Rocket science comes home : Improved design
uses 40% less energy
Oxford-designed Flare pan uses 40 per
cent less heat than conventional pans
With help from Isis Innovation, the University’s technology
commercialisation company, a new heat-efficient cooking pan based
on research by University of Oxford Professor of Engineering
Professor Thomas Povey has been launched by Lakeland (the UK’s
leading kitchenware specialist).
Flare PanProfessor Povey applied his research into the design of
high-efficiency cooling systems for next-generation jet-engines to
an everyday object which transfers heat: the domestic saucepan.
The brand new pan design considerably speeds up cooking, providing
substantial savings of time and energy consumption.
Formed from cast aluminium and incorporating patented ‘FIN-X’
technology, Flare Pans are most effective on gas hobs, estimated
to be used by over two thirds of the UK. The unique, patented,
finned design channels heat from the flame across the bottom and
up the sides of the pan, resulting in highly efficient, even heat
distribution. This means the pans heat up significantly more
quickly and food cooks faster, saving time and using much less
energy too – in fact, an equivalent pan of conventional design was
shown to need 40% more energy to heat up than a Flare pan.
Tom Hockaday, managing director of Isis Innovation said: "This is
a great example of clever thinking from Oxford being applied to an
everyday object, one which anyone can use to speed up our cooking
and improve our energy consumption. Isis is delighted to have
helped Professor Povey and Lakeland commercialise the Flare Pan".
Linda Naylor, Executive Director at Isis, said: “This project has
been a rewarding one in that we were able to bring together the
right expertise and co-ordinate with multiple parties, in order to
enable a quick launch to market.”
Even before their official launch, Flare pans have already become
an award winning product. The Worshipful Company of Engineers, a
Livery Company of the City of London operating under Royal
Charter, has awarded Professor Povey their prestigious ‘2014
Hawley Award’ for ”the most outstanding Engineering Innovation
that delivers demonstrable benefit to the environment”.
Commenting on winning the award, Professor Povey said, "I am
delighted that the Worshipful Company of Engineers have recognised
the engineering complexity that lies behind Flare’s apparently
simple design and have selected it for their Hawley Award for
engineering innovation that benefits the environment."
Professor Povey and Isis Innovation went through Design Council’s
Design Leadership Programme, a mixture of workshops and direct
support part-subsidised by the Department for Business, Innovation
It is designed to help turn scientific and technological ideas
into innovative, profitable products and services. John Mathers,
Design Council CEO, commented: “The Flare Pan is a fantastic
example of British design. Design Council is delighted to have
been part of developing Professor Povey’s idea. It resonates well
with our values - it is innovative, beneficial for users and also
the environment. We are sure that it will prove to be a great
Commenting on the launch, Matthew Canwell, Lakeland’s Buying
Director said, "Innovative thinking has been cemented into all
that Lakeland do for 50 years, and we’re always looking for new
innovations that will save our customers both time and money.
Flare does just that, and we’re extremely excited to be able to
bring this incredible new technology to our customers."
The new range of innovative pans will be available in the UK
exclusively through Lakeland stores and website.
Flare Pans at Lakeland
Lakeland actively seeks out innovation, so
Matthew, our Buying Director, was really excited by these
scientific saucepans that cook faster and cook better…
A world first, Flare® pans embrace the latest breakthrough
FIN-X technology, developed in conjunction with Dr. Tom Povey,
a real-life rocket scientist from Oxford University.
Exceptionally effective on a gas hob, the uniquely-designed,
high-performance ‘fins’ channel heat from the flame across the
bottom and up the sides of the pan, resulting in really
efficient, even heat distribution. This means the pans heat up
significantly quicker so food cooks faster, saving you time
and using less energy too – in fact, they cook about 44%
faster than standard pans!
They’ve been given a thorough trial by our Buyer Veronica who
made a big stockpot of her trademark chilli and achieved an
even, low simmer that remained consistent throughout cooking,
so it was much easier to avoid messy boil-overs or food
catching on the bottom of the pan and it cooked so much
quicker than usual. Suitable for gas, electric, ceramic and
halogen hobs. Oven safe up to 205°C.
Performance ‘fins’ funnel flames into position around the pan.
Heat is distributed uniformly across the base and up the
Food cooks much quicker without burning or scorching.
Formed from cast aluminium for excellent heat conduction, with
stainless steel handles and fins.
[ EXPENSIVE ! ]
A vessel (1 ) for heating the contents thereof by means of an
external heat source (8) comprises a non-horizontal side wall (2)
and a heat transfer structure (6) attached to and in good thermal
contact with, or formed integrally on, an outer surface of said
This invention relates to vessels for heating the contents thereof
by means of an external heat source, e.g. cooking pans, in
particular vessels designed to improve the heat transfer into the
vessel, e.g. on gas stoves.
Cooking pans, as used in kitchens around the world, are generally
simple vessels whose designs have not changed much over many
years. Typically they will have a horizontal base and a typically
circular side wall extending upwards from the base to contain a
volume within which liquid and foodstuffs can be heated. The
Applicant has recognised however that such pans, particularly when
used on gas stoves, allow lots of heat energy from the heat source
to dissipate into the surrounding atmosphere rather than being
captured by the pan to heat its contents. As will be appreciated,
this results in the heating of the pan's contents being far from
efficient, thus wasting time and energy.
It is an aim of the present invention to provide an improved
heating vessel. The invention provides a vessel for heating the
contents thereof by means of an external heat source comprising:
a non-horizontal side wall; and a heat transfer structure attached
to and in good thermal contact with, or formed integrally on, an
outer surface of said side wall.
Thus it will be appreciated that the invention provides a heat
transfer structure in good thermal contact with the side wall of
the vessel, so that heated air and/or any flame which travels up
the side of the vessel can be captured by the heat transfer
structure and the heat conducted into the walls of the vessel and
so be used to heat the contents of the vessel. This contrasts with
known cooking pans in which the majority of the heat from the gas
flame and the heated air passing up by the side of the pan is
lost. The increased heat energy available for heating the contents
of the vessel thus greatly increases the efficiency of the heating
process, i.e. the heating of the vessel's contents is quicker and
uses less fuel. Such a design, in certain embodiments, has been
found by the Applicant to increase the efficiency with which
energy available from a gas flame is transferred into the vessel
from 30% to 80%, with the greatest benefit being obtained when the
gas flame is largest, because this results in more of the flame
and heated air travelling up the side wall of the vessel. The
vessel of the present invention is particularly suitable for
placing on a gas stove because of the resultant flame and hot air
which pass up the side wall of the vessel during use, the heat
from which is captured more effectively by embodiments of the
invention. However vessels in accordance with the invention do not
need to be used exclusively on gas stoves, they could be used with
a number of different heat sources, e.g. a hot plate, an induction
heater, an electric ring or a halogen hob, albeit with a smaller
enhancement to efficiency compared to a conventional pan.
The vessel could comprise any container which is suitable for
heating liquid or food contents, e.g. a cooking pan, frying pan,
wok, steamer, pressure cooker, casserole, kettle or a moka maker.
In vessels suitable for receiving and heating liquids and
foodstuffs, generally the side wall will be continuous around the
vessel and will extend upwardly from a horizontal base. The side
wall could be any suitable shape. Commonly it may comprise a
circular cylinder shape but equally it could be bowed, tapered,
waisted etc. in vertical profile. Similarly the side wall need not
be circular in plan profile - it could be faceted - i.e. polygonal
in cross section, or even asymmetric.
The vessel may have a discrete horizontal base, however this is
not essential. Embodiments are envisaged in which there is no
defined transition between the bottom of the vessel and the side
wall, e.g. the vessel may be continuously curved as can be found
in woks. In such vessels it is desirable that the heat transfer
structure is provided on or extends to a part of the side wall
outside the region which a typical gas flame plays on directly.
Thus in a set of embodiments the heat transfer structure is
provided on a portion of the side wall spaced at least 7 cm, or at
least 10 cm from the centroid of the underside of the vessel.
The side wall may have the same outer and inner profiles, e.g. if
it is made of a relatively thin material of constant thickness.
However, particularly if the vessel has a double walled structure,
the side wall may have a different inner profile to its outer
profile. For example, the vessel could have a flat base and
straight sides on the outside to provide better heating and
stability, and a more continuously curved interior to facilitate
cleaning and stirring of the contents. The Applicant has found
that the present invention delivers a greater benefit with vessels
which are tall sided, e.g. pasta pans or coffee makers, than with
shallower pans and woks. Therefore in one set of embodiments the
height of the vessel is greater than its diameter. If the vessel
is non-circular, the diameter is taken to be the greatest
dimension of the vessel perpendicular to the height of the vessel
when the vessel is placed in its natural operating orientation,
i.e. when being used on a heat source.
The heat transfer structure could comprise any suitable member or
members or other physical structure which is attached to and in
good thermal contact with the side wall of the vessel. To maximise
the conduction of heat energy from the heat transfer structure to
the side wall of the vessel, the heat transfer structure could be
directly and/or permanently attached to the side wall, e.g.
brazed, welded or soldered, though the method of attachment may
depend on the materials used for the side wall and heat transfer
structure. Attachment by mechanical fixings is also envisaged
although these would not typically be such that they are intended
to allow removal of the structure by a user.
In one set of embodiments the heat transfer structure comprises a
plurality of ribs or fins attached to the side wall. The ribs or
fins may take any convenient shape. For example they could
comprise discrete protrusions. In a set of embodiments they
comprise strips. The ribs or fins could, for example, have a
cross-section which is rectangular - with the short or long side
attached to the vessel side wall - square, semi-circular,
triangular, semi-elliptical, L, T or U-shaped etc. Having the ribs
or fins tapering in a direction away from the side wall has been
found to give a good performance for a given volume of material.
The fins or ribs may have a flange or tab for attachment to the
The ribs or fins could extend horizontally or diagonally but
preferably they extend vertically. This still allows heated air
and any flame to pass up the side of the vessel and thus encounter
a large surface area (comprising the side wall itself and t e ribs
or fins) to maximise the transfer of heat into the side wall. The
ribs or fins could extend part of the way up the side wall, e.g.
more than half the way, but preferably the ribs or fins extend
along the whole length of the side wall. The ribs or fins could be
parallel, divergent or convergent. The cross-section and/or shape
thereof could increase, decrease or otherwise change along their
length. For example in a set of embodiments the ribs or fins are
wider, e.g. in a direction away from the side wall, at the ends
(generally the top and bottom of the ribs or fins) than in the
middle, as this has been found to capture heat more effectively.
The fins or ribs could be a continuous strip of material, e.g.
with a shape that is wider at the ends as discussed above, but in
one set of embodiments the fins comprise one or more cut outs. The
cut outs could be positioned anywhere along the fins, e.g. in the
middle as holes or at the outer edge (away from the side wall),
but in one set of embodiments the fins comprise one or more cut
outs along the inner edge of the fin, i.e. the side of the fin
attached to the side wall of the vessel. The Applicant has
appreciated that, particularly in the set of embodiments in which
a fin is attached to the side wall, providing cut outs along the
inner edge of the fin enables more accurate contact of the fin to
be achieved with the side wall of the vessel which aids the
operation of attaching the fin to the side wall, e.g. by laser
welding. The cut outs could be any suitable shape but,
particularly in the embodiments in which the cut out is along the
inner edge of the fin, preferably the cut outs extend in a
direction generally perpendicular to the side wall of the vessel,
i.e. their horizontal width is greater than their vertical height.
The fins, ribs or any other type of discrete heat transfer
structure, could be arranged in an irregular pattern around the
side wall. However in one set of embodiments the ribs or fins are
equally spaced around the side wall, i.e. around the perimeter of
the side wall, though there may be a different, e.g. larger,
spacing where a handle is provided on the vessel. In one set of
embodiments there are at least four, e.g. at least eight, e.g. at
least twelve, e.g. at least twenty-four ribs or fins. The heat
transfer structure may project from the side wall. The heat
transfer structure may project at least 5% of the diameter of the
vessel, e.g. at least 10% of the diameter of the vessel, e.g. at
least 15% of the diameter of the vessel. This could also be
defined absolutely, e.g. the heat transfer structure could project
at least 1 cm from the side wall, e.g. at least 2 cm, e.g. at
least 3 cm, which will generally be taken to be in the radial
direction, i.e. perpendicular to the side wall. In the case of
fins or ribs having a width which varies along the length thereof,
this is taken to be the maximum width of the fin or rib (defined
in a direction perpendicular to the side wall) as in some
embodiments the width of the fins or ribs may taper to zero.
The fins or ribs could be separate members attached to the side
wall or could be joined - e.g. at one or both ends or part-way
along their length. In other embodiments a plurality thereof (e.g.
all of them) could be formed integrally - e.g. by a suitably
In another set of embodiments the heat transfer structure is
formed directly on the side wall of the vessel, e.g. by being
cast, milled or drilled. The heat transfer structure so formed may
have any of the shapes or forms described above in relation to
structures attached to the wall. Of course both integral forming
and attachment could be used in combination.
The vessel and heat transfer structure will generally be made from
materials with a high thermal conductivity, e.g. metal. When not
formed integrally, the vessel and heat transfer structure could be
made from the same or different materials depending on their
suitability for manufacture. Typical materials include aluminium,
copper and stainless steels. Stainless steels are easy to weld
thus enabling the heat transfer structure to be attached easily to
the side wall. The material could be laminated, e.g. aluminium
with stainless steel either side. This is advantageous because
aluminium has a high thermal conductivity and stainless steels are
corrosion resistant, give a good finished appearance and are also
easy to clean. The material could be metal plated, e.g. using
copper, to give an attractive finish without detracting from the
mechanical and/or thermal properties of the vessel. Using such
materials the vessel, e.g. a pan, could be made using known
techniques. The heat transfer structure could be stamped, water
jet or laser cut before being attached to the side wall, e.g. by
brazing, welding or soldering.
In one set of embodiments a heat transfer structure is also
provided on a base of the vessel. Although the Applicant has found
that this does not give as great a benefit as the heat transfer
structure provided on the side wall of the vessel, an improvement
over the heat transfer into the vessel from a conventional base is
noticed. All the features discussed above regarding the heat
transfer structure provided on the side wall are applicable to a
heat transfer structure on the base of the vessel. The heat
transfer structure provided on the base of the vessel could be
separate from the heat transfer structure provided on the side
wall. However in one set of embodiments the heat transfer
structure provided on the side wall extends to the base of the
vessel. For example, the ribs or fins could extend from the side
walls underneath the vessel onto the base.
For heat transfer structures, e.g. ribs or fins, which are shaped,
or for a vessel which is shaped, the outer profile of the vessel
does not need to match the outer profile of the heat transfer
structure. For example, the side wall of the vessel could be
straight and the ribs or fins could be shaped differently as
described above, or the side wall of the vessel could be curved
and the ribs or fins could have a straight outer edge.
This also extends to the set of embodiments comprising a heat
transfer structure provided on the base of the vessel, where
preferably the heat transfer structure is arranged to stand flat
on a flat surface. For example, if the vessel comprises ribs or
fins provided on the base, their bottom edge is preferably flat so
they are able to stand stably on a surface or a gas stove.
Furthermore, even if the vessel does not comprise a heat transfer
structure provided on the base, the heat transfer structure
provided on the side wall could project below the level of the
base of the vessel. Again, preferably the heat transfer structure
is arranged to stand flat on a flat surface. This allows vessels
which do not have a flat base to be able to stand stably on a flat
surface or stove.
In the sets of embodiments in which a heat transfer structure is
provided on the base, extends from the side wall and/or projects
from the side wall below the level of the base, the vessel could
comprise a mount arranged to stand flat on a flat surface, e.g.
attached to the heat transfer structure or the base of the vessel.
Thus, even if the heat transfer structure is not arranged to stand
flat, the mount provides a base which can stand flat, e.g. for
enabling the vessel to be stably placed on a stove or other
surface. Typically the mount comprises a continuous flat surface,
e.g. a ring, which enables it to stand on the pan support of a gas
stove. Such a mount could be removable so that it can be fitted
when required and removed after use for cleaning and storage. The
removable mount could fit onto the vessel in any number of ways,
e.g. directly onto the base of the vessel or onto the heat
transfer structure itself, and be spring or clip mounted for easy
attachment and removal. Alternatively the mount could be
permanently attached to the vessel. Preferably the mount comprises
holes to allow the heated air and any flame to flow easily through
and around the mount.
Certain preferred embodiments of the invention will now be
described, by way of example only, with reference to the
accompanying drawings in which:
Fig. 1 shows a schematic diagram of a vessel in accordance with
Fig. 2 shows a plan view of the vessel shown in Fig. 1 ;
Fig. 3 shows vertical cross section of a variant of the
embodiment shown in Figs. 1 and 2;
Fig. 4 shows a close up of a variant of the heat transfer
Fig. 5 shows a vertical cross section of a variant of the
embodiment shown in Figs. 1 and 2;
Fig. 6 shows a vertical cross section of a variant of the
embodiment shown in Fig. 3;
Figs. 7a and 7b show perspective and underside views
respectively of another vessel in accordance with the invention;
Figs. 8a and 8b show perspective and underside views
respectively of a further vessel in accordance with the
Fig. 9 shows a graph of heat transfer efficiency for
vessels in accordance with the invention.
Figs. 1 and 2 show a vessel 1 , e.g. a cooking pan, in accordance
with the present invention. The vessel 1 comprises a cylindrical
side wall 2 with a circular cross- section that projects
perpendicularly from the base 4 of the vessel 1 . The main body of
the vessel 1 , i.e. the side wall 2 and base 4, is made from a
material such as aluminium or stainless steel as is conventional.
Attached to the outer surface of the side wall 2 is a heat
transfer structure comprising a plurality of fins 6. The fins 6
are made from rectangular strips of the same material as the main
body of the vessel 1 , e.g. aluminium or stainless steel, which
are produced by laser cutting a blank sheet of the material, and
are laser welded to the side wall 2 to attach them in good thermal
contact. Though not shown, a handle could be attached to the
vessel 1 to allow it to be carried, particularly when hot. In
operation, a gas flame 8, e.g. from a gas stove, is applied to the
base 4 of the vessel 1 to heat contents, e.g. liquid or other
foodstuffs, (not shown) contained within the vessel 1 . Owing to
convection, the air heated by the gas flame 8 passes from
underneath the base 4 of the vessel 1 and up along the outer
surface of the side wall 2. If the gas flame 8 is particularly
large compared to the size of the base 4 of the vessel 1 , part of
the edges of the gas flame 8 will also protrude from the base 4
and up the side wall 2. For a conventional pan, most of this heat
is lost, as only a very small layer of the heated air and/or gas
flame 8 is able to conduct heat into the side wall 2 of the
vessel. However, for the vessel 1 shown in Figs. 1 and 2, the fins
6 act to capture this lost heat, owing to the increased surface
area and greater penetration into the heated air layer presented
by the side wall 2 and fins 6 to the heated air and/or gas flame
8. As the heated air and/or gas flame 8 passes up the side wall 2
of the vessel, the fins 6 are heated. The fins 6 are attached to
and in good thermal contact with the side wall 2 of the vessel 1
so this heat is conducted into the side wall 2 where it acts to
heat the contents of the vessel 1 .
Fig. 3 shows a vertical cross section through a vessel 101 which
is a variant of the vessel shown in Figs. 1 and 2. For this vessel
101 the fins 106, as well as being attached in good thermal
contact to the side wall 102 also extend under the base 104 of the
vessel 101 where they are also attached in good thermal contact.
The operation of the vessel 101 shown in Fig. 3 is the same as the
vessel shown in
Figs. 1 and 2, with the portion of the fins 106 attached to the
base 104 of the vessel 101 also acting to increase the surface
area of the vessel 101 available to be heated, thus increasing the
heat energy transferred into the contents of the vessel 101 . A
mount 107, in the form of a ring, is attached, by welding, to the
underside of the portion of the fins 106 extending under the base
104 of the vessel 101 , thus enabling the vessel 101 to be stably
placed on a stove or flat surface, e.g. a gas stove in which the
pan support ring generally has radially aligned prongs.
Fig. 4 shows a vertical cross section through a vessel 201 which
is another variant of the vessel shown in Figs. 1 and 2. The
vessel 201 has a curved side wall 202 and base 204, with fins 206
attached to the side wall 202. The fins 206 have a curved portion
in the middle to match the profile of the side wall 202, and
extend partly to the base 204 of the vessel 201 . As in Fig. 3 a
mount 207 is attached to the underside of the bottom portion of
the fins 206 to enable the vessel 201 to stand on a stove and a
flat surface. Operation of the vessel 201 shown in Fig. 4 is the
same as has been described above.
Fig. 5 shows a plan view of a segment of a vessel 301 showing an
alternative embodiment of the fins 306 attached to the side wall
302. In this embodiment the fins 306 have a tapered distal edge
which has been found to increase the heat transfer into the vessel
301 . The fins 306 are each attached to the side wall 302 by means
of a flange 310, e.g. by welding.
Fig. 6 shows a vertical cross section through a vessel 401 which
is a variant of the vessel shown in Fig. 3. The vessel 401 is
cylindrical with a flat base 404, and as in Fig. 3, the fins 406
attached to the side wall 402 extend under the base 404 of the
vessel 401 . In this embodiment the fins 406 are shaped with a
wider upper and lower portion and a waisted middle. This profile
of the fins 406 has been found to be more effective in
transferring heat into the vessel 401 . The top and bottom corners
of the fins are curved, i.e. blunt, to protect the user from sharp
edges. As the fins 406 extend radially, there is not a continuous
bottom to enable the vessel 401 to be placed stably on a gas
stove. Therefore a removable mount 412 with a circular base 407 is
provided to create a flat bottom for the vessel 401 . The
removable mount 412 is sprung so that it simply clips on and off
over the fins 406.
Figs. 7a and 7b show perspective and underside views respectively
of another vessel 501 in accordance with the invention, along with
two ring jigs 514 and a star jig 516 to hold the components of the
vessel 501 in place during assembly. The vessel 501 , similar to
some of the vessels shown in the previous drawings is cylindrical
with a straight side wall 502 and a flat base 504. As in Figs. 3
and 6, the fins 506 extend under the base 504 of the vessel 501 .
Also as in Fig. 6, the fins 506 are shaped with a wider upper and
lower portion and a waisted middle.
However, in this embodiment the fins 506 comprise cut outs 518
which extend in a direction perpendicular to the side wall 502.
These assist the laser welding of the fins 506 to the side wall
502 and base 504 of the vessel 501 . An additional feature shown
in this embodiment is the provision of a ring mount 507 which is
welded to the bottom of the fins 506 in order to provide a
continuous flat surface to allow the vessel 501 to be stably
placed on a gas stove. The mount 507 comprises a plurality of
holes 520 which allow the gas flame, entrained cold air and/or
heated air through the mount 507.
Also shown in Figs. 7a and 7b are two ring jigs 514 and a star jig
516 which each comprise a plurality of slots 522 corresponding to
the fins 506. The ring jigs 514 and star jig 516 hold the fins 506
in place during welding and are removed when this has been
completed. Operation, during normal use, of the vessel 501 shown
in Figs. 7a and 7b is the same as for the previous embodiments.
Figs. 8a and 8b show perspective and underside views respectively
of a further vessel 601 in accordance with the invention, similar
to the vessel shown in Figs. 7a and 7b but without the assembly
jigs shown. The vessel 601 shown in Figs. 8a and 8b again has fins
606 attached to the side wall 602 which are shaped with a wider
upper and lower portion and a waisted middle, and which extend
underneath the base 604 of the vessel 601 . As in Figs. 7a and 7b
the fins 606 comprise cut outs 618 which extend in a direction
perpendicular to the side wall 602, and have a ring mount 607
attached to the bottom of the fins 606. The vessel 601 shown in
Figs. 8a and 8b is different from the vessel shown in Figs. 7a and
7b in that it has a tapering side wall 602 such that the opening
at the top of the vessel 601 is narrower than the base 604, but in
use its operation is the same. Fig. 9 shows a graph of heat
transfer efficiency for vessels in accordance with the invention.
The graph plots efficiency against heat flux into the air, for
experimental test data taken by the Applicant using a normal gas
burner in a purpose built test rig. Pan 1 (724) is a conventional
pan without any heat transfer structure attached to the side
walls, and Pan 2 (726), Pan 3 (728) and Pan 4 (730) are vessels in
accordance with the present invention, i.e. similar to those shown
in the embodiments in the drawings. Best fit lines for each of the
vessels shown are also plotted through the data points. The graph
shows that an improved efficiency, particularly at high heat flux,
is obtained for all the vessels in accordance with the present
invention. At a heat flux of 4 kW, the (extrapolated) efficiency
of Pan 1 (724) is 45%, whereas the other vessels have efficiencies
between approximately 60% and 67%, representing an improvement of
between 33% and 49% in efficiency. At higher heat flux the
improvement is expected to be even greater.
It will be appreciated by those skilled in the art that only a
small number of possible embodiments have been described and that
many variations and modifications are possible within the scope of
the invention. For example the vessel and fins could be any shape
and made from any material, and the fins may only extend part way
up the sides of the side wall of the vessel. Furthermore, any
number of fins could be provided and it is not necessary for them
to be equally spaced around the perimeter of the side wall or to
be parallel to each other. Heat transfer structures other than
fins could be provided. Rather than being attached to a vessel the
heat transfer structure could be formed integrally in the side
wall of the vessel through casting or machining.