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Micro-refrigeration

Micro-refrigeration. Gareth F. Davies SIRAC Meeting, SELEX Galileo, Luton 20 October 2011. Overview. Need for microprocessor cooling Conventional microprocessor cooling Alternative technologies Development of micro-refrigeration system Results from modelling work

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Micro-refrigeration

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  1. Micro-refrigeration Gareth F. Davies SIRAC Meeting, SELEX Galileo, Luton 20 October 2011

  2. Overview • Need for microprocessor cooling • Conventional microprocessor cooling • Alternative technologies • Development of micro-refrigeration system • Results from modelling work • Benefits and future applications • Next steps

  3. Need for microprocessor cooling • Moore’s Law: approx. doubling of transistors every 2 years • Concentration of chip components results in increased heat output • To keep chip to acceptable temperature (< 85°C) need more efficient cooling than heat sinks/fans

  4. Conventional microprocessor cooling • Typical microprocessor package attached to heat sink • Expanded section showing heat spreader and heat sink

  5. Heat distribution across microprocessor • The microprocessor die generally has a surface area of 2 to 3 cm2 • Heat generation is unevenly distributed across the surface of the microprocessor die • overall heat flux from current high performance chips • typically 150 W cm-2 • - however, within “hot spots” heat fluxes are approaching 1kW cm-2

  6. Alternative IC cooling technologies

  7. Fan Hot Gas Line High Pressure Liquid Line Condenser Expansion Orifice Compressor Low Pressure Liquid/Gas Line Suction Line Evaporator Microprocessor Development of a micro-refrigeration system • LSBU in collaboration with the University of Oxford and Newcastle University has developed an electronic cooling device which uses a porous media heat exchanger in a micro-refrigeration system together with a small oil-free compressor

  8. Porous media evaporator • A porous media heat exchanger has been developed by Newcastle University in conjunction with Thermacore • Current device is designed to lift 350 W from 2.75 cm2, with 2 g s-1refrigerant (R134a) and a pressure drop of < 20 kPa

  9. Design of Oil-Free Compressor • Low cost components • High efficiency • Simple, robust construction • Compressor is designed to provide 100W shaft power • Expected to provide 250W cooling at COP 2.5 (Image supplied by University of Oxford) • Static part of motor consists of a series of wire wound laminated cores • Cores are slotted to leave a rectangular gap • Moving assembly comprises a number of rectangular magnets arranged in a line and occupying the gap

  10. Development of model for micro-refrigeration system • A 1-D transient, lumped parameter model of the micro-refrigeration system has been developed at London South Bank University (LSBU). • Model used to analyse system performance and investigate control of system “transients” • A detailed model of the oil-free compressor has also been developed • Output screen shows many parameter values, updated each time step

  11. Results for Compressor Model Piston Displacement and Motor Force Piston Velocity and Damping Force • Piston displacement oscillates similar to motor force • Displacement lags motor force by approx. 90 (phase angle) • Steady sinusoidal pattern seen when transient forces have decayed • Piston velocity is mirror image of damping force • Damping  -(velocity) i.e. deceleration effect • Piston velocity has sharper peak in compression phase

  12. Benefits and Applications • Benefits of micro-refrigeration: efficient removal of heat from specific areas/surfaces; control of temperatures; reduced thermal stress; increased lifetimes for high power systems • In the future, micro-refrigeration systems are likely to provide cooling for a wide range of applications • Examples include: • use of liquid microchannel heat exchangers in 3D chip architecture i.e. interspersed between layers of vertically stacked chips • cooling of personal protective clothing for use in hot, hazardous environments • cooling of defence electronics; high power electronics; laser diode cooling • cooling of server racks in data centres

  13. Next steps • Main focus for developing micro-refrigeration systems during recent years has been on single phase pumped refrigerant e.g. water • Now turning to two-phase cooling systems – a range of small scale micro-refrigeration systems of different capacities have been reported recently • One problem that has been highlighted for a number of the systems is the need for oil-free compressors • It is planned to continue with development of the micro-refrigeration system described here and to adapt it to work with ammonia

  14. Further Information See website: http://www.minicool.co.uk or Email: info@minicool.co.uk

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