Appliance Design - June 2008 - (Page 40)

efficient power FaNS & BlowErS Typical flow assumptions include incompressible or compressible, laminar or turbulent, and slip or no-slip wall conditions. Typical thermal assumptions include perfect thermal contact, radiation or no radiation, adiabatic external walls or external leakage. In a heating situation, for example, assuming perfect thermal contact is a non-conservative approach. Any contact resistance between two parts (which inevitability exists in real life) will cause actual temperatures to be higher than predicted by simulation. The “no body-to-body radiation” assumption, on the other hand, is typically conservative. Radiation between components and the exterior housing is an extra heat flow path alongside conduction and convection. Ignoring this path will typically cause higher temperatures in the simulation results. 4Keep it simple at first. Make the first simulation on a geometrically simple, but representative model of the system. Start with a relatively coarse mesh, but seek to include all the significant physical effects. This is most important for new designs or for someone early in their experience with the analysis tool. One reason for the simple approach is purely pragmatic. When mistakes are inevitably made, it’s important to discover the effects quickly and clearly. In addition, the initial simple representative model can be used to understand the general performance of the system, particularly in areas that require special attention. Where is the highest temperature? Where is the highest pressure gradient or choke-point in the flow? If using a fan, roughly where is the fan operating on its performance curve? Focusing more simulation attention on these critical areas can be accomplished later. Keeping first models rough and simple permits the rapid processing of initial results and the ability to quickly move on to other scenarios. This approach also makes it possible to quickly test the relative importance of factors such as variance in material properties and mesh sensitivity. If it is determine later to run a model with production-level details, there will already be established a good sense of the potential impact of these factors on final results. < For more information, enter . . . . . . . . . 301 Or email: Jeff .Waters@cfdesign .com Rosenberg EC fans outperform the competition with quiet power and efficiency. Our axial designs deliver airflow up to 16,900 cfm. Our backward curved fans provide up to six inches of steady static pressure. Both operate 15-20% more efficient than traditional AC fans with VFD. They’re ideal for main-secondary or pressure control, and RS485 networks. Put the power of Rosenberg EC fans to work for you. Call: (704) 893-0883 • Fax: (704) 882-0755 sales@rosenbergusa.com • www.rosenbergusa.com Representatives Wanted For more Information Enter 113 40 applianceDESIGN AD05084Rose.indd 1 a typical fan-curve plot. June 2008 4/7/08 12:08:36 PM www.applianceDESIGN.com http://www.rosenbergusa.com http://www.rosenbergusa.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - June 2008

Appliance Design - June 2008 Contents Editorial Shipments/Forecasts News Watch 21st Annual Excellence in Design Winning Designs Combine State-of-the-art Technology with . . . Meet the Judges Design Marts Fans & Blowers Mother Nature Has Her Own Ideas About Designing for Fluid Flow . . . Using CFD Simulation Software Early in the Product Development . . . Electronics Digital Signal Controllers Enable Digital Motor Control . . . Classifieds Meetings Advertiser’s Index Association Report: AHRI

Appliance Design - June 2008

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