Biomedical Engineering Reference
In-Depth Information
Table 4.1
Uses of Biofluid Flow Analysis
Analysis of Physiological System Design of Devices, Instruments, and Diagnostic T ools
Artificial hearts, prosthetic heart valves, stents, vascular grafts,
extracorporeal blood circuits, cardiac bypass, kidney dialysis, cell
separator, wound healing and tissue regeneration, nanomedicine,
drug delivery systems
Blood flow through the
circulatory system
Heart-lung machines, artificial oxygen carriers, mechanical
ventilators, mucosal drug delivery, evaluation of pollutant
particles, replacement surfactants
Gas flow in lungs
Cerebral circulation
Drug delivery systems, forced convection systems
Synovial fluid flow in cartilage
Artificial joints, cartilage regeneration
Eye
Contact lenses
4.2
Fluid Flow Characteristics
4.2.1
Conservation of Mass
In nature, matter exists in three states: solids, liquids, and gases. Liquids and gases
are combined as fluids as their shape is determined by the container in which they
are present, unlike solids. Further, fluids lack the ability to resist forces in contrast
to solids; a deformation force on a solid may result in no effect due to resistance or
may cause some defined displacement. Since fluids cannot resist forces, they move
or flow under the action of the forces. Their shape changes continuously as long
as the force is applied and their characteristics such as density and viscosity could
also change. Despite sharing many similar characteristics liquids and gasses pos-
sess distinct characteristics. For example, application of pressure on liquids does
not change the volume. Also, liquid density does not change with pressure and is
often regarded as being incompressible. However, gases compress with increasing
pressure (i.e., change volume) and are considered compressible. The density of gas
is a function of the pressure and temperature. If the liquid volume is smaller than
the container volume, then liquid only occupies its volume, leaving the rest of the
container volume unoccupied. However, a gas has no fixed volume and expands to
fill the entire volume of the container.
In any system of solid or fluid whether stationary or moving, the total mass of
the system does not change and is conserved. This is called the law of conservation
of mass. Consider the case of blood flowing through a tubing (Figure 4.1) (or air
flowing through ventilator tubing). Based on the conservation of mass principle,
the mass of blood entering the tube per unit time
(
m
is equal to the mass of blood
leaving that tubing assuming there is no accumulation in the tubing. In the math-
ematical form this can be represented as
Figure 4.1
Fluid movement in a tube.
