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By:Narendra Babu NM110247METHERMAL ANALYSIS OF MICROPROCESSOR

CONDUCTION

needs mattermolecular phenomenon (diffusion process)without bulk motion of matter

CONVECTION

heat carried away by bulk motion of fluidneeds fluid matter RADIATION

does not needs mattertransmission of energy by electromagnetic wavesMODES:Electric current flow through a resistance is always accompanied by heat generation.

the essence of thermal design is the safe removal of this internally generated heat by providing an effective path for heat flow from electronic components to the surrounding medium.CONDUCTION

CONVECTIONAn energy transfer across a system boundary due to a temperature difference by the combined mechanisms of intermolecular interactions and bulk transport. Convection needs fluid matter.

Common classifications: A. Based on geometry: External flow / Internal flow B. Based on driving mechanism :Natural convection / forced convection / mixed convection C. Based on number of phases :Single phase / multiple phase D. Based on nature of flow :Laminar / turbulent E. Liquid cooling: direct & indirect , open & closed system

Inside the boundary layer, we can apply the following conservation principles: Momentum balance: inertia forces, pressure gradient, viscous forces, body forces Energy balance: convective flux, diffusive flux, heat generation, energy storage

Typical values of h (W/m2K)

Free convection gases: 2 25, liquid: 50 100

Forced convection gases: 25 250, liquid: 50 - 20,000

Boiling/Condensation 2500 -100,000

RADIATION Radiation heat transfer involves the transfer of heat by electromagnetic radiation that arises due to the temperature of the body. Radiation does not need matter.

cooling techniques commonly used in electronic equipment, such as conduction cooling, natural convection and radiation cooling, forced-air convection cooling, liquid cooling, immersion cooling, and heat pipes.

The epoxy board used in PCBs is a poor heat conductor, and so it is necessary to use copper cladding or to attach the PCB to a heat frame in conduction-cooled systems.

SUMMARYHigh-power electronic components can be cooled effectively by immersing them in a dielectric liquid and taking advantage of the very high heat transfer coefficients associated with boiling. The simplest type of immersion cooling system involves an external reservoir that supplies liquid continually to the electronic enclosure.

This open-loop-type immersion cooling system is simple but often impractical.

Immersion cooling systems usually operate in a closed loop, in that the vapor is condensed and returned to the electronic enclosure instead of being purged to the atmosphere.

CONCLUSIONSystem thermal management considerations are not a trivial task. Many issues are involved in selecting the proper component, heat sink and air flow source.

These issues need to be considered early in the design cycle to insure all options are available to implement the lowest cost, and most efficient thermal management solution.

REFERENCSHeat transfer by CENGEL (2nd edition) Text book.

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