Basic principles of heat cold
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BASIC PRINCIPLES OF HEAT & COLD PowerPoint PPT Presentation


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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.

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BASIC PRINCIPLES OF HEAT & COLD

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Basic principles of heat cold

BASIC PRINCIPLES OF HEAT & COLD


How the body produces heat

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

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

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

Factors That Effect Body Comfort

  • Temperature

  • Humidity

  • Air Movement


Temperature

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

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

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

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 & 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 cold1

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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