Heat sink

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A heat sink (also usually spelled heatsink ) is a passive heat exchanger that transfers heat generated by electronic or mechanical devices to a liquid medium, often air or coolant, where it scattered away from the device, thus allowing the device's temperature setting to its optimum level. On a computer, a heat sink is used to cool the central processing unit or graphics processor. Heat sinks are used with high-power semiconductor devices such as power and optoelectronic transistors such as lasers and light-emitting diodes (LEDs), where the heat dissipation capability of the component itself is not sufficient to moderate its temperature.

Heat sinks are designed to maximize the surface area with the cooling medium that surrounds them, such as air. Air velocity, material choice, protrusi design and surface treatments are factors that affect heat sink performance. The heat sink attachment method and the thermal interface material also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improves heat sink performance by filling the air gap between the heat sink and heat spreader on the device. Heat sinks are usually made of copper or aluminum. Copper is used because it has many desirable properties for efficient and durable heat exchangers. First and foremost, copper is an excellent heat conductor. This means that the high thermal conductivity of copper allows heat to pass through quickly. Aluminum heat sinks are used as an inexpensive, lightweight alternative to copper heat sinks, and have a lower thermal conductivity than copper.

Video Heat sink

Prinsip transfer panas

Heat sinks transfer heat energy from higher temperature devices to lower temperature liquid medium. The fluid medium is often air, but it can also be water, refrigerant or oil. If the fluid medium is water, the heat sink is often called the cold plate. In thermodynamics, a heat sink is a heat reservoir that can absorb some heat without significantly altering the temperature. The practical heat sink for electronic devices must have higher temperatures from the vicinity to transfer heat through convection, radiation, and conduction. The electronic power supply is not 100% efficient, so extra heat is generated which may damage the functioning of the device. Thus, the heat sink is included in the design to disperse the heat.

To understand the heat sink principle, consider the Fourier heat conduction law. The Fourier heat conduction law, simplified into a one-dimensional form in x -direction, indicates that when there is a temperature gradient in the body, the heat will be transferred from a higher temperature region to a lower one. temperature region. The value at which heat is transferred by conduction, ${\ displaystyle q_ {k}}$ , proportional to the product of the temperature gradient and the cross-section of the hot-dipped heat transfer.

$Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; Âq_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂkÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â-Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂkÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂAÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\frac{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂdÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂTÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂdÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂxÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â}Â\; Â\; Â\; ÂAnnotation\; encoding\; =\; "application/x-tex">\; \{\backslash \; displaystyle\; q\_\; \{k\}\; =\; -\; kA\; \{\backslash \; frac\; \{dT\}\; \{dx\}\}\}\; Â\; Â$

Consider the heat sink in the channel, where the air flows through the channel. It is assumed that heat sink bases are higher in temperature than in air. Implementing energy conservation, for steady-state conditions, and Newton's law cooling to the temperature nodes shown in the diagram gives the following set of equations:

$Â\; ÂÂ\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\stackrel{?}{Q}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â=Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\stackrel{?}{m}Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; ÂÂ\; Â\; Â\; Â\; Â\; Â\; Â\; Âc_{Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; Âp}}$,             me             n                   ()                   T                      a             me             r ,             o             u             t                           -                   T                      a             me             r ,             me             n                           )           {Annotation encoding = "application/x-tex"> {\ displaystyle {\ dot {Q}} = {\ dot {m}} c_ {p, in} (T_ {air, air, in})}   (1)

${\ displaystyle {\ dot {Q}} = {\ frac {T_ {hs} -T_ {air, av}} {R_ {hs}}} } Â Â$ (2)

dimana

${\ displaystyle T_ {air, av} = {\ frac {T_ {udara, dalam} T_ {udara, keluar}} {2}}}  ÂÂ$ (3)

Menggunakan suhu udara rata-rata adalah asumsi yang berlaku untuk heat sink yang relatif pendek. Ketika penukar panas kompak dihitung, suhu udara rata-rata logaritmik digunakan. ${\ displaystyle {\ dot {m}}}  ÂÂ$ adalah laju aliran massa udara dalam kg/s.

The equation above shows it

• When the airflow through the heat sink decreases, this results in an increase in average air temperature. This in turn increases the temperature of the heat sink base. In addition, heat resistance from heat sink will also increase. The net result is a higher base heat sink temperature.
  • Increasing the heat sink heat resistance by decreasing the flow rate will be shown later in this article.
• The temperature of the inlet is strongly related to the base temperature of the heat sink. For example, if there is air recirculation in a product, the temperature of the inlet is not the ambient air temperature. The inlet air temperature from the heat sink is higher, which also results in a higher base temperature of the heat sink.
• If there is no airflow around the heat sink, the energy can not be transferred.
• Heat sinks are not devices with "magical ability to absorb heat like a sponge and transmit it to a parallel universe".

Natural convection requires free air flow above the heat sink. If the fins are not aligned vertically, or if the fins are too close together to allow sufficient airflow between them, the efficiency of the heat sink will decrease.

Maps Heat sink

Design factor

Thermal resistance

For semiconductor devices used in various consumer and industrial electronics, the notion of heat resistance simplifies the selection of heat sinks. The heat flow between the dead semiconductor and ambient air is modeled as a series of resistance to heat flow; there is resistance from die to case device, from case to heat sink, and from heat sink to ambient air. The sum of these resistances is the total thermal resistance of the die to ambient air. Thermal resistance is defined as the rise in temperature per unit of power, analogous to the electrical resistance, and expressed in terms of degrees Celsius per watt (Ã, Â ° C/W). If the device dissipation in watts is known, and total heat resistance is calculated, the temperature rise of the die above the ambient air can be calculated.

The idea of ​​thermal endurance of semiconductor heat sinks is approximate. It does not take into account the uniform heat distribution above the device or the heat sink. This is just a system model in thermal equilibrium, and does not take into account temperature changes with time. Nor does it reflect non-linearity of radiation and convection with respect to temperature rise. However, manufacturers tabulate the typical values ​​of heat resistance for heat sinks and semiconductor devices, allowing the selection of commercially produced heat sinks for simplification.

Commercial extrusion aluminum heat sinks have thermal resistance (heat sinks for ambient air) ranging from 0.4â € <â € <Ã, ° C/W to large sinks intended for TO3 devices, to as high as 85 Ã,  ° C/W for heat sink clip-on for small plastic box TO92. The popular 2N3055 power transistor in TO3 case has internal thermal resistance from the connection to the case 1.52 Ã,  ° C/W . Contact between the chassis of the device and the heat sink may have a thermal resistance between 0.5 to 1.7 Ã,  ° C/W , depending on the size of the casing, and the use of mica or isolation lubricants.

Materials

The most common heat sink material is the aluminum alloy. Aluminum alloy 1050 has one of the higher heat conductivity values ​​at 229 W/moK but is mechanically soft. Aluminum alloys 6060 (low voltage), 6061 and 6063 are commonly used, with thermal conductivity values ​​of 166 and 201 W/moK, respectively. The values ​​depend on the nature of the alloy.

Copper has excellent heat sink properties in terms of thermal conductivity, corrosion resistance, biofouling resistance, and antimicrobial resistance (See also Copper in heat exchanger) . Copper has about twice the thermal conductivity of aluminum, about 400 W/moK for pure copper. Its main applications are in industrial facilities, power plants, solar hot water systems, HVAC systems, gas water heaters, forced air heating and cooling systems, geothermal heating and cooling, and electronic systems.

Copper is three times denser and more expensive than aluminum. Copper heater sinks are worked and filtered. Another method of manufacture is to solder the fins to the bottom of the heat sink. Aluminum heat sinks can be extruded, but less ductile copper can not.

Fin efficiency

The fin efficiency is one of the parameters that make the higher thermal conductivity material important. The heat sink fins can be thought of as flat plates with heat flowing at one end and dissipated into the surrounding liquid as it flows into the other. When heat flows through the fins, the combination of the thermal resistance of the heat sink inhibits the flow and heat lost due to convection, the fin temperature and, therefore, the transfer of heat to the fluid, will decrease from the base to the tip of the fin. The fin efficiency is defined as the heat actually transferred by the fins, divided by the heat transfer is the fin to isothermal (hypothetical fin has an infinite thermal conductivity). Equations 6 and 7 apply to straight fins.

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{          ?                 Â                           =                                             tanh                         (    Â ï <½    Â     Â <                                  c        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â             )                            Â ï <½    Â     Â <                                  c        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â                                        {\ displaystyle \ eta _ {f} = {\ frac {\ tanh {m} {}} { >  Â} (6)

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂmÂ\; Â\; Â\; Â\; Â\; Â\; Â}$ _{          L                 ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂï <½                          =                                                           2    ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...       Â   <Â>  h                                    f     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        Â        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                        Â     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...                  t                                    f     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        Â        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,          ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                   L                 Â                                 {\ displaystyle mL_ {c} = {\ sqrt {\ frac {2h_ {f}} {kt_ {f}}}} L_ {f}}  Â} (7)

Where:

• h _f is the finer convection coefficient
  • Air: 10 to 100 W/(m ² K)
  • Water: 500 to 10,000 W/(m ² K)
• k is the thermal conductivity of the fin material
  • Aluminum: 120 to 240 W/(mÃ, Â · K)
• L _f is a fin (m)
high
• t _f is a fin (m)
piece

The fin efficiency increases by decreasing the aspect ratio of the fin (making it thicker or shorter), or by using more conductive materials (copper, not aluminum, for example).

Spread obstacles

Other parameters concerning the thermal conductivity of the heat sink material spread resistance. The spread of resistance occurs when heat energy is transferred from a small area to a larger area in a substance with limited thermal conductivity. In a heat sink, this means that the heat is not evenly distributed through the heat sink base. The phenomenon of spreading resistance is indicated by how heat moves from the location of the heat source and causes a large temperature gradient between the heat source and the edge of the heat sink. This means that some fins are at a lower temperature than if the heat source is uniform at the base of the heat sink. This unfamiliarity increases the effective heat resistance of heat sinks.

To reduce the deployment resistance at the base of the heat sink:

• Improve base thickness
• Choose different materials with better thermal conductivity
• Use a steam room or heat pipe at the bottom of the heat sink.

Fin Settings

Heat sink pin fin is a heat sink that has a pin that extends from the base. Pin may be cylindrical, elliptical or square. Pin is one of the more common types of heat sinks available on the market. The second type of cooling fin is a straight fin. It runs the entire length of the heat sink. The variation on a straight fin heat sink is a cross cut heat sink. Heat sinks are cut straight at regular intervals.

In general, the larger the surface of the heat sink, the better it works. However, this is not always true. The concept of pin fin heat sink is to try to pack as much surface area as possible to a certain volume. In addition, it works well in any orientation. Kordyban has compared the performance of pin fin and straight fin heat sink with the same dimensions. Although the pin fin has 194Ã,2 surface area while the straight fin has 58Ã, cm ² , the temperature difference between the heat sink base and the ambient air for the pin fin is 50 Ã,  ° C . For the straight fin it is 44Ã,  ° C or 6Ã,  ° C is better than the pin fin. The performance of the pin fin heat sink is significantly better than the straight fin when used in the intended application where the fluid flow is axially along the pin (see figure 17) rather than merely tangential across the pin.

Another configuration is a flared flared heat sink; the fins are not parallel to each other, as shown in figure 5. Flying the fins reduces the flow resistance and makes more air pass through the heat sink fin channel; otherwise, more air will pass through the fins. Tilt them to make the whole dimension stay the same, but offer a longer fins. Forghan, et al. has published data on tests performed on pin fin, straight fin, and fin fin fin. They found that for low-speed air approaches, typically about 1 m/s, thermal performance is at least 20% better than straight-fin heat sinks. Lasance and Eggink also found that for the bypass configuration they tested, flared heat sinks performed better than other heat sinks tested.

Cavity (inverted fin)

The cavity (inverted fins) embedded in a heat source is an area formed between adjacent fins that stand for the nucleus promoter of nucleation or nucleation condensation. These holes are usually used to extract heat from various heat-generating bodies into heat sinks.

Conductive thick plates between heat source and heat sink

Placing a conductive thick plate as a heat transfer interface between a heat source and a cold flowing fluid (or other heat sink) can improve cooling performance. In such settings, the heat source is cooled under a thick plate rather than cooled in direct contact with the coolant. This suggests that thick plates can significantly increase heat transfer between heat and coolant sources by optimally conducting heat flow. Two of the most interesting advantages of this method are that there is no additional pumping power and no additional heat transfer surface area, which is very different from the fin (extended surface).

Color surface

Heat transfer from the heat sink occurs due to the surrounding air convection, conduction by air, and radiation.

Heat transfer by radiation is a function of both heat sink temperature, and the temperature of the heat sink environment is optically coupled with. When these two temperatures are in the order of 0 Â ° C to 100 Â ° C, the radiation contribution compared with convection is generally small, and this factor is often overlooked. In this case, heat sinks operating either in natural convection or forced flow will not be significantly affected by surface emissivity.

In situations where convection is low, such as a non-finned flat panel with low airflow, cooling radiation can be a significant factor. Here the surface properties can be an important design factor. The black-matte surface will radiate much more efficiently than the shiny bare metal. The glossy metal surface has low emissivity. The emissivity of the material is heavily dependent on the frequency, and is related to absorptivity (the surface of the shiny metal has very little). For most materials, emissivity in the spectrum looks similar to emissivity in the infrared spectrum; but there are exceptions, especially certain metal oxides used as "selective surfaces".

In a vacuum or in space, there is no convective heat transfer, so in this environment, radiation is the only factor that governs the heat flow between the heat sink and the environment. For satellites in the sky, the surface of 100Ã, Â ° C (373 Kelvin) facing the sun will absorb a lot of radiant heat, because the sun's surface temperature is nearly 6,000 Kelvin, while the same surface facing space will emit a lot of heat, since the inner chamber has a temperature effective only some Kelvin.

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Engineering applications

Refrigeration microprocessor

Heat dissipation is an unavoidable byproduct of electronic devices and circuits. In general, the temperature of the device or component will depend on the thermal resistance of the component to the environment, and the heat dissipated by the component. To ensure that the components are not overheated, a thermal engineer seeks to find efficient heat transfer paths from the device to the environment. The heat transfer path may be from components to printed circuit boards (PCBs), to heat sinks, to the airflow provided by the fan, but in all cases, eventually to the environment.

Two additional design factors also affect the thermal/mechanical performance of the thermal design:

1. The method in which the heat sink is installed on the component or processor. This will be discussed under the attachment method section.
2. For each interface between two touching objects, there will be a temperature drop across the interface. For such composite systems, the temperature drop across the interface may be quite large. These temperature changes can be attributed to what is known as thermal contact resistance. Thermal interface material (TIM) lowers thermal contact resistance.

Attachment method

As component dissipation power increases and packet size decreases, thermal engineers must innovate to ensure the components are not overheated. The device runs cooler for longer. The heat sink design must meet both thermal and mechanical requirements. Regarding the latter, the component must remain in thermal contact with its heat sink with reasonable shock and vibration. Heat sinks can be copper foils from circuit boards, or separate heat sinks fitted to components or circuit boards. Attachment methods include thermally conductive or epoxy threads, wire z clips, flat spring clips, spacer deadlocks, and thrust pins with ends expanding after installation.

Thermally conductive tape

Thermally conductive ribbons are one of the most cost-effective hot-attachment heat attachments. It is suitable for low bulk heat sinks and for components with low power dissipation. It consists of a conductive thermal carrier material with a pressure-sensitive adhesive on each side.

The tape is applied to the base of the heat sink, which is then affixed to the component. Here are the factors that affect thermal band performance:

1. Surface components and heat sinks should be clean, with no residue like a silicone film.
2. Pre-load pressure is essential to ensure good contact. Inadequate pressure generates non-contact areas with trapped air, and results in higher than expected thermal resistance of the interface.
3. The thick bands tend to provide better "wettability" with uneven surface components. "Wettability" is the percentage area of ​​tape contact on a component. Thick bands, however, have higher heat resistance than thin tapes. From a design standpoint, it is best to balance the balance by selecting a band thickness that provides maximum "wettablilty" with minimum thermal resistance.

Epoxy

Epoxy is more expensive than tape, but provides greater mechanical bonding between heat sinks and components, as well as increased thermal conductivity. The selected epoxy should be formulated for this purpose. Most epoxies are two-part liquid formulations that must be mixed thoroughly before they are applied to the heat sink, and before heat sinks are placed on the component. The epoxy is then cured for a prescribed time, which can vary from 2 hours to 48 hours. A faster healing time can be achieved at higher temperatures. The surface where the epoxy is applied should be clean and free of any residue.

The epoxy bond between the heat sink and the component is semi permanent/permanent. It makes the job very difficult and sometimes impossible. The most common damage caused by rework is the separation of heat spreader components from the package.

The wire forms a Z-clip

More expensive than tape and epoxy, the wire forms a z-clip that installs the heat sink mechanically. To use z-clips, printed circuit boards must have an anchor. The anchors can be soldered to the board, or pushed. Either type requires a hole to be designed onto the board. The use of RoHS soldering should be permitted because such solder is mechanically weaker than traditional Pb/Sn solder.

To assemble with a z-clip, attach one side to one anchor. Bending the spring to the other side of the clip can be placed in another anchor. The deflection develops a spring load on the component, which maintains excellent contact. In addition to the mechanical attachment provided by the z-clip, it also allows the use of high-performance thermal interface materials, such as phase change types.

Clip

Available for processor and ball grid array (BGA) components, clip allows attachment of BGA heat sink directly to component. The clip utilizes a crack made by a ball box array (BGA) between the bottom of the component and the top surface of the PCB. Therefore the clip does not require a hole in the PCB. They also allow easy rework of components.

Push the pin with the compression spring

For larger heat sinks and higher preload, push pins with compression springs are very effective. Pin thrust, usually made of brass or plastic, has a flexible spine at the end connected to the hole in the PCB; once installed, the thorn maintains the pin. The compression spring holds the assembly and maintains the contact between the heat sink and the components. Care is required in the pin pin size selection. An overly large insertion force can cause cracking and consequent component damage.

Threaded standoffs with compression springs

For very large heat sinks, there is no substitute for threaded encoding and compression spring compression methods. The threaded deadlock is essentially a hollow metal tube with an internal thread. One end is secured with screws through a hole in the PCB. The other end receives a screw that presses the spring, completes the assembly. Typical heat sink assemblies use 2-4 deadlocks, which tend to make it the most expensive heat sink attachment design. Another disadvantage is the need for a hole in the PCB.

Thermal interface material

Thermal contact resistance occurs due to cavities created by surface roughness effects, defects and interface misalignment. Void present in interface filled with air. Therefore heat transfer due to conduction across the actual contact area and conduction (or natural convection) and radiation in the gap. If the contact area is small, due to the rough surface, the main contribution to resistance is made by the gap. To reduce the thermal contact resistance, surface roughness can decrease while the interface pressure increases. However, this repair method is not always practical or possible for electronic equipment. Thermal interface material (TIM) is a common way to overcome this limitation,

Properly applied thermal interface material removes the air present in the gap between two objects with a material having a much higher thermal conductivity. Air has a thermal conductivity of 0.022 W/moK whereas TIM has a conductivity of 0.3 W/moK and higher.

When choosing a TEAM, care must be taken with the value provided by the manufacturer. Most manufacturers value the thermal conductivity of a material. However, thermal conductivity does not take into account interface barriers. Therefore, if the TEAM has high thermal conductivity, it does not mean that the interface barrier will be low.

The selection of TEAM is based on three parameters: the interface gap to fill TIM, contact pressure, and TIM electrical resistance. The contact pressure is the pressure applied to the interface between two materials. The selection does not include material costs. Electrical resistivity may be important depending on the electrical design details.

Light-emitting diode lamp

The performance of light-emitting diode (LED) and lifetime is a powerful function of their temperature. Effective cooling is very important. Case studies of LED-based downlighter show examples of calculations performed to calculate the heat sink required for effective cooling of lighting systems. This article also shows that to gain confidence in the results, it takes some independent solutions that give similar results. In particular, the results of experimental, numerical and theoretical methods should all be within 10% of each other to provide a high confidence in the results.

In soldering

Temporary heat sinks are sometimes used when soldering circuit boards, preventing excessive heat damaging sensitive electronics nearby. In the simplest case, this means gripping some components using heavy metal crocodile clips, hemostats or similar clasps. Modern semiconductor devices, designed to be assembled with reflow soldering, can usually tolerate solder temperatures without damage. On the other hand, electrical components such as magnetic alang-alang switches can be damaged if soldered by hot solder, so this practice is still very widely used.

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Methods for determining performance

In general, heat sink performance is a function of the material's thermal conductivity, dimensions, fin type, heat transfer coefficient, airflow rate, and channel size. To determine the thermal performance of the heat sink, a theoretical model can be made. Alternatively, thermal performance can be measured experimentally. Due to the highly complex nature of 3D flow in this application, numerical methods or computational fluid dynamics (CFD) can also be used. This section will discuss the above-mentioned methods for determining the thermal performance of heat sinks.

Theoretical heat transfer model

One method for determining heat sink performance is to use the theory of heat transfer and fluid dynamics. One such method has been published by Jeggels et al., Although this work is limited to the flow of channeling. The flow channeled is where the air is forced to flow through a channel that fits perfectly with the heat sink. This ensures that all air passes through the channel formed by the fins of the heat sink. When airflow is not channeled, a certain percentage of the airflow will pass through the heat sink. Bypass currents are found to increase with increasing density and fin distance, while remaining relatively insensitive to inlet velocity.

Model resistan termal heat sink terdiri dari dua resistensi, yaitu resistansi dalam basis heat sink, ${\ displaystyle R_ {b}}  ÂÂ$ , dan hambatan dalam sirip, ${\ displaystyle R_ {f}}  ÂÂ$ . Resistor termal tahan panas, ${\ displaystyle R_ {b}}  ÂÂ$ , dapat ditulis sebagai berikut jika sumbernya secara seragam menggunakan basis heat sink. Jika tidak, maka resistansi dasar terutama menyebarkan resistansi:

${\ displaystyle R_ {b} = {\ frac {t_ {b}} {kA_ {b}}}}  ÂÂ$ (4)

di mana ${\ displaystyle t_ {b}}  ÂÂ$ adalah ketebalan dasar heat sink, ${\ displaystyle k}  ÂÂ$ adalah konduktivitas panas dari bahan heat sink dan ${\ displaystyle A_ {b}}  ÂÂ$ adalah area basis heat sink.

The flow rate can be determined by the intersection of the cooling system curve and the fan curve. The heat sink system curve can be calculated by channel flow resistance and inlet and outlet losses as done in standard fluid mechanics textbooks, such as Potter, et al. and white.

Setelah basis heat sink dan resistansi sirip diketahui, maka heat sink thermal resistance, ${\ displaystyle R_ {hs}}  ÂÂ$ dapat dihitung sebagai: ${\ displaystyle R_ {hs} = R_ {b} R_ {f}}  ÂÂ$ (14).

Using equations 5 through 13 and inner dimensional data, the thermal resistance for the fins is calculated for various airflow rates. Data for thermal resistance and heat transfer coefficients are shown in the diagram, which shows that for an increased airflow rate, the thermal resistance of the heat sink decreases.

Experimental method

Experimental tests are one of the more popular ways to determine the thermal performance of heat sinks. For determining heat sink heat resistance, flow rate, input power, inlet temperature and coolant base temperature shall be known. The data provided by the vendor is usually provided for the test results distributed. However, the results are optimistic and can provide misleading data when heat sinks are used in applications that are not downloaded. More details on heat sink testing methods and general surveillance can be found in Azar, et al.

Numerical method

In industry, thermal analysis is often overlooked in the design process or done too late - when design changes are limited and become too expensive. Of the three methods mentioned in this article, theoretical and numerical methods can be used to determine the approximate heat sink or temperature of the product components before a physical model is made. Theoretical models are usually used as first order estimates. The online heat sink calculator can provide a reasonable estimate of conventional and natural forced heat convection performance based on a combination of theoretical and empirical correlations. The numerical method or dynamics of computational fluid (CFD) provides a qualitative (and sometimes even quantitative) prediction of fluid flow. This means it will provide simulated or visual results, such as the pictures in Figures 16 and 17, and CFD animations in Figures 18 and 19, but the quantitative or absolute accuracy of the results is sensitive to the inclusion and accuracy of appropriate parameters.

CFDs can provide insight into difficult flow patterns, expensive or impossible to learn using experimental methods. Experiments can provide a quantitative description of the flow phenomenon using measurements for a quantity at a time, at a limited number of time points and time samples. If a full scale model is not available or is not practical, a model scale or doll model may be used. Experiments can have a limited range of problems and operating conditions. Simulations can provide predictive flow phenomena using CFD software for all desired quantities, with high resolution in space and time and almost all realistic operating problems and conditions. However, if important, the results may need to be validated.

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See also

• Computer cooling
• Hot spreader
• Heat pipe
• Heat pump
• Radiator
• Thermal management of devices and electronic systems
• Thermal resistance in electronics
• Thermoelectric Cooling

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References

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External links

• Heat Sink - Basics
• Design Heat Sinks
• Heat Sink Calculator

Source of the article : Wikipedia