Methodologies Thermal management (electronics)

1 methodologies

1.1 heat sinks
1.2 high conductivity materials
1.3 cold plate

1.3.1 principle
1.3.2 construction , materials
1.3.3 performance


1.4 convective air cooling
1.5 forced air cooling
1.6 heat pipes
1.7 peltier cooling plates
1.8 synthetic jet air cooling
1.9 electrostatic fluid acceleration
1.10 recent developments

methodologies
heat sinks

heat sinks used in electronics, , have become essential modern central processing units. in common use, metal object brought contact electronic component s hot surface—though in cases, thin thermal interface material mediates between 2 surfaces. microprocessors , power handling semiconductors examples of electronics need heat sink reduce temperature through increased thermal mass , heat dissipation (primarily conduction , convection , lesser extent radiation). heat sinks have become essential modern integrated circuits microprocessors, dsps, gpus, , more.

a heat sink consists of metal structure 1 or more flat surfaces ensure thermal contact components cooled, , array of comb or fin protrusions increase surface contact air, , rate of heat dissipation.

a heat sink used in conjunction fan increase rate of airflow on heat sink. maintains larger temperature gradient replacing warmed air faster convection would. known forced air system.

high conductivity materials

in recent years, utilization of high-conductivity materials (inserts) proposed electronic cooling , enhancing heat removal small chips heat sink. because space occupied high conductivity materials cost 2 elements of major concern. therefore, seeking more efficient designs of high conductivity pathways, embedded heat generating body constitutes formidable challenge.

cold plate

placing conductive thick metal plate, referred cold plate, heat transfer interface between heat source , cold flowing fluid (or other heat sink) may improve cooling performance. in such arrangement, heat source cooled under thick plate instead of being cooled in direct contact cooling fluid. shown thick plate can improve heat transfer between heat source , cooling fluid way of conducting heat current in optimal manner. 2 attractive advantages of method no additional pumping power , no heat transfer surface area, quite different fins (extended surfaces).

principle

heat sinks function efficiently transferring thermal energy ( heat ) object @ high temperature second object @ lower temperature greater heat capacity. rapid transfer of thermal energy brings first object thermal equilibrium second, lowering temperature of first object, fulfilling heat sink s role cooling device. efficient function of heat sink relies on rapid transfer of thermal energy first object heat sink, , heat sink second object.

the common design of heat sink metal device many fins. high thermal conductivity of metal combined large surface area result in rapid transfer of thermal energy surrounding, cooler, air. cools heat sink , whatever in direct thermal contact with. use of fluids (for example coolants in refrigeration) , thermal interface material (in cooling electronic devices) ensures transfer of thermal energy heat sink. similarly, fan may improve transfer of thermal energy heat sink air.

construction , materials

a heat sink consists of base 1 or more flat surfaces , array of comb or fin-like protrusions increase heat sink s surface area contacting air, , increasing heat dissipation rate. while heat sink static object, fan aids heat sink providing increased airflow on heat sink—thus maintaining larger temperature gradient replacing warmed air more passive convection achieves alone—this known forced-air system.

ideally, heat sinks made thermal conductor such silver, gold, copper, or aluminum alloy. copper , aluminum among most-frequently used materials purpose within electronic devices. copper (401 w/(m·k) @ 300 k) more expensive aluminum (237 w/(m·k) @ 300 k) twice efficient thermal conductor. aluminum has significant advantage can formed extrusion, making complex cross-sections possible. aluminum lighter copper, offering less mechanical stress on delicate electronic components. heat sinks made aluminum have copper core trade off. heat sink s contact surface (the base) must flat , smooth ensure best thermal contact object needing cooling. thermally conductive grease used ensure optimal thermal contact; such compounds contain colloidal silver. further, clamping mechanism, screws, or thermal adhesive hold heat sink tightly onto component, without pressure crush component.

performance

heat sink performance (including free convection, forced convection, liquid cooled, , combination thereof) function of material, geometry, , overall surface heat transfer coefficient. generally, forced convection heat sink thermal performance improved increasing thermal conductivity of heat sink materials, increasing surface area (usually adding extended surfaces, such fins or foam metal) , increasing overall area heat transfer coefficient (usually increase fluid velocity, such adding fans, pumps, etc.).

online heat sink calculators companies such novel concepts, inc. , @ www.heatsinkcalculator.com can accurately estimate forced , natural convection heat sink performance. more complex heat sink geometries, or heat sinks multiple materials or multiple fluids, computation fluid dynamics (cfd) analysis recommended (see graphics on page).

convective air cooling

this term describes device cooling convection currents of warm air being allowed escape confines of component replaced cooler air. since warm air rises, method requires venting @ top or sides of casing effective.

forced air cooling

if there more air being forced system being pumped out (due imbalance in number of fans), referred positive airflow, pressure inside unit higher outside.

a balanced or neutral airflow efficient, although positive airflow can result in less dust build if filtered properly

heat pipes

a heat pipe heat transfer device uses evaporation , condensation of two-phase working fluid or coolant transport large quantities of heat small difference in temperature between hot , cold interfaces. typical heat pipe consists of sealed hollow tube made of thermoconductive metal such copper or aluminium, , wick return working fluid evaporator condenser. pipe contains both saturated liquid , vapor of working fluid (such water, methanol or ammonia), other gases being excluded. common heat pipe electronics thermal management has copper envelope , wick, water working fluid. copper/methanol used if heat pipe needs operate below freezing point of water, , aluminum/ammonia heat pipes used electronics cooling in space.

the advantage of heat pipes great efficiency in transferring heat. thermal conductivity of heat pipes can high 100,000 w/m k, in contrast copper, has thermal conductivity of around 400 w/m k.

peltier cooling plates

peltier cooling plates /ˈpɛlti.eɪ/ take advantage of peltier effect create heat flux between junction of 2 different conductors of electricity applying electric current. effect commonly used cooling electronic components , small instruments. in practice, many such junctions may arranged in series increase effect amount of heating or cooling required.

there no moving parts, peltier plate maintenance free. has relatively low efficiency, thermoelectric cooling used electronic devices, such infra-red sensors, need operate @ temperatures below ambient. cooling these devices, solid state nature of peltier plates outweighs poor efficiency. thermoelectric junctions typically around 10% efficient ideal carnot cycle refrigerator, compared 40% achieved conventional compression cycle systems.

synthetic jet air cooling

a synthetic jet produced continual flow of vortices formed alternating brief ejection , suction of air across opening such net mass flux zero. unique feature of these jets formed entirely working fluid of flow system in deployed can produce net momentum flow of system without net mass injection system.

synthetic jet air movers have no moving parts , maintenance free. due high heat transfer coefficients, high reliability lower overall flow rates, synthetic jet air movers used @ chip level , not @ system level cooling. depending on size , complexity of systems can used both @ times.

electrostatic fluid acceleration

an electrostatic fluid accelerator (efa) device pumps fluid such air without moving parts. instead of using rotating blades, in conventional fan, efa uses electric field propel electrically charged air molecules. because air molecules neutrally charged, efa has create charged molecules, or ions, first. there 3 basic steps in fluid acceleration process: ionize air molecules, use ions push many more neutral molecules in desired direction, , recapture , neutralize ions eliminate net charge.

the basic principle has been understood time in recent years have seen developments in design , manufacture of efa devices may allow them find practical , economical applications, such in micro-cooling of electronics components.

recent developments

more recently, synthetic diamond cooling sinks being researched provide better cooling. also, heat sinks constructed of multiple materials desirable characteristics, such phase change materials, can store great deal of energy due heat of fusion.