Week 1 - Flow

Question 1

What are fluids?

Answer 1

Any material that has the ability to flow.

Fluids have a definite volume but not a definite shape.

Both liquids & gases are considered fluids.

Gases in particular are easily compressible and expandable.

Question 2

What are solids?

Answer 2

A material with sufficient intermolecular forces to fix the atoms, molecules or ions in place with respect to each other.

Solids have a definite shape & volume.

Ice is a solid.

Question 3

What’s colder than cold?

Answer 3

Ice cold.

all right all right all right all right all right

Question 4

What are tangential forces?

Answer 4

the stress parallel to the vessel wall, defined as shear stress.

(shear stress is responsible for the slowing of flow along the vessel wall, making the highest flow rates in the center of the vessel lumen)

Question 5

What are perpendicular forces?

Answer 5

the stress perpendicular to the vessel wall, defined as normal (or tensile) stress.

(this represents the dilating force of blood pressure on the vessel wall or the dilating force of air on the alveoli)

Question 6

What is force, pressure, friction, viscosity and their relationship with one another?

Answer 6

Force: (mass x acceleration) defined as a response to stress

Pressure: (Force/Area) is the force per unit area applied in a direction perpendicular to the surface of an object

Friction: Resistance to flow from surface interaction. It is proportional to viscosity.

Viscosity: has to do with shearing forces that occur as “layers” of fluids or gases move relative to each other while flowing.

Question 7

What is laminar flow?

Answer 7

Laminar flow is smooth flow.

Laminar flow is characterized by an unchanging flow pattern where adjacent layers of fluid smoothly slide past each other

Question 8

What is turbulent flow?

Answer 8

Turbulent flow is not smooth flow.

Turbulant flow has a continuously carrying pattern of flow.

Question 9

Who’s law deals with laminar flow?

Answer 9

Poiseuille’s Law

Question 10

Who’s principle deals with turbulent flow?

Answer 10

Bernoulli’s Principle

Question 11

What Reynold’s numbers equals laminar flow? Turbulent flow? And what is meant by critical velocity?

Answer 11

less than 2000 = laminar flow

greater than 2000 = turbulent flow

critical velocity = when laminar flow transitions to turbulent flow

Question 12

What is Pouiseulle’s Law?

Answer 12

π r⁴ ∆P
F= ———-
8 n l

F=flow
π=constant pi
r⁴=radius to the fourth power
∆P=pressure gradient
n=viscosity
l=length of the tube

Question 13

Regarding Pouiseulle’s Law, what would be considered directly proportional and what would be considered inversely proportional?

Answer 13

direct:
r⁴=radius to the fourth power
∆P=pressure gradient

inverse:
n=viscosity
l=length of the tube

(doubling the radius = 16-fold increase in flow)

Question 14

Viscosity & Density - Which is more significant at low flows, high flows?

Answer 14

low flows - viscosity

high flows - density

(this was in the technology stuff as well)

Question 15

What is the result of doubling length or radius in regards to Pouiseulle’s Law? How about halving length or radius?

Answer 15

doubling the radius = 16-fold increase in flow

doubling the length = doubling the resistance to flow

halving the radius = 16-fold decrease in flow

halving the length = halving the resistance to flow

Question 16

Which liter NS IV bag would flow faster; one infusing through an 8 inch, 20 gauge central line or a peripheral, 16 gauge, 1.5 inch angiocath?

Answer 16

plug the numbers in the equation and figure that shit out!

    π r⁴ ∆P F=    ----------
      8 n l

F=flow
π=constant pi
r⁴=radius to the fourth power
∆P=pressure gradient
n=viscosity
l=length of the tube

Question 17

What is Bernoulli’s Principle?

Answer 17

as fluid passes through a narrowing, the velocity increases and the pressure decreases

Question 18

What is the Venturi effect?

Answer 18

first we consider Bernoulli’s Principle:
as fluid passes through a narrowing, the velocity increases and the pressure decreases

Due to the decrease in pressure in the narrow portion, an opening on the side of the tube will allow entrainment of air due to more pressure being outside than in. Hence, the Venturi effect.

Question 19

What does flow actually mean?

Answer 19

the quantity of fluid passing a point per unit of time