Webinar: When Heat Sinks Aren't Enough, Go beyond traditional heat sinks

Webinar: When Heat Sinks Aren't Enough, Go beyond traditional heat sinks

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Hello everyone, thank you for joining us  today. Today we're going to talk about when   heat sinks aren't enough and the concept here  is that you're running into limitations with   very routine metallic based heat sinks and you  need some improvement and we're going to look at   a bunch of two-phase technologies to improve the  performance and enhance your heat sink capability. So again, thanks for joining us, my name  is Bryan Muzyka i'll be kind of running   through the slides with you today and also do  want to encourage please type in questions in   the in the question box. We'll make  sure to go through all of those after the   webinar concludes and get you all responses  with a lot of detail on those so please ask   as many questions as come to mind  during this, there's a lot to cover and we'll   get into kind of some of the basics but  yeah, certainly not enough time here   today to go through in significant detail so  please feel free to to ask questions as we go. So for those of you who haven't joined  us in the past we do want to just   kind of touch base on the act we are a thermal management solutions company and we handled the   entire gambit of thermal solutions from passive  two-phase heat transfer technologies kind of at   the component and sub-assembly level all  the way to full solutions fairly complex   active systems looking at pump single phase pump  two-phase as well as vapor compression cycles   so we do have a lot of tools in our toolbox  and we work very closely with our customers   to make sure that the optimal solution is is  determined and over the course of our history   showing there we have won several awards  i'll just maybe go through the most recent past couple of years we've won three different  military and aerospace electronics innovators   awards so those were for our ICE-lok  product line our Pumped two-phase product line   and we're in our space copper water heat pipe  product line so we're very proud of those awards   and last year we also won the AHR product of  the year award in the green building category.

For some of the work we do in energy recovery, for large HVAC systems and overall we are   slightly over 220 employees and over  200, 000 square feet in two facilities   here in Pennsylvania, one in Lancaster  Pennsylvania and one in york Pennsylvania. So the agenda for today we're going to look at  as i mentioned two-phase technologies that are   used to enhance performance of your heat sink  or of your system so the first one we'll dive   into here is heat pipes then we'll go into kind  of more of an application with HiK plates.  i'll talk about vapor chambers and then we'll  talk about phase change material heat sinks as   well as pulsating heat pipes so a lot to cover  here we'll go through each very quickly but as   I mentioned please type in as many questions  as come to mind as we go through these slides. so heat pipe technology I know a lot of those  who are joining us today um have joined   past webinars and are probably familiar with heat  pipes so I won't go through in a lot of detail the   operating principles but effectively they are a  two-phase liquid and vapor heat transfer device   a closed-loop system where  we run a vacuum on the pipe   wherever heat is input it will create a boiling  effect use the lean heat of vaporization to   enhance your heat transfer coefficient and  that boiling will create an internal pressure   and temperature gradient which will push the  fluid to wherever it's colder in the system   and wherever it's colder and coupled with the  heat sink the fluid will give up its latent heat   condense back to a liquid and then be transferred  back from the condenser to the evaporator either   by gravity or some type of internal wick structure that creates a capillary pressure   so overall you have a very low delta t from  evaporator to condenser which gives you that   kind of really good thermal performance  as you integrate these into your system so most of the customers that come to us are  really looking for design help with heat pipes   so a lot of the questions we get are how how  can we bend them how can we flatten them how   can we retrofit fit them into current designs  so just looking at those areas we'll give some   general guidelines here the first is bending  so we do recommend a centerline bend radius of   3x the outside diameter so you can see the figure to the right there is kind of showing   you the centerline bend radius and if we keep  that 3x the OD we should be in good shape to not   degrate performance on the flattening side again  this is kind of a general guideline rule of thumb   but usually, we recommend keeping it above  two-thirds the outside diameter so you can go   flatter in certain instances as you change your  profile you calculate your power capabilities   based on the hydraulic diameter instead of  the you know circular diameter of the pipe   so that will limit performance a little bit but  sticking above two thirds of the outer diameter   still can move pretty significant power and then  the last question we typically get is is on how to   integrate these into your system how do we  get a good heat transfer path into the heat   pipe so that we can take advantage of the fluid effects and the vaporization and there we   typically recommend solders as the best mechanical  and thermal performing bonding technique usually   it's a lead-tin solder but there are also rojas  compliance solders that can be used as well   outside of that we can also use epoxy which has  some advantages as far as ease of manufacturing   but not quite as good mechanically or  thermally as a solder joint would be   and then along the bottom there you can kind of  see just a general thermal resistance network   and the goal here with with any thermal  solution is to keep the device temperature   as low and close to the safe operating to improve  the life of your electronics and so analyzing   each resistance separately and optimizing  each will provide you the best performance   but the heat pipe resistance itself there is  somewhat of a short circuit to that resistance   network it'll provide a very low delta t to move  heat fairly long distances so it's a really nice   way to improve your overall thermal resistance  network with a pretty easy straightforward design and now jumping into the design route a little  more we do have some tools that are free to the   public that you can use to help with your heat  pipe design the first one we want to talk about   here is the heat pipe calculator which is on our  website under the resources tab and this gives a   pretty basic diagram of a heat pipe it talks about  kind of how to set it up your evaporator length   being the length that's coupled with your heat  input and the condenser length is basically the   length that is coupled to your heat sink or your  heat rejection area and then anything in between   there would be called the adiabatic section and we  kind of just use the total length of the heat pipe   to run the calculations here so you can see the  inputs required on our tool there to the bottom   right and the other input that i haven't mentioned  yet is the height against gravity and that is   basically the height differential between your  evaporator and your condenser so if you do have   a system that has bends or more complex geometry  just taking the overall height difference from   your evaporator to the condenser or the height  difference of the longest region where the   working fluid would need to pump against gravity  is basically what we're trying to calculate there and so here's just kind of a basic  design looking at one example   so this is an example where you have about  an inch and a quarter of heat input area   um the the pipe goes up is bends at a 90  degree and then couples the heatsink with   the two inch area and has a about  four inch of total height change now you can see in that one the the height  change is actually favorable for heat pipe   performance because the evaporator is below the  condenser so when we input that we actually put a   -4 as the height against gravity and then we can  run our calculations so the plot you see there is   the results and if if you go above to the title  bar of the plot the red areas the red figures   are the um inputs that you put into your system  so you can see we use a minus four instead of a   four operating height against gravity but overall  you can move some pretty good heat here with a   seven inch long pipe in these conditions and then  from there you kind of have the option to use   a single pipe that can move the entire heat  load or use two smaller pipes that can move   the heat load so for this example we have between  60 and 70 degrees wanting to move about 70 watts   and you can see kind of your options there  so in this case you had you could use one six   millimeter pipes or two eighth inch pipes  or something larger than eight inch pipe so that gives a kind of an example of heat  pipes and how they're used um so the second   module here is on high k plates which is the  application of heat pipes into aluminum frames   so again the idea here is to embed heat  pipes completely within an aluminum frame   high k is an acronym for high thermal connectivity  so by doing this you can actually increase your   thermal conductivity of aluminum which is  the most typical material because of its   easy to machine low cost and a lot of the  different mechanical properties associated   with aluminum but you can increase your  your thermal conductivity or k value   of like 160 to 180 watts per meter k upward to  500 to 1200 watts per meter k and that value there   is real-world examples where we've actually built  high k plates tested them to real customer inputs   and then went back to our models and put a bulk  thermal conductivity until we matched our test   results so those are very real-world solutions  we're not strategically putting our heat input   or heat pipes in in conditions where it would show  favorable results those are very real world and we   usually tell customers if you put 600 watts  per meter k that's something we can achieve   the other benefits outside of thermal performance  is strength and weight by integrating heat pipes   into aluminum with a soldered assembly you're  not affecting the weight very much and you are   um staying at very similar strength  and we've done a lot of programs with   defense primes and things like that to verify  those claims and in many conditions we   can because the heat pipes are doing all your  thermal work we can actually reduce the weight   of the system by taking out some of the area  that's not needed for thermal performance anymore   as long as you're maintaining the  structural strength integrity required   of the system you could a lot of times  reduce the overall weight of your system and then here's one kind of example  case study this is a very large plate   it's roughly three and a half by two feet  and you can see there is several hot spots   from the initial design requirements the goal here  was to get it out to those liquid-cooled rails so   that's the blue rail temperature you can see there  and you can see in the couple hotspots we'll call   them three main hotspots there was the two on  the top have a very small thermal path but they   had such a high heat flux that they were still  creating kind of that failure mechanism up there   so if you look to the heat pipe  layouts on the the two right figures   you can see that it was it was a matter  of not only getting the heat to the edge   but routing the heat pipe along the edge to  lower that heat flux into the liquid coolant   and drive down those temperatures and then on the  bottom figure uh or bottom hot spot it was really   all about the length the conduction path so there  we just wanted to get as many heat pipes in there   and bring it out to the rail as efficiently  as possible so the overall design here was   dropping the component temperatures of those three  main hotspots by about 20 degrees so significant   thermal performance improvements and again no  real impact on weight or strength of the system and here's one example of actually reducing weight  using a high k design so in a standard heatsink   your conduction is mainly due to  the the thickness of the material   and then your convection is on kind of the  the fin area so you need large enough um   volume to lower your volumetric resistance  enough to get the convection benefits and then   the spreading within the aluminum by increasing  your thermal conductivity significantly you can   actually thin down your base and you can also get  better fin efficiency by operating most of the fin   length at similar temperatures so you can achieve  similar performance in a smaller form factor   using high k heat sinks versus straight metal  heat sinks and here's an example that you can   see the the final design was over three pounds  lighter and had a much thinner base and also   got better performance out of their fins and this  is the test results of of the case study you just   saw so we've again put in the same inputs  in both areas we ran the system and   we designed it to be very similar performing  we actually match the the performance there   in both cases but you did get a much more  lightweight design with the high k heat sink and then looking at just some different  form factors with high k plate technology   the uh we talked about high k heat sinks that's  where you're basically embedding heat pipes into   the base of the fan assembly you can see an  example there in the top left with a folded   fit and cover which is used and the heat pipes  are embedded right under those folded fins   so again better fin efficiencies better  thermal conductivity to drive down not   only your conduction gradients but also your  convection gradients in those designs and then   two on kind of the embedded computing side  are HiK board frames and HiK chassis   so the board frames is fairly routine done  a lot in especially military embedded computing   systems where they have kind of standardized  form factors 3u 6u card frames and we can   pretty quickly embed heat pipes and route them to  the edge which is then coupled into the chassis   so again the requirements we we basically need  to know where the heat inputs are where those   critical electronics are and then usually the  design methodology is routing it to um avoid any   through-holes and things like that and getting  it out to the edge as efficiently as possible   and then finally on the chassis side  there's a lot of uh different options   here if you have an air-cooled chassis again  you can increase the fin efficiency if you   have a liquid-cooled chassis a lot of times you  can increase the reliability of the system by integrating where the liquid cooling is seeing  so the bottom right is a good example of that this   is one where originally the customer had liquid  flowing through each of those vertical channels   but by integrating heat pipes taking  advantage of the thermal conductivity gains   they actually were able to move the liquid  loop to the top and bottom of the chassis   and still keep the temperature  under safe operating conditions   so there you're adding an additional  reliability factor if anything were to   happen leaks in the system or things like that  you're not damaging your electronics instantly so the next technology we'll talk about  is vapor chambers this is another heat   spreading technology similar to um heat pipe  operation used using a two phase heat transfer   but it does have some unique advantages in terms  of thermal performance and heat flux capabilities so again the the operating principles are are  very similar it's it's mainly a planar heat   pipe so it's it's a heat pipe that's using the  vaporization of the working fluid the spreading to   cooler areas and then the condensing and wicking  back to the evaporator zone but you can do this   in a in a two-dimensional form factor so you  can get even better spreading across your area   but the really big benefit to to vapor  chambers is the high heat flux capabilities   even compared to heat pipes which can  operate in the you know 10 25 maybe 50   watts per centimeter squared range uh vapor  chambers can increase that dramatically to   roughly 100 watts per centimeter squared for  fairly straightforward designs and then even   up to we've demonstrated over a thousand watts  per centimeter squared for some advanced wicks   so a very high heat flux capability um and  a lot of thermal benefits the the penalty   to vapor chambers compared to high k plates is  the ruggedization so high k plates are a more   rugged technology because you're fully embedding  them the aluminum adds strength to the system   compared to a planar vapor chamber which has as a  name suggests vapor space in the middle so it has   some structural posts and integrity there but not  as much as embedding into a rugged aluminum plate and again here's some examples and  some specifications you you would   normally see in a vapor chamber design  the the thickness we typically recommend   upward of three millimeters the wick structure  would be customally designed as i mentioned if   you're below 100 watts per centimeter square  you can go with a fairly straightforward   continuous powder finish if you go into really  high heat flux that's where we get into some   of the intricate press designs for for wicks  that give you higher heat flux capabilities   um and then operating conditions fairly similar  to to heat pipes minimum temperature we'd say   um any anywhere below zero since water is usually  the working fluid you're not getting performance   but you can survive and then maximum temperatures  around 105 degrees c so not quite as high as   a heat pipe or a high case solution because the  pressure containment is a little more challenging   in vapor chambers but they're they're usually  pretty suitable for the high end of electronics   temperature range which typically our design  point is in like the 70 to 85 degrees c range so vapor chambers again high  heat plus capabilities and   very strong spreading similar to other two  phase liquid vapor heat transfer devices   shifting a little bit we're going to talk  next about phase change material heat sinks   so as the previous three modules talked about  liquid to vapor phase change this is going to   be talking about solid to liquid phase change  and when that might be applicable in your system so i guess first what is phase change material it  is any material going from solid to liquid that   we can take advantage of the latent heat of that  phase transition to store thermal energy so if you   look at the figure to the top right you can keep  see kind of a a profile here where you're using the specific heat of a material to a certain  point but once you hit that solid to liquid phase   transition you transfer into the lean heat zone  and the lane heat is typically several orders of   magnitude above the specific heat so that allows  you to hold temperature with a constant heat input   and absorb energy for a specific period of  time and then once you're fully melted you   would go back to the specific heat of the now  liquid of the of the phase change material   but in real application what you're attempting  to do is you're taking advantage of that phase   transition you're storing energy and then  it's used in either single time use or pulsed   operation electronics and then you're refreezing  during the off cycle and that allows you to   kind of take advantage and take advantage of  the repeatability of phase change material   so the bottom right finger gives  you kind of an idea of that so   you have these peak pulse input loads  and by utilizing a phase change material   you can absorb that energy and then slowly dampen  it off so that in this case this one was using   dumping heat to a vapor compression loop but you  only need to size that vapor compression loop or   heat sink or whatever your rejection area  is you only need to size that to average   load based on the duty cycle and power of your  your peak pulses so a very nice nice and simple   um design and it can be used in a lot of different  applications um a lot of the first questions we   get on face change material is what would you  recommend in terms of the actual material and   most applications we've designed and  worked with call for paraffin waxes the   main reasons are that it's chemically  compatible with metal so there's no corrosion   during long-term operation when integrating into  metal heat sinks again metal is preferred for   the ruggedization and the thermal conductivity   they can be there's a lot of different options  for paraffins and they have a wide operating range   so every couple degrees there's a different  paraffin wax that could be design points so   you can set set your pcm for a lot of  different design points fairly easily   without affecting your overall capabilities and  they also have a proven high cycle count compared   to some of the others that don't have a lot of  data on paraffin waxes do have a fairly good   data set and have shown you know thousands of  cycles from solid to liquid and then the biggest   considerations um for designing with phase change  material is the the lane heat number so how much   energy can you store that'll kind of determine  how you size these um but the other big area is   that most materials especially paraffin wax have  low thermal conductivity so how do you design the   remainder of the enclosure that you can properly  melt your pcm without causing thermal run away so we'll go into one um one example here and  this one was um an application for a spacecraft   i was looking at over 300 watts at a  15 duty cycle and the goal here was to   reduce as much as possible the radiator  panel size so first we determined if pcm   is the best solution we looked at the operating  temperature ranges looked at the size of the pcm   compared to the gains we would get  by reducing the radiator panel size   and then we worked with locating the  the pcm strategically in the system to   absorb the thermal load at the critical juncture  and create that mass savings on the radiator side   so in this application there's a little more  complexity that will then we'll get into today   but it did use a series of heat pipes as well  to transfer heat to the radiators and along the   radiators and then we coupled the the pcm in  between the high density electronics and the   aluminum ammonia cchps and here's kind of the  the results here these were thermal desktop   numbers but you can see um without the pcm you you  could size your radiator and this again would need   to be sized for peak load and then we explored  many different pcm options and we're able to   keep driving down that radiator area required for  full rejection so all these are showing kind of   similar thermal performance results but again  reducing the radiator area by selecting the   appropriate pcm and integrating it in the proper  position within the thermal resistance network and just kind of quickly  summarizing phase change material   again they're used to absorb energy so they  work kind of like a thermal battery or thermal   capacitor to absorb transient loads impulse  operating applications they can benefit the   end user by simplifying the thermal solution so a  lot of times they're used to avoid complex liquid   loops or things like that if you could just  put phase change material as a way to absorb   melt re-freeze it's a fairly straightforward  simple thermal design it can reduce mass and   volume that was the case study we went into from  a space radiation application but similar things   would be for convection or liquid heat sinks as  well you can reduce the onus on your ultimate   heatsink based on the duty cycle and power of the  electronics and the the other area we didn't talk   too much but is a nice benefit and where pcm has  been used in the past is adding operational safety   so in many cases if you have a liquid cooled  design you do need to protect the system against   pump failure or leaks in the system and to do that  you neither either need to have a very responsive   electronics backlink where if the pump fails they  are immediately shut down or the the option that   we've seen in some of these systems that have you  know extremely high cost electronics in it is to   create a pcm that goes in between the electronics  and the liquid loop and when the liquid loop is   running the pcm stays frozen the entire time  but as soon as there's any issue with the   liquid loop that pcm can absorb the energy of the  electronics and allow the user to safely shut down   buying them time for the system feedback to  work and the electronics to safely shut down   so that can save a lot of hassle in your  system and add an additional layer of safety   and then the the final bullet point here is  that the internal design is is critical so   i mentioned the low thermal conductivity of  phase change material but it really is a very   important design aspect to have good conduction  into the pcm so a lot of times that's done with   fins or some type of foam material  or keeping the layers really thin so   there's a lot of different options but  making sure that you melt efficiently   and don't create kind of a bottleneck  at your melt front is really important okay so final module here we have is on  pulsating heat pipes so we'll introduce   you the concepts of pulsing heat pipes and  talk a little bit about the uh the benefits   so we really just have one slide here i want to  kind of introduce the technology i don't think   we've done a webinar topic on pulsating heat pipes  in the past but this is an emerg emerging passive   heat spreading technology and you can see kind  of the figure at the top right is a fairly basic   design of a pulsating heat pipe where you  have kind of a serpentine channel design   and it's a full loop and then you create you  charge it to have a fair amount of working fluid   compared to the void volume and as you introduce  heat it uh pulses the fluid along uh creating   vapor regions and liquid regions so operates kind  of similar to a heat pipe but it doesn't have a   wick structure and doesn't rely on  the capillary action it relies on the   um pulsating nature of of the design to move  the fluid along the benefits here so while uh   you can't charge it with with water because  of the freezing concerns um so you're never   going to get really similar performance at the  high end electronics temperature so if you're   operating the 70 85 c's a high case solution is  probably your your better choice but for some   of the lower operating temperatures you can  achieve thinner designs very low mass designs   it does have very good geometric flexibility and  you can do a lot of unique things with 3d printing   to create orientation independence and very  unique geometry for pulsating heat pipes so   yeah there's a lot of good applications for it but  there there is kind of a need to be very cognizant   of your design requirements and figure out if  this is the right solution or if a high k approach   is the right solution but overall it does have a  lot of capabilities and if the boundary conditions   are are adequate for it it'll give you good  performance at a very low mass low volume solution and before we wrap up today did want to share the  online resources i think this presentation will be   distributed to anyone who registers they'll have  some some of these links in there some of the   design areas we talked about like the heat pipe  calculator and also a webinar of libraries and   or webinars and white papers that have been  done in the past that might be useful and   just as we wrap up here again we'll leave  it open for you to type questions in for for   another minute or so and as i mentioned we aren't  doing live Q&A here but we will make sure to get   you very detailed responses as we go through  all the questions that have been submitted so I really appreciate everyone joining today I  hope there are a lot of good questions and we'll   certainly get back to you in a very short order  here but again please keep an eye out for ACT as   we put more and more content out there and we  look forward to working with you on any of   your heat pipe, Phase Change material or active solutions in the future. Thanks a lot take care!

2022-04-12 00:26

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