Previous Page | Contents | <strong>Zoom</strong> in | <strong>Zoom</strong> out | Front Cover | Search Issue | Next PageABE FMaGSlighting | HEAT REMOVALin the natural convection mode.The flared structure has a largetotal surface area combined witha wide spacing between pins thatallows air to circulate in a significantlymore efficient manner thanin a heatsink with vertical pins. Thestaggered pin design and the omnidirectionalstructure, which allowsair to enter and exit the pin arrayfrom any direction, both contributeAdvanced Thermal Solutionsto the efficiency.Dagan claims that flared pin findesigns often can be used in situationsthat would otherwise requirea much larger conventional heatsink,or an additional cooling device such asa fan. He said that flared pin fins are a greatfit for extreme, high-temperature outdoorenvironments, for very hot LED applications,and for large LED assemblies. “Although theLED market wasn’t an initial target for thesedevices,” said Dagan, “the calls started pouringin” when the products were unveiled (seewww.ledsmagazine.com/press/17958).Advanced Thermal Solutions, based inNorton, MA, offers several heatsink optionsfor use in LED fixtures of different types. Forexample, the company’s linear heatsinks areavailable specifically for LED strips, whichare widely used in architectural lighting. Itspatented spread-fin array reportedly maximizessurface area for more effective convectioncooling, particularly when air flowis limited, such as inside display cases. Thecompany also offers round heatsinks specificallyfor round LED boards, which are usedto replace halogen lamps in applicationssuch as spotlights and down lighting. Theround heatsink (see Fig. 2) has a special starshapedprofile fin design that maximizessurface area for effective convection andradiative cooling in the vertical mountingorientation, for example, inside ceilings.Heat pipesWhen heat is concentrated in an area whereadequate airflow is limited, heat pipes can beused to move the heat to where it can be efficientlyremoved by either a stand-alone heatsink,or a heatsink with a fan. Additionally,as heat pipes can be formed into differentshapes, they can be incorporated intothe heatsink design, allowing for a smallerFIG. 2. An LED-based spotlight with a round, fi nned heatsink. An IRview is shown at right.Noren ProductsHeat inEvaporator sectionLiquidVaporAdiabatic sectionWickheatsink to be used.According to Dennis Scott of Noren Products,a heat pipe manufacturer based inMenlo Park, California, copper heat pipesare isothermal structures that utilize a phasechangeprocess to create a passive heat pumpthat moves heat from the source (e.g. an LEDboard) to the output (e.g. a heatsink). <strong>In</strong>sidethe copper tube is a wick structure, along withenough fluid to “wet the wick”. When heat isintroduced to the copper tube, the water inthe wick vaporizes and pushes the heat downthe length of the tube to the outlet. As it cools,vapor condenses and re-wets the wick, creatinga closed loop system (Fig. 3).Scott points out that the heat pipe by itselfis not a cooling device, but requires a heatsource at the input, and method of removalat the outlet. The way in which the pipe isattached to the heat source and to the outletis important, and Noren works only withcustom designs. “As simple as the concept is,it provides a pretty complex solution,” saidScott. “Once it’s in place, it’s a passive solution.But putting it in placeisn’t as easy as most peoplethink.”Scott said heat pipe technologyis fairly new to theLED industry, and is provingto be especially suited tohigh power LEDs in applicationssuch as street lighting,where a longer lifetime ofcooling is required – such as10 or more years. Heat pipescan distribute heat over anLED street light’s housingfor 10-15 years. Another LEDapplication suited to heatpipes is track lighting. “<strong>In</strong>stead of individualheatsinks for each light, heat pipes canbe used to move the heat to a single, efficientheatsink,” explained Scott.Synthetic jetsSynthetic jets are an alternative option tofans as a method of active cooling. This proprietarytechnology, developed by Nuventix,comprises a module that creates turbulent,pulsated air-jets that can be directed preciselyto locations where thermal managementis needed. According to Mick Wilcox,reliability is the biggest advantage syntheticjets have over fans, because their lifetime istwice that of the LEDs themselves.Here’s how it works. Wilcox compared itto the simple act of breathing, with inflowand outflow through the same opening, andpulses of air being created by a diaphragm.<strong>In</strong> the case of a SynJet (Fig. 4), the chamberis powered electromagnetically, oscillatinga diaphragm made of elastomer upand down at 50 HzHeat outCondenser sectionFIG. 3. Heat pipes use a phase-change process to transfer heatfrom the source to the output device. See www.ledsmagazine.com/news/6/2/10 ________ for an example of a street lighting fi xture in which aheat pipe transfers thermal energy from the optical module to theheat sink.to propel rapid-firepulses of turbulentair out of the chamberand through theheatsink. The pulsesmaintain a higherheat coefficient, andtherefore can coolthe same amount ofair with half the airflowof a fan.Acoustically, the50 Hz frequencyis below human42 APRIL 2009 LEDsmagazine.comPrevious Page | Contents | <strong>Zoom</strong> in | <strong>Zoom</strong> out | Front Cover | Search Issue | Next PageABE FMaGS
Previous Page | Contents | <strong>Zoom</strong> in | <strong>Zoom</strong> out | Front Cover | Search Issue | Next PageABE FMaGSlighting | HEAT REMOVALFIG. 4. Nuventix has supplied SynJetcooling modules to a number ofluminaire manufacturers. A blackSynJet and heat sink (left) areattached to a Fortimo light enginefrom Philips. Synthetic jets (right)are created by rapid-fi re pulsesof turbulent air produced by anoscillating diaphragm.Nuventixhearing levels, while fans run at a higherRPM right in prime hearing frequency,explained Wilcox. The form-factor advantageis that it cuts the size of the heatsinkby 2 or 3×, including the SynJet module.Wilcox said this allows system integratorsto design much more compact lighting fixtures,and allows them to shrink or moldthe heatsink to suit the aesthetic appealof the fixture.Synergies exist between different technologies,and several can be included in thedesign of one LED cooling solution. Accordingto Wilcox, one scenario might involveattaching the heat source to a heat sink withan integrated heatpipe and then attachingthe synthetic jet module to the heatsink. Headded this solution would be proposed in a“very thermally challenging situation” due toits cost. The heat pipe would be eliminated,if possible, to keep the cost down.ConclusionAs the LED market matures, so do the solutionsto thermal management limitations.Advancements in heatsink technologies,copper heat pipes and synthetic jet modulesare paving the way for aesthetically pleasing,efficient, acoustically tolerable, reliable LEDfixtures that light our way._________Previous Page | Contents | <strong>Zoom</strong> in | <strong>Zoom</strong> out | Front Cover | Search Issue | Next PageABE FMaGS
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