FLuid mechanics

Question 1

What is pressure

Answer 1

force/unit area

Question 2

What is a fluid?

Answer 2

A fluid is a substance that continually deforms (or flows) under an applied shear stress.

‘Fluid’ can be used to describe different phases of matter that behave similarly under flow conditions:

Gases
Liquids
Plasma
Even some plastic solids

Question 3

What is the fluid rpessure?

Answer 3

THe pressure at some point in a fluid

Question 4

What is flow

Answer 4

Flow is the quantity of fluid (gas, vapour or liquid) passing a point per unit time. The units typically used in medicine are L/min.

Flow is represented by the equation: Flow = Quantity/Time

Question 5

what is the most important fluid factor in laminar flow?

Answer 5

viscosity

Question 6

What is the most important fluid component of turbulent flow?

Answer 6

Density

Question 7

What is the significance of reynolds number

Answer 7

Re <2000 flow is likely to be laminar
Re >2000 flow is likely to be turbulent

Question 8

resistance equation

Answer 8

delta P/delta Q

Question 9

What devices use the venturi effect

Answer 9

Venturi oxygen masks - driving oxygen entrains room air, which dilutes the 100% oxygen driving gas to a value calibrated by the entrainment ratio of the nozzle aperture, Fig 1
Nebulizers - gas entrains liquid as droplets small enough to be inhaled
Sanders injector for ventilation
Suction

Question 10

What is a vitalograph

Answer 10

Single expired breth acts on bellows. marks paper moving at a constant speed

Question 11

What is a bell spirometer

Answer 11

Gas expired into a bell in water- rises and falls depending on gas volume

Question 12

What is a rotameter?

Answer 12

VAriable orifice and constant pressure- accurate to within 2%

Question 13

Pneumotachograph

Answer 13

Variable pressure and constant orifice. Can use different heads that cause a pressure drop across a transducer

Question 14

Vane meter?

Answer 14

eg wrights spirometer- flow moves a turbine that is linked to a dial

Question 15

MEchanical flow transducers?

Answer 15

small disc in the flow is bent against a strain gauge- force depends on flow

Question 16

Hot wire anemometers?

Answer 16

gas flows over heated wires, degree of cooling is realted to gas flow

Question 17

Ultrasonic flow meters

Answer 17

gas flows in the same direction, an increase in signal velocity occurs

Question 18

how do rotameters work?

Answer 18

valve opening causes mroe flow which acts on a bobbin. te bobbin rises to a position where the force of the gas upwards is equal to the gravity pulling down

Question 19

how do rotameters work at low flow?

Answer 19

Narrow end of tube, flow is laminar

Question 20

HOw does a rotameter behave at high flow

Answer 20

bobbin rises higher, obstruction is greater diameter and reduced length- turbulent flow

Question 21

WHy are rotameters gas specific

Answer 21

Because gases have different densities and viscosities, which in turn affect flow under different conditions.

Question 22

What might affect rotameter accuracy?

Answer 22

Warmer gas is less dense and viscous, may cause overreading