Direct measurements of steady heat transfer maintained by oscillating pipe flow in thermoacoustic system

This study reports direct measurements of steady heat transfer in a heat exchanger pipe of a thermoacoustic heat pump driven by an oscillating helium gas flow. From simultaneous measurements of gas temperature, pressure, and velocity fluctuations, the steady heat transfer rate is determined from the radial profile of the temporal mean temperature and from the axial distribution of the enthalpy flux density. The heat transfer coefficient h is determined to be given by h = 2 k / r 0 consistently in the range of 1.6 ≤ r 0 / δ α ≤ 6.6, where k is the gas thermal conductivity, r 0 is the tube radius, and δ α = 2 α / ω is the characteristic transverse length given by using the thermal diffusivity and angular frequency.