Effect of blood viscosity on the performance of virtually wall-less venous cannulas

Perfusion ◽  
2019 ◽  
Vol 35 (5) ◽  
pp. 393-396
Author(s):  
Saad Abdel-Sayed ◽  
Philippe Abdel-Sayed ◽  
Denis Berdaj ◽  
Enrico Ferrari ◽  
Maximilian Halbe ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Target Volume ◽  
Inlet Pressure ◽  
Thin Wall ◽  
Test Medium ◽  
Lower Reservoir ◽  
Pump Flow Rate ◽  
Pump Inlet ◽  
And Control

Aim: This study was designed to quantify the influence of blood as test medium compared to water in cannula bench performance assessment. Methods: An in vitro circuit was set-up with silicone tubing between two reservoirs. The test medium was pumped from the lower reservoir by centrifugal pump to the upper reservoir. The test-cannula was inserted in a silicone tube connected between the lower reservoir and the centrifugal pump. Flow rate and pump inlet-pressure were measured for wall-less versus thin-wall cannula using a centrifugal pump in a dynamic bench-test for an afterload of 40-60 mmHg using two media: blood 10 g/dL and 5.6 g/dL and water 0 g/dL. Results: The wall-less cannula showed significantly higher flows rates as compared to the thin-wall cannula (control), with both hemoglobin concentrations and water. Indeed, for a target volume of 200-250 mL of blood (Hg 10 g/dL) in the upper reservoir, the cannula outlet pressure (P) was −14 ± 14 mmHg versus −18 ± 11 mmHg for the wall-less and control respectively; the cannula outlet flow rate (Q) was 3.91 ± 0.41 versus 3.67 ± 0.45 L/min, respectively. At the same target volume but with a Hg of 5.7 g/dL, P was −16 ± 12 mmHg versus −19 ± 12 mmHg and Q was 4 ± 0.1 versus 4 ± 0.4 L/min for the wall-less cannula and control respectively. Likewise, P and Q values with water were −1 mmHg versus −0.67 ± 0.58 mmHg and 4.17 ± 0.45 L/min versus 4.08 ± 0.47 L/min for the wall-less and control respectively. Conclusion: Walls-less cannula showed 5.6% less pump inlet-pressure differences calculated between blood and water, as compared to that of thin-wall cannula (−21 times). Flow differences were 6% and 10% for the walls-less and thin-wall cannula respectively. We conclude that testing the cannula performance with water is a good scenario and can overestimate the flow by a 10%. However, superiority for wall-less is preserved with both water and blood.

scholarly journals New, Virtually Wall-Less Cannulas Designed for Augmented Venous Drainage in Minimally Invasive Cardiac Surgery

2016 ◽  
Vol 11 (4) ◽  
pp. 278-281 ◽  
Author(s):  
Ludwig Karl von Segesser ◽  
Denis Berdajs ◽  
Saad Abdel-Sayed ◽  
Piergiorgio Tozzi ◽  
Enrico Ferrari ◽  
...  
Keyword(s):  
Cardiac Surgery ◽  
Minimally Invasive ◽  
Hollow Fiber Membrane ◽  
Venous Drainage ◽  
Minimally Invasive Cardiac Surgery ◽  
Inlet Pressure ◽  
Thin Wall ◽  
Pump Flow ◽  
Pump Inlet

Objective Inadequate venous drainage during minimally invasive cardiac surgery becomes most evident when the blood trapped in the pulmonary circulation floods the surgical field. The present study was designed to assess the in vivo performance of new, thinner, virtually wall-less, venous cannulas designed for augmented venous drainage in comparison to traditional thin-wall cannulas. Methods Remote cannulation was realized in 5 bovine experiments (74.0 ± 2.4 kg) with percutaneous venous access over the wire, serial dilation up to 18 F and insertion of either traditional 19 F thin wall, wire-wound cannulas, or through the same access channel, new, thinner, virtually wall-less, braided cannulas designed for augmented venous drainage. A standard minimal extracorporeal circuit set with a centrifugal pump and a hollow fiber membrane oxygenator, but no inline reservoir was used. One hundred fifty pairs of pump-flow and required pump inlet pressure values were recorded with calibrated pressure transducers and a flowmeter calibrated by a volumetric tank and timer at increasing pump speed from 1500 RPM to 3500 RPM (500-RPM increments). Results Pump flow accounted for 1.73 ± 0.85 l/min for wall-less versus 1.17 ± 0.45 l/min for thin wall at 1500 RPM, 3.91 ± 0.86 versus 3.23 ± 0.66 at 2500 RPM, 5.82 ± 1.05 versus 4.96 ± 0.81 at 3500 RPM. Pump inlet pressure accounted for 9.6 ± 9.7 mm Hg versus 4.2 ± 18.8 mm Hg for 1500 RPM, −42.4 ± 26.7 versus −123 ± 51.1 at 2500 RPM, and −126.7 ± 55.3 versus −313 ±116.7 for 3500 RPM. Conclusions At the well-accepted pump inlet pressure of −80 mm Hg, the new, thinner, virtually wall-less, braided cannulas provide unmatched venous drainage in vivo. Early clinical analyses have confirmed these findings.

Method and Implementation of Energy-Saving Control for Industrial Cooling Water Tower Pump

2012 ◽  
Vol 512-515 ◽  
pp. 1163-1166
Author(s):  
Li Zhong Zhang ◽  
Shu Hong Jia ◽  
Xiao Jun Zhao ◽  
Yan Sun ◽  
Guo Dong Shi
Keyword(s):  
Energy Saving ◽  
Flow Rate ◽  
Control Method ◽  
Water System ◽  
Cooling Water ◽  
Cold Pool ◽  
Pump Flow Rate ◽  
Energy Saving Process ◽  
Energy Saving Control ◽  
And Control

This article introduce a kind of energy-saving control method and implementation for a tower pump in industrial cooling water system (hot tub→ up tower pump→ cooling tower→ cold pool). Under the conditions without changing the original industrial cooling water’s normal operating, the method of temperature control liquid-level under the protection of pressure to regulate and control the energy-saving process of cooling water on tower pump was used. According to the hot tub’s actual temperature and cold pool’s temperature which has process requirements can automatically regulate the hot tub’s liquid height or the height difference between hot tub and cold pool. It can finally automatically control the natural flow rate of the connected overflow hole or connecting pipe, thereby reducing the pump flow rate on tower to ensure the purpose of siginificant energy-saving on the basis of process demand. The comprehensive energy-saving rate can be 40% to 60% or more.

Coupling simulation of the fast startup of a centrifugal pump with cavitation in a closed-loop pipeline system

2018 ◽  
Vol 35 (5) ◽  
pp. 2010-2024 ◽  
Author(s):  
Long Meng ◽  
Meng Liu ◽  
Lingjiu Zhou ◽  
Wanpeng Wang ◽  
Cuilin Liao ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Closed Loop ◽  
Simulation Method ◽  
Transient Processes ◽  
Pipeline System ◽  
Content Type ◽  
Cavitation Phenomenon ◽  
Startup Process ◽  
Pump Inlet

Purpose Cavitation inside pumps affects not only the steady state fluid flow, but also the unsteady or transient characteristic of the flow. However, cavitation inside pumps under transient processes is difficult to predict when the influence of the pipelines system is considered. In this paper we present a simulation method applied to a centrifugal pump and its related pipeline to analyze the induced unsteady cavitation phenomenon during the startup process. Design/methodology/approach In order to effectively predict transient processes of a pump and its pipeline system, the simulation method uses a coupled 1D and 3D scheme, which reduces the simulation cost. The simulation of the startup process of a centrifugal pump in a closed-loop pipeline system with and without cavitation has been performed to verify the proposed method. Findings The evolution of the pressure and flow rate obtained with the simulation method agrees well with the experimental results. It is found that the mass flow rate at the pump inlet and outlet is highly related to the cavitation vapor volume and that the pressure at the outlet of the impeller is greatly influenced by the discharge. Originality/value The 1D-3D coupling simulation method used in this paper is proven to be highly accurate, efficient and can be used to solve transient processes combined with cavitation or other complex phenomena.

Flow Field and Performance Analysis of a Centrifugal Pump During Unstable Operating Conditions

2019 ◽  
Author(s):  
Romain Prunières ◽  
Chisachi Kato
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Flow Instabilities ◽  
Pressure Recovery ◽  
Strong Increase ◽  
Impeller Outlet ◽  
Pump Flow Rate ◽  
Performance Curves

Abstract Centrifugal pump performance curves instability, characterized by a local dent, can be the consequence of flow instabilities in rotating or stationary parts. Such flow instabilities often result in abnormal operating conditions, causing severe problems such as increased pressure pulsation, noise and vibration which can damage both pump and system. For the pump to have reliable operation, it is necessary to understand the onset and the mechanism of the phenomenon resulting in performance curves instability. Present paper focuses on performance curves instability of a centrifugal pump of low specific speed (ωs = 0.65, Ns = 1776) and aims at a better understanding of the mechanism leading to the head drop observed during tests at part load. For that purpose, Computation Fluid Dynamic (CFD) was performed using a Large-Eddy Simulation (LES) approach. The geometry used for present research is in fact the first stage of a multi-stage centrifugal pump and is composed of a suction chamber, a closed-type impeller, a vaned diffuser and return guide vanes to next stage (not included). Leakages at wear ring and stage bush were also included in the computed geometry in order to consider their potential influence on pump stability. The occurrence of the instability in CFD is found at a higher flow rate than in the experiments. It is observed that the pre-swirl angle is under-predicted by several degrees which leads to change the impeller operating conditions. Nevertheless, the analysis of the CFD results is still useful to have a better understanding of the onset of the head drop. When the head drops, a switching of low radial and axial velocities at the impeller outlet from the hub side to the shroud side is observed. This change of flow pattern goes along with a strong increase of the diffuser inlet throat recirculation and the development of stall, that impairs pressure recovery between the impeller outlet and the diffuser inlet. As the pump flow rate is further decreased below the head drop flow rate, recirculation at the diffuser throat extend toward the impeller outlet and impact Euler head. Conversely, the pressure recovery from the impeller outlet to the diffuser inlet throat increases again as the flow velocity slowdown can be effective again. Consequently, the pump head increases again.

Centrifugal pump inlet pressure site affects measurement

Perfusion ◽  
2010 ◽  
Vol 25 (5) ◽  
pp. 313-320 ◽  
Author(s):  
Simon Augustin ◽  
Alison Horton ◽  
Warwick Butt ◽  
Martin Bennett ◽  
Stephen Horton
Keyword(s):  
Centrifugal Pump ◽  
Inlet Pressure ◽  
Pump Inlet

Slip Factor for Centrifugal Impellers Under Single and Two-Phase Flow Conditions

2004 ◽  
Vol 127 (2) ◽  
pp. 317-321 ◽  
Author(s):  
José A. Caridad ◽  
Frank Kenyery
Keyword(s):  
Fluid Dynamics ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Prediction Models ◽  
Two Phase Flow ◽  
Specific Capacity ◽  
Phase Flow ◽  
Two Phase ◽  
Slip Factor ◽  
Pump Flow Rate

Throughout the history of turbomachines investigators have tried to develop reliable methods for prediction of centrifugal pump behavior. Among the parameters available to estimate the performance of this kind of machine is the slip factor. In spite of being regarded as a variable of great significance in the analysis of turbomachinery, there seem to be a misconception regarding its concept and application. Indeed, empirical correlations have been widely used to estimate the slip factor, even in the case of two-phase flow applications, where it has not been investigated. Moreover, these correlations provide a constant value of the slip factor for a given impeller only at the best efficiency point, which is an important restriction to the pump performance prediction, considering that slip factor varies with the pump flow rate. In this study, three-dimensional computational fluid dynamics simulations were carried out on an impeller of known geometry (NS=1960) from which values of slip factor were calculated for both single- and two-phase flow (water and water-air). These results include curves of the slip factor as a function of the specific capacity and the gas-void fraction. Additionally, results for the slip factor in the case of single-phase flow (water) are given for various centrifugal impellers (NS=1157, 1447, 1612, and 3513) in order to illustrate the influence of the flow rate on this parameter. Finally, based on the numerical results, a methodology for prediction of the pump head is presented. Excellent agreement with experimental results has been found. This paper attempts to contribute to a better understanding of the fluid dynamics within centrifugal pump impellers and to shed more light on the path that prediction models should follow in the future.

Numerical Simulation Research on Vortex Characteristics of Centrifugal Pump Inlet Recirculation

2012 ◽  
Vol 468-471 ◽  
pp. 2235-2240
Author(s):  
Jian Ping Yuan ◽  
Wei Sun ◽  
Long Yan Wang ◽  
Yun Liang
Keyword(s):  
Turbulent Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Outlet Section ◽  
Simulation Research ◽  
Eddy Simulation ◽  
Whole Process ◽  
Ansys Cfx ◽  
Steady Simulation ◽  
Pump Inlet

The 3-D steady turbulent flow in a centrifugal pump under different conditions was simulated by ANSYS CFX software. The intensity, location and the morphology of the inlet recirculation vortex were analyzed using standard k-ε turbulent model through steady simulation. Based on the results, the turbulent flow in the impeller inlet was simulated by Large Eddy Simulation. The dynamic characters and the whole changing process of the recirculation vortex during the rotation of the impeller were analyzed. The results indicate that the critical flow rate of the recirculation onset is 0.7Qd. As the flow rate decreases, the size and the intensity of the recirculation vortex increase and the vortex partially block the flow passage. The vortex first appears in the passage which passes by the outlet section of the volute. During one rotating, the vortex undergoes a whole process of onset, developing, decreasing and disappearing. As the relative speed and the pressure gradient change under different conditions, the vortices present different morphologies.

scholarly journals Mathematical simulation of choking under self-oscillations in hydraulic systems with cavitating pumps of liquid-propellant rocket engines

2020 ◽  
Vol 2020 (4) ◽  
pp. 35-42
Author(s):  
S.I. Dolgopolov ◽  
Keyword(s):  
Mathematical Simulation ◽  
Flow Rate ◽  
Cavity Flow ◽  
Inlet Pressure ◽  
Rocket Engines ◽  
Liquid Propellant ◽  
Inlet Flow ◽  
Inlet Flow Rate ◽  
Pump Inlet ◽  
Propellant Rocket

As known from the study of cavity flows in fixed channels (Venturi tube), with decreasing channel outlet pressure there comes a point where the flow rate ceases to increase. To increase the flow rate, the inlet pressure must be increased. This phenomenon of flow rate limitation at a fixed inlet pressure is due to a critical regime of cavity flow at the narrowest cross-section and is termed choking. Impeller pumps also exhibit choking regimes described by the so-called chocking characteristic, which relates the critical pump flow rate to the inlet pressure. This work is aimed at extending a hydrodynamic model of cavitating pumps of liquid-propellant rocket engines (LPREs) by including a mathematical simulation of chocking regimes. A mechanism of realization of the chocking process in pumps is proposed. The mechanism is as follows. When the parameter oscillation amplitudes are high enough, the inlet flow rate and pressure computed at integration step i may be in the inadmissible range, i.e., below the chocking regime characteristic. In this case, the flow rate and the pressure must be refined. It is found that the computed decrease in the cavitation self-oscillation frequency in comparison with the eigenfrequency of a hydraulic system with a cavitating pump is close to its experimental value in the case where the inlet flow rate and pressure are assumed to be coordinates of the point of intersection of the choking characteristic and the line that connects the values of the pump inlet flow rate and pressure computed at integration steps i-1 and i. It is shown that the LPRE pump choking characteristic is a specific nonlinearity associated with the critical cavity flow in the pump and may manifest itself at high parameter oscillation amplitudes. It is found that the choking characteristic of an LPRE pump affects the cavitation oscillation parameters to a greater extent than the cavity volume vs. pump inlet pressure and flow rate relationship does and is the governing nonlinearity in the pump system in choking.

Stabilization of the Speed of the Hydraulic Motor Through Throttle Compensation for Volume Losses

2020 ◽  
Vol 26 (3) ◽  
pp. 126-130
Author(s):  
Krasimir Kalev
Keyword(s):  
Flow Rate ◽  
Hydraulic Drive ◽  
Pressure Change ◽  
Operating Conditions ◽  
Drive System ◽  
Inlet Pressure ◽  
Schematic Diagram ◽  
Hydraulic Characteristics ◽  
Hydraulic Motor ◽  
Flow Through

AbstractA schematic diagram of a hydraulic drive system is provided to stabilize the speed of the working body by compensating for volumetric losses in the hydraulic motor. The diagram shows the inclusion of an originally developed self-adjusting choke whose flow rate in the inlet pressure change range tends to reverse - with increasing pressure the flow through it decreases. Dependent on the hydraulic characteristics of the hydraulic motor and the specific operating conditions.

scholarly journals Backflow effects on mass flow gain factor in a centrifugal pump

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042199886
Author(s):  
Wenzhe Kang ◽  
Lingjiu Zhou ◽  
Dianhai Liu ◽  
Zhengwei Wang
Keyword(s):  
Centrifugal Pump ◽  
Mass Flow ◽  
Flow Rate ◽  
Low Frequency ◽  
Gain Factor ◽  
Low Flow ◽  
Cavity Volume ◽  
Cavitating Flows ◽  
Inlet Tube ◽  
Low Flow Rate

Previous researches has shown that inlet backflow may occur in a centrifugal pump when running at low-flow-rate conditions and have nonnegligible effects on cavitation behaviors (e.g. mass flow gain factor) and cavitation stability (e.g. cavitation surge). To analyze the influences of backflow in impeller inlet, comparative studies of cavitating flows are carried out for two typical centrifugal pumps. A series of computational fluid dynamics (CFD) simulations were carried out for the cavitating flows in two pumps, based on the RANS (Reynolds-Averaged Naiver-Stokes) solver with the turbulence model of k- ω shear stress transport and homogeneous multiphase model. The cavity volume in Pump A (with less reversed flow in impeller inlet) decreases with the decreasing of flow rate, while the cavity volume in Pump B (with obvious inlet backflow) reach the minimum values at δ = 0.1285 and then increase as the flow rate decreases. For Pump A, the mass flow gain factors are negative and the absolute values increase with the decrease of cavitation number for all calculation conditions. For Pump B, the mass flow gain factors are negative for most conditions but positive for some conditions with low flow rate coefficients and low cavitation numbers, reaching the minimum value at condition of σ = 0.151 for most cases. The development of backflow in impeller inlet is found to be the essential reason for the great differences. For Pump B, the strong shearing between backflow and main flow lead to the cavitation in inlet tube. The cavity volume in the impeller decreases while that in the inlet tube increases with the decreasing of flow rate, which make the total cavity volume reaches the minimum value at δ = 0.1285 and then the mass flow gain factor become positive. Through the transient calculations for cavitating flows in two pumps, low-frequency fluctuations of pressure and flow rate are found in Pump B at some off-designed conditions (e.g. δ = 0.107, σ = 0.195). The relations among inlet pressure, inlet flow rate, cavity volume, and backflow are analyzed in detail to understand the periodic evolution of low-frequency fluctuations. Backflow is found to be the main reason which cause the positive value of mass flow gain factor at low-flow-rate conditions. Through the transient simulations of cavitating flow, backflow is considered as an important aspect closely related to the hydraulic stability of cavitating pumping system.

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