He.at Exchanger Manifolds

This invention relates to heat exchanger headers, in particular those used in natural gas liquefaction processes .

The general concept of heat exchangers is to bring gaseous and/or liquid media (generally referred to as "fluids") at different temperatures into thermal contact with each other such that heat transfer can occur to respectively heat and cool the fluids .

Heat exchangers are commonly used in gas liquefaction plants to cool and liquefy natural gas . In addition there are numerous other situations within process and chemical plants in which heat exchangers can be used to transfer heat between two fluids .

Heat exchangers are also frequently used within air conditioning and cooling systems. In comparison to such systems, heat exchangers for LNG plants must be able to cope with higher pressures , greater extremes of temperature and larger capacities.

Currently, LNG heat exchangers are either spiral wound or plate fin types. Traditionally, plate fin heat exchangers consist of a core made up of alternating layers of corrugated fins, these fins forming channels along which fluids can pass . The layers are separated by parting ^' sheets and sealed along their edges by means of side bars so that fluid within- one particular layer cannot leave this layer except at the top or base of the channels. By feeding ^• fluids at different temperatures along adjacent layers heat transfer can occur between the fluids without these coming into contact with one another .

Fluids are distributed into the different layers of channels by means of headers welded to the top and base

of the core. At least four headers are required to provide inlet and outlet streams for both the heating and cooling fluid. These headers run perpendicular to the heat exchanger channels so that a number of layers can be fed by a single header. Often more headers are used to supply and collect fluid from different areas of the core. Openings are formed in the parting sheets under the headers through which the liquid or gas is distributed to the channels. Such heat exchangers are usually built according to the standards set by ALPEMA (Brazed Aluminium Plate Fin Heat Exchanger Manufacturers' Association).

.Due to the bulky nature of the headers, the headers for carrying the ^" two separate heat exchanger fluids must be fixed onto the core at ^' different angles, e.g. one component is fed into the top of the core and the other at the side. This either requires the two fluids within the heat exchanger to flow perpendicular to one another, i.e. in cross flow, or for the layers to contain a complex pattern of re-directional fins so that fluid entering the core via the side header can flow in co- or counter-flow with the fluid entering via the top header. It is beneficial during LNG liquefaction and other cooling processes for the refrigerant to be at the liquid/gas boundary upon entry into the heat exchanger

^" channels, in order. to achieve the most effective phase distribution and heat exchange. In practice, this results in a small amount of vapour being present in the refrigerant upon entry to the heat exchanger,- resulting in a two phase flow. The headers described above are not suited to evenly distributing this two phase flow to each channel and therefore the two phases must be fed in separately, which increases the complexity of the system:

Other forms of header are known. WO2004/033947 discloses a co- or counter- flow heat exchanger in which a number of alternating heat exchanger channels, i.e. each channel carrying a different fluid than its adjacent channels, are connected directly to their respective headers . In order to accommodate this , at their ends the channels are bent out of the plane of the main heat exchanger core towards the headers . Headers for one fluid are located on one side of the core (e.g. the top of the core) and headers for the other on the other side' (e.g. the bottom of the core) . The headers at each end of the core are parallel to each other but are positioned out of the plane of flow through the heat exchanger core. The fact that the channels must be bent out of this plane in order to connect to the headers complicates the design of the heat exchanger and also reduces the proportion of the heat exchanger channel over which heat transfer can take place. Further, this design in not viable when many small diameter channels are used in the heat exchanger, as the machining intricacy required becomes too complex. It is often desired to have numerous, small heat exchanger channels to increase the surface area/volume ratio and thus improve heat transfer. .US 4,470,455 discloses a plate type heat exchanger commonly known as a "drawn cup" heat exchanger., In this design plates are stamped to create collars and the edges turned upward such that, when two plates are brazed together along these upturned edges, an enclosed fluid channel is formed between the plates with the collars aligning to form headers for transporting the fluid to and from this channel; The plates can have further indents to form fins or .guides for the fluid within the channel, or separate fin components can be

inserted into the channel during manufacture. Gaps are left between each pair of brazed plates (which form a single channel) to provide for a cross flow of air or other fluid. Such systems are usually used in evaporators for air conditioners in vehicles and are not suitable for high pressure fluids as the channel strength is lbw.

US 6,918,434 discloses a similar heat exchanger to the drawn cup arrangement, with- a plurality of plates stacked together to provide channels between the plates. However in this instance both the heating and cooling fluid are transported in these channels and run in co- or counter- flow as opposed to cross flow. Each plate contains four openings, one at each corner, which align when stacked to provide four passages through the stack. These act as input and output headers for the two fluids passing through the system. In order to direct these fluids down separate channels, seals are provided between the plates around selected openings in order to allow only one of the fluids to pass through each channel . The channels can be provided with fins to improve distribution within the channel and to increase heat transfer.

Such systems are only suitable for low pressure applications, e.g. 5-10 bar. Although US 6,918,434 describes the use of a reinforcing member that is positioned in one or more of the headers to increase the exchanger's load bearing capacity, this does not add to the structural integrity of the heat changer channels themselves and so is not suitable for the high pressures experienced within LNG heat exchangers, e.g.- 60-70 bar. It is becoming desired within the industry to use extruded heat exchanger elements, as very small diameter channels can be created using this method, e.g. 1mm.

Such extruded elements can also cope with high pressures due to the integral nature of the element.

One problem with such elements is evenly distributing fluid to such small channels. Headers in chemical and process plants often have large diameters (for example around Im) ¹ and therefore connecting such tubing together is challenging. ■

US 6,739,387 is an example of the use of extruded heat exchanger channels within the automotive industry. The channels are extruded as a single element, the element having a smooth outer surface and containing a row of internal small diameter channels . Each extruded element is inserted into the header through holes punched in the header tube. In this way each channel opens directly into the header, as with WO2004/033947. _. However, the dimension of the stamped hole in the header corresponds to the dimensions of the extruded element rather than the individual channels, making this easier to produce. This heat exchanger is designed for use with a cross (perpendicular) flow of air, which flows through the gaps left between each element and through air holes created within the elements themselves. Because the heat exchanger is designed for cross flowing fluids, the headers can be placed in the plane perpendicular to the heat exchanger channels without blocking or interfering with the headers of the other- fluid (if indeed headers are needed for the second heat exchanger fluid) . This is not possible with co- or counter- flows, which leads to the need .for redirectional means such as used in the traditional plate fin heat exchanger or the diversion of the heat exchanger channels away from the plane of flow, as in WO2004/033947.

The present invention is concerned with providing an improvement to existing heat exchanger/header interfaces, especially one which is suitable for use in an LNG heat exchanger in which the header needs to supply many small diameter channels , preferably in the form of extruded tubes .

According to one aspect, the present invention provides a fluid distribution element for transporting heating or cooling fluid to or from a series of heat • exchanger channels, said element 'Comprising; at least . one port extending through the element in a first direction; at least one localised distribution cavity shaped so as to allow said series of heat exchanger channels to open into said cavity and spaced apart from the port in a second direction perpendicular to the first direction; and at least one passageway connecting the port to the localised distribution cavity such that fluid passing through said port can be transported through said passageway into said cavity for localised distribution to said series of heat exchanger channels, the passageway being narrower than the port and the cavity in a third direction perpendicular to said first and second directions .

Therefore a single element can be used to supply a series, of heat exchanger channels with a particular fluid. In use a number of fluid distribution elements are aligned in the first direction such that the ports define a header through the stacked assembly, each port having an associated localised distribution cavity for supplying a series of heat exchanger channels with fluid. It is not necessary however for the header to be formed only from these distribution elements, other components can also assist in the creation of a complete

header, for example split tubing or additional ports interlinking the ports of the distribution elements.

Each cavity is spaced apart from the port in the second direction and extends in the third direction such that a series of heat exchanger channels aligned in this direction, i.e. perpendicular to the header formed by the ports, can open into the cavity. By providing a plurality of cavities spaced along the created header, the distribution elements of the present invention allow fluid to be distributed to a large number of heat exchanger channels at different points throughout a heat exchanger core without the need to directly connect these to the header, which can be a difficult task, especially when small channels are used. Using the fluid distribution element of the present invention, a series of individual heat exchanger channels are arranged to open into a ¹ single . cavity . This prevents the need for the ends of these channels to be welded/ soldered etc which would risk blocking them. The cavity then acts as an "intermediate header", supplying these individual heat exchanger channels with fluid. Therefore the present invention provides a means by which independent heat exchanger channels can be fed from (or feed into) a header by means of a plurality of intermediate headers formed by cavities, the intermediate headers connected to the header by means of at least one passageway. This passageway has a smaller diameter than either the cavity or the port as measured in the third direction. As such the passageway acts as a restriction through which fluid must pass in order to reach the localised distribution cavity, which reduces the pressure loss along the header.

Preferably the fluid distribution element further comprises a second port extending through the element in

the first direction, wherein said second port is not in fluid communication with said cavity.

In this way, when a number of distribution elements are stacked together in the first direction, two separate headers are formed running parallel to each other. One of these headers communicates with a plurality of heat exchanger channels by means- of the above described passageways and cavities . The other header can be connected to different heat exchanger channels via alternative means.

Therefore the distribution element of the present invention can be used to supply both heating and cooling fluid to a heat exchanger.

This allows two different fluids to flow in co- or counter-flow to each other without the need for one fluid to be redirected within the heat exchanger or the need to bend heat exchanger channels* out of contact with each other. Thus the design of the heat exchanger channels can be simplified -and these can stay in thermal contact throughout their entire length, increasing the amount of heat transfer which can occur. Ideally therefore the heat exchanger channels to be connected to the distribution element of the present invention are straight, so that they can be placed in a heat exchanging relationship with other channels along their entire length.

This form of distribution element also enables compact packaging of the heat exchanger components .

Preferably in use therefore the first and second ports of the fluid distribution element are arranged to transport different heat exchanger fluids. For example, the first port may transport the heating fluid and the second port the cooling fluid or vice versa.

The first and second ports can be positioned side- by-side on the fluid distribution element, at an equal distance from the cavity. However, this limits the diameter of the ports and therefore preferably the second port is positioned between said first port and said cavity such that the at least one passageway provides a bypass around the second port.

This is considered inventive in its own right and therefore, viewed from another aspect the present invention provides a fluid distribution element for transporting heating or cooling fluid to or from a series of heat exchanger channels, said element comprising a first port extending through the element in a first, direction, at least one localised distribution cavity shaped so as to allow said series of heat exchanger channels to open into said cavity and spaced apart from the port in a second direction, ^• a second port extending through the element in a first direction positioned between the first port and the cavity, and at ^' least one passageway connecting the first port to the cavity such that fluid passing through said first port can be transported through said passageway into s.aid cavity for localised distribution to said series of heat exchanger channels, said passageway bypassing said second port.

By "by-pass" it is meant that the passageway is physically removed from the second port, i.e. the passageway does not pass through the second port but allows the fluid travelling within the first port to reach the cavity without interfering with the flow of fluid in the second port.

In one embodiment two versions of fluid distribution element are provided, each having two ports and one localised distribution cavity. The first

version of the distribution element provides" at least one passageway between one port and the cavity, whereas in the second version of distribution element the other port is connected to the cavity by the passageway (s) . When the ports are spaced apart from each other in the second direction therefore one of these versions has a passageway which acts as a bypass . By stacking these elements in an alternating fashion, two separate headers are formed, each header connected to a plurality of cavities along its length. Each cavity can then be ^• connected to a different series of heat exchanger channels such that the headers supply adjacent series of heat exchanger channels with different fluids, thus allowing heat transfer to occur between these channels. ^' This configuration provides a very compact heat exchanger, with both headers, being in line with each other and perpendicular to the plane of flow through the heat exchanger channels .

Preferably the series of heat exchanger channels to be connected to a particular cavity are arranged side by side to form a row of heat exchanger channels. This row can then be placed in the plane of the third direction in contact with the cavity. Preferably the row of heat exchanger channels are formed in a single heat exchanger element, i.e. the channels are formed as a single integral element. However, within this element the channels are separate from each other such that fluid cannot pass from one channel to another.

The cavity could be formed in one ¹ side of the distribution element only, i.e. the cavity does not extend across the entire length of the element in the first direction (the thickness) , as the ports do, but instead forms a hollow on one side of the element. In use this hollow must be closed off so that fluid can

only enter and exit the cavity by way of the passageway (s) and connected channels. This can be achieved by aligning the cavity with a flat surface, such as a partition plate or the side of a further distribution element. Alternatively the cavity could be formed internally within the fluid distribution element.

It is possible for the distribution element to be integrally formed with the series of heat exchanger channels to which it supplies fluid, i.e. an element containing both heat exchanger channels and distribution components could be injection moulded, extruded etc. However, it is often simpler to provide the fluid distribution element in the form of a separate plate which can then be used with a variety of heat exchanger channels.

Viewed from another aspect therefore, there is provided a fluid distribution plate for transporting heating or cooling fluid to or from a series of heat exchanger channels, said element comprising; at least one port; ^' at least one localised distribution cavity open at one end so as to allow said series of heat exchanger channels to open into said cavity and spaced apart from the port; and at least one passageway connecting the port to the localised distribution cavity such that fluid passing through said port can be transported through said passageway into said cavity for localised distribution to said series of heat exchanger channels, the passageway being narrower than the port and the cavity in a third direction perpendicular to said first and second directions.

When the distribution element takes the form of a distribution plate, it is preferable that the cavity comprises a cut out at one end of the distribution plate. By cut out it is meant that the cavity extends

through the element in the first direction such that the cavity is open on both sides and at one end of the fluid distribution element. This eases construction. In use the series of heat exchanger channels can be connected to the cavity where it is open at the end of the distribution plate and the open sides of the cavity sealed off by other elements of the heat exchanger, for example other distribution elements.

When the cavities of one or both of the above described versions of the distribution element (which connect their cavities to different ports) comprise cut outs., separator plates could be provided between adjoining elements in order to separate the cavities from one another and keep the heating and cooling fluids separate. However, alternatively the lengths of the elements in the second direction (the length) can vary such that, when different versions -of the el-ements are aligned, the cut outs do not overlap. In other words the cavity of the first version of distribution element is spaced away from the ports by a different amount in the second direction than the cavity of the second version.

When the distribution elements are differing lengths, the series, or row, of heat exchanger channels opening onto the cavity of the shorter distribution element can provide at least a roughly planar surface to close off one side of the cut out of the adjacent, longer distribution element. In other words, the longer distribution element extends past the cavity of the shorter distribution element, closing off one side of this cavity. A series of heat exchanger channels are connected to the base of the cavity of the shorter distribution element and extend away from it in the second direction past the cavity of the longer

distribution element, therefore closing off one side of this . The other side of the cut out can be closed off in a similar fashion or an identical distribution element can be placed in alignment to ^' create a larger cavity which can provide access to a greater number of heat exchanger channels e.g. two rows of heat exchanger channels .

Although both headers can therefore be connected to different series of heat exchanger channels by way of a cavity and at least one passageway, it is preferable that the second port is arranged to provide a more • direct fluid connection to a series of heat exchanger channels. This simplifies the design of the distribution element as it reduces the number of passageways required and allows only a single version of distribution element to supply both heating and cooling fluids to the heat exchanger.

In one embodiment the distribution element can be used with extruded (or other) heat exchanger channels, the heat exchanger channels forming an integral heat exchanger element in which a through hole has been machined. By creating a through hole almost as wide as the element nearly all the channels, within the element will. open into this hole. Such heat exchanger elements- can be stacked in the first direction in an alternating fashion with the fluid distribution elements of the present invention to build up header consisting of the second ports of the distribution elements and the through holes of the heat exchanger elements. The ^' channels within the heat exchanger elements open directly into this header by means of the through holes . The heat exchanger element can also comprise an additional through hole for alignment with the other, first, port of the distribution element to create a

second header. This second through hole would need to be sealed to prevent the channels within the heat exchanger element from opening into this second header. Therefore fluid passing through the second header could not pass into the channels within the machined heat exchanger elements but could be linked to other heat exchanger channels by way of the first port, passageway (s) and cavity of the distribution element

To prevent the need for machining this additional through hole to create the second header, a separator plate could instead be provided having the same width and thickness as the heat exchanger element and comprising an aperture for alignment with the first port of the distribution element. Alternatively the portion of the distribution element comprising this port could have an increased thickness such that in use this portion abuts the distal end of the heat exchanger element and connects to the adjacent distribution element. However, the machining of such through holes within heat exchanger elements presents, difficulties when very small channels are contained within the element, as the creation of the through hole often results in closing off the channels within it-. While some deformation of the channels can be tolerated in larger sized heat exchanger channels, it is harder to maintain small, lmm channels fully open.

Alternatively therefore, and more preferably, the fluid distribution element further comprises a hollow portion shaped so as to allow a second series' of heat exchanger channels to open into said hollow portion, the second port opening directly into this hollow portion. In this way the heat exchanger element containing the heat exchanger channels does not need to be machined

or otherwise altered. Instead the end of the heat exchanger element can be abutted directly against the hollow portion of the fluid distribution element such that the heat exchanger channels within this element open directly into the hollow portion, which in turn leads directly into the header formed by the second port of the distribution element. Therefore, like the cavity, the hollow portion can also be seen to act as an intermediate header for supplying a series of heat exchanger channels with fluid, although in the case of the hollow portion fluid is supplied from the second port rather than the first. Therefore, the cavity and the hollow portion act as intermediate' headers for different fluids. - Preferably the fluid distribution element is shaped such that, in use, the series of heat exchanger channels opening into the cavity are in heat exchanging relationship with the second series of heat exchanger channels opening into the hollow portion. Unlike the first port, the second port is directly connected to the hollow portion such that the hollow, portion is in effect an extension of the second port. There is no passageway, joining the two areas and hence no restriction through which fluid must pass . The second series of heat exchanger channels can be integrally formed with the distribution components in a similar way as described in relation to the heat exchanger channels for connection to the cavity. However, preferably the fluid distribution element is in the form of a plate and hence is separately formed -from the channels .

Preferably the hollow portion extends only part way through the element in the first direction, with a first end of the hollow portion joining to the second port and

a second end of the hollow portion being wider than the second port in the third direction and open to allow connection to said second series of heat exchanger channels . Of course, in use the cavity and hollow portion must be kept out of fluid communication with each other to avoid mixing of the heating and cooling fluids . This can be achieved by placing the cavity on one side of the distribution element and the hollow portion on the other. However in preferred embodiments, as discussed above, when the distribution element comprises a distribution plate, the cavity comprises a cut out at one end of the distribution plate and therefore extends through the whole element. In such embodiments, the hollow portion can be formed in one side of the distribution element above the cut out.

Therefore, in effect, in such embodiments one side of the ^' distribution element has a reduced length in comparison to the other. The hollow portion is formed in the shorter side and the cut out is formed in the extra length of the other side. These two "sides" of the distribution element can also be considered as two separate versions of fluid distribution element, which are used in combination within a heat exchanger. Indeed, it is preferred that the sides of the above described fluid distribution element are constructed separately before being joined together to form a single element. Such -elements can be made by injection moulding, extrusion or other known methods . In use, the heat exchanger channels connected to the hollow portion must extend past the cut out to abut against the hollow portion on the shorter side of the fluid distribution element. These heat exchanger channels, preferably contained within a heat exchanger

element, therefore 'close off' one side of the cavity and isolate this from the hollow portion. The other side of the cavity may be closed off by another heat exchanger element .arranged to abut the hollow portion of an adjacent distribution element, or by some other planar surface such as a separator or end plate.

Preferably the at least one passageway is dimensioned to provide a minimum pressure drop. This helps to reduce the pressure drop in the heat exchanger. In order to reduce the pressure drop the passageway must be small in diameter.

In some embpdiments the at least one passageway is dimensioned to form a throttling orifice tube between the port and the cavity. This is very useful in LNG heat exchangers as the final expansion required to bring the refrigerant to the gas/ liquid boundary can be achieved within the passageways, thus ensuring that each series of heat exchanger channels connected to the cavities of the distribution elements are provided with similar proportions of gas and liquid. In such situations the liquid medium travels through the header created by the first ports at a pressure above its boiling point, thus giving uniform flow distribution. As the liquid travels through the passageway and enters the cavity it reaches a desired vaporisation pressure. This is considered inventive in its own right and therefore, viewed from a . further aspect, the present invention comprises a fluid distribution element for transporting. heating or cooling fluid to or from a series of heat exchanger channels, said element comprising at least one port extending through the element in a first direction, at least one localised distribution cavity shaped so as to allow said series of heat exchanger channels to open into said cavity and

spaced apart from the port in a second direction, and at least one passageway connecting the first port to the cavity such that fluid passing through said first port can be transported through said passageway into said cavity for localised distribution to said series of heat exchanger channels, said passageway being dimensioned to provide a throttling orifice tube.

The passageways are preferably formed as internal passageways within the distribution element. However it is possible for the at least one passageway to be exposed on at least one side of the element and closed off in use by a further distribution element or other means, in a similar fashion- to preferred forms of the cavity and hollow portion. It is possible, where desired, for the distribution element to comprise a plurality of first ports, that is, ports connected to said cavity by means of at least one passageway. This can be beneficial depending on the geometry of the connector pi-pes-. -Multi-pie -second -ports can similarly be provided on each distribution element. As discussed above, the .fluid distribution element can be integral with the series of heat exchanger channels to which it distributes fluid/ or it can comprise a separate component. Therefore in one embodiment the fluid distribution element is integral with the series of heat exchanger channels to which it distributes fluid. However, it is preferred that the fluid distribution element comprises a fluid.. distribution plate, produced separately from the heat exchanger channels and connected thereto only upon assembly of the heat exchanger.

In a preferred embodiment each fluid distribution element is arranged to connect to one or more heat exchanger elements, i.e. the series of heat exchanger

channels to which the cavity and/or hollow portion connect during use are contained in one or more integral heat exchanger elements. This eases the connection of the channels to the distribution element. Preferably the heat exchanger elements comprise one or more rows of heat exchanger channels, the longitudinal axes of which are, in use, aligned with the distribution element in the second direction such that the row(s) of heat exchanger channels are lined up in the third direction facing, into the cavity or hollow portion of the distribution element. The elements can be designed such that more than one heat exchanger element opens into the same cavity or hollow portion. In use, the heat exchanger elements connected to the cavities and the heat exchanger elements connected to the hollow portions are arranged in heat exchanging relationship with each other.

In a preferred embodiment the fluid distribution elements- are -used in- -a heat exchanger -f-o-r l-ique-fying natural gas, wherein the first ports align to form first headers for transporting, a refrigerant and the second ports align to form second headers for transport of the natural gas . Preferably the distribution elements forming the inlet header for the refrigerant comprise passageways forming throttling orifice tubes for the refrigerant. Preferably the hollow portions joined to the second ports are connected to extruded heat exchanger elements . The heat exchanger channels for carrying the refrigerant can also be extruded. Viewed from another aspect therefore the present invention provides a heat exchanger comprising, ¹ a plurality- of first heat exchanger elements, each element comprising a plurality of heat exchanger channels arranged in one or more rows; a plurality of second heat

exchanger elements, each element comprising a plurality of heat exchanger channels arranged in one or more rows, the first and second heat exchanger elements being arranged in heat exchanging relationship with one another; distributing means at either end of the heat exchanger elements for transporting heating and cooling fluid to and from said heat . exchanger channels, each distributing means comprising at least one first header ^■ and at least one second header, the distribution means further comprising cavities spaced along the length of the first header, each cavity opening onto the heat exchanger channels of at least one first heat exchanger element and being in fluid communication with said first header by way of at least one passageway, such that fluid can be transported between the first header and the cavities for local distribution from the cavities to said first heat exchanger elements.

The heat exchanger elements can be formed in any traditional manner. For example, they could be individual metal tubes grouped together in rows . Preferably however at least some of the elements, preferably the second heat exchanger elements, are extruded. In one embodiment the extruded heat exchanger elements comprise a smooth exterior with a row of channels contained within. In another embodiment the extruded heat exchanger elements comprise a plurality of external fins and a plurality of internal channels. When two such elements are placed in contact the external fins combine to form a set of heat exchanger channels . In this way both first and second heat exchanger elements can be formed from a single type of extrusion. It is also possible for a separate extrusion to form the first heat exchanger elements. Alternatively at least some of the heat exchanger

elements can be formed by corrugated fins sandwiched between planar walls, e.g. the walls of extruded elements or parting sheets .

The distribution means can comprise a plurality of the distribution elements described above. In one embodiment distribution elements in. the form of distribution plates can be used, these elements being operatively connected to a plurality of first heat exchanger elements such that the channels within these elements face onto the open ends of the cavities of the distribution plates. The cavity of each distribution plate is in fluid communication with the first port(s-) (which form the first header (s) ) by way of the at least one passageway. In order to transport the other fluid from the distribution means to the second heat exchanger elements, these heat exchanger elements can be arranged to open directly into the second header. In other words the second heat exchanger elements can comprise at least one port formed at their distal ends which forms part. of the second header. Further, closed ports into which the heat exchanger channels cannot open can also be formed in the second heat exchanger element to ^" form the first headers ^' with the distribution plates. By creating layers of alternating distribution plates and second heat exchanger elements the distribution means is formed. Therefore in this embodiment the distal ends of the second heat exchanger elements form part of the distribution means .

Alternatively, the distribution means can further comprise, spaced along the length of the second header, a plurality of second cavities, each second cavity opening onto the heat exchanger channels of at least one second heat exchanger element and being in fluid communication with said second header by way of at least

•one passageway. In this way therefore, fluid travelling through both first and second headers is directed through passageways to secondary or intermediate headers, formed by the cavities, from where fluid is distributed to one or more heat exchanger elements . In a further embodiment the distribution means comprises, spaced along the length of the second header, a plurality of hollow portions, each hollow portion opening onto the heat exchanger channels of at least one second heat exchanger element and also directly opening into the second header, in effect forming part of the - ^■ • header. In such embodiments, one set of heat exchanger elements, for example the first heat exchanger elements, terminate and face into a cavity, such that fluid within these channels can be transported via the cavity and passageways to a header. The second heat exchanger elements terminate and face into a hollow portion such that fluid within these elements can be transported via the hollow portion to the other header. Preferably the heat exchanger is an LNG heat exchanger. In such systems, the heating medium is . , natural gas and the cooling medium is a refrigerant such as multicomponent refrigerant (MCR) . Preferably the heat exchanger elements for carrying the LNG are extruded. The heat exchanger ■ tubes for carrying the MCR can be thicker, and formed by extrusion or corrugated fins .

Preferably the heat exchanger elements are arranged in a cold-cold-hot-hot arrangement or more preferably in a hot-cold-hot-cold arrangement.

Preferably . the heat exchanger .is. arranged such that the heating and cooling fluid flow in counter flow. Therefore, at one end of the heat exchanger the distributing means distributes heating fluid into either

the first or second heat exchanger elements and collects cooling fluid from the other of the first or second heat exchanger elements while at the other end the distributing means collects heating fluid and delivers cooling fluid.

Preferably the distribution means for distributing the cooling fluid comprises passageway(s) which' are dimensioned to act as throttling orifice tubes. This ensures the refrigerant is uniformly distributed to each cavity as two phase flow does not occur within the

■ header itself, but only after the refrigerant has passed through the orifice tubes.

Preferably split tubes are inserted through the headers. This increases the stability of the headers. Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG 1 shows a simplified heat exchanger having heat distribution means in accordance with the present invention;

FIG 2 shows a plan view of the heat exchanger of FIG 1;

FIGs 3A and B show cross sections through the distribution means taken along lines A-A and B-B ^' respectively;

FIG 4 shows ' a heat exchanger containing distribution elements according to the present invention;

FIG 5 shows a single heat exchanger unit with - distribution elements according to the present invention;

FiG 6 shows a close up of a distribution elements according to the present invention as seen from the refrigerant side; ^•

FIG 7 shows a perspective view of the refrigerant side of the distribution element; • FIG 8A shows a plan view of an alternative version of a refrigerant side distribution element; FIG 8B shows a cross section through the distribution element of FIG 8A along line B-B;

FIG 9 shows a single heat exchanger unit shown in FIG 5 from the opposite side;

FIG 10 shows a close up of the distribution element as seen from the cooled fluid side;

FIG 11 shows a detail of the connection between heat exchanger element and the distribution element;

FIG 12A shows a plan view of an alternative version of a cooled fluid side distribution element; FIG 12B shows a cross section through the distribution element of FIG 12A along line ^" B-B;

FIGs 13A and B shows the refrigerant side of an alterative distribution element;

FIG 14 shows the cooling fluid side of the distribution element of FIG 13;

FIGs 15A and B show alternative fluid distribution elements in accordance with the present invention; and FIG 16 shows a heat exchanger unit for use in the present invention.

FIG 1 shows a simplified heat exchanger 20 consisting of a number of extruded heat exchanger elements 21. Each element 21 contains a row of individual channels through which heat exchanger fluid flows. At each end of the elements 21 distribution means are formed by two ports which align with the equivalent ^" ports of the adjoining elements to form headers 22, 23, 24, 25 through the heat exchanger 20. ^• Heating and cooling fluids are delivered to and removed

from the elements ^' 21 via these headers. The heating and cooling fluid can flow through the heat exchanger 20 in either co- or counter-flow. In counter flow for example heating fluid can be delivered via header 22 and removed via header 23 while the cooling fluid is delivered by header 24 and removed by header 25. As the heating and cooling fluids flow along the heat exchanger channels they are in thermal contact with one another and therefore heat exchange occurs . FIG 2 shows a plan view of the heat exchanger 20, indicating the location of the cross sections shown in FIGs 3A and B. Element 211 carries a cooling fluid whereas element 212 contains heating fluid.

FIG 3A shows a cross section along line A-A through the ends of cooling element 211. Port 224 forms part of header 24 while port 223 forms part of header 23. As can be seen from the cross sectional view, passageways 228a are formed within element 211 which link port 224 to a cavity 226. A row of heat exchanger channels 221 open into this cavity 226. Therefore, the cavity can be seen to act as an intermediate header, distributing fluid to a plurality of heat exchanger channels 221. The cavity 226 is connected to the port 224 by the passageways 228a. These are narrow and so allow fluid to be drawn off from the main header 24 into cavity 226 without any significant pressure drop. In addition, the passageways 228a allow fluid to be transported to the heat exchanger channels 221 while bypassing the second port 223, which in use will contain the heating fluid. Therefore this system allows all the headers to pass through the plane of the heat exchanger channels .

At the base of element 211 a similar construction exists. Again heat exchanger channels 221 open into a cavity 227 which is connected to cooling fluid port 225

by passageways 228b. In this way the cooling fluid can traverse the length of the element without coming into contact with the heating fluid ports 223, 222. Identical elements to this are spaced throughout the ^• heat exchanger 20. At each element 211 cooling fluid is siphoned off the main header 24 by passageways 228a so that a plurality of cavities 226 can distribute fluid to separate layers of channels 221. After the cooling fluid has passed through the heat exchanger channels 221, where it is in a heat transferring relationship with heating fluid being carried through other heat exchanger elements 212, it collects in cavity 227 and is transferred to exit header 25 by passageways 228b.

As can be seen from FIG 3A, passageways 228a are narrower than passageways 228b. This is because passageways 228a are designed to act as throttling orifice tubes. This allows the cooling fluid to be transported through header 24 at a pressure above its boiling point, such that all the fluid within this header 24 is liquid. As it passes through passageways

228a however and into cavity 226, the pressure drops and two phase flow is formed. By preventing two phase flow ^' until the fluid is in the intermediate header formed by the cavity 226,' a more even distribution of fluid is achieved.

Turning to FIG 3B, this shows element 212, which contains heat exchanger channels for transporting heating fluid. Therefore, in this element 212 ports 224, 225 are not connected to the heat exchanger channels 231. Instead ports 223, 222 which form part of headers 23, 22 respectively are shaped such that they open directly into hollow portions ^' 229, 230. As with cavities 226, 227 hollow portions 229, 230 act as intermediate headers and distribute fluid to a row of

heat exchanger channels 231 within the element 212. When element 212 is stacked between elements 211, hollow portions 229, 230 are closed off, as shown in dotted lines in FIG 3B. In this way heating fluid can be contained in element 212.

FIG 4 shows a heat exchanger 1 for cooling and liquefying natural gas. The heat exchanger 1 comprises a core 8 comprising a large number of heat exchanger units 2, most of which have been removed for clarity. These units 2 consist of at least one heat exchanger element for transport of the cooling fluid 21 and at least one heat exchanger element for transport of the ' heating fluid 22. The heat exchanger elements 21, 22 can be made in a number of ways, such as by extrusion or using corrugated fins, and can each contain one or more rows of heat exchanger channels . The units 2 can be made in a number of ways, including the creation of separate heat exchanger 'elements 21, 22 later fixed together or by integral moulding of these elements . The different elements 21, 22 of the unit 2 can be seen most clearly in FIG 5.

In reality the core 8 of the heat exchanger 1 would be filled with heat exchanger units 2 arranged to transport a refrigerant, usually a multi-component refrigerant (MCR) , and the gas to be cooled and liquefied (LNG) through the core. At either end each unit 2 is connected to a distribution element, in this embodiment in the form of a distribution plate 10. These plates 10 align to form headers through the heat exchanger core 8. The headers connect to delivery pipes. Delivery pipe 3 transports cooled MCR to one of the headers formed by the distribution plates 10. As will be detailed below, as the MCR passes through the header it is fed through distribution plates 10 into

heat exchanger elements 21. The MCR then exits the core 8 via a header formed in the opposing distribution element 10 and into exit pipe 5. Delivery pipe 4 ^' provides LNG to the core 8 where the header formed by the distribution plates 10 delivers this to heat exchanger elements 22. The LNG flows in counter flow to the MCR and exits from the top of the heat exchanger 1 via exit tube 6. Although the distribution plates 10 align to create headers, as can be seen from FIG 4 each , header also contains split tubing 7 to strengthen and support the headers .

FIG 5 shows a single heat exchanger unit 2 in ⁽ isolation. The mid-sectioh of the unit 2 has been shortened for simplicity as, for the purposes of this invention, it is the ends of the unit 2 and the distribution plates that are of interest. The heat exchanger unit 2 is connected to a top distribution plate 11 and a bottom distribution plate 12. In this figure, the plates 11, 12 are shown from the refrigerant side.

A close up of bottom distribution plate 12 can be seen in FIG 6. Here it can be seen that the plate 12 comprises a first port 121 for transport of the refrigerant away from the heat exchanger 1, and a second. port 122 for delivery of the LNG to the heat exchanger 1. It can be seen from FIG 5 that the top plate 11 also has a second port 112 for transport of LNG (this time away from the heat exchanger) however the top plate 11 has two first ports Ilia, 111b for transport of the refrigerant to the heat exchanger 1. The number of ports used to carry the MCR or LNG can be chosen according to the needs of the plant.

Returning to FIG 6, distribution plate 12 has a cavity 123 located at the end of the ■ distribution plate

12 furthest from the first port 121 and in contact with the heat exchanger unit 2. Cavity 123 is formed by a cut out, however one side of this cut out has been closed off by the ¹ heat exchanger element for carrying ■5 LNG 22. In comparison, the heat exchanger element for carrying the refrigerant 21 is shorter and abuts the end of cavity 123, resulting in the channels within this element opening into the cavity 123. Distribution plate 12 contains internal passageways 124, indicated by 0 arrows, which connect the cavity 123 to port 121 to allow transport of the MCR from, the cavity 123 to the port 121 bypassing LNG port 122. The passageways 124 open into the port 121 at outlets 125, one of which can be seen in FIG 6. Top distribution plate 11 contains 5 similar passageways, one connecting each first port Ilia, 111b to cavity 113.

FIG 7 shows this indirect connection between the heat exchanger channels and the port 121 more clearly. Here the MCR element 21 is provided by corrugated fins 0 while the LNG element 22 is provided by an extruded element. By sandwiching the corrugated fins between two LNG elements, or another planar surface, MCR channels 21a are created. MCR element 21 abuts the cavity 123 of the distribution plate 12 such that channels 21a open 5 out into the cavity 123. In contrast, extruded LNG element '22 can be seen to extend past the cavity 123 such that the channels of this element 22 do not open into the cavity 123. At one side of the cavity 123 passageway 124 can be seen. This extends through the 0 plate 12 to first port 121, bypassing second port 122. The outlet 125 of ^• the passageway 124 opens into port 121.

Therefore, MCR flowing through channels 21a would enter cavity 123 and flow through passageways 124 within

the distribution plate 10 and out through outlets 125 into port 121 and away from the heat exchanger core 8. This sequence is reversed in top plate 11 where the refrigerant would flow from the first ports Ilia, 111b through- the passageways and cavity 113 into the heat exchanger channels 21a.

FIG 8A shows a plan view of a variant to the refrigerant side of the distribution plate. Here two ports 511a, 511b are used to transport MCR within the header and each port 511a, 511b is connected to the cavity 523 by a passageway 524. These passageways 524 can also be seen in FIG 8B. FIG 8A also clearly shows the cut out nature of the cavity 523. This eases construction of the plate and the sides of cavity 523 are closed off during use by other elements of the heat exchanger 1.

While MCR is delivered to and from the heat exchanger core 8 indirectly by way of the cavity 123 and passageways 124, the LNG is delivered more directly. FIG 9 shows the unit 2 of FIG 5 from the opposite side, showing the "cooled fluid" sides of distribution plates 11, 12.

A close up of bottom distribution plate 12 is shown in FIG 10. Here again first port 121 can be seen with outlet 125 of passageway 124 visible. However from this angle it can also be seen that second port 122 comprises a hollow portion 126 shaped to received the end of the LNG element 22. This hollow portion 126 allows the channels of the LNG element 22 to open directly into port 122. FIG 11 shows this in more detail. In this figure shoulder 127, against which the LNG element 22 abuts, is clearly shown. This figure also shows how.the other side of distribution plate 12 extends down past

the hollow portion 126. It is in this extended portion that cavity 123 is formed.

FIG 12A shows a plan view of the LNG side of an alternative distribution plate. Here two ports 911a, 911b transport the MCR while the direct connection between hollow portion 926 and port 922 is clearly visible. Port 922 is closed off by the refrigerant side of the plate, not shown here but equivalent to, for example, that shown in FIG 8A. As can be been in FIG 12B, no passageways are formed in this side of the distribution plate as no indirect connections are required.

FIGs 13A, B and 14 show alternative MCR and LNG sides, 100a, 100b of a distribution plate for use at the top of the heat exchanger 1. MCR side 100a comprises a second port 120 for transport of LNG and two first ports 101a, 101b for transport of the MCR prior to delivery into the heat exchanger core 8. At this time the pressure of the MCR is very important. As discussed previously the MCR should enter the heat exchanger channels 21 at the liquid/gas boundary. This results in ^■ two phase flow which can create uneven distribution to the channels. Using the distribution plates of the present invention the MCR can be transported through ports 101a, 101b at a pressure above this point, so that the MCR flows in liquid form. The passageways 134 used to connect ports 101a, 101b to cavity 130 are narrower than those provided within MCR exit distribution plate, shown in FIG 8A. The narrow width of the passageways 134 provides a throttling effect on the MCR passing through these, such that within the cavity 130 de- pressurisation occurs and reduces the MCR to the desired pressure. In order to evenly distribute' the MCR to all

channels opening into the cavity 130 foam, sintered metal or fins can be introduced.

FIG 14 shows the LNG side 100b of the alternative ^• distribution plate. This provides the hollow portion 136 in connection with second port 120.

The MCR and LNG sides of any of the distribution plates made according to the present invention can be manufactured separately and then joined by welding or other means to form a single plate. Alternative distribution plates are also possible. FIGs 15A and B show first and second distribution plates 400, 450 respectively. First distribution plate 400 is similar to the MCR side of the distribution plates described above in that a first port 410 is connected to a cavity 430 by passageways 440. Second port 420 is not connected to the cavity 430. In this embodiment cavity 230 is closed on one side by wall 431. In use a series of heat exchanger channels are connected to the cavity 430 and so by using this distribution plate 400 a first fluid can be transported from the port 410 to these channels by way of the passageways 440 and cavity 430 and vice versa.

Distribution plate 450 shown in Fig 15B also comprises a first port 460 and a second port 470, however in this plate it is the second port 470 which is connected to cavity 480 by way of passageways 490. When connected to a series of heat exchanger channels this plate therefore allows a second fluid to by indireptly communicated between the heat exchanger channels and the second port 470.

These distribution plates 400, 450 can be stacked together to provide headers ^~~ tur heating and cooling fluids, wherein both fluids are connected to the heat exchanger channels indirectly. By having one side of

the cavities 430, 480 closed off by a wall 431, 481 the cavities can be closed off simply by stacking the plates, the heat exchanger elements do not need to be involved in this process . Alternatively parting sheets could be placed between adjacent plates to close off cut out cavities. In a similar vein, although passageways 440, 490 are shown as closed, internal passageways, these could also be open on one side to be closed off upon alignment with another distribution plate or parting sheet.

Finally, in a further embodiment the heat exchanger elements themselves can assist in the formation of headers. It is possible for a heat exchanger element to be formed with all of the distribution components discussed above, i.e. ports, cavities and passageways as shown in FIGs 1 to 3. However in another variation one or more ports can be formed at the' distal ends of a heat ■ exchanger element.

This is shown in FIG 16. Here heat exchanger unit 30 comprises first and second heat exchanger elements

31, 32. First heat exchanger element 31 is shorter than second heat exchanger element 32 leaving exposed areas 42 when the two elements are joined together. In the exposed areas 42, at either end of second heat exchanger element 32, first and second ports 33, 36 are formed.

The channels 34 of the second heat exchanger element 32 open out into first port 33 but are blocked from entering second port 36.

A distribution plate such as that shown in FIG 15A can ,be positioned within the exposed area 42 such that cavity 430 connects with the channels 35 of the first heat exchanger element 31, port 410 is aligned with port 36 and port 420 with port 33. In this way fluid can be transported to and from first heat exchanger channels 35

by means of the cavity 430 and passageways 440 of the distribution plate 400 while fluid can be transported from ports 33, 420 directly into the heat exchanger channels 34, which open into port 33. It will be noted that when distribution plate 400 is used in this way wall 431 is not necessary as the cavity 430 will be closed off by heat exchanger element 32.

To avoid the complexity of creating a second port 36 in the heat exchanger element 32 however, the element can be cut and sealed along lines 37 and a further component, containing port 36, introduced into the system. Alternatively the distribution plate could be dimensioned to provide this .

Other variations are also possible, for example first and second ports could be placed side by side or different shapes and numbers of passageways could be used.

Therefore the present invention provides a means of allowing headers to be formed in the plane of the heat exchanger elements . The indirect connection provided between one header and the heat exchanger channels allows the fluid to bypass another header in the same plane. The distribution elements can easily be connected to extruded and other forms of heat exchanger element and also allows two phase flow to be evenly distributed.

Throughout the specification, the terms "cavity" and "hollow portion" have been used to distinguish between spaces which are attached to the ports by passageways and those which are not, there need not be any- other difference between them.