Heat Transfer

Conduction Heat transfer via particle collision. via = “by way of” particle = electron normally occurs between solids that are in direct contact with each other Question for thought: Why do pots and pans have a wooden or plastic handle?

Conduction Good Conductors: solids with loosely held electron ex) metals (silver is the best conductor) Poor Conductors: (AKA: Insulators) solids with firmly held electron slows down conduction in either direction, but does not stop conduction. ex) wood, air (thermal underwear)

Convection Heat transfer via movements of fluids. expansion and cooling occurs between liquids or gases denser (cooler) fluids go to the bottom less dense (warmer) fluids move to the top Question for thought: Why does air become warm when pumping up a bike tire? speed up air molecules = temp increase

Convection atmospheric convection produces winds Lakeshore winds: Daytime: ground warms faster than water leads to sea breeze from water. Night: ground cools faster than water (warmer) leads to breeze out to sea. land land

Gas Relationships Temperature increase  volume increase Pressure increase  volume decrease Density increase  volume decrease Remember when an object is heated, temperature goes ___ so molecules move _____. The results is a _______ volume otherwise known as ______ ________. up faster larger thermal expansion

Radiation Heat transfer via radiant energy. Energy travels from the Sun to the Earth with no material in between. Radiant energy is electromagnetic energy (or electromagnetic waves).

Radiation Frequency is directly related to temp. Frequency is how often a wave occurs. High frequency = short waves = high temp Low frequency = long waves = low temp

Radiation All materials emit radiation…but they also absorb radiation. Good emitters are good absorbers Black in color Feels warmer Poor emitters are poor absorbers White in color Feels cooler At constant temp emission = absorption

Radiation Terrestrial radiation Energy emitted by the Earth Infrared or heat radiation Source: radioactive decay in the Earth

Radiation Since radiation is a wave, radiation has wave properties Reflection Not all radiant energy will reflect some will absorb.

What heat transfer process is used? Boiling water on a stove top conduction Heating your house convection Green house effect radiation Lake turnover

What heat transfer process is used? Heat lamp or camp fire for warmth radiation Wind convection Sunlight heating the Earth Electric blanket conduction

Is energy transfer a perfect process? No Energy conversion is not 100% efficient. Most energy is lost in the form of heat.