# 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

### 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.

• 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