Estimation of slip of viscoplastic fluid in laminar hagen poiseuille flow using optical coherence tomography

Particle and fibre suspensions are prone to wall depletion which leads to effects like apparent slip, often characterized by a slip velocity, which often dictate the suspension flow behaviour. Heretofore this has complicated the interpretation of rheological measurements both in microscopic and macroscopic scales. A new experimental method based on velocity profile measurements in fully developed pipe (18.5 mm diameter) flow is presented for direct measurement of the rheological behaviour of any opaque fluid . In our work Magnetic Resonance Imaging (MRI) or the Ultrasound Doppler Velocimetry (UDV) technique is utilized for measuring the velocity profile in the interior parts of the pipe and Optical Coherence Tomography (OCT) is applied for high-resolution measurements of the boundary layer flow and structure near the pipe wall. While MRI and UDV are well established techniques OCT has only recently been utilized for rheological characterizations. As MRI and UDV, OCT is a non-invasive technique that allows real time imaging of the internal structure and velocity of opaque media with very high spatial and temporal resolution.