(Georgia Institute of Technology, 2008-05)
Landrum, E. C.; Conrad, T. J.; Pathak, M. G.; Ghiaasiaan, S. Mostafa; Kirkconnell, Carl Scott; Crittenden, Thomas M.; Yorish, S.
An experimental investigation was carried out to determine the effect of frequency on the porous media hydrodynamic closure relations for steady periodic flow. Using room temperature helium as the working fluid, stacked discs of #635 stainless steel and #325 phosphor bronze wire meshes were subjected to an oscillatory flow field. Dynamic pressure transducers recorded waveforms upstream and downstream of the porous section at charge pressures of 2.86 and 3.55 MPa. Tests were performed in the axial direction at frequencies ranging from 50 to 200 Hz. Hydrodynamic parameters were determined using a CFD-assisted methodology. The experimental test section and its vicinity were simulated using the Fluent code and mesh fillers were modeled as a porous structure. Model porous media hydrodynamic parameters were iteratively adjusted to match the model predictions to the experimental results. Directional resistances related to the Darcy permeability and Forchheimer’s inertial coefficients were obtained at discrete frequencies and errors were quantified. The experimental results indicate that Forchheimer’s inertial coefficient may depend rather strongly on frequency. More detailed experiments are needed to ascertain the observed trends.
(Georgia Institute of Technology, 2008-05)
Conrad, T. J.; Ghiaasiaan, S. Mostafa; Kirkconnell, Carl Scott; Crittenden, Thomas M.
Miniature cryocoolers are suitable for space applications and installation in portable devices. They can also be useful as final stages for applications where small cooling loads must be carried at temperatures lower than that required by the primary load. Strong regeneration, near plug-flow regime in the pulse tube and good flow control are essential for these cryocoolers to function. Miniature cryocoolers that use wire mesh as regenerator filler generally have a much larger ratio of regenerator filler pore size to regenerator diameter than their larger counterparts. For this reason, the significance of gaps existing between the porous regenerator filler and the interior wall of the regenerator shell will likely be greater for miniature cryocoolers. These gaps provide a low resistance flow path which may decrease the effectiveness of the regenerator. In this investigation the effects of such gaps on the performance of miniature pulse tube cryocoolers are examined using 2-D CFD simulations. Miniature scale pulse tube cryocooler designs whose suitability for cooling under ideal conditions that have been theoretically demonstrated are used as the basis for this study. The results confirm that extra precision and robustness are needed for miniature cryocoolers.