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Flow visualization with blood analog fluid
.I Btomechnn~~. 1976. Vol. 9. pp. 663464.
Pergamon
Press.
Prmted m Great Bream
FLOW VISUALIZATION
WITH BLOOD ANALOG FLUID*
Abstract-A new type of tracer particle useful in visualizing the flow of a blood analog fluid is presented. Neutrally buoyant particles are formed from a white ion exchange resin and an aqueous solution of sodium bromide. These particles, when used with the flow visualization system of Wieting, produce excellent results and do not reduce the clarity of the blood analog fluid even after prolonged periods of testing.
INTRODUCTION
In a recent review article, Werlt (1973) discussed the importance of flow visualization studies in understanding fluid flow phenomena. Such information often provides valuable physical insight that is useful in solving the various problems associated with the flow phenomena being investigated. By suspending tracer particles in the test fluid it is possible to visualize regions of flow separation, turbulence and stasis as well as other fluid dynamic phenomena. In addition, quantitative information such as particle velocities can be determined from filmed records of the flow events. Somerscales (1974) reviewed the techniques of fluid velocity measurement by particle tracking and included information on various tracers used in water and in air. Merzkirch (1974) discussed the importance of matching the density of the tracer particles with that of the test fluid, especially for liquid flow velocities below 30cm/sec. Somerscales also presented a useful discussion of the forces that prevent tracer particles from moving with the same velocity as the fluid and Werlt briefly reviewed flow visualization of unsteady flows. Hemodynamic studies can also benefit from flow visualization results and these often employ a blood analog fluid to simulate the flow of blood through prosthetic devices and through various segments of the human cardiovascular system. The purpose of this Note is to present a new type of tracer particle that is useful in visualizing the flow of a blood analog fluid. THETRACER PARTICLES
Wieting (1969) has described a very useful system for visualizing the flow of a blood analog fluid consisting of a mixture of glycerine (36.7% by volume) and distilled water. This mixture is clear and has a viscosity and specific gravity that are comparable to those of whole human blood. In addition, the index of refraction of the fluid is close to that of plexiglas (used for test section construction), resulting in minimal optical distortion of the flow patterns. The authors have found that the flow visualization system of Wieting produces excellent results when tracer particles formed from a white ion exchange resint (in bead form) are used. Since the beads have a density that is slightly less than that of the blood analog fluid, they were made to be neutrally buoyant by the following process:
(a) Approximately 250ml of IRA-93 beads with dia. between 200 and 5OOpm were immersed in an aqueous solution of sodium bromide (SOO-1OOOgof NaBr in 11. of water) for a period of co. 24 h. While in the sodium bromide solution, the ion exchange resin undergoes an exchange process in which bromide ions replace hydroxide ions on the resins’ molecular structure. Since the bromide ions are heavier than the hydroxide ions, the beads tend to increase in weight. (b) The beads were sieve-screened from the sodium bromide solution, blotted with filter paper, mixed with a vertical column (70 cm high and 4 cm wide) of blood analog fluid and allowed to stand for ca. 1 h. (c) The neutrally buoyant beads were carefully withdrawn from the column through a side tapleaving behind the beads that either floated to the top of the column or sank to the bottom. Figure 1 illustrates the excellent quality of results obtainable using these tracer particles with the flow visualization system of Wieting. Shown is the flow pattern across a Starr-Edwards aortic valve during systoie at a pulse rate of 72 beats/min and an average flow rate of 5.6 l/min. The highly disturbed flow distal to the valve in the aorta is clearly visible and contrasts sharply with the laminar flow in the left ventricular test chamber. It should be noted that the present work was motivated when satisfactory results could not be consistently obtained with the tracer particles described by Wieting (1969). It was found that after a relatively short period of testing, the blood analog fluid became contaminated (very cloudy in appearance) necessitating a time-consuming filtration process in order to reclaim the blood analog fluid for future use. The beads of ion exchange resin used by Wieting were treated with mineral oil in order to maintain neutral buoyancy. The authors believe that the mineral oil was forced into the blood analog fluid by mechanical forces acting on the particles during testing. Such difficulties with the clarity of the blood analog fluid have not been encountered with the tracer particles described here, even after prolonged periods of testing. However, particles suspended in blood analog fluid for periods exceeding 2 weeks have shown a slight tendency to become lighter in weight. This is due to the slow release of bromide ions from the ion exchange resin and is easily corrected by retreatment with the sodium bromide solution.
* Received 10 February 1976. t IRA-93 Amberlite Ion Exchange Resin, Rohm & Haas Co.. Philadelphia, PA 19105, U.S.A. $ Research Assistant. 9 Research Assistant. ‘IIProfessor. 663
Acknowledgements-The authors wish to thank the Engineering Foundation for supporting this work through Grant No. RC-A-73-6 and Edwards Laboratories for their donation of a Starr-Edwards aortic ball valve. Mechanical
Engineering Department, Union College. Schenectady. NY 12308. U.S.A.
S.
V.J. MILLERS R. BUSWLARI$
J.R. SHANEBROOK~
Technical Notes
664
Werle, H. (1973) Hydrodynamic
REFERENCES
Merzkirch. W. (1974) Flow Visualization.
Academic Press.
NY.
Somerscales, by particle in Science Society of
E. F. C. (1974) Fluid velocity measurement tracking. Flow-its Measurement and Control and Industry 1, Part 2, 795-807. Instrument America, Pittsburgh, PA.
flow visualization. Ann.
Rev. Fluid Mech. 5. 361-382.
Wieting, D. W. (1969) Dynamic flow characteristics of heart valves. Ph.D. dissertation, The University of Texas at Austin. Available from University Microfilms. Inc., Ann Arbor. MI (O.N. 69-21904).
Fig 1. Flow pattern across a Starr-Edwards aortic valve (Model No. 1200, size 13A). The direction of flow is from right to left.
mv2ing
p. 664)
Pergamon
Press.
Prmted m Great Bream
FLOW VISUALIZATION
WITH BLOOD ANALOG FLUID*
Abstract-A new type of tracer particle useful in visualizing the flow of a blood analog fluid is presented. Neutrally buoyant particles are formed from a white ion exchange resin and an aqueous solution of sodium bromide. These particles, when used with the flow visualization system of Wieting, produce excellent results and do not reduce the clarity of the blood analog fluid even after prolonged periods of testing.
INTRODUCTION
In a recent review article, Werlt (1973) discussed the importance of flow visualization studies in understanding fluid flow phenomena. Such information often provides valuable physical insight that is useful in solving the various problems associated with the flow phenomena being investigated. By suspending tracer particles in the test fluid it is possible to visualize regions of flow separation, turbulence and stasis as well as other fluid dynamic phenomena. In addition, quantitative information such as particle velocities can be determined from filmed records of the flow events. Somerscales (1974) reviewed the techniques of fluid velocity measurement by particle tracking and included information on various tracers used in water and in air. Merzkirch (1974) discussed the importance of matching the density of the tracer particles with that of the test fluid, especially for liquid flow velocities below 30cm/sec. Somerscales also presented a useful discussion of the forces that prevent tracer particles from moving with the same velocity as the fluid and Werlt briefly reviewed flow visualization of unsteady flows. Hemodynamic studies can also benefit from flow visualization results and these often employ a blood analog fluid to simulate the flow of blood through prosthetic devices and through various segments of the human cardiovascular system. The purpose of this Note is to present a new type of tracer particle that is useful in visualizing the flow of a blood analog fluid. THETRACER PARTICLES
Wieting (1969) has described a very useful system for visualizing the flow of a blood analog fluid consisting of a mixture of glycerine (36.7% by volume) and distilled water. This mixture is clear and has a viscosity and specific gravity that are comparable to those of whole human blood. In addition, the index of refraction of the fluid is close to that of plexiglas (used for test section construction), resulting in minimal optical distortion of the flow patterns. The authors have found that the flow visualization system of Wieting produces excellent results when tracer particles formed from a white ion exchange resint (in bead form) are used. Since the beads have a density that is slightly less than that of the blood analog fluid, they were made to be neutrally buoyant by the following process:
(a) Approximately 250ml of IRA-93 beads with dia. between 200 and 5OOpm were immersed in an aqueous solution of sodium bromide (SOO-1OOOgof NaBr in 11. of water) for a period of co. 24 h. While in the sodium bromide solution, the ion exchange resin undergoes an exchange process in which bromide ions replace hydroxide ions on the resins’ molecular structure. Since the bromide ions are heavier than the hydroxide ions, the beads tend to increase in weight. (b) The beads were sieve-screened from the sodium bromide solution, blotted with filter paper, mixed with a vertical column (70 cm high and 4 cm wide) of blood analog fluid and allowed to stand for ca. 1 h. (c) The neutrally buoyant beads were carefully withdrawn from the column through a side tapleaving behind the beads that either floated to the top of the column or sank to the bottom. Figure 1 illustrates the excellent quality of results obtainable using these tracer particles with the flow visualization system of Wieting. Shown is the flow pattern across a Starr-Edwards aortic valve during systoie at a pulse rate of 72 beats/min and an average flow rate of 5.6 l/min. The highly disturbed flow distal to the valve in the aorta is clearly visible and contrasts sharply with the laminar flow in the left ventricular test chamber. It should be noted that the present work was motivated when satisfactory results could not be consistently obtained with the tracer particles described by Wieting (1969). It was found that after a relatively short period of testing, the blood analog fluid became contaminated (very cloudy in appearance) necessitating a time-consuming filtration process in order to reclaim the blood analog fluid for future use. The beads of ion exchange resin used by Wieting were treated with mineral oil in order to maintain neutral buoyancy. The authors believe that the mineral oil was forced into the blood analog fluid by mechanical forces acting on the particles during testing. Such difficulties with the clarity of the blood analog fluid have not been encountered with the tracer particles described here, even after prolonged periods of testing. However, particles suspended in blood analog fluid for periods exceeding 2 weeks have shown a slight tendency to become lighter in weight. This is due to the slow release of bromide ions from the ion exchange resin and is easily corrected by retreatment with the sodium bromide solution.
* Received 10 February 1976. t IRA-93 Amberlite Ion Exchange Resin, Rohm & Haas Co.. Philadelphia, PA 19105, U.S.A. $ Research Assistant. 9 Research Assistant. ‘IIProfessor. 663
Acknowledgements-The authors wish to thank the Engineering Foundation for supporting this work through Grant No. RC-A-73-6 and Edwards Laboratories for their donation of a Starr-Edwards aortic ball valve. Mechanical
Engineering Department, Union College. Schenectady. NY 12308. U.S.A.
S.
V.J. MILLERS R. BUSWLARI$
J.R. SHANEBROOK~
Technical Notes
664
Werle, H. (1973) Hydrodynamic
REFERENCES
Merzkirch. W. (1974) Flow Visualization.
Academic Press.
NY.
Somerscales, by particle in Science Society of
E. F. C. (1974) Fluid velocity measurement tracking. Flow-its Measurement and Control and Industry 1, Part 2, 795-807. Instrument America, Pittsburgh, PA.
flow visualization. Ann.
Rev. Fluid Mech. 5. 361-382.
Wieting, D. W. (1969) Dynamic flow characteristics of heart valves. Ph.D. dissertation, The University of Texas at Austin. Available from University Microfilms. Inc., Ann Arbor. MI (O.N. 69-21904).
Fig 1. Flow pattern across a Starr-Edwards aortic valve (Model No. 1200, size 13A). The direction of flow is from right to left.
mv2ing
p. 664)