WO2017203230A1

WO2017203230A1 - Heat exchanger unit, heat exchanger assembly and method of assembling a heat exchanger

Info

Publication number: WO2017203230A1
Application number: PCT/GB2017/051435
Authority: WO
Inventors: David Bland Pierce
Original assignee: Power Fin Technologies Limited
Priority date: 2016-05-25
Filing date: 2017-05-23
Publication date: 2017-11-30
Also published as: GB201609172D0

Abstract

The invention relates to a heat exchanger unit comprising at least one tube and a number of fins, the fins having an aperture for each of the tubes, the heat exchanger unit having a plurality of connector plates by which one heat exchanger unit can be connected to another heat exchanger unit. A plurality of the heat exchanger units can be connected together to form a heat exchanger assembly, suited in particular for retro-fitment around a flue or exhaust so as to recover some of the waste heat from the gases flowing along the flue or exhaust. The invention also relates to a method of assembling a heat exchanger around a heat source such as a flue or exhaust.

Description

HEAT EXCHANGER UNIT, HEAT EXCHANGER ASSEMBLY

AND METHOD OF ASSEMBLING A HEAT EXCHANGER

FIELD OF THE INVENTION

The invention relates to a heat exchanger unit. A plurality of the heat exchanger units can be connected together to form a heat exchanger assembly. The invention also relates to a method of assembling a heat exchanger.

BACKGROUND TO THE INVENTION

Often it is necessary to transfer heat to or from a location or material and it is known to use a heat exchanger for this purpose.

Heat exchangers usually comprise a number of tubes. Depending upon the function of the heat exchanger the tubes can carry a fluid to be cooled (or heated), or the fluid to be cooled (or heated) can flow around and between the tubes. In both cases heat flows through the tube wall(s) to or from the fluid within the tubes.

The ends of the tube(s) are connected to conduits which are in turn connected to other parts of the heat exchanger circuit, perhaps including a pump and fluid reservoir as required.

The heat exchanger can comprise a single tube or a plurality of tubes. Generally, if a single tube is used it will be bent in serpentine fashion to increase the heat transfer. Many heat exchangers have external fins which are mechanically coupled to or integral with the tube(s). The fins are in thermal contact with the tubes and increase the available surface area for heat transfer. Often, each fin will engage more than one tube, with the fins substantially filling the space between the tubes. A fin which engages more than one tube is herein referred to as a "common fin". During the manufacture of a heat exchanger the manufacturer will often make sub-assemblies comprising a chosen number of tubes fitted with a chosen number of common fins. These sub-assemblies are referred to herein as "heat exchanger units". The heat exchanger is constructed by assembling together the desired number and array of heat exchanger units, with the tube(s) of the respective heat exchanger units being interconnected as required.

Heat exchangers are most often constructed from metallic materials, i.e. metallic fins fitted to metallic tubes. Metals are commonly used because of their good thermal transfer properties. To secure a fin to the tube it is known to provide an aperture in the fin and to weld or braze the fin onto the tube. In an alternative known method of manufacture the required number of fins is initially located as a loose fit upon the tubes and the tubes are thereafter mechanically expanded by a specialised expanding machine into thermal engagement with the fins.

Alternative and improved methods of mounting fins (including common fins) upon heat exchanger tubes are described in WO96/35093, WO02/30591 , and WO2012/107757.

Any of the known machines and methods may be used to manufacture the heat exchanger unit of the present invention.

Heat exchangers are typically manufactured for a dedicated product or piece of equipment, the requirement for heat exchange, and the heat exchanger design, being included in the original design of the product or equipment. There are, however, many sources of heat which do not include a heat exchanger, such as the flue of a domestic or commercial boiler, or the exhaust of a commercial gas oven or fryer, for example.

There is an increasing awareness that it is unnecessarily wasteful simply to allow hot gas to pass into the atmosphere through a flue or exhaust. The owners and operators of commercial facilities in particular are becoming increasingly aware of their responsibilities to the environment and will often seek to minimise the wastage of heat energy at the facilities which they own or control.

The owner and operator of a chain of fast-food restaurants for example is responsible for a significant amount of waste heat which passes to the atmosphere through the flues from their restaurants' boilers and through the exhausts from their restaurants' gas ovens and fryers. The fitment of heat exchangers to the flues and exhausts can recover some of that heat energy, and whilst the heat may be recoverable only at a relatively low temperature, it can nevertheless be used for underfloor heating or for heating water for washing, for example.

SUMMARY OF THE INVENTION

Whilst it is possible to avoid the wastage of some of the heat in a new facility by designing heat exchangers into the flues and exhausts of the facility, it is more difficult to reduce the wastage of heat from existing facilities. The inventor has therefore sought to provide a heat exchanger unit which can be assembled into a heat exchanger for an existing flue or exhaust as a retro-fitment, and ideally without dismantling or replacing the existing flue or exhaust.

Thus, whilst it is possible to provide a replacement flue or exhaust including the desired heat exchanger, the removal and replacement of the existing flue or exhaust is a time consuming task which can be undertaken only by property qualified persons. Generally, the boiler or other piece of equipment to which the flue or exhaust is connected must be switched off before the flue or exhaust can be removed, often with a delay to allow the flue or exhaust to cool sufficiently to be safe to touch. It is usually not desired for the boiler or other piece of equipment at commercial premises such as a fast-food restaurant to be switched off for several hours as is typically required to remove and replace an existing flue or exhaust. According to the invention there is provided a heat exchanger unit comprising at least one tube and a number of fins, the fins having an aperture for each of the tubes, the heat exchanger unit having a plurality of connector plates by which one heat exchanger unit can be connected to another heat exchanger unit.

Preferably, each connector plate has an aperture for each of the tubes. The connector plate can therefore engage the tube(s) in a same way as a fin and can also transfer heat to and from the tube(s). Desirably, a connector plate is located substantially parallel to and alongside a fin.

Preferably, each connector plate has an opening to receive a connector member by which the connector plate of one heat exchanger unit is connected to the connector plate of another (adjacent) heat exchanger unit. Desirably, the fins (and ideally also the connector plates) have an engagement surface adapted to engage the outside of a flue or exhaust. Preferably, the engagement surface is part-circular with a radius of curvature matching that of the flue or exhaust (it being recognised that most flues and exhausts are circular in cross-section). The engagement surface of each fin may be enlarged so as to increase the area of contact between the fins and the flue or exhaust. The engagement surface may be enlarged by deforming the fin.

The heat exchanger unit is therefore designed to fit to the outside of an existing flue or exhaust, and to cover a part of the circumference of the flue or exhaust. It is intended that a plurality of heat exchanger units is assembled together into a "ring" which almost completely surrounds the flue or exhaust. Preferably, there is a small gap in the ring, which gap is spanned by a resilient member acting in tension so as to clamp the heat exchanger units against the flue or exhaust. Resilient clamping of the heat exchanger units is desired so that the heat exchanger units are maintained in contact with the flue or exhaust as it expands and contracts as it is heated up and cooled down during use. There is also provided an assembled heat exchanger comprising a plurality of heat exchanger units as herein defined, the connector plates of adjacent heat exchanger units being interconnected by a connector member and the tube(s) of adjacent heat exchanger units being interconnected by respective conduits.

Accordingly, in the assembled heat exchanger it is arranged that fluid flows through the tube(s) of one heat exchanger unit and then through the tube(s) of a neighbouring heat exchanger unit. In such an arrangement, only the terminal ends of the tube(s) needs to be connected to the remainder of the heat exchanger circuit.

There is also provided a method of assembling a heat exchanger comprising the steps of:

{i} providing a plurality of heat exchanger units as herein defined;

{ii} interconnecting the connector plates of adjacent heat exchanger units to provide a linked chain of heat exchanger units, the chain having a first end heat exchanger unit at one end and a second end heat exchanger unit at its other end;

{iii} fitting conduits to the tube(s) of the adjacent heat exchanger units so that the tubes of the heat exchanger units in the chain are interconnected;

{iv} passing the chain of interconnected heat exchanger units around a chosen heat source; and

{v} fitting a connector member between the connector plates of the first end and second end heat exchanger units to secure the chain of interconnected heat exchanger units in a ring around the heat source.

It will be understood that there is no requirement to cut or otherwise damage the heat source (typically a flue or exhaust), and the method can be used to install a heat exchanger to an existing flue or exhaust. It may not even be necessary to switch off the boiler, oven of the like as the heat exchanger can be fitted to a hot flue or exhaust (provided the installer takes the necessary precautions). Step {iii} is preferably undertaken before step {iv}, ideally at the manufacturing location, but that is not necessarily the case. If step {iii} is undertaken by the installer it may be undertaken after step {v}. The present invention therefore enables the fitment of a heat exchanger to an existing flue or exhaust without the requirement to remove or replace the flue or exhaust. Nevertheless, some installers might prefer to fit the heat exchanger to a length of replacement dusting and then fit the replacement dusting as a replacement for all or part of an existing flue or exhaust. Whilst such a method of installation avoids one major benefit of the invention it is still within the scope of the present claims.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

Fig.1 shows a perspective view of part of a heat exchanger unit according to the present invention;

Fig.2 shows a plan view of a ring of assembled heat exchanger units;

Fig.3 shows a plan view of a ring of assembled heat exchanger units of alternative design fitted around an exemplary flue; and

Fig.4 shows a set of four fins during a manufacturing step of the heat exchanger. DETAILED DESCRIPTION

The heat exchanger unit 10 of Fig.1 comprises a number of fins 12. In this embodiment the heat exchanger unit is designed to have two tubes (or one U- shaped tube), which are not shown, so that the fins 12 each have two apertures 14, the apertures 14 in all of the fins being aligned to receive the tube(s). The fins are preferably pressed onto the tube(s) by a tube finning machine (such as described in WO96/35093, WO02/30591 , or WO2012/107757), the engagement between the fins and tube(s) being sufficient to allow heat to flow readily between the tube(s) and fins. The fins can have collars to surround the tube(s) and enhance the thermal contact, if desired or required.

The heat exchanger unit 10 has three connector plates 16, which extend beyond the fins as shown. The connector plates 16 also have two apertures 14, aligned with the apertures of the fins, and which can similarly accommodate and engage the tube(s).

In addition to the apertures 14, the connector plates 16 each have two openings 20 by which one heat exchanger unit 10 can be connected to another heat exchanger unit 10, as seen in Fig.2. Specifically, a ring of identical heat exchanger units 10A-10G are connected together by way of their respective connector plates 16, adjacent heat exchanger units being slightly misaligned so that the connector plate 16 of one heat exchanger unit (10A) overlies the connector plate 16 of the neighbouring heat exchanger unit (10B).

The connector plates 16 of the neighbouring heat exchanger units 10 can be interconnected by discrete connector members (e.g. bolts or link pins) passing through each pair of adjacent openings 20, but preferably an elongated connector member passes through all of the aligned openings 20 between each pair of neighbouring heat exchanger units, reducing the number of connector members required to be fitted and secured. Thus, a single connector member in the form of a rod or bar can pass through all of the aligned openings 20 between a pair of neighbouring heat exchange units. Importantly, the connector members which are located in the openings 20 do not secure the neighbouring heat exchanger units 10 in the relative positions shown in Fig.2, and it is necessary that the neighbouring heat exchanger units can pivot relative to one another about the connector members. The interconnected heat exchanger units 10A-10G form a chain which can flex between the "ring" shape of Fig.2 and a substantially linear array.

The chain of interconnected heat exchanger units 10A-10G can be assembled at the manufacturing location and provided in a substantially flat condition to the location of use. Alternatively, but less preferably, the connector members can be fitted to the openings 20 by the installer at the location of use.

Fig.2 represents a cross-section through the heat exchanger units 10A-10G. Whilst the tubes which are located in the apertures 14 are not shown, it will be understood that the tubes are interconnected in the assembled heat exchanger.

Considering the heat exchanger unit 10A, for example, this has a first row of aligned apertures 14A and a second row of aligned apertures 14B, each of which will accommodate a tube in the heat exchanger unit and assembled heat exchanger of the invention. The far end of these tubes (i.e. the ends farthest from the viewer) are interconnected together, and since the tubes are parts of the same heat exchanger unit 10 they can be permanently interconnected, for example being two parts of the same U-shaped tube, with the base of the U located at the far end of the tubes. The near end of the tube occupying the apertures 14B can be interconnected to the near end of the tube occupying the apertures 14C of the neighbouring heat exchanger unit 10B. It will be understood that because the tubes occupying the apertures 14B and 14C can move relative to one another they must be interconnected by a flexible conduit or by a conduit which can rotate relative to one or both of the tubes. The conduits interconnecting the tubes of neighbouring heat exchanger units 10A-10G can be fitted at the manufacturing location, or by the installer, as desired, the former being preferred as this minimises the on-site activity required by the installer. It will therefore be understood that the tubes of the heat exchanger units 10A-10G are all interconnected and fluid flows through those tubes in serpentine fashion. The terminal ends of the tubes, one of which terminal ends is the near end of the tube occupying the apertures 14A, can be connected by the installer to the remainder of the heat exchanger circuit as part of the installation procedure.

The heat exchanger units 10 each have a heat exchanger surface 22 which is curved (with a radius of curvature R) to match the curvature of the (circular) wall of the flue or exhaust for which the heat exchange unit 10 is designed. In use, therefore, the surface 22 of the heat exchanger units 10A-10G engages the (hot) wall of the flue or exhaust, and transfers heat from the flue or exhaust to the fluid within the tubes by way of the fins 12 and connector plates 16. The manufacturer of the heat exchanger unit 10 will know in advance the radius R of the flue or exhaust to which the assembled heat exchanger is to be fitted, and can form the surface 22 to match the radius of curvature. The manufacturer can also determine the number and disposition of the apertures in the fins, the material and wall-thickness of the tubes fitted thereto, the spacing between the fins, and the material from which the fins are made, to match the heat exchange performance required. The fins can be deformed (flattened) at their engagement surface 22 to increase the area of engagement and thereby increase the thermal transfer. It is expected that the fins 14 will be made from aluminium which has good heat transfer properties and is lightweight so as to minimise the weight of the heat exchanger units 10 and the assembled heat exchanger. Alternatively, the fins could be copper, stainless steel, or a suitable alloy or other material. The fin spacing is expected to be between 1 mm and 3 mm in many practical embodiments. The tube (outer) diameter may be 10 mm, for example. Whilst the heat exchanger unit 10 will have two tubes which are equally spaced from the engagement surface 22, alternative embodiments could utilise one tube, or three or more tubes, as desired for a particular application. If multiple tubes are used, they do not need to be located equally spaced from the engagement surface, and could instead be arranged in two or three distinct rows, as desired. In heat exchanger units having three or more tubes, it may be preferable to fit a manifold at each end of the heat exchanger unit rather than separate conduits interconnecting individual tubes.

It will be seen from Fig.2 that the heat exchange unit 10A is not connected to the heat exchange unit 10G. This is necessary so that the installer can wrap the interconnected chain of heat exchanger units around an existing flue or exhaust. When the interconnected chain of heat exchanger units 10A-10G has been wrapped around the flue or exhaust (and forms a ring as seen in Fig.2) it is necessary for the installer to secure the heat exchanger in place by interconnecting the first end heat exchanger unit 10A to the second end heat exchanger unit 10G. The installer can fit a spring or the like (or a suitable resilient clamp) between the openings 20A and 20G, a resilient connection being desired so as to accommodate thermal expansion and contraction of the flue or exhaust during use.

Whilst it is expected to be easiest for the installer to fit the resilient connection between the end heat exchanger units 10A and 10G, it is alternatively possible to fit a resilient connection between another neighbouring pair of heat exchanger units, which resilient connection is put under tension during installation in order to allow the interconnection of the end heat exchanger units 10A and 10G, the end heat exchanger units 10A and 10G being interconnected by a non-resilient connector member.

It is desirable to make the connector plates 16 of stainless steel since that material will not soften at the temperatures which might be encountered in use (the exhaust of a gas oven or fryer might reach 350°C - 450°C for example). With lower temperature applications the connector plates could be made of aluminium or copper but it is necessary to ensure that the temperature does not exceed the annealing point of the connector plates as that would cause the connector plates to soften and the thermal contact to reduce.

Ideally, the installer will fit a sleeve around the assembled heat exchanger so as to trap heated air around the fins 14 and maximise the heat transfer. The sleeve may in turn be surrounded by a thermally-insulating jacket or the like.

The heat exchanger unit 10 which is shown in Fig.1 has a total length L with three connector plates 16, one at the top of the heat exchanger unit as drawn, one at the bottom and one in the middle. The number and disposition of the connector plates can be varied as desired. In a particular installation, the heat exchanger unit has a total length of 500 mm, with a connector plate at each end and intermediate connector plates at 50 mm intervals along the unit. Such a heat exchanger unit can be handled and installed by one person. If it is desired to extract waste heat from a flue or exhaust which is longer than 500 mm, two or more heat exchangers may be fitted end to end, with the tubes of the heat exchangers being interconnected if desired. Alternatively, the heat exchanger units can be made longer, for example 1 ,000 mm long if desired. Fig.3 shows an alternative arrangement of heat exchange units 1 10A-K wrapped around a flue 30. In known fashion, the flue 30 is double-walled, with a serpentine spacer 32 between the walls. The present invention is not limited to the specific type of flue, and is also not limited to a flue having a circular periphery. The heat exchanger units 1 10A-K differ from the heat exchanger units 10A-G in that each fin has surface deformations 34. The surface deformations can increase the surface area and induce turbulence into the air flowing between the fins, both of which can increase the heat exchange. In this embodiment the surface deformations comprise "bridges" pressed into the surface of the fin. The present invention is not limited to the specific form of the fins.

Eleven heat exchange units 1 10A-K are fitted around the flue 30. It will be seen that there is approximately sufficient space for a twelfth heat exchange unit 1 10, but the twelfth heat exchange unit 1 10 is omitted to permit the fitment of the resilient connector member(s) between the heat exchange units 1 10K and 1 10A.

Fig.4 shows an arrangement in linked fins 1 12 during their manufacture. Rather than fit individual fins to the tubes (not shown), the arrangement of Fig.4 allows a fin (or more likely a batch or group of fins) to be fitted to eight tubes at the same time. The time to manufacture each heat exchange unit, and thereby the cost of each heat exchange unit, can be significantly reduced. It will be seen that the fins 1 12A, B, C and D are interconnected by respective small sections of material 34. The small sections of material 34 are sufficient to maintain the alignment of the respective fins 1 12A-D during manufacture, but will readily deform or break when desired, i.e. either during a later manufacturing step, or when bent around the flue or exhaust. It is expected that a heat exchanger constructed as described and assembled to the flue of a gas boiler might experience temperatures of up to 700°C and can raise the temperature of ambient water to around 50°C or more, which is suitable for use in underfloor heating and for washing.

Claims

1 . A heat exchanger unit comprising at least one tube and a number of fins, the fins having an aperture for each of the tubes, the heat exchanger unit having a plurality of connector plates by which one heat exchanger unit can be connected to another heat exchanger unit.

2. A heat exchanger unit according to claim 1 in which each connector plate has an aperture for each of the tubes.

3. A heat exchanger unit according to claim 1 or claim 2 in which each connector plate is located substantially parallel to and alongside a respective fin.

4. A heat exchanger unit according to any one of claims 1 -3 in which each connector plate has an opening to receive a connector member by which the connector plate of one heat exchanger unit can be connected to the connector plate of another heat exchanger unit.

5. A heat exchanger unit according to any one of claims 1 -4 in which there is a first connector plate at a first end of the heat exchanger unit and a second connector plate at a second end of the heat exchanger unit.

6. A heat exchanger unit according to claim 5 in which there is at least one intermediate connector plate located between the first and second ends of the heat exchanger unit.

7. A heat exchanger unit according to any one of claims 1 -6 in which the fins have an engagement surface adapted to engage the outside of a flue or exhaust.

8. A heat exchanger unit according to claim 7 in which the engagement surface is part-circular with a radius of curvature matching that of the flue or exhaust.

9. A heat exchanger unit according to claim 7 or claim 8 in which the engagement surface of each fin is enlarged so as to increase the area of contact between the fins and the flue or exhaust in use.

10. A heat exchanger unit according to any one of claims 7-9 in which the engagement surface is enlarged by a deformation of the fin.

1 1 . A heat exchanger assembly comprising a plurality of heat exchanger units according to any one of claims 1 -10 in which a pair of neighbouring heat exchanger units are interconnected by at least one connector member, the neighbouring heat exchanger units being able to articulate relative to one another about the connector member(s).

12. A heat exchanger assembly according to claim 1 1 in which a tube of a first heat exchanger unit is connected to a tube of a second heat exchanger unit by a conduit.

13. A heat exchanger assembly according to claim 12 in which the conduit is flexible and/or movable relative to the tubes.

14. A heat exchanger assembly according to any one of claims 1 1 -13 in which at least one pair of neighbouring heat exchanger units are interconnected by a resilient connector member.

15. A method of assembling a heat exchanger comprising the steps of:

{i} providing a plurality of heat exchanger units according to any one of claims 1 -10;

{ii} interconnecting the connector plates of respective heat exchanger units to provide a linked chain of heat exchanger units, the chain having a first end heat exchanger unit at one end and a second end heat exchanger unit at its other end; {iii} fitting conduits to interconnect the tube(s) of all of the heat exchanger units in the chain;

{iv} passing the linked chain of heat exchanger units around a chosen heat source; and

The method according to claim 15 in which the connector member fitted in step {v} is resilient and is under tension when fitted.