Using the Design Environment for Low-amplitude Thermoacoustic Energy Conversion in the Classroom.

The Design Environment for Low-amplitude Thermoacoustics Energy Conversion (DeltaEC) is a free software package that is capable of modeling quasi-one-dimensional, multi-domain acoustical networks and includes a 300-page users' guide. The program is a versatile differential equation solver that analyzes a series of "segments" representing ducts, compliances, speakers, etc., that are specified using MKS units.

Periodic self-modulation of an electrodynamically driven heated wire near resonance.

A thin nichrome wire driven near resonance by the Lorentz force and heated by an alternating electrical current is a popular lecture demonstration. Due to the convective cooling of the portions of the wire moving with the greatest amplitude, only glowing regions near a velocity node will be visible in a darkened room. Nonlinear effects and the thermal expansion coefficient of the wire displace the wire's tensioning mass.

Dynamic stabilization of the Rayleigh-Bénard instability by acceleration modulation.

This paper presents the results of an experimental investigation of the parametric stabilization of Rayleigh-Bénard convection through the imposition of sinusoidal vibration. The ability to dynamically stabilize Rayleigh-Bénard convection using acceleration modulation is of interest to groups who design and study thermoacoustic machines as the introduction of parasitic convection can have deleterious effects on the desired operation and thermodynamic efficiency of the device. These performance issues caused by suspected convective instability have been seen both in traveling wave thermoacoustic refrigerators and cryogenic pulse tube chillers.

Note: A kinematic shaker system for high amplitude, low frequency vibration testing.

This note describes a shaker system capable of high peak-velocity, large amplitude, low frequency, near-sinusoidal excitation that has been constructed and employed in experiments on the inhibition of Rayleigh-Bénard convection using acceleration modulation. The production of high peak-velocity vibration is of interest in parametric excitation problems of this type and reaches beyond the capabilities of standard electromagnetic shakers. The shaker system described employs a kinematic linkage to two counter-rotating flywheels, driven by a variable-speed electrical motor, producing peak-to-peak displacements of 15.