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By Michael Engelman and Scott Del Porte, Enductive Solutions, Lebanon, NH; and Bhavin Desai, Fluent India
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CFD analysis of a bonded fin heat sink design using Icepak
During the last 20 years, the electronics cooling industry has made widespread use of CAE technology for design. Today, it is one of the fastest changing industries, because of rapid hardware advances, ever shorter design cycles, and a constant drive to cut costs and improve unit productivity. Moreover, as computer speed and memory capacity continue to increase, there is a need to remove more heat from computers in the same or less space than before. Hence, heat sink manufacturers like Aavid Thermalloy Inc., a sister company of Fluent, have become commodity suppliers, outsourcing some of their manufacturing offshore to Asia. Unfortunately, the design expertise in such companies resides in the heads of a few senior engineers back in their base country. This has led to a demographic time-bomb of sorts, as these senior engineers approach retirement during the next decade or two. Companies like Aavid Thermalloy are now facing the question of how to protect their biggest asset: design intellectual property and know-how, especially with manufacturing operations moving off-shore.
The HSDP decision tree structure
Sample input panels for ambient conditions...
Simulation process and data management, or SPDM, is the application of information technology (IT), especially in the areas of data archiving and mining, to the engineering design and analysis processes of today’s CAE tools. SPDM comprises the management of both the CAE process as well as the data, and must take into account issues such as multiple platforms on a network, client/server needs, and security issues. SPDM systems are often built using an infrastructure toolkit with open standards. This allows them to evolve as new versions of software become available. The interface between the SPDM system and software tools is often in the form of a CAE portal – a window through which employees can gain access to their company’s design process and data. In short, SPDM is a systematic approach and infrastructure for managing the simulation process and the data generated in a virtual product development environment.
Enductive Solutions Inc., a subsidiary of Fluent, was formed several years ago to develop customized software tools for companies where CAE products are routinely employed. Often, the customized tools involve more than one CAE product, as needed for a given application. Enductive engineers interviewed senior engineers at Aavid Thermalloy to understand their current design processes, and generated a process flowchart. They then created a customized heat sink design portal (HSDP) using MSC SimManager™ as its infrastructure toolkit. An Aavid sales engineer anywhere in the world can enter this secure website via a browser and define a number of heat sink requirements, with the goal of identifying the optimum heat sink design. This triggers the system to notify Aavid’s senior design and analyst group, logging that someone has begun work on a custom design or a search of previous designs.
After entering the HSDP, the first step for the engineer is to specify the desired heat sink specifications, such as chip size, wattage, and available cooling flow conditions, all of which are standard inputs. If the name of the chip manufacturer is known, it can be selected from a pull-down menu, and the dimensions and wattage of a specific model can be entered into the system automatically. There are many categories of heat sinks with different geometric features, such as solid or hollow fins and embedded heat pipes. Each category represents a trade-off between cost and performance for a given application. All of Aavid’s previous designs are stored in a database, and the system uses established rule-based designs along with the cooling inputs that have been collected to narrow down the part categories that could meet the current needs. The system then queries the database of previous designs in the chosen categories to see if any fit the design envelope. It selects one of the existing designs, but also proposes an optimal design based purely on the design rules given to it. If there is nothing suitable in the database, the sales engineer would then notify a design engineer that additional work needs to be done to meet the client’s needs.
Once a design solution has been proposed, the design engineer will use the HSDP to refine the design, using built-in guidelines. By modifying parameters such as fin spacing or height, he can come up with a revised design that more closely meets the client’s requirements. Throughout the process, the system can check against databases for material stock and manufacturing processes to estimate a finished cost for the part.
If the designer wants a more in-depth thermal analysis, he can launch simulations on the proposed geometry using CFD and finite element analysis (FEA). For CFD simulations, Icepak is embedded within the HSDP, and the customized interface takes the model requirements and sets up and solves the problem with no user interaction. In fact, the design engineer does not need to know anything about CFD. Once the simulation is complete, a series of predefined contour, vector, and other plots are returned, along with bulk flow results like pressure drop and thermal resistance for the heat sink. In addition, all of these results get archived so that they can be used at a later date.
A cost estimate for the heat sink part, with a comparison of Aavid’s two manufacturing plants in China and the United States can be made at any stage. It takes into account the type of tooling and quantity of machining required, and tallies the cost. At any point in the design, the engineer can jump back to this page and see what effect a design change has on the per-unit cost.
Schematic of Aavid’s Heat Sink Design Portal
Parameters for Input Device Specifications and mechanical heat sink specifications
The final CAD design
Finally, the HSDP has a CAD module that takes the parametric design description – the lengths, widths, number of fins, and spacing – and generates a solid model in ProE, which can then be used to generate manufacturing drawings. These CAD models also get archived for future use. A finished report is generated that the sales engineer can use along with the cost estimate to develop a quote. It can be a customer specific report with certain information included or excluded as necessary. Finally, even if the design is not used to make a part, the final configuration can be saved and re-used at a later time.
Overall, the HSDP system makes more efficient use of experienced analysts at the company, allowing them to spend more time on analysis and less time on repetitive tasks. It captures their knowledge in a form that can be used long after they have retired, while protecting the intellectual property of the company. It also pushes CAE upstream in the product design cycle, so that the company saves time and money by spending less time building prototypes to best meet the client’s needs.
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