The frequency dependent regenerator cold section and hot section positional reversal in a coaxial type thermoacoustic Stirling heat pump

► We constructed two coaxial thermoacoustic travelling wave heat pumps. ► Changing frequency will reverse the hot section and cold section of the regenerator. ► The change in frequency changes the magnitudes of positive and negative direction travelling waves. ► Magnitude change of travelling waves is influenced by attenuation within the regenerator. ► This results in a change of net acoustic power flow and heat pumping direction.