Characterization of Porous Material Used for Thermoacoustic Devices
Open Access
- Author:
- Liu, Jin
- Graduate Program:
- Acoustics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 09, 2005
- Committee Members:
- Steven Lurie Garrett, Committee Chair/Co-Chair
Thomas B Gabrielson, Committee Member
Victor Ward Sparrow, Committee Member
James Gordon Brasseur, Committee Member - Keywords:
- Thermoacoustics
porous material
regenerator
stack - Abstract:
- Three new compact experimental apparatuses were developed and calibrated to quickly and accurately characterize heat transfer and fluid drag in bulk porous media that may be useful candidates for standing-wave (stack-based) and traveling-wave (regenerator-based) thermoacoustic machines. In the first apparatus, the thermal properties of the testing sample were determined by exploiting the transition of heat transfer from the isothermal to the adiabatic limits for gas compressions and expansions within the porous media, using the thermoviscous f-function. For the first time, the complex Nusselt number is related to the thermoviscous f-function allowing the heat transfer coefficient for oscillating flow to be determined without measuring temperatures and without requiring the use of heat exchangers. In the limit appropriate to heat exchangers, the new technique produced results that agreed with several other theoretical and experimental determinations of the heat transfer coefficient for oscillatory flow through heat exchangers. In the second apparatus, the pressure gradient for the oscillating flow through several samples was measured by a phase sensitive technique to resolve the pressure drop into two parts: the viscous drag and the oscillating inertia (Kelvin drag). Unlike the measurements of previous investigators, who did not separate the viscous and inertial effects, these measurements of viscous drag agreed with the published drag coefficients made by steady flow techniques in the appropriate limit. An additional dimensionless variable was created that allowed pressure drop measurements to be correlated through the transition from the low-frequency Poiseuille flow (parabolic) to high-frequency plug flow (boundary layer) regimes. The third apparatus was designed specifically to separate thermal and viscous losses in porous ceramic materials (automotive catalytic converter substrates) used in standing-wave thermoacoustic machines. By sealing the walls of the ceramic using an in situ polymerization technique, it was shown that wall porosity had no effect on thermal-relaxation dissipation at low frequencies.