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Reaction drive energy transfer device

Reaction drive energy transfer device description/claims

This application claims the benefit of U.S. Provisional Application No. 60/638,195, filed Dec. 23, 2004, the contents of which are incorporated herein by reference in their entirety.

1) Field of Invention

This invention relates generally to apparatus and methods for conveying energy into a volume of fluid and more specifically to the field of linear pumps, linear compressors, and other fluidic devices.

2) Description of Related Art

For the purpose of conveying energy to fluids within a defined enclosure, prior technologies have employed a number of approaches, including positive displacement, agitation such as with mechanical stirring or the application of traveling or standing acoustic waves, the application of centrifugal forces, and the addition of thermal energy. The transfer of mechanical energy to fluids by means of these various methods can be for a variety of applications, which could include for example, compressing, pumping, mixing, atomization, synthetic jets, fluid metering, sampling, air testing for bio-warfare agents, ink jets, filtration, or driving physical changes due to chemical reactions, or other material changes in suspended particulates such as comminution or agglomeration, or a combination of any of these processes, to name a few.

Within the category of positive displacement machines, diaphragms have found widespread use. The absence of frictional energy losses makes diaphragms especially useful in downsizing positive displacement machines while trying to maintain high energy efficiency. The interest in MESO and MEMS scale devices has lead to even further reliance on diaphragm-type devices for conveying hydraulic energy into fluids within small pumps. The term “pump” as used herein refers to devices designed for providing compression and/or flow to either liquids or gases. The term “fluid” used herein is understood to include both the liquid and the gaseous states of matter.

The actuators used to drive larger diaphragm pumps have proved problematic for MESO or MEMS machines since it is difficult to maintain their efficiency and low cost as they are scaled down in size. For example, the air gaps associated with electromagnetic and voice coil type actuators must be scaled down in order to maintain high transduction efficiency and this adds manufacturing complexity and cost. Also, motor laminations become magnetically saturated as motors are scaled down while seeking to maintain a constant mechanical power output. Within acceptable product cost targets, it is widely accepted that the electro-mechanical efficiency of these transducers will drop off significantly with size reduction.

These scaling challenges, associated with magnetic actuators, have led to the widespread use of other technologies, such as piezoceramics and magnetostrictive actuators, for MESO and MEMS applications. A piezo disk naturally combines the fluid diaphragm and actuator into a single component.

The advantages of using the piezo as the fluidic diaphragm are offset by the piezo's inherent displacement limitations. Since ceramics are relatively brittle, piezoceramic diaphragms/disks can only provide a small fraction of the displacements provided by other materials such as metals, plastics, and elastomers, for example. The peak oscillatory displacements that a clamped circular piezoceramic disk can provide without failure are typically less than 1% of the disk's clamped diameter. Since diaphragm displacement is directly related to the fluidic energy transferred per stroke, piezos impose a significant limitation on the power density and overall performance of small fluidic devices such as MESO pumps and compressors. These displacement-related energy limitations are especially true for gases.

Other types of piezo actuators that depend on the bulk flexing properties of the piezo material can provide high energy transfer to liquids by operating at very high frequencies, but at even smaller strokes. These small actuator strokes make the design of pumps impractical. Further, high-performance pumps employ passive valves that open and close each pumping cycle to provide optimal pumping efficiency. These pump valves may not provide the needed performance in the kHz-MHz frequency range of the bulk-piezo actuators.

Currently, the demand is increasing for ever smaller fluidic devices which may not be attainable or functionally consistently useful with current piezo pump technology. For example, pumps and compressors are needed that can provide higher specific flow rates (i.e. fluid volume flow rate divided by the pump's physical volume) at higher pressure heads and in ever smaller sized units. Examples of applications that require high performance MESO-sized pumps include the miniaturization of fuel cells for portable electronic devices such as portable computing devices, PDAs and cell phones, self-contained thermal management systems that can fit on a circuit card and provide cooling for microprocessors and other semi-conductor electronics, and portable personal medical devices for ambulatory patients. Thus, there is a need for a compact, economically viable piezo pump that remedies at least some of the deficiencies of current piezo pumps.

To satisfy these needs and overcome the limitations of previous efforts, the present invention is provided as a fluid energy-transfer device that uses a new reaction-drive actuator for driving diaphragm fluidic devices, such as pumps and compressors, at or near their system resonance. A fluidic energy transfer device according to one embodiment comprises a fluid chamber having an inner wall shaped so as to form a chamber volume with an opening and a fluidic diaphragm being rigidly attached to the perimeter of the opening and with a bender-type actuator being attachment to the fluidic diaphragm. The reaction-drive energy-transfer device according to some embodiments of the present invention provides a unique system for driving displacements of the fluidic diaphragm which can be an order of magnitude larger than the displacement of prior piezo diaphragms.

The reaction-drive system according to most embodiments of the present invention enables high-performance for devices such as MESO-sized pumps and compressors and synthetic jets. The pumps and compressors according to some embodiments of the present invention may include tuned ports and valves that allow low-pressure fluid to enter and high-pressure fluid to exit a compression chamber in response to the cyclic compressions. The reaction-drive system may use a variety of bender actuators, such as uni-morph, bi-morph and multilayer PZT benders, piezo-polymer composites such as PVDF, crystalline materials, magnetostrictive materials, electroactive polymer transducers (EPTs), electrostrictive polymers and various “smart materials” such as shape memory alloys (SMA), and radial field PZT diaphragm (RFD) actuators.

The fluidic devices according to the present invention are operated at a drive frequency that allows energy to be stored in the system's mechanical resonance, thereby providing diaphragm displacements that are larger and typically much larger that the actual bending displacements of the bender-actuator. The system resonance may be determined based on the effective moving mass of the diaphragm, bender actuator and related components and on the spring stiffness of the fluid, the fluidic diaphragm, and other optional mechanical springs; and or other components/environments that influence the resonant frequency.

The pumps according to some embodiments of the present invention may be utilized in a variety of applications including by way of example only the general compression of gases such as air, hydrocarbons, process gases, high-purity gases, hazardous and corrosive gases, with the compression of phase-change refrigerants for refrigeration, air-conditioning and heat pumps with liquids, and other specialty vapor-compression or phase-change heat transfer applications. The pumps according to some embodiments of the present invention may also pump liquids such as fuels, water, oils, lubricants, coolants, solvents, hydraulic fluid, toxic or reactive chemicals, depending on the particular pump design. The pumps of the present invention can also provide variable capacity for either gas or liquid operation.

More specifically, an exemplary embodiment of the present invention includes a fluid chamber having an inner wall shaped so as to form a chamber volume and having an opening. A fluidic diaphragm is rigidly attached to the perimeter of the opening in the fluid chamber and the diaphragm has a flexible portion capable of moving with respect to the outer perimeter between a plurality of first positions and a plurality of second positions, the first and second positions being of varying distances from the inner wall of the fluidic chamber. The chamber is filled with a fluid that comprises part of the load of the system. The fluid within the fluid chamber comprises a spring and the fluidic diaphragm also comprises a spring. A bender actuator having an attachment point is attached to the fluidic diaphragm. A mass-spring mechanical resonance frequency is determined by the combined effective moving masses of the bender actuator and fluidic diaphragm and by the mechanical spring and the gas spring, and the bender actuator is operable at a drive frequency so as to store energy in the mass-spring mechanical resonance and provide displacements of the fluidic diaphragm that are larger (and in many instances much larger) than the bending displacements of the bender actuator, such that increased energy is transferred to the fluidic load within the fluid chamber.

In another embodiment of the invention, there is a fluid energy transfer device comprising:

a fluid chamber adapted to receive a predetermined fluid, the fluid chamber including a fluidic diaphragm rigidly attached to structure of the fluid chamber substantially at the perimeter of the diaphragm, wherein the diaphragm includes a flexible portion adapted to move with respect to the perimeter attached to the structure, between a first position and a second position; and

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