Appliance Design - June 2008 - (Page 39)

FaNS & BlowErS Simulation of a 65-CFM fan operating underneath a cooktop. Simulation of a PCB with a multi-fin heat sink operating under a cooktop. efficiency, while saving money on costly physical prototyping. According to Hanson, upfront CFD does not just save money by reducing the need for prototyping, it uncovers performance issues that cannot be ferreted out by physical testing. Wolf uses thermocouples and infrared imaging for temperature measurements, but finds it difficult to do physical testing to measure flow. Hanson says that to physically perform tests, it was often necessary to disrupt the flow areas to insert the measurement equipment. He also notes that using smoke to analyze flow only provides a general idea of flow. By contrast, upfront CFD delivers a more comprehensive analysis that can be directly verified with the smoke traces, helping the engineers to visualize situations that are difficult to prototype in the physical world. Another example can be found in the recent development of a Wolf 36-inch electric cooktop line, where the use of CFdesign in the early design stages eliminated multiple rounds of physical prototyping and enabled Wolf to develop the product in half the time it would have taken otherwise. For appliance designers to fully benefit from performing CFD analysis in the early design stages, good practices are essential, and those practices can be summed up with four imperatives. www.applianceDESIGN.com 1. Provide adequate training. While upfront CFD tools are marketed based on ease of use, some companies mistakenly think that means “no training required.” It is important to train all the engineers who might need to use these tools and schedule follow-up training when the tools will be used sporadically. 2. Avoid the risk of placing all CFD expertise with a single person. Upfront technologies provide the optimal benefit when implemented throughout the engineering team. A thorough implementation will enhance the entire group’s efficiency and innovation, and the cumulative effect will reinforce a regular cycle of usage and success. 3. Build upfront CFD into the formal development process. Neglecting to schedule time for upfront activities in the official process will result in a “business as usual” process. If a company typically tracks and manages projects with Gantt charts and gate review systems, CFD milestones should be built into the plan. 4. Don’t lock onto one design only, but consider many. Upfront CFD tools are more fully exploited when used to evaluate many design options at the conceptual stages. When integrated with parametric CAD tools, upfront CFD allows engineers to perform numerous what-if studies with very little project defini- tion. Dozens, or even hundreds, of potential directions can be quickly compared to help focus engineering effort. Once an upfront CFD tool is in place, there are several tips for optimizing the investment. 4Start with a basic model. Prepare a conceptual model containing only the most important geometry and indicate the fluid and heat-flow paths. Understand the critical physical effects to be studied. If the fluid is a gas, are compressibility effects significant? If the fluid is a liquid, are any phase changes expected such as solidification or cavitation? Is the flow expected to be laminar or turbulent? What will move the fluid – a fan, buoyancy, known-pressure supply line, or some combination? Where does heat enter the system, and where does it leave? How does heat leave – via conduction, convection, and/or radiation? Are internal body-to-body radiation effects significant? 4Check assumptions. Every calculation is founded on certain underlying assumptions, and upfront CFD is no different. It is important to understand whether the assumptions are conservative or non-conservative in relation to critical results such as the peak temperature, total flow through the system, and pressure drop in a system. applianceDESIGN June 2008 39 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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