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RSPT 1060

RSPT 1060. Module C-7 THERMODYNAMICS 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

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RSPT 1060

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  1. RSPT 1060 Module C-7 THERMODYNAMICS and HUMIDITY

  2. 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.

  3. 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.

  4. 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.

  5. 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/LDifferentiate between the following: • Absolute humidity • Relative humidity • Humidity deficit

  6. 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.

  7. 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

  8. 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

  9. Temperature • Definitions: • One method of quantifying matter. • How cold or hot an object is. • The amount of Kinetic activity.

  10. 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

  11. 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.

  12. 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.

  13. Temperatures to Know

  14. Figure 6-2, page 95

  15. 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

  16. °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 °K - °C - °F Convert K into C then into F °F - °C - °K Convert F into C then into K FORMULAS FOR TEMPERATURE CONVERSION

  17. Using the formula: 5°F = 9°C + 160 212 °F = __________ °C  

  18. 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?

  19. 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.

  20. 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

  21. 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

  22. “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.

  23. 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

  24. Conduction • Transfer of heat by direct contact • Solid objects like metal conduct heat away quickly • They have a high thermal conductivity and often feel cool to the touch as they remove heat from your hand.

  25. Convection • Transfer of heat by mixing of fluid molecules • Gases or liquids mixing in currents or forced air heating • Convection oven

  26. Radiation • Transfer of heat to a cooler, distant object. • No direct physical contact • Conventional oven

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

  28. 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).

  29. Humidity

  30. 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)

  31. Definitions • Absolute humidity – the 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)

  32. 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

  33. Relative Humidity Calculations • A gas at 26° C with an absolute humidity of 19 mg/L

  34. Relative Humidity Calculations • A gas at 35° C with an absolute humidity of 30 mg/L

  35. 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

  36. Body Humidity Calculations • A gas with an absolute humidity of 30 mg/L.

  37. 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 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

  38. Isothermic Saturation Boundary normally 5 cm below carina where temp. needs to be 37° Cwith a RH of 100% 37° C RH 100% 43.8 mg/L 47 mmHg

  39. 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.

  40. 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.

  41. 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.

  42. More Practice • Sibberson • See charts on pages 24 & 25 • Chapter 7 • Sample Problems First & Second Set • Practice Problems 1-30

  43. Factors affecting humidity levels • Temperature • Pressure(altitude) • Surface Area • Exposure Time

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

  45. 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. A Warm gas can hold more water. B Cooling gas forms condensation.

  46. 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.

  47. 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!

  48. Cooking = Temperature x Time

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