Recent work suggests that Stirling device performance can be improved using a decoupled, actively controlled displacer piston to directly shape the device's thermodynamic behavior. In this paper, the authors validate the controlled displacer concept using a low-frequency thermocompressor platform whose displacer and power output mechanisms are not kinematically coupled. As a little-known class of Stirling devices whose work output is pneumatic rather than mechanical, the thermocompressor presents new challenges for modeling and experi-mental validation because few devices have actually been built and tested. The device presented here is currently the highest pressure experimental research platform of a Stirling thermocompressor known to the authors. A third-order dynamic model is derived using first principles and is validated against experimental results. The model contains parameters that are known and/or measurable and as such is not a "fitted" model. This first -principles model is used to explore the influence of different displacer motion profiles on the output of the thermocompressor. The model is able to incorporate an arbitrarily-specifiable displacer motion profile. Using a controlled displacer piston profile, we experimentally demonstrate 1.45X higher peak cycle power and 3.6X higher work output, compared to a traditional sinusoidal displacer motion. This model is appropriate for opti-mizing the control of the displacer motion with respect to desired thermocompressor power, efficiency, or other performance metrics for any general Stirling thermocompressor.

Mechanical circulatory support (MCS) devices, i.e., ventricular assist devices (VADs) and total artificial hearts (TAHs), while effective and vital in restoring hemodynamics in patients with circulatory compromise in advanced heart failure, remain limited by significant adverse thrombotic, embolic and bleeding events. Many of these complications relate to chronic exposure, via these devices, to nonpulsatile flow and the high shear stress created by current methods of blood propulsion or use of prosthetic valves. Here we propose a novel noncompressing single sliding vane MCS device to: 1) dramatically reduce pump operating speed thus potentially lowering the shear stress imparted to blood; 2) eliminate utilization of prosthetic valves thus diminishing potential shear stress generations; 3) allow direct flow rate control to generate physically desired blood flow rate include pulsatile flow; and 4) achieve compactness to fit into the majority of patients. The fundamental working principle and governing design equations are introduced first with multiple design and performance objectives presented. A first prototype was fabricated and experimental tests were conducted to validate the model with a 93.10% match between theoretical and experimental flow rate results. After model validation, the proposed MCS was tested to illustrate the ability of pulsatile flow generation. Finally, it was compared with some representative MCS pumps to discuss its potential of improving current MCS design. The presented work offers a novel MCS design and paves the way for next steps in device hemocompatibility testing.

This work proposes the theory and design of an experimental setup to mimic the dynamic impedance of the human circulatory system for testing the dynamic characteristics of an artificial heart. This platform has the same resistance, compliance, and inertance elements as the well-studied 4-element Windkessel model. As opposed to a circuit analogy model commonly seen in the literature, our platform remains within the same energy domain as the circulatory system. This allows an artificial heart designer to test pump performance and dynamic pressure characteristics under realistic loading. A test platform is designed using a non-hazardous working fluid with the same density and viscosity as blood. The system uses as few custom components as possible and interchangeable parts allow for system tuning.

The thermocompressor, a little-known class of Stirling devices that efficiently compresses gas, presents new challenges for modeling and experimental validation. In modeling, traditional analytic assumptions about displacer motion are limiting. In experimental verification, few devices have actually been built and tested. In this paper, the authors test the feasibility of a lumped-parameter approach for predicting the performance of Stirling thermocompressors subject to different displacer motion profiles. Since the displacer of a thermocompressor can be controlled independently, unlike kinematic Stirling engines or dynamic Stirling engines, and has a large influence on output power and efficiency of the device, it is crucial that this is well captured by a system dynamics model for control. Key model parameters are simulated and results are experimentally verified on one of the few, if only, experimental thermocompressor platforms in the world. Conclusions are drawn regarding simplified modeling of the regenerator's effectiveness and the effects on device work output by varying the displacer piston's motion profile using different waveforms.

Stirling engines are silent, high-efficiency power sources that generate work by shuttling a working fluid between hot and cold volumes while exploiting the working fluid's change in pressure. Stirling engines are able to use multiple sources of heat to create this needed temperature difference, making them ideally suited for diverse waste heat recovery applications. A novel application of this technology would be to reuse waste heat from one industrial process to generate compressed air to power a second, pneumatic process, thus increasing a manufacturing facility's overall energy efficiency. In this paper the authors explore the expected performance of using a modified Stirling engine, known as a Stirling thermocompressor, to intake air at standard atmospheric conditions and compress it into a storage container. Simulations were conducted with a multi-stage experimentally validated dynamic model, using input variables that match the author's physical prototype. Models employing 5 or more thermocompressor stages predicted a 10-fold increase in compressed air pressure compared to ambient conditions. Future work will experimentally verify the paper's conclusions.

A number of national organizations have recently expressed interest in research to develop materials and devices that achieve greater energy storage capacity, power density and increased energy efficiency on the heels of a report finding that the pneumatic sector of the fluid power industry averages only 15% efficiency. One way of improving efficiency is the use of compressed air storage and recycling devices. The pneumatic Strain Energy Accumulator is a recently developed device that recycles exhaust gas from one pneumatic component, stores it in a highly efficient process, and reuses the stored exhaust gas at a constant pressure to power another pneumatic component. This work analyzes system efficiency increases directly attributable to the implementation of a pneumatic strain energy accumulator by applying an analytical methodology for system level efficiency improvement calculations, experimental validation, and compressed air savings projections. Experimentally determined efficiency increases ranged between 32% and 78%, demonstrating that the pneumatic strain energy accumulator can be a viable part of the solution to the fluid power efficiency challenge. (C) 2017 Elsevier Ltd. All rights reserved.

There is heightened interest in research to develop materials and devices that achieve greater energy storage capacity, power density and increased energy efficiency. This work analyses the performance of a novel energy storage device, the pneumatic strain energy accumulator (pSEA), which is designed to exploit the advantageous aspects of the non-linear behaviour of elastomeric materials. An analytical method for simultaneously characterising the pneumatic energy and strain energy stored in a strain energy accumulator (SEA), and more generally for pneumatic and strain energy systems, has been employed. Component efficiency along with the expansion and contraction pressures of the pSEA are determined experimentally so that a system level efficiency calculation can be performed. Incorporating uncertainty analysis, the efficiencies of the SEA are measured to be consistently over 93% in over 800 cycles of testing. The steady-state expansion and contraction pressures of the accumulator have steady-state values with errors of less than 3 hundredths of a kilopascal from their means.