodiments, the fin of the plate-fin heat exchanger mainly has the following structural parameters: L is fin length; W is fin width; R is radius of dimple/protrusion; h f . fin height; d is diameter of hole structure; δ is fin thickness; S is fin spacing; C f  is horizontal distance between adjacent perforated dimple/protrusion; e is vertical distance between adjacent perforated dimple and perforated protrusion; bf is distance from perforated dimple/protrusion structure to fin edge; and a is hole offset. 
     Compared with the prior art, the present invention has the following beneficial effects.
         1. The fin of the plate-fin heat exchanger has the advantages of ordinary porous and dimple/protrusion fins. That is, the fin increases a heat exchange area, enhances a turbulent effect, thins a boundary layer, and improves the heat transfer efficiency.   2. The hole structure forms a local jet, which promotes the mixed convection of a fluid in the adjacent channels of the fin and reduces a recirculation zone of the dimple/protrusion fin structure. Therefore, the fin improves the local heat transfer coefficient of the fluid in the fluid channel and achieves enhanced heat transfer.   3. The perforated dimple/protrusion structure plays a certain supporting role to the fin, improves the pressure-bearing capacity of the plate-fin heat exchanger, and improves the strength of the porous fin.   4. The processing technic of the plate-fin heat exchanger is simple and versatile, and can be used alone and mixed with other fins.       

     In summary, the present invention has the following advantages. The present invention efficiently utilizes the effective heat transfer area of the fin, effectively reduces the flow resistance of the plate-fin heat exchanger while enhancing the turbulence, and improves the comprehensive heat transfer efficiency of the plate-fin heat exchanger. The present invention reduces the recirculation zone of the dimple/protrusion fin structure, and improves the local enhanced heat transfer coefficient of the dimple/protrusion fin. The present invention obviously improves the heat exchange performance of the porous fin and the pressure-bearing capacity of the porous fin. The present invention improves the compactness of the plate-fin heat exchanger, reduces the weight, and saves the manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompany drawings constituting a part of the present application provide further understanding of the present invention. The schematic embodiments and description thereof are intended to be illustrative of the present invention and do not constitute an undue limitation of the present invention. Accompanying Drawings: 
         FIG. 1  is a structural diagram of an embodiment of a plate-fin heat exchanger core; 
         FIG. 2  is a distribution diagram of an embodiment of adjacent fluid channels of a fin of a plate-fin heat exchanger; 
         FIG. 3  is a comprehensive diagram of an embodiment of a non-offset perforated dimple/protrusion fin of a plate-fin heat exchanger; 
         FIG. 4  is a front view of an embodiment a non-offset perforated dimple/protrusion fin of a plate-fin heat exchanger; 
         FIG. 5  is a side view of an embodiment of a non-offset perforated dimple/protrusion fin of a plate-fin heat exchanger; 
         FIG. 6  is a comprehensive diagram of an embodiment of a perforated dimple/protrusion fin of a plate-fin heat exchanger with an offset a; 
         FIG. 7  is a rear view of an embodiment of a perforated dimple/protrusion fin of a plate-fin heat exchanger with an offset a; 
         FIG. 8  is a front view of an embodiment of a perforated dimple/protrusion fin of a plate-fin heat exchanger with an offset a; 
         FIG. 9  is a structural diagram of an embodiment of a perforated dimple/protrusion fin of a plate-fin heat exchanger with an offset a; 
         FIG. 10  is an outside view of an embodiment of a plate-fin heat exchanger; 
         FIG. 11  is a comparison diagram of an embodiment of a Nusselt number Nu in the flow heat transfer performance of a plate-fin heat exchanger of the present invention, a dimple/protrusion fin and a straight fin; 
         FIG. 12  is a comparison diagram of an embodiment of a resistance coefficient f in the flow heat transfer performance of plate-fin heat exchanger of the present invention, a dimple/protrusion fin and a straight fin. 
     
    
    
     Reference Numerals:  1  is partition plate,  2  is perforated protrusion,  3  is perforated dimple,  4  is hot fluid channel,  5  is cold fluid channel,  6  is partition plate,  7  is sealing strip,  8  is offset perforated protrusion,  9  is header, and  10  is side plate. 
     Explanation of Symbols: L is fin length; W is fin width; R is radius of dimple/protrusion; hf is fin height; d is diameter of hole; δ is fin thickness; S is fin spacing; C f  is horizontal distance between adjacent perforated dimple/protrusion; e is vertical distance between adjacent perforated dimple/protrusion; bf is distance from perforated dimple/protrusion structure to fin edge; and a is hole offset. 
     DETAILED DESCRIPTION 
     Aspects of the inventive concepts will be described in detail below with reference to the accompanying drawings and the embodiments. It should be noted that the embodiments in the application and features in the embodiments may be combined with each other in a non-conflicting situation. 
     The following detailed description is exemplary and is intended to further describe the present invention. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. The terms used herein are merely intended to describe the specific implementations, rather than to limit the exemplary implementations of the present invention. 
     Referring to  FIG. 1  and  FIG. 2 , the present invention provides a plate-fin heat exchanger core, including a plurality of partition plates ( 1 ,  6 ), a fin  100  and a sealing strip  7 . Fins  100  are mutually supported by two corresponding partition plates ( 1 ,  6 ). Adjacent partition plates ( 1 ,  6 ) are sealed with the sealing strip  7  to form a hot fluid channel  4 /cold fluid channel  5 . A plurality of fluid channels are stacked and connected by diffusion welding or brazing to form the plate-fin heat exchanger core. The fluid channel realizes the flow of different fluid and the flow of down-flow, counterflow, cross flow of different fin layers. 
     Referring to  FIG. 3  to  FIG. 9 , a structural diagram of the fin  100  of the plate-fin heat exchanger, the fin  100  is mainly composed of a fluid channel of a perforated protrusion  2 /perforated dimple  3  structure. A hole  200  includes a non-offset hole and a hole with an offset a. The perforated dimple/protrusion structure is staggered on both sides of the channel, and a fluid flows through the perforated protrusion  2 /perforated dimple  3  structure. The perforated dimple/protrusion structure enhances turbulence, destroys a boundary layer, effectively reduces a recirculation zone of the dimple/protrusion structure, and reduces flow resistance. Therefore, the fin structure improves the comprehensive performance of the plate-fin heat exchanger. 
     The fin channel of the plate-fin heat exchanger has a variety of structural forms such as straight fin, wavy fin and offset strip fin to improve the heat exchange structure, effectively reduce the flow resistance and achieve enhanced heat transfer. The two sides of the fin channel have a variety of structural forms such as the perforated protrusion  2  structure, the perforated dimple  3  structure and the perforated dimple/protrusion mixed structure. The versatile perforated dimple/protrusion fin can be combined with other types of fins to achieve the best heat transfer performance under different working conditions. 
     The plate-fin heat exchanger core of the present invention combines the advantages of the dimple/protrusion structure and the porous structure. The fin increases a heat exchange area, and the dimple/protrusion structure improves the pressure-bearing capacity of the plate-fin structure and improves fluid turbulence, thinning a flow boundary layer and a hot boundary layer. The hole structure forms a local jet to promote mixed convection of a fluid in the adjacent fluid channels of the fin, and reduces a recirculation zone of the dimple/protrusion structure, achieving enhanced heat transfer and reducing flow resistance. 
     Referring to  FIG. 10 , the plate-fin heat exchanger core is sealed by an end plate  10  and a header  9  to form the plate-fin heat exchanger. 
     Referring to  FIG. 11  and  FIG. 12 , which provide a comparison of the flow heat transfer performance of the plate-fin heat exchanger of the present invention, a dimple/protrusion fin and a straight fin.  FIG. 11  shows that compared with the existing dimple/protrusion fin and straight fin, the fin of the present invention has a larger Nusselt number Nu under the same conditions.  FIG. 12  shows that compared with the existing dimple/protrusion fin and straight fin, the fin of the present invention has a smaller resistance coefficient f under the same conditions. Therefore, the plate-fin heat exchanger of the present invention has better flow heat transfer performance. 
     It is known from technical common sense that the present invention may be realized through other embodiments that do not deviate from its spiritual essence or necessary characteristics. Therefore, the above-disclosed embodiments are merely illustrative and not exclusive in all respects. All changes which are within the scope of the present invention or within a scope equivalent to the scope of the present invention shall be included within the present invention.