GB2397642A

GB2397642A - Heat transfer element

Info

Publication number: GB2397642A
Application number: GB0229285A
Authority: GB
Inventors: Philip Andrew Kennedy
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-12-16
Filing date: 2002-12-16
Publication date: 2004-07-28
Also published as: GB0229285D0

Abstract

A heat transfer element 1 comprises first 2 and second metal sheets 3 fused together and having a tube 4 disposed between the sheets 2, 3. Metal sheets 2, 3 may be aluminium or aluminium alloy, may be square or rectangular, may be of the same or different size and may have perforations on one or both sheets for sound absorption. Tube 4 may be copper or copper alloy and have a serpentine shape and may be a flattened tube which is expanded or inflated with compressed air so that either one side or both sides of the heat transfer element 1 has a raised surface. The tube 4 may be formed from two sheets of metal foil placed together and fixed together along their edges by welding, brazing or an adhesive and expanded or inflated from one another. The elements may be used as radiative and convective elements and a plurality of elements assembled side by side to form a heat exchange beam for heating or cooling that may be incorporated into ceilings, walls or floors of domestic or business premises.

Description

1 2397642

HEAT TRANSFER ELEMENT

This invention relates to a heat transfer element for use in indoor heating or cooling duties. It is especially concerned with the heating or cooling of rooms in domestic or business premises.

The efficiency of room heating and cooling systems is a matter of increasing concern in order to minimise the energy they consume. Systems which circulate heated or cooled air are commonly employed but air has a low thermal capacity such that a relatively large volume is required, necessitating relatively large air ducts. The large volumes of air may also create an unacceptable level of noise from vents through which it is supplied. Air heating and cooling relies mainly on good convection and some conduction but derives little or no input from radiation. Radiators receiving hot water from a central boiler are the other main system in current use for heating purposes.

These rely largely on radiation into the room, with some conduction to the room air and some convection of it. They are generally effective but have the disadvantages of occupying much of the available wall space in the room and of taking some time to warm up the room from cold. Moreover the traditional types of room radiator are not well suited to cooling duties.

Interest has therefore been growing in the use of heat transfer tiles in room ceilings and walls for one or both of heating and cooling. Tiles have the advantages of providing radiant heating or cooling across a wide surface area without intruding into the useable room space. One previous type of tile comprises a flat metal plate facing the room space with copper tubing attached to the rear surface of the plate. Cooled or heated water is circulated through the copper tubing and heat is transferred to or from it through the metal plate to the room space.

The previous plate/tubing configuration has presented problems in achieving high levels of efficiency in heat transfer between the room and the circulating water. Direct contact between the tubing and plate occurs over only a small portion of the tube circumference.

The direct contact can be improved by fins or flanges on the tubing but these significantly increase the cost and complexity of the tile.

An improved type of heat transfer tile is disclosed in EP-A-0772006, in which a serpentine tube is sandwiched between two metal layers. The metal layers may be fixed together by a conventional means, such as adhesive. However, there can be problems with degradation of the adhesion between the elements during use. Mechanical fixing is also disclosed, but does not provide good heat transfer between the elements.

British patent application no. GB-A-2361529 discloses a heat transfer tile for cooling or heating a room, which tile comprises a flat facing sheet, a heat exchange element and an insulation board, wherein the heat exchange element is a channelled member comprising a first plate adjacent to the facing sheet and a shaped plated welded or fused to the flat plate, wherein the configuration of the shaped plate provides an elongate channel between the plates for passage of an energy transfer fluid through the tiles. In this invention, the heat transfer fluid is in direct contact with material of the plates. This gives good heat transfer, but can cause problems if the heat transfer fluid is of a corrosive nature.

The present invention sets out to provide a heat transfer element for cooling or heating a room, which overcomes the problems of the prior art. In particular, it is desired to provide a heat transfer element which is resistant to corrosion but which still has good heat transfer properties.

The present inventor has realised that a tube can be sandwiched between two metal sheets which are subsequently fused together in the area between sections of the tube.

This gives excellent heat transfer contact between the tube and the metal sheets. The tube itself can be constructed of a material which is resistant to corrosion.

Accordingly, the present invention provides a heat transfer element comprising: at least two tube sections for carrying heat transfer fluid, a first metal plate and a second metal plate, the tube sections being held between the metal plates, the metal plates being fused together in the region between the tube sections.

The present invention further provides a method of producing a heat transfer element, the method comprising placing at least two tube sections for carrying heat transfer fluid between a first metal plate and a second metal plate, applying heat and pressure to the first metal plate and second plate, to cause them to fuse at least in the area between the tube sections.

The at least two tube sections may comprise separate sections of tube for carrying separate streams of heat transfer fluid. However, they are preferably continuous with one another, forming sections of a single heat transfer fluid tube. This implies that the tube sections comprise sections of a tube length which comprises at least one bend.

Preferably, the tube length is of serpentine shape, with a plurality of bends.

Preferably, the tube lengths are substantially parallel to one another. Preferably, the tube sections define at least two sides of an area in which the metal sheets are fused, for example the parallel sides of a substantially rectangular area.

The tube sections, or the tube length of which the sections each form a part, will have tube connections such as tail pipes at the ends, for connection to a supply of heat transfer fluid, in a manner which is known in the art.

The tail pipes may be formed of any suitable material, as is known in the art. For example, they may be formed of standard copper tubing or flexible tubing as is well known. Any suitable connection may be formed between the tail pipes and the tube sections.

The tube sections may be formed of any suitable material. Suitably, the tube sections are made of a metal, such as copper.

In a particularly preferred embodiment which will be described below, the tube sections are inflated or expanded from a flattened tube. In order to allow this to happen, it is preferable that tube sections comprise thin walled metal tubes, having a wall thickness of about 0.2 to l.Omm, preferably about 0.5mm. Preferably copper tubes are used. The tube may also comprise thermoplastic material, which has good resistance to corrosion.

The metal sheets may be formed of the same metal to one another or of different metal.

Preferably, they are formed of the same metal. The sheets may be formed of any suitable material for example aluminium on aluminium alloy, which is relatively easy to fuse and which has good heat conductivity.

By "fused" it is meant that the metal sheets are welded or otherwise fused together in such a way that, in at least a part of the area between the tube sections, they are continuous and have no interface between each other. Preferably, they are fused over an area which is at least 50% of the area between the tube sections, preferably at least 70% of the area between the tube sections and preferably at least 90% of the area between the tube sections.

Having a large fused area gives a very good heat transfer and a strong bond between the sheets. A strong bond between the sheets also ensures that the tube is held securely, further improving the strength of the element and the heat transfer from the element to the heat transfer fluid.

The first and second metal sheets are preferably co-extensive with one another, though one may be larger than the other.

Preferably, the heat transfer element comprises a face for facing into a room and a face for facing away from the room.

The face for facing into the room may be suitably treated to improving its aesthetic appearance. For example, it may lay substantially flat. It may be painted or polished.

It may also have an acoustic treatment, to reduce sound reflection. For example, it may be perforated with a pattern of holes or indentations to absorb sound. These perforations may be of diameter 0.1 - 1.5mm.

The surface that the faces away from the room may be a surface on which connections to a supply of heat transfer fluid are located, so that these are not visible in normal use.

At least two shaped channels may be formed in at least one of the metal sheets, for accommodating the tube sections. For example, one of the sheets may be substantially flat (for example the sheet whose outer surface defines the surface for facing into the room) and the other sheet may comprise the at least two channels.

Alternatively, both sheets may be channelled so that, between, they define at least two channels in which the tubes sections are located.

Where one sheet comprises two shaped channels and the other sheet does not, the sheet which does not comprise the channels may be formed of a thicker or stiffer material, for example an aluminium/zirconiurn alloy as will be described further below.

The metal sheets may have a thickness in the range 0.4mm to S.Omm.

The elements of the invention are especially well suited to use as ceiling tiles for cooling duties. It is however emphasised that the elements are also well suited to use on wall or floor surfaces and to use as heating panels. Used in association with a heat pump or similar device they can be used for both heating and cooling, thereby simplifying a room's heating and cooling infrastructure.

In a ceiling tile, it is preferred that the surface of the tile for facing into the room is formed substantially completely by a face of the heat exchange element to provide maximum heat transfer. The remainder may be formed by a tile frame. Preferably, the heat exchange element represents at least 75% more preferably at least 80% and more preferably at least 90% of the area for facing into the room. The remainder may be formed by a tile frame.

For many purposes the energy transfer fluid is simply water, either heated or chilled, and possibly containing anti-freeze and corrosion inhibitors. Alternatively it may be a refrigerant fluid such as a CFC- free refrigerant.

The tile may be used as part of a wall or ceiling of the room. The tiles are intended to be employed in a conventional framework for a room ceiling or wall, with associated pipe-work to carry heating or cooling fluid to and from the tiles being located behind the tiles. Preferably, the heat exchange element is formed at its edges with suitable configurations for connecting to suspending means of known design. For example, it may be configured to engage with conventional suspending means for false ceiling systems In use each tile includes at least two connectors or tail pipes, one at each end of the channel, to connect it to the pipe-work. Depending upon the configuration of the room and of the framework the heating or cooling means associated with the tiles may be located in a space behind the tiles or located remote from the tiles, for example outside the room.

The heat exchange element of the invention may be of any suitable shape, for example rectangular or square.

Suitably, the heat exchange element of the present invention comprises upturned edges to provide extra rigidity and strength. Suitably, where the element is square or rectangular, the edges are turned up on at least two sides, preferably at least three sides, most preferably all four sides.

The element is suitably made by a process as described below.

The heat exchange element is formed from two thin flat metal sheets.

The method of forming the heat exchange element preferably comprises the steps of placing together a first metal sheet and a second metal sheet, with at least two tube section forming means arranged in the desired configuration between the first sheet and the second sheet, subjecting the first and second sheets, at least in areas between the tube sections forming means, to heat and pressure to cause the sheets to fuse or weld together The pressure in the fusing step may be applied using a thirty tonne press to cause the metal sheets to fuse together.

The tube section forming means may simply comprise the tube sections themselves in their eventual shapes. However, in order fomm a particularly strong bond between the tube section and the metal sheets, it is preferred that the tube section fomming means comprise flattened tube sections. This may be constructed by taking a pre-fommed tube and flattening it. In order to prevent bonding inside the tube, a non-bonding material, for example graphite or titanium lining, may be located inside the tube bore. Where a flattened tube forming means is used, the flattened tube may be inflated or expanded by placing the fused sheets between a first surface and a second surface, feeding a fluid under pressure to the tube sections so that the tube sections are inflated in expanding.

In the step of inflating the tube section, at least one of first and second surfaces may comprise a resilient surface, for example a hard rubber surface. The sheet adjacent to the resilient surface is then inflated into the resilient surface.

Alternatively, another process may be used. The metal sheets may each be provided with an upstanding sealing pattern in the fomm of a closed loop around the periphery of the sheet. When the metal sheets are fused together, the sealing patterns project from opposite faces of the fused sheets. In the inflating step, the fused sheets are held between two substantially flat surfaces which engage the sealing fommations so that two spaces are defined between the flat surfaces and the faces of the fused metal sheet, which space is bounded by the sealing pattem. During the expanding step, compressed fluid is fed into the tube sections. Compressed fluid may also be fed into the space defined between the flat surface and fused sheets. If the pressure in the space between the flat surface and the fused sheets is equal to the pressure in the tube section, no inflation occurs. In this way, inflation on only one side can be obtained. Alternatively, if the pressure in each space is less than the pressure in the tube sections, the tube sections will be inflated in both directions. In a particularly preferred embodiment the sealing pattern is formed as follows: When the first and second sheets are placed together, means defining a pattern comprising a closed loop may be provided between the first and second sheets. In the fusing step, the first and second sheet's are fused together in an area outside the closed loop and an area inside the closed loop. In the inflating step, fluid under pressure is first of all fed into the area defined by the pattern of the closed loop. As a result, an upstanding sealing pattern is formed around the periphery of the metal sheets After the heat exchange element has been formed, the sealing pattern may be removed, for example, by cutting.

Where the tube sections are made of metal, the action of folding the metal into a coil and flattening it may be lead to the metal becoming work hardened. Accordingly, the process preferably includes an annealing step, so that coil can be inflated.

Preferably, during the fusing step, the sheets are only fused together. Preferably, they are not deformed, for example to increase their surface area, because this could damage the tube contained between the sheets.

The pressure required to inflate the tube may be any suitable pressure, but is preferably in the range 100-200 bar, preferably about 150 bar.

A heating panel may be manufactured using a heat transfer element according to the present invention. The heating panel may comprise a first, bottom sheet comprising zirconium/aluminium alloy for facing into the room and a second, top sheet, comprising an aluminium material. The element can then be inflated on the top, aluminium side only. The heat exchange element may subsequently be formed into a tray with four 90 upturned edges 30mm deep.

In a heating panel, tail pipes comprising l 7mm long, 12mm diameter copper tubes may be brazed into position in the tube sections for transfer of transfer fluid.

The heat exchange element of the present invention can be incorporated into a heating tile, panel or other apparatus of the type shown in GB2361529 or European patent application Not 1227281.

A chilled ceiling tile may be formed in a similar manner, but the bottom sheet, for facing into the room, may be pre-heated for acoustic effect, by drilling a plurality of perforations in the surface.

It is possible that both sheets of the heat exchange element may be perforated. In this case, they may be perforated with a similar pattern and they may be constructed so that the perforations in the first metal sheet can be lined up with perforations ceiling of the second metal sheet, so that perforations extending right through the resulting heat exchange element are formed, for good sound absorption.

The heat exchange element according to the present invention may be used to assemble a heat exchange beam. For example a heat exchange beam may comprise a plurality of heat exchange elements according to the invention placed side by side and substantially parallel to one another. Where a heat transfer beam is assembled from heat exchange elements according to the invention, each heat exchange element is preferably separated from adjacent heat exchange elements by a distance in the range 5-20mm, preferably 12-17mm and most preferably 10-15mm. It is found that, surprisingly, the spacing in this range gives an improved heat transfer capacity.

Separation between heat exchange elements may be defined by a ratio of the separation to the height of the heat exchange element. For example, the ratio of the separation to the height is suitably in the range of 0. 05 to 0.2, more preferably 0.12 to 0.17, and most preferably 0.10 to 0.15.

The distance between the heat exchange elements is measured at their closest point. For example, if either or both heat exchange elements comprise an upstanding channel, separation is measured from the outside edge of the channel to the outside edge of the corresponding upstanding channel on the other heat exchange element.

Preferably, the heat exchange elements in the heat exchange beam are substantially parallel to one another. Preferably, there are between 5 and 50 heat transfer elements, most preferably between 10 and 30.

The heat transfer beam according to the invention may have any suitable dimensions.

The dimensions are typically defined by the depth (dimension normal to the plane of the heat exchange element), height and length. Suitably, the depth is in the range 5-50cm, more preferably 10-30cm. The length is suitably in the range 0.5-5.0 metres preferably 0.80- 2.0metres. The height is suitably in the range 5-50cm, more preferably 10-20cm.

Header means may be provided for feeding heat transfer fluid to and from the heat exchange elements. Any suitable header means may be used. For example, inlet or outlet tubes may be bonded to the ends of the tubes of the heat exchange elements by known methods and the header engaged with the ends of the inlet and outlet tubes, for example, by brazing. Heat exchange beams according to the invention may be used for convective heating or cooling.

In the embodiments described above, the tube sections comprise ordinary tube material.

However, in a possible alternative, the tube section forming means may comprise two layers of sheet material. The sheets of sheet material may be cut to the desired form.

This has the advantage that a bending step is not required. The sheet material, such as metal foil, can simply be cut to the desired shape. Two layers of the cut material are placed in contact with one another and fixed together along the edges, for example by welding, brazing or adhesive. It is possible for the sheets of material not to be bonded along the edges, sufficient bonding being obtained by the grip between the metal sheets of the heat exchange element. For example, copper foil can be used.

The present invention will be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a sketch isometric view of a first embodiment of heat exchange element according to the present invention.

Figure 2 is a sketch isometric view of the second embodiment of heat exchange element according to the present invention.

Figure 3 is a sketch isometric view of a first step in the manufacture of a heat exchange element according to the present invention.

Figure 4 is a sketch isometric view of an intermediate product in the method of manufacturing the heat exchange element according to the invention.

Figure 5 is a sketch isometric view of a second intermediate stage in the manufacture of a heat exchange element according to the present invention.

Figure 6 is a schematic cross section through an inflating device for use in the method of the present invention.

In figure 1, a heat exchange element, generally designated 1, is shown in sketch isometric view. The heat exchange element I comprises a first metal sheet 2 and a second metal sheet 3. The metal sheets are separated by a dotted line, which indicates that they are fused over substantially their whole overlapping area. A copper tube 4 can be seen which extends in a serpentine path from one side of the heat exchange element to the other. The tube 4 is located between the metal sheets 2 and 3. In the embodiment shown in figure 1, the top sheet 2 has been deformed to define a serpentine channel into which the tube 4 fits. In use, heat exchange fluid can be pumped through the copper tube 4. Excellent heat transfer from the heat exchange fluid to the tube 4 and then to the metal sheets 2 and 3 is obtained. Accordingly, the metal sheets 2 and 3 can be used as radiative or convective heat exchange elements, for example in a chilled ceiling, radiator or other heat exchange device.

The embodiment shown in figure 2 is generally similar to that shown in figure 1, except that the heat exchange tube 4 is held between the metal sheets 2 and 3 which are both deformed to define a serpentine channel in which the tube 4 is held. That is, a serpentine channel is visible on both sides of the heat exchange element as shown in figure 2.

The heat exchange element 1 shown in figures 1 and 2 may be of any suitable dimensions. As will become apparent below, the heat exchange element shown in figure 1 which has a channel on one side only is suitably formed by using metal sheets of different compositions. The metal sheet 3 may comprise aluminium/ zirconium alloy which is relatively stiffand the aluminium sheet 2 may comprise substantially pure aluminium.

The copper tube 4 visible in figures 1 and 2 may be integral with a copper tube which extends inside the serpentine channel or it may comprise a tail pipe brazed to the end of the copper tube contained in the channel.

The copper tube is suitably of diameter 1 2mm.

Figure 2 shows a first step in a method according to the invention. In this method, a first metal sheet, 5 and a second metal sheet 6 are placed together, with a flattened tube 7 which is formed to a serpentine pattern located between them.

Further, a pattern of non-bonding ink, for example made from titanium paste 8 is formed in a continuous loop around the periphery of one of the metal plates 5. This can be applied, for example by silk screen-printing in a manner which is known in the art.

This is represented by the stippled area 8.

In a second step in the method of the invention, the sheets 5 and 6 are pressed together in a thirty tonne press at a temperature of about 450 C. During this process, the metal sheets are fused and bonded together over substantially their whole area, except in the area 8 where the nonbonding ink is present and in the area where they are separated by the flattened tube 7. A non-bonding ink may be present inside the flattened tube 7 to prevent the walls of the tube from adhering together. The resulting element is shown in figure 4. Dotted lines indicate that path of the non-bonding ink 8 and of the tube 7. In a third step, a connection is drilled into the position of the non bonding ink and compressed air is supplied to it at a pressure of about 150 bar, whereby the sheets 5 and 6 are each inflated in their respective areas to provide an upstanding ridge which can be seen in figure 5. This ridge forms a continuous loop which extends from the face of sheet 6. A corresponding ridge is also formed extending from the face of the sheet 5.

The bonded sheets 5 and 6 can then be placed between the platters of an inflation press as shown in figure 6. A first platen 10 can be seen engaging the top side of the bonded sheets and a second platter 11 can be seen engaging the bottom side. It can be seen that the platters 10 and 11 engage the upstanding ridges 9. The upstanding ridge 9 forms a sealing gasket, so that the space inside the ridge 9 is sealed. Compressed air can be fed through the holes in the platters 12 and 13 into the space defined between the platen, the fused sheets 5 and 6 and the ridge 9. Further, a connection is made to the flattened copper tube 4 so that compressed air at l SO bar may be fed into the tube.

If a heat exchange element according to figure 1 is to be formed, compressed air 150 bar is fed through the tube 13 to one face of the heat exchange element and also into the tube 4. As a result, the tube 4 will be inflated upwards to the platter 10. However, it cannot inflate downwards towards the platter 11, because the pressure is equal on that side to the pressure inside the tube.

However, if a heat exchange element according to figure 2 is to be formed, compressed air is only fed into the flattened tube 4 so that it inflates in both directions towards platters 10 and 1 1, as there is no counter pressure to resist.

Claims

1. A heat transfer element comprising: at least two tube sections for carrying heat transfer fluid, a first metal plate and a second metal plate, the tube sections being held between the metal plates, the metal plates being fused together in the region between the tube sections.

2. A heat transfer element according to claim 1, wherein the metal plates comprise aluminium or aluminium alloy.

3. A heat exchange element according to claim 1 or 2, wherein the tube sections comprise copper or copper alloy.

4. A heat exchange element according to any preceding claim, wherein the tube sections comprise sections of a single continuous tube of serpentine shape.

5. A method of producing a heat transfer element, the method comprising placing at least two tube section forming means between a first metal plate and a second metal plate, applying heat and pressure to the first metal and second metal plates to cause them to fuse, at least in the area between the tube section forming means.

6. The method according to claim 5, wherein the metal plates are fused over at least 50% of the area between the tube section forming means, preferably at least 70% of the area between the tube section forming means and preferably at least 90% of the area between the tube sections forming means.

7. A method according to claim 6 or 7, wherein the metal plates are fused together by heat and pressure.

8. A method according to any of claim 6 to 7, wherein the tube section forming means are defined by two sheets of metal foil placed together and subsequently expanded or inflated away from one another.

9. The method of claim 6 or 7, wherein the tube section each comprise flattened tube sections which are subsequently expanded or inflated after the metal sheets are fused or welded together.

10. The method of claim 9 wherein the tube sections are inflated on one side only or on both sides of the heat exchange element.

I 1. A method according to any of claim 6 to 10, wherein at least one of the metal sheets is perforated for sound absorption.

12. A method according to claim 11, wherein both of the sheets are perforated, the perforations in the sheets being of the same pattern and the perforations of the sheets being aligned so that the heat exchange element comprises perorations passing from one side to the other.