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Definition. Heat sinks are devices that enhance the heat dissipation from hot surfaces. It is high thermal conductivity materials that makes low impedance, are often used on circuit boards to reduce component operating temperatures by minimizing the component to sink temperature difference.The heat

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    1. Part-C Main topics B1- Electronics cooling methods in industry Heat sinks and cold plates for electronic cooling "Heat sinks" Heat pipes in electronic cooling Thermoelectric cooling Immersion cooling Cooling techniques for high density electronics

    2. 13. Heat sinks and cold plates for electronics cooling

    3. Heat sinks Heat sink classification 1- Heat sink without using Fins

    4. Heat sink classification 2- Heat sink with extended surfaces ( Fins)

    5. 2- Heat sink with extended surfaces ( Fins) Besides adding fins the effective heat transfer coefficient could be increased by using fans mounted to extended surfaces as shown and hence the surface temperature could be more reduced and the rate of heat dissipation also increased.

    6. 2- Heat sink with extended surfaces ( Fins) Fin Performance

    7. Cold plates High power electronic components or high heat density assemblies that result from miniaturization often require a more effective heat removal system than is offered by conductive heat sinks. The cold plate combines the effects of a conductive heat sink with convection heat transfer to reduce the impedances between the generating heat sources and the thermal sink.

    8. Heat sink attachment 1-Mechanical attachment Mechanical attachment generally consists of screws or clips that affix the heat sink directly to the device or to the PCB. The issues to consider here are the interface between the heat sink and the device, the number and type of parts needed, and the stresses imparted to the PCB and the device. 2-Adhesive attachment Adhesive attachment is accomplished with double-sided tapes or dispensed adhesives such as epoxies.

    9. Specifying filter for air forced electronics convection cooling Several specifications are required before an appropriate filter can be selected. The available area for the filter. The system's volumetric flow rate. The maximum pressure drop allowed for the filter. Filter efficiency. Ability to create laminar air flow. Type of contaminants to be filtered size of particles. corrosive or non-corrosive.

    10. Specifying filter for air forced electronics convection cooling Even more important than the filter selection is the orientation of the filter with respect to the fan or blower. The filter should be placed several inches away from the blower and also be oriented perpendicular to the desired air flow direction to create a laminar air flow , for example as shown; cooling system for the telecommunications application

    11. Case study Find experimentally the relation between the thermal resistance and both heat input and number of fins. Show the effect of fan speed on the heat sink heat input, base temperature and finally the thermal resistance.

    12. 14. Heat pipes technique in electronic cooling

    13. Boiling and Condensation heat transfer Due to the heat pipe technique depends on two phase flow heat transfer, so that we should devote apart to the concept of Boiling and Condensation heat transfer. The convection coefficient for both boiling and condensation could depend on: the difference between the surface and saturation temperatures, ?T = Ts Tsat the body force arising from the liquid vapor density difference, (?L ?v)g surface tension s of the coolant the latent heat hfg of the coolant characteristic length thermophysical properties of the liquid or vapor (?, cp, , k), so that

    17. Circulation in pool boiling systems Pool boiling

    37. 15. Heat pipes in electronic cooling (cont.) Condensing section Evaporating section Working fluid Container Wick or capillary structure

    38. Features of heat pipes 1- Very high thermal conductivity The Heat pipe effective thermal conductivity is several orders of magnitudes greater than that of the best solid conductor.

    39. Features of heat pipes 2- Low relative weight 3- Reliable in operation 4- Flexible

    40. Features of heat pipes 5- The temperature operating range

    41. Limitations of operation with heat pipes

    42. Applications of heat pipe for cooling of electronic systems 1- Cooling of Laptop Computer

    43. Applications of heat pipe for cooling of electronic systems 2- Cooling of high Power electronics

    44. Applications of heat pipe for cooling of electronic systems

    45. Heat pipe performance Performance factor of the heat pipe is a function of its working fluid.

    46. The energy transferred at the evaporator in terms of the wick flow rate is The flow rate depends upon the cross-sectional wick area and porosity in addition to the density and capillary diffusion rate of the fluid. Heat pipe performance

    47. 16. Pulsating heat pipes and thermosyphons 1- Pulsating heat pipes (PHP) A PHP consists of a plain meandering tube of capillary dimensions with many U-turns as shown in Figure.

    48. 1- Pulsating heat pipes (PHP)

    49. 2- Thermosyphons system Thermosyphons transfer heat in exactly the same way as the Heat Pipe by evaporation followed by condensation. However no capillary structure is present to aid liquid transport from the condenser back to the evaporator, and thus the evaporator must be located vertically below the condenser, gravity will then ensure that the condensate returns to the evaporator. To avoid the confusion because the term "Heat Pipe" is commonly used to describe both the Heat Pipeand Thermosyphone the term "Gravity AssistedHeat Pipe"has been used to describe Thermosyphons.

    50. 2- Thermosyphons system Different Structure of modern Thermosyphons

    51. 2- Thermosyphons system Effect of Inclination on the Thermosyphone

    52. 17. Thermoelectric cooling (TEC)

    53. The typical thermoelectric module is manufactured using two thin ceramic wafers with a series of P and N doped bismuth-telluride semiconductor material sandwiched between them. The ceramic material on both sides of the thermoelectric adds rigidity and the necessary electrical insulation. 17. Thermoelectric cooling (TEC)

    54. Thermal analysis and parameters needed for TEC

    55. Thermal analysis and parameters needed for TEC

    56. Example

    58. Solution

    59. Solution

    60. Solution

    61. Performance curves

    62. Performance curves

    63. Thermoelectric multistage devices

    64. Advantages of TEC systems

    65. 18. Immersion Cooling

    66. Passive Immersion Cooling - Passive in that the module is a self-contained, sealed enclosure with no moving parts, where Electronic components are immersed in the fluid contained within and the liquid acts as heat spreader to module cold plate, aided by vigorous boiling process. - The passive cooler doesn't use any pumps to move the fluid around, this system depend on free convection to work.

    67. Advantage and Limitation Advantages: - Very wide operating temperature range. - Able to handle much larger heat loads than other methods. - Absolutely silent. Disadvantages: - Suitable dielectric fluid may be expensive. - Hardware upgrades are made difficult, since the module must be opened and drained to access the components.

    68. Active immersion liquid cooling

    69. Active immersion liquid cooling

    70. Direct liquid immersion cooling system

    71. 19,20: Cooling Techniques for High Density Electronics 1. Cold plate technology for high density server

    72. 1. Cold plate technology for high density server

    73. 1. Cold plate technology for high density server

    74. 1. Cold plate technology for high density server

    75. Nontraditional heat transfer surfaces North and Cho described a porous metal heat sink in which spheroid particles are bonded together, shown in Figure below. Nominal particle diameters were 274, 325 and 537 m.

    76. Nontraditional heat transfer surfaces Prechtl and Kurtz .presented a microstructured fabrication process in which etched layers were joined together to form a multilayer heat sink, as shown in Figure. The resulting channels were 400 x 600, 200 x 300 and 100 x 200 m.

    77. 2. Direct impingement cooling In this method, components are cooled directly by blowing air. Then the temperature difference between the component and air flow will be decreased.

    78. 2. Direct impingement cooling The process of developing impingement cooled equipment requires: - Determination and description of heat generating components. - Definition of the allowable maximum temperature for different classes of circuits or components used. - Selection of candidate flow paths accounting for equipment configuration, interfaces and assembly arrangement in terms of generated heat distribution, coolant temperature rise and allowable component temperatures. - Determination of flow rates and pressure losses along each flow path - Determination of component operating temperatures and equipment cooling requirements, e.g. inlet air temperature, flow rate and flow loss.

    79. 3. Jet impingement cooling Jet impingement cooling of microelectronic chips is accomplished by passing a coolant under pressure through a capillary tube or orifice aimed at the surface to be cooled. The coolant strikes the chip and absorbs its heat dissipation.

    80. 3. Jet impingement cooling For single-phase free jet impingement cooling is influenced by many variables, such as jet diameter d, velocity V , number of jets n, jet-to-source distance x, jet configuration, size of heat source area and coolant properties. The correlation data for FC-77 and water is

    81. 4. Hybrid cooling This simply implies a combination of liquid and air cooling for high power dissipation electronics.

    82. 4. Hybrid cooling

    83. 5. Vapor compression cooling This is a relative newcomer to the electronics industry.

    84. 5. Vapor compression cooling

    85. 5. Vapor compression cooling Advantages: Vapor compression can lift large heat loads. low mass flow rate. high COP. ability to transport heat away from its source.

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