Week 1 - Flow
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What are fluids?
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.
What are solids?
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.
What’s colder than cold?
Ice cold. all right all right all right all right all right
What are tangential forces?
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)
What are perpendicular forces?
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)
What is force, pressure, friction, viscosity and their relationship with one another?
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.
What is laminar flow?
Laminar flow is smooth flow. Laminar flow is characterized by an unchanging flow pattern where adjacent layers of fluid smoothly slide past each other
What is turbulent flow?
Turbulent flow is not smooth flow. Turbulant flow has a continuously carrying pattern of flow.
Who’s law deals with laminar flow?
Poiseuille’s Law
Who’s principle deals with turbulent flow?
Bernoulli’s Principle
What Reynold’s numbers equals laminar flow? Turbulent flow? And what is meant by critical velocity?
less than 2000 = laminar flow greater than 2000 = turbulent flow critical velocity = when laminar flow transitions to turbulent flow
What is Pouiseulle’s Law?
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
Regarding Pouiseulle’s Law, what would be considered directly proportional and what would be considered inversely proportional?
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)
Viscosity & Density - Which is more significant at low flows, high flows?
low flows - viscosity high flows - density (this was in the technology stuff as well)
What is the result of doubling length or radius in regards to Pouiseulle’s Law? How about halving length or radius?
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
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?
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
What is Bernoulli’s Principle?
as fluid passes through a narrowing, the velocity increases and the pressure decreases
What is the Venturi effect?
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.
What does flow actually mean?
the quantity of fluid passing a point per unit of time