Oscillatory flow and thermal field measurements at the interface between a heat exchanger and a regenerator of a Stirling engine

A physical model of a stacked-screen Stirling engine regenerator with a porosity of 90% was constructed to be representative of modern free-piston engines. Such a model allows conducting detailed fluid mechanics and thermal measurements and simulating representative entry flow geometry to a regenerator. Present focus is on the flow and thermal fields at the interface between the regenerator matrix and a cooler tubular heat exchanger. Velocity measurements within the plenum between the regenerator and the cooler were taken and similarities with previous measurements of oscillatory flow in a pipe were noted. Fine-wire thermocouples were employed to take unsteady temperature measurements, resolved in space and time within the plenum. Such measurements show thermal dispersion of the jets within the plenum in one half of the cycle and sink flow to the discrete cooler tubes in the other half of the cycle. When the program is completed, measurements of thermal spreading will have been taken and the results will indicate the fraction of the matrix material that is participating fully in thermal exchange with the fluid. The present paper introduces the program and presents progress to date. Some focus is given to the secondary flows within the matrix, including flows near the canister wall that are influenced by sealing between the matrix and the canister. All cases are run under conditions characterized by a Valensi number of 14.3 and a maximum Reynolds number of 20700 (the length scale is the cooler tube diameter and the velocity scale is the cycle maximum bulk mean velocity in the cooler tubes).