Appliance Design - June 2008 - (Page 34)

FaNS & BlowErS a fan based on PaX technology that was used in a refrigeration evaporator application. Photo: PAX Scientific. an image of a PaX-designed fan showing the hub. also observed other examples of fluid movement such as tornadoes, fire storms and water spouts, as well as much more common phenomena such as water draining out of the bathtub, says Kim Shekar, vice president of product development for PaxFan. Harman worked for many years to isolate the geometries that underlie natural fluid flows. His observations led to design principles that were contrary to generally accepted practice. Historically, devices employed to move liquids and gases — from paddleboats to propellers, fans and pumps — have been designed under the assumption that a straight line is the path of least resistance. Harman’s observation differed from this assumption. Fluids, he discovered, always want to follow a particular path, not a straight line. From these examples, Harman began seeing recurrent patterns in nature, specifically spiraling, logarithmic shapes, that is, shapes whose curves are mathematically defined by logarithms. Seaweed, for instance, would spiral as a wave crashed over it and remain unscathed. By “going with the flow,” the underwater plant remained undamaged. In the shell of a mollusk he saw the same three-dimensional logarithmic spiral that he saw in the twisting, turning kelp and noticed that the fluids would flow centripetally — toward the center — with less friction and more efficiency. Harman wondered if there was a way to design equipment that takes advantage of the observed phenomena. From this curiosity, he developed what he calls the Streamlining Principle. This concept is based on finding the most ideal way 34 applianceDESIGN June 2008 that fluids prefer to flow and then creating specific geometries that will encourage and generate that type of flow pattern. The results stem from one of the general truths that biologists have known for a long time, says Shekar. In nature, he says, strengthto-weight ratios, drag reductions and efficiencies have outstripped what can be achieved by man-made designs that begin with straight lines. “You don’t see a straight line in nature,” he says. “As Jay Harman has said, ‘After billions of years of trial and error, and an unlimited R&D budget, nature has developed better ways to improve fluid flow.’” Harman first applied the Streamlining Principle to produce boats, and then founded PAX Scientific to extend the concept to fluidhandling technology, such as fans, mixers, pumps, turbines, heat exchangers, ducts, propellers, and other applications. At PAX Scientific, researchers use Computational Fluid Dynamics (CFD) and CAD software to design the fans. With the CFD software, numerical methods and algorithms are used to solve and analyze problems that involve fluid flows. This technology is based on the Navier-Stokes equations, which establish that changes in momentum in infinitesimal volumes Fan 95mm Benchmark PAX Summary at 0.03 inches H20 Q Speed Power [CFM] [RPM] [W] 58 2764 5.55 57 3075 4.15 Noise [Sones] 0.60 0.29 Fig. 1. In comparing a 95-mm evaporator fan for a refrigeration application, the PAX design required 25 percent less power for equivalent airflow and dropped sound by half. Motor/Fan Baseline 1 PAX/AO 1 Static Pressure (inches H20) 0.03 0.03 airﬂow (CFM) 57.0 55.8 Power (w) 5.56 4.29 rPM 2,661 2,943 Fig. 3. A.O. Smith’s testing of a PAX fan showed that airflow can remain about the same, while greatly reducing power consumption. Motor/Fan Baseline 1 PAX/AO 1 rPM 2,517 2,710 Sound Power (dBa) 41.4 39.5 Sound Quality (sones) 0.43 0.33 Fig. 4. In addition to improving power consumption and airflow, A.O. Smith’s tests showed a reduction in sound levels emanating from a PAX fan. www.applianceDESIGN.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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