RSPT 1060

Module C-7THERMODYNAMICS

and HUMIDITY

OBJECTIVES

• At the end of this module, the student should be able to…

– Define terms associated with thermodynamics.

– List the following on the Fahrenheit, Celsius, and Kelvin temperature scales: • Freezing point• Boiling point• Body temperature• Absolute zero.

OBJECTIVES• At the end of this module, the student

should be able to…– Convert between the following

scales:– Fahrenheit and Celsius

temperature scales.– Celsius and Kelvin temperature

scales.– Define heat.– Differentiate between a calorie

and a kilocalorie.

OBJECTIVES

• At the end of this module, the student should be able to…

– State the number of kilocalories obtained for 1 gram of each of the following substances: • Carbohydrate• Fat• Protein

– Compare and contrast the four methods of heat transfer.

OBJECTIVES

• At the end of this module, the student should be able to…

– State the water vapor pressure of alveolar gas in the following units: • mm Hg

– mg/L Differentiate between the following:• Absolute humidity• Relative humidity• Humidity deficit

OBJECTIVES

• At the end of this module, the student should be able to…

– Explain the relationship between surface area and evaporation.

– Given appropriate information and conversion factors, determine the relative humidity of a gas.

– Describe how properties of gases may change under extreme temperatures and pressures.

– Describe what the critical point is and how it is used in gas therapy.

OBJECTIVES

• At the end of this module, the student should be able to…

– Given appropriate information, determine the duration of use of a liquid cylinder of gas.

– Given appropriate information determine the duration of use of a gaseous cylinder of gas

Practice

• Sibberson’s Practical Math For RC:– Ch4: Inspiratory Flow Rates, Sample

Problems First & Second Set, pgs. 47-49.•Practice problems, pgs 53-54

– Ch 12: I:E Ratio, Sample Problems Eighth Set, pgs 146-147•Practice Problems, pg. 156

Temperature• Definitions:

– One method of quantifying matter.

– How cold or hot an object is.

– The amount of Kinetic activity.

Measurement Systems

• °F = Fahrenheit (British)

• °C = Celsius (Centigrade) (European)

• °K= Kelvin (Standard International) • °R = Rankine (used in engineering; not in

medicine)

http://www.dandantheweatherman.com/Bereklauw/Celsius.htm

Other Temperature Scales• Delisle (°D)

– Russian– 2,400 grauations– Zero as boiling; 100 as freezing

• Newton (°N)– Initially “cold air in winter” to “glowing coals in

the kitchen fire”– Zero as melting snow; 33 as boiling water

• Réaumur (°Re or °R)– French– Zero as freezing; 80 as boiling.– Still in use in some cheese manufactuing

• Rǿmer (°Rǿ)– Danish astronomer– Zero was freezing brine; 60 as boiling water.

Body Temperature• Normal body temperature is 37°C (98.6°F).

– Or is it? http://www.amstat.org/publications/jse/v4n2/datasets.shoemaker.html#mackowiak

• Exercise can increase it to 100 - 103° F.

• Individual daily patterns may cause 1 - 3 degree change in a day.– Called diurnal variation.– Morning people peak temp by mid

morning.– Night people peak in evening.

Temperatures to Know

°F °C °K

Absolute Zero

-460 -273 0

Freezing of Water

32 0 273

Body Temperature

98.6 37 310

Boiling of Water

212 100 373

Figure 6-2, page 95

Conversion

• We will be doing conversions from one system to the other.

• The rules for rearranging formulas, canceling and (+) & (-) numbers will be used.

• Conversions will be used at the patient bedside, in blood gas labs and pulmonary function labs

FORMULAS FOR TEMPERATURE CONVERSION

°F = 1.8(°C) + 32 (Using a decimal)

°F = 9/5(°C) + 32 (Using a fraction)

°C = .555(°F-32) (Using a decimal)

°C = 5/9(°F-32) (Using a fraction)

5°F = 9°C + 160 

°K = °C + 273 °C = °K - 273 

°F - °C - °K 

Convert F into C then into K

°K - °C - °F 

Convert K into C then into F

Using the formula: 5°F = 9°C + 160

212 °F = __________ °C   

Practice:

• The highest land temperature ever recorded was 136°F in Al Aziziyah, Libya, on September 13, 1922. What is this temperature on the Celsius scale?

Heat

• Heat is a form of kinetic energy that is transferred from a hotter object to a colder object when the two come in contact.

• Most common form of energy is heat energy.

• Many chemical reactions produce heat energy.

How is heat energy measured?

• Metric – calorie (cal) or the amount of heat

needed to raise 1 gram of water 1 degree Celsius

– On food label 1 kilocalorie (Cal or kcal) = 1,000 calories (cal)

• S.I. – 1 cal. = 4.184 joules

EXAMPLE:

• 12g of sugar when burned yields 45 Cal (or 45 kilocalories or 45,000 cal) of heat energy– Adult males need 3,000 Cal/day– Adult females need 2,200 Cal./day

• Food calories:– 1 g carbohydrate yields 4 kcal– 1 g fat yields 9 kcal– 1 g protein yields 4 kcal

“Specific” heat

• The amount of heat that will raise the temperature of 1 gram of a substance 1°C

– Water = 1 cal/g x °C– Gold = 0.031 cal/g x °C– Iron = 0.106 cal/g x °C

• The body is 60% water so it takes a larger transfer of heat to change body temperature.

• This is why body temperature remains relatively stable.

How does heat transfer?

• Heat moves from an object of higher temperature to an object of lower temperature in four ways.

• Conduction • Convection • Radiation • Evaporation

Conduction

• Transfer of heat by direct contact • Solid objects like metal conduct

heat away quickly • They have a high thermal thermal

conductivityconductivity and often feel cool to the touch as they remove heat from your hand.

Convection

• Transfer of heat by mixing of fluid molecules

• Gases or liquids mixing in currents or forced air heating

• Convection oven

Radiation

• Transfer of heat to a cooler, distant object.

• No direct physical contact• Conventional oven

Evaporation

• Form of vaporization where liquid turns to gas and heat is taken away from the air surrounding the liquid

EXAMPLE:

• Newborn babies are kept warm by– Drying them off (reduces

evaporation)– Placing them in a preheated

isolette or warmer (reduces radiation & conduction)

– Keeping them out of drafty areas (reduces convection).

Humidity

Definitions & Measurements

• Humidity – Water in a gas or molecular form, also called a vapor.

• Measurement: hygrometer or psychrometer

– Vapor Pressure (mm Hg)– Water Content (mg/L)

(see chart provided)

TEMPERATURE(C)

WATER VAPOR PRESSURE

(mmHg)

WATER CONTENT(mg/L)

ATPS to BTPS Correction Factor

20 17.5 17.3 1.102

21 18.6 18.4 1.096

22 19.8 19.4 1.091

23 21.1 20.6 1.085

24 22.4 21.8 1.080

25 23.8 23.0 1.075

26 25.2 24.4 1.068

27 26.7 25.8 1.063

28 28.3 27.2 1.057

29 30.0 28.8 1.051

30 31.8 30.4 1.045

31 33.7 32.0 1.039

32 35.7 33.8 1.032

33 37.7 35.6 1.026

34 39.9 37.6 1.020

35 42.2 39.6 1.014

36 44.0 41.7 1.007

37 47.0 43.8 1.000

Definitions

• Absolute humidity – the actual actual measurement of the amount of water in a gas. (mg/L)– This is the content.

• Water vapor pressure – the pressure exerted by water in the gaseous form (mm Hg)

Definition

• Saturated - A gas containing the maximum amount of water it can possibly hold (100% humidity)

• %Relative humidity

• %Body Humidity– Where the capacity is 43.8 mg/L

%% 100Capacity

ContentRH

%@

% 10037

CCapacity

Humidity AbsoluteBH

Relative Humidity Calculations

• A gas at 26° C with an absolute humidity of 19 mg/L

%% 100Capacity

ContentRH

Relative Humidity Calculations

• A gas at 35° C with an absolute humidity of 30 mg/L

%% 100Capacity

ContentRH

Body Humidity Calculations

• Body humidity is ALWAYS measured at 43.8 mg/L & 37 ° C

• A gas with an absolute humidity of 19 mg/L

%@

% 10037

CCapacity

Humidity AbsoluteBH

Body Humidity Calculations

• A gas with an absolute humidity of 30 mg/L.

%@

% 10037

CCapacity

Humidity AbsoluteBH

Humidity Deficit

• The difference between the absolute humidity and the body humidity (43.8 mg/L @ 37° C) in mg/L is called the humidity deficithumidity deficit.

• This is the amount of humidity the tracheobronchial tree has to make up to attain 43.8 mg/L and 47 mm Hg at 37° C at the Isothermal Saturation Boundary (ISB).

• Humidity Deficit (HD) = Absolute Humidity - Body Humidity

Isothermic Saturation Boundary

normally 5 cm below carina where temp. needs to be 37° C

with a RH of 100%

37° C

RH 100%

43.8 mg/L

47 mmHg

Humidity Deficit Calculations• Body humidity = always 47 mmHg or 43.8

mg/L @ 37° C • Humidity Deficit (HD) = Absolute Humidity-

Body Humidity • Gas at 26°C with absolute humidity of 19

mg/L.

Humidity Deficit Calculations• Body humidity = always 47 mmHg or 43.8

mg/L @ 37° C • Humidity Deficit (HD) = Absolute Humidity-

Body Humidity • Gas at 35° C with absolute humidity of 30

mg/L.

AARC CPG on Humidification During Mechanical Ventilation• The AARC CPG recommends that

inspired gas be warmed to 33 + 2° C and with a minimum of 30 mg/L of water vapor.

More Practice

• Sibberson – See charts on pages 24 & 25 – Chapter 7

•Sample Problems First & Second Set•Practice Problems 1-30

Factors affecting humidity levels

•Temperature•Pressure (altitude)•Surface Area•Exposure Time

Temperature

• As temperature increases, the rate of evaporation increases and more water moves into gas as well as the gas can hold more water.

CAPACITY vs. CONTENT

A, The effect of increasing capacity without changing content, as when heating a saturated gas.

B, The effect of decreasing capacity, as when cooling a gas.

Warm gas can hold more water.

Cooling gas forms condensation.

A

B

TEMPERATURE(C)

WATER VAPOR PRESSURE

(mmHg)

WATER CONTENT(mg/L)

ATPS to BTPS Correction Factor

20 17.5 17.3 1.102

21 18.6 18.4 1.096

22 19.8 19.4 1.091

23 21.1 20.6 1.085

24 22.4 21.8 1.080

25 23.8 23.0 1.075

26 25.2 24.4 1.068

27 26.7 25.8 1.063

28 28.3 27.2 1.057

29 30.0 28.8 1.051

30 31.8 30.4 1.045

31 33.7 32.0 1.039

32 35.7 33.8 1.032

33 37.7 35.6 1.026

34 39.9 37.6 1.020

35 42.2 39.6 1.014

36 44.0 41.7 1.007

37 47.0 43.8 1.000

Gases leaving a standard heated humidifier are cooled en route to the patient. Although the gas remains saturated (100% relative humidity [RH]), cooling reduces its water

vapor capacity and condensation forms.

Pressure

• As pressure increases (decreases in altitude), rate of evaporation decreases.

• This is why water boils (evaporates) at a lower temperature as you rise in altitude.– But also why cooking time is longer!

Cooking = Temperature x Time

LOCATION BAROMETRIC PRESSURE

BOILING POINT OF WATER

MICHIGAN 750 mm Hg 100° C

DENVER 640 mm Hg 95° C (increase cooking time – not as hot when boiling)

MOUNT EVEREST

235 mm Hg 70° C(increase cooking time)

Surface Area

• As you increase surface area (such as an increase in number and reduction in size of bubbles), the rate of evaporation will increase.

Lots of tiny bubbles increase surface area

Exposure Time

• An increase in exposure time means there is more time for evaporation to occur and means an increase in evaporation rate.

• A close monitoring of water level in the humidifier is important.

Keep water levels high for increased exposure time

Adverse effects of poor humidity

• Decreased ciliary motility• Airway irritation• Increased mucus production• Thickening of secretions• Inspissated secretions (mucus

plugging)• Destruction of airway epithelium• Atelectasis

Critical Points

• Every liquid has a temperature, above which, the kinetic activity is too great to keep the molecules at the surface from breaking free.– This is the critical temperature.

• The pressure at which equilibrium between the liquid and gaseous phases at the critical temperature is known as the critical pressure.

• Together they are known as the critical point of a substance.

Importance of Critical Point

• This is the point at which a substance can no longer be held in the liquid phase, and conversion to a gas occurs.

• In order to liquefy a gas (like oxygen) you have to two choices: – Cool it to below its boiling point (-183°

C or -297° F) – or –– Cool it to its critical point (-118.8° C or -

181° F and 49.7 atmospheres)•The more you cool it, the less

pressure is needed.

Storage of Oxygen as a Liquid

• Bulk oxygen systems store oxygen as a gas and allow the temperature to slowly rise resulting in gaseous oxygen to escape.

• For portable liquid systems, the amount of oxygen in the cylinder must be determined by weight.– 1 L of liquid oxygen weighs 2.5 pounds and

produces 860 L of gaseous oxygen when allowed to warm and expand.

– Once you determine the amount of gas in Liters, you can determine the duration of the cylinder by dividing by the gas flow rate.

Liquid Oxygen Systems

Method to Determine Liquid Oxygen System Duration

• You have a patient using a liquid oxygen cylinder who is planning to go Christmas shopping. She reports that her cylinder weighs 5 pounds and she has it connected to a nasal cannula running at 2 L/min. How long will the cylinder last?

Duration of Gaseous Cylinder

• Whole lot easier!– So long as you know

the cylinder factor…For oxygen:•E: 0.28•H: 3.14

Method to Determine Liquid Oxygen System Duration

• You have a patient using a liquid oxygen cylinder who is planning to go Christmas shopping. She reports that her E cylinder has 1,500 psig in it and she has it connected to a nasal cannula running at 2 L/min. How long will the cylinder last?

Practice Problems

• Sibberson– 2nd Set – Page 37– 3rd Set – Page 40 – 4th Set – Page 41

– Practice Exercises – Pages 41 – 45