PHASE CHANGE MATERIALS

Transcription

1 18 TECHNOOGY REVIEW: PHASE CHANGE MATERIAS Qpedia continues its review of tecnologies developed for electronics cooling applications. We are presenting selected patents tat were awarded to developers around te world to address cooling callenges. After reading te series, you will be more aware of bot te istoric developments and te latest breaktrougs in bot product design and applications. We are specifically focusing on patented tecnologies to sow te breadt of development in termal management product sectors. Please note tat tere are many patents witin tese areas. imited by article space, we are presenting a small number to offer a representation of te entire field. You are encouraged to do your own patent investigation. Furter, if you ave been awarded a patent and would like to ave it included in tese reviews, please send us your patent number or patent application. In tis issue our spotligt is on pase cange materials (PCMs), in particular some more recent applications for tese versatile termal management products. Tere is muc activity in tis product arena, and tese patents sow some of te salient features tat are te focus of different inventors. IQUI COOANT WITH MICROENCAPSUATE PHASE CHANGE MATERIAS FOR AUTOMOTIVE BATTERIES US B2, WANG, X. A microencapsulated pase cange material used in conjunction wit a cooling fluid as part of a termal management system for an automotive battery pack assembly. Te microencapsulated pase cange material is made to ave enanced latent eat transfer properties at lower (colder) temperatures and iger (elevated) temperatures suc tat a veicle employing suc an automotive battery pack assembly is more resistant to environments were freezing and overeating migt oterwise be prevalent. Terefore, tere is a need for an improved termal management of portable and/ or wearable electronic devices tat take into account oter factors and consideration wen performing termal management. itium-ion batteries are being used in automotive applications as a way to supplement, in te case of ybrid PATENT NUMBER TITE INVENTORS ATE OF AWAR US B2 IQUI COOANT WITH MICROENCAPSUATE PHASE CHANGE MATERIAS FOR AUTOMOTIVE BATTERIES Wang, X. Jan 7, 2014 US B2 THERMA INTERFACE MATERIA Razeeb, K. et al Apr 22, 2014 US B2 E AMP ASSEMBY WITH THERMA MANAGEMENT SYSTEM Hitccock, R. et al Jul 22, 2014 Table 1. Patents Reviewed Featuring Pase Cange Material Qpedia ISSUE 94

2 19 TECHNOOGY REVIEW can provide te ability to maintain te cell temperature in a desired temperature range witout drawing power from te battery or anoter energy source. An example of a PCM-based approac to battery termal management may be found in a co-pending U.S. patent application Ser. No. 13/175,483 entitled BATTERIES WITH PHASE CHANGE MATERIAS wic was filed on te same day as te present application, owned by te Assignee of te present invention and ereby incorporated in its entirety by reference. electric veicles (HEVs), or supplant, in te case of plug-in electric veicles (PEVs), conventional internal combustion engines (ICEs). In eiter variant, HEVs or PEVs belong to a larger class of veicles known as electric veicles (EVs). Te ig volumetric eat generation rate and generally passive construction of litium-ion batteries provides bot te durability and functionality needed to serve as a propulsion system for cars, trucks, buses, motorcycles and related automotive or veicular platforms. According to one aspect of te invention, a termal management system for an automotive battery pack employs a microencapsulated version of a PCM-based termal management system. Tis version, known as a micropcm, is made up of very small bi-component particles or capsules tat include a core material tailored to latent eat canges witin a temperature range typically countered in an automobile battery pack, along wit an outer sell or capsule made from a polymer or related material suc tat togeter, te core and sell define a generally sperical foam-like material. A battery termal management system based on a pase cange material (PCM) as te potential to limit battery temperature extremes, tus acting to increase temperature uniformity, as well as to reduce eating and cooling requirements. Tis elps to prolong te life of eatsensitive components, suc as te carge-carrying battery cells tat form te building blocks of battery modules and battery packs. PCMs can absorb and release a large amount of latent eat (in some instances up to fifty times iger tan sensible eat) during isotermal (i.e., constant temperature) canges of pase, suc as from solid-to-liquid or liquid-to-solid. As suc, te use of PCMs can elp to reduce or eliminate te need for active cooling components suc as a fan, blower or pump in forced-air or forcedliquid cooling systems. Tis is beneficial in tat te PCM THERMA INTERFACE MATERIA US B2, RAZEEB, K. ET A A termal interface material (1) comprises a bulk polymer (2) witin wic is embedded sub-micron (c. 200 to 220 nm) composite material wires (3) aving Ag and carbon nanotubes ( CNTs ) 4. Te CNTs are embedded in te axial direction and ave diameters in te range of 9.5 to 10 nm and ave a lengt of about 0.7 μm. In general te pore diameter can be in te range of 40 to 1200 nm. Te material (1) as particularly good termal conductivity because te wires (3) give excellent directionality to te nanotubes (4) providing very low resistance eat transfer pats. Te TIM is best suited for use between semiconductor devices (e.g. power semiconductor cip)

3 20 interface material (TIM) are used between packaged semiconductor device and te termal management system e.g. eat sink. Present TIMs (aving termal conductivity of Wm 1K 1) are not sufficient to remove te eat of tese power semiconductors. Te TIM te invention as a termal conductivity of >80 Wm 1K 1 and tereby is able to dissipate te eat very efficiently. and any type of termal management systems for efficient removal of eat from te device. Te invention relates to a termal interface material ( TIM ) for uses suc as ig termal conductivity. One of te main limitations in power semiconductor device cooling is te microscopic unevenness and non-planarity between te mating surfaces (cip and eat sink). Asperities on eac of te surfaces prevent te two solids forming a termally perfect contact. Terefore tere ave been proposals to move away from TIMs in te form of bulk rigid bodies suc as Cu films. Te MWCNT (multiwall carbon nanotubes) and metal composites are embedded in polymer as ig aspect ratio wires and tereby act as a termal pat between two mating surfaces, wic can conform to te surface rougness due to teir submicron diameters and micron lengts. Because te template witin wic tey are embedded as some flexibility tere is excellent conformity wit te mating surfaces. As te metal co-deposited wit carbon nanotubes ave ig termal conductivity (3000 Wm 1K 1), te overall conductivity of te wires is increased. Unlike te prior art, it does not depend on te percolation tresold property of te filler materials of commercial TIM product to constitute a termal pat between two surfaces. Te invention is directed towards providing an improved TIM for applications were tere is unevenness, generally were conformity and ig termal conductivity are required. According to te invention, tere is provided a termal interface material comprising: a body aving opposed faces, and aligned submicron wires in pores in te body and extending between te opposed faces, eac submicron wire including a metal. Te aligned sub-micron wires give excellent eat transfer pats and te body may be cosen for te required degree of flexibility for conformity wit te end-application devices wit wic it is in contact. Te TIM is best suited for use between semiconductor devices (e.g. power semiconductor cip) and any type of termal management systems for efficient removal of eat from te device. Tis material as te potential to acieve termal conductivity beyond state of te art termal interface material pads. In te near future, te power level for power semiconductor devices will rise to about 200 W, or about an effective power density of 500 Win 2. In order to remove te eat efficiently, different types of termal Examples of metal of te submicron wire can be nickel, gold, copper, or silver. Nickel, copper, and silver submicron wires were fabricated aving room temperature termal conductivity of 90.7, 401 and 429 Wm 1K 1 in teir bulk form, respectively. Among tem silver was te preferred metal of coice as bulk silver as te igest room temperature termal conductivity of 429 Wm 1K 1. In te present invention a single submicron wire aving ig aspect ratio will be able to make a termal pat between te device and te eat sink witout depending on any percolation and tereby eliminating te interparticle termal interface resistance as well found in te commercial TIM products.

4 21 TECHNOOGY REVIEW E AMP ASSEMBY WITH THERMA MANAGEMENT SYSTEM US B2, HITCHCOCK, R. ET A A ligting system is described. Te ligting system includes a lamp and a first container including a first pase cange material termally connected to te lamp. Heat generated by te lamp during operation is conducted to te first pase cange material. Te system also includes a second container including a second pase cange material termally connected to te lamp. Heat generated by te lamp during operation is also conducted to te second pase cange material, and te second pase cange material as a transition point temperature lower tan te transition point temperature of te first pase cange material of te first container to account for a temperature drop between te second container and te first container. Te ligting system also includes a temperature sensor for reducing lamp power if te lamp becomes too ot, and a mounting bracket wic may also conduct eat away from te lamp. PCM ( pase cange material ) unit 106 includes, in one embodiment, a ig eat latency pase cange material enclosed in a termally conductive container. Pase cange materials typically ave a ig latent eat of fusion suc tat a large amount of eat energy must be applied to cange te PCM from, for example, a solid to a liquid, or from a solid aving a first caracteristic to a solid aving a second caracteristic. Illustrative PCMs are sodium sulpate, magnesium cloride, and barium ydroxide compositions. At temperatures below and above a PCM's transition point temperature, te PCM temperature rises as te PCM absorbs eat. However, at te PCM's transition point temperature, te PCM absorbs eat witout increasing in temperature until a cange of state occurs. As suc, a PCM can clamp te temperature of its surroundings at its transition point temperature. PCM unit 106 is effectively clamped at te transition point temperature until a complete PCM cange of pase as occurred. E 102 and PCM unit 106 are coupled via termal connector 104 so tat te eat generated by E 102 can be transferred to PCM unit 106. Because tere is a known temperature drop along termal connector 104, te clamping temperature of PCM unit 106 effectively clamps te temperature of E 102 at a sligtly iger temperature. uring te clamping period, PCM unit 106 absorbs all or at least a portion of te eat or energy released into ligting system 100 wile keeping a steady temperature so tat ligting system 100 may continue to work witin a normal working temperature range. Tis clamping effect is especially important for E-based ligting systems because te available output capacity, efficiency, and life of an E are igly dependent upon te E junction temperature, and te E junction temperature can rise if te temperature of ligting system 100 rises. Te clamping effect can provide benefits in several different ways. For example, in one embodiment te clamping effect can be used to drive a configuration of Es wit a iger current, under ordinary ambient conditions, to provide more ligt output tan would oterwise be possible or sustainable at tat current. In anoter embodiment, te clamping effect can be used to drive a configuration of Es wit an ordinary current, under extreme ambient conditions (e.g., in a ot desert environment), to provide more ligt output tan would oterwise be possible or sustainable in tose conditions.

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