WO2008075240A1

WO2008075240A1 - A heat exchanger

Info

Publication number: WO2008075240A1
Application number: PCT/IB2007/054940
Authority: WO
Inventors: Pinar Unsal
Original assignee: Turk Demir Dokum Fabrikalari Anonim Sirketi
Priority date: 2006-12-19
Filing date: 2007-12-06
Publication date: 2008-06-26

Abstract

The present invention relates to a heat exchanger, in which resistance arising between the tubes (2) and fins (3) is decreased, and which comprises fins (3) where heat transfer is increased by homogenization of heat distribution.

Description

Description A HEAT EXCHANGER

[ 1 ] Field of the Invention

[2] The present invention relates to a heat exchanger, in which resistance arising between the tubes and fins is decreased, and which comprises fins where heat transfer is increased by homogenization of heat distribution.

[3] Background of the Invention

[4] Heat exchangers are devices which perform heat transfer between two fluids of different temperatures. In the heat exchangers used in condensing boilers, heat exchange is realized between the water that is desired to be heated and the natural gas which will transfer the combustion energy to the water. In the heat exchangers, natural gas should combust in the most efficient way and the domestic water should be heated most efficiently by the said combustion gas. For that reason, there are the following parts in the system: a mixer providing the pre-mixing of natural gas and air, a burner in which the air-gas mixture is burned, a combustion chamber where the movement of the combustion gas is directed and which accommodates the heat exchanger, a heat exchanger inside of which domestic water and outside of which combustion gas circulates, a flue gas outlet which discharges the flue combustion gas from the combustion chamber after the heat exchange is completed and a condensation water outlet which discharges the water generated by the condensation of flue combustion gas from the combustion chamber after the heat exchange is completed.

[5] Heat transfer surface needs to be increased in order to provide an efficient heat transfer between water and gas in heat exchangers. For that reason, fins are fitted around the tubes through which water passes. The tubes and the fins are connected to each other via hard soldering. The fins, increasing the heat transfer area in the heat exchangers, are designed as plates with a smooth form having a rectangular outline. However, a regular temperature distribution does not occur on a fin with the said form. Some parts of the plates are overheating while some parts remain unnecessary in terms of heat transfer and do not play an effective role. Additionally, the fixed distance between the fins, located in the heat exchanger in the state of the art, cannot be maintained. Difficulties are arising due to the fact that the fixed distance cannot be maintained during disposition of the fins and arrangement of the tubes.

[6] In the European patent application No. EP0325553, which is a state of the art application, heat exchangers in which developments enhancing the heat transfer area between adjacent tube holes on the fin plate are disclosed.

[7] USA patent application No. US2006005956, in which another state of the art application is described, fins designed in sinusoidal shape so as to increase the heat transfer are disclosed.

[8] Another heat exchanger known in the art is disclosed in the French patent application

No. FR2532409. In the designs of the said application, in which heat exchangers which comprise separate parallel tubes and which are obtained by disposition of a plurality of fin plates are disclosed, there are openings on each plate to which the tubes are fitted.

[9] In the applications known in the art, there is a process of welding the interface at the contact point of tube and fin by hard soldering. However, a heat exchanger, in which small holes formed at the contact surface are designed with the purpose of injecting the solder in between the tube and fin, is not present in the state of the art. The fins are in the form of flat plates, not allowing heat transfer to be performed regularly.

[10] Summary of the Invention

[11] The objective of the present invention is to realize a heat exchanger in which heat transfer is rendered efficient by providing complete contact of the tubes and fins.

[12] Another objective of the present invention is to realize a heat exchanger in which the fixed distance between the fins, which are disposed back- to-back, is maintained.

[13] Another one of the objectives of the invention is to realize a heat exchanger in which heat transfer is enhanced and heat distribution is homogenized by the minimized fin surface area.

[14] Detailed Description of the Invention

[15] The heat exchanger realized to fulfill the objectives of the present invention is illustrated in the accompanying figures, in which;

[16] Figure 1 is the perspective view of the heat exchanger.

[17] Figure 2 is the perspective view of the fin used in prior art.

[18] Figure 3 is the perspective view of the inventive fin.

[19] Figure 4 is the top view of the injection hole.

[20] The parts shown in the figures are numbered individually where the numbers refer to the following:

[21] 1. Heat exchanger

[22] 2. Tube

[23] 3. Fin

[24] 4. Hole

[25] 5. Protrusion

[26] 6. Interface

[27] 7. Aperture

[28] 8. Bore

[29] 9. Corrugated structure

[30] The inventive heat exchanger (1) comprises at least one tube (2) in which the water, to which combustion gas transfers its heat, circulates, and at least one fin (3) which is located at the medium where the gas circulates and which is fitted around the tube (2) in order to increase the heat transfer surface.

[31] Fins (3) comprise at least one hole (4) at the welding point of the interface (6) and the tube (2) where soldering is injected and which ensures the fin (3) and the tube (2) to be welded to each other.

[32] On the fins (3) disposed back to back, there are side protrusions (5) which ensure the distance between the fins (3) to remain constant.

[33] The heat exchanger (1) comprises fin (3) forms where heat distribution is homogenized and the heat transfer is increased upon minimizing the surface area.

[34] In order for the domestic water to receive the heat of the combustion gas efficiently, the heat transfer surface should be large. For this reason, fins (3) are fitted around the tubes (2) with the purpose of enlarging the heat transfer surface and it is ensured that the tube (2) and the fin (3) completely contact each other so that no resistance occurs at the welding surface.

[35] If the tube (2) and the fin (3) do not completely weld each other, conduction of heat will not be possible in accordance with the principle of conduction heat transfer. In the case that there is no welding between the tube (2) and the fin (3), conduction of heat between the contacting material molecules by conduction method will not be realized. Self heating fins (3) will not be able to transfer heat and will burn after a while.

[36] In the case that the welding between the tubes (2) and the fins (3) is poor, there will be some heat transfer from the fins (3) to the surface of the tube (2). But since sufficient heat transfer is not realized, the desired efficiency regarding water heating will not be achieved and deformation will occur due to overheating at the form of the fin (3) which can not conduct its heat. The conducting medium in between is a combination of air and welding material. This medium will create a thermal resistance at the interface (6) and will hinder highly efficient heat transfer.

[37] When the tube (2) and the fin (3) completely weld each other, there will not be a resistance causing loss of heat and the heating fins (3) will directly transfer their heat to the tube (2). Materials creating low resistance facilitate heat conduction whereas media with high resistance make the transfer difficult.

[38] In the inventive heat exchanger (1), the tubes (2) and the fins (3) are welded to each other by hard soldering. In welding AISI 304 quality stainless steels, soldering is applied by hard soldering at the controlled atmosphere oven so that they exhibit high sensitivity and working performance. Additionally, a solder paste with a high amount of nickel content is used which enables the heat exchanger (1) to overcome the compelling conditions in work environment such as high temperature and acidic corrosion. When the medium in the interface (6) is 100% full with high nickel base solder paste which is welding material and stainless steel materials, the targeted heat conduction performance is reached.

[39] Importance of the interface (6) at the contact of the tubes (2) and the fins (3) is major from the point of soldering. In the case that the interface (6) area is large, if sufficient amount of solder paste does not fuse into that region, an efficient soldering is not performed. When the interface (6) area is small, even if sufficient amount of solder is used, the adherence surface between the fin (3) and the tube (2) does not suffice whereby the surfaces do not weld each other. Holes (4) are formed at the interface (6) in order for the solder paste to be injected in between the tube (2) and the fin (3). The hole (4) opens to the apertures (7) through which the tube (2) passes. The purpose of the holes (4) on the fins (3) is to ensure that the solder paste is conveyed to the interface (6). Solder paste is conveyed in between the tube (2) and the fin (3) by passing through the holes (4) a long needle and thus penetration of the solder paste is facilitated. Diameters of the holes (4) are designed so that they are bigger than the diameter of the needle that will ensure injection of the required amount of paste at one go, but small enough to be able to be covered by soldering.

[40] In order to maintain the fixed distance between the fins (3) during disposition of the fins (3) and arrangement of the tubes (2), side protrusions (5) have been designed on the fins (3) in the inventive heat exchanger (1). A fixed distance is maintained between the fins (3) disposed back to back, by means of the protrusions (5) and it is ensured that the fins (3) do not engage into each other even if forced. Protrusions (5) are pieces arranged vertically between tubes (2), projecting along the sides of the fins (3). One of the long sides of the protrusion (5) is adjacent to the fin (3) while the short side of the protrusion (5) is positioned to be parallel to the tubes (2).

[41] In order to provide a regular temperature distribution on the fin (3), surface areas of the plates designed in a rectangular shape are minimized. This way, heating of the regions which are functionless in terms of heat transfer is hindered while overheating of some regions is prevented. Functionless regions of the fin (3) are taken out from the rectangular fin (3) shape and the final form of the fin (3) is attained. Along both sides of the fins (3) parallel to the tubes (2), the corrugated structure (9), which is above and below the apertures (7) through which the tubes (2) pass, is taken out of the fin (3) so as to constitute a wavy form along the side of the fin (3). Additionally, there are bores (8) between the apertures (7) taken out of the fin (3) form so that they will preferably be above or below the hole (4). The fin (3) is finalized upon removing these parts which irregularize the heat distribution.

[42] Within the framework of the basic principles described herein, development of various embodiments of the invention is possible. The inventive heat exchanger (1) cannot be limited with the examples provided above to facilitate understanding of the subject. The invention is essentially according to the claims.

Claims

[1] A heat exchanger (1) comprising at least one tube (2) in which the water, to which combustion gas transfers its heat, circulates, characterized by at least one fin (3), fitted around the tube (2), comprising at least one hole (4) located at the welding point of the interface (6) and the tube (2) where the solder paste is injected.

[2] A heat exchanger (1) according to Claim 1, comprising at least one fin (3) characterized by at least one hole (4) which is designed to be bigger than the diameter of the needle that will ensure injection of the solder paste at one go, but smaller than the diameter suitable for covering by soldering.

[3] A heat exchanger (1) according to any of the preceding claims, characterized by at least one fin (3) comprising side protrusions (5) which ensure maintenance of the fixed distance between the fins (3) arranged around the tubes (2).

[4] A heat exchanger (1) according to any of the preceding claims, comprising at least one fin (3) characterized by a protrusion (5), arranged perpendicularly between the tubes (2) projecting along the sides of the fins (3), said protrusion comprising a long side adjacent to the fin (3) and a short side parallel to the tubes (2).

[5] A heat exchanger (1) according to any of the preceding claims, characterized by a fin (3) where functionless regions are removed from the rectangular form and surface area is minimized by removing, along both sides of the fins (3) parallel to the tubes (2), the corrugated structure (9), which is above and below the apertures (7) through which the tubes (2) pass, so as to constitute a wavy form along the side of the fin (3) and taking the bores (8), located between the apertures (7) preferably above or below the holes (4), out of the fin (3) form.