Ricardo P. Dias

Asymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcation

In microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear, and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations, human red blood cells suspended in dextran 40 with about 14% of hematocrit level (14 Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0 × 10(-12) m(3)/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region.

Single and Two-Phase Flows on Chemical and Biomedical Engineering

Hydrogenation of vegetable oils is an important process in the food industry because of its widespread application to produce margarines, shortenings, and other food components. Supercritical technology has proven to be a reliable alternative to conventional hydrogenation process because not only the trans isomer levels can be reduced, but also offers a clean, economic and environmental friendly process. Computational Fluid Dynamics (CFD) modeling applied to the supercritical hydrogenation reaction can be useful in visualizing and understanding the mass transfer phenomena involved. CFD is applied to the study of the catalytic hydrogenation of sunflower oil in the presence of a supercritical solvent. A mix of sunflower oil, hydrogen and supercritical propane (used as a solvent) is the flowing fluid. Their transport properties at high pressure are incorporated within a CFD commercial code in order to estimate them online within the simulation process. A 2D CFD model of a single Pd-based catalyst pellet is presented. Intra-particle and surface concentration profiles and surface mass fluxes for all species present in the mixture (oil triglycerides and hydrogen) are obtained and compared against experimental results. Different temperatures, flow velocities and particle sizes are studied and external and internal mass transfer phenomena are analyzed. External mass transfer coefficients for hydrogen and oil triglycerides are obtained and a correlation for estimating them is presented.

Flow of Physiological Fluids in Microchannels: The Sedimentation Effect

Microfluidic devices are becoming one of the most promising new tools for diagnostic applications and treatment of several chronic diseases. Hence, it is increasingly important to investigate the rheological behaviour of physiological fluids in microchannels. The main purpose of the present experimental work is to investigate the flow of two different physiological fluids frequently used in microfluidic devices. The working fluids were physiological saline (PS) and dextran 40 (Dx40) containing about 6% of sheep red blood cells (RBCs), respectively. The capillaries were placed horizontally on a slide glass and the flow rate of the working fluids was kept constant by using a syringe pump. By means of a camera the images were taken and transferred to the computer to be analysed. Generally, the results show that PS and Dx40 have different flow behaviour due to the sedimentation of the RBCs.

New plates for different types of plate heat exchangers

The first patent for a plate heat exchanger was granted in 1878 to Albretch Dracke, a German inventor. The commercial embodiment of these equipments has become available in 1923. However, the plate heat exchanger development race began in the 1930s and these gasketed plate and frame heat exchangers were mainly used as pasteurizers (e.g. for milk and beer). Industrial plate heat exchangers were introduced in the 1950s and initially they were converted dairy models. Brazed plate heat exchangers were developed in the late 1970s. However, copper brazed units did not start selling until the early 80s. Nickel brazing came to market around ten years later, since copper presents compatibility problems with some streams (e.g. ammonia). All-welded and semi-welded (laser weld) plate heat exchangers were developed during the 1980s and early 90s. Shell and plate heat exchangers were recently introduced in the market and can withstand relatively high pressures and temperatures, as the shell and tube does. The fusion bonded plate heat exchangers (100% stainless steel) are a technology from the 21 st century, these equipments being more durable than brazed plate heat exchangers. The plates are the most important elements from the different plate heat exchangers mentioned above. This paper initially introduces the gasketed plate and frame heat exchanger and common chevron-type plates. Resorting to computer fluid dynamics techniques, the complex 3D flow in cross-corrugated chevron-type plate heat exchanger passages is visualized. Recent patents related with the plates from different plate heat exchangers are then outlined.