CRRT circuit venous air chamber design and intra-chamber flow dynamics: a computational fluid dynamics study

BackgroundVenous air trap chamber designs vary considerably to suit specific continuous renal replacement therapy circuits, with key variables including inflow design and filter presence. Nevertheless, intrachamber flow irregularities do occur and can promote blood coagulation. Therefore, this study employed computational fluid dynamics (CFD) simulations to better understand how venous air trap chamber designs affect flow.MethodsThe flow within a venous air trap chamber was analyzed through numerical calculations based on CFD, utilizing large eddy simulation. The working fluid was a 33% glycerin solution, and the flow rate was set at 150 ml/min. A model of a venous air trap chamber with a volume of 15 ml served as the computational domain. Calculations were performed for four conditions: horizontal inflow with and without a filter, and vertical inflow with and without a filter. Streamline plots and velocity contour plots were generated to visualize the flow.ResultsIn the horizontal inflow chamber, irrespective of filter presence, ultimately the working fluid exhibited a downstream vortex flow along the chamber walls, dissipating as it progressed, and being faster near the walls than in the chamber center. In the presence of a filter, the working fluid flowed uniformly toward the outlet, while in the absence of a filter the flow became turbulent before reaching the outlet. These observations indicate a streamlining effect of the filter.In the vertical inflow chamber, irrespective of filter presence, the working fluid flowed vertically from the inlet into the main flow direction. Part of the working fluid bounced back at the chamber bottom, underwent upward and downward movements, and eventually flowed out through the outlet. Stagnation was observed at the top of the chamber. Without a filter, more working fluid bounced back from the bottom of the chamber.ResultsIn the horizontal inflow chamber, irrespective of filter presence, ultimately the working fluid exhibited a downstream vortex flow along the chamber walls, dissipating as it progressed, and being faster near the walls than in the chamber center. In the presence of a filter, the working fluid flowed uniformly toward the outlet, while in the absence of a filter the flow became turbulent before reaching the outlet. These observations indicate a streamlining effect of the filter.In the vertical inflow chamber, irrespective of filter presence, the working fluid flowed vertically from the inlet into the main flow direction. Part of the working fluid bounced back at the chamber bottom, underwent upward and downward movements, and eventually flowed out through the outlet. Stagnation was observed at the top of the chamber. Without a filter, more working fluid bounced back from the bottom of the chamber.ConclusionsCFD analysis estimated that the flow in a venous air trap chamber is affected by inflow method and filter presence. The "horizontal inflow chamber with filter" was identified as the design creating a smooth and uninterrupted flow throughout the chamber.