IMAGINiT Manufacturing Solutions Blog

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Heat Sink modeling with Autodesk CFD

Embedded within the Autodesk CFD software is the ability to define a heatsink as a subcomponent of your design.  The heat sink module has been developed using well know heat transfer formulas for different style heatsinks that can be found in advanced heat transfer engineering text.  (REF 1, REF 2)

It may be useful in some cases to directly model the heatsink geometry itself as shown in this image.  Many projects and design studies have been performed in such a manner.    The image below shows pin fins modeled geometrically and with flow and heat transfer simulated using Autodesk CFD.   Model results showed that using the k-epsilon turbulence model with Advection Scheme 1, the results were very close to expected based on hand calculations and empirical data.

Despite the robust capabilities of the Autodesk CFD software, in some instances it may be advantageous to reduce the model to a more simple approach.  This can be done in Autodesk CFD using the “Heat Sink” module.  An embedded model that can be signed as a material property to a rectangular cube that is embedded in the geometry.  The only requirements to setup such a module is to have a sufficient volume of fluid at the entry plane and exit plane of the geometry, and the heatsink be fully immersed in the flow.

 

It is necessary to  define the “approach surface” or the direction the flow will enter the heat exchanger, as well as the base surface, or the surface side on which the physical base of the heat sink will be located and surface touching the object that is being cooled.

 

Once the material has been defined as a heat sink, switching the database to the default customized material database, “My Materials” is the next step.  This allows the user to define the parameters and characteristics of the heat sink they will be including in the simulation.

 

 The next step is to define the base thickness as well as the material thermal conductivity.  In this example a typical .1” or approximately 2.5 mm was used.  A thermal conductivity of Aluminum 6061-T6 was used as well being a standard Aluminum Alloy that is easily machined.

  
 

Once these parameters have been defined, the next step is to select the type of heat sink you would like to use.  There are several options.  The options include, offset strip, pin fin in-line, pin-fin staggered, and microchannel.  The microchannel may also be thought of as mini-channel rectangular straight-fin heat sink.  The ability to accurately and effectively model a large variety of heat sinks with only a small number of resources being used by the software is very effective and adds value by reducing the complexity and size of the model.

  

 

Utilizing the embedded heatsink module within Autodesk CFD provides the ability to accurately model heatsink performance saving valuable engineering time and resources.  This module within the software provides significantly value to the CFD user.

 

References:

 

1)      “Convection Heat Transfer,  2nd Edition”,  Bejan, A., Wiley Interscience, NY, 1995. Ch7, pp. 326-331.

2)      “Cooling Techniques for Electronic Equipment”, Steinberg, D.S., Wiley Interscience, NY, 1991. Ch 6.

3)      “Compact Heat Exchangers, 3d Ed.”, Kays, W.M.; London, A.L., Krieger Publishing Co., Malabar, FL, 1998.

4)      “Electronics Cooling Quick Start Tutorial”, Autodesk.com, 2015. http://help.autodesk.com/view/SCDSE/2014/ENU/?guid=GUID-F9435F15-8684-4FD5-A329-E6EC8B45B640

5)      “Error: "GBI File: Unable to write mesh data file" in Simulation CFD”, Discussion on Heat Sink Materials setup, Autodesk.com, Dec 09 2014. http://knowledge.autodesk.com/support/cfd/troubleshooting/caas/sfdcarticles/sfdcarticles/Error-GBI-File-Unable-to-write-mesh-data-file-in-Simulation-CFD.html

6)       “Optimization of pin-fin heat sinks using entropy generation minimization”, Khan, W.A.; Culham, J.R.; Yovanovich, M.M., Thermal and Thermomechanical Phenomena in Electronic Systems, 2004. ITHERM '04. The Ninth Intersociety Conference, 2004, Pages: 259 - 267 Vol.1, DOI: 10.1109/ITHERM.2004.1319183

7)      http://knowledge.autodesk.com/support/cfd/learn-explore/caas/CloudHelp/cloudhelp/2015/ENU/SimCFD-Learning/files/GUID-AA06A2FE-065E-44CD-A43C-B4C167BF6A28-htm.html

 

8)      http://knowledge.autodesk.com/support/cfd/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/SimCFD-UsersGuide/files/GUID-8A3028B0-1ECB-4EE8-832F-FD165C6B3167-htm.html

 

CFD Analysis for Cooking Equipment design

Whether it's baking bread for the general population or maintaining product temperatures during food delivery; end product quality is directly proportional to the effectiveness of the device used to heat or cool that product.

Attend this complimentary webcast on CFD thermal and flow simulation for equipment design in the food industry.  IMAGNiT CFD Expert Rob Taylor will discuss the impact that analysis insight can have on performance areas like uneven heating, flow uniformity, reliability, energy efficiency, air curtains, increasing production speeds and keeping food fresher longer.

Don't miss this valuable webcast.  Sign up here: http://www.imaginit.com/events/registration?eventid=a2w70000000050kAAA

Cool aerodynamic CFD study Thule cargo box

Check out our write up in Desktop Engineering Magazine.  We're proud of the CFD analysis services work we did for Thule to design a new cargo box line.  Desktop Engineering wrote a nice article...

 

http://www.deskeng.com/articles/aabkrk.htm 

 

 

Solving HVAC redundancy issues and lowering cost with CFD analysis consulting

Our very own Jason Pfeiffer, Director of CFD consulting at IMAGINiT, writes about this topic in Properties Magazine.  In his brief article he addresses common challenges with ASHRAE guidelines and ventilation design challenges to eliminate redundancy and save money.

 

By Jason Pfeiffer - IMAGINiT Technologies

Engineers often – and unnecessarily – specify redundant HVAC equipment because they’re not sure what they really need. Although ventilation system specifications are known, it’s not easy to predict local thermal discomfort factors such as drafts, cyclic variations in operating temperature and radiant temperature asymmetry. To make up for this lack of intangible, yet extremely important information, conservative designers tend to throw higher-capacity, additional redundancy and/or more equipment at the problem. This tendency to oversupply increases upfront capital costs, the total cost of energy and produces more greenhouse gases than necessary.  Read the full article here 

CFD Engineering

I was asked the other day by an engineer friend of mine “what is CFD engineering?”  I had to ask what he meant.  He said that his understanding of what my company does is CFD engineering.  And that he didn’t really get what we do. 

It certainly makes sense that many will not intuitively understand our consulting services when described as “CFD analysis consulting”.    Kind of leaves the listener without much detail.  (Unless, of course, that person is an engineer that deals with thermal or flow attributes daily and has been exposed to CFD analysis simulation software tools.  In that case they’re squarely in our circles anyway.)  So, I suppose having heard me describe our consulting business with CFD in there he put CFD engineering together and decided to ask the question.

So, the short conversation prompted me to write this about CFD Engineering.  First off, for anyone that just found their way to this page and is wondering what the letters CFD mean, here you go.  CFD is Computational Fluid Dynamics.  It’s the science of using computers to simulate fluid and thermal behavior.  Wikipedia describes it.

Think airflow through a laptop to cool the chips, a hair dryer blowing hot air, water moving through a valve or airflow over a race car. 

In one sense, CFD engineering might be considered the process of engineering or designing CFD methods or developing CFD software.  In another… our company, IMAGINiT, could be dubbed as doing CFD engineering in the sense that we use CFD software to solve design problems for our clients as a consulting service.

I’m very curious what engineers in the market think when they hear CFD Engineering?  What are your thoughts?

IMAGINiT CFD Consulting – Welcome Greg Keller

We love when we add to the team.  So when we do we want everyone to know.  It’s exciting and it means that we’re doing what we set out to do: be a value to our customers and have a positive impact on people around us.

We’re excited to announce our newest team member, Greg Keller.  He just joined our CFD consulting team to fill an important position in business development.  He lives in Rome, NY and has worked for a number of years as an account manager in the CAE/design world.  In fact, he came from another division of IMAGINiT where he managed business development in New York for the last few years.

Greg will work with many of our clients and prospective clients to identify where and how flow and thermal simulation design services can impact their business and overcome pressing design challenges.  He’s already settled in and making things happen.  Greg can be reached @ [email protected] or by phone @ (315) 271-9713.

Superman Syndrome on a CFD for Filter Design project

Have you ever noticed that consultants seem to say “yes” to everything? Why is that? I don’t want to walk away from business any more than the next guy, but it better be business that fits my capabilities and expertise. Otherwise, I’ll spend more money than I’m earning. Where’s the business sense in that? I like to focus on problems we can knock out of the park.

Consultants certainly walk a fine line to secure business now and then. To get better we have to stretch ourselves, but at the same time know when to say no. I’m starting to realize, however, that the product development community has an expectation that CFD consultants actually CAN solve anything. Last Thursday we were defining a project scope to apply CFD for filter design optimization. The CFD analysis would be for a self-cleaning air filter housing with blasts of supersonic flow pulsing numerous times over a few milli-seconds. Wow! That one gets complex in a hurry. I politely said our services are not the best fit for his design. You would have thought I told him his application was the kryptonite that was the ultimate weakness of Superman. He was astonished by our transparency to be clear. He appreciated it for sure.

Don’t you think consultants ought to stick to their strengths and walk away when it doesn’t make sense? After all, isn’t that why we hire consultants anyway? For their strengths!

Go with the flow – Heat transfer without heat

If you’re around CFD simulation for any length of time you’ll see there are many tricks of the trade that make CFD analysis sing. You’ll further observe the most effective users are well versed in methods steeped in a bag of tricks. My favorite and certainly, from my experience, the single biggest time saver in heat transfer optimization is to run the simulation without using “heat transfer”. Yes, perfectly intuitive! Hang in with me… 

CFD software programs such as Fluent, CFX, Star-CD, Flotherm, CFdesign and others include features to enable flow and thermal to be calculated simultaneously. This means the program uses calculations from one to influence the other. There’s even a name for it: Conjugate Heat Transfer. An illustration of this is calculating buoyant airflow (natural convection) as a device heats the air environment. The program uses the heating of the air to calculate the speed and direction of the airflow. Meanwhile as the airflow velocity increases the program accounts for the cooling effects of the increased speed of the moving air across the same device creating the convective flow in the first place and so on…

Here’s the point. Just like CFD programs can “couple” the solution they can also “de-couple” the solution and run one without the other. This is a powerful feature that when leveraged in the right design simulation saves enormous amounts of time.

Think ovens, heaters, process equipment, industrial dryers, electronics cooling with fans, air handlers, and a hundred other similar types of products involving fan, pump, compressor or blower driven flow for heating or cooling. Designs that heat or cool with forced fluids like air or water are heavily dependent upon even flow distribution for good thermal performance. Consider using flow only on your next thermal project to improve the flow distribution first. Good heat transfer performance depends on it. This simplifies the approach and save tons of time! 

CFD Analysis – Solving Everyday Problems

Many mechanical engineers I know have a knee jerk reaction at the mention of CFD analysis. Most often is they quickly pigeon hole it as something those crazy aerospace engineers use for aerodynamics on the space shuttle.   Or they dismiss it as not applicable to anything I’m working on. The truth is that
the vast majority of CFD analyses are applied to products that we use every day. Products like computers, cell phones, car radios, stoves, ovens, the office building you’re sitting in. The value of CFD analysis is unlimited in product development. I’m writing this post because I want to help engineers remove the limiting perceptions of where CFD technology can be leveraged.

Here’s an example that got me charged up. An everyday griddle for the kitchen. Think pancakes and French toast… CFD for griddle design. Makes sense when you consider the goals for even heating distribution and lowered energy consumption. Wonderful thermal optimization… This was a project with Spectrum Brands http://www.spectrumbrands.com on their latest griddle design.

Our team worked directly with Jacob Smith, Sr Mechanical Engineer and below is a comment he sent our way. You’ll see why I mention it got me charged up. Hopefully, somewhere out there is an engineer this will help by spawning some new ideas…

“IDP’s collaborative consulting model fits very well with how we develop new products at Spectrum Brands and I cannot say enough about their expertise and value-add compared to previous CFD consultants we’ve used.  From the beginning they were very clear of the actual problem we were trying to solve and clearly communicated all results in that context, which greatly enhanced our product knowledge, eliminated exploratory testing and will allow us to present a solid business case to marketing and NPD on a recent griddle R&D project.  We’re already strategizing with IDP on our next few projects.”

Jacob Smith – Sr. Mechanical Engineer, Spectrum Brands