(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)
Pathak, M. G.; Ghiaasiaan, S. Mostafa
Solid-fluid thermal interactions during unsteady flow in porous media play an important role in the regenerators of pulse tube cryocoolers. Pore-level thermal processes in porous media under unsteady flow conditions are poorly understood. The objective of this investigation was to study the pore-level thermal phenomena during pulsating and unidirectional sinusoidal flow through a generic, two-dimensional porous medium by numerical analysis. Furthermore, an examination of the effects of flow pulsations on the thermal dispersion and heat transfer coefficient that are encountered in the standard, volume-average energy equations for porous media were carried out. Pulsating and unidirectional sinusoidal inlet flow rates were chosen as an intermediate step towards the more difficult problem of periodic flow. The investigated porous media are periodic arrays of square cylinders. Detailed numerical data for the porosities of 0.75 and 0.84, with flow pulsation frequencies of 0 - 80 Hz, were obtained at Reynolds numbers of 560 and 980. Based on these numerical data, the instantaneous as well as cycle-average thermal dispersion and heat transfer coefficients, to be used in the standard unsteady volume-average energy conservation equations for flow in porous media, were derived.