Inhomogeneous co-flowing fluids inside a microchannel exposed to an acoustic standing wave can lead to the relocation of the fluids. Here we investigate the use of combined acoustic relocation and acoustophoretic migration for the transfer of particles between co-flowing fluids inside a microchannel exposed to a standing pressure half-wave with a pressure nodal plane along the channel center line and antinodal planes along the walls. We show that under the influence of the applied field, particles suspended in a carrier fluid of low acoustic impedance flowing along the channel center are initially dragged toward the walls along with the relocating fluid and later migrate into the target fluid that relocates from the walls to the channel center. We found that the particle motion is initially controlled by the dominant fluid relocation-induced Stokes drag force and later governed by the primary acoustic radiation force as stable fluid configuration is reached. Experimentally we unraveled that depending on the operating parameters-particle size, flow rates, and acoustic energy density-the final locations of the particles at the end of the channel leads to three distinct regimes-complete medium exchange, partial medium exchange, and no medium exchange. Our study reveals that the relocation and migration dynamics of the particles is underpinned by the relevant timescales â advection timescale, acoustophoretic timescale, and the relocation timescale, which in turn govern the different regimes observed. Numerical simulations predicted the complete migration and nonmigration of particles of two different sizes, in agreement with the experimental observations. We also demonstrate the medium exchange and size-based sorting of biological cells, which shows the potential application of the study in biochemical assays. © 2021 American Physical Society.