HEAT TRANSFERHEAT TRANSFERSC Standard 6-5.5SC Standard 6-5.5

Tuesday, January 4, 2011Tuesday, January 4, 2011

Complete plannerComplete planner

Get out a sheet of paper and entitle HEAT Get out a sheet of paper and entitle HEAT TRANSFER NOTES…complete header & TRANSFER NOTES…complete header & Entry # 10Entry # 10

Copy TABLE on WHITEBOARDCopy TABLE on WHITEBOARD

RADIATIONRADIATION

- thermal energy that is transferred in the form of - thermal energy that is transferred in the form of (electromagnetic) rays or waves and can (electromagnetic) rays or waves and can occur in solids, liquids, or gases. occur in solids, liquids, or gases.

Radiation (cont.)Radiation (cont.)

All objects emit radiation, but hot objects All objects emit radiation, but hot objects emit more than cool objects. The hotter emit more than cool objects. The hotter the object, the more radiation it emits. the object, the more radiation it emits.

Radiation (cont.)Radiation (cont.)

There is NO TOUCHING of the object, you There is NO TOUCHING of the object, you can feel the thermal energy without can feel the thermal energy without touching it. (emit means gives off)touching it. (emit means gives off)

example: energy from the sun by rays or example: energy from the sun by rays or heat from a fire.heat from a fire.

CONDUCTIONCONDUCTION

-the direct transfer of thermal energy that -the direct transfer of thermal energy that occurs when molecules bump into one occurs when molecules bump into one another when two substances are another when two substances are touching. When fast moving molecules touching. When fast moving molecules (warmer object) bump into slower moving (warmer object) bump into slower moving molecules (cooler object) it transfers molecules (cooler object) it transfers some of it’s energy..some of it’s energy..

Conduction (cont.)Conduction (cont.)

The closer together the molecules in a The closer together the molecules in a substance are, the more effectively they substance are, the more effectively they can conduct heat. can conduct heat.

Conduction (cont.)Conduction (cont.)

It works well in solids such as metals where the It works well in solids such as metals where the molecules are closer together (because they molecules are closer together (because they only have to move a short distance to bump into only have to move a short distance to bump into each other), but not as well in gases or liquids. each other), but not as well in gases or liquids. Thermal energy ALWAYS travels from HOT to Thermal energy ALWAYS travels from HOT to COLD!COLD!

example: hot sand/pavement transferring to your example: hot sand/pavement transferring to your feet when you walk on it, or ice melting in your feet when you walk on it, or ice melting in your handhand

CONVECTIONCONVECTION

the transfer of thermal energy by the flow the transfer of thermal energy by the flow of gases or liquids. In gas and liquids, of gases or liquids. In gas and liquids, molecules can move much more easily molecules can move much more easily than they can in a solid, as a result, the than they can in a solid, as a result, the more energetic molecules can travel more energetic molecules can travel from one place to another, and carry from one place to another, and carry their energy along with them. their energy along with them.

Convection (cont.)Convection (cont.)

example: pot of water boiling (because the example: pot of water boiling (because the molecules are farther apart in the warm molecules are farther apart in the warm water, this water is less dense than the water, this water is less dense than the cooler water. As a result, the warm water cooler water. As a result, the warm water rises and is replaced at the bottom of the rises and is replaced at the bottom of the pot by cooler water.) or water in a bath pot by cooler water.) or water in a bath tub, preheating an oven.tub, preheating an oven.

Heat Transfer QUIZHeat Transfer QUIZ

1.1. Microwaving methodMicrowaving method2.2. Warmth from a fireWarmth from a fire3.3. Accidentally touching a hot light bulbAccidentally touching a hot light bulb4.4. Sunbathing on the beachSunbathing on the beach5.5. Noodles boiling in a potNoodles boiling in a pot6.6. ““Nuking” your hot chocolateNuking” your hot chocolate7.7. Burning your finger as you remove it from the Burning your finger as you remove it from the

microwavemicrowave8.8. Air popping methodAir popping method9.9. A pot sitting on a HOT stovetop eyeA pot sitting on a HOT stovetop eye10.10. Jiffy Pop methodJiffy Pop method

Condensed Heat Transfer NotesCondensed Heat Transfer Notes

RADIATIONRADIATION

- electromagnetic rays or waves- electromagnetic rays or waves

- solids, liquids or gases- solids, liquids or gases

- EMIT (to give off)- EMIT (to give off)

- NO TOUCHING- NO TOUCHING

EX: sun’s rays, campfire, microwave EX: sun’s rays, campfire, microwave popcorn methodpopcorn method

Condensed Notes (cont.)Condensed Notes (cont.)

CONDUCTIONCONDUCTION - direct transfer of heat- direct transfer of heat - TOUCHING or direct contact- TOUCHING or direct contact - faster molecules = warmer temperatures- faster molecules = warmer temperatures slower molecules = cooler temperaturesslower molecules = cooler temperatures - TRANSFERS HOT TO COLD- TRANSFERS HOT TO COLD - Solids = more molecules = best conductors- Solids = more molecules = best conductors EX: walking across hot pavement / sandEX: walking across hot pavement / sand touching a HOT stovetop eyetouching a HOT stovetop eye Jiffy Pop popcornJiffy Pop popcorn

Condensed Notes (cont.)Condensed Notes (cont.)

CONVECTIONCONVECTION - gases & liquids- gases & liquids - MOVEMENT to transfer heat- MOVEMENT to transfer heat - warm air rises, cool air is lower- warm air rises, cool air is lower EX: preheating an ovenEX: preheating an oven cooking noodles in boiling watercooking noodles in boiling water Air Pop popcorn Air Pop popcorn