Advanced Thermal Solutions, Inc. (ATS) is hosting a series of monthly, online webinars covering different aspects of the thermal management of electronics. This month’s webinar will be held on Thursday, Feb. 21 from 2-3 p.m. ET and will cover heat sink design and selection. Learn more and register at https://qats.com/Training/Webinars.
Marketing Communications Specialist Josh Perry sat down with Product Engineering Manager Greg Wong to discuss the process that Advanced Thermal Solutions, Inc. (ATS) engineers go through to create a heat sink and find a thermal solution for customers.
Watch the full conversation in the video below and scroll down to read the transcript of the interview.
JP: Greg, thanks again for joining us here in marketing to explain what it is that goes into designing a heat sink for a customer. So, how does that process begin?
GW: We usually start with a few basic parameters; we call them boundary conditions. So, we start with a few boundary conditions, basics like how much airflow we have, how much space constraint we have around a heat sink, and how much power we’re dissipating, as well as the ambient temperature of the air coming into the heat sink.
So, those are the real basic parts that we need to start out with and sometimes the customer has that information and they give it to us, and usually we double-check too, and then other times the customer has parts of the information, like they know what fan they want to use and they know what kind of chassis they’re putting it in and we take that information and we come up with some rough calculations so we can arrive at those things like air flow and stuff like that.
JP: When you get the data from the customer, how do you determine what the problem is, so that way you can move forward?
GW: We usually start out with an analytical analysis. So, we put pen to paper and we start out with basic principles of heat transfer and thermal resistance and stuff like that so we can understand if what we’re trying to achieve is even feasible and we can come up with some basic parameters just using that analytical analysis.
Like we can calculate what kind of heat sink thermal resistance we need or we can calculate how much air flow we need or, if we have several components in a row, we can calculate what the rough air temperature rise is going to be along that chain of parts. So, there’s a lot we can do when we get the basic information from the customer just on pen and paper.
JP: What’s the next step beyond analytical?
GW: Well, we can do some lab testing or a lot of times we also use CFD simulations and, if our customer has a model they can supply us, we can plug that into the CFD simulations and we can come up with an initial heat sink design and we can put that into the simulations as well and then we set those up and run them.
The great thing, having done these analytical analyses beforehand, we know what to expect from CFD simulations. So that way, if the simulations don’t run quite right, we already have an understanding of the problem, we know what to expect, because CFD is not 100 percent reliable.
I mean, you can go and plug all this stuff in there but you really have to understand the problem to know if the CFD is giving you a good result. So, oftentimes that’s the next stage of the process and from there we can actually produce low-volume prototypes right here in Norwood (Mass.), in our factory. We have CNC machines and manual milling machines, lathes, all that kind of stuff, and we can produce the prototypes and test them out here in our labs.
JP: How much of a benefit is it to be able to create a prototype and to be able to turn one around quickly like that?
GW: Oh, it’s great. I mean, if we had to wait to get parts from China it will take weeks to get. We can turn them around here in a few days and the great thing about that is we can test them in our labs and, you know, when it comes to getting results nothing beats the testing.
I mean, you can do analytical analysis, you can do CFD simulations, but when you actually test the part in a situation that is similar to what the actual thing is going to be that’s where the real meat comes down.
ATS engineers take customer data and using analytical modeling and CFD simulations can design the right cooling solution to meet the customer’s specific thermal needs. (Advanced Thermal Solutions, Inc.)
JP: So, we test the prototypes before sending them out to the customer? We do the testing here or do we send it to them first?
GW: It all depends on what the customer requires. Sometimes the customer has a chassis that we really can’t simulate in our labs, so we might send the prototype heat sinks to the customer and the customer will actually put them into their system to test them out.
Other times, a customer might have a concept and they don’t actually have a product yet, so we’ll mock something up in our labs and we’ll test it and it all just depends what the customer needs and also how complex the problem is.
If it’s a simple heat sink and pretty simple airflow, we might not need to test that because we understand that pretty well, but the more complex the chassis is and how the airflow bends and stuff like that, the greater benefits we get out of lab testing.
JP: Well, I appreciate it Greg. Thank you for taking us through the process of making a heat sink and solving thermal problems for our customers.
GW: Sure Josh. We love seeing new thermal challenges and coming up with ways of keeping stuff cool.
For more information about Advanced Thermal Solutions, Inc. thermal management consulting and design services, visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.
Posted in CFD, Chassis, Consulting, Engineering, heat sink, heat sink design, Heat Sinks, PCB, Thermal Design
Tagged Analytical Modeling, CFD, Greg Wong, heat sink design, Josh Perry
Advanced Thermal Solutions, Inc. (ATS) was recently tasked with creating a more cost-effective and lighter solution for a customer that was looking to replace a relatively large heat sink, which was dissipating the heat from four components on a printed circuit board (PCB). The customer did not want a skived heat sink, so ATS engineers created a custom aluminum heat sink embedded with copper heat pipes to draw the heat away from the components.
ATS engineers worked on a comparison of a copper heat sink with an aluminum heat sink that had embedded heat pipes running above the components. Analysis showed that the aluminum heat sink nearly matched the thermal performance of the copper and was within the margin required by the client. (Advanced Thermal Solutions, Inc.)
ATS engineers used analytical modeling and CFD simulations to examine the thermal performance of two aluminum heat sink designs: one with heat pipes that stopped at the edge of the components and the other with heat pipes that ran above the components. Analysis demonstrated that the design with heat pipes running above the components kept junction temperatures within 2°C of the original copper heat sink and an average difference of less than 1°C.
Peter Konstatilakis, a Field Application Engineer at ATS who worked with the client on this analysis, sat down with Marketing Communications Specialist Josh Perry to discuss the technical details behind the thermal analysis and the results that were presented to the customer.
JP: Thanks for taking the time to talk about this project Peter. What was it that they approached you with? What was the problem or the challenge?
PK: There was a long lead time with sourcing this copper; it’s a relatively large and heavy part. This size bar of copper isn’t typically stocked. So, we were having sourcing issues with this non-standard copper stock and they were having weight and cost issues. They had to cut this heat sink in half for testing because they were overweight on the board. Through shock and vibe testing, if the heat sink is too heavy then it can actually rip out of the board.
An alternative was to make the heat sink through a manufacturing process called skiving. Skived heat sinks have a fin count tolerance, so you may have more fins than are specified or you might have less fins, and some of the fins may be curved, which poses cosmetic issues with skived heat sinks; the fins aren’t perfectly straight. It’s not really an issue thermally, especially if companies don’t see the heat sinks too often, but this client’s customers see the boards, see the heat sinks, and they wanted them to look perfect.
Instead of having to get this copper, we thought, why don’t we make an aluminum heat sink with heat pipes? That’s sort of where this came from.
JP: So the problem with skiving a heat sink was mostly an issue with aesthetics?
PK: Yeah, exactly. The tolerance on the fin spacing was +/- three fins, due to the high number of fins. I did a quick analytical analysis with our heat sink calculation tool and the difference in thermal resistance was maybe 1%. That was because the heat sink has such a large surface area and losing a fin or two only changes the performance by a percent or less. On a smaller heat sink, you will see a greater difference. I told the customer but they said that they still didn’t want to go with skived for aesthetic reasons. Instead, we extruded aluminum and then we put heat pipes in the base.
JP: Why was it necessary to add heat pipes to the heat sink?
PK: The big thing, in this case, is the spreading. You can see the locations of the components and then how large the heat sink is. There’s definitely a lot of spreading resistance in the base because there’s so much distance between the heat sink and all the components, so that’s the main issue that we were trying to take care of with the heat pipes. An aluminum heat sink with heat pipes is definitely a lot lighter than a copper heat sink, about three times lighter. Overall it’s much easier to source and also much cheaper. I think it’s again about three times as much for copper.
JP: When this challenge came across your desk, what was the first thing that you looked at? How did you approach the challenge?
PK: What I did was look at our analytical tool again and I modeled this heat sink in all copper. Since there are four components it’s a little complicated, but I modeled them as one component in the middle of the heat sink with gap pad and everything and got the performance of that heat sink. Once I did that, I ran CFD simulations on the copper heat sink with the components placed as they are in the application and the performance values were within 15%. So, doing that, we knew that we had a good CFD model.
After running the baseline simulations on the copper, I moved onto the aluminum heat sink knowing that we had a good CFD model and that we could trust the results. I used the aluminum heat sink and put heat pipes in the base. I started with heat pipes out in front of the components and then the next simulation was with heat pipes above the components. Obviously, if the heat pipes are above the component then you’ll get a little better spreading resistance and the heat will flow better.
The first of two aluminum heat sink designs had heat pipes that stopped at the components. This design was not as effective as when the heat pipes ran above the components. (Advanced Thermal Solutions, Inc.)
JP: How significant of a difference was it?
PK: From the base line of the copper heat sink, it was around a 1-2°C difference, on average.
After looking at these two simulations, I met with Dr. Kaveh Azar (founder, CEO and President of ATS) to discuss the results. With the heat pipes above the components, we were seeing an average difference of less than 1%. It performs worse by less than 1% and I’m currently doing a couple of other simulations to see if we can improve that by adding more heat pipes, making the heat pipes wider, or even running less conservative heat pipes since the conductivity I’m running with is 2000 W/m-K axially and 400 W/m-K through the cross section. Really, the axial conductivity should be around 20,000-50,000 W/m-K, and the copper wall and wick effective conductivity is around 100-200 W/m-K due to the low conductivity of the porous copper sintered wick. The conservative values I used were to get the simulation up and running, while I’ll end up analytically determining the respective heat pipe conductivity.
I’m also doing an all-aluminum simulation just so we can see what that looks like and so we can see how much better the copper heat sink is in general.
This turned into just looking at the heat sink and trying to put heat pipes in them to seeing if we could also vary the length and see if we could get better performance. Your pressure drop increases as the length increases, so the higher the pressure drop then the lower the air flow is going to be in the system, the lower the airflow then the lower the performance. There is sweet spot for the length. I’m looking at that with our analytical calculator. And then the base thickness as well, we’re looking at that too.
The results of the CFD analysis showed that the average temperature difference between the copper and the second aluminum heat sink design was less than one degree. (Advanced Thermal Solutions, Inc.)
JP: With the aluminum heat sink within 1% of the copper, did that make switching from copper worth it for the customer?
PK: It definitely did. If you’re within 1% and the customer has a little margin already, then it’s worth it because it’s three times lower cost, lower weight, and it will look better because it’s extruded rather than skived.
JP: Just to clarify, what is the difference between skiving and extruding?
PK: Extruding, basically, is pushing a hot piece of metal through a die that is in the shape of a heat sink, so it’s like putting play-doh through a die. You get a heat sink with the fin pitch and everything, where skiving uses a copper block and they come in with a blade and peel the fin out. The blade comes in and pushes a layer up. You can skive aluminum as well and they’re about the same cost, but you can’t extrude copper for a heat sink.
This showed our thermal capability to the customer. It showed that we can design custom heat sinks. We can make them more cost-effective, better performing, whatever they need.
JP: When you’re working through these types of challenges, how much of it becomes a foundation of knowledge that you can then take to another customer’s project?
PK: The more experience that you have, the better. Like any field, the more experience you have then you can look at something and know right off the bat if it’s going to work or not. It also helps in terms of understanding how to model certain applications and where to start with the design.
JP: Did we run these simulations here or did we have (ATS engineer) Sridevi Iyengar run the simulations in India?
PK: We did it here. Sri does a lot, but she uses FloTHERM and I’m quicker with Autodesk CFDesign. FloTHERM can be used for bigger systems because it takes less of a mesh. Generally, FloTHERM only works in rectangular coordinates, where CFDesign works with tetrahedrons, allowing the simulation of angled objects. Since it works with tetrahedrons though, it takes longer to mesh and run than FloTHERM. You can’t really have anything angled in FloTHERM and obtain accurate results. We ended up having to angle the heat pipes in order to contact the components, which are in a different plane than the rest of the heat sink.
JP: I know it is a priority at ATS, but why was it important to have an analytical component, not just CFD, in finding a solution?
PK: Analytical modeling is used to ensure that the CFD results make sense. When you see the graphs from CFD, it looks appealing to the eye and you get drawn to it. It’s science and engineering that is made visible, whereas heat transfer and fluid dynamics (for air) are invisible to the naked eye. Another method of ‘seeing’ heat transfer is using an infrared thermal camera or liquid crystal thermography, while a water tunnel or inducing smoke into the flow can be used to see fluid flow. The analytical also gives us a good first judgement and solid design direction.
Optimization for the length of the heat sink and the base thickness, I did with our analytical tool. CFD simulations take a lot of time, so I can narrow down the number of designs and determine what we want to simulate. Rather than doing 10 different simulations, when each takes on average three or four hours, I can get instant results and say, okay, a 5 mm base is the sweet spot, so let me try in CFD 4 mm thickness, 5 mm, and 6 mm; narrowing it down to three simulations.
Analytical modeling gives us quick what-if scenarios, which we say a lot, and it definitely helps give you an understanding of what to expect. If the numbers are way off then I know something is wrong in the CFD model and I check to see if my mesh and other parameters are correct. It humbles you almost and it helps you understand the application and what you’re simulating. The last thing you want to do is give a customer incorrect data.
It gives you two independent solutions. We say analytically this solution is validated, so we have faith in the model. Now, here is the model and it shows better what we want to do.
To learn more about Advanced Thermal Solutions, Inc., visit www.qats.com or contact ATS at 781.769.2800 or ats-hq@qats.com.
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Posted in heat, heat sink, Heat Sink Attach, heat sink design, Heat Sink Material, Heat Sinks, Heat Spreaders, Manufacturing, materials, semiconductor, sink, Thermal Design, thermal engineering, thermal management, Uncategorized
Tagged Advanced Thermal Solutions, education, electronics, electronics cooling, engineering, heat sink, heat sink attach, heat sink design, mechanical engineer, thermal analysis, thermal characterization, thermal management, thermal research
Advanced Thermal Solutions John O’Day and Len Alter showcase the patented heat sink attachments maxiGRIP and superGRIP. With its patented and discrete design, these heat sink attachments are well worth it for being your only choice for a cost-effective, high performing thermal solution.
Posted in Analysis, Engineering, Engineering & Science Chat, heat, heat sink, Heat Sink Attach, heat sink clip, heat sink design, Heat Sink Material, Heat Sinks, heat transfer, Manufacturing, materials, Thermal, Thermal Analysis, Thermal Design, thermal electronic coolers, thermal management, Thermal Research