The development of a theoretical model of valveless pumping and its numerical solution is presented in this work, applied for the case of a closed hydraulic loop, consisting of a soft and a rigid tube. A periodic compression and decompression of the soft tube causes a unidirectional flow, under certain conditions. The integration of the governing flow equations (continuity and momentum), over the tube cross-sectional area results in a quasi-one-dimensional unsteady model. A system of nonlinear partial differential equations of the hyperbolic type is solved numerically, employing three finite difference schemes: Lax-Wendroff, MacCormack, and Dispersion Relation Preserving, the last being the most accurate one. When the excitation takes place far from the midlength of the soft tube, a phase difference between the pressures at the two edges of each tube is developed, being in advance the one that is closer to the excitation area. Increasing the tube occlusion or the length of the excited part of the loop the mean flow rate increases and maximizes at the natural frequency of the loop. The direction of the maximum mean flow rate, for a given tube occlusion, is from the excitation area toward the edge of the stiff tube, which is located closer to the excitation area. Varying the excitation frequency both above and below the resonance frequency, local flow rate extremes appear, manifesting the complex character of the valveless pumping phenomenon.

We assembled an experimental arrangement for the measurement of the velocity field of glycerol suspensions, in the diametric plane, inside glass capillaries with internal diameter of the order of 200 µm. Glass spheres of mean diameter of 10 µm were used to seed the flow. The velocity fields were determined by the particle image velocimetry (PIV) method, whereby, in contrast to the usual implementations of this method based on light-sheet imaging, a forwards-scattering technique with the entire volume flow illuminated was used and the plane of interest was determined by the objective lens of a microscope. Statistical analysis of acquired experimental results was performed and possible limitations of the proposed technique were investigated. The method, with its present implementation, was used to measure velocities up to 4 mm s-1 and seems to be promising for similar measurements in glass capillaries or in microcirculation.

A numerical model for the simulation of aerosol flows via an Eulerian-Eulerian, one-way coupled, two-phase flow description is presented. An in-house computational fluid dynamics code is used to simulate the gaseous (continuous) phase, whereas a modified convective diffusion equation models particle transport. The convective diffusion equation, which includes inertial, gravitational, and diffusive particle transport, is solved by computational fluid dynamics techniques. The model is validated by comparing the calculated laminar fluid flow and particle deposition fractions to analytical and experimentally studied aerosol flows in a laminar flow 90• bend of circular cross section available in the literature. Model predictions are also compared with numerical predictions of Eulerian-Lagrangian models. Particle concentration profiles at different cross sections are calculated, and deposition sites on the wall boundary are indicated. For the range of studied particle diameters, the Eulerian-Eulerian model predicts deposition fractions satisfactorily, being in good agreement with the experimental data.

Despite the well-known beneficial effects of the intra-aortic balloon pump (IABP) generally, there are still some clinical conditions accompanied by IABP ineffectiveness. The aim of this study was the investigation of the independent effects of arterial stiffness and blood pressure on acute IABP effectiveness. For this purpose, a mock circulatory system and 20 patients with cardiogenic shock due to acute myocardial infarction, were employed. It was shown that IABP acute efficiency was determined primarily by arterial compliance (AC) rather than blood pressure alone. IABP induced low hemodynamic effects in patients with systolic blood pressure > 80 mm Hg but with increased AC, whereas IABP resulted in greater hemodynamic effectiveness in cases with systolic pressure < 70 mm Hg but lower AC. The present study provides evidence concerning the hemodynamic conditions, which might lead to optimization of IABP or to the prediction of its acute hemodynamic performance, based on both measurements of AC and blood pressure.

In the present paper a perturbation method is developed in order to study viscous laminar flows through wavy-walled channels. The stream function of the flow is expanded in a series thereby the wall amplitude being the perturbation parameter. The walls of the channel are transformed into parallel straight lines in order to simplify the boundary conditions of the problem on the wall. Flow field and wall-shear stresses are calculated numerically up to the first perturbation order.The position of the beginning separation on the channel walls and the associated critical Reynolds number are determined, as well as the extension of the region of the separated flow. The position of separation and reattachment points are given as functions of Reynolds numbers lying above the critical Reynolds number. The results are discussed and compared with the experimental results of other papers and further theoretical analysis.