This invention relates to an apparatus for chilling fluids, particularly
but not exclusively canned or bottled beverages. More particularly, the present
invention is directed towards a fluid chilling apparatus of the type in which the
temperature reduction caused by the desorption of a gas from an adsorbent is used
to chill a beverage, such as is disclosed in European patent number 0752564.
In known apparatus for chilling fluids, of the type disclosed in EP0752564,
a chilling cartridge is in either direct or indirect thermal contact with the fluid
to be chilled (that is, the cartridge is either immersed in the fluid, or forms
part of the fluid container, or it is adapted to fit into a recess formed in the
container wall, or to fit around the container). The cartridge comprises a sealed
thin-walled vessel (the thinness being preferable to promote heat transfer) containing
an adsorbent for receiving and adsorbing under pressure a quantity of gas. For
example, the adsorbent is activated carbon and the gas is carbon dioxide. On breaking
the vessel seal and releasing the pressure, the gas is desorbed, and the endothermic
process of desorption of the gas from the adsorbent causes a reduction in the temperature
of the adsorbent and of the desorbed gas. Because the cartridge is in thermal contact
with the fluid, this reduction in temperature leads to heat transfer from the fluid,
through the vessel wall, to the adsorbent and desorbed gas therein, which serves
to chill the fluid.
It is known that most adsorbents are poor conductors of thermal energy.
For example, activated carbon can be described as an amorphous material, and consequently
has a low thermal conductivity even when tightly compacted. This is disadvantageous
because poor heat transfer to the adsorbent in the centre of the body of adsorbent
in the vessel reduces the chilling rate and/or wastes the "chilling power" of the
central adsorbent. Accordingly, a number of embodiments of heat transfer means
are disclosed in our co-pending European patent application number 97309199.4 which
improve heat transfer between the centre of the adsorbent and the vessel walls.
A further problem with conventional arrangements arises from the flow
of desorbed gas. !n the interest of maximising the quantity of adsorbed gas in
the adsorbent, it is desirable that the adsorbent be highly compacted. However,
such compaction reduces the porosity of the body of adsorbent, and so tends to
retard the rate of desorption from within the body of the adsorbent, which slows
the rate of chilling of the fluid. Secondly, although part of the desorbed gas
leaves the adsorbent adjacent the nearest wall, and then travels along the vessel
walls to the exit valve, a significant portion also permeates through the adsorbent
to the exit valve of the vessel without coming into contact with the vessel walls,
and thus a significant amount of "chilling power" (in the desorbed gas lost in
this way) is effectively wasted as "sensible heat".
The present invention aims to address these problems.
Consequently, the present invention provides a chiller for chilling
a quantity of fluid comprising a thin-walled vessel for placement in thermal contact
with the fluid to be chilled and containing an adsorbent for receiving and adsorbing
under pressure a quantity of gas, in use the desorption of gas from the adsorbent
causing a reduction in temperature of the adsorbent and of the desorbed gas, which
temperature reduction is effective in use to chill the fluid, wherein the chiller
comprises a plurality of heat transfer elements, formed of thermally-conductive
material and in direct thermal contact with the adsorbent and adapted to transfer
heat between the vessel walls and the adsorbent therein, and wherein the elements
are configured so as to co-operate in use in order to conduct desorbed gas from
the adsorbent to the vessel walls and thence along the vessel walls prior to its
exit from the vessel.
Such an arrangement adds little complexity to the chilling cartridge
(nor indeed to the manufacture thereof) but simultaneously provides both good thermal
transfer between the adsorbent and the vessel walls (with which preferably, each
heat transfer element is in direct contact) and thermal conductivity between the
desorbed gas and the vessel walls, and also provides preferential pathways for
the desorbed gas to travel to the vessel walls and along those walls before leaving
the vessel. Accordingly, the heat transfer elements of the invention co-operate
so as to permit relatively free passage of the gas on both desorption and adsorption,
thus accelerating the chilling process and also the "loading" of the cartridge
with gas - so permitting the cartridge manufacturing time to be reduced.
Preferably substantially all the heat transfer members are the same
shape, and they may be configured such that they can be disposed in a stack, with
successive elements at least partially nested within elements immediately preceding
in the stack. With such a stack, the topmost element (or elements, depending on
the degree of nesting) will normally have a slightly different shape, in order
to "top off" the stack for fitment within the vessel.
In a particularly suitable embodiment the heat transfer elements are
frustro-conical, and preferably have a corrugated rim, so that they resemble in
shape and configuration the paper cases commonly used in baking cup cakes (in the
United Kingdom) or muffins (in the United States of America and Canada).
Such elements are of course usually circular, so as to fit snugly
within the vessel, which itself is normally cylindrical. Such elements are used
to manufacture a chilling cartridge in the following manner. Firstly, a layer of
activated carbon particles is introduced into the empty vessel, then a heat transfer
element "cup" is slid down into the vessel. As the "cup" is slid into the vessel,
the corrugated sides fold and pucker. Then, a further layer of carbon is placed
inside this "cup", to be followed by a further "cup", more carbon, and so on. As
the stack of "cups" reaches the top of the vessel, a shorter "cup" or "cup" is
added so as to "top off" the stack without requiring an excessively thick final
layer of carbon and so that the folded wall of the topmost "cup(s)" does not project
above the edge of the cartridge vessel. Finally, the pressure is applied to the
stack within the vessel to compact the carbon in order to obtain the desired overall
density of the carbon, the gas is introduced into the vessel under pressure for
adsorption and the vessel sealed.
The valve by which desorbed gas leaves the vessel may be located adjacent
the top of the stack or, more preferably, at the base of the stack, so as to maximise
the distance along which the desorbed gas travels in close proximity to the vessel
wall, and thus to optimise heat transfer therewith.
On breaking the vessel seal and thus releasing the pressure on the
adsorbent, the gas is desorbed and travels along the flat portion of the heat transfer
element, which form a rapid thermal conducting path between the relatively thin
layers of carbon (preferably between about 5mm and 10mm, more preferably about
8mm in thickness) and the vessel walls, whilst the folded and puckered corrugations
of adjacent "cups" co-operate so as to provide passages for the desorbed gas to
escape (and for the passage of gas to be adsorbed, on manufacturing the cartridge,
of course). Moreover, the desorbed gas is constrained to flow along the crimped
passages in the element rim which are adjacent the wall of the vessel, and thus
heat transfer into the gas is promoted and consequently the chilling effect on
the fluid is increased.
We have found that for a "cup" shaped heat transfer element the ideal
range of diameter: rim height aspect ratio is between about 5:1 and about 5:4 (which
ratios are intended to be equivalent to the aspect ratio of a paper cake case for
a British cup cake and the aspect ratio of a British milk bottle top, respectively).
Preferably, the heat transfer elements are formed of a resilient,
heat conducting material, such as a foil of aluminium, or of an alloy thereof,
and are in the range of thickness' at which aluminium foil (or items made thereof)
is/are readily available for domestic use (ie about 0.25mm).
In certain applications it may be desirable to provide, in addition
to the co-operating crimped rims of the heat transfer elements, channel means adapted
to provide a preferential pathway for the desorbed gas along and adjacent to the
wall of the vessel - to promote more rapid desorptions, for example. Those skilled
in the art will appreciate that there are many ways by which such preferential
pathways may be created, and thus many forms which the channel means might take:
a perforated or porous tube may be inserted along one side of the vessel before
filling with carbon and heat transfer elements; a similar insert may be used but
withdrawn after the vessel is filled with adsorbent and "cups", leaving an open
"channel" in the easily deformed stacked "cup" rims; a hole may be drilled through
the compacted mass of carbon and heat transfer "cups", close to the vessel wall;
or the vessel may be formed as a cylinder with a longitudinal or spiral bulge extending
along the length of the vessel.
It will also be appreciated that the present invention also encompasses
both a beverage container (bottle or can) comprising such a chiller, and a method
of manufacturing such a chiller.
An embodiment of a chiller in accordance with the invention will now
be described by way of example and with reference to the accompanying drawings,
- Figure 1 is a partial schematic cross-sectional view of one embodiment of a
fluid chiller cartridge in accordance with the invention;
- Figure 2 is a schematic view of one of the heat transfer "cups" of the chiller
of Figure 1;
- Figure 3 is a schematic view of a second embodiment of a fluid chiller cartridge
in accordance with the invention, and
- Figure 4 is a schematic view of a fluid chiller cartridge having only a single
heat transfer element.
The fluid chiller cartridge 2 shown (not to scale) in Figure 1 comprises
a thin-walled aluminium vessel 4, cylindrical in shape, containing a number of
aluminium "cups" stacked within the vessel 4 with intervening layers 8 of carbon
adsorbent. Each "cup" 6 (seen more clearly in Figure 2) comprises a circular base
section 10 and a tapering corrugated rim 12. The "cups" are sized relative to the
vessel 4 so as to slide snugly therein, and so that the corrugations in the rim
12 of each "cup" is crimped, so that the rims of adjacent or contiguous "cups"
co-operate, to provide passages for gas to travel into and from the layers 8 of
adsorbent. The corrugated rim 12 of each "cup" is sufficiently resilient as to
maintain good surface contact between the rims of adjacent "cups" and also between
the extreme edge of each rim 12 and the walls of the vessel 4.
In use, the cartridge 2 shown in Figure 1 (which for clarity is shown
only partially filled; in use, the cartridge would be full of alternate layers
of adsorbent and heat transfer "cups") would contain a quantity of gas under pressure
and adsorbed by the adsorbent, and would be disposed in thermal contact with a
container (not shown) of fluid to be chilled. To chill the fluid, a valve (not
shown) would be opened, or the wall of the vessel 4 ruptured, so as to relieve
the pressure on the adsorbent, thereby permitting desorption of the adsorbed gas.
The valve could be located at the top of the stack (ie at the top of the vessel
4 shown in Figure 1) or at the bottom of the stack; this latter is more preferable,
as it increases the distance along which the desorbed gas must travel in close
contact with the walls of the vessel 4, thus optimising the heat transfer therebetween
and the efficiency of chilling. The desorption process being endothermic, there
is a significant temperature reduction in the carbon adsorbent and in the desorbed
carbon dioxide gas. Heat is transferred from the fluid, via the walls of the vessel
4 and the heat transfer "cups" to the desorbed gas and also to the adsorbent, thereby
chilling the fluid. The desorbed gas is able rapidly to move towards the walls
of the vessel 4 and thence is constrained to move in close contact therewith, along
the gas passages formed in the crimped corrugations, thereby promoting enhanced
heat transfer so as fully to utilise the chilling effect of the desorption process.
Having described an embodiment of a fluid chiller cartridge in accordance
with the invention which has significant functional advantages over conventional
arrangements and also is both simple and inexpensive to manufacture, those skilled
in the art will appreciate that there are several straight-forward modifications
which could be made. For example, although the vessel illustrated in Figure 1 is
cylindrical, and of circular cross-section, there is no reason why the cross-section
cannot be of a shape other than circular, and indeed it need not even be of constant
shape along the length of the vessel. Furthermore, adsorbents other than activated
carbon and gases other than carbon dioxide may be used. Also, the chiller may be
adapted to fit releasably within a specially shaped recess in a beverage container
(ie, not in direct thermal contact with the beverage) or it may simply be immersed
in the beverage (and in direct thermal contact therewith). Although an embodiment
is described and shown in which the heat transfer elements are "cup" shaped, these
elements could equally be hemispherical, conical, box-shaped or indeed any shape
which would enable them to form a nested stack.
The chiller 2' shown in Figure 3 is very similar to that of Figure
1, however the heat transfer "cups" 6 are inverted; with the valve (not shown)
for the egress of desorbed gas at the top of the vessel as shown, the desorbed
gas travels for the maximum distance in close contact with the walls of the vessel
4, thus optimising heat transfer during chilling. As can be seen the use of but
a single "cup" 6' in the chiller 2" of Figure 4 will increase to the maximum the
distance by which the desorbed gas will travel in contact with the walls of the
vessel 4 before leaving via valve means 14 but at the cost of reducing the rates
of gas desorption and of heat transfer to the centre of the body of carbon adsorbent
8, although in practice these disadvantages might be addressed by providing gas
channel means and/or heat transfer means, such as those disclosed in EP0752564
(or such as a cylindrical heat transfer element, disposed along the axis of the
body of carbon adsorbent shown in Figure 4).
It might equally be advantageous to provide separate valve means,
for the egress of desorbed gas and for the ingress of the gas to be adsorbed, the
'egress' valve being located at the bottom of the stack so as to maximise the distance
along which the gas must travel in close contact with the walls of the vessel before
leaving, and the 'ingress' valve being located at the opposite end of the vessel,
so as to minimise the distance travelled by the gas in close contact with the vessel
walls before being adsorbed.