KR20200019410A - Composite heat sink and cooling method of heated objects using the same - Google Patents

Abstract

The present invention aims to provide a composite heat sink for cooling a heat-generating object and a method of cooling the heat-generating object using the same. To this end, according to the present invention, provided is the composite heat sink for cooling a heat-generating object comprising: a microchannel unit; and a pin-fin unit, in which the pin-fin unit is formed at a position on the composite heat sink coming in contact with a high-temperature unit of the heat-generating object and the microchannel unit is located at a position on the composite heat sink coming in contact with a low-temperature unit of the heat-generating object. In addition, the present invention provides a method of cooling the heat-generating object having a temperature gradient which places the pin-fin unit on the composite heat sink to come in contact with the high-temperature unit of the heat-generating object and places the microchannel unit to come in contact with the low-temperature unit of the heat-generating object. According to the present invention, the method can evenly cool the temperature of the heat-generating object having a temperature gradient, thereby being capable of remarkably increasing the performance of the heat-generating object which has a lowered performance when there is a temperature gradient, for instance, like a microprocessor.

Description

COMPOSITE HEAT SINK AND COOLING METHOD OF HEATED OBJECTS USING THE SAME}

The present invention relates to a composite heat sink and a cooling method of a heating element using the same.

The first microprocessor developed by Intel in 1971 contained only 2300 transistors. As predicted by Gordon More, this number increased to 5.4 billion. The increase in design complexity in single core processors has led to design changes to multi-core technology. The heat flux generated at the core of the microprocessor is significantly greater than the heat flux at the rest of the microprocessor (background area). Such high heat flux is generally called a hot spot. Large temperature gradients caused by heat flux differences between the core and the background region can reduce the useful life of the microprocessor. About 55% of electronic device damage comes from poor thermal management.

In actual conditions, the location and extent of the hot spot depends on the processor's usage environment, and the heat flux at the hot spot can be as high as eight times the heat flux of the average background. Because of the difference between the hot spots and the high heat flux in the background, conventional uniform cooling techniques make it impossible to maintain isothermal conditions on the chip surface. If the heatsink is designed taking into account only the high heat flux of the hot spot, the background area of the chip will be unnecessarily supercooled, which will still form a high temperature gradient. Moreover, in this design, the economics of the heat sink can be reduced due to the increase in pumping power.

For example, Korean Patent Laid-Open Publication No. 10-2003-0040982 relates to an integrated circuit cooling apparatus. Specifically, a compressor for compressing a refrigerant used in a refrigeration process and converting the refrigerant into a high temperature and high pressure gas refrigerant, and the high temperature and high pressure. A gas condenser that exchanges a gaseous refrigerant with an external atmosphere and converts the liquid refrigerant into a medium-temperature high-pressure liquid refrigerant, an expander that converts the refrigerant passing through the condenser into a low-temperature low-pressure refrigerant, and a low-temperature low-pressure liquid refrigerant that passes through the expander. An integrated circuit cooling apparatus including an evaporator for converting into a refrigerant, a module substrate on which the compressor condenser expander evaporator is disposed on one side, and an integrated circuit which is in close contact with the evaporator on one side of the module substrate and is cooled by an evaporation process of the evaporator. In the air supply, the medium temperature air flowing out of the condenser is blown to the high temperature compressor And a duct connecting the condenser and the compressor to smoothly guide the air blown by the fan, and a plurality of cooling fins formed on the outer circumferential surface of the compressor to increase the cooling efficiency of the compressor. The compressor is a linear compressor, the condenser is a microchannel heat exchanger, the microchannel heat exchanger is the air flows through the hole is processed in the module substrate, the integrated circuit cooling device, characterized in that at least one fan. It is starting. However, since the above technique does not disclose a configuration for improving the temperature gradient of the hot spot portion and the background portion of the integrated circuit, the performance degradation of the integrated circuit due to such a temperature gradient is still a problem.

In addition, the Republic of Korea Patent No. 10-0790790 relates to a heat sink and cooler for an integrated circuit, specifically, at least one flat plate formed of a structure in which a refrigerant is injected into the inside, the refrigerant is circulated in the interior space Spreader; A base block having one surface adhered to the integrated circuit and provided with at least one groove on the other surface for mounting the flat plate spreader upwardly; And a heat dissipation plate formed of a plurality of heat dissipation plates having a shape of engaging with each of the flat plate spreaders, and including a heat dissipation unit for receiving heat from each of the flat plate spreaders and dissipating them to the outside. A heat sink is disclosed. However, the above technique also discloses only a configuration for efficiently dissipating heat from the integrated circuit, and does not disclose a configuration that can improve the temperature gradient on the surface of the integrated circuit. Degradation of the performance is a problem.

The inventors of the present invention have completed the present invention by studying a heat sink capable of cooling a heating element having a temperature gradient and generating heat to a uniform temperature.

Republic of Korea Patent Publication No. 10-2003-0040982 Republic of Korea Patent No. 10-0790790

An object of the present invention to provide a composite heat sink for cooling the heating element and a cooling method of the heating element using the same.

To this end, the present invention includes a microchannel portion and a fin heat sink, and is a composite heat sink for cooling the heating element, wherein the fin heat sink is formed at a position in contact with the high temperature part of the heat generator among the composite heat sinks, and the micro channel portion is made of the composite heat sink. The present invention provides a composite heat sink formed at a position in contact with a low temperature portion of the heating element, and the present invention further provides a fin heat sink portion in contact with the high temperature portion of the heating element, and the microchannel portion is in contact with the low temperature portion of the heating element. It provides a cooling method of a heating element having a temperature gradient characterized in that the arrangement.

According to the present invention, it is possible to uniformly cool the temperature of the heating element having a temperature gradient, for example, when the temperature gradient, such as a microprocessor, there is an effect that can greatly improve the performance of the heating element is degraded.

1 is a schematic diagram of the entire composite heat sink according to an embodiment of the present invention,
2 is an enlarged view of a fin fin of a composite heat sink according to an embodiment of the present invention,
3 is an enlarged view of a microchannel unit of a composite heat sink according to an embodiment of the present invention;
4 is a cross-sectional view of the upper portion of the composite heat sink according to an embodiment of the present invention,
5 is a photograph confirming the cooling behavior of the heating element while changing the Reynolds number,
6 is a graph showing the cooling characteristics of the heating element measured while changing the Reynolds number,
7 is a photograph confirming the cooling behavior of the heating element while changing the heat flux of the high temperature portion, and
8 is a graph showing cooling characteristics of the heating element measured while changing the heat flux of the high temperature portion.

-Definition of Terms-

In the present invention, 'heat sink' or 'heat sink' means an integral heat dissipation structure which helps to release heat of a heating element.

In the present invention, the "microchannel part" is a configuration for forming a composite heat sink, and means a configuration including a plurality of microchannels formed in a direction perpendicular to the heat flux discharge direction from the heating element.

In the present invention, 'pin fin' is a configuration that forms a composite heat sink, a plurality of columnar structures extending in a direction parallel to the heat flux discharge direction from the heating element means a configuration formed by being spaced apart from each other Each columnar structure is defined as 'pin fin'.

In the present invention, the 'heating element' means any object that emits heat generated by electricity or other external force through its surface.

In the present invention, 'high temperature portion' and 'low temperature portion' is a relative concept in one heating element, and particularly at a high temperature on the surface of the heating element, a portion requiring a special configuration in order to exhibit the normal performance of the heating element 'hot portion' or 'hot spot' In this regard, other parts having a relatively low temperature are referred to as 'low temperature parts' or 'background'. Specifically, for example, when the ambient temperature is assumed to be 20 to 30 ° C. in a microprocessor, a portion at which a temperature of about 50 to 100 ° C. is measured may be referred to as a “hot part” or a “hot spot”.

Hereinafter will be described in detail the present invention.

The present invention includes a microchannel portion and a fin heat sink, and is a composite heat sink for cooling the heating element, wherein the fin heat sink is formed at a position in contact with the high temperature part of the heat generating element among the composite heat sinks, and the micro channel part is the heat generating element of the complex heat sink. It provides a composite heat sink, characterized in that formed in the position in contact with the low temperature portion of.

Hereinafter, the composite heat sink according to the present invention will be described in detail for each component.

The composite heat sink according to the present invention is a heat sink for cooling the heating element, including a microchannel portion and a fin fin portion.

The microchannel portion is a component included in the composite heat sink of the present invention, and is a portion in which a plurality of microchannels are formed. The microchannel portion is formed from a heating element while a cooling fluid (for example, air or other refrigerant) flows along the microchannel. Helps heat dissipation.

In this case, the plurality of heat sinks may be disposed to be spaced apart from each other, and may be vertically aligned with respect to the bottom surface of the composite heat sink, and the channels may be formed in parallel with each other. That is, a plurality of aligned heat sinks may be defined as microchannels. In the case of using a configuration such as a microchannel unit for heat dissipation of the heating element, there is an advantage in that the pumping power for the cooling fluid is increased, but there is a problem that the cooling efficiency may not be sufficient.

The fin fin is a configuration included in the composite heat sink of the present invention, and is a portion in which a plurality of fin fins are spaced apart from each other, and helps the heat dissipation from the heating element while fluid flows around the fin fin. In the case of using a configuration such as fin fin for heat dissipation of the heating element, the cross-sectional area for heat dissipation is greatly increased, and cooling efficiency is greatly improved. However, pumping power for cooling fluid is greatly increased.

The composite heat sink according to the present invention is intended to help heat dissipation of the heating element, wherein the heating element is a heating element having a surface temperature that is different depending on its position, that is, a surface temperature gradient is not particularly limited. For example, in the case of microprocessors, for electrical reasons, the surface of a particular location of the microprocessor is much hotter than the surface of other locations. This is generally referred to as a 'hot spot' and in the present invention it is also referred to as a 'hot spot'. In addition, the portion other than the 'hot spot' or the 'hot portion' is referred to as 'background', and in the present invention, this is also referred to as the 'low temperature portion'.

In the case of a microprocessor, the temperature must be kept below a certain temperature (eg, below about 373 K) to ensure sufficient performance, as well as to ensure sufficient performance if the temperature of the entire microprocessor surface is kept uniform. That is, even if the temperature of the surface of the microprocessor as a whole is less than a specific temperature, there is a problem that the performance is not sufficiently guaranteed when there is a gradient in the surface temperature. However, due to uneven power distribution during the operation of the microprocessor, a temperature gradient occurs on the surface of the microprocessor, thereby degrading the performance of the microprocessor.

Accordingly, the composite heat sink of the present invention is an invention for cooling the surface temperature of the heating element having a temperature gradient on the surface to be uniform. Thus, among the components constituting the composite heat sink of the present invention, in particular, the fin heat sink is the heating element of the composite heat sink. Is formed at a position in contact with the high temperature portion of the, and the microchannel portion is formed at a position in contact with the low temperature portion of the heating element of the composite heat sink. Through such a configuration, the hot part of the heating element is cooled more, and the cold part of the heating element is cooled relatively less, thereby eliminating a temperature gradient on the surface of the heating element and cooling to a uniform temperature. Furthermore, by forming the fin fin only in a part of the composite heat sink, there is an effect of preventing excessive increase in pumping power.

For example, when using a heat sink formed only by fin fin for heat dissipation of the microprocessor, since the fin fin is excellent in heat dissipation performance, the microprocessor surface temperature is considerably lowered overall, but the low temperature portion of the microprocessor becomes supercooled, eventually There is still a problem that the temperature gradient is maintained on the surface of the microprocessor, thereby limiting the performance of the microprocessor. In addition, in the case where the heat sink is formed only by the fin portion, the pumping power for the cooling fluid may be excessively increased.

On the other hand, when using a heat sink formed only of the microchannel portion for heat dissipation of the microprocessor, it is possible to prevent excessive increase in pumping power for the cooling fluid, but it may not lower the surface temperature of the microprocessor sufficiently. Furthermore, the most important problem is that the surface temperature gradient of the microprocessor cannot be eliminated as in the case of forming the heat sink with the fin fin alone. That is, since the high temperature and the low temperature of the microprocessor are cooled in the same manner, a temperature gradient is maintained on the surface of the microprocessor even after cooling, and thus there is a problem in that the performance of the microprocessor is not sufficiently exhibited.

The heating element, which is a target to be cooled by the composite heat sink according to the present invention, is a target whose performance is not sufficiently exhibited when a gradient is formed at the surface temperature of the target. For example, a heating system to which a local heat flux is applied such as a microprocessor is used. You can be a target.

The pin pin portion according to the present invention includes a plurality of columnar structures, that is, a plurality of pin pins as described above. In this case, the ratio (D _pin / P _pin ) of the length of the longest diagonal line of the horizontal cross section of each column structure (or the diameter if the cross section is the long axis diameter if the ellipse is caused) to the distance between each column structure is 0.25 to 0.60. Is preferably. The distance between each columnar structure is then measured as the distance between the center of each column and the center of the next adjacent column. If the ratio is less than 0.25, the surface area for heat dissipation is insufficient, so that the cooling efficiency is lowered. If the ratio exceeds 0.60, a problem may occur in relation to other structures in the apparatus, or the mechanical strength of the fins themselves. There is a problem that can be degraded.

On the other hand, the horizontal cross section of the columnar structure may be circular or polygonal, it is preferably circular in that it is excellent in terms of cooling performance and pressure drop.

The fin fin that forms the composite heat sink of the present invention preferably contains 49 to 100 fin fins per 4,000,000 μm ² area. If less than 49, the cooling performance can not be sufficiently expected, there is a problem that the temperature gradient on the surface of the heating element can not be removed sufficiently, if more than 100 there is a problem that the pumping power for the cooling fluid is excessively increased.

The material forming the microchannel part and the fin fin part forming the composite heat sink of the present invention is a material having excellent thermal conductivity, and may be, for example, one or more selected from the group consisting of silicon, copper, and aluminum.

The composite heat sink according to the present invention is an invention for cooling while removing the temperature gradient of the surface of the heating element such as a microprocessor that the performance is not sufficiently exhibited when the temperature gradient is formed on the surface, the high temperature portion of the heating element through the fin By cooling, the low temperature part of the heating element is cooled by the microchannel part, and thus the surface temperature of the heating element can be cooled to be uniform. Furthermore, the pumping power for the cooling fluid is excessively increased by forming fins only in a part of the heat sink. It also has the effect of suppressing the increase.

In addition, the present invention provides a method of cooling a heating element having a temperature gradient using the composite heat sink.

Hereinafter, the cooling method of the present invention will be described in detail.

The present invention provides a method of cooling a heating element having a temperature gradient, wherein the fin fin portion of the composite heat sink is disposed in contact with the high temperature portion of the heating element, and the microchannel portion is disposed in contact with the low temperature portion of the heating element.

Among the heating elements to which the heat sink is subjected to cooling, there are heating elements that have a temperature gradient formed on the surface for various reasons, and there are heating elements that do not sufficiently perform performance when the temperature gradient is formed. Specifically, for example, a heating system to which a local heat flux such as a microprocessor is applied. In the case of a microprocessor, not only must the temperature be kept below a certain temperature for sufficient performance, but also the formation of temperature gradients on the surface must be prevented. However, a temperature gradient occurs on the surface of the microprocessor due to uneven power distribution and the like during the operation of the microprocessor. The present invention provides a cooling method that can solve such a problem.

The present invention utilizes a composite heat sink including a fin fin and a microchannel portion capable of cooling the hot and cold portions of the heating element with different performances as described above. The heating element having a temperature gradient is cooled by arranging it in contact with the low temperature portion of the heating element. In the case of arranging the composite heat sink as described above, the high temperature part of the heating element is cooled relatively more by the fin fin part, and the low temperature part of the heating element is relatively cooled by the microchannel part, and finally the temperature of the heating element surface The gradient can be effectively removed.

The cooling method according to the present invention has the effect of preventing the deterioration of performance due to the temperature gradient of the heating element by cooling the temperature of the heating element having the temperature gradient to be uniform with respect to the whole, and furthermore, the cooling fluid at the time of cooling There is an effect that can be prevented from excessively increasing the pumping power for.

Hereinafter, the present invention will be described in detail through Examples, Comparative Examples, and Experimental Examples. The following contents are intended to explain the present invention more specifically, and are merely for explaining the effects thereof, and the scope of the present invention is not limited to the description below.

<Example 1>

Fabrication of Composite Heatsinks

Each of the microchannel and fin fins was made of silicon, and a composite heat sink was manufactured according to the following specifications. The microchannel portion was manufactured such that a straight microchannel was formed by using a plurality of heat sinks having the following specifications, and the pin fin portion was manufactured by aligning a plurality of cylindrical fin fins having the following specifications.

In the present invention, the axis constituting the plane on which the heat sink is placed is defined as the x axis and the z axis, and the height direction is defined as the y axis.

Micro channel section (μm) W _ch H _ch W _w W _b L _x L _y L _z 250 500 250 200 10000 700 10000 Pin part D _pin H _pin P _{pin, x} P _{pin, z} L _hs W _hs 120 500 200 200 2000 2000

The Table 1 W _ch is the width of the microchannel, H _ch is the height of the microchannel, W _w is the width of the heat sink forming a microchannel, W _b is the microchannel of the bottom thickness, L _x is the x-axis direction microchannel portion The length, L _y, is the y-axis length of the microchannel portion, that is, the thickness, and L _z means the z-axis length of the microchannel portion. In Table 1, D _pin is the diameter of _{pin pin} , H _pin is the height of _{pin pin} , P _{pin, x} is the x-axis distance between _{pin pin and pin pin,} P _{pin, z} is z-axis distance between _{pin pin and pin pin} , L _hs Denotes the length of the hot spot region, that is, the length of the fin region, and W _hs denotes the width of the hot spot region, that is, the width of the fin region. The distance between the pinch and pinch is measured as the distance between the pinch's center point and the adjacent pinch's center point. The above description can be more clearly described with reference to FIGS. 1 to 4.

Comparative Example 1

The heat sink was manufactured in the same manner as in Example 1, except that the fin channel was not formed and the microchannel was formed entirely.

Experimental Example 1

In order to confirm the heating element cooling behavior according to the Reynolds number change, the following experiment was performed.

Cooling behavior was confirmed by changing the Reynolds number from 200 to 1000 for the heat sinks of Example 1 and Comparative Example 1, and the results are shown in FIG. 5. Specifically, we simulated the actual flow area inside the microheat emitter using ANSYS CFX 15.0, a commercial heat flow analysis program, for the three-dimensional Reynold-averaged Navier-Stokes equation.

What is described in the upper right of FIG. 5 is the Reynolds number in each case, and what is described in the lower right is the high temperature part temperature in each case.

At this time, it is assumed that the refrigerant flow is in a steady state and flows in laminar flow, and the effect of gravity and heat transfer by radiation are ignored. The specific heat of the silicon was set to 712 J / kg · K, the density is 2330 kg / m ^3, the thermal conductivity is 148 W / m · K. The refrigerant was water. The heat flux was 300 W / cm ² for the portion corresponding to the high temperature portion and 50 W / cm ² for the portion corresponding to the low temperature portion.

According to FIG. 5, in the case of Comparative Example 1, it can be seen that the temperature gradient between the hot portion and the cold portion is significantly maintained, whereas in Example 1, the temperature gradient between the hot portion and the cold portion is greatly improved.

Experimental Example 2

Through the data obtained in Experimental Example 1, the total heat resistance, total pumping power, MATD at the high temperature portion, and the maximum temperature rise at the high temperature portion for each Reynolds number were confirmed, and the results are shown in FIG. 6. Each value was calculated by the following equations.

Total thermal resistance (R _{th, tot} ) = (T _{s, max} -T _{f, in} ) / Q _tot

In the above formula, T _{s, max} is the maximum temperature at the heat sink base, T _{f, in} is the refrigerant temperature at the refrigerant inlet, and Q _tot is the total heat supplied to the base of the heat sink, and is obtained from the following equation.

Q _tot = q _bg A _bg + q _hs A _hs

In the above formula, q _bg and q _hs are heat fluxes applied to the cold and hot portions of the heat sink, respectively, and A _bg and A _hs are the cold and hot portion region areas of the heat sink, respectively.

Total pumping power (P _tot ) = n _ch u _avg A _c ΔP _{avg, ch}

Where n _ch is the total number of channels, u _avg is the average injection velocity of the fluid, A _c is the cross-sectional area of the channel, and ΔP _{avg, ch} is the average pressure drop over a single channel.

Mean Absolute Temperature Deviation (MATD) (δ _T )

In the above formula, T _{max, hs} , T _{min, hs} , and T _{avg, hs} are the maximum, minimum, and average temperatures in the hot portion, respectively.

According to FIG. 6, in the case of Example 1 (indicated by 'H-MPF' in FIG. 6) of the present invention for all values except pumping power, the case of Comparative Example 1 (indicated by 'NH-RM' in FIG. 6) It can be seen that it is superior to the case. In the case of pumping power, in the case of Example 1 of the present invention, it is slightly higher than in the case of Comparative Example 1, but it can be seen that the increase is not large. For example, in the case of Reynolds number 200, the pumping power of Example 1 is 11.7% higher than that of Comparative Example 1. However, referring to FIG. 5, the temperature of the high temperature portion of Example 1 is 338.2 K in the Reynolds number 200, and in the case of Comparative Example 1, the Reynolds number must be 800 (the temperature is 339.1 K) in order to obtain such a temperature. And, applying this again to Figure 6, in the case of Comparative Example 1 it can be seen that the pumping power should be increased by 2838%. In other words, it can be seen that the composite heat sink of the present invention is cooled to uniformly form the temperature of the surface of the heating element while suppressing a large increase in the pumping power.

In addition, the MATD graph shows that Example 1 according to the present invention actually removes the temperature gradient on the surface of the heating element more effectively than Comparative Example 1. Furthermore, as the Reynolds number increases, the temperature gradient is more and more removed. Able to know.

Experimental Example 3

In order to confirm the heating element cooling behavior according to the change of heat flux, the following experiment was performed.

The experiment was carried out in the same manner as in Experimental Example 1, wherein the Reynolds number was fixed at 800 and the low temperature heat flux was also fixed at 50 W / cm ² , while the high temperature heat flux was changed from 300 to 900 W / cm ² . Was performed, and the results are shown in FIG. 7. In FIG. 7, the upper right part is a heat flux applied to the high temperature part in each case, and the lower right part is the high temperature part temperature in each case.

According to FIG. 7, in the case of the composite heat sink according to Example 1 of the present invention, the surface temperature gradient of the heating element is effectively removed, whereas in the heat sink of Comparative Example 1, the temperature gradient is not effectively removed, and further, the high temperature portion heat flux. Is 600 W / cm ² , the hot part temperature is already 368.6 K, and there is a problem of approaching 373 K, the maximum limit temperature required by the microprocessor.

Experimental Example 4

The total heat resistance, total pumping power, MATD in the high temperature portion, and the maximum temperature rise in the high temperature portion for each Reynolds number were confirmed through the data obtained in Experimental Example 3, and the results are shown in FIG. 8. Each value was calculated by the formulas described in Experimental Example 2 above.

According to FIG. 8, in all cases except pumping power, the heat sink of Embodiment 1 (indicated by 'H-MPF' in FIG. 8) according to the present invention is comparative example 1 (indicated by 'NH-RM' in FIG. 8). It can be seen that there is an excellent effect than the heat sink of. In addition, even in the case of pumping power, Example 1 of the present invention is increased by only about 12 to 13% compared to Comparative Example 1, it can be seen that the pumping power does not increase rapidly.

Claims (9)

And a microchannel portion and a fin heat sink, the heat sink for cooling the heating element, wherein the fin heat sink is formed at a position in contact with the high temperature portion of the heat generator among the composite heat sinks, and the micro channel portion is formed with the low temperature portion of the heat generator in the composite heat sink. Composite heat sink, characterized in that formed in the contact position.
The composite heat sink of claim 1, wherein the heating element is a microprocessor.
The composite heat sink of claim 1, wherein the plurality of heat sinks are disposed to be spaced apart from each other, and the channels are formed by being vertically aligned with respect to the bottom surface of the composite heat sink and aligned in parallel with each other.
The plurality of columnar structures of claim 1, wherein the _pin length portion has a ratio (D _pin / P _pin ) of the longest diagonal length of the horizontal cross section of each columnar structure to the distance between the columnar structures of 0.25 to 0.60. Composite heat sink, characterized in that formed by the alignment.
5. The composite heat sink of claim 4, wherein the horizontal cross section of the columnar structure is circular or polygonal.
The composite heat sink of claim 1, wherein the fin fin comprises 49 to 100 fin fins per 4,000,000 μm ² area.
The composite heat sink of claim 1, wherein the microchannel part and the fin fin are made of at least one material selected from the group consisting of silicon, copper, and aluminum.
The method of cooling a heating element having a temperature gradient, wherein the fin fin portion of the composite heat sink according to claim 1 is disposed to be in contact with the high temperature portion of the heating element, and the microchannel portion is arranged to be in contact with the low temperature portion of the heating element.
The method of claim 8, wherein the heating element is a microprocessor.

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