PIVOxy – Experimental Flow Visualization in Membrane Oxygenators
The hemocompatibility of oxygenators is commonly evaluated in prototype-based and standardized blood trials. Besides this being a rather cost and time consuming approach, only integral values can be determined. Thus, to determine locally or time resolved values Computational Fluid Dynamics (CFD) is well established. CFD can be used to evaluate initial designs regarding stagnation areas or an inhomogeneous flow distribution. However, considering the complexity of the fiber bundle geometry major assumptions have to be made which are not validated so far. Particle Image Velocimetry (PIV) is an approved optical measurement method for flow visualization which in this study is applied on the blood-sided flow through membrane oxygenators. The reason for the missing validation is the challenging application of optical measurement methods to the opaque fiber bundle. Furthermore, an appropriate optical resolution of the delicate and dense fiber arrangement was a limiting factor.
Wound Fiber Arrangement
The oxygenator to be investigated is the NeonatOx. For the optical accessibility a transparent replica was manufactured. All fibers and relevant housing parts are made of PMMA. The angle between two following fiber layers is kept at 24°. For a good spatial resolution an upscaled model by a factor of S = 3.3 was developed. The theory of similarity ensures the same flow distribution and the transferability of the results compared to the original device. Due to the optical accessibility a transparent fluid was used. The fluid mechanical refractive properties were also covered by the dimensionless numbers. A third parameter that includes the pressure drop over the model was used to verify the theory of similarity. For a three dimensional vector field 3C-PIV was applied.
For the validation of the numerical approach we need to differentiate between flow on a macroscopic and a microscopic level. Regarding the overall flow distribution the stagnation areas show a good agreement in size and position. However, the CFD does not account for the physically existence of the fibers in the flow. This leads to the fact that effects on a microscopic level are neglected in the simulation.
The results from these experimental investigations will be used to develop more sophisticated simulation techniques. Those simulation techniques are required during the development of artificial lungs to benefit from the cost and time reductive advantages of CFD.
- Schlanstein PC, Hesselmann F, Jansen SV, Gemsa J, Kaufmann TA, Klaas M, Roggenkamp D, Schröder W, Schmitz-Rode T, Steinseifer U, and Arens J. Particle image velocimetry used to qualitatively validate computational fluid dynamic simulations in an oxygenator: A proof of concept. Cardiovascular Engineering and Technology, pages 1–12, 2015