Observation and Quantification of Gas Bubble Formation on a Mechanical Heart Valve

2000 ◽  
Vol 122 (4) ◽  
pp. 304-309 ◽  
Author(s):  
Hsin-Yi Lin ◽  
Brian A. Bianccucci ◽  
Steven Deutsch ◽  
Arnold A. Fontaine ◽  
J. M. Tarbell
Keyword(s):  
High Speed ◽  
Heart Valves ◽  
Bubble Formation ◽  
Mechanical Heart Valve ◽  
Gas Bubbles ◽  
Co2 Concentration ◽  
Video Camera ◽  
Gas Content ◽  
Gas Bubble ◽  
Cavitation Intensity

Clinical studies using transcranial Doppler ultrasonography in patients with mechanical heart valves (MHV) have detected gaseous emboli. The relationship of gaseous emboli release and cavitation on MHV has been a subject of debate in the literature. To study the influence of cavitation and gas content on the formation and growth of stable gas bubbles, a mock circulatory loop, which employed a Medtronic-Hall pyrolytic carbon disk valve in the mitral position, was used. A high-speed video camera allowed observation of cavitation and gas bubble release on the inflow valve surfaces as a function of cavitation intensity and carbon dioxide CO2 concentration, while an ultrasonic monitoring system scanned the aortic outflow tract to quantify gas bubble production by calculating the gray scale levels of the images. In the absence of cavitation, no stable gas bubbles were formed. When gas bubbles were formed, they were first seen a few milliseconds after and in the vicinity of cavitation collapse. The volume of the gas bubbles detected in the aortic track increased with both increased CO2 and increased cavitation intensity. No correlation was observed between O2 concentration and bubble volume. We conclude that cavitation is an essential precursor to stable gas bubble formation, and CO2, the most soluble blood gas, is the major component of stable gas bubbles. [S0148-0731(00)00204-1]

Nuclei and Cavitation

1970 ◽  
Vol 92 (4) ◽  
pp. 681-688 ◽  
Author(s):  
J. William Holl
Keyword(s):  
Bubble Growth ◽  
Scale Effects ◽  
Gas Bubbles ◽  
Gas Content ◽  
Gas Bubble ◽  
Cavitation Nuclei ◽  
The Stability

This paper is a review of existing knowledge on cavitation nuclei. The lack of significant tensions in ordinary liquids is due to so-called weak spots or cavitation nuclei. The various forms which have been proposed for nuclei are gas bubbles, gas in a crevice, gas bubble with organic skin, and a hydrophobic solid. The stability argument leading to the postulation of the Harvey model is reviewed. Aspects of bubble growth are considered and it is shown that bubbles having different initial sizes will undergo vaporous cavitation at different liquid tensions. The three modes of growth, namely vaporous, pseudo, and gaseous are presented and implications concerning the interpretation of data are considered. The question of the source of nuclei and implications concerning scale effects are made. The measurement of nuclei is considered together with experiments on the effect of gas content on incipient cavitation.

Air Bubble Injection Into a Liquid Stream in a Minichannel

2013 ◽  
Author(s):  
Randy Samaroo ◽  
Masahiro Kawaji
Keyword(s):  
High Speed ◽  
Liquid Velocity ◽  
Bubble Formation ◽  
Video Camera ◽  
Velocity Profiles ◽  
Bubble Behavior ◽  
Particle Image Velocimetry Technique ◽  
Air Bubble ◽  
Cfd Models ◽  
Laminar And Turbulent Flow

Air bubble injection experiments have been performed to obtain a better understanding and detailed data on bubble behavior and liquid velocity profiles to be used for validation of 3-D Interface Tracking Models and CFD models. Two test sections used were vertical rectangular minichannels with a width and gap of 20 mm × 5.1 mm and 20 mm × 1.9 mm, respectively. Subcooled water at near atmospheric pressure flowed upward under laminar and turbulent flow conditions accompanied by air bubbles injected from a small hole on one of the vertical walls. The experiments yielded data on bubble formation and departure, and interactions with laminar or turbulent water flow. Instantaneous and ensemble-average liquid velocity profiles have been obtained using a Particle Image Velocimetry technique and a high speed video camera.

Modifying a Tilting Disk Mechanical Heart Valve Design to Improve Closing Dynamics

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Luke H. Herbertson ◽  
Steven Deutsch ◽  
Keefe B. Manning
Keyword(s):  
Heart Valves ◽  
Liquid Core ◽  
Mechanical Heart Valve ◽  
Blood Damage ◽  
Mechanical Valves ◽  
Mitral Position ◽  
Disk Valve ◽  
Cavitation Intensity ◽  
The Moment ◽  
The One

The closing behavior of mechanical heart valves is dependent on the design of the valve and its housing, the valve composition, and the environment in which the valve is placed. One innovative approach for improving the closure dynamics of tilting disk valves is introduced here. We transformed a normal Delrin occluder into one containing a ”dynamic liquid core” to resist acceleration and reduce the moment of inertia, closing velocity, and impact forces of the valve during closure. The modified occluder was studied in the mitral position of a simulation chamber under the physiologic and elevated closing conditions of 2500 mm Hg/s and 4500 mm Hg/s, respectively. Cavitation energy, detected as high-frequency pressure transients with a hydrophone, was the measure used to compare the modified valve with its unaltered counterpart. The cavitation potential of tilting disk valves is indicative of the extent of blood damage occurring during valve closure. Initial findings suggest that changes to the structure or physical properties of well established mechanical valves, such as the one described here, can reduce closure induced hemolysis by minimizing cavitation. Compared with a normal valve, the cavitation intensity associated with our modified valve was reduced by more than 66% at the higher load. Furthermore, the modified valve took longer to completely close than did the standard tilting disk valve, indicating a dampened impact and rebound of the occluder with its housing.

Experimental Study on Pressure Transients With Cavitation in Low Pressure Water-Hydraulic Pipeline

2018 ◽  
Author(s):  
Dan Jiang ◽  
Cong Ren ◽  
Qing Guo
Keyword(s):  
High Speed ◽  
Gas Bubbles ◽  
Video Camera ◽  
Low Pressure ◽  
Pressure Pulsations ◽  
Pressure Transients ◽  
Pressure Transducers ◽  
High Speed Video Camera ◽  
Pressure Water ◽  
Water Hydraulic

In this study, pressure transients are triggered by a steel ball, which is released from an upstream reservoir to hit a valve seat and shut off water flow in a horizontal straight copper pipeline. The pressure pulsations, cavitation and gas bubbles growth and collapse in the low pressure water-hydraulic pipeline are recorded by two pressure transducers and a high speed video camera, respectively. In addition, the influences of initial volume of gas bubbles in water and instant leakage in valve are investigated. The experimental results indicate that increasing initial gas bubble volume in water and the instant leakage of the valve will help to reduce magnitudes and numbers of pressure peaks during pressure transients. Then methods to reduce pressure pulsations in pipelines are put forward.

In Vitro Determination of the Curvatures and Bending Strains Acting on the Leaflets of Polyurethane Trileaflet Heart Valves During Leaflet Motion

1995 ◽  
Vol 209 (4) ◽  
pp. 243-253 ◽  
Author(s):  
J Corden ◽  
T David ◽  
J Fisher
Keyword(s):  
High Speed ◽  
Heart Valves ◽  
Video Camera ◽  
Casting Technique ◽  
Modes Of Failure ◽  
Bending Strain ◽  
High Speed Video Camera ◽  
Valve Opening ◽  
Valve Operation

Leaflet tears originating from the free leaflet edge and calcification around the commissural region are common modes of failure exhibited by explanted bioprosthetic trileaflet heart valves. These may be a result of the cyclic bending and high levels of curvature that affect the leaflets within these areas during normal valve operation. These high leves of curvature occur in a short time period (approximately 20 ms) during rapid leaflet opening and to a lesser degree during leaflet closure. The curvatures that occur at the free leaflet edge of two designs of polyurethane trileaflet heart valve were determined in vitro at various stages during a cardiac cycle using a high-speed video camera (1000 frames/s). Significant deformations at the free leaflet edge were observed and bending radii as low as 0.55 ± 0.125 mm (mean ± standard deviation) were present during leaflet opening, 0.76 ± 0.24 mm during leaflet closure and 1.01 ± 0.27 mm while the valve was fully open during peak systole. The values of curvature were used to determine the values of bending strain and bending stress acting at the free leaflet edge using thin shell bending theory. The calculated values of bending strain were a maximum during the leaflet flexure associated with valve opening. These high levels of bending strain, which occur for short periods of time, are likely to be an important determinant of the valve's durability. It has been shown that the method of manufacture significantly influenced the level of bending strain in the valve leaflets. Valves manufactured using a dip-casting technique resulted in open leaflet bending strains up to 31 per cent lower than valves manufactured from solvent-cast sheets of polyurethane.

scholarly journals Effect of gases released during solidification of castings on microstructure of alloys

2020 ◽  
pp. 12-14
Author(s):  
E. I. Marukovich ◽  
V. Yu. Stetsenko
Keyword(s):  
Bubble Formation ◽  
Gas Bubbles ◽  
Gas Bubble ◽  
Spherical Bubble ◽  
Metal Melt ◽  
Flat Surfaces ◽  
Second Stage ◽  
Water Wetting ◽  
Two Stages ◽  
Effect Of Gases

Thermodynamic calculation of formation of spherical gas bubbles different in water – wetting on flat surfaces by metal melt is made. This process consists of two stages. The first stage is formation of equilibrium gas bubble in the form of ball segment. The second stage is its swinging into a spherical bubble. Calculations were made for gas bubbles with constant volume. It is shown that Gibbs energy of spherical gas bubble formation on water – wetting metal melt substrate is three times less than on nonwettable melt substrate. Thus, gases released by solidification of the castings will preferably be formed and removed as bubbles on the molten metal surfaces of the crystallizable phases of the alloys and directly affect on their microstructure.

Bubble Detachment in Variable Gravity Under the Influence of Electric Fields

2002 ◽  
Author(s):  
Cila Herman ◽  
Shinan Chang ◽  
Estelle Iacona
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
High Speed ◽  
Bubble Formation ◽  
Experimental Studies ◽  
Video Camera ◽  
Contact Angles ◽  
Uniform Electric Field ◽  
Bubble Behavior ◽  
Insulating Liquid

The objective of the research is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Situations were considered with both uniform and nonuniform electric fields. Bubble formation and detachment were visualized in terrestrial gravity as well as for several levels of reduced gravity (lunar, martian and microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angles at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment in an initially uniform electric field was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. The results of the study indicate that the level of gravity and the electric field magnitude significantly affect bubble behavior as well as shape, volume and dimensions.

Modeling and Influence Study of Gas Bubbles on Characteristics of a Piezoelectric Valve-Less Micropump

2012 ◽  
Author(s):  
Songjing Li ◽  
Jixiao Liu ◽  
Dan Jiang
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Dynamic Pressure ◽  
Experimental Studies ◽  
Gas Bubbles ◽  
Video Camera ◽  
Pump Chamber ◽  
High Speed Video Camera ◽  
Outlet Flow ◽  
Trapped Gas

The aim of this paper is to develop a theoretical model of a piezoelectric valve-less micropump for liquid delivery with entrapped gas bubbles and evaluate the influence of gas bubbles on the dynamic characteristics of the micropump by using this model. In the model, we consider the vibration of piezoelectric diaphragm, the pressure loss through the nozzle/diffuser and the compressibility of working liquids with entrapped gas bubbles. In order to validate the developed model and make it useful as a design and prediction tool, experimental studies are carried out to investigate the flow rate and dynamic pressure inside the pump chamber when gas bubbles are absent or present in the micropump. The presence of gas bubbles inside the pump chamber is also observed with a high-speed video camera. The outlet flow rate of the micropump with different size of trapped gas bubbles are calculated and compared.

scholarly journals THE WAYS OF PRODUCING AN UNIFIED MATHEMATICAL MODEL FOR THE CAVITATING FLOW IN HYDRODYNAMIC CAVITATION REACTORS

2020 ◽  
Vol 42 (2) ◽  
pp. 31-38
Author(s):  
G.K. Ivanitsky ◽  
B.Ya. Tcelen ◽  
A.E. Nedbaylo ◽  
L.P. Gozhenko
Keyword(s):  
Mathematical Model ◽  
General Model ◽  
Gas Bubbles ◽  
Cavitating Flow ◽  
Hydrodynamic Cavitation ◽  
Gas Content ◽  
Liquid Temperature ◽  
Wide Range ◽  
Cavitation Intensity

Possible ways of constructing a general model of cavitation reactors are considered. A mathematical model is proposed that without using any limiting assumptions describes adequately the dynamics of vapor-gas bubbles and the behavior of a cavitation cluster in a wide range of regime parameters. In the framework of the model, the influence of gas content and liquid temperature on the  cavitation intensity is considered. The possibility of modifying the model as applied to optimizing the operation of cavitation reactors is discussed.

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