U.S. patent application number 12/302240 was filed with the patent office on 2010-03-11 for pulse electrothermal deicing of complex shapes.
Invention is credited to Victor Petrenko.
Application Number | 20100059503 12/302240 |
Document ID | / |
Family ID | 39402323 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100059503 |
Kind Code |
A1 |
Petrenko; Victor |
March 11, 2010 |
Pulse Electrothermal Deicing Of Complex Shapes
Abstract
A pulse electrothermal deicing apparatus comprises at least one
complex shape characterized by a thickness profile configured to
generate uniform power per unit area to melt an interfacial layer
of ice. A method of optimizing thicknesses of complex shapes for a
pulse electrothermal deicing system includes assigning initial
estimates of the pulse electrothermal deicing system parameters. A
temperature distribution, a temperature range and a refreezing time
produced by a deicing pulse are modeled. Shape thicknesses are
adjusted according to the temperature range, deicing pulse
parameters are adjusted according to the deicing pulse, and the
modeling and adjusting is repeated until the temperature range and
the refreezing time are within predetermined limits.
Inventors: |
Petrenko; Victor; (Lebanon,
NH) |
Correspondence
Address: |
LATHROP & GAGE LLP
4845 PEARL EAST CIRCLE, SUITE 201
BOULDER
CO
80301
US
|
Family ID: |
39402323 |
Appl. No.: |
12/302240 |
Filed: |
May 22, 2007 |
PCT Filed: |
May 22, 2007 |
PCT NO: |
PCT/US2007/069478 |
371 Date: |
March 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60802407 |
May 22, 2006 |
|
|
|
Current U.S.
Class: |
219/507 ;
62/3.1 |
Current CPC
Class: |
H05B 3/84 20130101; F25C
5/08 20130101 |
Class at
Publication: |
219/507 ;
62/3.1 |
International
Class: |
F25D 21/08 20060101
F25D021/08; F25B 21/00 20060101 F25B021/00 |
Claims
1. Pulse electrothermal deicing apparatus comprising at least one
complex shape characterized by a thickness profile configured to
generate uniform power per unit area to melt an interfacial layer
of ice.
2. Pulse electrothermal deicing apparatus of claim 1, further
comprising a power supply and a switch to alternatively connect and
disconnect the power supply from the complex shape.
3. Pulse electrothermal deicing apparatus of claim 1, wherein the
complex shape comprises a cone, and thickness t of the cone varies
according to the t = .rho. I 0 2 4 .pi. 2 x 2 tan 2 ( .theta. ) W
##EQU00007## wherein the cone is characterized by a linear
dimension x along an x-axis and an angle .theta. with respect to
the x axis, and the power supply supplies a current I.sub.0 to
provide a power W per unit area.
4. Pulse electrothermal deicing apparatus of claim 1, wherein the
complex shape comprises a sphere, and thickness t of the sphere
varies according to the equation: t = .rho. I 0 2 4 .pi. 2 R 2 sin
2 ( .theta. ) W ##EQU00008## wherein the sphere is characterized by
a radius R and an angle .theta. with respect to an axis along which
power is supplied, and the power supply supplies a current I.sub.0
to provide a power W per unit area.
5. Pulse electrothermal deicing apparatus of claim 1, wherein the
complex shape comprises a crescent, and thickness t of the sphere
varies according to the equation: t = .rho. I 0 2 4 .pi. 2 R 2 ( x
) W ##EQU00009## wherein the crescent is characterized by a linear
dimension x and an offset value R(x), and the power supply supplies
a current I.sub.0 to provide a power W per unit area.
6. Pulse electrothermal deicing apparatus of claim 1, the complex
shape formed by one of die casting, injection molding, machining,
and successive application of conductive layers.
7. A method of optimizing thicknesses of complex shapes for a pulse
electrothermal deicing system, comprising: assigning size and
geometry to each shape of the pulse electrothermal deicing system
and connectivity of the shapes; assigning initial thicknesses to
each shape; assigning an initial estimate to a deicing pulse
duration; modeling a temperature distribution over the surface of
each shape based upon the deicing pulse duration and the thickness
of each shape; determining a refreezing time for each shape after
application of the deicing pulse; adjusting the thickness of each
shape based upon the modeled temperature distribution if the
modeled temperature distribution is not within a desired tolerance;
adjusting the deicing pulse duration based upon the determined
refreezing time and if the determined refreezing time is not within
defined limits; and repeating the steps of modeling, determining
and adjusting until the temperature distribution is within the
desired tolerance and the refreezing time is within defined
limits.
8. The method of claim 7, the step of adjusting the thickness
comprising: increasing the thickness of the shape where the
temperature distribution is higher than the desired tolerance; and
decreasing the thickness of the shape where the temperature
distribution is lower than the desired tolerance.
9. The method of claim 7, the step of assigning initial thicknesses
to each shape comprising assigning a fixed thickness to each
shape.
10. The method of claim 7, the step of assigning initial
thicknesses to each shape comprising assigning a variable thickness
to each shape.
11. The method of claim 7, the step of adjusting the deicing pulse
duration comprising shortening the duration if the determined
refreezing time is above the defined limits.
12. The method of claim 7, the step of adjusting the deicing pulse
duration comprising lengthening the duration if the determined
refreezing time is below the defined limits.
13. Pulse electrothermal deicing apparatus comprising at least one
axially symmetric complex shape characterized by a thickness
profile configured to generate uniform power per unit area to melt
an interfacial layer of ice.
14. Pulse electrothermal deicing apparatus of claim 13, further
comprising a power supply and a switch to alternatively connect and
disconnect the power supply from the axially symmetric complex
shape.
15. Pulse electrothermal deicing apparatus of claim 13, wherein the
axially symmetric complex shape comprises a cone, and thickness t
of the cone varies according to the equation: t = .rho. I 0 2 4
.pi. 2 x 2 tan 2 ( .theta. ) W ##EQU00010## wherein the cone is
characterized by a linear dimension x along an x-axis and an angle
.theta. with respect to the x axis, and the power supply supplies a
current I.sub.0 to provide a power W per unit area.
16. Pulse electrothermal deicing apparatus of claim 13, wherein the
axially complex shape comprises a sphere, and thickness t of the
sphere varies according to the equation: t = .rho. I 0 2 4 .pi. 2 R
2 sin 2 ( .theta. ) W ##EQU00011## wherein the sphere is
characterized by a radius R and an angle .theta. with respect to an
axis along which power is supplied, and the power supply supplies a
current I.sub.0 to provide a power W per unit area.
17. Pulse electrothermal deicing apparatus of claim 13, wherein the
axially symmetric complex shape comprises a crescent, and thickness
t of the sphere varies according to the equation: t = .rho. I 0 2 4
.pi. 2 R 2 ( x ) W ##EQU00012## wherein the crescent is
characterized by a linear dimension x and an offset value R(x), and
the power supply supplies a current I.sub.0 to provide a power W
per unit area.
18. Pulse electrothermal deicing apparatus of claim 13, the axially
symmetric complex shape formed by one of die casting, injection
molding, machining, and successive application of conductive
layers.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority to
commonly-owned and copending U.S. Provisional Patent Application
No. 60/802,407, filed 22 May 2006. This application is also a
continuation-in-part of commonly-owned and copending
PCT/US2006/002283, filed 24 Jan. 2006, which claims the benefit of
priority to U.S. Provisional Patent Applications Nos. 60/646,394,
filed 24 Jan. 2005, 60/646,932, filed 25 Jan. 2005, and 60/739,506,
filed 23 Nov. 2005. This application is also a continuation-in-part
of commonly-owned and copending U.S. patent application Ser. No.
11/571,231, filed 22 Dec. 2006, which claims the benefit of
priority to PCT/US2005/022035, filed 22 Jun. 2005, which claims the
benefit of priority to U.S. Provisional Patent Applications Nos.
60/581,912, filed 22 Jun. 2004, 60/646,394, filed 24 Jan. 2005, and
60/646,932, filed 25 Jan. 2005. This application is also a
continuation-in-part of commonly-owned and copending U.S. patent
application Ser. No. 11/338,239, filed 24 Jan. 2006, which claims
the benefit of priority to U.S. patent application Ser. No.
10/939,289, now U.S. Pat. No. 7,034,257, filed 10 Sep. 2004, which
is a divisional application that claims the benefit of priority to
U.S. patent application Ser. No. 10/364,438, now U.S. Pat. No.
6,870,139, filed 11 Feb. 2003, which claims the benefit of priority
to U.S. Provisional Patent Applications Nos. 60/356,476, filed 11
Feb. 2002, 60/398,004, filed 23 Jul. 2002, and 60/404,872, filed 21
Aug. 2002. All of the above-identified patent applications are
incorporated herein by reference.
BACKGROUND
[0002] Deicing by melting or detaching ice with electrically
generated heat (Joule heat) has many applications. Some of these
applications benefit from minimizing the energy that is applied to
the ice and/or object to which the ice is adhered. For example,
generation of more heat than is necessary to melt or at least
detach ice requires excess expenditure of energy. In some
applications, such as in ice making or deicing of refrigeration
equipment, the expenditure of extra energy in detaching ice is
especially disadvantageous; not only is the ice melting energy
expended, but still more energy may be expended by a cooling system
to re-cool the part of the system that the ice was detached
from.
SUMMARY
[0003] In one embodiment, a pulse electrothermal deicing apparatus
comprises at least one complex shape characterized by a thickness
profile configured to generate uniform power per unit area to melt
an interfacial layer of ice.
[0004] In one embodiment, a method of optimizing thicknesses of
complex shapes for a pulse electrothermal deicing system includes:
assigning size and geometry to each shape of the pulse
electrothermal deicing system and connectivity of the shapes;
assigning initial thicknesses to each shape; assigning an initial
estimate to a deicing pulse duration; modeling a temperature
distribution over the surface of each shape based upon the deicing
pulse duration and the thickness of each shape; determining a
refreezing time for each shape after application of the deicing
pulse; adjusting the thickness of each shape based upon the modeled
temperature distribution if the modeled temperature distribution is
not within a desired tolerance; adjusting the deicing pulse
duration based upon the determined refreezing time and if the
determined refreezing time is not within defined limits; and
repeating the steps of modeling, determining and adjusting until
the temperature distribution is within the desired tolerance and
the refreezing time is within defined limits.
[0005] In one embodiment, a pulse electrothermal deicing apparatus
comprises at least one axially symmetric complex shape
characterized by a thickness profile configured to generate uniform
power per unit area to melt an interfacial layer of ice.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 shows one exemplary pulse electrothermal deicing
(PETD) apparatus including a flat plate, in accordance with an
embodiment.
[0007] FIG. 2 shows one exemplary PETD apparatus including a
cylinder, in accordance with an embodiment.
[0008] FIG. 3 shows one exemplary PETD apparatus including a cone,
in accordance with an embodiment.
[0009] FIG. 4 shows one exemplary PETD apparatus including a
sphere, in accordance with an embodiment.
[0010] FIG. 5 shows one exemplary PETD apparatus including a
crescent, in accordance with an embodiment.
[0011] FIG. 6 shows a rendition of an exemplary ice tray for a
residential icemaker having an axially symmetric shape.
[0012] FIG. 7 is a flowchart illustrating one exemplary method for
optimizing thicknesses of complex, conductive shapes in a design of
a PETD system, in accordance with an embodiment.
DETAILED DESCRIPTION OF THE DRAWINGS
[0013] Pulse electrothermal deicing (PETD) may be utilized to
separate "ice" from an object by melting at least an interfacial
layer of the ice. As used herein, the term "ice" refers to any of
ice, snow, frost and other forms of frozen water, with or without
admixed substances. An "interfacial layer of ice" shall refer to a
thin layer of ice proximate to the object. Melting of the
interfacial layer of ice is generally sufficient to detach bulk ice
(i.e., the unmelted portion of the ice) from the object. An
interfacial layer of ice may have a thickness of less than about 5
centimeters, preferably less than about 3 centimeters, more
preferably between about one centimeter and one micron, and most
preferably between about one millimeter and one micron. It will be
appreciated that energy applied to heat the interfacial ice will
also heat a portion of the object in contact with the interfacial
ice. It is desirable that heat diffuses a distance of less than
about 5 centimeters into the object and/or ice, preferably less
than about 3 centimeters into the object and/or ice, more
preferably between about one centimeter and one micron into the
object and/or ice, and most preferably between about one millimeter
and one micron into the object and/or ice.
[0014] Energy expended during PETD is advantageously minimized by
providing a uniformly melted interfacial layer. Excessively thick
melted interfacial layers correspond to higher deicing
temperatures, and represent wasted energy in the deicing process;
that is, more energy is applied than is needed to separate bulk ice
from the object. For example, in an icemaker, a "hot spot" created
during deicing requires re-cooling, after deicing, before ice
making can resume at that spot; this lowers yield of the ice making
process by melting more of the intended product than necessary.
Excessively thin melted interfacial layers correspond to a risk
that the bulk ice will refreeze to the object before the ice can be
removed.
[0015] In order to optimize energy expenditure for deicing, an
apparatus utilizing PETD should provide an approximately constant
density of heating power per surface area of the interfacial ice
layer. However, a constant density of heating power per surface
area can be difficult to achieve when an object to be deiced has a
complex shape. As used herein, a "complex shape" is a portion of an
object having one or more non-uniformly thick walls. The complex
shape can be described by a "thickness profile", which defines the
thickness of the wall over a distance (e.g., from one point on the
object to another point on the object).
[0016] A heating layer of an object is characterized by an
electrical resistivity .rho. and a thickness t. When heating power
per unit area W (in W/m.sup.2) is applied, the following
relationship applies:
W = E I S = E 2 t .rho. = .rho. I S 2 t Eq . ( 1 ) ##EQU00001##
where E is an electric field strength (V/m) developed through the
heating layer by the application of an electric current density
I.sub.S (A/m). In order to keep W constant at various portions of
the heating layer, the following relationship further applies:
t = W .rho. E 2 or t = .rho. I S 2 W Eq . ( 2 ) ##EQU00002##
[0017] Equation (2) is approximate because it does not take into
account dependence of heat capacitance of the heating layer on the
object thickness. However, Eq. (2) is very useful because heat
capacitance is usually a very small term in total PETD energy
requirements as compared to heat capacitance of ice, underlying
structure, and latent heat of the melted interfacial ice layer.
[0018] FIG. 1 shows one exemplary PETD apparatus 10(1) including a
flat plate 40(1). FIG. 1 may not be drawn to scale. A power supply
20(1) connects to flat plate 40(1) through a switch 30(1) to supply
power to plate 40(1) for deicing. Length L and thickness t of plate
40(1) are indicated in FIG. 1. Where power supply 20(1) supplies a
voltage V, the power W supplied by power supply 20(1) may be
expressed in terms of power per unit area as:
W = V 2 t .rho. L 2 Eq . ( 3 ) ##EQU00003##
[0019] FIG. 2 shows one exemplary PETD apparatus 10(2) including a
cylinder 40(2). FIG. 2 may not be drawn to scale. A power supply
20(2) connects to cylinder 40(2) through a switch 30(2) to supply
power to cylinder 40(2) for deicing. Length L and thickness t of
cylinder 40(2) are indicated in FIG. 2. Where power supply 20(2)
supplies a voltage V, the power W supplied by power supply 20(2)
may be expressed in terms of power per unit area as shown in Eq.
(3), which describes objects having constant thickness.
[0020] FIG. 3 shows a cross-section of one exemplary PETD apparatus
10(3) including a cone 40(3). FIG. 3 may not be drawn to scale. A
power supply 20(3) connects through a switch 30(3) to supply power
to cone 40(3) for deicing. A linear dimension x, an angle .theta.
with respect to the x axis, and a thickness t of cone 40(3) are
indicated in FIG. 3. Note that thickness t varies with position
along the x axis of cone 40(3). Where power supply 20(3) supplies a
voltage V and a current I.sub.0, thickness t, required to provide a
constant power W per unit area, may be expressed as:
t = .rho. I 0 2 4 .pi. 2 x 2 tan 2 ( .theta. ) W Eq . ( 4 )
##EQU00004##
[0021] FIG. 4 shows a cross-section of one exemplary PETD apparatus
10(4) including a sphere 40(4). FIG. 4 may not be drawn to scale. A
power supply 20(4) connects to sphere 40(4) through a switch 30(4)
to supply power to sphere 40(4) for deicing. A radius R, an angle
.theta. with respect to an axis along which power is supplied, and
a thickness t of sphere 40(4) are indicated in FIG. 4. Note that
thickness t of sphere 40(4) varies with angle .theta.. Where power
supply 20(4) supplies a voltage V and a current I.sub.0, thickness
t, required to provide a constant power W per unit area, may be
expressed as:
t = .rho. I 0 2 4 .pi. 2 R 2 sin 2 ( .theta. ) W Eq . ( 5 )
##EQU00005##
[0022] FIG. 5 shows one exemplary PETD apparatus 10(5) including a
crescent 40(5). FIG. 5 may not be drawn to scale. Crescent 40(5)
may be generated by revolving a line about an axis of rotation.
Such shapes may be useful, for example, in icemakers wherein a
shape is (1) filled with liquid water, (2) cooled until the water
freezes to form ice, (3) rotated so that the ice faces downward,
and (4) heated with a deicing pulse to release the ice from the
shape. A power supply 20(5) connects through a switch 30(5) to
supply power to crescent 40(5) for deicing. A linear dimension x,
an offset value R(x) that is a function of position on the x axis,
and a thickness t of crescent 40(5) are indicated in FIG. 5. Note
that thickness t of shape 40(5) varies with R(x). It can be shown
that if power supply 20(5) supplies a voltage V and current
I.sub.0, thickness t, required to provide a constant power W per
unit area, may be expressed as:
t = .rho. I 0 2 4 .pi. 2 R 2 ( x ) W Eq . ( 6 ) ##EQU00006##
[0023] Several technologies may be utilized to manufacture any of
the shapes 40 described above, including but not limited to die
casting, injection molding, consecutive applications of conductive
paint or other coatings and machining.
[0024] FIG. 6 shows a rendition of an ice tray 50 for a residential
icemaker. An icemaker utilizing ice tray 50 may be made of a
thermally and electrically conductive composite material, such as
E5101 by CoolPolymers, Inc. An inner shape 40(6) of ice tray 50 is
axially symmetric. To form ice, tray 50 is disposed with inner
shape 40(6) facing upward. Tray 50 is then filled with water. After
the water freezes into ice, tray 50 is rotated about its long axis
by about 120.degree. and a two second pulse of electrical power is
applied across copper bus bars disposed on terminal ends 60(1),
60(2) of tray 50. The electrical power heats tray 50 uniformly to a
temperature just above the melting point of the ice, thus melting
an interfacial layer of the ice. The ice then slides off tray 50
and into a collection bin (not shown). It is appreciated that tray
50 includes a complex, variable thickness. The thickness may be
calculated utilizing Eq. (6), then the thickness may be adjusted at
certain locations, such as corners, according to a method described
below.
[0025] FIG. 7 is a flowchart illustrating one exemplary method 100
for optimizing thicknesses of complex, conductive shapes in a PETD
system design. It will be appreciated that some or all of the steps
illustrated in FIG. 7 may be performed by a computer under control
of software instructions; alternatively, some or all of the steps
of FIG. 7 may be performed by a human. In step 102, method 100
assigns a size and geometry type to each shape of the deicing
system, and connections among the shapes. In step 104, method 100
assigns an initial thickness configuration to each shape; such
configuration may include a fixed thickness (e.g., as shown in
FIGS. 1 and 2, and Eq. (3)) and/or a thickness that varies as a
function of position and/or angle (e.g., as shown in FIGS. 3-5 and
Eqs. (4)-(6)) where the shape is complex. In step 106, deicing
pulse parameters, such as voltage or current supplied, and an
initial estimate of a deicing pulse duration are assigned. In step
108, a temperature distribution, a temperature range and a
refreezing time achieved for the specified shapes with the
specified deicing pulse are determined. Step 108 may be performed,
for example, utilizing finite element method modeling using a
package such as FEMLAB 3.1 by Comsol, Inc. Step 110 is a decision
that determines whether or not the temperature range is within a
specified tolerance. If the temperature range is outside of the
specified tolerance (i.e., there is a larger than desired
difference between the lowest temperature and the highest
temperature generated by the deicing pulse), then shapes are
thickened or thinned in steps 112 and 114 according to whether the
modeled temperature of the shape is too high or too low,
respectively. Step 116 is a decision. In step 116, the refreezing
time is compared to specified minimum and maximum limits. If the
refreezing time is too short (i.e., below the specified minimum
limit), the deicing pulse is lengthened in step 118; if the
refreezing time is too long (i.e., above the specified maximum),
the deicing pulse is shortened in step 120. It will be appreciated
that power parameters of the deicing pulse may also be modified,
such as to provide more or less power, instead of or in addition to
changing the duration of the deicing pulse. If any of the shape
thicknesses and the refreezing times changed in steps 112, 114, 118
and/or 120, the method returns to step 108; otherwise, the method
finishes and outputs a set of optimized thickness and deicing pulse
parameters in step 122.
[0026] The changes described above, and others, may be made in the
pulse electrothermal deicers for complex shapes and associated
methods described herein without departing from the scope hereof.
For example, variations in heating may be provided by varying
electrical resistivity, as opposed to thicknesses of, complex
shapes. The principles described herein are also applicable to
configurations such as evaporator plates of refrigeration or air
conditioning systems that may require periodic deicing. It should
thus be noted that the matter contained in the above description or
shown in the accompanying drawings should be interpreted as
illustrative and not in a limiting sense. The following claims are
intended to cover all generic and specific features described
herein, as well as all statements of the scope of the present
methods and systems, which, as a matter of language, might be said
to fall there between.
* * * * *