HYBRID COOLING SYSTEMS-nitesh

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Information about HYBRID COOLING SYSTEMS-nitesh
Science-Technology

Published on February 10, 2009

Author: nitesh003

Source: authorstream.com

HYBRID COOLING TECHNIQUE : HYBRID COOLING TECHNIQUE CONTENTS : CONTENTS Microchannel Cooling Microjets Cooling Hybrid micro-channel/micro-jet cooling MICROCHANNEL COOLING : MICROCHANNEL COOLING DEFINITION : DEFINITION Microchannel heat exchanger consists of an array of rectangular microchannels A coolant passes through the array of microchannels and takes away the heat Size: Small channels (typically < 1mm) 3-D VIEW OF A MICROCHANNEL HEAT SINK : 3-D VIEW OF A MICROCHANNEL HEAT SINK Lhs– Length of heat sink Whs –Width of heat sink Lch – Length of channels Wch–Width of channels Wfin–Width of fins Tb – Thickness of base plate qw – Heat Fig. 1 COOLING PROCESS : COOLING PROCESS Most frequently used coolants............ Air, Water & Flourochemicals Coolant is forced through these narrow channels Convective cooling is achieved WHY HIGH CONVECTION HEAT TRANSFER?? : WHY HIGH CONVECTION HEAT TRANSFER?? Conv. Heat transfer = hA(Ts-T8) To increase this heat transfer.. Increase h – but cost can increase Reduce T8 – impractical Increasing the surface area So microchannels increase the surface area along which convection occurs ALSO HIGHER HEAT TRANSFER COEFFICIENTS : ALSO HIGHER HEAT TRANSFER COEFFICIENTS SMALL CHANNELS PROVIDE HIGHER HEAT TRANSFER COEFFICIENT……… h=Nu*k/d Nu: Nusselt number h: heat transfer coefficient d: Hydraulic diameter k: thermal conductivity Microchannel heat exchanger.. High surface area/volume ratio High heat transfer per unit volume Smaller channel gap Higher volumetric flux Small diameter results in large heat transfer coefficient in microchannels MICROJET COOLING : MICROJET COOLING WHAT IS MICROJET COOLING ?? : WHAT IS MICROJET COOLING ?? A nozzle forms one end of a partially enclosed chamber Nozzle creates the jet of coolant Typically the jet is turbulent Maximum turbulence is below the slot Fig. 2 nozzle Slide 11: A liquid is delivered through an array of tiny nozzles to hit the semiconductor devices A dielectric liquid is needed to prevent an electrical short Microjet cooling provides an equivalent cooling with improved uniform temperature distribution MICROJET COOLING PROCESS TYPICAL MICROJET COOLING STRUCTURES : TYPICAL MICROJET COOLING STRUCTURES DIRECT COOLING Fig. 3 Fig. 4 INDIRECT COOLING Characteristics of a MicroJet Cooling : Characteristics of a MicroJet Cooling The breakdown of vortices increases velocity fluctuations normal to the impingement surface. These fluctuations result in enhanced heat transfer Equivalent cooling is achieved by large number of jets These factors combine to give superior heat transfer characteristics Slide 14: MICROCHANNEL MICROJET COOLING COOLING HYBRID SYSTEM : HYBRID SYSTEM Clearly, both jet-impingement and micro-channel heat sinks can dissipate the high heat fluxes anticipated in future high performance devices. Both have drawbacks so recently, the researchers proposed HYBRID SYSTEM CONTINUEDGives rise to hybrid cooling system which consists of slot jets that feed fluid into micro-channels..Can meet challenges of high performing electronic devices + taking care of uniformity in cooling : HYBRID SYSTEM CONTINUEDGives rise to hybrid cooling system which consists of slot jets that feed fluid into micro-channels..Can meet challenges of high performing electronic devices + taking care of uniformity in cooling This scheme involves feeding coolant from a series of circular micro-jets to each micro-channel in a modified micro-channel heat sink module.This scheme is capable of cooling chips that produce more than 1,000 watts of heat per square centimeter : This scheme involves feeding coolant from a series of circular micro-jets to each micro-channel in a modified micro-channel heat sink module.This scheme is capable of cooling chips that produce more than 1,000 watts of heat per square centimeter HYBRID SYSTEM CONTINUED THREE KEY OBJECTIVES OF NEW HYBRID COOLING SYSTEM : THREE KEY OBJECTIVES OF NEW HYBRID COOLING SYSTEM Dissipating large heat fluxes Maintaining low surface temperatures Reducing surface temperature gradients. NEW HYBRID TECHNOLOGY : NEW HYBRID TECHNOLOGY This cooling system is made of grooves narrower than a millimeter These channels are formed on top of a chip and covered with metal plate containing tiny holes The coolant is pumped through the holes forming microjets As the liquid is heated up it bubbles and momentarily becomes vapor, facilitating cooling process COMPONENTS IN EXPERIMENTAL SET-UP.. : COMPONENTS IN EXPERIMENTAL SET-UP.. Copper heating block. Six copper-constantan (type-T) thermocouples 16 cartridge heaters. A lower support plate An upper plenum plate Micro-channels which were machined into the top surface of a copper heating block Six copper-constantan (type-T) thermocouples A Micro-jet plate An absolute pressure transducer Insulation blanket Solid ceramic insulation O-rings WORKING : WORKING The micro-channels were machined into the top surface of a copper heating block. Six copper-constantan (type-T) thermocouples were inserted below the test surface Blanket insulation around the copper block is provided Machined into its top surface were five 1 mm wide and 3 mm deep slots Five parallel arrays of fourteen 0.39 mm diameter circular holes were drilled Slide 23: O-rings were used to prevent liquid leakage between the jet plate and the upper plenum plate Pressure transducer and a type-T thermocouple connected to the inlet plenum in the top plenum plate Sixteen holes were drilled into the large underside of the heating block to accommodate the cartridge heaters. WORKINGcontinued HEATING BLOCK STRUCTURE : HEATING BLOCK STRUCTURE Fig. 6 Slide 25: Unit cell consisting of single row of circular micro-jets and single micro-channel Fig: 7 Slide 26: A dielectric liquid is used as a coolant as….. It is shock resistant Hydrofluorocarbons are used as a coolant because They are not harmful to ozone layer They have low global warming effect But they are not efficient coolers. Usually with Hydrofluorocarbons you are able to cool only 200w/cm2 …………but this hybrid design boosted the performance dramatically CONCLUSIONS : CONCLUSIONS Jet velocity has a profound influence on the single-phase cooling performance of the hybrid cooling module A superpositioning technique is introduced which is able to remove heat fluxes more than 1000W/m2

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