Cardiac Axial Blood PUmp Analysis and Performance Prediction

The affinity law is widely used in pump design and experiments. The applicability of the affinity law in an emergency drainage pump at different rotating speeds was studied. Experiments and numerical simulation through ANSYS CFX (Computational Fluid Dynamics X) 15.0 software were used to research the affinity law characteristics. Results show that the simulation of characteristics is basically consistent with the experimental curves. In small flow rate conditions, due to the existence of obvious differential pressure between the pressure side and the suction side in the impeller blade tip area, the leakage flow occurs at the tip clearance, which collides with the main stream at the inlet and generates vortices at the leading edge of the impeller. The tip leakage flows of the pump at four different rotating speeds were compared, and it was found that the tip leakage increased with increasing rotation speed, and at the same rotation speed, the tip leakage flow was large in the small flow rate condition, which led to the simulation value of the characteristics being greater than the scaling value. As the flow rate increased, the anti-cavitation performance of the pump became worse and the hydraulic loss was larger, so the pump’s performance curve deviated from the scaling curve.

Rotating electrodes can effectively improve the processing performance of micro-electrical discharge machining (micro-EDM), but there is still a lack of systematic research on the specific effects of electrode rotation and rotational speed changes. In this paper, the effects of electrode rotation and rotational speed on the discharge channel, debris stress, and debris motion in micro-EDM were analyzed theoretically. An AISI304 sheet was used as the workpiece and helical tungsten carbide alloy as the electrode. The through-hole drilling experiments of micro-EDM were carried out at low and high discharge energy and different electrode rotational speeds. In terms of processing efficiency, the effects of electrode rotation and rotational speed on material removal rate (MRR), relative tool wear ratio (RTWR), and short circuit number were analyzed. The results show that MRR increases first and then decreases, RTWR and short circuit number decrease first and then increase. In the aspect of processing precision, the impacts of electrode rotation and rotational speed on taper angle and overcut were analyzed. The results show that the electrode rotational speed has little effect on the change of the taper angle. In addition, when the electrode rotational speed is small, there is no obvious change in overcut. When the speed is too high, the overcut increases obviously and shows a trend of continuous increase. Finally, by comparing the experimental results, the optimal electrode rotational speeds of micro-EDM with two kinds of discharge energy were determined. The final experimental results also verify the correctness of the previous theoretical analysis.

The objective of this translational study was to evaluate the FDA-approved PediMag, CentriMag, and RotaFlow centrifugal blood pumps in terms of hemodynamic performance using simulated neonatal and pediatric extracorporeal membrane oxygenation (ECMO) circuits with different sizes of arterial and venous cannulae. Cost of disposable pump heads was another important variable for this particular study. The experimental circuit was composed of one of the centrifugal pump heads, a polymethylpentene membrane oxygenator, neonatal and pediatric arterial/venous cannulae, and 1/4-inch ID tubing. Circuits were primed with lactated Ringer's solution and packed human red blood cells (hematocrit 35%). Trials were conducted at 36°C using the three pump heads and different cannulae (arterial/venous cannulae: 8Fr/18Fr, 10Fr/20Fr, and 12Fr/22Fr) at various flow rates (200-2400 mL/min, 200 mL/min increments) and rotational speeds. Pseudo patient pressure was 60 mmHg. Real-time pressure and flow data were recorded for analysis. The RotaFlow pump had a higher pressure head and flow range compared with the PediMag and CentriMag pumps at the same rotational speed and identical experimental settings (P<0.001). The PediMag pump had lower flow output than others (P<0.001). Small-caliber arterial cannulae and higher flow rates predictably created higher circuit pressures and pressure drops. There was no significant difference in hemodynamic energy delivered to the pseudo patient with each of the three pumps. The arterial cannula had the highest pressure drop and hemodynamic energy loss in the circuit when compared to the oxygenator and arterial tubing. The RotaFlow centrifugal pump had a significantly better hemodynamic performance when compared to the PediMag and CentriMag blood pumps at identical experimental conditions in simulated neonatal and pediatric ECMO settings. In addition, the cost of the RotaFlow pump head ($400) is 20 to 30-fold less than the other centrifugal pumps [CentriMag ($12000) or PediMag ($8000)] that were evaluated in this translational study.

Dynamics of a powered disk in clay soil

We have developed a tiny rotary centrifugal blood pump for the purpose of supporting circulation of children and infants. The pump is designed to provide a flow of 0.1-4.0 L/min against a head pressure of 50-120 mm Hg. The diameter of the impeller is 30 mm with six straight vanes. The impeller is supported by a hydrodynamic bearing at its center and rotated with a radial coupled magnetic driver. The bearing that supports rotation of the impeller of the tiny centrifugal blood pump is very critical to achieve durability, and clot-free and antihemolytic performance. In this study, computational fluid dynamics (CFD) analysis was performed to quantify the secondary flow through the hydrodynamic bearing at the center of the impeller and investigated the effects of bearing clearance on shear stress to optimize hemolytic performance of the pump. Two types of bearing clearance (0.1 and 0.2 mm) were studied. The wall shear stress of the 0.1-mm bearing clearance was lower than that of 0.2-mm bearing clearance at 2 L/min and 3000 rpm. This was because the axial component of the shear rate significantly decreased due to the narrower clearance even though the circumferential component of the shear rate increased. Hemolysis tests showed that the normalized index of hemolysis was reduced to 0.0076 g/100 L when the bearing clearance was reduced to 0.1 mm. It was found that the CFD prediction supported the experimental trend. The CFD is a useful tool for optimization of the hydrodynamic bearing design of the centrifugal rotary blood pump to optimize the performance of the pump in terms of mechanical effect on blood cell elements, durability of the bearing, and antithrombogenic performance.

A 195 cm³ swash-plate piston expander was tested in an ORC using R245fa as working fluid. Rotational speeds ranging from 1000 RPM to 4000 RPM and pressure ratios from 7 to 12 were imposed. In total, 65 steady state points were measured. With these measurements, performance maps were generated to point out the influence of rotational speed and levels of pressure on mechanical power and isentropic efficiency. These maps have highlighted the existence of an optimal rotational speed of around 3000 RPM maximizing the mechanical power, while the speed that maximizes the isentropic efficiency lies between 2000 and 2500 RPM. The maximal mechanical power and isentropic efficiency were 2.8 kW and 53%, respectively. Then the measurements were used to analyze the losses. This analysis has shown that, under the expansion and compression limit, the theoretical isentropic efficiency has values comprised between 90% and 70% for pressure ratios of 7 to 12. The filling factor affects the isentropic efficiency for low rotational speeds and low pressure ratios. Indeed, indicated isentropic efficiency is around 60% for 1000 RPM and around 75% for 4000 RPM. These values stay quite constant with the pressure ratio. Finally, a mechanical efficiency comprised between 40% and 90% was observed, which lowers the isentropic efficiency to values comprised between 30% and 53%. Finally, a model based on energy and mass conservation inside a cylinder volume was successfully calibrated and was able to predict mass flow rate, mechanical power and exhaust temperature with good agreement. This model has enabled desegregation of the influence of pressure drops and leakages on the filling factor, then on the isentropic efficiency. This analysis has shown that pressure drops mainly affect the compactness of the expander, and not so much the isentropic efficiency (except for low rotational speeds where pressure drops can lower the isentropic efficiency by 14%). In contrary, leakages have a strong impact. The importance of the different sources of losses varies with the speed. For the optimal speed of 2500 RPM, under-expansion and compression have the strongest impact, followed by mechanical losses, leakages and pressure drops. respectively.

Crystallization is a puriification process during which molecules of a crystal compound bond together arranging themselves in a compound specific orderly lattice structure in which foreign molecules known as impurities do not precisely fit the structural pattern of the growing crystal. Thus their inclusion in the crystal lattice while not impos sible is certainly difficult resulting in a largely pure crystal. Crystalization is a key process in the pharmaceutical industry as it is used to produce the active pharmaceutical ingredient (API) that is absor bed in a patient's body to deliver the desired medical effect, thus high product purity is paramount. During crystallization processes undesirable quantities of nanocrystals are commonly generated causing challenges in downstream processing such as clogging of fillters. The lack of complete understanding of the cause of fines prevents the achievement of consistent particle size distributions (PSDs). In pharmaceutical laboratory experiments increased rotational speeds have brought about large increases in particle numbers with much of the product material lost to fines. The increased particles numbers are assumed to be caused by increased shearing of nuclei off the surface of seed particles. This thesis examines the change of phase resolved fluid velocity and shear stress as a result of rotational speed and impeller type and examines the infuence of baffles. An experimental set-up was designed to best replicate the mixing vessel of a Labmax where the initial crystallization experiments of Paracetamol in IPA yielding large particle numbers were carried out. Particle Image Velocimetry (PIV) was used to measure particle ow velocities from which turbulent shear stresses are calculated. Finally, the direct influence of impeller type on particle size distribution (PSD) was examined in cooling batch crystallization experiments again of Paracetamol in IPA in an Optimax using a mixing vessel of the same size and dimensions of both a Labmax and the mixing vessel used in PIV experiments. Results conclusively show an increase of particle count with increased shear stress as the impeller types that generate the highest shear stresses also produce the highest particle counts. Particle size distributions for all impeller types also show lower mean values for higher shear impellers but also a larger number of finnes and a lower number of large particles. Knowledge of the effects of shear stresses in crystallization processes permit better control over final PSDs whether through impeller type selection, rotational speed selected, the use of baffles or a combination of all. Based on extensive experimental data an equation to predict turbulent shear stress in stirred vessels is pro- posed to prevent the necessity of complex measurement techniques for newly designed crystallization experiments.

Thermal performance of a new nanofluid containing biologically functionalized graphene nanoplatelets inside tubes equipped with rotating coaxial double-twisted tapes

Compared with conventional high-specific-speed axial flow pump, better cavitation performance and compact size have been achieved in contra-rotating axial flow pump, where the rear rotor is employed additionally to the front rotor to convert the swirling flow to the pressure rise. Meanwhile, significantly deteriorated performance has also been observed at well off-design flow rates with design rotational speed. The rotational speed control (RSC) of front and rear rotors has been experimentally proved to be effective to enhance the performance. However, thorough investigations are necessary to find the optimum rotational speeds of rotors. It may be done by computational fluid dynamics (CFD) simulations, whereas it is time-consuming to cover the wide ranges of rotational speeds. Therefore, in the present paper, a fast and effective performance prediction model is established by considering radial equilibrium condition, conservation of rothalpy and mass, empirical deviation angle, bladerows interaction and empirical losses. Experimental and CFD results are employed to validate the proposed prediction model. It is found that the proposed model shows good enough accuracy in predicting performances of contra-rotating axial flow pump under RSC in broad flow rate range. Furthermore, an energy saving application of the proposed model is also illustrated for two typical system resistances. Compared with the traditional valve control under the design rotational speed operation, the RSC method can well modify the pump head to satisfy the system resistance at wide flow rate range with the significantly improved energy performance.

In this article, a numerical investigation was performed on a quadrotor UAV propeller with the aim of examining effects of airspeed and rotational speed on thrust coefficient, which is one of the most important parameters on propeller aerodynamic performance. In that purpose, Computational Fluid Dynamics (CFD) analyses of an 11-inch propeller were carried out at different airspeeds and rotational speeds in vertical climbing flight condition. In order to have optimum number of mesh elements in computational domain, mesh independence analyses were also conducted. In conclusion, results of the analyses with k-ω SST turbulence model were shown that, increase in rotational speed was leaded to higher turbulent kinetic energy. Furthermore, higher rotational speeds also resulted in higher differences between numerical estimations and experimental data, but found to become more independent from airspeed.

Turbocharger surge remains an area of concern for the automotive industry as it limits the permissible operating range on the compressor map, while also adversely impacting the compressor’s pressure rise, efficiency, and acoustics. The present study uses Stereoscopic Particle Image Velocimetry (SPIV) to investigate the flow field at the inlet of an automotive turbocharger compressor without a recirculating channel. Experiments were carried out at four different speeds, including 80, 100, 120, and 140 krpm, which represent a substantial portion of the compressor map. The mass flow rates investigated ranged from choke to deep surge, thus spanning the entire mass flow regime at each rotational speed. The current work aims to characterize how the compressor inlet velocity field varies with rotational speed, with a specific emphasis on surge. The qualitative nature of the flow field (radial dependence of axial and tangential velocity profiles), over the choke to mild surge range, was observed to be nearly independent of rotational speed for comparable operating conditions (for example, comparison of mild surge at different rotational speeds). A quantitative comparison of the velocity profiles at the choke or mild surge operating points showed an increase in the velocity magnitudes with increasing rotational speed. The flow field at deep surge, however, was observed to change substantially from 80 krpm to 140 krpm. At 80 krpm, the character of the flow field at different times (at different points on the surge cycle) was observed to be similar: the core flow near the center of the duct was always directed into the impeller, whereas the reversed flow occupied an annular region near the periphery in nearly all time instances. However, as the rotational speed was increased to 140 krpm, the variation in the flow field at different instances within a deep surge cycle increased. At 140 krpm, the negative flow rate (where the cross-sectional average flow is directed out of the inducer back into the inlet duct) portion of the surge cycle was still similar to the overall surge flow field at 80 krpm, but over a substantial part of the positive flow rate (cross-sectional average flow is directed into the impeller) portion of the surge cycle, there was no sign of reversed flow within the visualization domain. As the rotational speed was increased, the surge loop (obtained by combining the PIV and pressure transducer data) extended over a wider portion of the compressor map with higher maximum (positive) and minimum (negative) flow rates, along with higher amplitude pressure fluctuations. The mean amplitude of mass flow rate and pressure ratio fluctuations at deep surge increased in nearly a quadratic fashion with rotational speed. The deep surge frequency did not change substantially over the range of rotational speeds examined in this study.

Experimental investigation of the fluid dynamics inside any blood pumping device is necessary for several reasons. First, improved understanding about the flow near the walls of a blood pump is important since thrombus formation (blood clotting) may occur when the shear stress is nearly zero. If the shear stress is in the opposite direction to the main body of the flow, a region of stagnation or recirculation is indicated, which may also lead to thrombosis. A second problem of importance to blood flows is hemolysis, the destruction of red blood cells. Hemolysis can be caused by high shear stresses imposed on the blood cells by the flow. Since hemolysis is a function of at least shear stress and residence time, an understanding of how these two variables are coupled is desirable. Third, an accurate measurement of wall shear stress and flow patterns is also necessary to validate computational fluid dynamics (CFD) predictions in the design of blood pumps. It is widely known that improper meshing of the numerical pump model, the use of an incorrect turbulence model, or errors in choosing boundary conditions can lead to a model that is in contradiction to experimental results. Quantitative oil streaking has been implemented in order to measure the wall shear stresses in the pump and supply the necessary information needed to ensure a good pump design.

Theoretical Study of Flow Phenomena in the Constricted Tubes

Aneurysms that bulge on intracranial carotid arteries can be detected by using medical imaging technologies. Aneurysm, which is detected in this scope of study, is isolated from the rest of the arteries and vessel cloud with the help of Computer Aided Design (CAD) programme. Obtained geometry is transferred into Computational Fluid Dynamics (CFD) with applicable extension. Drop in pressure, velocity values (x, y, z plane) and wall shear stress (WWS) is recorded through the aneurysm and arteries which aneurysm initialize on. At the same time, this study gave us an opportunity to analyze parameters that affect aneurysm and its' around via visual way. We observed homogenous WWS distribution and consistent velocity values in our simulation outputs. In addition, change in pressure through the aneurysm was recorded. As a result, patient-specific investigation of hemodynamics parameters in-vivo is a quite challenging problem so that image-based CFD is powerful and convenient tool to acquire mentioned parameters for the diagnosis and treatment procedure.

The tribological behavior of self-lubricating spherical bearings in aerospace applications is crucial for ensuring reliability under dynamic loads. This study employs Computational Fluid Dynamics (CFD) to analyze the interactions between contacting surfaces, focusing on pressure distribution, shear stress, heat flux, and elastic deformation. By simulating various operational conditions, including different rotational speeds and the use of solid lubricants like talc and graphite, the research evaluates their effectiveness in reducing friction and managing thermal effects. Findings reveal that rotational speed significantly influences tribological performance, with graphite outperforming talc in minimizing friction, heat generation, and wear at high speeds. While talc reduces friction, it induces higher shear stresses and elastic deformation, making graphite a more suitable lubricant for demanding aerospace applications. This, study contributing to enhanced performance and durability of self-lubricating bearings in critical aerospace.