AU2017206160B2 - Heat Exchanger - Google Patents

Abstract

A heat exchanger comprises a primary flow path arranged to contain a first heat exchanging medium. A secondary flow path 5 arranged to contain a secondary heat exchanging medium, wherein the primary flow path surrounds the secondary flow path for exchanging heat between the two paths. 10 (FIGURE 10) 26 9/18 18 17 16a Figure 10 -A 15 16 20 15 'Figure 11

Description

9/18

18

17 16a

Figure 10

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15 16

20

'Figure 11

HEAT EXCHANGER TECHNICAL FIELD

The present invention relates generally to heat exchangers

methods for forming the same. More specifically, but by no

means exclusively, the invention relates to tubing

configurations for improving heat transfer characteristics of

a heat exchanger.

BACKGROUND OF THE INVENTION

Heat exchangers can be found in many devices where cooling or

heating of fluids, including liquids and gases, is required.

The basic principle of any heat exchanger is to provide

efficient transfer of heat from one heat exchanging material

(e.g. gas, fluid, etc.) to another, without any direct

contact between the two. Heat exchangers are commonly found,

for example, in refrigeration units, power plants, air

conditioning systems, among others.

One well-known type of heat exchanger is the Fin and Tube

exchanger commonly found, for example, in refrigeration

condensers. Fin and Tube exchangers employ a plurality of

inter-connected tubes positioned within, and thermally

coupled to, a metal structure which is exposed to a flow of

air. Often, the metal structure takes the form of a plurality

of metal "fins" which run perpendicular to the inter

connected tubes and which serve to increase the effective

surface area of the heat exchanger.

Fluid circulating through the tubes gives off its heat by

convection to a flow of air passing through the fins. For

certain applications, the flow of air may be forced through

the fins by way of a fan. Clearly, the larger the heat

exchanger, the larger the fan required to move the air for suitably affecting suitable heat transfer. As may be appreciated by those skilled in the art, despite being well known and used, heat exchangers employing fluid carrying pipes, such as those previously described, have a number of drawbacks. For example, in order to provide sufficient heat transfer for many processes, the interconnected pipes need to be many meters in length leading to the exchangers being relatively large in size when compared to the refrigeration unit (or an equivalent water cooling tower of the same heat load capacity). This in turn not only limits the range of sites that the device can be installed in, but also leads to appreciable manufacturing and operational costs.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is

provided a heat exchanger comprising: a primary flow path

arranged to contain a first heat exchanging medium; and a

secondary flow path arranged to contain a secondary heat

exchanging medium, wherein the primary flow path surrounds

the secondary flow path for exchanging heat between the two

mediums.

In an embodiment the primary flow path is helical.

In an embodiment the primary flow path is partitioned.

In an embodiment the primary flow path is surrounded by one

or more heat exchanging fins.

In an embodiment the exchanger further comprises a length of

tube and wherein the secondary medium is carried within a

body of the tube and the first medium is carried within a

circumferential outer wall of the body.

In an embodiment the tube has a circular cross section.

In an embodiment the exchanger further comprises an inlet

manifold coupled to a first end of the tube and having a

fluid path flow in fluid connection with the primary flow

path of the tube for delivery of the first medium.

In an embodiment the exchanger further comprises an outlet

manifold coupled to a second end of the tube and having a

fluid path flow in fluid connection with the primary flow

path for expelling the primary medium.

In an embodiment the exchanger further comprises a plurality

of tubes and wherein the inlet and outlet manifold each

comprise a manifold tube having openings defined along their

length for receiving corresponding ends of the respective

exchanger tubes.

In an embodiment an inner surface of the circumferential wall

for each tube extends through the manifold tube and meets

with a second opening in the manifold tube for

receiving/expelling the secondary medium.

In accordance with a second aspect there is provided a method

of constructing a heat exchanger comprising forming a primary

path flow arranged to contain a first heat exchanging medium,

so as to surround a secondary path flow arranged to carry a

secondary heat exchanging medium.

In an embodiment the primary flow path is a helical flow

path.

In an embodiment the method further comprises forming the

helical flow path by winding or extruding a length of a

primary tube having a generally elongate cross section such

that the length extends along a helical path.

In an embodiment the method further comprises

winding/extruding the length of tube such that a closed outer circumferential wall is formed so as to define the secondary flow path.

In an embodiment the method further comprises locating an

inner tube arranged to carry the secondary flow path within

the wound length of primary tube.

In an embodiment the method further comprises coupling a

first end of the primary tube to an opening in an inlet tube

arranged to deliver the first medium such that the primary

flow path is in fluid communication with the inside of the

inlet tube.

In an embodiment the method further comprises coupling a

second end of the primary tube to an opening in an outlet

tube arranged to expel the first medium such that the primary

flow path is in fluid communication with the inside of the

outlet tube.

In an embodiment the method further comprises passing the

secondary flow path through a second opening in the

respective inlet/outlet tube for delivering/expelling the

secondary medium. In accordance with a further aspect there

is provided a heat exchanger comprising one or more tubes

arranged to carry a flow of a first heat exchanging medium,

the first medium arranged to exchange heat with a second heat

exchanging medium in thermal contact with the one or more

tubes; and a flow direction control insert located within

each tube and operable to control flow of the first medium.

In an embodiment the flow direction control inserts is

operable to vary the effective path length of the conduit.

It an embodiment the conduits are in the form of tubes of

cylindrical cross section, although it will be understood

that other forms of tube or conduit are equally applicable

and are not limited to being of cylindrical cross section

(e.g. square conduits, hexagonal conduits and the like are

envisaged).

In an embodiment, the flow direction control insert comprises

an elongate body having an outer surface which controls the

flow. In an embodiment the outer surface is operable to

direct the flow within the tube to increase the effective

length of the tube for the purposes of heat exchange.

In an embodiment, the elongate body extends the length of

each tube. In an embodiment, the elongate body is in the form

of a helical screw. The outer circumference of the helical

screw may, for example, sealingly contact an inner surface of

the tube to create a helical flow channel. In an embodiment,

the pitch of the helical screw is varied to adjust the

effective length of the tube. Alternatively, the diameter of

the tube along with the diameter of the helical screw body

may be varied to adjust the effective length.

In an embodiment, the two heat exchanging mediums may be

selected from air, steam, water, refrigerant, oil, beverage,

or any combination thereof.

In an embodiment, the heat exchanger is one of a condenser,

evaporator, cooling tower, radiator, Shell & Tube and Tube in

Tube heat exchanger configuration. In an embodiment, the

insert is formed from a plastic, polymer, elastomer, or

rubber material. Alternatively, the insert may be formed from

a corrosion resilient metal or alloy, or any other suitable

material.

In an embodiment, each insert comprises one or more sections.

The one or more sections may direct the flow in a different

manner to other sections. For example, the temperature

difference through the first few passes (i.e. tube lengths)

may be substantially greater than for the subsequent passes,

allowing rapid heat transfer and thus not requiring any form of insert to be implemented (although in an embodiment, an insert may well be provided depending only on the desired implementation). For the remaining passes, a helical insert as previously described may be incorporated within the tubing to account for the loss in heat transfer (i.e. this will effectively reduce the speed of the circulating fluid to allow more time for the circulating fluid to contact the inner wall of the tubing). The flow direction control insert may be implemented at a section of the tubing where the temperature difference is not much different from the second medium, which allows more time for heat transfer.

In an embodiment the tube comprises an outer surface having

one or more fins located thereon which are in thermal contact

with the second heat exchanging medium. In an embodiment the

one or more fins are helical outer fins which wrap around the

outer surface of the body. In an embodiment a pitch of the

helical insert corresponds with a pitch of the helical fins.

In an embodiment a plurality of helical fins are located on

the outer surface having progressively staged start

locations.

In an embodiment the tube and at least one of the helical

outer fins and helical insert are extruded from a single

blank. In an embodiment the tube and helical insert and/or

fin are formed from a single aluminium extrusion. A heat

exchanger formed from such a one piece extrusion may

significantly reduce construction time and cost.

In accordance with a further aspect of the present invention

there is provided a flow direction control insert arranged to

be located inside a heat exchanger comprising a tube arranged

to carry a flow of a first heat exchanging medium arranged to

exchange heat with a second heat exchanging medium which is

in thermal contact with the tubes, whereby the flow direction

control insert is operable to control flow of the first medium within the tube to thereby vary the effective path length of the tube and in turn adjust the heat transfer characteristics of the heat exchanger.

In accordance with another aspect of the present invention

there is provided a method for varying a heat transfer

characteristic of a heat exchanger comprising a tube arranged

to carry a flow of a first heat exchanging medium arranged to

exchange heat with a second heat exchanging medium which is

in thermal contact with the tube, the method comprising the

steps of: locating a flow direction control insert within the

tube, the flow direction control insert having an outer

surface which is arranged to control flow of the first medium

within the tube to thereby vary the effective path length of

the tube and in turn vary the heat transfer characteristic.

In accordance with yet another aspect of the present

invention there is provided a method of forming a heat

exchanger comprising extruding a length of heat transmissive

material through a die so as to form a tube having one or

more helical fins which extend around an outer surface of the

tube, the tube arranged to carry a flow of a first heat

exchanging medium, the first medium arranged to exchange heat

with a second heat exchanging medium in thermal contact with

the one or more helical fins.

In an embodiment the method further comprises extruding the

length of heat transmissive material to form a flow direction

control device within the tube, the flow direction control

device having an outer surface which is arranged to control

flow of the first medium within the tube to thereby vary the

effective path length of the tube and in turn vary the heat

transfer characteristic.

In accordance with a still further aspect of the present

invention there is provided a method of forming a heat

exchanger comprising extruding a length of heat transmissive material through a die so as to form a tube having an inner surface in which is defined a flow direction control device, the device arranged to control the flow of a first heat exchanging medium arranged to be passed through the tube and which medium is arranged to exchange heat with a second heat exchanging medium in thermal contact with an outer surface of the tube . In an embodiment the flow direction control device comprises a helical screw as described in accordance with the first aspect.

In an embodiment the heat transmissive material is aluminium.

In accordance with a sixth aspect of the present invention,

there is provided a method of improving a heat transfer

characteristic of an existing heat exchanger comprising a

tube arranged to carry a flow of a first heat exchanging

medium arranged to exchange heat with a second heat

exchanging medium which is in thermal contact with the tube,

the method comprising the steps of: locating a flow direction

control insert within the tube, the flow direction control

insert having an outer surface which is arranged to control

flow of the first medium within the tube to thereby increase

the effective path length of the tube and in turn improve the

heat transfer characteristics.

In an embodiment the method could be used to adapt existing

exchangers.

In an embodiment, the flow direction control insert comprises

an elongate body and has the characteristics as previously

described with reference to a first and/or second aspect.

According to a further aspect of the present invention there

is provided a tube for a heat exchanger, the tube arranged to

carry a flow of a first heat exchanging medium, the first

medium arranged to exchange heat with a second heat

exchanging medium in thermal contact with the tube, and a flow direction control device located within the tube and operable to control flow of the first medium.

In an embodiment the flow direction control device is

integrally formed with the tube. In an alternative embodiment

the device is provided as a separate removably coupled

insert.

In accordance with an eighth aspect of the present invention

there is provided a method for varying a heat transfer

characteristic of a heat exchanger comprising a tube arranged

to carry a flow of a first heat exchanging medium arranged to

exchange heat with a second heat exchanging medium which is

in thermal contact with the tube, the method comprising

controlling a direction of the flow of the first heat

exchanging medium within the tube so that it flows a greater

distance than the tube length.

It should be appreciated from the above description that

according to at least certain aspects there may be provided

an improved heat exchanger design including modified tube

design, lower mass and overall dimensions, modified methods

to assemble the exchanger (or retro-fit an existing heat

exchanger) using flow direction control techniques that are

operable to vary the effective length of the heat exchanger

tubing. The advantages which should be apparent to those

skilled in the art may include an increased heat transfer

efficiency, lower manufacturing and running costs through

reduced materials, reduced power consumption, simplified

installation and the ability to cost effectively retrofit an

existing exchanger for improving fluid transfer

characteristics.

BRIEF DESCRIPTION OF DRAWINGS

Features and advantages of the present invention will become

apparent from the following description of embodiments

thereof, by way of example only, with reference to the

accompanying drawings, in which:

Figure 1 is a schematic of a heat exchanger assembly

illustrating installation of a flow direction control insert,

in accordance with an embodiment of the present invention;

Figures 2a and 2b are sectional top and side elevation views,

respectively, of a heat exchanger employing a flow direction

control insert, in accordance with an embodiment of the

present invention;

Figure 3 is a schematic of a helical flow direction control

insert, in accordance with an embodiment of the present

invention;

Figure 4 is a perspective view showing hidden detail of the

Figure 1 heat exchanger embodiment;

Figure 5 is a process flow diagram showing method steps for

varying heat transfer characteristics of a heat exchanger, in

accordance with an embodiment of the present invention;

Figures 6 and 7 show heat exchanger configurations pre and

post insertion of flow direction control insert in a SKOPE 2

door drink merchandising cabinet refrigeration unit model No

SK650-C a for test, in accordance with an embodiment of the

present invention;

Figure 8 is a graph showing test results for the Figures 6

and 7 configurations;

Figure 9 is a schematic of a tube carrying a helical flow

direction control insert in accordance with a further

embodiment of the present invention;

Figure 10 is a schematic of an exchanger tube in accordance

with yet a further embodiment of the present invention;

Figure 11 is a detailed view of section A identified in

Figure 10;

Figure 12 is an exploded isometric view of a single exchanger

tube and manifold, in accordance with an embodiment;

Figure 13 is a partially assembled front view of the

exchanger tube and manifold of Figure 12;

Figure 14 is an assembled isometric view of an exchanger

including an inlet and outlet manifold connected to five

exchanger tubes, in accordance with an embodiment;

Figure 15 is a front view of Figure 14 with a section of the

inlet/outlet manifolds shown in hidden detail, illustrating

fluid flow directions within the exchanger;

Figures 16 and 17 are isometric and end views respectively of

an exchanger tube in accordance with another embodiment of

the present invention;

Figure 18 is a schematic of an exchanger tube in accordance

with another embodiment of the present invention;

Figure 19 is a detailed view of section A identified in

Figure 18;

Figures 20a, 20b and 20c are various schematic views of an

extruded length of micro-channel incorporating fins for

forming a heat exchanger tube, in accordance with an

embodiment;

Figures 21a and 21b show the extruded length of micro-channel

of Figure 20 in a tightly helically wound state in accordance

with an embodiment;

Figure 21c is a close up view of detail A shown in Figure

21a;

Figures 22a to 22c show perspective, front and end views,

respectively, of a number of the helically wound tubes of

Figure 21 connected to an inlet and outlet manifold;

Figure 23a shows one of the helically wound lengths of tube

with a plugged core;

Figure 23b is a close view of detail B shown in Figure 23a;

Figures 24a and 24b show various view of the heat exchanger

tube of Figure 20 in a loosely helically wound state in

accordance with an embodiment;

Figure 24c is a close up view of detail B shown in Figure

24a;

Figures 25a to 25c show perspective, front and end views,

respectively, of a number of the helically wound tubes of

Figure 24 connected to an inlet and outlet manifold, in

accordance with an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for the purpose of illustration

only, embodiments of the present invention are described in

the context of a heat exchanger for a refrigerator, and more

particularly to the tube configuration of the refrigerator's

condensing unit. It will be appreciated, however, that

embodiments may be implemented for any form of heat exchanger

which employs one or more tubes utilised to transfer heat

from one medium to another. For example, embodiments could be

implemented for small scale applications (such as the

refrigeration application described herein) right through to

large scale industrial applications including, for example,

radiator panels for cooling towers. It should also be

appreciated that many of the referenced figures are not to

scale, and only serve to conceptually illustrate the various

heat exchanger components and interactions between those

components for achieving improved heat transfer and

condensation draining characteristics when compared to

conventional exchanger designs.

With reference to Figure 1 there is shown a heat exchanger in

accordance with a first embodiment of the present invention.

As mentioned above, the heat exchanger is in the form of a

fin and tube-type exchanger for a refrigeration condensing

unit.

According to the first embodiment, the heat exchanger 1

comprises a plurality of tubes 2 which are arranged to carry

a flow of a first heat exchanging medium in the form of a

refrigerant (e.g. such as R134A-R410, R22, R404A refrigerant

that are particularly suited for refrigeration applications).

The tubes 2 extend through, and are in thermal contact with,

a plurality of stacked fins 3 which are in perpendicular

alignment to the tubes 2. As persons skilled in the art will

appreciate the configuration of the tubes 2 and fins 3, act to transfer heat from the refrigerant circulating through the pipes to a second medium to thereby cool the refrigerant. In the illustrated embodiment the second medium is air which absorbs the heat from the refrigerant thereby allowing it to cool, condense and turn into a liquid before being recycled to an expansion device and an evaporator unit of the refrigerator.

At the bottom left hand section of Figure 1 there is shown a

flow direction control insert 4 which is arranged to be

located within each tube (as shown in partial hidden detail

in the right most tube 2c) and operable to control flow

direction of the first medium through the tube to thereby

vary the effective path length of the tube. With additional

reference to elevation views shown in Figures 2a and 2b and

3, the flow direction control inserts are in the form of

helical screws 4 that effectively extend the length of each

tube (and in turn improve the heat transfer characteristics

as will be described in subsequent paragraphs). In the

illustrated example, the screws are made of a deformable

rubber and are sized such that outer circumference of each

helical rib 4a is in direct contact with an inner surface of

the tube to thereby form a flowpath (denoted in the drawings

as a "gas channel") that serves to increase the effective

length of the tube 2. This is best shown in Figure 2a. While

in the illustrated example the ribs 4a of the helical screw 4

sealingly engage the tube's inner surface (i.e. an outer edge

5 of each rib 4a is arranged in an interference fit with an

inner surface 6 of the tube), in other embodiments the ribs

may not extend right the way thereto. According to such an

alternative embodiment, the insert 4 may still serve to vary

the effective path length, albeit not to the same extent as

where they extend right the way. It will be understood that

different helical screw configurations and dimensions will

have an effect on the extent of the flow path variance. For

example, different capacity units will require different size chambers to allow correct flow. Different capacities may be achieved by means of increasing pipe and helical screw diameter and increasing/decreasing the inner diameter (shank) of the helical screw. The helical screw pitch will also adjust the effective length of the flow path; the smaller the pitch of the screw, the longer the effective flow path of the chamber. Furthermore, it will be appreciated that the helical screw may not have a shank but instead be in the form of a spring made from flat rather than a round section.

A method of forming a heat exchanger panel in accordance with

the first embodiment of the present invention will now be

described with additional reference to the flow diagram 500

of Figure 5.

With reference to Figure 5 (section A) , a conventional fin

and tube heat exchanger is manufactured from a plurality of

fins with holes punched evenly, the quantity of which is

commensurate with the heat load for the design of the

condensing unit. Loose fitting tubes are then inserted

through the punched holes and expanded so that the tube is a

tight fit in the punched holes (step 502).

At step 504, a flow direction control insert in the form of a

helical screw is inserted into one or more of the tubes,

depending on the heat transfer characteristics required (in

the illustrated embodiment it will be noted that all tubes

have been used) . Insertion may be achieved by utilising an

insert formed of a product that will deform on insertion and

reform once in place (e.g. elastomeric type material). An

alternative method may be to insert a thin walled metal

helical screw with a bore through the centre that will allow

a (bullet) to be drawn through the tube expanding the screw

to the inner surface of the tube. According to such an

embodiment the ends of the tube would need to be sealed prior

to soldering the elbows on (described later). To retrofit an existing heat exchanger, the elbows on one end of the heat exchanger would need to be removed, the helical screw inserted and the elbows replaced.

At step 506, the ends of the tubes then have elbows soldered

to one another to form a continuous serpentine arrangement.

This is best illustrated in Figure 6. A fan (not shown) may

be added to force air over the fins.

EXPERIMENTAL RESULTS

A two door drink fridge condensing unit was used for the

trial. For expedience, the condenser tubing was split in two

sections as can be seen from the Figure 7 schematic. Passes A

to I (only some passes are shown in the schematic for

illustrative purposes) were modified to accept the helical

screw and used as the complete condensing unit, while passes

J to U were kept standard (i.e. no flow direction control

insert). Due to the halving of the capacity of the condenser,

the trial was conducted in a low ambient temperature

atmosphere. The results were then compared with the results

using the passes J to U again in a low ambient temperature

atmosphere. Whilst modifying the left hand part of the

condenser some of the passes were damaged and could not be

used. Two temperature reading tubes were soldered 50 mm into

the gas flow, the end of which was sealed, in the positions

marked on tubes A and U of Figures 6 & 7. A temperature probe

was then inserted into these tubes for accurate temperature

measurements. The test results are shown in Figure 8. It can

be observed from the test results that by using a helical

screw with fewer passes, a significant positive improvement

in relation to efficiency of the heat exchanger is achieved.

A further test was carried out in respect of an air

conditioning system for a vehicle. A conventional condenser

unit from a Holden Astina (hereafter "the Astina condenser")

was set up on a test bench alongside a condenser incorporating a plurality of tubes including helical flow direction control inserts (hereafter "the helical screw condenser" ) , in accordance with an embodiment of the invention.

The Astina condenser had a block size of 580 mm long x 300

high (i.e. effective fin area) and included a total of 28

tubes having 8 micro-channels defined therein. The micro

channels measured 1.7 mm wide x 1.5 mm high. The helical

screw condenser on the other hand measured only 490 mm long x

310 mm high. 10 tubes formed of 3/4" copper pipe were

included in the screw condenser body. Each of the tubes

incorporated helical screws of 17.6 mm O/D (outside diameter)

14.9 pitch (i.e. which in this case is the distance in

millimeters between the leading edge of each turn of the

helical thread), 1 mm blade thickness and centre stem

diameter of 2.5 mm. A schematic of the tubing configuration

of the helical screw condenser is shown in Figure 9, where

the screw body is designated by the reference numeral 10, the

thread is designated by the reference numeral 12 and the fins

are designated by reference numeral 14.

It was demonstrated that the volume of gas through the

helical screw condenser body 10 was measured as twice that of

the volume through the Astina condenser. From the

demonstration it was calculated that a pass of 13.9 mm in the

micro channel condenser equated to approximately 57 mm in the

new condenser, which increases the effective path length of

the helical screw condenser by a factor of 4. Thus, for the

same physical size of heat exchanger, the length of the new

condenser would be 4 times longer at twice the volume

(thereby, by calculation, making the new condenser 8 times

bigger in capacity for the same physical size).

The above embodiments described the helical insert as being

removably coupled to the tubing. However, in an alternative embodiment, the helical insert and outer tubing may be formed as one piece (i.e. integrally formed). For example, the heat exchanger may be formed by extruding a length of heat transmissive material, such as aluminium, through a die so as to form a tube having an inner surface in which the flow direction control insert is formed. Alternatively, or in addition, the outer fin(s) may be extruded with the tubing to minimise construction costs.

A second embodiment of an exchanger will now be described

with reference to Figures 10 through 25. According to the

second embodiment, improved heat transfer characteristics may

be achieved without the aid of a spiral insert, as previously

described. Instead, and is evident from the figures, a heat

exchanger tube 17 comprises at least one primary flow path 15

arranged to carry the flow of the first heat exchanging

medium. The primary flow path 15 may surround a secondary

flow path 16 which carries a second heat exchanging medium.

Such a configuration advantageously allows heat from the

first heat exchanging medium to not only be exchanged with

air (or another suitable medium) passing over the outer wall

18 of the primary flow path(s) 15, but in addition to

exchange heat with a medium flowing through the enveloped

secondary flow path 16. To further assist with the heat

transfer, at least one of the primary and secondary flow

paths 15, 16 may be helical for increasing their effective

path length. Another advantage arising from the afore

mentioned tubular construction is that condensation is unable

to pool on either of the flow path surfaces.

In more detail, and with particular reference to Figures 10

and 11, a single heat exchanger tube 17 formed of a suitable

heat transmissive material (e.g. copper, aluminium, etc.)

comprises a circumferential wall 18 which is surrounded by

one or more heat exchanging fins 14 in the same manner as

previously described with reference to Figure 9. According to the illustrated embodiment, the secondary heat exchanging medium is carried within a separate inner tube 16a, while the first medium is carried within a flow path defined in the circumferential wall 18. According to the embodiments shown in Figures 10 and 11, the primary flow path 15 is partitioned by way of internal webs 20 so as to create a plurality of separate helical flow paths 15 which extend along the length of the tube 17. This may serve to increase the heat transfer capabilities, as well as increase the structural strength of the exchanger tube 17. It will be understood, however, that the primary flow path(s) need not necessarily be helical and could instead, for example, deviate in a serpentine or other suitable non-linear path. Alternatively, the path(s) may be straight and non-deviating along the length of the tube as is shown in Figures 16 and 17.

A plurality of exchanger tubes 17 may be connected to an

inlet and outlet manifold 21a, 21b for receiving/expelling

the respective heat exchanging mediums, as shown in Figure

14. Figure 12 shows an exploded view of the exchanger of

Figure 14, with an inlet manifold 21a in the form of a copper

pipe. As shown, the outer wall 18 of the tube 17 is paired

away adjacent each end 19a, 19b, exposing a length of the

inner tube 16a. The first end 19a is then inserted into an

aperture 22 defined in a wall of the inlet manifold 21a such

that the primary flow path is in fluid communication with the

inlet manifold for delivering the first heat exchanging

medium (in this case refrigerant gas). A portion of the

inner tube extends through a slightly smaller opposing

aperture 23 in the inlet manifold wall, for receiving the

secondary medium (in this case air, which may either be

ambient air or alternatively air forced through the secondary

flow path using a fan or the like). A second end 19b of the

tube 17 is coupled to the outlet manifold 21b (which may, for

example, be under vacuum) having the same form as the inlet

manifold 21a in an identical manner.

In a particular embodiment, the exchanger tube 17 (including

its partitioned circumferential wall 18) may be formed by an

extrusion process (i.e. in a linear fashion). With specific

reference to the embodiment shown in Figures 18 and 19, the

tube 17 may be formed by coiling/winding a straight length of

micro-channel tubing 17' of generally elongate cross section,

such that the length extends along a helical path. Such a

technique may advantageously allow manufacturers to utilise

readily available straight lengths of micro-channel

tubing 17' which are found in conventional heat exchanger

designs (e.g. such as micro-channel tube lengths used in

micro-channel heat exchangers) for forming the primary flow

paths 15. Internal webs 20 formed within and extending along

the length of micro-channel tubing 17' may advantageously

serve to direct the flow in a helical path (once coiled), for

increasing the heat transfer characteristics. According to

the particular embodiment shown in Figures 18 and 19, the

micro-channel tubing 17' is coiled or otherwise formed to

create a sealed inner flow path for carrying the secondary

flow (i.e. such that a separate inner tube is obviated).

With reference to Figures 20a, 20b and 20c there is shown

another alternative micro-channel design, whereby the fins

14'' are integrally extruded with a length of micro-channel

tubing 17''. The spiralled fin design advantageously

prevents water from collecting on the outer surface of the

tubing 17'' which is counter-productive to water assisted

cooling in extreme conditions (and which is a significant

issue on both existing planar micro-channel and horizontally

mounted fin and tube condenser configurations). As shown in

Figures 20a, 20b and 20c, the side walls of the tubing 17''

are substantially planar and devoid of fins. This may allow

the tubing 17'' to be tightly coiled, as shown in the

figures. An underside of the tubing 17'' may also be

substantially planar. The helical winding results in a

plurality of helical flow paths 15'' for carrying a heat exchanging medium. This is best shown in Figures 21a to 21c.

The helically wound micro-channel tubing 17'' may be

incorporated into a heat exchanger 30, as shown in Figure 22.

Depending on the desired implementation, the micro-channel

tubing 17'' may be connected to the respective inlet and

outlet manifolds such that the inner core/flow path 16''

remains open, such as to the atmosphere (as shown in Figure

22c). Alternatively, the open inner flow path 16'' may be

utilised to carry a second heat exchanging medium, as for the

earlier embodiments described herein. In the embodiment

shown in Figure 22, the extruded fins 14'' stop short of the

tubing ends, thereby allowing a fin-less end section of the

tubing 17'' to be inserted into a correspondingly shaped

opening in the respective manifold for receiving/expelling

the medium carried therein.

In yet another alternative embodiment, the inner core 16''

may be blocked, or be filled with a suitable material (which

may be a solid, liquid, or gas, depending on the desired

implementation), so as to prevent flow of air or fluid there

through. For example, a bung or plug 32 may be inserted in

either end of the core 16''. An example of this blocked

arrangement is shown in Figure 23. In yet another

embodiment, the inner core may be filled with a solid

material that has desirable heat exchanging properties.

With additional reference to Figures 24a, 24b and 24c, there

is shown an alternative configuration whereby the length of

micro-channel tubing 17'' shown in Figure 21 has been loosely

wound or coiled in a helical fashion. The gaps 37 between

the windings of the micro-channel tubing 17'' allow for air

(or another desired heat exchanging medium) to flow both over

the fins 14'' and through the micro-channel tubing 17'', for

exchanging heat with a medium flowing there through. Figures

25a, 25b and 25c show an exchanger incorporating five vertically stacked lengths of loosely coiled micro-channel tubing 17''.

It will be understood that in one embodiment the number of

flow paths defined in each tube of the exchanger may vary.

For example, for an automotive exchanger where the tubes are

connected in series, the number of flow paths may reduce for

each pass so as to account for changes in the state of the

primary heat exchanging medium (e.g. liquid to gas or vice

versa). Furthermore, it will be understood that the heat

exchanging medium passing through the primary and secondary

flow paths may be any suitable medium and should not be seen

as being restricted to those described above. For example,

rather than the secondary flow path carrying air it could

instead carry water such that the primary heat exchanging

medium is exchanging heat with two different mediums (i.e.

air through the fins and water through the secondary flow

path).

In a particular embodiment, a heater element could be

disposed within the inner core 16'' to facilitate defrosting.

For example, if the exchanger were being used in a freezer,

the heater element could be used to defrost the tubing 17''.

Alternatively, the heater element could be used to defrost

the tubing 17'' if the exchanger was being used as a heat

pump.

It is to be understood that, if any prior art publication is

referred to herein, such reference does not constitute an

admission that the publication forms a part of the common

general knowledge in the art, in Australia or any other

country.

It is acknowledged that the term 'comprise' may, under

varying jurisdictions, be attributed with either an exclusive

or an inclusive meaning. For the purpose of this

specification, and unless otherwise noted, the term

'comprise' shall have an inclusive meaning - i.e. that it

will be taken to mean an inclusion of not only the listed

components it directly references, but also other non

specified components or elements. This rationale will also be

used when the term 'comprised' or 'comprising' is used in

relation to one or more steps in a method or process.

Aspects of the present invention have been described by way

of example only and it should be appreciated that

modifications and additions may be made thereto without

departing from the scope thereof as defined in the appended

claims.

Claims (4)

CLAIMS:

1. A heat exchanger comprising:

a length of conduit having at least one channel extending

the length thereof and operable to contain a first heat

exchanging medium, the length of conduit being loosely coiled

such that a surrounding air or fluid flow can pass between the

coils and such that each of the channels define a helical flow

path through which the first heat exchanging medium flows;

one or more fins integrally formed with the conduit

through an extrusion process and which extend from an outer wall

of the helically wound length of conduit for facilitating

exchange of heat between the heat exchanging medium and a

surrounding air or fluid flow.

2. A heat exchanger comprising:

a length of conduit having at least one channel extending

the length thereof and operable to contain a first heat

exchanging medium, wherein the length of conduit is wound or

coiled such that each channel therein defines a helical flow

path through which the first heat exchanging medium flows and

whereby an inner core of the helically wound length of conduit

is either blocked or partially filled with a solid heat

exchanging medium;

one or more fins integrally formed with the conduit

through an extrusion process and which extend from an outer wall

of the helically wound length of conduit for facilitating

exchange of heat between the heat exchanging medium and a

surrounding air or fluid flow.

3. A heat exchanger according to claim 1 or 2, wherein the

side walls of the conduit have a generally planar profile.

4. A heat exchanger according to any one of the preceding

claims, wherein the inner surface of the helically wound conduit

has a generally planar profile.

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