Oscillatory heat transfer correlation for annular mini channel stirling heater

Annular mini-channel Stirling heater are replacing conventional tubular heater in modern free piston Stirling engines due to reliability and manufacturing issues. Heat transfer characteristics of a new mini channel heater with variable cross section are analyzed under oscillating flow. The effect of oscillating speed and dimensionless fluid displacement (Aₒ) on heat transfer rate is evaluated. The variation of operating speed from 150 to 1200 rpm enhanced heating power requirement from 191 to 581 W for wall temperature in 473–773 K range. However, hot space gas temperature is decreased by 66–162 K under same conditions. The change in Aₒ from 10.98 to 15.09 resulted in 13.2% enhancement in heat transfer at 300 rpm whereas maximum enhancement of 27.6% was noticed at 1200 rpm with maximum hot space temperature drop of 9.5 K. Based on the data, an empirical correlation for heat transfer in annular mini channel Stirling heater is proposed, the correlation covers kinetic Reynolds number (Reω) in 0.48–1.94 range.