WO2008078211A1

WO2008078211A1 - A heat exchanger

Info

Publication number: WO2008078211A1
Application number: PCT/IB2007/054951
Authority: WO
Inventors: Pinar Unsal
Original assignee: Turk Demir Dokum Fabrikalari Anonim Sirketi
Priority date: 2006-12-20
Filing date: 2007-12-06
Publication date: 2008-07-03

Abstract

The present invention relates to a heat exchanger (1), in which heat transfer is enhanced by using two types of tubes with different diameters and which comprises two sections, one of the said sections being the first step (2) which includes tubes of big diameter (4) with fins (6) and the other being the second step (3) which includes tubes of small diameter (5) without fins (6).

Description

Description A HEAT EXCHANGER

[ 1 ] Field of the Invention

[2] The present invention relates to a heat exchanger, in which heat transfer is enhanced by using two types of tubes with different diameters and which comprises two sections, one of the said sections being the first step which includes tubes of big diameter with fins and the other being the second step which includes tubes of small diameter without fins.

[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] In the heat exchanger types operating in accordance with the principle of multi-pass cross-flow, the reciprocal media with highest and lowest temperatures of the media which will exchange heat are in transfer relation. The hottest portion of the combustion gas and the domestic water with the highest temperature, which is about to leave the exchanger, exchange heat at the interface of the exchanger. Thus, in the multi-pass cross-flow exchanger system, the hottest and coldest portions of both of the media that will exchange heat will meet each other. In the region where the combustion gas has relatively cooled, the cold water returning from the installation exchanges heat with the combustion gas. At the region where combustion gas is weakest in terms of heat transfer capacity, the cold water returning from the installation will be pre-heated and as it moves forward within the exchanger it will be in transfer with the hotter combustion gas and eventually will reach the highest temperature. From the point of the combustion gas, condensation will be more efficient at the region where it meets with the relatively cold domestic water. [6] In heat exchangers, the heat transfer surface needs to be increased in order to provide an efficient heat transfer between water and gas. For that reason, fins are fitted around the tubes through which water passes.

[7] The International patent application No. WO9706398, which is a state of the art, discloses a heat exchanger comprised of a plurality of metal tubes. The tubes are disposed in parallel with each other and there are fins in between the said tubes providing heat transfer. The heat exchanger on which the metal support plates are arranged includes first and second holes on the plates. The second holes through which the tubes pass have a smaller diameter than the first holes.

[8] USA patent application No. US2004188076, in which another state of the art application is described, discloses an invention including a heat exchanger header made of a plastic material. Efficiency of the exchanger is enhanced by employment of tubes having a smaller diameter than the aluminum tubes.

[9] Two pass heat exchangers are disclosed in the European patent application No.

EP0844453, which is another state of the art application. The first pass is the section which includes a plurality of tubes. The second pass is the section including a single tube. The inventive heat exchanger also functions as a condenser. Diameter of the tube in the second section is bigger than the diameter of the tubes in the first pass.

[10] In the applications known in the art, employment of tubes with different diameters in heat exchangers is mentioned. However, there are not provided two sections for tubes with different diameters, one of the said sections being with fins and the other without fins. In this case heat transfer is not realized effectively.

[11] Summary of the Invention

[12] The objective of the present invention is to realize a two step heat exchanger in which efficiency of heat transfer is enhanced by using two types of tubes with different diameters.

[13] Another objective of the present invention is to realize a heat exchanger comprising tubes of big diameter wherein fins are used and tubes of small diameter wherein fins are not used.

[14] Detailed Description of the Invention

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

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

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

[18] 1. Heat exchanger

[19] 2. First step

[20] 3. Second step [21] 4. Tube of big diameter

[22] 5. Tube of small diameter

[23] 6. Fin

[24] 7. Aperture

[25] The inventive heat exchanger (1) comprises at least one tube (4) of big diameter in which the water, to which combustion gas transfers its heat, circulates; at least one tube (5) of small diameter in which cold water returning from the installation circulates, and at least one fin (6) fitted around the tube of big diameter.

[26] The heat exchanger comprises the sections of first step (2) consisting of the tubes of big diameter with fins (6) and the second step (3) consisting of only the tubes of small diameter.

[27] The tubes of big diameter and the ones with small diameter are disposed parallel to each other. The tubes (5) of big diameter are arranged to be passed through the apertures (7) on the fin (6).

[28] The region where the combustion gas initially enters in the heat exchanger (1) is the first step (2) of the exchanger (1) where the first stage of heat transfer takes place. The region where the combustion gas is about leave the heat exchanger (1) is the second step (3) where the next stage of the heat transfer is realized. The exchanger (1), which is designed in two steps in different configurations for the heat transfer to be realized most efficiently, enables benefiting from the combustion gas at the maximum level.

[29] In the first step of the heat exchanger (1), the temperature difference between the combustion gas and the domestic water, i.e. the heat transfer potential is very high. Accordingly, for the water to efficiently receive the heat provided by the gas at the first step (2), the surface of the heat transfer should be large, and the water, which is the medium to receive the heat, should be in large masses. Fins (6) are fitted around the tubes (4) with the purpose of enlarging the surface of the heat transfer for the domestic water to efficiently receive the heat of the combustion gas. At the first step (2) of the exchanger (1), tubes (4) of big diameter are used between fins (6) which will provide intense transition of water masses. The first step (2) of the heat exchanger (1) comprises fin (6) forms where heat distribution is homogenized and the heat transfer is enhanced by optimizing the surface area.

[30] The combustion gas, which has transferred almost all of its energy (all of the bottom thermal value of natural gas) to the domestic water at the first step (2) and whose temperature has fairly decreased, circulates around the tubes (5) with small diameter at the second step (3) of the heat exchanger (1). Due to this decrease in temperature, water vapor within the combustion gas reaches dew point temperature. At this point, combustion gas transfers the hidden energy (top thermal value of natural gas) arising upon the transformation of the water vapor it includes into water, to the domestic water.

[31] In the second step (3) where the combustion gas condenses and the temperature difference is less, fine meshed and flat surfaces are formed for the condensation to be realized with ease. In order to increase the heat transfer and the condensation resulting therefrom, a close arrangement of tubes (5) with small diameter was designed. Diameter of the tubes with small diameter in the arrangement has been designed so that on one hand it will turbulate combustion gas and on the other hand minimize pressure loss. There are not any fins (6) around the tubes (5) used in the second step (3) of the exchanger (1).

[32] In the inventive exchanger (1), since there are the risks of high temperature and acidic corrosion, stainless steel material at the optimum intersection point for corrosion strength, processability and cost criteria is used. Upon theoretical and experimental observation of the said criteria, the grade of the stainless steel material has been determined as AISI 304 quality.

[33] 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) characterized in that it comprises a first step (2) section wherein the combustion gas initially enters and is at its hottest state, the coldest state of the water, to which the said gas transfers its heat, circulates, the first step comprising at least one tube (4) of big diameter through which the intense transition of water masses is realized and at least one fin (6) fitted around the said tube (4); and a second step (3) section comprising tube of small diameter (5) which is disposed in parallel with the said tube (4) of big diameter, in which the cold water returning from the installation, to which the gas that has transferred almost all of its energy to the domestic water at the first step (2) transferred its heat, circulates, which does not have fins (6) around it, designed with a diameter allowing it to turbulate combustion gas and minimize pressure loss, arranged as fine meshed and flat surfaces.