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Research Papers

Multiphase Stirling Engines

[+] Author and Article Information
Artin Der Minassians1

Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, 518 Cory Hall, Berkeley, CA 94720artin.der.minassians@gmail.com

Seth R. Sanders

Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, 518 Cory Hall, Berkeley, CA 94720sanders@eecs.berkeley.edu

1

Corresponding author.

J. Sol. Energy Eng 131(2), 021013 (Apr 15, 2009) (11 pages) doi:10.1115/1.3097274 History: Received March 02, 2008; Revised January 08, 2009; Published April 15, 2009

Analysis, design, fabrication, and experimental assessment of a symmetric three-phase free-piston Stirling engine system is discussed in this paper. The system is designed to operate with moderate-temperature heat input that is consistent with solar-thermal collectors. Diaphragm pistons and nylon flexures are considered for this prototype to eliminate surface friction and to provide appropriate seals. In addition, low loss diaphragm pistons, etched and woven-wire screen heat exchangers, and plastic flexures, as the main components of the system, are outlined. The experimental results are presented and compared with design analysis. Experiments successfully confirm the design models for heat exchanger flow friction losses and gas spring hysteresis dissipation. Furthermore, it is revealed that gas spring hysteresis loss is an important dissipation phenomenon for low-power Stirling engines and should be carefully addressed in design. Analysis shows that the gas hysteresis dissipation is reduced drastically by increasing the number of phases in a multiphase Stirling engine system. It is further shown that for an even number of phases, half of the engine chambers could be eliminated by utilizing a reversing mechanism within the multiphase system. The mathematical formulation and modal analysis of multiphase Stirling engine system are then extended to a system that incorporates a reverser. By introducing a reverser to the fabricated prototype, the system successfully operates in engine mode. The system proves its self-starting capability and validates the computed start-up temperature.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of a multiphase Stirling engine system

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Figure 2

Simulated piston positions of a symmetric three-phase Stirling engine system: (a) startup and (b) steady state

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Figure 3

Mass-spring equivalent of the multiphase Stirling engine system in Fig. 1. KG represents the gas spring stiffness.

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Figure 4

Approximated effect of system dissipation on the eigenvalues

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Figure 5

Fabricated heat exchanger frame and the screens

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Figure 6

(a) Liquid rubber is cast in printed wax molds to fabricate the diaphragms. (b) Top wax mold and corrugated diaphragm after being separated from the molds.

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Figure 7

Close-up view of the fabricated diaphragm with one ring of corrugation

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Figure 8

Fabricated magnetic actuator (control circuitry not shown)

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Figure 9

Fabricated three-phase Stirling engine system. Photograph taken before custom corrugated silicone diaphragms were fabricated and installed.

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Figure 10

Gas spring hysteresis loss versus fractional volumetric variation. The graph is a quadratic regression through the measured points (shown in dots) taken from Table 4.

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Figure 11

Schematic of a multiphase Stirling engine system that incorporates a reversing mechanism within piston r

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Figure 12

Simulated piston positions of the three-phase system with reverser: (a) startup and (b) steady state

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Figure 13

Implementation of reverser mechanism within the fabricated three-phase Stirling engine prototype

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Figure 14

Recorded acceleration signals of the three phases in the revised three-phase Stirling engine system

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Figure 15

Fundamental frequency components of the three acceleration signals. Compare to Fig. 1.

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Figure 16

Acceleration signal of one piston at full-amplitude oscillation

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