physics including gases Flashcards
what is 1 atm equal to
1 atm = 1 bar = 101.3kPa = 101 325 Pa = 760mmHg = 1033cmH2O = 14.5PSI
mmHg -> kPa = Divide by 7.6 i.e. 760mmHg = 101kPa
cmH2O ->mmHg = multiply by 0.76
what is Hagen-Poiseuille
The Hagen-Poiseuille equation describes the flow of a fluid through a cylindrical tube (such as a blood vessel or an airway) and is used to model laminar flow. It’s especially important in contexts like vascular resistance, airway resistance, and fluid dynamics in physiology and medicine.
radius has the largest impact because if radius were to decrease by half, flow rate would decrease by 16 times.
Viscosity impact laminar flow
density impacts turbulant flow
Tell me about pin index system
Air= 1, 5
O2= 2, 5
N2O= 3, 5
how many psi is 1 atm
1atm= 14.7 psi
tell me about reynolds number
-Reynolds number is a dimensionless quality used to predict if flow is laminar or turbulent through a pipe or conduit.
-Re=pvD/μ
p=fluid density
v= flow velocity
D= diameter or length
μ = viscosity
Re <2000 is laminar
2000-4000 transitional where both may occur
>4000 turbulent
what pressure are o2 cylinders stored at?
13, 700 kpa (approx 137 bar) [1bar=100kpa]
O2 cylinder pin index positions = 2 and 5
how many litres in each of the following O2 cylinders
C
D
E
F
G
J
CD
C 170L
D 340L
E 680L
F 1360
G 3400
J 6800
C starts 170 and doubles
then G starts 3400 and doubles
??CD= 460 at 23,000 (the others are at 13,700 kPa)
how many litres in each of the following N2O cylinders
C
D
E
F
G
J
C 450
D 900
E 1800
F 3600
G 9000
J -
C start 450 and doubles
G goes its own way with 9000
what colours are the different cylinders
how to calculate how long a cylinder of o2 will last
Eg question: patient using 5L/min O2, you have an E-size cylinder with a pressure of 100bar. how long will this cylinder last?
step 1: calculate available O2 volume
= (cylinder capacity at full (L) x current pressure)/ full pressure
e.g E cylinder of O2= 680L capacity
(680L x 100bar)/ 137bar = 496L remaining
Step 2: Calculate duration
duration = available O2 volume/ flow rate
e.g 496L/ 5L/min => 99 minutes remaining
This equation can be re-arranged to find the remaining pressure if the other values are known.
How to calculate how many cylinders needed on patient transfer
e.g ventilated pt needs 45 min transfer. FiO2 0.6, VT 500ml, RR 20
only have size E cylinders, how many are needed
step 1: calculate MV
MV=VT x RR
e.g 0.5 x 20=> 10L
Step 2: calculate O2 consumption per min
10L x FiO2 0.6 => 6L/min
Step 3: times this by transfer time
6x45= total for transfer=270L
step 4: Always times this by 2
270 x 2=540L needed.
Divide this by cylinder volume
E has 680L
540/680L =0.79, therefore only 1 cylinder is needed.
Whereas size C (170L)
540/170= 3.17 cylinders needed
therefore round it up to 4
how is entonox stored
what is the pseudocritical temp of entonox
whats the risk if below this?
horizontally, wick in the middle
-7
if below, risk of hypoxic mixture being given due to seperation/ lamination.
what pressure and temp is VIE?
what pressure is oxygen released into pipeline at?
-150 degrees celcius
1000 kPa (safety valve at 1500) (10bar)
414 kPa pipeline (4 bar)
bp of O2 -183 at 1 atm
What pressure is N2O stored
what is the filling ration?
44 bar (4400 kPA)(x100 to get kpa)
filing ratio 0.7, or 0.67 in warm/ temperate countries (weight of fluid compared with weight when completly full with water)
-store vertically
-Tare weight is the weight of the empty cylinder
-contents cannot be determined by pressure until all liquid has been vapourised
O2 cylinder pressure
s stored as gas at 137 bar (13, 700 kPa)
pressure reducing valve ensures safe delivery to anaesthetic back bar
define specific latent heat
the heat required to convert 1 kg of a substance from one phase to another J/kg. must be quoted with reference to temp
define adiabatic change
state of a gas is altered without a change in heat energy to or from the gas into the surroundings. The energy causes a change in gas temp.
e.g decompression- gases expand and energy is required to overcome van der vaals forces. the gas cools as energy comes from the molecules own kinetic energy
eg compression- temp rises with rapid gas compression. e.gcylinder connected to anaesthetic maching may expokde inn presence of combustibles, as temp rises with rapid gaseous compression
define absolute humidity
mass of vapour/ volume
define relative humidity
actual vapour pressure/ SVP
can be measured using wet and dry bulbs
hair hygrometer
how to measure dew point?
The relationship between humidity
and dew point can be used to
calculate relative humidity when the
dew point and saturated vapour
pressure is known.
Regnault’s Hygrometer: has a silver
tube containing ether through which
air is bubbled reducing its
temperature. The point at which
condensation forms on the outside of
the tube is the dew point (100%
relative humidity).
