Online proceedings - EDA Publishing Association

24-26 September 2008, Rome, ItalyPhase change heat dissipater of aluminiumcontainerJ.Esarte , C. Wolluschek , E.ArmendárizCEMITEC (Fundación CETENA), Polígono Mocholí-Plz. Cein, nº4, 31110 Noain (Spain). Telef: +34848 420800, Fax: +34 48 317754, e-mail: jesarte@cemitec.comAbstract-Due to the cupper’s increasing cost there is a trendto use more and more the aluminium instead of cupper. Whenusing aluminium in phase change dissipaters there are twoaspects that must be consider: one is the welding difficultyand other is the surface cleaning for a better wetting. It is verywell known how much the solid surface quality affects on theliquid’s wetting capacity. At this point little is done on thealuminium cleaning process in order to improve the liquidwetting without damaging the material itself, that’s to say,corrosion appearance.Once the aluminium surface is cleaned the next step is toexperimentally measure the wick structure capillary pumpingattached to the aluminium in both against and in favour ofgravity.Under all previous processes a prototype of a phase changeheat dissipater made of aluminium is constructed forrefrigerating a specific electronic application. Flat instead ofpipes has sense in applications where the electronics isrequired to be inside a hermetic box.I- INTRODUCTIONIn the last 50 years, electronics has considerableboosted a wide range of industrial sectors such as:computers, telecommunications, automotive, etc, Thisboost has been possible thanks to the electronicsevolution what has allowed reducing the electronicsdevices’ size and cost as well as increasing theircapacities what results in a heat dissipationincrement. In case this heat dissipation is noteffectively removed from the electronic device orcomponent its temperature could increase above itsmaximum one being very harmful to its efficiency andoperating life. For instance, semiconductors with a200ºC thermal limit should always be working at alower temperature to guarantee its reliability. For thisreason heat dissipation is now a key matter inelectronics development, more efficient (lower thermalresistance) and smaller heat dissipaters are required.Among them, those based on the phase change of aliquid appear as the most efficient one (heat pipes,and heat spreaders) [1]. As known, these dissipaterstake advantage of the liquid’s heat latent whenrunning a thermodynamic cycle (evaporation at thehot zone, vapour transport at the adiabatic zone,condensation at the cold zone and liquid return to thehot zone) to remove the heat out of the electroniccomponent. In some cases, the liquid return isboosted by capillary wicks (sintered powder, mesh,grooves).In industries such as space, military and computers,heat pipes are widely used. However in industrieswith a lower technical requirements and where thecost is an essential factor to consider, its use isprogressively being carried out (heat spreaders toimprove the Peltier pellets efficiency in domesticrefrigerators) [2].II- PHASE CHANGE HEAT DISSIPATER PROTOTYPEThe specific application (not specified due toconfidentiality issues) to which a heat dissipater ofthis kind is being analysed in this work, requires 10 Wof heat power extraction, a component limittemperature of 120ºC, a 62x62x62 mm close volumeand aluminium as dissipater material. All this forcesthe dissipater to have a specific geometry andoperability. The dissipater’s design parameters are:water as working fluid, 80ºC the operatingtemperature, aluminium base material, a stainlesssteel mesh as wick structure and with a 25x25mmevaporator area and 60x60mm condenser area (onewall of the hermetic box), free convection isconsidered outside the condenser area, figure 1.1: Aluminium phase change heat dissipater.Fig.A- Prototype constructionNormally heat pipes are made of copper, howeverbecause of its so high prize aluminium appears moreappropriate for low cost applications as this one. Forthis case the material is aluminium 6000 withmagnesium alloy. Because aluminium is not an easy©EDA Publishing/THERMINIC 2008 97ISBN: 978-2-35500-008-9