Biomedical Engineering Reference
In-Depth Information
the scaling and the forces throughout the model are matched. The basis for collecting data
with PIV is through the use of reflective beads, which are placed within the fluid that will
be circulated throughout the model. A high-intensity light source (usually a laser source)
is focused onto a region of interest within the flow chamber. A digital camera with a high
acquisition frame rate is also focused at this region of interest to collect data on the particle
motion over time. Particle motion is obtained through the light reflection from the seeded
particles, which is captured by the digital camera. Using a computer algorithm, each sub-
sequent image is correlated to the previous image, temporally, so that each particle's
velocity can be calculated from a known change in position divided by the known frame
rate. By collecting multiple data sets at each region of interest, it is possible to obtain mean
velocities (magnitude and direction) throughout the flow field. A typical PIV setup is
schematized in
Figure 14.1
. It should be noted that it is possible for the algorithm to not
correlate the correct particles in subsequent images. For instance, if the particles are too
concentrated within the flow field, then the reflected light could be outside the cameras
resolution limit. It would therefore be difficult for an algorithm to discriminate individual
particles. However, if the particles are too sparsely populated, then not enough informa-
tion about the flow field can be obtained. Therefore, it is necessary to optimize the particle
seeding density within the flow chamber.
The usefulness of PIV systems in biofluid mechanics research is that new designs for
cardiovascular implantable devices can be tested to determine if they disrupt the flow field
and by how much the flow field is altered. Computational methods provided a limited
Reflective particles
Pulsed laser light
Reflected light
Mechanical heart valve
Digital camera
FIGURE 14.1
Schematic of a typical PIV system, which consists of a flow chamber (shown with a bileaflet
mechanical heart valve), a fluid seeded with reflective particles, a high-intensity laser light source, and a digital
camera. Not shown is the computer system that would be coupled to both the laser and the camera to calculate
particle velocities.
Search WWH ::
Custom Search