Appliance Design - April 2008 - (Page 47)

FLUID HANDLING Fig. 2. Three silicon layers in exploded view. of aluminum to allow the wire bonding of electrical connections. The bottom layers get a separate metallization deposition to facilitate solder connection of the flow ports to a manifold or other fluid distribution structure. The current generation of silicon valves are pressure-balanced, sliding-plate valves. They can be configured in U-flow or flow-through designs. In the flow-through design, the valve is positioned in the fluid flow path. Electrical connections are made by covering the electrical leads with glass or other insulating and sealing media and feeding the wires through the valve mounting plate to the outside of the assembly. In the U-flow design, the valve can be exposed to the atmosphere and still be sealed and leak-free. The sliding-plate valve can be configured for two-way, three-way or four-way oper- ation. In a simple three-way valve, the valve is built with one port closed and one port open, with a common port in between. The fluid connection determines whether the valve is normally open or normally closed. These silicon valves have two different actuation methods. One type is electrically actuated. This direct-acting valve leverages the resistive properties of silicon to generate heat when electrical power is applied. The heat generated by the resistance of the silicon causes the silicon to expand and generate the actuation motion of the valve. Since the silicon valve responds to total power input, several control signals can be used. The preferred method is the application of a fixed voltage and varying the power via PWM duty cycle. However, silicon resistivity can be adjusted prior to the fabrication process to allow other power/signal combinations. The other type of silicon valve is actuated hydraulically, similar to a conventional hydraulic spool valve. The silicon spool valve is also a sliding-plate valve that provides generally higher flow than the direct-acting type. The silicon spool valve can be driven by the direct-acting valve that acts as a pilot. In the future, Microstaq will offer a MEMS pressure sensor integrated with the silicon valve. The pressure-sensor element can be bonded or attached to the valve and be in direct contact with the fluid pressure running through the valve. In an expansion valve application for air conditioning and refrigeration, access to pressure at the site of the expansion orifice will allow accurate calculation of superheat and prediction of phasechange location in the refrigeration circuit. Compared to conventional solenoids, the Microstaq silicon valve consumes up to 40 percent less power in equivalent pressure flow and temperature settings. The silicon valve is 100 times smaller and weighs around 150 times less than a conventional solenoid valve. The compact package size allows appliance designers to integrate valves right into the electronic control package. Table 1 summarizes the key features of the Microstaq silicon valve compared to a solenoid valve. (The solenoid valve used for comparison is a refrigerant system valve.) In the case of air conditioning and refrigeration, regulatory and market demands for increased energy efficiency have caused Fig. 3. Flow-through with glass feed-through. Fig. 4. Three-way valve in normally open configuration. www.applianceDESIGN.com applianceDESIGN April 2008 47 http://www.appliancedesign.com

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Appliance Design - April 2008 Contents Editorial Shipments/Forecasts News Watch A Variant of Thermoacoustic Refrigeration Known as Acoustic-Stirling is Expanding Its Range Outside Cryocooling Into More Conventional Applications Such As Refrigeration and Air Conditioning Free-Piston, Stirling Coolers Are Now Showing Up in Mainstream Applications As Costs Come Down and Heat Transport Solutions Are Devised Heat Exchanger Innovations Are Helping To Improve the Overall Efficiency of Vapor Compression Systems Environmental Concerns Have Once Again Ignited a Debate Over Refrigerants A New Glass Ceramic Material for Induction Cooktops Can Be Decorated In a Variety of Glimmering Metallic, 3-D Looks That Can Employ a Number of Shades, Patterns, Styles, Colors, Intensities, and Textures Colorful, Reflective Coatings for Glass Create a Variety of Design Options To Help Designers Establish a Unique Look for Their Products Appliance Designers Faced With Different Motor and Drive Options Need To Understand the Differences and Tradeoffs Before Choosing A New MEMS Valve Offers a Number of Advantages Over Solenoids In Certain Applications, Including the Opportunity To Cut Energy Use The AHR Expo Set Attendance Records and Showcased Thousands of Innovative New Products Classifieds Design Marts Advertiser’s Index Association Report: CEA

Appliance Design - April 2008

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