AU2017101057A4 - Double Finned Tube for a Heat Exchanger - Google Patents

Abstract

There is disclosed a method of manufacturing a double finned tube for a heat exchanger comprising forming fins on an inner tube, inserting the inner tube into an outer tube, and forming finds on the outer tube. Also disclosed is a double finned tube 5 comprising a finned inner tube and a finned outer tube wherein an outer diameter of the fins surrounding the inner tube is between 12 mm and 19.05 mm. 9246305_1 (GHMatters) P105138.AU 3/08/17 N)LL

Description

-1 - 2017101057 03 Aug 2017

DOUBLE FINNED TUBE FOR A HEAT EXCHANGER TECHNICAL FIELD

There is disclosed a double finned tube for a heat exchanger.

BACKGROUND ART 5 Various types of heat exchangers are known for transferring thermal energy from one body or fluid medium to another. Two types of heat exchangers that are widely used are shell and tube heat exchangers and radiators.

Radiators are commonly provided in automobiles, in air-conditioning units for buildings and in machinery or electronics, wherein the radiators are normally arranged to io dissipate heat from such bodies. For example, the heat generated in an engine block of a motor vehicle is absorbed into a cooling liquid that is pumped through the engine block. The cooling liquid is then transferred to the radiator where it is distributed through a matrix of many fine tubes. Ambient air is blown through the tube matrix, either by a fan or by movement of the automobile, so that the heat dissipates from the is tubes to the air. It is common to provide fins on the tubes or extending between the tubes to increase the surface area of the tubes so as to increase the rate of heat transfer from the tubes to the ambient air.

Radiators are also used in industrial machinery, such as provided at a mine. In one application, the radiators are used in air-conditioning units for cooling air that is 2 0 circulated through the tunnels of an underground mine. In another application the radiators are used to cool operating fluids, such as water and oil used in the mining machinery. Such radiators are normally large scale units requiring a large volume of air to be blown through the finned tubes by fans to obtain the requisite amount of cooling. Accordingly, the fans used to blow the air are normally relatively large and 25 operate at high speeds. One problem that is often encountered with such large, highspeed fans is noise pollution. Although the fan motors can be designed to operate relatively quietly, the major source of the fan noise pollution derives from the rotational movement of the fans blades through the air. Many countries have health regulations prescribing the maximum volume of noise that may be generated and this thus limits 30 the speed at which the fans can operate. For example, in Western Australia current 9246305_1 (GHMatters) P105138.AU 3/08/17 -2- 2017101057 03 Aug 2017 legislation stipulates a workplace exposure standard of 85dB averaged over an eight hour period, or a peak noise level of 140dB. Where these values are exceeded, all practicable measures must be taken to reduce the noise level by engineering noise control. Failing this, ways must be explored to reduce the exposure time by half for 5 every 3dB the level is above the exposure standard. Thus the noise generated by the fans should preferably be below 85db and ideally should be below 80dB, to avoid the necessity of wearing protective gear. For this reason, there tends to be a limit on the maximum rate of heat transfer that can be achieved with such industrial radiators.

Shell and tube heat exchangers are more often used in chemical processes and ίο production plants, such as oil refineries and offshore oil drilling rigs, to transfer thermal energy between two fluids. The heat exchanger comprises an outer shell enclosing a cavity in which a number of tubes are located. A first fluid passes through the tubes while a second fluid passes through the cavity of the shell to flow over the tubes so that thermal energy is transferred between the two fluids. Similarly to radiators, tubes of the is shell and tube heat exchangers are provided with fins to increase the surface area of the tube and to thereby increase the rate of heat transfer, which enables the size of the shell and tube heat exchangers to be reduced.

The fins can be formed on the tubes by attaching or winding a fin strip externally onto the tubes. Alternatively, the fins can be integrally formed by roll extruding the tubes. 2 0 For example, Wieland-Werke GmbH provides a series of low finned tubes wherein the fins are integrally formed on the outer surface of the tubes. The inner surface of the tubes can be smooth (their GEWA-K range of tubes) or the inner surface can be provided with additional grooves (their GEWA-KS range of tubes) to further increase the heat transfer surface area. In comparison to smooth tubes, Wieland-Werke GmbH 25 discloses that the finned tubes allow size reductions in evaporators and condensers of between 30-65%. This is advantageous in that the total weight of the heat exchangers can be reduced and also the pressure drop of the fluid flowing through the tubes is reduced.

However, it will be appreciated that there are both manufacturing and operational 30 difficulties that are encountered when in making smaller diameter tubes. Firstly, it becomes difficult to insert any tools within the tubes to support the tubes during the roll extrusion process and to form the grooved inner surface. Also, in use, the reduced 9246305_1 (GHMatters) P105138.AU 3/08/17 -3- 2017101057 03 Aug 2017 diameter will increase the pressure drop of fluid flowing through the tubes is increased. The applicant is aware that the smallest finned tube currently offered by Wieland-Werke GmbH has an outer diameter of % inch.

Such tubes used in heat exchangers may be subject to puncture or other failure, 5 causing a leak. A leak can result in the heat exchanger ceasing to function, and a resulting shut down of operations while the tube is removed and fixed. To alleviate some of these problems double tubes may be used. Such tubes comprise an inner tube and an outer tube. If the inner tube perforates, the cooling liquid can flow between the inner and the outer tubes, and this can be easily detected, and repaired, without a ίο catastrophic failure.

In order to maintain the heat transfer properties of the double tube, it is important to keep the distance between the inner and outer tubes of such a double tube within small tolerances. Therefore, arranging the inner and outer tubes relative to one another can be problematic. is It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a method of 2 0 manufacturing a double tube for a heat exchanger, the method comprising: providing an inner tube; forming fins on an outer surface of the inner tube; providing an outer tube; inserting the inner tube into the outer tube; and 25 forming fins on an outer surface of the outer tube; wherein the step of forming fins on the outer surface of the outer tube creates a bond between the inner tube and the outer tube.

The bond may be a friction bond between one or more fins of the inner tube and an inner surface of the outer tube. 9246305_1 (GHMatters) P105138.AU 3/08/17 -4- 2017101057 03 Aug 2017

The step of forming fins on the outer tube and/or the inner tube may be carried out by rolling. The rolling may be carried out using a die. The die may have three discs.

The method may further comprise inserting a sensor into a flow path between the inner tube and the outer tube. 5 A double tube for a heat exchanger comprising: an inner tube having an inner tube body; an outer tube having an outer tube body; one or more fins integrally formed on and extending outwardly from both the inner tube body and the outer tube body; 10 wherein an outer diameter of the inner tube is between 12 mm and 19.05 mm. A double tube as claimed in claim 4, wherein the inner diameter of the outer tube is between 12.5 mm and 20.05 mm.

The inner tube or the outer tube may have a wall thickness of about 1 mm.

The fins may have a fin height of about 0.5 mm. is The fins may be provided in the form of a spiral that helically surrounds the inner tube body or the outer tube body.

The inner tube body or the outer tube body may be manufactured from a Copper-Nickel metal alloy in the ratio 90/10. In a further embodiment the inner tube body or the outer tube body may be manufactured from carbon steel or stainless steel. 20 According to another aspect of the present invention, there is provided a heat exchanger comprising at least one double tube as described herein.

The finned tubes may be arranged in a straight tube configuration within the heat exchanger.

The heat exchanger may comprise a radiator. 25 The heat exchanger may comprise a shell and tube heat exchanger. 9246305_1 (GHMatters) P105138.AU 3/08/17 -5- 2017101057 03 Aug 2017

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example, with reference to the accompanying schematic drawings, in which:

Figure 1 is a side view of a of a double finned tube for a heat exchanger; and 5 Figure 2 is an enlarged partial sectional side view of one end of the double finned tube shown in Figure 1.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to Figures 1 and 2, there is shown a double finned tube 10 in accordance with a first embodiment of the invention. ίο The double finned tube 10 comprises an inner tube 12 and an outer tube 14. The inner tube 12 comprises a smooth portion 20 and a finned portion 24. Similarly, the outer tube 14 comprises a smooth portion 22 and a finned portion 26.

The finned portion 26 of the outer tube 14 is provided with radially projecting fins 16. The finned portion 24 of the inner tube 12 is provided with radially projecting fins 18. 15 Both the inner tube 12 and the outer tube 14 are provided with respective end portions 20 and 22 which are smooth (i.e. without fins), and which are used for connecting the double finned tube 10 to other components in a heat exchanger (not shown).

The fins 16 of the outer tube 14 are omitted from a central portion of the double finned tube 10 illustrated in Figure 1 for clarity. 20 It will be appreciated that in other embodiments the double finned tube 10 can be provided without the end sections so that the fins 16 and 18 extend along the full length of the tube 10.

The tube 10 can have any suitable length for use in a heat exchanger.

As is more clearly shown in Figure 2, the unfinned end section 22 of outer tube 14 has 25 an outer diameter ODou, Similarly, the unfinned end section 20 of inner tube 12 has and a uniform outer diameter ODiu. In the embodiment shown, OD0u is19.05 mm and ODiu is 16 mm. Both the inner tube 12 and the outer tube 14 are annular and have a 9246305_1 (GHMatters) P105138.AU 3/08/17 -6- 2017101057 03 Aug 2017 sidewall (i.e. a radial thickness) of 1 mm. In a further embodiment, the radial thickness of a tube may be between 0.5 mm and 1 mm.

However, it is to be realised that the primary purpose of the unfinned sections of the inner and outer tube are to form attachments with other parts of a heat exchanger and 5 therefore, the diameters may be sized appropriately.

The finned portion 26 of the outer tube 14 has an outer diameter OD0f and the finned portion 24 of the inner tube 12 has an outer diameter OD|F. In both cases, the outer diameter is measured to include the height of the fins. In the embodiment shown, OD0f is 17.9 mm and OD|F is 14.5mm. However, in further embodiments, different ίο sizes may be chosen for the respective outer diameters.

In the embodiment illustrated, the outer diameter of the inner tube is 0.5 to 1 mm less than the inner diameter of the outer tube as this provides for a mechanical bond within the tolerances of certain manufacturing techniques (as described below). In further embodiments, there is less differences between the outer diameter of the inner tube 15 and the inner diameter of the outer tube. For this manufacturing technique, it has been found that an outer diameter of the inner tube between 12 mm and 19.05 mm and an inner diameter of the outer tube between 12.5 mm and 20.05 mm may form a good bond between the inner and outer tubes.

In the embodiment the fins 16 and have substantially rectangular in cross-sectional 2 0 shape defining rectangular troughs between neighbouring fins. However, it will be appreciated that the fins can have other cross-sectional shapes, such as triangular or arcuate.

The fins 16 and 18 are integrally formed in the sidewall of the corresponding tube by roll forming the sidewall. The fins 16 and gradually increase in size through a lead-in 25 section until they reach their desired uniform height in a central section. Thereafter the height of the fins remains constant throughout the central section. A similar lead-in section is provided at the opposed end of the respective tube. In the embodiment illustrated the fins 16 and 18 are in the form of a single spiral that helically surrounds the respective tube . It will be appreciated that the fins could comprise multiple fins 30 arranged parallel to each other and having multiple run starts. Alternatively, the fins 9246305,1 (GHMatters) P105138.AU 3/08/17 -7- 2017101057 03 Aug 2017 can be in the form of discrete planar discs orientated parallel to each other and being orientated substantially perpendicular to the respective tube body.

In the embodiment shown, the fin height is 0.5 mm.

The fins 16 have a pitch of 0.876 mm and a helix angle of 2.28 degrees. However, it 5 will be appreciated that variations of these values are permissible.

The inner tube 12 is formed with fins by roll extrusion of a smooth tube to form the fins 18 along the tube body. The roll extrusion is performed in a conventional manner using a roll extrusion machine (not shown) comprising a number of rolling discs, typically three discs, being equally spaced circumferentially around the tube. By pressing the ίο rolling discs against the tube 12, the material of the sidewall is deformed and displaced to form the outwardly projecting fins 18. Depending on the desired dimensions of the fins 18 and the configuration of the rolling discs, the fins 18 may comprise less material than is displaced from the sidewall. This results in a stretching of the tube 18 to accommodate the additional material, whereby the tube 10 may be elongated by about 15 10-20% of its length during the roll extrusion process. Optionally the roll extrusion machine can include a mandrel to internally support the tube 10 during the roll extrusion.

The finned inner tube 18 is then placed inside a smooth outer tube, and the resulting arrangement is subjected to rolling, causing the formation of the fins 16 on the outer 20 surface of the outer tube14. Advantageously, this further causes a small reduction in the inner diameter of the outer tube 14 over the portion where the fins are formed. The outer diameter of the inner tube and the inner diameter of the outer tube are chosen (with reference to the specifics of the fin forming dies and process) so that the formation of the fins on the outer tube causes the outer tube to adhere to the inner 25 tube.

In this arrangement, the thread of the fins 18 of the inner tube 12 forms a leak path so that if the inner tube is compromised, the liquid within the double tube will flow along the helix of the fins 18. 9246305_1 (GHMatters) P105138.AU 3/08/17 -8- 2017101057 03 Aug 2017

The finned double tube 10 further comprises a leak sensor 30 accommodated between the inner and outer tubes which can detect the presence of cooling liquid and alert an operator, thereby avoiding costly damage and disruption of service.

The tube 10 is arranged to be used in either a radiator or a shell and tube heat 5 exchanger.

When used in a radiator, multiple tubes 10 are arranged in a straight tube configuration having an inlet plenum at one end of the radiator and an outlet plenum at an opposed end of the radiator. One or more baffles can extend transversally across the tubes 10 in the radiator. Due to the small footprint of each of the tubes 10 of an embodiment, io the radiator can include many more tubes 10 and in closer proximity to each other than would normally be the case using prior art tubes. Although it is appreciated that there is likely to be a greater pressure drop over each tube 10, this is at least partially offset by the increased number of tubes 10 in the radiator. Advantageously, the smaller outer diameter of the tube 10 greatly increases the ratio of volume of fluid flowing through the 15 tube 10 to the heat exchange surface area of the tube 10, which provides a higher rate of heat transfer within the radiator. The result of this is that when the tube 10 is utilised in an industrial radiator, such as would be provided at a mine, the cooling fan can be operated at slower rotational speeds and thereby causing less noise pollution. In tests, it has been found by the applicant that sufficient heat transfer is achieved with fans 20 operating at speeds causing noise levels below 80dB.

When used in shell and tube heat exchangers, the tubes 10 are arranged in a straight tube configuration having an inlet plenum at one end of the shell and an outlet plenum at an opposed end of the shell. Again, one or more baffles can extend transversally across the tubes 10 in the radiator. Due to the small footprint of each of the tubes 10, 25 the tube sheets can be designed with a small ligament thickness. The smooth end sections 14 enable the tubes 10 to be securely welded to tube sheets of the heat exchanger to prevent any leakage of the shell side fluid through the tube sheets.

The tubes 12,14can be made of metal or a metal alloy. In one embodiment, the tubes 12, 14 are made of a Copper-Nickel alloy in the ratio of 90/10. In further 30 embodiments the tubes are made from carbon steel or stainless steel. 9246305,1 (GHMatters) P105138.AU 3/08/17 -9- 2017101057 03 Aug 2017

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and 5 not restrictive.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to ίο preclude the presence or addition of further features in various embodiments of the invention. 9246305_1 (GHMatters) P105138.AU 3/08/17

Claims (5)

1. A method of manufacturing a double tube for a heat exchanger, the method comprising: providing an inner tube; forming fins on an outer surface of the inner tube; providing an outer tube; inserting the inner tube into the outer tube; and forming fins on an outer surface of the outer tube; wherein the step of forming fins on the outer surface of the outer tube creates a bond between the inner tube and the outer tube.

2. The method according to claim 1 wherein the step of forming fins on the outer tube and/or the inner tube is carried out by rolling.

3. The method according to claim 1 or claim 2 further comprising inserting a sensor into a flow path between the inner tube and the outer tube.

4. A double tube for a heat exchanger comprising: an inner tube having an inner tube body; an outer tube having an outer tube body; one or more fins integrally formed on and extending outwardly from both the inner tube body and the outer tube body; wherein an outer diameter of the inner tube is between 12 mm and 19.05 mm.

5. A double tube as claimed in claim 4, wherein the inner diameter of the outer tube is between 12.5 mm and 20.05.