Jet penetration into a Stirling engine regenerator matrix with various Regenerator-To-Cooler Spacings

Experiments have been performed under oscillatory flow conditions to investigate the penetration of jets from Stirling engine cooler or heater tubes into a regenerator matrix. The experimental model geometry and operational conditions simulate a Stirling engine. The regenerator porosity is 90%. Fine-wire thermocouples are employed to take unsteady flow temperature measurements, resolved in space within the regenerator matrix and time within the oscillation cycle. Such measurements show thermal dispersion within the regenerator matrix of the jets that issue from the cooler or heater tubes. Also measured are distances into the regenerator needed for the jets to merge completely and the fraction of the matrix material within that penetration depth that is not participating fully in thermal exchange with the fluid. By comparing the jet growth within the regenerator to the growth of a free, turbulent, circular jet, the effective eddy diffusivity is estimated. To document the plenum spacing effect on the jet penetration behavior, experiments are conducted with different plenum widths. All cases are run at a Valensi numberof 14.3 and a Reynolds number of 20,700 (based upon the cooler tube diameter and the cycle maximum bulk mean velocity in the cooler tubes). Results indicate that the effect of plenum thickness on the flow entering the matrix is weak. Some effect is seen when a small plenum is introduced but the effect becomes very weak as the thickness of that plenum is increased.