Heating system for defrosting household appliances, method of manufacturing a resistive element and household appliance

Abstract

The present invention refers to a heating system (10) for defrosting household appliances (20), to a method (100) of manufacturing a resistive element (1) of a heating system (10) for defrosting household appliances (20) and to a household appliance (20). The heating system (10) comprising: a resistive element (1); a sealed protective tube (2) encapsulating the resistive element (1) and an electrically insulating material (3) therewith; and an electric terminal (4) attached to at least one end of the resistive element (1 ), wherein the power density (P) of the resistive element (1 ) is variable along the length (L) of the resistive element (1) as a function of at least one geometric feature of the resistive element (1).

Description

[0001] HEATING SYSTEM FOR DEFROSTING HOUSEHOLD APPLIANCES, METHOD OF MANUFACTURING A RESISTIVE ELEMENT AND HOUSEHOLD APPLIANCE

[0002] FIELD OF THE INVENTION

[0003] The present invention refers, in a general manner, to a heating system for defrosting components of household appliances, a method of manufacturing a resistive element of the heating system and a household appliance comprising such heating system to defrost its components. In particular, the power density of the resistive element is variable along its length as a function of at least one geometric feature of the resistive element.

[0004] BACKGROUND OF THE INVENTION

[0005] Heating systems for defrosting household appliances have long been known in the art. These heating systems are usually applied to whitegoods, such as frost-free refrigerators, and operate based on the Joule effect, which is globally defined by the following equation:

[0006] Q = I2Rt (i)

[0007] Wherein Q is the amount of heat, measured in Joules, dissipated by the resistive element; I is the electric current, measured in Amperes, applied throughout the resistive element; R is the resistance of the resistive element, measured in Ohms to the flow of the electric current; and t is the time interval, measured in seconds, in which the electric current I is applied to the resistive element.

[0008] In straightforward terms, the Joule effect is caused by the flow of electrons e~ along the resistive element, which is usually induced by applying the electric current I on either end of the resistive element.

[0009] These resistive elements are usually made of metallic alloys and are shaped as coils, having constant pitch and constant helical diameter throughout their length, which is then fitted inside a sealed protective tube and filled with an electrically insulating material, usually magnesium oxide. An electric terminal at the end of the resistive element is configured to apply the electric current I that induces the Joule effect on the latter, causing it to melt the ice buildup on the evaporator of the frost-free refrigerators and on the freezer.

[0010] However, in these known heating systems, due to the constant pitch and constant helical diameter of the resistive elements which can be verified from Figure 3a, the power density P, measured in Watt / meter, is constant, while the temperature distribution throughout its length is not constant. In fact, when the power density P is constant, the temperature distribution is totally non-linear and is influenced by how efficiently heat is dissipated from the resistive element to its surroundings. In this regard, different sections of the heating system may have varying efficiencies in heat dissipation due to many parameters, such as their specific position relative to the evaporator, exposure to airflow or contact with heat sinks or heat sources, natural convection, and surface emissivity.

[0011] In other words, there are zones of thermal variance a in the volume comprising the evaporator and the heating system, which varies from case to case in each household appliance. These zones of thermal variance a result in the nonlinearity of the temperature distribution throughout the resistive element’s length.

[0012] Taking for example the resistive element of the prior art, illustrated in Fig. 3a, having a constant pitch Xn, and constant diameter d, the helical length L is also constant, according to the equation below:

[0013] Therefore, the incremental contribution of dissipated power Q in each pitch is also constant, according to the equation below: likewise, the power density P will also be constant, according to the equation below:

[0014] P = 7 [— ] (4) LLmJ

[0015] Another deficiency of the heating systems of the prior art is that the loss in efficiency due to the zones of thermal variance a inducing the non-linearity in the temperature distribution along the resistive element increases the defrost time and further results in a heterogeneous defrost.

[0016] An additional deficiency of the heating systems of the prior art is that the resistance R of most conductive materials which the resistive elements are made of, increases with temperature, creating hot spots in which the temperature is higher and in which the resistance R is even higher than initially designed. This leads to a reduction in power and higher energy loss in the form of / 2 / ?, thereby increasing the overall energy consumption of the heating system.

[0017] A further limitation is that in Europe, particularly for heating systems applied to evaporators of frost-free refrigerators using hydrocarbon refrigerant R600A, the International Electrotechnical Commission - IEC, establishes on standard IEC 60335-1 that the temperature limit in any part of the heating system must be up to 360°C, instead of the current limit of 394°C. In Brazil, this will also come into force after 2026.

[0018] The issue of the heating systems of the prior art is that in order to have an adequate defrost power without overpassing the new IEC temperature limit of 360°C there are two alternatives: the first one without cost impact is to maintain the current resistive element’s length but at the expense of a reduction of the total power that will impact in the degradation of the defrost performance because to maintain the same defrost energy measured in Joules, it will be necessary to increase the defrost time; and the second alternative would be an increase in the length of the heating system to confine a bigger resistive element to reduce the surface temperature with the same energy, therefore increasing the cost of manufacturing such heating systems.

[0019] In view of the above, it is clear that the state of the art lacks technological innovations in heating systems, particularly for defrosting household appliances.

[0020] It is also evident that both the industry and consumers would benefit from an energy-saving heating system with a homogenous temperature distribution, which is reliable, offers improved performance and can help avoid cost impacts.

[0021] PURPOSES AND DESCRIPTION OF THE INVENTION

[0022] Thus, a first general objective of the present invention is to provide a heating system for defrosting household appliances capable of eliminating or at least reducing the limitations of currently known techniques.

[0023] A particular objective of the present invention is to provide the heating system that accounts for the non-linear zones of thermal variance a in the volume comprising the heating system and a component of the household appliance, which is subjected to thermal variation to output a linear temperature distribution throughout the resistive element’s length.

[0024] Further, the present invention has the purpose of providing the heating system which offers a higher defrost efficiency when compared to the heating systems of the prior art, decreasing the defrost time and resulting in a homogeneous defrost.

[0025] It is also a purpose of the invention to provide an energy-saving heating system that, due to the linear temperature distribution, maximizes the power, decreases the defrost time, increasing in this way the defrost performance, and contributes to the overall reduction in energy consumption of the appliance. An alternative objective of the present invention is to provide a heating system compliant with the current version of the IEC standard 60335-1 without incurring great cost impacts.

[0026] A second general objective of the present invention is to provide a method of manufacturing the resistive element of the heating system for defrosting household appliances capable of eliminating or at least reducing the limitations and deficiencies of the prior art.

[0027] A particular objective of the present invention is to provide the method of manufacturing the resistive element that accounts for the zones of thermal variance a in the volume comprising the heating system and the component of the household appliance which is subjected to thermal variation to output a linear temperature distribution throughout the resistive element’s length, in a way that there’s cost reduction in the manufacturing process and raw material savings, since it allows to vary the power density P without having to increase the length of the heating system.

[0028] One or more objectives of the present invention are obtained by a household appliance comprising such heating system.

[0029] The inventors surprisingly discovered that by varying at least one geometric feature of the resistive element accounting for the zones of thermal variance a, it is possible to obtain a resistive element in which the power density P varies along the length of the resistive element, resulting in a homogenous temperature distribution.

[0030] One or more purposes of the present invention, mentioned above, among others, is(are) reached by means of a heating system for defrosting household appliances, comprising, at least:

[0031] - a resistive element;

[0032] - a sealed protective tube encapsulating the resistive element and an electrically insulating material therewith; and

[0033] - an electric terminal attached to at least one end of the resistive element, wherein the power density P of the resistive element is variable along the length L of the resistive element as a function of at least one geometric feature of the resistive element.

[0034] One or more purposes of the present invention, mentioned above, among others, is(are) reached by means of a method of manufacturing the resistive element of the heating system for defrosting household appliances, comprising at least the following steps: - executing a thermal model for at least a component of the household appliance, the component being subjected to thermal variation;

[0035] - determining, based on the thermal model, the zones of thermal variance a;

[0036] - determining the dimensions and positions of the at least one geometric feature of the coiled-shaped resistive element based on the zones of thermal variance a; and

[0037] - manufacturing the resistive element according to the determined dimensions and positions.

[0038] One or more purposes of the present invention, mentioned above, among others, is(are) reached by means of a household appliance, comprising, at least:

[0039] - the component subjected to thermal variation; and

[0040] - the heating system, applied to the component.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The purposes, technical effects and advantages of the present invention will be clear to the skilled in the art from the following detailed description which refers to the attached figures, which illustrate exemplary embodiments, but not limiting, of the claimed objects and method:

[0043] - Figure 1 a illustrates the heating system 10 attached to a component 21 of a household appliance 20 which is subjected to thermal variation, according to an embodiment of the present invention;

[0044] - Figure 1 b is a zoomed out version of Figure 1 a and illustrates in more detail, the household appliance 20;

[0045] - Figure 1 c is a zoomed out version of the household appliance 20;

[0046] - Figures 2a and 2b respectively illustrate a front and top view of the heating system 10 for defrosting household appliances 20, according to the present invention;

[0047] - Figure 3a shows an example of a coiled-shaped resistive element of a heating system known from the prior art and used to defrost household appliances;

[0048] - Figure 3b illustrates a coiled-shaped resistive element 1 of the heating system 10 having a variable pitch X1 , X2, X3, X4, Xn along its length L, according to an embodiment of the present invention;

[0049] - Figure 3c illustrates a coiled-shaped resistive element 1 of the heating system 10 having a variable helical diameter D1 , D2, D3, D4, Dn along its length L, according to an embodiment of the present invention;

[0050] - Figure 4 illustrates boundary conditions in a thermal model of the heating system 10, according to an embodiment of the present invention;

[0051] - Figures 5a and 5b illustrate the dimensions of an exemplary variance in the pitch X1 , X2, X3, X4, Xn of the coiled-shaped resistive element 1 along its length L, within the boundary conditions of the thermal model of the heating system 10, according to an embodiment of the present invention;

[0052] - Figure 6 illustrates a thermal distribution map of the variance in temperature throughout the length L of the heating system 10, based on the calculated heat transfer through natural convection of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, according to an embodiment of the present invention;

[0053] - Figure 7 illustrates a thermal distribution map of the variance in temperature throughout the length L of the heating system 10, based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, according to an embodiment of the present invention;

[0054] - Figure 8 illustrates a line graph showing the variance in temperature throughout the length L of the heating system 10 over time, based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, according to an embodiment of the present invention;

[0055] - Figures 9 and 10 illustrate thermal distribution maps of the variance in temperature throughout the length L of the heating system 10, based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, and accounting for the heat dissipation of end brackets 22 and water tray 23 of the component 21 , according to an embodiment of the present invention;

[0056] - Figure 11 illustrates a line graph showing the variance in temperature throughout the length L of the heating system 10 over time, based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, and accounting for the heat dissipation of end brackets 22 and water tray 23 of the component 21 , according to an embodiment of the present invention; - Figure 12 illustrates a thermal distribution map of the variance in temperature throughout the length L of the heating system 10, based on the calculated heat transfer through natural convection, radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, and accounting for the heat dissipation of end brackets 22, water tray 23 of the component 21 and the air volume confining the heating system 10 and said component 21 parts 22, 23, according to an embodiment of the present invention;

[0057] - Figure 13 illustrates a line graph showing the variance in temperature throughout the length L of the heating system 10 over time, based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, and accounting for the heat dissipation of end brackets 22, water tray 23 of the component 21 and the air volume confining the heating system 10 and said component 21 parts 22, 23, according to an embodiment of the present invention;

[0058] - Figure 14 illustrates a line graph showing the variance in temperature throughout the length L of the heating system 10, based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, and accounting for the heat dissipation of end brackets 22, water tray 23 of the component 21 and the air volume confining the heating system 10 and said component 21 parts 22, 23, when combined with results of another thermal model for at least the component 21 of the household appliance 20, according to an embodiment of the present invention;

[0059] - Figure 15 illustrates a line graph showing a resistive element according to the prior art, having a fixed pitch distance and a resistive element 1 according to an embodiment of the present invention, having a variable pitch distance;

[0060] - Figure 16 illustrates a line graph showing a constant power density of the resistive element according to the prior art as a function of its fixed pitch distance, as shown in Figure 15, and a variable power density of the resistive element 1 according to an embodiment of the present invention, as a function of its variable pitch distance, as shown in Figure 15;

[0061] - Figure 17 illustrates a flowchart comprising the steps 101 , 102, 103, 104 of a method 100 of manufacturing the resistive element 1 of the heating system 10 for defrosting household appliances 20, according to an embodiment of the present invention. DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0062] Initially, it must be highlighted that the objects and method of the present invention, namely, a heating system 10 for defrosting household appliances 20, a method 100 of manufacturing a resistive element 1 of the heating system 10 and a household appliance 20 comprising such heating system 10 will be described in accordance with particular, but non-limiting embodiments, since the embodiments thereof can be carried out in different manners and variations according to the desired application.

[0063] In one embodiment, the present invention discloses a heating system 10 for defrosting household appliances 20. In this regard, although the objects and method of the present invention in their preferred embodiments are carried out in a frost-free refrigerator 20 (such as illustrated in figure 1c), specifically adapted to an evaporator 21 of the frost-free refrigerator 20, the term “household appliance 20” must be read as encompassing any appliance 20 which relies on a heating system to defrost ice buildups, such as frost-free refrigerators, commercial freezers, automatic ice makers, dishwashers, air conditioners and the like, which are non-limiting examples of appliances in which the heating system 10 according to the present invention may be carried out.

[0064] Likewise, the term “component 21” must be read as encompassing any component of the household appliance 20 subjected to thermal variation, preferably when heat must be transferred from the heating system 10 to the component 21 to defrost ice buildups. In case the household appliance 20 is one of frost-free refrigerators (such as illustrated in figure 1c), commercial freezers, automatic ice makers, dishwashers, or air conditioners, the component 21 would respectively be one of an evaporator, an ice mold, an interior surface, or an outdoor unit, which are nonlimiting examples of components to which the heating system 10 according to the present invention may be specifically adapted.

[0065] In a preferred embodiment wherein the heating system 10 is carried out in a frost-free refrigerator 20 (such as illustrated in figure 1 c), specifically in the freezer compartment and adapted to evenly melt ice buildups in the evaporator 21 and freezer compartment, such as illustrated in figure 2, the heating system 10 according to figures 2a and 2b comprises:

[0066] - a resistive element 1 ;

[0067] - a sealed protective tube 2, encapsulating the resistive element 1 and an electrically insulating material 3 therewith; and an electric terminal 4, attached to at least one end of the resistive element 1.

[0068] In this preferred embodiment, the resistive element 1 may be made of single metallic material or metallic alloys which offer high electrical resistance R to give out a large amount of heat though the Joule effect when the electric current I from the electric terminal 4 is applied through the resistive element 1 .

[0069] The sealed protective tube 2 which encapsulates the resistive element 1 serves the purpose of protecting the resistive element 1 from environmental factors such as humidity which could cause the resistive element 1 to corrode or oxidate. It may also be made of a thermally conductive material such that it evenly conducts the heat to its surroundings. By encapsulating the resistive element 1 , the sealed protective tube 2 also safeguards the resistive element 1 from mechanical damages and further prevents direct contact with the resistive element 1 and with the component 21 and / or some of the household appliance 20 parts, enhancing the overall safety of the heating system 10.

[0070] The electrically insulating material 3 encapsulated by the sealed protective tube 2 surrounds the resistive element 1 , keeping it in place and preventing it from coming into contact with the inner walls of the sealed protective tube 2. Thus, the electrically insulating material 3 also enhances the safety of the heating system 10 by reducing the risk of short circuits, fires and the like.

[0071] In this preferred embodiment, as illustrated in figure 3b, the resistive element 1 is shaped as a coil and at least one geometric feature of the coiled-shaped resistive element 1 is variable along its length L. Specifically, the variable geometric feature of the coiled-shaped resistive element 1 is a variable pitch X1 , X2, X3, X4, Xn along the length L of the coiled-shaped resistive element 1 .

[0072] In an alternative embodiment, according to figure 3c, the variable geometric feature of the coiled-shaped resistive element 1 is a variable helical diameter D1 , D2, D3, D4, Dn along the length L of the coiled-shaped resistive element 1.

[0073] In either of these embodiments, the inventors surprisingly discovered that by locally varying the dimensions of the pitches X1 , X2, X3, X4, Xn or the dimensions of helical diameters D1 , D2, D3, D4, Dn of the resistive element 1 , the power density P of the resistive element 1 will also vary as a function of these local geometric variations. For instance, when the pitches X1 , X2, X3, X4, Xn are compressed in a given location by reducing the distance between each pitch, more resistive material is packed in a given unit length. Thus, the power density P in that location will increase. Likewise, when the pitches X1 , X2, X3, X4, Xn are stretched apart in a given location by increasing the distance between each pitch, the power density P in that location will decrease.

[0074] By the same token, when the helical diameters D1 , D2, D3, D4, Dn are reduced in a given location, the surface area of the coil per unit length also decreases, and since the same amount of electrical power is distributed over a smaller surface area, the power density P in that location will increase. Accordingly, when the helical diameters D1 , D2, D3, D4, Dn are increased in a given location, the power density P in that location will decrease.

[0075] For the heating system 10 according to the present invention to solve one or more of the above-mentioned objective technical problems, the exact dimensions, and positions of each variable pitch X1 , X2, X3, X4, Xn or each variable helical diameter D1 , D2, D3, D4, Dn along the length L of the coiled-shaped resistive element 1 need to be determined.

[0076] This is particularly achieved by running a Multiphysics joule effect simulation coupled with heat transfer equations to create a thermal model that represent properly the system behavior for at least the component 21 of the household appliance 20 to determine the zones of thermal variance a in the volume comprising the component 21. Alternatively, the thermal model can be generated by a result of practical tests, applying thermocouples distributed over a standard heating system 10. The specific thermal values of these zones of thermal variance a serve as correction factors, indicating the positions in which the power density P of the resistive element 1 should be higher or lower locally compensating for these zones of thermal variance a. The result is a heating system 10 having a variable power density P along the length L of the resistive element 1 , and a homogenous temperature distribution along the length L of the resistive element 1 , as illustrated by the line graph of figure 14. It should be noted that the temperature distribution of the line graph of figure 14 is below 360°C, therefore compliant with the IEC standard 60335-1.

[0077] In another preferred embodiment, according to figure 17, a method 100 of manufacturing the resistive element 1 of the heating system 10 is disclosed. The method 100 comprises the steps of: - executing 101 the thermal model for at least the component 21 of the household appliance 20,

[0078] - determining 102, based on the thermal model, the zones of thermal variance a;

[0079] - determining 103 the dimensions and positions of each variable pitch X1 , X2, X3, X4, Xn or each variable helical diameter D1 , D2, D3, D4, Dn along the length L of the coiled-shaped resistive element 1 based on the determined zones of thermal variance a; and

[0080] - manufacturing 104 the resistive element 1 according to the determined dimensions and positions.

[0081] Another preferred embodiment discloses a household appliance 20, comprising, at least:

[0082] - the component 21 subjected to thermal variation; and

[0083] - the heating system 10, applied to the component 21 .

[0084] SIMULATION OF THE HEATING SYSTEM

[0085] Subsequently it is disclosed a simulation of the heating system 10 having a coiled-shaped resistive element 1 with variable pitch X1 , X2, X3, X4, Xn along its length L, according to the principles of the preferred embodiments of the present invention. This simulation is run on a Multiphysics simulation software and aims to study the temperature profile of the heating system 10 alone in the following situations:

[0086] 1 - based on the calculated heat transfer through natural convection of the heating system 10;

[0087] 2 - based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10;

[0088] 3 - based on the calculated heat transfer through natural convection and radiation emissivity of the heating system 10 and accounting for the heat dissipation of end brackets 22 and water tray 23 of the component 21 ; and

[0089] 4 - based on the calculated heat transfer through natural convection, radiation emissivity of the heating system 10 within the boundary conditions of the thermal model of the heating system 10, and accounting for the heat dissipation of end brackets 22, water tray 23 of the component 21 and the air volume confining the heating system 10 and said component 21 parts 22, 23.

[0090] Reference is made to figure 4, which depicts boundary conditions of the simulation, which is a thermal model of the heating system 10. In this simulation, there is a first heat zone, defined as heat zone 1 which has a length L of 0.37 m and a total power of 60.3 W, resulting in a power density P of 163 W / m. There is also a transition zone to a second heat zone, defined as heat zone 2 which has a length L of 0.28 m and a total power of 56 W, resulting in a power density P of 200 W / m. The total length of the heat zones is 0.65 m, and the total power is 116 W.

[0091] Figure 5a is a magnified photograph of the pitches X1 , X2, X3, X4, Xn of the coiled-shaped resistive element 1 in the heat zone 1 . In this zone, the lengths L of the pitches X1 are constantly 1.117 mm. This means that the power in each pitch X1 of the heat zone 1 is 0.182 W and that the heat zone 1 has approximately 316 pitches along its length L.

[0092] Likewise, figure 5b is a magnified photograph of the pitches X1 , X2, X3, X4, Xn of the coiled-shaped resistive element 1 in the heat zone 2. In this zone, the lengths L of the pitches X2, X3 are respectively, 0.789 mm and 0.728 mm. However, in this simulation, the lengths L of the pitches in the heat zone 2 were normalized as being 0.73 mm considering X3 for simplification purposes. This means that the power in each pitch of the heat zone 2 is 0,146 W and that the heat zone 2 has approximately 384 pitches along its length L.

[0093] The resistive element 1 is made of Manganin, which is a copper, manganese and nickel alloy having an electrical resistivity R of 1.35 0mm2 / m, a thermal conductivity of 60.2 KJ / m.h.°C, and a linear expansion coefficient of 15.10A- 6 / °C. The sealed protective tube 2 is made of 1050 aluminum alloy or 321 stainless steel and the electrically insulating material 3 is MgO. A voltage proportional to the length L of the resistive element 1 is applied to result in an electric current I of 1 .03 A.

[0094] According to the literature, the heat transfer coefficient h for a natural convection of a heating system 10 to an evaporator 21 with the fans turned off can be calculated by the following equation: h = 1,32

[0095] Considering that the difference in temperature AT is 475°C and the diameter d of the resistive element 1 is 0.006 m, then the heat transfer coefficient h is:

[0096] 475QC y h = 1,32

[0097] 0.006 m /

[0098] W h = 22,14 m2.QC

[0099] Considering the heat transfer coefficient h of 22,14 W / m2 0C, the Multiphysics simulation gives out a thermal distribution map, according to figure 6, of the variance in temperature throughout the length L of the heating system 10, based on the heat transfer through natural convection of the heating system 10. It is observed that the temperature is lower on the heat zone 1 , where the power density P is lower and the temperature is higher on the heat zone 2, where the power density P is higher.

[0100] In a second step of the simulation, it was added to the heat transfer through natural convection a calculated heat transfer through emissivity, considering that the coefficient of emissivity E of the sealed protective tube 2 is 0.9.

[0101] Considering these parameters, the Multiphysics simulation gives out a thermal distribution map, according to figure 7, of the variance in temperature throughout the length L of the heating system 10, based on the heat transfer through natural convection and emissivity of the heating system 10.

[0102] Accordingly, the Multiphysics simulation gives out a line graph, according to figure 8, representing the variance in temperature throughout the length L of the heating system 10 over time. It is possible to see an offset of 80°C between the heat zone 1 and heat zone 2.

[0103] In a third step of the simulation, for a more precise result it was added the heat dissipation effect of end brackets 22 and water tray of the component 21 to the calculated heat transfer through natural convection and emissivity of the heating system 10. As a result, the Multiphysics simulation gives out thermal distribution maps, according to figures 9 and 10, of the variance in temperature throughout the length L of the heating system 10, based on the heat transfer through natural convection and emissivity of the heating system 10, and accounting for the heat dissipation of end brackets 22 and water tray 23 of the component 21 .

[0104] Accordingly, the Multiphysics simulation also gives out a line graph, according to figure 11 , representing the variance in temperature throughout the length L of the heating system 10 over time.

[0105] In a fourth step of the simulation, for even more precise results it was added the ambient heating effect of an air volume of 10A6 mm3confining the heating system 10 and the component 21 parts 22, 23. As a result, the Multiphysics simulation gives out a thermal distribution map, according to figure 12, of the variance in temperature throughout the length L of the heating system 10 and the air volume, based on the heat transfer through natural convection and emissivity of the heating system 10, and accounting for the heat dissipation of end brackets 22 and water tray 23 of the component 21 .

[0106] Accordingly, the Multiphysics simulation also gives out a line graph, according to figure 13, representing the variance in temperature throughout the length L of the heating system 10 over time. In the line graph it is possible to see that the temperature of the heating system 10 peaks at around 500 °C in the heat zone 2, dropping to around 250 and 240°C where the heating system 10 contacts the end backets which tend to dissipate the heat. The temperature in the transition zone is at around 375°C and in the heat zone 1 , the temperature is at around 430°C. Therefore, validating the principles of the preferred embodiments of the present invention, according to which by locally varying the dimensions of the pitches X1 , X2, X3, X4, Xn or the dimensions of helical diameters D1 , D2, D3, D4, Dn of the resistive element 1 , the power density P (and temperature) of the resistive element 1 will also locally vary as a function of these local geometric variations.

[0107] For demonstrative purposes, Figure 15 illustrates a line graph showing a resistive element according to the prior art, having a fixed pitch distance versus a resistive element 1 according to an embodiment of the present invention, having a variable pitch distance, in which there are 4 pitch variation ranges: A, B, C and D.

[0108] Figure 16 illustrates yet another line graph showing a constant power density of the resistive element according to the prior art as a function of its fixed pitch distance, as shown in Figure 15, versus a variable power density of the resistive element 1 according to an embodiment of the present invention, as a function of its variable pitch distance, as shown in Figure 15. Likewise, there are 4 power density variation ranges: A’, B’, C’ and D’.

[0109] The comparative graphs show the effect of the variable pitch calculation in order to achieve the variable power density distribution. In this particular example, through the application of equations 2, 3 and 4 were considered the following parameters for the resistive element.

[0110] TABLE 1

[0111] It’s possible to see in a comparative way the benefits of the present invention, such as a variable power density as a function of a variable pitch distance, the heat emitted being below the 360°C limit established by the IEC standard. Although the description of the particular embodiments above relates to certain embodiments, the present invention can present modifications in the manner of implementation thereof so the scope of protection of the invention is limited only by the contents of the attached claims, including therein the possible equivalent variations.

[0112] List of Reference Signs

Claims

SET OF CLAIMS1. HEATING SYSTEM (10) FOR DEFROSTING HOUSEHOLD APPLIANCES (20), comprising:- a resistive element (1 );- a sealed protective tube (2) encapsulating the resistive element (1 ) and an electrically insulating material (3) therewith; and- an electric terminal (4) attached to at least one end of the resistive element (1 ), the heating system (10) being characterized by the power density (P) of the resistive element (1 ) being variable along the length (L) of the resistive element (1 ) as a function of at least one geometric feature of the resistive element (1 ).

2. HEATING SYSTEM (10) according to claim 1 , characterized by the resistive element (1 ) being shaped as a coil.

3. HEATING SYSTEM (10) according to claim 2, characterized by the at least one geometric feature of the resistive element (1 ) being:- a variable pitch (X1 , X2, X3, X4, Xn) along the length (L) of the coiled- shaped resistive element (1 ); or- a variable helical diameter (D1 , D2, D3, D4, Dn) along the length (L) of the coiled-shaped resistive element (1 ).

4. HEATING SYSTEM (10) according to claim 3, characterized by the dimensions and positions of each variable pitch (X1 , X2, X3, Xn) or each variable helical diameter (D1 , D2, D3, D4, Dn) being determined based at least on a feature of a thermal model for at least a component (21 ) of the household appliance (20), the component (21 ) being subjected to thermal variation.

5. HEATING SYSTEM (10) according to claim 4, characterized by the at least one feature of the thermal model being the determination of zones of thermal variance a.

6. METHOD (100) OF MANUFACTURING A RESISTIVE ELEMENT (1 ) of a heating system (10) for defrosting household appliances (20) as defined in any one of claims 1 to 5, the method (100) being characterized by comprising the following steps:- executing (101 ) the thermal model for at least a component (21 ) of the household appliance (20), the component (21 ) being subjected to thermal variation;- determining (102), based on the thermal model, the zones of thermalvariance a;- determining (103) the dimensions and positions of the at least one geometric feature of the coiled-shaped resistive element (1 ) based on the zones of thermal variance a; and - manufacturing (104) the resistive element (1 ) according to the determined dimensions and positions.

7. HOUSEHOLD APPLIANCE (20), having a component (21 ) subjected to thermal variation, the household appliance (20), characterized by comprising a heating system (10) as defined in any one of claims 1 to 5, or obtained from the method as defined in claim 6, applied to the component (21 ).

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