Characterization of mixed convection in microfluidic channels with Defocus Particle Tracking

In this work, we present an experimental analysis of mixed convection within microchannels using the General Defocusing Particle Tracking (GDPT) technique. A the microscale, buoyancy forces are typically neglected due to the very small hydraulic diameter. However, in channels with dimensions exceeding 400 μm under moderate transverse temperature gradients (10-50 K/mm), buoyancy-driven swirling motion can occur. This effect, while often overlooked, is significant for mixed convection, offering potential applications in micro-mixing, particle separation, and flow manipulations. We reconstructed the three-dimensional flow fields under various thermal and flow conditions inside a square capillary glass channel with cross-sectional dimensions of 800 μm × 800 μm, using the GDPT technique.