BIOFLUID MECHANICS BASICS

Question 1

What are the MAJOR ROLES OF BLOOD?

Answer 1

• Carries oxygen and nutrients to active tissues
• Delivers carbon dioxide to the lungs
• Brings metabolic end products to kidneys
• Blood is a buffering reservoir that controls pH of biofluids
• Part of the immune system
• Mass and heat transfer

Question 2

What is a VISCOUS FLOW?

Answer 2

A flow where the frictional effects are significant

Question 3

What are INVICID FLOW REGIONS?

Answer 3

Regions (often not close to a solid surface) where viscous forces are negligibly small compared to inertia or pressure forces

Question 4

What does the CONSERVATION OF MOMENTUM LAW STATE?

Answer 4

F=ma
Total momentum in a system remains the same throughout although some objects may gain momentum others must lose it to balance.
This is TRUE WITHOUT EXCEPTION

Question 5

What does the CONSERVATION OF MASS LAW STATE?

Answer 5

The mass of the fluid must be conserved

Question 6

Why is the BERNOULLI EQUATION IMPORTANT IN FLUID MECHANICS?

Answer 6

• It is an approximate relation between pressure, velocity, and elevation
• It is valid in regions of steady, incompressible flow where net frictional forces are negligible.

Question 7

What are the LIMITATIONS OF THE BERNOULLI EQUATIONS?

Answer 7

• Flow must be STEADY
• DENSITY must be constant (incompressible flow)
• FRICTION losses are negligible
• The equation can only relate two points on the same STREAMLINE
• Not applicable if section involves a PUMP, TURBINE or FAN
• No/negligible HEAT TRANSFER can be present

Question 8

Is BLOOD A NEWTONIAN FLUID?

Answer 8

YES AND NO
* The combination of blood plasma and blood cells makes blood non-newtonian
* When blood is stationary for several seconds, rouleaux begin to form
* It is shear thinning
* At shear rates >100s^-1 the viscosity is nearly constant; therefore, blood can be assumed Newtonian.

Question 9

What is the NO-SLIP CONDITION?

Answer 9

The layer of fluid right next to a solid surface e.g. pipe wall is static: it is stationary compared to the rest of the flow.

Question 10

What REYNOLDS NUMBER IS A FLOW DESCRIBED AS LAMINAIR?

Answer 10

Re<2500

Question 11

What REYNOLDS NUMBER IS A FLOW DESCRIBED AS TRANSITIONAL?

Answer 11

2500<Re<4000

Question 12

What REYNOLDS NUMBER IS A FLOW DESCRIBED AS TURBULENT?

Answer 12

Re>4000

Question 13

What is meant by LAMINAR FLOW?

Answer 13

The highly ordered fluid motion is characterised by smooth
layers of fluid. The flow of high-viscosity fluids such as oils at low
velocities is typically laminar

Question 14

What is meant by TURBULENT FLOW?

Answer 14

The highly disordered fluid motion typically
occurs at high velocities and is characterised by velocity
fluctuations. The flow of low-viscosity fluids such as air at high velocities is
typically turbulent.

Question 15

What is meant by TRANSITIONAL FLOW?

Answer 15

A flow that alternates between being laminar and turbulent.

Question 16

What is the WORMERSLEY NUMBER?

Answer 16

• Symbol: α
• Indicates the extent to which the velocity profile in laminar flow in a long pipe differs from the Poiseuille profile when the fluid is subject to a sinusoidally varying pressure gradient of angular frequency ω
• The higher α, the greater the phase lag behind the flowrate

Question 17

What is a SEPARATION ZONE and WHAT CAUSES THEM TO FORM?

Answer 17

• If a tube expands too rapidly after a constriction the phenomenon of separation occurs
• When this happens there is no longer simple streamlined motion across the whole of the cross-section
• The flow near the walls becomes sluggish and the fluid starts to RECIRCULATE
• The separation is a consequence of increased pressure along the section

Question 18

What is a STENOSIS?

Answer 18

A constriction in a vessel due to the build-up of plaque causes the lumen to narrow.

Question 19

What are DEAN VORTICES?

Answer 19

When a flow goes around a corner the centrifugal force causes the flow profile to become distorted with the maximum velocity shifting to the outside (not the centreline), this causes a TRANSVERSE CIRCULATION (AKA secondary motion) - the Counter rotating vortices are Dean vortices

Question 20

What is WALL SHEAR STRESS (WSS)?

Answer 20

As blood flows through a vessel it exerts a force known as wall shear stress (WSS)
Should be 1-2Pa for blood vessels

Question 21

How do BLOOD VESSELS ADAPT TO WSS?