Fluid mechanics and heat transfer measurements within a porous regenerator under oscillatory flow conditions: Stirling cycle thermal regeneration

Porous media are commonly used in Stirling regenerators. In these applications, the flow oscillates within the regenerators in such a fashion that the porous matrix absorbs thermal energy from the working fluid when the flow temperature is high and releases the energy back to the fluid when the flow reverses.; Due to regenerator small feature scales and high operation frequencies, challenges arise when it is attempted to experimentally study the oscillatory flow within a real size porous regenerator. For detailed measurements, a large-scale porous regenerator is constructed and operated under oscillatory flow conditions with air as the working fluid and in a fashion dynamically similar to the situation in a Stirling engine.; Pressure drop through the porous regenerator is measured under both steady and oscillatory flow conditions at various oscillating frequencies. Comparisons between the two indicate a possibility that the flow can be treated as quasi-steady within the parameter range studied.; Fluid temperatures at the interface between the regenerator and an adjacent heat exchanger are measured at various thicknesses of plenum between the two. A model is derived to predict spreading within the porous regenerators of jets coming from the heat exchanger.; Convective heat transfer coefficients between the fluid and solid phases in the core region of the porous regenerator are experimentally studied under oscillatory flow conditions. A comparison with some other studies conducted under steady flow conditions indicates thermal non-equilibrium between the two phases during the accelerating portion of the oscillating cycle and a good agreement for the rest of the cycle.; Finally, turbulent momentum and thermal fields are measured immediately downstream of the porous regenerator. Data are used to describe thermal dispersion within the porous regenerator. Models based on the Prandtl mixing length theory are developed to describe the streamwise component of thermal dispersion and the cross-stream component of momentum dispersion.