6. Temperature & humidity Flashcards
What is absolute humidity
whats it in the upper trachea
amount of water bappour per unit volume of gas at given temp and pressure
34g/m3
34mg/l
Gas driven nebuliser droplet size & humidity
2-4um droplets
deposited upper airway
60g/m3
Ultrasonic neb
size
absolute humid
problems
<2um - capable reach alveloi
Absolute humid 90g.m3
Over-hydration - flood lung
increase resistance
Cold and hot water baths abs humidity
problems
produce an absolute humidity of 10 and 40 g/m
Hot - airway burns if water trap not used
HME benefit
abs humidity
how efficient
Retain heat+; moisture from expire gas
Cheap
Abs humid 25g/m3 (rel 60-80%)
> 70% efficient
not more efficient and effective as ambient temp inspired gas increases
IR principle
Stefan Boltzmann eqn
Directly related to the fourth power of the temperature.
Metal oxide Thermistor Principle
Change in electrical resistance
Wheatstone is part but not the principle
resitsance falls exponentuially with increase temp
Difficult claiblrate
Liquid expansion thermometers principle - Mercury
Thermal expansivity
Platinum wire principles
Electrical resistance
Thermocouple Relies on
Seebeck effect is
temperature between two dissimilar electrical conductors or semiconductors
produces a voltage difference between the two metals.
temp increase - flow increase
What is temperature
Property of system determins if heat is transferred to or from other systems
What in kelvin, C & F are
Absolute 0
Melting point Ice
Boiling point water
Abs 0
0 kelvin, -273.15°C or -459°F
Melting point Ice
273.15 kelvin, 0°C or 32°F
BP water
373 kelvin, 100°C or 212°F.
Triple point of water
what is it & temps
Water exists simultaneously in solid, liquid and gaseous states
273.16 K or 0.01°C
Mercury solidify at temp C
-38.87°C, so is a liquid at -37°C.
Absolute humidity
Depends on
Mass of water vapour present - given volume of air, g/m3 or mg/litre
Maximum water vapour present in a given volume air determined - temperature (both ambient and body).
Abs humidity can be increased
Tmperature increases the amount of water which can be present as vapour also increases
Hence fully saturated air at 20°C contains about 17 g/m3 whereas at 37°C it contains 44 g/m3 when saturated.
fully saturated air at 20° abs humidt
17g/m3
Increase temperature
To humidity
relative humidity
dew point
crease in temperature produces:
Increased absolute humidity
The same relative humidity
Increased dew point temperature.
Decrease or increase in barometric pressure affect on humidty
No change in absolute or relative humidity and dew point temperature.
Thermocouple
is
used
Consists of (what)
What happens when contact
A thermocouple is a device that is used to measure temperature ‘electronically’.
It consists of a pair of dissimilar metal wires or strips bonded together, typically copper and constantan (an alloy of 55% copper and 45% nickel).
When these wires contact each other, a small voltage is generated in the order of millivolts.
The magnitude of the thermojunction electromotive force (EMF) is proportional to applied temperature (the Seebeck effect).
This physical principle can be applied to the measurement of temperature. The electromotive force at the measuring junction is proportional to temperature.
Two wires bonded together with different coefficients of expansion can be used as a switch for thermostatic control.
The resistance of the measuring junction of a thermocouple is irrelevant.
The resistance of a platinum wire varies LINEARLY with temperature and the resistance of a thermistor varies exponentially with temperature. This unknown resistance is incorporated into a Wheatstone bridge to indirectly measure temperature.
Hygrometer
measure humidity.
By inserting a water-absorbing substance between the two plates, this has an effect on the resistance between the plates of the capacitor. The resultant change can be directly related to humidity.
Thermistor - response time
Response time any electrical device measure temp
-> size + material
mainly size
length width and site no relevance
smaller - smaller spec heat capacity = react quicker
.1-15sec
Filtration
- Direct inteception - >1um - too large to pass
- Inertial impaction 0.5-1um - collide w/ fibres held by VdW
3 Diffusion interception -[ small particle - sml mass - constant movement - inevitbale collision w, fibres
- Electrostati cttaction - charged
5 gravitational setting - large particles
Triple point
- 01C
273. 16K
Mercury therm take how long equil
2-3 mins
Poisonous
Freezes at -39C
Boils >250
Alcohol freezing and BP
-117 + 78.5
At absolute 0 an ideal gas
occupies 0 volume
Humidity 1cm air at 20c
17g m3
Humidity upper trach at 37
34
humid lower trach 37
44g m3
Humidity can be asses
measured
uv light transmission
measured blowing air thru ether - determine dew point in regnaults hygrometer
using hair hygrometer - accurate detecting humidity 30-90%
temp loss %
1 radiation 40-60% - ir rad patient to second system not direct contact - lower temp
prop to enciro core diff ^ 4
2 convection 30%
heat lose - air immed surround body - loss proport veolicty air
3 evaporation 8-15%
resp 8-10%
condcution
5%
Latent heat of vaporisation
water
at zero is
It is defined as the heat required to change one mole of liquid at its boiling point under standard atmospheric pressure. It is expressed as kg/mol or kJ/kg.
decrease with water is curved
its crit temp
Ntitrous oxide - latent heat
heat energy from liq N2O -> vapor
pressure falls - pressure decrease cooling
Viscosit of a gas w increase temp
increase - more energy
Viscosity liquid
reduces vdw forces - viscosity decreases
Effifiency low to high of humidification
cold water bubble thru
HME
change reg - mositure accum inc resist
Heated water bath
(40-45C)
Heated bernoulli neb + anvil
U/S neb
Latent heat vaporization trachea
how avoided
how much lost warming
15% heat loss in trachea
humidifaction
2% basal heat lost warm gas
more heat lost humdifying vs warming
Specific heat capactiy
mean value for tissue spec heat capcicty of person
gases high or low spec heat capcity
water spec heat cap
radiation proport to what
amt heat required raise temp 1kg sub by 1 kelvin (specific bit = 1kg)
3.5Kj/Kg per C
Gases low spec heat cap (low density)
Water = 4.18Kj / K
radiation is proportional to 4th power of absolute temperature
