McEntee Mechanical Design, LLC

LASER Stirling Machine Analysis

Overview
LASER is a computer application designed to simulate the dynamic and thermodynamic behavior of most any Stirling-cycle machine. LASER features an intuitive, schematic-based, graphical user interface running on the Windows platforms. The design engineer builds a Stirling machine representation by creating components (pistons, constraining mechanisms, springs, heat exchangers, etc.), then specifying their parameters and their interconnections. Such configurations are saved and restored from "device" (.DVC) files. With the machine fully or partially specified, the engineer creates a Model to simulate the machine behavior. LASER can simulate constrained, partially-constrained, and free-piston machines. LASER can simulate engines, heat pumps, duplex machines, and multi-cylinder machines.

The initial Model available in LASER is the robust and versatile "Linear Isothermal" Model. To calculate thermodynamic performance, it employs a lumped-parameter Isothermal analysis, which is an effective predictor of pressure swings (and therefore power-to-pistons), as well as gas mass flows. These last are used to calculate flow-friction pressure drops and exchanger "delta T's", using built-in correlations for the common heat exchanger types. The optimistic prediction of heat requirement (and therefore efficiency) of the Isothermal analysis can easily be factored in by the design engineer.

For dynamic analysis, the Linear Isothermal Model simulates inherently non-linear pressures in gas spaces by wrapping an iterative loop around a linear system solver: the coefficients in the linear system are updated at each iteration to reflect the dynamic solution from the previous iteration until convergence is obtained. The linear system solver can handle systems of arbitrary order, enabling simulation of free-cylinder machines, vibration absorbers, and so on.

Due to its speed, robustness, and ease of use, LASER version 1.0 is an excellent tool for quick, accurate sizing of constrained Stirling machines. The built-in correlations allow heat exchanger sizing, and mechanical design is facilitated by its calculation of mechanism forces.

For free-piston and partially-constrained Stirling machine design, LASER could well be the most versatile and powerful application available.