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BASIC PRINCIPLES OF HEAT & COLD

BASIC PRINCIPLES OF HEAT & COLD. How the Body Produces Heat. All food & drinks contain Calories A Calorie is the heat value of food Calories in the body are converted to energy & stored, this conversion process produces heat, which generates our body temp.

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BASIC PRINCIPLES OF HEAT & COLD

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  1. BASIC PRINCIPLES OF HEAT & COLD

  2. How the Body Produces Heat • All food & drinks contain Calories • A Calorie is the heat value of food • Calories in the body are converted to energy & stored, this conversion process produces heat, which generates our body temp. • Excess Calories are stored as fat cells • Average calorie intake is approx. 2000

  3. Calories & British Thermal Units (BTU) • One calorie is amount of heat required to raise 1 kilogram of water 1 degree C • 252 calories equals 1 BTU • 1 BTU will raise the temp of 1 lb of water 1 degree F Example: 1 lb H2O heated from 75 to 76 degrees, 1 BTU of heat energy absorbed into the H2O

  4. Three Ways the Body Removes Heat • Convection – Heat flows from a hot surface to a surface (or air) with less heat • Radiation – Heat flows from a heat source to an object, does not heat the air • Evaporation – as moisture vaporizes, it removes heat from the surface, lowering its temp.

  5. Factors That Effect Body Comfort • Temperature • Humidity • Air Movement

  6. Temperature • Cool air increases rate of convection, warm air slows it down • Cool air lowers temp of surrounding surfaces, increasing heat radiation • Warm air raises temp of surrounding surfaces, decreasing radiation • Cool air increases rate of evaporation, warm air slow it down • Evaporation rate dependant on humidity level of surrounding air & air movement

  7. Relative Humidity (RH) • 50% RH – air contains half of moisture it is capable of holding • Low RH (dry) readily absorbs moisture • High RH(Moist) slow down evaporation • Human comfort level – 72 – 80 degrees, 35 – 55% humidity

  8. Other Factors • Heat Index – Measurement of discomfort when heat & humidity combine • Dew Point – Is the amount of moisture in the air at a given temperature • Wind Chill – Measurement of discomfort when cold & wind combined • Condensation – Water vapor returned to its liquid state

  9. Air Movement • Evaporation increases – moisture carried away faster • Convection increases as layer of warm air around body is moved away • Radiation increases as heat on body surface is removed

  10. Heat & Cold • Heat – Energy of molecules in motion, sensation of warmth or hotness • Cold – Feeling of no warmth, removal of an objects original heat • Laws of heat & Cold: (Heat is present in all matter) • Sensible heat – any heat that can be felt & measured ie. Heat to cook • Latent heat – heat required to cause a change in state, can not be measured • Water boils at 212 degrees at sea level (14.7psi)

  11. Heat & Cold • Specific Heat – Amount of heat require to raise the temperature of solids, liquids, or gases • Heat Flow – Movement of heat from an object of higher temp to one of lower temp

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