BASIC PRINCIPLES OF HEAT &amp; COLD

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

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### 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.
• Excess Calories are stored as fat cells
• Average calorie intake is approx. 2000
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

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