Appliance Design - March 2009 - (Page 22)

POWER Nanoparticles Ions in Electrolyte Carbon Backing Material ic ib Rc Cc Fig. 1. Ragone Plot. The performance of electrical energy storage devices, engines, and fuel cells is often shown using Ragone Plots that display specific power (W/kg) on the vertical axis and specific energy (Wh/kg) on the horizontal axis. Fig. 2. Schematic of electrochemical capacitor. io + Rb Vb vo _ Fig. 3. Circuit diagram of hybrid electrochemical capacitor/battery system. carbon cloths or papers, which can be made from recycled sources as an electrode backing material. These materials can have relatively good electrical conductivity but their surface area is not extremely large. The new designs create high surface areas by depositing coatings of very small nanoparticles onto these electrode backing materials. A schematic of this new design is shown in Fig. 2. The carbon backing material is shown in gray. It provides structure and electrical conductivity. The nanoparticle coating is shown in blue, and the red circles represent charged ions in the electrolyte. When the capacitor is charged, a layer of positive charge accumulates on the high surface area nanoparticle coating on the positive electrode. Negative ions in the electrolyte are attracted to this A positive layer and are absorbed into C d the pores of the coating, thus creating a double-charged layer. The process is reversed on the negative electrode. A Portable battery-powered devices C d that operate in pulsed modes can benefit greatly from the incorporation of electrochemical capacitors into their design. In general, parallel power sources combining batteries with electrochemical capacitors can meet high-power pulsed loads more effectively than batteries alone. Often significant reductions in system size, weight, and cost are possible using a combined system. A basic hybrid battery/capacitor circuit is shown in Fig. 3. The battery is modeled as an ideal voltage source Vb in series with the internal resistance Rb. The electrochemical capacitor is modeled as a capacitance Cc in series with an equivalent resistance Rc. By A using this simplified circuit model it is C possible to derived useful design equations that can be used to estimate the peak power available for a given battery, capacitor and load duty cycle. For a pulsed load current, io, as a function of time, t, with a period of T and pulse duty ratio D, the current for k pulses is given by Equation 2, where Io is the amplitude of the current and 1 io ( t) ib ( t) ic ( t) 0 0.5 0.5 0 10 20 30 40 t (s) Fig. 4. Load current and current supplied by battery and electrochemical capacitor. 1 io ( t) ib ( t) ic ( t) 0 0.5 0.5 0 10 20 30 40 t (s) Fig. 5. Load current and current supplied by battery and electrochemical capacitor. Equation 2. Equation 3. Equation 4. 22 applianceDESIGN Equation 5. March 2009 Equation 6. www.applianceDESIGN.com http://www.appliancedesign.com

Table of Contents Feed for the Digital Edition of Appliance Design - March 2009

Appliance Design - March 2009 Contents Editorial Shipments/Forecasts News Watch Transmitting Power Wirelessly Promises to Reduce the Ever-Growing Tangle of Cords and Cables Found in the Modern Home. There Are Different Technological Approaches for Achieving this Goal, and Some Are Already on the Market. Electrochemical Capacitors Can Provide an Extra Peak-Power Boost in Battery-Operated Appliances, Allowing Product Designs to Have Smaller Battery Packs. Metallic Foams Put the Properties of Metals into Lightweight Packages. Applications for this Emerging Technology Include Gas Burners, Heat Exchangers, and Electronics Housings. Hall-Effect Switches Are Compact and Provide a High Degree of Reliability and Durability as They Virtually Eliminate Mechanical Wear, Shock, and Contact Oxidation. Blowing Agents for Polyurethane Foam Insulation Face Increased Scrutiny Due to Global Warming Concerns, but Alternatives with Lower GWP Values May Provide Solutions to Meet These Challenges. Design Marts Association Report: AHAM Advertisers' Index

Appliance Design - March 2009

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