A Viscosity Model for Blood Flows in Narrow Channels at High Reynolds Numbers Incorporating a Cell-Free Layer.

To better understand the actual flow fields in blood-contacting mechanical medical devices, such as ventricular assist devices (VADs), accurate in vitro and in silico studies are essential. Traditionally, these studies have treated blood as a single-phase fluid. In reality, however, blood is a multi-phase fluid consisting of plasma and suspended blood cells. Cell migration leads to heterogeneous cell distribution, which significantly impacts flow dynamics, particularly in the narrow gaps of these devices. This migration is not usually considered in in vitro analyses using blood analog fluids or in in silico simulations of VADs. This study presents an advanced viscosity modeling approach that accounts for cell migration effects under gap-relevant conditions. The model is based on local particle distribution data obtained from experiments with blood and particle-laden blood analog fluids in microchannels. It is applicable to both blood and particle-laden blood analog fluids, covering gap heights of 150 µm, Reynolds numbers in the range of 50 < Re < 150 and particle volume fractions of up to 30%. Previous works have investigated blood flows with significantly lower volume fractions of up to 5%. The model's accuracy was validated by comparing results with experimental data on pressure losses of blood flowing through a microchannel, demonstrating good agreement. By incorporating variations in local viscosity, this enhanced viscosity distribution model improves the accuracy of flow simulations, offering a more realistic representation of blood flow in narrow gaps compared to the single-phase assumption. Future work will extend the model to accommodate physiological particle volume fractions of up to 45%.