CONVECTIONAL HEAT EXCHANGER

Abstract: This convectional heat exchanger is structured of tube (1) inside which there is an inner medium. There are two ends of the tube operating as an inlet and an outlet of the inner medium, if that medium is forced to flow. This tube is bent into a spiral shape at the same time with its heat exchanging element (2) which is formed of at least one flat (5) and two corrugated (3 and 4) strips occuring alternatively. The outer band (7) being an extension of the flat strip ensures permanent reciprocal contact in the tangent places of the tube and the strips.

Description: Convectional heat exchanger This invention relates to a convectional exchanger to exchange heat from one medium which either exists or flows inside a tube and an outer medium in a gasoues phase, eg. the air being in a natural or forced movement. On the side of the gaseous medium there are fins in a shape of flat and corrugated strips which occur alternatively and build an exchanging heat element being placed between succeding flatted tube coils which form a spiral. The outer part of the element is formed into a band securing permanent and reciprocal pressure of mentioned the fins, the tube and this outer part to ensure good heat transfer contacts. The heat exchanger that way being performed comprises its outer enhanced surface, firm structure with lower total weight and provides better heat transfer coefficients for comperatively similar flow conditions in traditional stright tube heat exchangers. There are known convectional heat exchangers build of mainly circular tubes used mostly in shape of stright lines connected together by means of bends and inlet and outlet headers and of numerous fins which are positioned parallely and have shaped orifices provided to fit on the tubes or to perform the tubes. The necessary heat transfer contacts are obtained by internal expanding of the tubes in most cases or a special brazing method. The extremely thin fins are manufactured on a special kind of presses and collected into columns with dividers forming their future working spacing. The manufacturing proccess does not make possibility to increase the total heat transfer surface by adding planes parallel to the tubes and involving no increase in flow resistance of the gaseous medium. The created heat contacts are good when the fins are made of thicker material. There is no possibility to provide the thicker fin body part closer to the tubes to obtain similar conductive heat flow in the fins and better heat performance of the fins,as well. It is impossible to obtain the exchanger with its aproximately circular shape in a cross section in a plane perpendicular to the outer medium flow direction. The exchangers are mainly rectangular in that cross section which is less advantageous from the point of view of umformity of this flow and its direction. This results in lower total performance. Due to lower heat transfer performance of the traditional flat fins and their lower possible 'working surface' the convectional heat exchangers of the expressed art are havier, require more materials, are made by more complicated manufactaing proccess and the same way they cost more. Since there are applied more materials for the fins and the tubes, the exchanger is less compact and there is required some more material to provide the internal support of the structure for stright segments of tubes. This increases significantly the exchanger cost and its future installation, as well. The invention relates to the convectional heat exchanger which is characterized by increased heat transfer performance thanks to enhanced 'working surface' which is obtained by adding extra surfaces in general parallel to longitudinal axle of the tubes of the exchanger and higher flow turbulences and that means higher heat transfer coefficients in the gaseous outer medium side and in the inner medium if that last one is forced to flow. The increased density of fins in the cross section in the perpendicural plane to the outer medium flow direction causes only slight growth of the flow resistance and made possible and with common sense a change of direction of the flow comparing to traditional exchangers, that means the air is blown into the exchanger by the close operating fan, eg. an axial fan, provides higher flow turbulance and gives an advantage of much higher heat transfer coefficient on the fin surfaces. The primary object of the invention is to provide heat exchanger with strongly rounded corners seen in the flow direction as close as possible to a circle to avoid purer heat transfer performance in those corners in the case of the rectangural shape. The next object is to provide fin elements of thinner thickness when they are in larger distance from the tube to reduce usage of heat transfer material and better their average heat transfer performance. The following object of the invention is to gain significant changes in the heat 5 exchanger structure to decrease number of its elements, to simplify manufacturing proccess, especially avoiding of brazing of tubes and bends, and gaining operation on longitudinal, endless materials without seperating them to pieces. The next aim of the present invention is to provide the heat exchanger of more 0 rigid structure but with thinner materials applied at the same time, without internal supporting means and with properly arranged the heat transfer contacts. The succeding goal of the new idea is to reduce problems with getting proper size of the ready to use exchanger since adding extra active surface is extremely easy in this contineously manufactured construction. 5 The other object of the invention is to provide the exchanger made of different materials, eg. plastic tube and aluminium fin and easiness in obtaining the proper heat contacts. The following object is to provide heat exchanger sections which can easily be arranged into multi sectional unit of larger size while mamtaining the idea of o counter-flow directions of the exchange. And still the internal supporting means are unnecessary. The foregoing object is to reduce number of pieces that comprise the exchanger by applying one of the flat strips to create the outer band by wrapping the heat exchanging element more than once. The arranged into spiral tube allows to reduce size of the exchanger and length of the tube since the bends are now in the interior of the structure. That is the 5 next aim of the invention. Sofar, the bends with the best conditions of the heat transfer on the inner medium side, if it is forced to flow, are placed outside the outer medium stream and do not take part in the exchange. The next object is to provide an electrical heater element with significantly reduce outer surface point maximum temperature to increase safety of general o usage of such type of heaters. All these objects become realized by the convectional heat exchanger provided accordingly with the present invention. This convectional heat exchanger is structured of tube inside which there is existing or flowing the medium, called the inner medium. The tube may be of any 5 shape of its cross section, especially any closed one, and at least slightly flatted on its both opposite sides is preferred. There are two ends of the tube operating as an inlet and an outlet of the inner medium, if that medium is forced to flow. This tube is bent into a spiral shape at the same time with its heat exchanging element which is formed of the flat and corrugated strips occuring alternatively. 0 In the perpendicural direction to the plane of the spiral the outer medium flows. The external of the exchanger is made of the band securing permament and reciprocal pressure of the fins, the tube and this band in their common points of contacts. This serves to achieve proper heat conduction in the body of the exchanger on one side and rigid structure on other side still applying thinner fin 5 materials. The provided flat strips placed parallelly to the tube are increasing total 'working surface' and flow turbulence. Changes in the lengths of corrugated strips allow to obtain the outer band shape close to a circle. But other special shapes are still possible to reach. The outer band is formed of the flat strips which are basicly longer than the 0 corrugated strips, especially of about a length of two circumferences of the exchanger at least one is longer. An end of the longest flat strip is permamently secured to its outer surface on the mentioned circumference. The corrugated strips are of the thicker materials since they are positioned closer to the tube. The flat and corrugated strips are made profitably each of seperate piece of material. 5 That is obvious that the fin material requires good heat conductivity and the tube material has to be sufficiently plastic. The outer band might serve to secure to the exchanger body additional elements such as installation supports or fan supports or safety net supports. On the surfaces of the corrugated strips being out of direct contact with the flat 0 strips there are provided internal and external dents viewing from the same top of the corrugation. They make the strips more rigid and increase the flow turbulence. On the surfaces of the flat strips being out of direct contact with the corrugated strips there are provided convex and cocave extinctions existing alternatively, especially at least two of each. They allow to increase the reciprocal pressure of all elements and the flow turbulence,as well. 5 The foregoing and other characteristics, objects, features and advantages of the present invention will become more apparent upon consideration of the following detailed description, having reference to the accompanying figures of the drawing, wherein: Fig.1 shows the convectional heat exchanger having the tube bent into the spiral o shape in the view of the outer medium flow direction. Fig. 2 is a cross-section of the exchanger from fig. 1 in a plane parallel to that direction. Fig. 3 shows a detail "C" in an enlargement. Fig. 4 shows the flat strip and the corrugated strip in the cross-section B - B. 5 Fig. 5 is a detail of fig. 4 in the cross-section D - D. Referring to fig. 1, there is presented the convectional heat exchanger upon the recent invention, where the tube 1 with the inner medium is bent commonly with its heat exchanging element 2 into the shape of the spiral with coils 8. The element 2 comprises in this example embodiment four corrugated strips 3, 3a, o and 4, 4b and three flat strips 5, 51 and 52. It is possible to arranged different number of these strips upon special heat transfer applications. The corrugated strips are made of gradually different length and in this example the strip 3a is longer than 3 and the strip 3 is longer than 4b and 4b than 4. It is possible that the lengths of the flat strips are different and in this case the strip 52 is longer 5 than the others of more than about two outer circumference of the exchanger body and the end of that strip is durable fastened to its outer surface determining that circumference. It is to be impressed that the choice of sequence of variaties of the flat strip length is optional since the longest one with its end reaches this strip free outer surface to be fastened to it. The circumference of the exchanger is 0 pretty close to the circle. Fig. 2 presents the heat exchanger in the view of the cross section A - A from fig. 1. The tube I comprises two ends la and lb called respectively the inlet and the outlet of the inner medium and it is flattened on plane Ha and opposite to its longitudinal axle lib. The corrugated strips are in the direct contact with the tube 5 1 in places 14 and with the flat strips in places 10. Fig. 3 shows the detail numbered "C" of fig. 1 in an enlargement. The corugated strip 3, closer to the tube I is made of the thicker material than the next 3a. On the surface of the corrugated strip being out of contact with the flat strips there are provided internal dents 9a and external dents 9b of length from o point 11 to 12 on this surface. The dents have their width measured in the direcion of the outer medium flow no much different to the distance between the points 11 and 12. Fig.4 shows a depth of these dents which is about 0,25 mm to 5 mm and this depends on the heat transfer application and kind of fin materials. The flat strip comprises concave extrutions 5a and convex extructions 5b existing alternatively. These extructions have their lenght measured in direction of the strip lenght no larger than the distance between point l_3a and point 13b being on the strip surface placed out of contact with the corrugated strips. Places 10 of the flat and corrugated strips are devoided of any extructions and any dents and their avarage direction is across the strips. Fig. 5 shows that the concave and convex extructions are at least two of each on each side of the same corrugated strip top which covers with the places 10 and their depth is about 0,25 mm to 5 mm and this depends on the heat transfer application and the kind of fin materials. The width of these extructions is about their length. Although the invention is disclosed with reference to the particular embodiment thereof, it will become apparent to those skilled in the art that numerous modofications and variations can be made which will fall within the scope and spirit of the invention as defined by the attached claims.

Claims: Claims 1. A convectional heat exchanger characterized in that it comprises a tube (1) which cross section in a plane perpendicular to its longitudinal axle has a free- of-choice shape, especially forming closed figure having opposite parts (11a) and (1 lb) at least slightly flattened, with its end (la) and end (lb) and a heat 5 exchanging element (2) made of metal being a good heat conductive material and formed of at least two corrugated strips (3) and (4) which length may be different, placed with their corrugations along the tube and contacted with parts (11a) and (1 lb) and of at least one flat strip (5) positioned parallelly to the tube longitudinal axle separating the corrugated strips and contacted with them in o areas (10) placed across the strip and on tops (6) of the corrugations and a band (7) ensuring permament reciprocal contact in the tangent places of the tube, the corrugated strips and the flat strip. 2. An exchanger as set forth in claim 1 characterized in that ends (la) and (lb) are an inlet and an outlet respectively of the inner medium. 5 3. An exchanger as set forth in claim 1 characterized in that the tube (1) with a heat exchanging element (2) at the same time is bent into a spiral (8), while the band (7) reaches shape close to solid figure with rounded edges, especially a cylinder. 4. An exchanger as set forth in claims from 1 to 3 characterized in that 0 corrugated strips (3) and (4) are shaped into a wavy corrugation with side surfaces (9) being out of direct contact with the flat strip (5), on which there are provided internal (9a) and external (9b) dents, at least one of each viewing from the same top (6). 5. An exchanger as set forth in claim 4 characterized in that following dents (9a) 5 and (9b) are provided on the same side surface (9) alternatively in distances approximately equal to their width and their depth is at least 0,25 mm large and their length is not larger than distance between points (11) and (12) on the same side surface (9). 6. An exchanger as set forth in claims from 1 to 3 characterized in that a flat strip 0 (5) comprises concave (5a) and convex (5b) extructions, at least two of each on each side of the same corrugation top (6) existing alternatively in rows across the strip in optional distances, while their depth is at least 0,25 mm large and their width is not larger than a distance between following points (13a) and (13b) being on the strip surface placed out of direct contact with the corrugated strips and places (10) in that contact are devoided of any extructions. 7. An exchanger as set forth in claim 1 characterized in that following corrugated strips (3 a), (4b) and other counting from the tube (1) are made of tliinner material while this thickness is proportional to a conductive heat transfer in the strip body while a strip surface temperature is the same and close to the temperature on this surface of the closest to the tube (1) strip. 8. An exchanger as set forth in claim 1 characterized in that a band (7) is formed of at least one contineous flat strip (5) which length is longer than length of the longest corrugated stop of more than one full circumference of the exchanger body while end of the longest corrugated strip is fastened durably to its outer surface forming this circumference. 9. An exchanger as set forth in claim 8 characterized in that difference between both lenghts counts more than two mentioned circumferences.

Inventors: SOKULSKA ELZBIETA, SOKULSKI ANDRZEJ, SOKULSKA, ELZBIETA, SOKULSKI, ANDRZEJ
Applicants: SOKULSKA ELZBIETA, SOKULSKI ANDRZEJ, SOKULSKA, ELZBIETA, SOKULSKI, ANDRZEJ
Application year: 1999
Main classification: F28D7
IPC codes: F28D1, F28F1