1. GASES AND FLOW FRCA PRIMARY PHYSICS 1 Dr E Farnham-Davis MEPS 2016

2. States of Matter  Solid  Liquid  Vapour  Gas

3. Phases

4. Definitions  Triple point – pressure and temperature at which all three states can coexist  Critical temperature – temperature, above which, a gas cannot be compressed into a liquid  Critical pressure – minimum pressure required at the critical temperature to liquefy a gas

5. Change of Phase

6. Gas Laws

7. Universal Gas Law

8. More Gas Laws  Dalton’s Law  Total pressure = sum (partial pressure all other gases)  Henry’s Law  Solubility of a gas in a liquid is proportional to partial pressure above liquid

9. Flow  Quantity of a fluid passing a point in a given time  e.g. L/min  (fluid = liquid, vapour or gas)  Laminar vs Turbulent

10. Laminar vs Turbulent

11. Laminar Flow

12. Reynolds number

13. Laminar vs Turbulent

14. Measuring flow  Several devices used in different areas of anaesthesia  Fixed orifice variable pressure  Fixed pressure variable orifice

15. Rotameter  Forces acting in equilibrium

16. Pneumotachograph  Change in pressure proportional to flow (laminar)

17. Wright’s Respirometer

18. PEFR  Variable pressure, variable orifice

19. Benedict-Roth spirometer  Measures volumes

20. Spirometry trace

21. Bernoulli Effect  At a narrowing in a system in which fluid is moving the pressure will decrease as the velocity increases (conservation of energy)

22. Venturi  Utilisation of low pressure created by Bernoulli effect in order to entrain another gas (e.g. O2 in Venturi Mask).

23. Coanda Effect  Fluid will “cling” to surface as it flows past it (e.g. water from a tap on the back of a spoon).  Used in “fluid logic” ventilators.