U.S. patent application number 11/667287 was filed with the patent office on 2008-04-17 for method and apparatus for partially freezing an aqueous mixture.
Invention is credited to Jonathan Mark Allin, Daniel Anthony Jarvis, Christopher Donald Marriott, Andrew Baxter Russell.
Application Number | 20080087026 11/667287 |
Document ID | / |
Family ID | 34930779 |
Filed Date | 2008-04-17 |
United States Patent
Application |
20080087026 |
Kind Code |
A1 |
Allin; Jonathan Mark ; et
al. |
April 17, 2008 |
Method and Apparatus for Partially Freezing an Aqueous Mixture
Abstract
A method for partially freezing an aqueous mixture comprising
simultaneously or in either order the steps of: placing said
aqueous mixture in contact with at least part of a freezing
surface; cooling the freezing surface to below the freezing point
of the aqueous mixture; so that ice forms at the freezing surface;
and oscillating the freezing surface relative to the aqueous
mixture in a direction that is not perpendicular to at least part
of the freezing surface; characterised in that the oscillation is
linear with a frequency of between 20 and 200 Hz.
Inventors: |
Allin; Jonathan Mark; (West
Sussex, GB) ; Jarvis; Daniel Anthony; (Vlaardingen,
NL) ; Marriott; Christopher Donald; (Sharnbrook,
GB) ; Russell; Andrew Baxter; (Sharnbrook,
GB) |
Correspondence
Address: |
UNILEVER INTELLECTUAL PROPERTY GROUP
700 SYLVAN AVENUE,
BLDG C2 SOUTH
ENGLEWOOD CLIFFS
NJ
07632-3100
US
|
Family ID: |
34930779 |
Appl. No.: |
11/667287 |
Filed: |
October 26, 2005 |
PCT Filed: |
October 26, 2005 |
PCT NO: |
PCT/EP05/11558 |
371 Date: |
December 13, 2007 |
Current U.S.
Class: |
62/68 |
Current CPC
Class: |
A23G 9/22 20130101; A23G
9/045 20130101; A23G 9/12 20130101; A23G 9/08 20130101; A23G 9/18
20130101; F25C 1/12 20130101 |
Class at
Publication: |
062/068 |
International
Class: |
F25C 1/18 20060101
F25C001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2004 |
EP |
04256913.7 |
Claims
1. A method for partially freezing an aqueous mixture
simultaneously or in either order the steps of: placing said
aqueous mixtures in contact with at least part of a freezing
surface; cooling said freezing surface to below the freezing point
of said aqueous mixture; so that ice forms at the freezing surface;
and oscillating said freezing surface relative to said aqueous
mixture in a direction that is not perpendicular to at least part
of the freezing surface; characterized in that the oscillation is
linear with a frequency of between 20 and 200 Hz.
2. A method according to claim 1 wherein the frequency of the
oscillation is between 40 and 100 Hz.
3. A method according to claim 1 wherein the amplitude of the
oscillation is between 0.2 mm and 20 mm.
4. A method according to claim 1 wherein the amplitude of the
oscillation is between 4 mm and 10 mm.
5. A method according to claim 1 wherein the angle between the
direction of oscillation and the majority of the freezing surface
is less than 45.degree..
6. A method according to claim 1 wherein the freezing surface is
the surface of a cylinder with its axis parallel to the direction
of oscillation.
7. A method according to claim 6 wherein the freezing surface is
the surface of a vertical cylinder the lower end of which comprises
a hemispherical protrusion.
8. A method according to claim 1 wherein the freezing surface
comprises the inner and outer surfaces of a cylindrical tube with
its axis parallel to the direction of oscillation.
9. A method according to claim 1 wherein the freezing surface
comprises the surfaces of a plurality of members which are rigidly
mounted onto a single base.
10. A method according to claim 9 wherein the members are cylinders
or cylindrical tubes with their axes parallel to the direction of
oscillation.
11. A method according to claim 1 in which the temperature of the
freezing surface is between -1.degree. C. and -20.degree. C.
12. A method according to claim 1 in which the temperature-of the
freezing surface is cycled from a temperature between 5.degree. C.
and 25.degree. C. below the freezing point of the aqueous mixtures
to a temperature more than 0.degree. C. and less than 5.degree. C.
below the freezing point of the aqueous mixture.
13. A method according to claim 1 wherein the aqueous mixture
comprises an aqueous solution and/or suspension of edible
ingredients selected from the group consisting of sugars, food
acids, colours, flavours, proteins, fats emulsifiers and
stabilizers.
14. A method according to claim 13 in which the aqueous mixture is
a milk shake, water ice mix or an ice cream mix.
15. An apparatus for partially freezing an aqueous mixtures
comprising: a freezing surface; a cooling means capable of cooling
said freezing surface to below -1.degree. C. and an oscillation
means which is coupled to said freezing surface characterized in
that said oscillating means is capable of linearly oscillating said
freezing surface in a direction that is not perpendicular to at
least part of the freezing surface with a frequency of between 20
and 200 Hz.
16. An apparatus according to claim 15 wherein the oscillation
means is capable of oscillating said freezing surface with an
amplitude of between 1 mm and 20 mm.
17. An apparatus according to claim 15 wherein the oscillation
means is selected from the group consisting of a loud speaker, a
magnetic coil, an electrodynamic shaker and a reciprocating
electric motor.
18. An apparatus according to claim 15 wherein the oscillation
means is coupled to the freezing surface by a coupling means
selected from the group consisting of direct coupling, a resilient
member, and a cantilever beam.
19. An apparatus according to claim 15 wherein the freezing surface
comprises the surfaces of a plurality of members rigidly mounted
onto a single base and which are capable of being oscillated by a
single oscillation means.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a method and an apparatus
for partially freezing an aqueous mixture to form a dispersion of
ice crystals, and hence to produce a water ice slush, frozen
milkshake, ice cream or similar product.
BACKGROUND
[0002] Conventionally, ice cream or water ice slushes are produced
by placing a mixture, which is an aqueous solution and / or
suspension of the ingredients, in contact with a freezing surface.
A layer of ice forms on the surface. In order to prevent the
formation of very large ice crystals and to maintain good heat
transfer between the freezing surface and the mixture, it is
necessary continuously to remove the layer of ice. This has been
achieved by mechanically scraping the ice layer from the freezing
surface, for example in factory ice cream freezers (also known as
scraped surface heat exchangers), domestic ice cream freezers, and
in water ice slush machines such as those used in cafes and
convenience stores. This requires the provision of a scraping
mechanism and a driving mechanism. These features significantly add
to the size and complexity of the production equipment. Furthermore
scraping imposes a substantial energy cost, via the friction on the
scraping device which originates from overcoming the adhesion force
of the ice to the surface.
[0003] EP0584127 describes an alternative means of de-icing a
freezing surface using high frequency sound waves (ultrasound).
Ultrasound is believed to set up a resonance in the freezing
surface causing it to flex and bend thereby detaching the ice. This
allows ice generation without scraping and has the advantage of
simplifying the equipment since it does require moving parts.
However, this method has several drawbacks. Engineering the
freezing surface to allow ultrasonic resonance presents severe
restrictions on the size and design of the device. Also, the use of
ultrasound can lead to unpleasant high-pitched noise, which may not
be acceptable in a factory or public environment.
[0004] One of the big problems faced when making water ice slushes,
ice creams and frozen milk shakes is therefore to prevent the build
up of ice on the freezing surface without resorting to complex or
expensive equipment. Thus there is a need for a simple method of
removing ice from freezing surfaces.
[0005] It has now been discovered that it is possible to release
ice from a freezing surface which is in contact with an aqueous
mixture by linearly oscillating the freezing surface at low
frequencies.
Tests and Definitions
[0006] Partial freezing of an aqueous mixture means freezing the
mixture such that only part of the water in the mixture is
converted into ice crystals, such that the partially frozen product
is suitable for pumping, moulding, extruding, pouring, drinking,
spooning and the like.
[0007] The freezing point of the aqueous mixture means the
equilibrium freezing point of a solution of the initial
concentration. The equilibrium freezing point of a solution is
lower than the equilibrium freezing point of the pure solvent due
to freezing point depression. When a solution is partially frozen,
the concentration of the solution increases because water is
removed in the form of pure ice crystals (this is known as freeze
concentration). Therefore the freezing point decreases further. The
freezing point of an aqueous mixture can be determined by methods
well known to those skilled in the art.
[0008] The terms "milk shake", "water ice" and "ice cream" have the
meanings as stated in Chapter 1 of Ice Cream 4.sup.th Edition--W.
S. Arbuckle--AVI Publishing, 1986, except that in the context of
the present invention, "ice cream" also encompasses compositions
comprising vegetable fats.
[0009] The angle between the direction of oscillation and the
freezing surface at any particular point on the surface means
(90--theta) where theta is the smaller of the two angles between
the vector normal to the surface at that point and the oscillation
direction, as shown in FIG. 1.
Measurement of the Temperature of the Freezing Surface
[0010] The temperature of the freezing surface is measured by
attaching a self-adhesive thermocouple (T-type, Omega Engineering
Ltd, 1 Omega Drive, Riverbound Technology Centre, Northbank, Irlam,
Manchester, M44 5BD, UK) to the freezing surface.
Release of Ice From the Freezing Surface
[0011] Release of ice from the freezing surface is assessed by
visual inspection of the freezing surface. Ice release is judged to
be successful when no ice adheres to the surface at the end of the
freezing process.
Estimation of Ice Content
[0012] The concentration of a solution in equilibrium at a
temperature between its freezing point and its glass transition
temperature is given by the freezing point curve on the phase
diagram. (The phase diagram for sucrose solutions can be found in
S. Ablett, M. J. Izzard, P. J. Lillford J. Chem Soc Faraday Trans.
88 (1992) 789). For example, at -2.2.degree. C., the sucrose
concentration in equilibrium with ice is 22% (w/w). If the initial
concentration of the solution was 20% w/w then the amount of ice
formed can be estimated as follows.
Sucrose concentration (% w/w)
[0013] =mass of sucrose / mass of solution [0014] =mass
sucrose/(total mass-mass of ice) [0015] 22%=20/(100-x)*100 where
x=% (w/w) ice=9.8% in this example.
BRIEF DESCRIPTION OF THE INVENTION
[0016] It is the first object of the present invention to provide a
method for partially freezing an aqueous mixture comprising
simultaneously or in either order the steps of: placing said
aqueous mixture in contact with at least part of a freezing
surface, cooling said freezing surface to below the freezing point
of said aqueous mixture, so that ice forms at the freezing surface;
and oscillating said freezing surface relative to said aqueous
mixture in a direction that is not perpendicular to at least part
of the freezing surface, characterised in that the oscillation is
linear with a frequency of between 20 and 200 Hz.
[0017] Preferably the frequency of the oscillation is between 40 Hz
and 100 Hz. More preferably the frequency of the oscillation is
between 50 Hz and 80 Hz. It has been found that the higher the
frequency of the oscillation within these ranges, the better is the
removal of ice from the freezing surface.
[0018] Preferably the amplitude of the oscillation is between 0.2
mm and 20 mm. More preferably the amplitude of the oscillation is
between 1 mm and 15 mm. Most preferably the amplitude of the
oscillation is between 4 mm and 10 mm. It has been found that the
larger the amplitude of the oscillation within these ranges, the
better is the removal of ice from the freezing surface.
[0019] The oscillation may be of any suitable waveform, for example
sinusoidal, square wave or saw tooth. Preferably the oscillation is
sinusoidal.
[0020] It is desirable that the rate of partial freezing of the
aqueous mixture should be as rapid as possible, so that the rate of
production of the partially frozen product, such as water ice
slush, ice cream or frozen milkshake, is maximized. It is believed
that the rate of partial freezing depends on (at least) three
factors: the rate of formation of ice at the freezing surface, the
area of the freezing surface and the rate of release of ice from
the freezing surface.
[0021] It has been found that the more closely the freezing surface
is parallel to the direction of oscillation, the faster the release
of ice from the freezing surface. The shape of the freezing surface
is therefore chosen so that the angle between the direction of
oscillation and the majority of the freezing surface is less than
45.degree.. For example the freezing surface comprises the surface
of a rod with its axis is parallel to the direction of oscillation.
Preferably the freezing surface is the surface of a cylinder with
its axis parallel to the direction of oscillation. More preferably,
the cylinder is vertical and the lower end of the cylinder
comprises a protrusion. Most preferably the protrusion is a
hemisphere or a cone.
[0022] It has been found that the larger the area of the freezing
surface, the more ice is generated. The shape of the freezing
surface is chosen to have a large surface area. Preferably, the
freezing surface comprises the inner and outer surfaces of a
cylindrical tube with its axis parallel to the direction of
oscillation.
[0023] The freezing surface can comprise the surfaces of a
plurality of members which are rigidly mounted onto a single base.
Preferably the members comprise cylinders with their axes parallel
to the direction of oscillation. More preferably the cylinders are
vertical and lower end of the cylinder comprises a protrusion. Most
preferably the protrusion is a hemisphere or a cone. Alternatively
the members comprise cylindrical tubes with their axes parallel to
the direction of oscillation.
[0024] The area of the freezing surface can be increased by the
addition of fins. The fins may be flat plates or may be shaped, for
example twisted, to enhance axial mixing in the aqueous mixture.
Preferably one or more fins are attached to the freezing
surface.
[0025] The strength of the adhesion of the ice to the freezing
surface depends on the temperature of the freezing surface, and
also on the type of solute in the aqueous mixture. It has been
found that for temperatures in the range of 0.degree. C. to
-20.degree. C., the lower the temperature of the freezing surface,
the stronger the adhesion. However, the higher the temperature of
the freezing surface, the slower the rate of formation of ice (The
temperature of the freezing surface must be below the freezing
point of the aqueous mixture in order to form ice.). Thus the
optimal temperature of the freezing surface for a particular
aqueous mixture is determined by a compromise between these two
opposing effects. It has been found that a rapid rate of ice
formation and easy release is achieved when the temperature of the
freezing surface is between -1.degree. C. and -20.degree. C.
Preferably the temperature of the freezing surface is below
-5.degree. C. Equally preferably the temperature of the freezing
surface is above -10.degree. C. Most preferably the temperature of
the freezing surface is between -5.degree. C. and -10.degree.
C.
[0026] It has further been found that the ice removal can be
enhanced without significantly reducing the rate of ice formation
by cycling the temperature of the freezing surface from a
temperature between 5.degree. C. and 25.degree. C. below the
freezing point of the aqueous mixture to a temperature more than
0.degree. C. and less than 5.degree. C. below the freezing point of
the aqueous mixture.
[0027] The freezing surface is cooled by any suitable cooling
means, for example by flowing a coolant, such as aqueous ethylene
glycol or Freon, through the interior of the member whose surface
comprises the freezing surface.
[0028] It has been found that the method of the present invention
can be used to produce partially frozen foods or drinks when a
suitable aqueous mixture is used. Preferably the aqueous mixture
comprises an aqueous solution and/or suspension of edible
ingredients selected from the group consisting of sugars, food
acids, colours, flavours, proteins, fats emulsifiers and
stabilisers. More preferably the aqueous mixture is a milk shake,
water ice mix or an ice cream mix.
[0029] It is a second object of the invention to provide an
apparatus for partially freezing an aqueous mixture comprising a
freezing surface, a cooling means capable of cooling said freezing
surface to below -1.degree. C., and an oscillation means coupled to
said freezing surface characterised in that said oscillating means
is capable of linearly oscillating said freezing surface relative
in a direction that is not perpendicular to at least part of the
freezing surface with a frequency of between 20 and 200 Hz.
[0030] Preferably the oscillation means is capable of oscillating
the freezing surface with an amplitude of between 1 mm and 20
mm.
[0031] Preferably the cooling means is capable of cooling the
freezing surface to below -5.degree. C., more preferably to below
-10.degree. C.
[0032] It is desirable that the apparatus should be simple and
inexpensive. Preferably the oscillation means is a loud speaker, a
magnetic coil, an electrodynamic shaker or a reciprocating electric
motor.
[0033] The oscillation means may be coupled to the freezing surface
by direct coupling, or by a resilient member, or by a cantilever
beam. It has been found that direct coupling provides a simple,
inexpensive means of coupling. It has been further found that a
cantilever beam is suitable for oscillating heavy freezing
surfaces. It has also been found that by coupling the freezing
surface to the oscillation means with a resilient member, such as a
flexible beam or a spring, and oscillating at its resonant
frequency, large amplitude oscillations can be obtained.
[0034] The shape of the freezing surface is chosen so that the
angle between the direction of oscillation and the majority of the
freezing surface is less than 45.degree.. For example the freezing
surface comprises the surface of a rod with its axis is parallel to
the direction of oscillation. Preferably the freezing surface is
the surface of a cylinder with its axis parallel to the direction
of oscillation. More preferably, the cylinder is vertical and the
lower end of the cylinder comprises a protrusion. Most preferably
the protrusion is a hemisphere or a cone.
[0035] The freezing surface can comprise the surfaces of a
plurality of members which are rigidly mounted onto a single base
which is oscillated by a single oscillation means. This avoids the
necessity for more than one oscillation means. Preferably the
members comprise cylinders with their axes parallel to the
direction of oscillation. More preferably the cylinders are
vertical and lower end of the cylinder comprises a protrusion. Most
preferably the protrusion is a hemisphere or a cone. Alternatively
the members comprise cylindrical tubes with their axes parallel to
the direction of oscillation.
DETAILED DESCRIPTION
[0036] The present invention will be further described by reference
to the drawings, wherein;
[0037] FIG. 1 illustrates the definition of the angle between the
direction of oscillation and the freezing surface.
[0038] FIG. 2 represents a schematic view of the apparatus
according to the second aspect of the invention, together with an
aqueous mixture.
[0039] FIG. 3 represents a freezing surface in accordance with the
invention, comprising a cylinder with a hemispherical protrusion on
its lower end.
[0040] FIG. 4 represents a freezing surface in accordance with the
invention, comprising a cylindrical tube.
[0041] FIG. 5 represents a freezing surface in accordance with the
invention, to which fins are attached.
[0042] FIG. 6 represents a freezing surface in accordance with the
invention, comprising a plurality of members rigidly mounted on a
single base which is oscillated by a single driving mechanism.
[0043] FIG. 7 represents a detailed diagram of the apparatus in
accordance with the second aspect of the invention wherein the
oscillation means is a loudspeaker with a resilient beam
coupling.
[0044] FIG. 1 shows freezing surface 3, the vector 30 normal to a
point on the freezing surface 3 and the direction of oscillation 5.
The angle 31 is the smaller of the two angles between the vector 30
normal to the surface and the oscillation direction 5. The angle
between the direction of oscillation and the freezing surface is
given by (90.degree.--angle 31).
[0045] FIG. 2 represents a schematic view of the apparatus,
together with an aqueous mixture. In FIG. 2 the oscillation means 1
is coupled to the freezing surface 3 by means of a coupling 2. The
freezing surface 3 is immersed in an aqueous mixture 4. The
oscillation means 1 oscillates freezing surface 3 in direction
5.
[0046] FIG. 3 represents a freezing surface 3 comprising a cylinder
6 with a hemispherical protrusion 7 on its lower end. The
temperature of freezing surface 3 is controlled by flowing a
coolant liquid 8 through cylinder 6 via inlet 9 and outlet 10.
[0047] FIG. 4 shows a cross-sectional view of a cylindrical tube
11. The tube has outer surface 12 and inner surface 13 which
together comprise the freezing surface. The tube is hollow to allow
the freezing surface to be cooled with coolant liquid 8.
[0048] FIG. 5 shows a top view of a freezing surface 3 to which
fins 14 are attached. They may consist of flat plates or may be
shaped so as to enhance mixing of the aqueous mixture.
[0049] FIG. 6 represents a freezing surface comprising a plurality
of members 16 rigidly mounted on a single base 15 which can be
oscillated in direction 5 by a single oscillation means.
[0050] FIG. 7 shows an oscillation means consisting of a
loudspeaker (with its speaker cone removed) comprising a magnet 17,
pole pieces 18, coil 19 and frame 20. A lightweight tube 21 is
attached to the tube 22 around which the coil is wrapped. A linear
bearing 23 provides axial alignment for the tube 21. The tube is
coupled to the freezing surface 3 by means of a resilient beam 25
and rod 26. The beam is supported at both ends on knife edges 24
and the freezing surface 3 is attached to the centre of the
beam.
[0051] The present invention will be further described with
reference to the following examples which are illustrative only and
non-limiting.
EXAMPLE 1
Freezing Surfaces of Various Shapes
[0052] (a) A vertical hollow copper cylinder with length 90 mm,
diameter 16 mm and wall thickness 1 mm was directly coupled at its
upper end to an electrodynamic shaker (model V406, Ling Dynamic
Systems Ltd, Royston, Herts, UK). The lower end of the cylinder was
closed by a flat plate. An aqueous solution of 50% w/w ethylene
glycol at -20.degree. C. was passed through the interior of the
cylinder by means of a Haake refrigerated circulator. The cylinder
was sinusoidally oscillated along its longitudinal axis at a
frequency of 60 Hz and an amplitude of 6 mm. A cup containing 250
ml of a 20% w/w sucrose solution, initially at a temperature close
to 0.degree. C., was positioned under the cylinder so that the
cooled cylinder was fully immersed in the solution. Ice continually
formed on the curved surface of the cylinder and was released into
the solution by the oscillation. Ice also formed on the flat end of
the cylinder, but was not removed and continued to build up over
time.
[0053] (b) An identical cylinder was constructed except that it had
a hemispherical protrusion at its free end rather than a flat
plate. Use of this cylinder under the same conditions resulted in
successful release of ice from the entire surface and no build-up
at the free end.
[0054] (c) A third freezing surface consisting of a cylindrical
tube with length 115 mm, outer diameter 42 mm, inner diameter 34 mm
and wall thickness 0.9 mm was constructed from aluminium. The
surface was polished. The mass of the cylinder when empty was 118
g. The tube was cooled by flowing coolant through the walls. Use of
this cylinder under the same conditions resulted in the formation
of patches of ice on the inner and outer surfaces of the tube. The
ice was released into the surrounding solution by the
oscillation.
EXAMPLE 2
Amplitude and Frequency of Oscillation
[0055] Without wishing to be limited by theory, it is believed that
the ice is removed from the surface by the shear force between the
ice layer on the freezing surface and the aqueous mixture. This is
related to the maximum acceleration of the surface during the
oscillation in the direction parallel to the surface. The larger
the maximum acceleration, the greater the ice removal force.
Increasing both the amplitude and frequency of the oscillation
increases the maximum acceleration. The amplitude and frequency of
the oscillation required to remove the ice from the freezing
surface depends on the strength of the adhesion of the ice, which
in turn depends on the temperature of the surface and the nature
and concentration of the solutes in the aqueous mixture. Increasing
the frequency or the amplitude of the oscillation has been found to
increase the de-icing ability of the freezing surface.
[0056] The cylindrical tube was used as described in Example 1 (c)
to partially freeze a 20% w/w sucrose solution using a 50% w/w
ethylene glycol at -20.degree. C. as the coolant. The frequency and
amplitude of oscillation were varied. At each frequency the minimum
amplitude required to release ice from the freezing surface was as
follows: TABLE-US-00001 20% sucrose, -20.degree. C. Frequency (Hz)
Amplitude (mm) 150 .gtoreq.1.5 100 .gtoreq.2 80 .gtoreq.2.5 60
.gtoreq.3 40 .gtoreq.5
[0057] Thus at any given frequency, ice release can be achieved
when the amplitude of the oscillation is increased above a certain
value.
EXAMPLE 3
Effect of Solution Concentration
[0058] The experiment of example 2 was repeated using a 30% w/w
sucrose solution. Ice release was achieved under the following
conditions: TABLE-US-00002 30% sucrose, -20.degree. C. Frequency
(Hz) Amplitude (mm) 150 .gtoreq.1 100 .gtoreq.1.5 80 .gtoreq.2 60
.gtoreq.2.5 40 .gtoreq.4
[0059] Thus it can be seen by comparing Examples 2 and 3.that the
amplitude and frequency required for ice release depend on the
concentration of the solution. Increasing the sucrose concentration
from 20 to 30% w/w reduced the amplitude required for release at
any given frequency.
EXAMPLE 4
Effect of Coolant Temperature
[0060] The experiment of example 2 was repeated using an ethylene
glycol solution at -10.degree. C. Ice release was achieved under
the following conditions: TABLE-US-00003 20% sucrose, -10.degree.
C. Frequency (Hz) Amplitude (mm) 150 .gtoreq.0.5 100 .gtoreq.1 60
.gtoreq.1.5 40 .gtoreq.3 20 .gtoreq.5
[0061] Thus it can be seen by comparing Examples 2 and 4 that the
amplitude and frequency required for ice release depend on the
temperature of the freezing surface (which depends on the
temperature of the coolant). Increasing the temperature of the
coolant sucrose concentration from -10 to -20.degree. C. reduced
the amplitude required for release at any given frequency.
EXAMPLE 5
Effect of Cycling the Temperature of the Freezing Surface
[0062] The experiment of example 2 was repeated but with the flow
of ethylene glycol through the finger stopped periodically (20 s
on, 20 s off) causing the temperature of the freezing surface to
rise and fall periodically. The temperature was measured as
specified above using a thermocouple placed on the outside surface
of the cylinder, approximately 40 mm from the upper end and close
to the coolant inlet port.
[0063] The ice was released more easily when the surface
temperature was periodically cycled. This is due to the lower
adhesion at higher surface temperatures. This enabled a 10% sucrose
solution to be partially frozen using the amplitude and frequency
corresponding to that which enabled a 20% sucrose solution to be
partially frozen without temperature cycling.
EXAMPLE 6
Effect of Changing Solute
[0064] The experiment of example 2 was repeated using an 8%
glycerol solution instead of 20% sucrose solution. Ice release was
obtained under the following conditions: TABLE-US-00004 8% sucrose,
-20.degree. C. Frequency (Hz) Amplitude (mm) 150 .gtoreq.1 100
.gtoreq.2 80 .gtoreq.2.5 60 .gtoreq.3 40 .gtoreq.5
[0065] Thus it can be seen by comparing Examples 2 and 6 that the
amplitude and frequency required for ice release depend on the
nature of the solute as well as the concentration of the solution.
Ice release occurs with approximately the same conditions for 8%
w/w glycerol as for 20% w/w sucrose.
EXAMPLE 7
Ice Content After 2 Minutes Freezing
[0066] The experiment of example 2 was repeated. The cylinder was
placed in the 20% sucrose solution and oscillated at a frequency of
60 Hz. Three experiments were performed with different amplitudes.
In each case the cylinder was placed in the solution for a period
of 2 minutes, after which the partially frozen mixture was gently
stirred and its temperature was measured using a Comark temperature
probe. The ice content was estimated from the temperature using the
method described above and the results were as follows.
TABLE-US-00005 Amplitude (mm) Temperature (.degree. C.) Ice content
(% w/w) 4 -1.6 5 6 -1.7 10 8 -1.8 13
[0067] Higher ice contents were achieved at higher displacements
because the more effective de-icing process allowed higher rates of
heat transfer to be achieved.
EXAMPLE 8
Production of a Water Ice Slush
[0068] A mixture was prepared with the following composition:
TABLE-US-00006 (% w/w) Sucrose 10 Dextrose monohydrate 6 63 DE low
fructose corn syrup 6 Citric acid 0.6 Potassium sorbate 0.03 Lemon
and lime flavour 0.03 Water to 100
[0069] This was partially frozen using the set-up described in
example 2 with an oscillation frequency of 60 Hz and an amplitude
of 8 mm. The temperature was measured after 2 minutes to be
-2.3.degree. C. The resulting product was judged to contain
sufficient ice and to be an acceptable slush ice drink.
EXAMPLE 9
Production of an Ice Cream
[0070] A basic ice cream mix was prepared with the following
composition: TABLE-US-00007 (% w/w) Sucrose 20 Skim milk powder 10
Milk fat 10 Water to 100
[0071] This was frozen using the set-up described in example 2 with
an oscillation frequency of 60 Hz and an amplitude of 8 mm. The
temperature was measured after 2 minutes to be -4.9.degree. C. The
resulting product was judged to contain sufficient ice and to be an
acceptable soft ice cream.
EXAMPLE 10
Cantilever Beam Coupling
[0072] A larger freezing surface consisting of a cylindrical tube
was constructed from copper. The mass of the cylinder when empty
was approximately 1 kg. The directly coupled electrodynamic shaker
was not capable of oscillating the heavy tube with sufficiently
large amplitude. Instead the tube was coupled to the shaker by a
steel cantilever beam (255 mm.times.75 mm.times.10 mm). One end of
the beam was clamped to a large block of steel (the fixed end) and
the other was attached to the tube (the free end). The beam was
driven by a pushrod attached to the shaker between the fixed end
and the free end. The system was tuned to resonance by sweeping the
oscillation frequency until maximum amplitude was obtained. The
resonant frequency depends on the length of the beam, so the beam
was chosen such that its first bending resonant frequency was the
chosen operating frequency (50 Hz). Ice release was obtained in a
20% sucrose solution with using an ethylene glycol solution at
-10.degree. C. as the coolant at amplitudes of 2.4 mm and
above.
EXAMPLE 11
Loudspeaker with a Resilient Beam Coupling
[0073] An alternative oscillation means was constructed from a 100
W loudspeaker with the speaker cone removed. A lightweight tube was
attached to the tube around which the coil is wrapped. A linear
bearing was provided to provide axial alignment for the tube. The
linear bearing consisted of two perspex plates spaced 20 mm
vertically apart with concentric holes through which the tube could
slide. The tube was coupled to the freezing surface which consisted
of a copper cylinder (diameter 22 mm, length 110 mm) by means of a
resilient beam and rod. The beam was supported at both ends on
knife edges and the freezing surface was attached to the centre of
the beam. The beam was chosen so that its resonant frequency
matched the operating frequency (50 Hz). Large oscillation
amplitudes (>10 mm) could be achieved with this arrangement.
[0074] The various features of the embodiments of the present
invention referred to in individual sections above apply, as
appropriate, to other sections mutatis mutandis. Consequently
features specified in one section may be combined with features
specified in other sections as appropriate.
[0075] All publications mentioned in the above specification are
herein incorporated by reference. Various modifications and
variations of the described methods and products of the invention
will be apparent to those skilled in the art without departing from
the scope of the invention. Although the invention has been
described in connection with specific preferred embodiments, it
should be understood that the invention as claimed should not be
unduly limited to such specific embodiments. Indeed, various
modifications of the described modes for carrying out the invention
which are apparent to those skilled in the relevant fields are
intended to be within the scope of the following claims.
* * * * *