Steady Flow System Research Articles

In Vitro hydrodynamic evaluation of prosthetic polymer heart valves in steady flow

Hydrodynamic comparison of two polymer valves with two mechanical valves is presented. The valves were perfused in a steady flow system, and comparisons between the valves were made on the transvalvular pressure distribution and drop, opening area, and leakage volume. Particular emphasis was placed on a slit-type bileaflet polymer valve which was newly designed and fabricated in our research group. The results showed that the functional characteristics of a slit-type bileaflet polymer valve compared favorably with that of mechanical valves. This valve may be a viable and inexpensive alternative, especially for short-term use in TAH or VAD systems.

Quantification of asymmetric valvular regurgitant jets by color Doppler ultrasound in vitro.

Accurate quantification of regurgitant jets in natural and prosthetic heart valves has been a goal of health care workers and researchers for many years. One promising new method applies the law of conservation of momentum transfer to velocities measured by color Doppler ultrasound to calculate the flow rate in the jet. One complicating factor is that regurgitant jets from real heart valves may be highly asymmetric. The purpose of this investigation was to determine whether the accurate calculation of the flow rate in asymmetric jets imaged by color Doppler requires an asymmetric formulation of the conservation of momentum transfer, combined with a method for imaging the jet in three dimensions. Asymmetric jets issuing from narrow slits were imaged in an in vitro, steady flow system. The ultrasound transducer was rotated around the jet axis to image the jet in three dimensions. The three-dimensional imaging confirmed that jets from slits are indeed asymmetric, but become relatively axisymmetric far from the orifice. Images were analyzed by computer and the calculated flows compared to measured flows. The accuracy of an asymmetric formulation of the conservation of momentum transfer method was compared to a simpler, axisymmetric formulation. If axisymmetry was assumed in asymmetric jets, significant errors in the calculated flow rates occurred. In these cases, the calculated flow also varied widely with distance from the orifice. When asymmetry was taken into account, the errors were considerably reduced. The results suggest that, in asymmetric jets, the momentum transfer is convected around the jet axis.

Colour-coded echographic flow imaging and spectral analysis of cerebrospinal fluid (CSF). Part III. In-vitro study of low flow velocity detection related to decreasing particle concentration (hematocrit) and tube lumen.

An in-vitro steady flow system was designed to determine the lowest flow velocities that can be detected by echographic colour flow imaging and spectral analysis. The flow detection level was determined hydrostatically by reducing the fluid level to below the point at which a flow signal was visible, then increasing the height until the colour flow reappeared. This was confirmed in all instances by spectral analysis. The height (angle-corrected velocity) of the spectral envelope was also determined. Mean volume flow was then obtained by using a graduated cylinder and a stop watch. The lowest hematocrit detectable was identified using a stepwise dilution of packed human red blood cells with 0.9% sodium chloride. Three different PVC-tubes with inner diameters of 2.1 mm, 1.1 mm and 0.51 mm were used.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of Magnetic Resonance Velocimetry for Steady Flow

Whole body magnetic resonance (MR) imaging has recently become an important diagnostic tool for cardiovascular diseases. The technique of magnetic resonance phase velocity encoding allows the quantitative measurement of velocity for an arbitrary component direction. A study was initiated to determine the ability and accuracy of MR velocimetry to measure a wide range of flow conditions including flow separation, three-dimensional secondary flow, high velocity gradients, and turbulence. A steady flow system pumped water doped with manganese chloride through a variety of test sections. Images were produced using gradient echo sequences on test sections including a straight tube, a curved tube, a smoothly converging-diverging nozzle, and an orifice. Magnetic resonance measurements of laminar and turbulent flows were depicted as cross-sectional velocity profiles. MR velocity measurements revealed such flow behavior as spatially varying velocity, recirculation and secondary flows over a wide range of conditions. Comparisons made with published experimental laser Doppler anemometry measurements and theoretical calculations for similar flow conditions revealed excellent accuracy and precision levels. The successful measurement of velocity profiles for a variety of flow conditions and geometries indicate that magnetic resonance imaging is an accurate, non-contacting velocimeter.

「深江丸」推進プラントの熱力学的性能評価

Following the 1st. report of the main diesel engine system, the results of the performance evaluation of the emergency electric propulsion system on“Fukae-maru”are descibed in this paper. This system consists of the 200kW differential drive shaft generator-motor, the hydraulic system to drive the armature, and their attachments.Experiments have been made varing propeller pich angle and varing the direction of armature rotation on calm sea. In the analysis, the entire plant is assumed to be a steady-flow system, and both the first-and the second-law of thermodynamics are employed in order to clarify not only the quantity of energy but also the quality of energy.In consequence of these analyses, it becomes clear that the method of this analysis is effective to evaluate the performance of the plant which has the several forms of energy like in this plant. And, the Sankey diagrams (energy-flow diagrams) and the exergy efficiencies of this plant are also obtained.

「深江丸」推進プラントの熱力学的性能評価

It is important for the energy saving to evaluate the performance of the marine propulsion plant in operation. The object of this study is the diesel propulsion system rated at 1, 103kW, installed in a training ship “Fukae-maru” (449 Gross Tonnage) owned by Kobe University of Mercantile Marine.Experiments have been made under the various loads of this engine on calm sea. In the analysis, the entire plant is assumed to be a steady-flow system, and both the first-and the second-law of thermodynamics are employed in order to clarify not only the quantity of energy but also the quality of energy.In consequence of these analyses, the places where the energy losses are generated in this plant are made known, and the Sankey diagrams (energy-flow diagrams) and the exergy efficiencies of this plant are also obtained.

Contaminant movement under pumpage-recharge condition in steady ground-water flow system : Das Gupta, A; Onta Shrestha, P R Ground Water V24, N3, May–June 1986, P342–350

Contaminant movement under pumpage-recharge condition in steady ground-water flow system : Das Gupta, A; Onta Shrestha, P R Ground Water V24, N3, May–June 1986, P342–350

Red blood cell size is important for adherence of blood platelets to artery subendothelium

The hematocrit is one of the main factors influencing platelet adherence to the vessel wall. Raising the hematocrit causes an increase of platelet accumulation of about an order of magnitude. Our studies concern the role of red cell size. We have studied this effect using an annular perfusion chamber, according to Baumgartner, with human umbilical arteries and a steady-flow system. Normal human red blood cells (MCV 95 cu mu) increased platelet adherence sevenfold, as the hematocrit increases from 0 to 0.6. Small erythrocytes from goats (MCV 25 cu mu) caused no increment in adherence in the same hematocrit range. Rabbit erythrocytes (MCV 70 cu mu) caused an intermediate increase in adherence. Red blood cells from newborns (MCV 110–130 cu mu) caused a larger increase in platelet adherence than normal red cells at hematocrit 0.4. These results were further confirmed with large red blood cells from two patients. Experiments with small red cells (MCV 70 cu mu) of patients with iron deficiency showed that platelet adherence was similar to normal red cells, provided the red cell diameter was normal. Small red blood cells of a patient with sideroblastic anemia caused decreased adherence. These data indicate that red cell size is of major importance for platelet adherence. Red cell diameter is more important than average volume. However, for size differences in the human range, the hematocrit remains the dominant parameter.

Red Blood Cell Size Is Important for Adherence of Blood Platelets to Artery Subendothelium

The hematocrit is one of the main factors influencing platelet adherence to the vessel wall. Raising the hematocrit causes an increase of platelet accumulation of about an order of magnitude. Our studies concern the role of red cell size. We have studied this effect using an annular perfusion chamber, according to Baumgartner, with human umbilical arteries and a steady-flow system. Normal human red blood cells (MCV 95 cu mu) increased platelet adherence sevenfold, as the hematocrit increases from 0 to 0.6. Small erythrocytes from goats (MCV 25 cu mu) caused no increment in adherence in the same hematocrit range. Rabbit erythrocytes (MCV 70 cu mu) caused an intermediate increase in adherence. Red blood cells from newborns (MCV 110-130 cu mu) caused a larger increase in platelet adherence than normal red cells at hematocrit 0.4. These results were further confirmed with large red blood cells from two patients. Experiments with small red cells (MCV 70 cu mu) of patients with iron deficiency showed that platelet adherence was similar to normal red cells, provided the red cell diameter was normal. Small red blood cells of a patient with sideroblastic anemia caused decreased adherence. These data indicate that red cell size is of major importance for platelet adherence. Red cell diameter is more important than average volume. However, for size differences in the human range, the hematocrit remains the dominant parameter.

A model study of flow dynamics in human central airways. Part I: Axial velocity profiles

We measured detailed steady inspiratory and expiratory velocity profiles in a 3:1 scale model of the human central airways. The model was constructed out of acrylic plastic, mounted vertically, and connected to a specially designed steady-flow system. Laterally introduced hot-wire anemoneter probes were used to record axial velocities along 4 diameters at each of the 12 pre-drilled stations of measurement; the flow distribution among the five lobar bronchi was controlled by distally positioned linear resistors. Whether with a flat entrance profile or entering as a narrow jet, the inspiratory flow velocity profiles in the frontal plane showed a high degree of asymmetry in all branches, with peak velocities near the wall of the bifurcation. In the signal plane the velocity profiles were nearly symmetric, exhibiting a single peak near the center in the frontal plane and almost flat in the sagital plane. Overall, the velocity profiles were more sensitive to airway geometry than to flow rate. The only site of flow separation was observd in the right upper lobar bronchus. The most evident modification of axial velocity profiles in a single branch was found in the left main bronchus during expiratory flow.

Numerical Analysis of Flowfields Generated by Accelerating Flames

A numerical technique is presented for the analysis of nonsteady flowfields generated by accelerating flames in gaseous media. The problem is formulated in Eulerian coordinates and the solution is based on the extension of the floating shock-fitting technique to all the discontinuities and their interactions occurring in the flowfield. Besides shock waves, the discontinuities taken into account thus far consist of contact surfaces, deflagration, and detonation fronts. The governing partial differential equations are integrated by the use of an explicit second-order accurate, finite-difference scheme, while special algorithms are introduced for the treatment of segments of the flowfield where the influence zones of discontinuities overlap. Actual interactions between them are treated by the polar intersection method. The technique is applied to the case of a steady flame experiencing an abrupt increase in burning speed, leading either to the establishment of a new steady flame flow system or to further acceleration culminated by the transition to detonation. A demarcation line between the two regimes of solutions, depending on the value of the initial burning speed and the magnitude of its abrupt increase, is established, and the physical validity of this criterion is corroborated by experimental evidence.

Influence of Strip Mines on Regional Ground-Water Flow

The effect of an operational strip mine on regional ground-water flow is investigated using a finite element model of the steady flow system. Mine location, mine size, water-table configuration, and subsurface layering of aquifer units are examined. The results demonstrate that: (1)The impact of a mine can extend far beyond its radius of influence at the water table; (2)mines placed near regional discharge areas have a more significant effect on the regional system; (3)natural water-table variation due to topography masks the effects of some mines; and (4)buried aquifers beneath the mine excavation limit the amount of flow field distortion caused by the mine.

Erythrocyte destruction by prosthetic heart valves.

Immediate hemolysis induced by eight aortic and five mitral valve prostheses was measured in in vitro steady- and pulsatile-flow systems. The mean index of hemolysis (IH) for the aortic valves ranged from 0.010 to 0.031 and 0.012 to 0.035 with steady and pulsatile flow, respectively. The IH for the mitral valves ranged from 0.004 to 0.021 in the steady-flow system, and from 0.011 to 0.021 in the pulsatile system. The Barnard-UCT aortic valve and the Kay-Shiley and Portex-Hammersmith mitral valves produced the least hemolysis in each group. The graphite-benzalkonium-heparin-coated Gott-Daggett valve was the most hemolytic valve in both the mitral and the aortic groups. The degree of hemolysis demonstrated in these experiments appears to be important, particularly since several factors which are likely to have minimized these data have been cited. The calculated daily hemoglobin released from a single prosthetic valve represents a substantial fraction of a human's total hemoglobin clearance capacity and red cell regenerative capability.