Biomedical Engineering Reference
In-Depth Information
END OF CHAPTER SUMMARY
14.1
Particle imaging velocimetry (PIV) is a computer-based technique that tracks a sequence of
reflective particles through a flow chamber. A computer program is used to control a high-
intensity light source (normally a laser) and correlate the data obtained regarding the move-
ment of particles through the fluid. Based on the known particle displacement and the cam-
era frame rate, it is possible to obtain the velocity of the particles seeded within the fluid.
Through the use of multiple cameras, true three-dimensional velocity fields can be obtained.
Laser speckle velocimetry and holographic PIV are more specialized PIV systems.
14.2
Laser Doppler velocimetry is used to quantify the microstructures of flows. Two monochro-
matic light sources are focused at a region of interest and this forms a fringe pattern that is
based on the fluid velocity. By seeding particles within the fluid, the fringe pattern changes,
based on
2
v
sin
2
λ
and this is what is collected by the digital camera. Most laser Doppler systems have the
problem of transient fluctuations in the fluid properties, caused by imperfections in the
experimental system, which can confound the results. By using a dynamic time-averaging
system, these transient changes can be smoothed.
v
d
5
ω
5
14.3
Flow chambers are used to subject cells to particular shear stresses. Through the particular
design of the chamber, cells can either be subjected to uniform stresses along the walls of
the chamber or to varying stresses. It is most common to use either a parallel plate system
or a cone-and-plate viscometer system to model physiological conditions
in vitro
.
HOMEWORK PROBLEMS
*14.1
Compose a small algorithm that can be used to quantify approximately 10 particle velocities,
within subsequent digital images, for a particle imaging velocimetry (PIV) system.
In a laser Doppler system, two monochromatic laser light sources are placed 80
apart. The
wavelength of light emitted from these two lasers is 540 nm. Calculate the normal
fringe spacing for these laser light sources and the anticipated change in frequency if a par-
ticle intersects the laser at a velocity of 20 mm/sec. If the light sources are changed to a
laser that emits at 650 nm, how does this affect the calculations?
14.2
14.3
Using the Navier-Stokes equations, model the flow through a parallel-plate flow chamber
and a cone-and-plate viscometer. Assume that the parallel-plate is only under pressure-
driven flow
@
p
@x
, the channel height is
h
, and that the fluid viscosity is
μ
. The cone-and-
plate has a radius of
r
, an angle of
α
(assumed to be small), and an angular velocity of
ω
.
Gravity can be neglected for both systems.
14.4
Discuss a possible re-design of a flow chamber that can be used to model physiological
flows within the microcirculation.
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