US20100059503 Pulse Electrothermal Deicing (PETD) of Complex Shapes Application (IceMakers)

8/7/2019 US20100059503 Pulse Electrothermal Deicing (PETD) of Complex Shapes Application (IceMakers)

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1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1us 20100059503Al(19) United States(12) Patent Application PublicationPetrenko (10) Pub. No.: US 2010/0059503 Al(43) Pub. Date: Mar. 11,2010(54) PULSE ELECTROTHERMAL DEICING OF

COMPLEX SHAPES(76) Inventor: Victor Petrenko, Lebanon, NH(US)

Correspondence Address:LATHROP & GAGE LLP4845 PEARL EAST CIRCLE, SUITE 201BOULDER, CO 80301 (US)

(21) Appl. No.: 12/302,240(22) PCTFiled: May 22, 2007(86) PCTNo.: PCT /uS2007 /069478

371 (c)(I),(2), (4) Date: Mar. 20, 2009

Related U.S. Application Data(60) Provisional application No. 60/802,407, filed on May

22,2006.

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(51)Publication Classification

Int . Cl.F2SD 21108F2SB 21100

(2006.01)(2006.01)

(52) U.S. Cl. 219/507; 62/3.1

(57) ABSTRACTA pulse electrothermal deicing apparatus comprises at leastone complex shape characterized by a thickness profi le con-figured to generate uniform power per unit area to melt aninterfacial layer of ice. A method of optimizing thicknesses ofcomplex shapes for a pulse electrothermal deicing systemincludes assigning initial estimates of the pulse electrother-mal deicing system parameters. A temperature distribution, atemperature range and a refreezing time produced by a deic-ing pulse are modeled. Shape thicknesses are adjustedaccording to the temperature range, deicing pulse parametersare adjusted according to the deicing pulse, and the modelingand adjusting is repeated until the temperature range and therefreezing time are within predetermined limits.

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Patent Application Publication Mar. 11, 2010 Sheet 4 of 4

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ASSIGN SIZE, GEOMETRY, CONNECTION OF SHAPES

ASSIGN INITIAL THICKNESS CONFIGURATION TO EACH SHAPE

ASSIGN INITIAL ESTIMATE OF DEICING PULSE DURATION

DETERMINE TEMPERATURE DISTRIBUTION 108AND REFREEZING TIME ACHIEVED

WITH DEICING PULSE

110 >--yES,----,

N O112 THICKEN SHAPES IN AREAS MODELED AS

REACHING HIGHER TEMPERATURE

114 THIN SHAPES IN AREAS MODELED ASREACHING LOWER TEMPERATURE

W IT HIN L IM ITA B O V E

M A XIM U M LIM IT

B E L O W 122M IN IM U M L IM ITSHORTENDEICING PULSE

118LENGTHENDEICING PULSE

FIG . 7

DESIGNCOMPLETEOUTPUTOPTIMIZEDDESIGN


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PULSE ELECTROTHERMAL DEICING OFCOMPLEX SHAPES

RELATED APPLICATIONS[0001] This application claims the benefit of priority tocommonly-owned and copending U.S. Provisional PatentApplication No. 60/802,407, fi led 22 May 2006. This appli-cation is also a continuation-in-part of commonly-owned andcopending PCT/US2006/002283, filed 24 Jan. 2006, whichclaims the benefit of priority toU.S. Provisional Patent Appli-cations Nos. 60/646,394, filed 24 Jan. 2005, 60/646,932, filed25 Jan. 2005, and 601739,506, filed 23 Nov. 2005. This appli-cation is also a continuation-in-part of commonly-owned andcopending U.S. patent application Ser. No. 11/571,231, filed22 Dec. 2006, which claims the benefit of priority to PCTIUS2005/022035, filed 22 Jun. 2005, which claims the benefitof 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 isalso a continuation-in-part of commonly-owned and copend-ing U.S. patent application Ser. No. 11/338,239, filed 24 Jan.2006, which claims the benefit of priority to U.S. patentapplication Ser. No. 101939,289, now U.S. Pat. No. 7,034,257, filed 10 Sep. 2004, which is a divisional application thatclaims 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. ProvisionalPatent 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 areincorporated herein by reference.

BACKGROUND[0002] Deicing by melting or detaching ice with electri-cally generated heat (Joule heat) has many applications.Some of these applications benefit from minimizing theenergy that is applied to the ice and/or object to which the iceis adhered. For example, generation of more heat than isnecessary to melt or at least detach ice requires excess expen-diture of energy. In some applications, such as in ice makingor deicing of refrigeration equipment, the expenditure ofextra energy in detaching ice is especially disadvantageous;not only is the ice melting energy expended, but still moreenergy may be expended by a cooling system to re-cool thepart of the system that the ice was detached from.

SUMMARY[0003] In one embodiment, a pulse electrothermal deicingapparatus comprises at least one complex shape characterizedby a thickness profile configured to generate uniform powerper unit area to melt an interfacial layer of ice.[0004] In one embodiment, a method of optimizing thick-nesses of complex shapes for a pulse electrothermal deicingsystem includes: assigning size and geometry to each shapeof the pulse electrothermal deicing system and counectivityof the shapes; assigning initial thicknesses to each shape;assigning an initial estimate to a deicing pulse duration; mod-eling a temperature distribution over the surface of each shapebased upon the deicing pulse duration and the thickness ofeach shape; determining a refreezing time for each shape afterapplication of the deicing pulse; adjusting the thickness ofeach shape based upon the modeled temperature distributionifthe modeled temperature distribution isnot within a desired

Mar. 11,20101

tolerance; adjusting the deicing pulse duration based upon thedetermined refreezing time and if the determined refreezingtime is not within defined limits; and repeating the steps ofmodeling, determining and adjusting unti l the temperaturedistribution is within the desired tolerance and the refreezingtime is within defined limits.[0005] In one embodiment, a pulse electrothermal deicingapparatus comprises at least one axially symmetric complexshape characterized by a thickness profile configured to gen-erate uniform power per unit area to melt an interfacial layerof ice.

BRIEF DESCRIPTION OF THE DRAWINGS[0006] FIG. 1 shows one exemplary pulse electrothermaldeicing (PETD) apparatus including a flat plate, in accor-dance with an embodiment.[0007] FIG. 2 shows one exemplary PETD apparatusincluding a cylinder, in accordance with an embodiment.[0008] FIG. 3 shows one exemplary PETD apparatusincluding a cone, in accordance with an embodiment.[0009] FIG. 4 shows one exemplary PETD apparatusincluding a sphere, in accordance with an embodiment.[0010] FIG. 5 shows one exemplary PETD apparatusincluding a crescent, in accordance with an embodiment.[0011] FIG. 6 shows a rendition of an exemplary ice tray fora residential icemaker having an axially symmetric shape.[0012] FIG. 7 is a flowchart illustrating one exemplarymethod for optimizing thicknesses of complex, conductiveshapes in a design of a PETD system, in accordance with anembodiment.DETAILED DESCRIPTION OF THE DRAWINGS

[0013] Pulse electrothermal deicing (PETD) may be uti-lized to separate "ice" from an object by melting at least aninterfacial layer of the ice. As used herein, the term "ice"refers to any of ice, snow, frost and other forms of frozenwater, with or without admixed substances. An "interfaciallayer of ice" shall refer to a thin layer of ice proximate to theobject. Melting of the interfacial layer of ice is generallysufficient to detach bulk ice (i.e., the unmelted portion of theice) from the object. An interfacial layer of ice may have athickness of less than about 5 centimeters, preferably lessthan about 3 centimeters, more preferably between about onecentimeter and one micron, and most preferably betweenabout one mill imeter and one micron. Itwill be appreciatedthat energy applied to heat the interfacial ice will also heat aportion of the object in contact with the interfacial ice. Itisdesirable that heat diffuses a distance of less than about 5centimeters into the object and/or ice, preferably less thanabout 3 centimeters into the object and/or ice, more prefer-ably between about one centimeter and one micron into theobject and/or ice, and most preferably between about onemillimeter and one micron into the object and/or ice.[0014] Energy expended during PETD is advantageouslyminimized by providing a uniformly melted interfacial layer.Excessively thick melted interfacial layers correspond tohigher deicing temperatures, and represent wasted energy inthe deicing process; that is, more energy is applied than isneeded to separate bulk ice from the object. For example, inan icemaker, a "hot spot" created during deicing requiresre-cooling, after deicing, before ice making can resume at thatspot; this lowers yield of the ice making process by meltingmore ofthe intended product than necessary. Excessively thin


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melted interfacial layers correspond to a risk that the bulk icewill 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 approxi-mately constant density of heating power per surface area ofthe interfacial ice layer. However, a constant density of heat-ing power per surface area can be difficult to achieve when anobject to be deiced has a complex shape. As used herein, a"complex shape" is a portion of an object having one or morenon-uniformly thick walls. The complex shape can bedescribed by a "thickness profi le", which defines the thick-ness of the wall over a distance (e.g., from one point on theobject to another point on the object) .[0016] A heating layer of an object is characterized by anelectrical resistivity p and a thickness t. When heating powerper unit area W (in W/m2) is applied, the following relation-ship applies:

2.( p.l~W=ls=-=-P tEq. (1)

where E is an electric field strength (Vim) developed throughthe heating layer by the application of an electric currentdensity Is (Aim). In order to keep W constant at variousportions of the heating layer, the following relationship fur-ther applies:

Wp p.l~(=- or(=-2 WEq. (2)

[0017] Equation (2) is approximate because it does not takeinto account dependence of heat capacitance of the heatinglayer on the object thickness. However, Eq. (2) is very usefulbecause heat capacitance is usually a very small term in totalPETD energy requirements as compared to heat capacitanceof ice, underlying structure, and latent heat of the meltedinterfacial 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 aswitch 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 powerW supplied by power supply 20(1) may be expressed intermsof power per unit area as:

Eq. (3)

[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 aswitch 30(2) to supply power to cylinder 40(2) for deicing.Length L and thickness t of cylinder 40(2) are indicated inFIG. 2. Where power supply 20(2) supplies a voltage V , thepower W supplied by power supply 20(2) may be expressed interms of power per unit area as shown in Eq. (3), whichdescribes objects having constant thickness.

Mar. 11,20102

[0020] FIG. 3 shows a cross-section of one exemplaryPETD apparatus 10(3) including a cone 40(3). FIG. 3 may notbe drawn to scale. A power supply 20(3) connects through aswitch 30(3) to supply power to cone 40(3) for deicing. Alinear dimension x, an angle 8 with respect to the x axis, anda thickness t of cone 40(3) are indicated in FIG. 3. Note thatthickness t varies with position along the x axis of cone 40(3).Where power supply 20(3) supplies a voltage V and a current10 ' thickness t, required to provide a constant power W perunit area, may be expressed as:

(= p.ll;4 7 , , 0 2 - . x 0 2 : - . - ta n " " ' 2 " ( e " ' )- . W ; ; -;Eq. (4)

[0021] FIG. 4 shows a cross-section of one exemplaryPETD apparatus 10(4) including a sphere 40(4). FIG. 4 maynot be drawn to scale. A power supply 20(4) connects tosphere 40(4) through a switch 30(4) to supply power to sphere40(4) for deicing. A radius R, an angle 8 with respect to anaxis along which power is supplied, and a thickness t ofsphere 40(4) are indicated in FIG. 4. Note that thickness t ofsphere 40(4) varies with angle 8.Where power supply 20(4)supplies a voltage V and a current 10 ' thickness t, required toprovide a constant power W per unit area, may be expressedas:

p.ll;t = - ' - 4 , , - - : : 2 - . R - ' 2 ' - . - ' s i " " ' n 2 ; - ( e - ' - - ) - . W -

Eq. (5)

[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 anaxis of rotation. Such shapes may be useful, for example, inicemakers wherein a shape is (I) filled with liquid water, (2)cooled until the water freezes to form ice, (3) rotated so thatthe ice faces downward, and (4) heated with a deicing pulse torelease the ice from the shape. A power supply 20(5) connectsthrough a switch 30(5) to supply power to crescent 40(5) fordeicing. A linear dimension x, an offset value R(x) that is afunction ofposit ion on the x axis, and a thickness t ofcrescent40(5) are indicated in FIG. 5. Note that thickness t of shape40(5) varies with R(x). It can be shown that if power supply20(5) supplies a voltage V and current 10 ' thickness t, requiredtoprovide a constant power W per unit area, may be expressedas:

pll;(= 74,,02-.R " " ' 2 . - : ' ( x - - ' - ) - - ; .W . , . ,

Eq. (6)

[0023] Several technologies may be utilized to manufac-ture any of the shapes 40 described above, including but notl imited to die casting, injection molding, consecutive appli-cations of conductive paint or other coatings and machining.[0024] FIG. 6 shows a rendition of an ice tray 50 for aresidential icemaker. Anicemakeruti lizing ice tray 50 may bemade of a thermally and electrically conductive compositematerial, such as E5101 by CoolPolymers, Inc. An innershape 40(6) of ice tray 50 is axially symmetric. To form ice,tray 50 is disposed with inner shape 40(6) facing upward.


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Tray 50 is then filled with water. After the water freezes intoice, tray 50 is rotated about its long axis by about 1200 and atwo second pulse of electrical power is applied across copperbus bars disposed on terminal ends 60(1), 60(2) of tray 50.The electrical power heats tray 50 uniformly to a temperaturejust above the melting point of the ice, thus melting an inter-facial layer of the ice. The ice then slides off tray 50 and intoa collection bin (not shown). It is appreciated that tray 50includes a complex, variable thickness. The thickness may becalculated utilizing Eq. (6), then the thickness may beadjusted at certain locations, such as comers, according to amethod described below.[0025] FIG. 7 is a flowchart illustrating one exemplarymethod 100 for optimizing thicknesses of complex, conduc-tive shapes in a PETD system design. Itwill be appreciatedthat some or all of the steps illustrated in FIG. 7 may beperformed by a computer under control of software instruc-tions; alternatively, some or all of the steps of FIG. 7 may beperformed by a human. In step 102, method 100 assigns a sizeand geometry type to each shape of the deicing system, andconnections among the shapes. In step 104, method 100assigns an initial thickness configuration to each shape; suchconfiguration may include a fixed thickness (e.g., as shown inFIGS. 1and 2, and Eq. (3)) and/or a thickness that varies as afunction of position and/or angle (e.g. , as shown in FIGS. 3-5and 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 areassigned. In step 108, a temperature distribution, a tempera-ture range and a refreezing time achieved for the specifiedshapes with the specified deicing pulse are determined. Step108 may be performed, for example, uti lizing finite elementmethod modeling using a package such as FEMLAB 3.1 byComsol, Inc. Step 110 is a decision that determines whetheror not the temperature range iswithin a specified tolerance. Ifthe temperature range is outside of the specified tolerance(i.e., there is a larger than desired difference between thelowest temperature and the highest temperature generated bythe deicing pulse), then shapes are thickened or thinned insteps 112 and 114 according to whether the modeled tem-perature of the shape istoo high or too low, respectively. Step116 is a decision. In step 116, the refreezing time is comparedto specified minimum and maximum limits. Ifthe refreezingtime istoo short (i.e., below the specified minimum limit), thedeicing pulse is lengthened in step 118; if the refreezing timeis too long (i.e., above the specified maximum), the deicingpulse is shortened in step 120. Itwill be appreciated thatpower parameters of the deicing pulse may also be modified,such asto provide more or less power, instead of or inadditionto changing the duration of the deicing pulse. Ifany of theshape thicknesses and the refreezing times changed in steps112, 114, 118 and/or 120, the method returns to step 108;otherwise, the method finishes and outputs a set of optimizedthickness and deicing pulse parameters in step 122.[0026] The changes described above, and others, may bemade in the pulse electrothermal deicers for complex shapesand associated methods described herein without departingfrom the scope hereof. For example, variations inheating maybe provided by varying electrical resistivity, as opposed tothicknesses of, complex shapes. The principles describedherein are also applicable to configurations such as evapora-tor plates of refrigeration or air conditioning systems that mayrequire periodic deicing. It should thus be noted that thematter contained in the above description or shown in the

Mar. 11,20103

accompanying drawings should be interpreted as illustrativeand not in a limiting sense. The following claims are intendedto cover all generic and specific features described herein, aswell as all statements of the scope of the present methods andsystems, which, as a matter of language, might be said to fallthere between.What is claimed is:1. Pulse electrothermal deicing apparatus comprising at

least one complex shape characterized by a thickness profi leconfigured to generate uniform power per unit area to melt aninterfacial layer of ice.2. Pulse electrothermal deicing apparatus of claim 1, fur-

ther comprising a power supply and a switch to alternativelyconnect and disconnect the power supply from the complexshape.3. Pulse electrothermal deicing apparatus of claim 1,

wherein the complex shape comprises a cone, and thickness tof the cone varies according to the

p./6t = - ; - 4 n ' 2 - . x - ' 2 : - - . - ta n - ' o 2 ; - C ( e - : : C ) - . w " " '

wherein the cone is characterized by a linear dimension xalong an x-axis and an angle 8 with respect to the x axis,and the power supply supplies a current 1 0 to provide apower W per unit area.

4. Pulse electrothermal deicing apparatus of claim 1,wherein the complex shape comprises a sphere, and thicknesst of the sphere varies according to the equation:

p./6t = -C4 n - -= 2 - . -R " - 2 . : s - : - ' i n C c 2 - - = ( e - ) . - w -

wherein the sphere is characterized by a radius R and anangle 8 with respect to an axis along which power issupplied, and the power supply supplies a current 1 0 toprovide a power W per unit area.

5. Pulse electrothermal deicing apparatus of claim 1,wherein the complex shape comprises a crescent, and thick-ness t of the sphere varies according to the equation:

p/6t = - ; - 4 n ' 2 - '- . R " " ' 2 " ' (x ' - c )- - o .w '"

wherein the crescent is characterized by a linear dimensionx and an offset value R(x), and the power supply suppliesa current 1 0 to provide a power W per unit area.

6. Pulse electrothermal deicing apparatus of claim 1, thecomplex shape formed by one of die casting, injection mold-ing, machining, and successive application of conductive lay-ers.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 pulseelectrothermal deicing system and connectivity of theshapes;

assigning initial thicknesses to each shape;assigning an initial estimate to a deicing pulse duration;


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modeling a temperature distribution over the surface ofeach shape based upon the deicing pulse duration andthe thickness of each shape;

determining a refreezing time for each shape after applica-t ion of the deicing pulse;adjusting the thickness of each shape based upon the mod-eled temperature distribution if the modeled temperaturedistribution is not within a desired tolerance;

adjusting the deicing pulse duration based upon the deter-mined refreezing time and if the determined refreezingtime is not within defined limits; and

repeating the steps of modeling, determining and adjustingunti l the temperature distribution is within the desiredtolerance and the refreezing time is within defined lim-its.

8. The method of claim 7, the step of adjusting the thick-ness comprising:increasing the thickness of the shape where the tempera-ture distribution is higher than the desired tolerance; and

decreasing the thickness of the shape where the tempera-ture distribution is lower than the desired tolerance.

9. The method of claim 7, the step of assigning initialthicknesses to each shape comprising assigning a fixed thick-ness to each shape.10. The method of claim 7, the step of assigning initial

thicknesses to each shape comprising assigning a variablethickness to each shape.11. The method of claim 7, the step of adjusting the deicing

pulse duration comprising shortening the duration if thedetermined 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 thedetermined refreezing time is below the defined limits.13. Pulse electrothermal deicing apparatus comprising atleast one axially symmetric complex shape characterized by a

thickness profile configured to generate uniform power perunit 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 alterna-tively connect and disconnect the power supply from theaxially symmetric complex shape.

Mar. 11,20104

15. Pulse electrothermal deicing apparatus of claim 13,wherein the axially symmetric complex shape comprises acone, and thickness t of the cone varies according to theequation:

t = p./6- ; - 4 n 0 2 - . x - ' 2 C - . -ta n - " o 2 " ( e " ' ) - . w ; ; - ;

wherein the cone is characterized by a linear dimension xalong an x-axis and an angle 8 with respect to the x axis,and the power supply supplies a current 1 0 to provide apower W per unit area.16. Pulse electrothermal deicing apparatus of claim 13,wherein the axially complex shape comprises a sphere, andthickness t of the sphere varies according to the equation:

p./6t = -4 n -C2 -. - R " -2 . : s - - ' i n C c 2 - ( e - ) . - w -

wherein the sphere is characterized by a radius R and anangle 8 with respect to an axis along which power issupplied, and the power supply supplies a current 1 0 toprovide a power W per unit area.17. Pulse electrothermal deicing apparatus of claim 13,wherein the axially symmetric complex shape comprises acrescent, and thickness t of the sphere varies according to theequation:

t = p./6- ; - 4 n 0 2 - ' - . R " " , 2 , c (x ' - : -) - - ;.w ""

wherein the crescent is characterized by a linear dimensionx and an offset value R(x), and the power supply suppliesa current 1 0 to provide a power W per unit area.18. Pulse electrothermal deicing apparatus of claim 13, theaxially symmetric complex shape formed by one of die cast-ing, injection molding, machining, and successive applica-tion of conductive layers.* * * * *

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US20100059503 Pulse Electrothermal Deicing (PETD) of Complex Shapes Application (IceMakers)