Pressure-drop losses in porous regenerator materials significantly affect the efficiency of Stirling cryocoolers and related oscillating-flow systems. Regenerator materials such as woven screens, random fibre(felt) materials, and other porous media have been widely studied, and several correlations for the friction factor are available in the literature. However, in practical applications, these materials are often compressed during fabrication, leading to changes in geometry and flow behaviour. Therefore, the applicability of existing correlations to porous materials remains uncertain.
To investigate this, a closed-loop experimental test rig is being developed to measure pressure drop under both steady and oscillating flow across regenerator materials relevant to Stirling cryocoolers. The study focuses on porous samples, approximately 10 mm in diameter and 116 mm in length, covering porosity ranges between 0.60 and 0.90. The experimental setup is designed to operate with helium at mean pressures around 22 bar, mass flow rates between 10–200 mg/s, and differential pressure ranges of approximately 0.01–0.2 bar.
The setup will measure pressure drop, pressure amplitude, piston displacement amplitude in case of oscillating flow, mass flow rate, oscillation frequency, mean pressure, and temperature for different porous samples and compression levels. These measurements will be used to establish friction factor versus Reynolds number relationships for regenerator materials under both steady and oscillating flow conditions. One of the key objectives of the ongoing work is to compare the hydrodynamic behaviour under steady and oscillating flow conditions and assess whether existing modified Ergun-type correlations remain valid for porous media. 
 

Keywords
Stirling cryocooler|Oscillating flow|Pressure drop|Friction factor|Regenerator materials