U.S. patent application number 12/495829 was filed with the patent office on 2011-01-06 for method and apparatus for ultrasonic freezing.
Invention is credited to Stephen A. McCORMICK, Suling ZHAI.
Application Number | 20110000231 12/495829 |
Document ID | / |
Family ID | 42668748 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110000231 |
Kind Code |
A1 |
McCORMICK; Stephen A. ; et
al. |
January 6, 2011 |
METHOD AND APPARATUS FOR ULTRASONIC FREEZING
Abstract
An apparatus for reducing a temperature of a product includes a
housing in which cryogenic fluid is provided for being exposed to
the product, and at least one ultrasonic transducer assembly
disposed in the housing for generating ultrasonic energy to contact
the cryogenic fluid and a surface of the product to facilitate heat
transfer at the surface of the product. The cryogenic fluid can be
selected from nitrogen and carbon dioxide.
Inventors: |
McCORMICK; Stephen A.;
(Warrington, PA) ; ZHAI; Suling; (Shanghai,
CN) |
Correspondence
Address: |
The BOC Group, Inc.
575 MOUNTAIN AVENUE
MURRAY HILL
NJ
07974-2082
US
|
Family ID: |
42668748 |
Appl. No.: |
12/495829 |
Filed: |
July 1, 2009 |
Current U.S.
Class: |
62/63 ; 62/374;
62/64 |
Current CPC
Class: |
A23L 3/375 20130101;
F25D 2400/30 20130101; A23L 3/30 20130101; F25D 3/11 20130101 |
Class at
Publication: |
62/63 ; 62/374;
62/64 |
International
Class: |
F25D 3/11 20060101
F25D003/11; F25D 13/06 20060101 F25D013/06 |
Claims
1. An apparatus for reducing a temperature of a product,
comprising: a container; a cryogenic substance provided to the
container to reduce a temperature of at least a surface of the
product; a conveyor assembly for moving the product through the
container for the surface of the product to be exposed to the
cryogenic substance; an ultrasonic transducer assembly disposed at
the container in spaced relation from the product, the ultrasonic
transducer assembly providing ultrasonic energy to the cryogenic
substance to induce cavitation of nucleation at a surface of the
product during exposure to the cryogenic substance.
2. The apparatus according to claim 1, wherein the chamber
comprises an immersion bath through which the conveyor and product
are moved.
3. The apparatus according to claim 2, wherein the ultrasonic
transducer assembly is disposed in the immersion bath.
4. The apparatus according to claim 3, wherein the ultrasonic
transducer assembly is mounted to a sidewall of the container.
5. The apparatus according to claim 2, wherein the ultrasonic
transducer assembly is mounted above the immersion bath.
6. The apparatus according to claim 1, wherein a transmission
surface of the ultrasonic transducer assembly is disposed at a
distance of up to 30 mm from the product.
7. The apparatus according to claim 1, wherein the product is
selected from a food product and a metallic product.
8. The apparatus according to claim 1, wherein the cryogenic
substance comprises nitrogen (N.sub.2).
9. The apparatus according to claim 1, further comprising a housing
containing the container, the housing comprising an inlet and an
outlet for the conveyor assembly.
10. The apparatus according to claim 9, wherein the ultrasonic
transducer assembly is mounted beneath the conveyor assembly.
11. The apparatus according to claim 9, further comprising a
barrier disposed in the container and having at least one nozzle
through which the cryogenic substance may pass, the barrier aligned
with the ultrasonic transducer assembly.
12. An apparatus for reducing a temperature of a product,
comprising: a housing in which cryogenic fluid is provided for
being exposed to the product; at least one ultrasonic transducer
assembly disposed in the housing for generating ultrasonic energy
to contact the cryogenic fluid and a surface of the product to
facilitate heat transfer at the surface of the product.
13. The apparatus according to claim 12, wherein the cryogenic
fluid comprises a liquid bath.
14. The apparatus according to claim 13, wherein the cryogenic
fluid comprises nitrogen.
15. The apparatus according to claim 12, wherein the cryogenic
fluid comprises a fog.
16. The apparatus according to claim 15, wherein the cryogenic
fluid comprises nitrogen.
17. A method of reducing a temperature of a product, comprising:
exposing a surface of the product to a cryogenic substance for heat
transfer at said surface; providing ultrasonic energy to the
cryogenic substance and the product for destroying nucleation at
the surface of the product.
18. The method according to claim 17, wherein the exposing
comprises immersing at least a portion of the surface of the
product in the cryogenic substance, and the destroying comprises
cavitating the nucleation at the surface of the product.
19. The method according to claim 17, wherein the exposing
comprises spraying the surface of the product with the cryogenic
substance.
20. The method according to claim 17, wherein the cryogenic
substance is selected from nitrogen and carbon dioxide.
Description
[0001] The embodiments relate to freezing of products, such as for
example food products, in immersion and convection freezing
systems.
[0002] For a more complete understanding of the present
embodiments, reference may be had to the detailed description which
follows taken in conjunction with the drawings, of which:
[0003] FIG. 1 is a side view of one embodiment of the
invention;
[0004] FIG. 2 is a side view of another embodiment of the
invention; and
[0005] FIG. 3 is a view of a portion of an alternative embodiment
from that shown in FIG. 2.
[0006] FIGS. 1-3 show ultrasonic immersion and convection tunnel
freezing system embodiments to prepare and treat products, such as
food products for example, for subsequent processing.
[0007] Referring to FIG. 1, an immersion freezer embodiment is
shown generally at 10. The freezer 10 may be constructed as a
container which includes an insulated sidewall 12 in which a bath
14 of liquid nitrogen (N.sub.2) is disposed and contained. A
conveyor belt 16 extends through the bath 14 to deliver products
18, such as for example food products, through the bath 14. (As
shown in FIG. 2, the sidewall 12 may be extended to form the
container as a housing covering the bath 14, and provide an inlet
and outlet for the belt 16 at the housing.) The conveyor belt 16 is
constructed and arranged to accommodate different types and sizes
of the product 18 to be immersed into the bath 14. That is,
depending upon the product 18, regardless of whether it is a food
product or otherwise, the conveyor belt 16 can be adjusted such
that all of the product 18 is immersed in the bath 14, or only a
select portion of the product 18 is immersed in the bath 14.
Residence time of the product 18 in the bath 14 will be determined
by the particular product to be frozen. Such construction for the
conveyor belt 16 may be of wire mesh or slat-like longitudinal
members having spaces therebetween for the cryogenic bath to more
readily access and contact the product 18.
[0008] Ultrasonic transducers arranged singly, in pairs or in any
other numerical combinations and arrangements, are disposed with
respect to the system 10. A transducer 20 may be disposed in the
liquid nitrogen bath 14 either alone, or as a pair or any number of
transducers 20. Depending upon the volume and the dimensions of the
housing 12 for the bath 14, there may be a plurality of pairs of
the transducers 20. Similarly, transducers 22 may be mounted singly
or as a pair or any number of transducers 22 at an inner sidewall
of the housing 12 for exposure as well to the nitrogen bath 14. A
transducer 24 may be disposed above the nitrogen bath 14 either
singly or as a pair of transducers 24. With respect to the
transducers 20-24, any number of ultrasonic transducers may be
employed depending upon the particular freezing application, the
size and depth of the liquid nitrogen bath 14, and the physical
characteristics of the product 18 being processed.
[0009] The transducers 20-24 are connected, as shown generally at
25, to an ultrasonic generator 26, which in turn is connected to
and can be controlled by a controller device (not shown). The
system 10 is provided with an inlet 26 and an outlet 28 for the
conveyor belt 16, and hence the product 18 for introduction into
and out of the bath 14.
[0010] In operation, the product 18 such as for example a food
product, is loaded on the conveyor belt 16 and introduced by the
conveyor belt 16 in a batch or continuous process into the liquid
nitrogen bath 14. Upon contact of the product 18 with the liquid
nitrogen bath 14, heat transfer occurs and boil off is immediate.
Such heat transfer of the product 18 and boil off in the bath 14
causes nucleation, which is the formation of extremely small
nitrogen gas bubbles at the surface of the product 18 exposed to
the liquid nitrogen in the bath 14. As the bubbles rapidly increase
in number, they provide a shielding effect and create a boundary
layer at a surface of the product 18, in effect insulating or
encapsulating the product in a multiplicity of nitrogen gas bubbles
which substantially reduces heat transfer effectiveness at the
surface of the product 18.
[0011] Accordingly, prior to or upon entry of the product 18 into
the bath 14 one or more of the ultrasonic transducers 20-24 are
actuated, such that sound waves 27 provide cavitation to counteract
the nucleation, i.e. the cavitation destroys the bubbles and
boundary layer created by the nucleation to thereby prevent the
formation of an insulatory bubble or gas layer at the surface of
the product 18 so that heat transfer at the surface is not reduced
by the nucleation. The efficiency and effectiveness of this process
is farther realized by the product being directly exposed and in
contact with the liquid nitrogen bath 14 and the ultrasonic waves
27 throughout the process while the waves are in contact the with
product 18. In other words, in the present embodiment the product
18 is directly exposed to the liquid nitrogen in the bath 14 so
that the cavitation with respect to the nucleation is complete and
total. Heat transfer is also increased by way of microstreaming
which means that as gas bubbles at the surface of the product are
rapidly destroyed by ultrasonic energy, pulses of high pressure gas
are released which increase surface heat transfer.
[0012] As shown in FIG. 1, the transducers 20-24 can be arranged in
the liquid nitrogen bath 14 or in the atmosphere above the bath 14,
such as is shown with the transducers 24. The effectiveness of the
ultrasonic energy to provide cavitation and destroy nucleation is
increased the closer the transducers 20-24 are to the liquid
nitrogen and the product 18. That is, the transducers 20 are more
effective than the transducers 22, which in turn are more effective
than the transducers 24. The further away the ultrasonic
transducers 20-24 are from the product 18, the more energy is
required to provide the sonic energy to the product 18, which of
course translates into a higher cost to operate the system. In
addition, and by way of example only, a distance d1 of 30 mm is
provided between the product 18 and a transmitting surface of the
transducers 20-24.
[0013] Referring to FIG. 2, a convection tunnel embodiment is shown
generally at 40 having ultrasonic transducers. The embodiment
includes a housing 42. The housing includes a top 43, sidewalls 45
and a bottom 47, which define a chamber 44 disposed therein. A
conveyor belt 46 extends from an inlet 48 to an outlet 50 of the
housing 42. The housing 42 may be insulated.
[0014] Product 52, such as food product, is transported along the
conveyor belt 46 between the inlet 48 to the outlet 50 of the
housing 42. Cryogenic liquid, such as nitrogen (N.sub.2) or carbon
dioxide (CO.sub.2), is delivered from a remote source (not shown)
through a conduit 54 which extends into the chamber 44 of the
housing 42 and is connected to a manifold 56 having one or a
plurality of spray nozzles 58 extending therefrom. The cryogenic
liquid nitrogen or carbon dioxide is transported through the
conduit 54 into the manifold 56 for being distributed in gaseous or
liquid phase jets 59 from the spray nozzles 58 into the chamber 44.
Fans 60, impellers, blowers or a combination of such, in the
chamber 44 are connected to corresponding motors 62 for circulating
the cryogen liquid in the chamber 44.
[0015] Disposed between the manifold 56 and the conveyor belt 46 is
an impingement plate 64 having a plurality of a jet nozzle
apertures 65 arranged therein. The impingement plate 64 may be
arranged to extend across an entire length of the chamber 44,
thereby segregating a portion of the chamber from the conveyor belt
46. Ultrasonic transducers 68 are arranged in the chamber 44
proximate the impingement plate 64. The ultrasonic transducers 68
provide ultrasonic energy proximate the impingement plate 64. The
cryogenic liquid spray 66 being sprayed by the impingement jet
nozzles 65 is directed toward the product 52. The ultrasonic energy
will atomize the liquid cryogen spray 66 into a fog, for example a
nitrogen fog. CO.sub.2 will be injected in a solid state, for
increased heat transfer at the product 52 surface. Similar to the
embodiment of FIG. 1, the ultrasonic energy destroys any nucleation
of the cryogenic bubbles that may form at the surface of the
product 52. The microstreaming effect will also occur at this stage
with this embodiment.
[0016] Other embodiments of the system embodiment 40 of FIG. 2
include arranging ultrasonic transducers 72 beneath the conveyor
belt 46 or alternatively arranging ultrasonic transducers 74
proximate a side of the conveyor belt 46. It should be understood
that use of the transducer 68, 72, 74 is not limited to one of
each, but rather the transducers 68, 72, 74 may be arranged singly,
in pairs or in any combination arranged within the housing 42.
[0017] In operation the product 52 or products are loaded onto the
conveyor belt 46 and transferred from the inlet 48 into the housing
42 of the system 40 for treatment at the chamber 44 prior to being
removed at the outlet 50. In the chamber 44, the fans 60 circulate
the cryogenic jet spray 59 emitted from the spray nozzles 58 for
circulation in the chamber 44. The jet spray 59 from the spray
nozzles 58 is forced toward the impingement plate 64 and
accordingly through the impingement nozzle 65 or nozzles to provide
the spray 66 of the cryogenic substance to contact a surface of the
product 52. The transducers 68, 72, 74, regardless of their number
and disposition within the chamber 44, are actuated to provide
ultrasonic waves 71 to the cryogen spray 66 to provide a cryogenic
fog (when nitrogen is used) from the spray at the surface of the
product 52. The ultrasonic wave 71 energy will also destroy the
boundary layer of any gas that surrounds the product 52 surface and
which inhibits freezing of the product. This causes a high heat
transfer effect, as it does with the embodiment of FIG. 1, to
provide for a rapid crusting of the surface of the product 52 for
subsequent treatment or processing.
[0018] The transducers 68, 72, 74 are at a select distance from the
product 52, which by way of example only, is a distance d2 of not
more than 30 mm. Of course, the distance d2 can be selected
depending upon the type and amount of the product 52 being crust
frozen, the residence time of the product 52 when being subjected
to the cryogen, and the size and number of the transducers 68, 72,
74 being employed in the housing.
[0019] FIG. 3 shows an alternate embodiment of that which is shown
in FIG. 2 with respect to the disposition of ultrasonic transducers
for the freezing operation. As shown in FIG. 3, the conduit 54 is
connected to the manifold 56 from which the nozzles 58 provide the
spray 59 of the cryogen fluid, such as either liquid nitrogen or
carbon dioxide, into the chamber 44. The conveyor belt 46 extends
and travels through the chamber 44 for transporting the product 52
through the chamber for the freezing operation. The conveyor belt
46 shown in FIG. 3 may be of construction similar to the conveyor
belt shown in FIG. 2 and the conveyor belt 16 of FIG. 1. Such
construction for the conveyor belt 46 may be of wire mesh or
slat-like longitudinal members having spaces therebetween for the
cryogenic liquid spray to access and contact the product 52.
[0020] The impingement plate 64 with the impingement jet nozzle
apertures 66 are constructed and arranged to accommodate the
ultrasonic transducers 68. The transducers 68 are arranged above
the conveyor belt 46 parallel or alternatively aligned with the
impingement plate 64. A distance d3 between a transmission surface
69 of the transducer 68 to the product 52 is 30 mm by way of
example only.
[0021] The transducer 72 or transducers may also be disposed
beneath the conveyor belt 46 to provide ultrasonic energy from
below the product 52. Another impingement plate 76 with impingement
jet apertures 78 can be arranged beneath the conveyor belt 46, with
the transducers 72 arranged in parallel or alternatively aligned
with the impingement plate 76. Sound waves 80 generated from the
transducers 68, 72 are therefore able to be directed toward a lower
surface as well of the product 52. The distance d3 would also be
selected, measured from the transmission surface of the transducer
72 to the product 52. As with FIG. 2, the embodiment of FIG. 3 with
the arrangement of the transducer 68, 72 provides for the
atomization of the cryogen liquid spray to create a cryogen fog
when nitrogen is used to increase the heat transfer at a surface of
the product 52 and to reduce a boundary layer at the product
surface to increase convective surface heat transfer.
[0022] With all embodiments discussed above with respect to FIGS.
1-3, the products 18, 52 may be for example metal parts and
components, or food products such as for example food items as
large as chicken patties and chicken cutlets. For all the
embodiments described above, the freezer apparatus may be a liquid
cryogen immersion bath, a freezing tunnel, a fluidized bed or any
combination thereof. In that regard, the embodiments also provide
for an "in-line (post-cooling) process", wherein for example the
inlet 48 of the convection tunnel is connected to the outlet 28 of
the immersion freezer 10 and the respective embodiments are
fabricated as modules. The embodiments described above may also be
used on the products 18, 52 that are metallic or alloy products
that require quenching.
[0023] For the convective tunnel embodiment of FIGS. 2 and 3, the
sound waves 80 may actually contact the product 52.
[0024] The embodiments may also be provided with a closed-loop
cryogen delivery system having control valves to enable to
continuous or pulse jets of cryogen flow to the chamber 44, wherein
a portion of the evaporated/sublimed cryogen can be recycled as
additional intake for cryogen impingement.
[0025] During operation of any of the embodiments above, power for
the ultrasound produced by the transducers 20-24, 68, 72, 74 may
have a frequency of approximately 20-200 kiloHertz (kHz), such as
for example 20-30 kHz. The power intensity of the transducers is
also tunable, such as for example tuning to the range of 1-50
kW/m2. The direction of the ultrasonic field emitted from the
transducers 20-24 and 68, 72, 74 and sensors to trigger the
transducers upon entry of the product 18, 52 into the bath 14 or
chamber 44, respectively, can be adjusted depending upon
particulars of the products 18, 52 to be treated. Exposure time for
the products to one pulse of ultrasonic energy would be
approximately a minimum of 0.5 second, while the interval between
ultrasonic energy pulses would be adjusted according to the speed
of advance of the conveyor belt 16, 46. The ultrasonic transducers
20-24 and 68, 72, 74 may be magnetostrictive or piezoelectric. In
certain freezing applications, it may be necessary to precool the
product 18, 52 to a temperature of approximately 1-5.degree. C.
lower than the products freezing point. In a precooling
application, the product 18, 52 could be subcooled to below its
normal freezing point, then ultrasonic energy could be used to
induce a rapid freeze throughout the product.
[0026] It will be understood that the embodiments described herein
are merely exemplary and that a person skilled in the art may make
many variations and modifications without departing from the spirit
and scope of the invention. All such variations and modifications
are intended to be included within the scope of the invention as
described and claimed herein. It should be understood that the
embodiments described herein are not only in the alternative, but
may be combined.
* * * * *