Controlling Heat Controlling Heat TransferTransfer

Chapter Six REVIEWChapter Six REVIEW

Absorbing and Losing Absorbing and Losing HeatHeat Heat Absorption- refers to the rate Heat Absorption- refers to the rate

at which materials absorb heat. at which materials absorb heat. Every material absorbs heat at a Every material absorbs heat at a particular rate. particular rate.

Which will absorb more heat: a black Which will absorb more heat: a black sweater or a white sweater? Why?sweater or a white sweater? Why?

Specific Heat Capacity Specific Heat Capacity (SHC)(SHC) DefinitionDefinition: a measure of the ability : a measure of the ability

to absorb or lose heat. (J/gto absorb or lose heat. (J/g• + C)• + C) SHC of waterSHC of water: 4.19 : 4.19 J/gJ/g• + C• + C

– So, one gram of water absorbs 4.19 So, one gram of water absorbs 4.19 Joules to raise the temp. by 1 degreeJoules to raise the temp. by 1 degree

– One gram of water loses 4.19 Joules to One gram of water loses 4.19 Joules to lower the temp. by 1 degreelower the temp. by 1 degree

SHC of sandSHC of sand: 0.66 J/g: 0.66 J/g• + C. Compare • + C. Compare this to water’s SHC. Which will heat this to water’s SHC. Which will heat up faster?up faster?– Sand. Since it has a lower heat Sand. Since it has a lower heat

capacity it will warm up quicker. Think capacity it will warm up quicker. Think about being on a beach. The water is about being on a beach. The water is much cooler than that of the sand, much cooler than that of the sand, because it takes longer to heat up because it takes longer to heat up water.water.

Look at the table on page 109….tell Look at the table on page 109….tell me the heat capacity of:me the heat capacity of:– AirAir

0.995 0.995 J/gJ/g• + C• + C

OceansOceans

You remember from chapter five You remember from chapter five that oceans heat up slower than that oceans heat up slower than the land…with the knowledge of the land…with the knowledge of specific heat capacity tell me why?specific heat capacity tell me why?– Water has a higher SHC than the land Water has a higher SHC than the land

therefore the land is going to heat up therefore the land is going to heat up faster while the water will heat up faster while the water will heat up slower…storing lots of thermal slower…storing lots of thermal energy which will be released at energy which will be released at night with the warm night sea night with the warm night sea breeze.breeze.

Keeping Heat at HomeKeeping Heat at Home

Insulation- any type of material that Insulation- any type of material that will slow the heat transfer. will slow the heat transfer. – Home insulation:Home insulation:

Winter: keeps the heat in and the cold outWinter: keeps the heat in and the cold out Summer: keeps the cold in and the heat out.Summer: keeps the cold in and the heat out.

R-ValueR-Value

Definition: measure of how well an Definition: measure of how well an insulating material slows the heat insulating material slows the heat transfer. transfer.

High R-values = good insulatorsHigh R-values = good insulators Low R-values = poor insulatorsLow R-values = poor insulators Just like math, you can put Just like math, you can put

insulators together and add their insulators together and add their R-values…this would make a R-values…this would make a Total Total R-value.R-value.

ExampleExample You make a home with 25 mm of You make a home with 25 mm of

soild wood, 25 mm of fibreglass, soild wood, 25 mm of fibreglass, and 25 mm of clay brick. What is and 25 mm of clay brick. What is the R-value of your insulation? the R-value of your insulation? (Look at the table on page 111 to (Look at the table on page 111 to find the separate R-values).find the separate R-values).– WoodWood R-value: 1.25 R-value: 1.25– FibreglassFibreglass R-value: 4.25 R-value: 4.25– Clay BrickClay Brick R-value: 0.11 R-value: 0.11

TOTAL R-value = 5.61TOTAL R-value = 5.61

Wall CavityWall Cavity

DefinitionDefinition: This is the space : This is the space between the inside wall and the between the inside wall and the outside wall of a house. Usually outside wall of a house. Usually this space is filled with insulation this space is filled with insulation which has pockets of still air (air which has pockets of still air (air that does not move). that does not move).

Windows and DoorsWindows and Doors

Old: “Old: “storm windowsstorm windows” and “” and “storm storm doorsdoors”…they are double ”…they are double windows/doors to keep heat in…windows/doors to keep heat in…as heat likes to sneak out as heat likes to sneak out between the panes of the windowbetween the panes of the window

New: “New: “double glazingdouble glazing”…this is a ”…this is a double pane of glass with a space double pane of glass with a space in between filled with argon gas. in between filled with argon gas. This slows heat transfer. This slows heat transfer.

Controlling Heat Controlling Heat TransferTransfer Pizza delivery (box and insulated Pizza delivery (box and insulated

envelope)envelope) Vacuum bottleVacuum bottle: container that slows : container that slows

conduction, convection, and radiation.conduction, convection, and radiation.– Double glass jarDouble glass jar– Some air is removed from between jarsSome air is removed from between jars– Have a silver reflective coatingHave a silver reflective coating– Rubber or plastic keeps glass away from Rubber or plastic keeps glass away from

outer caseouter case– Cap insulated.Cap insulated.

What is insulated?What is insulated?

StovesStoves RefrigeratorsRefrigerators FreezersFreezers DishwashersDishwashers PotsPots the plastic or wooden handle the plastic or wooden handle

allows you to pick them up.allows you to pick them up. ToastersToasters encased in plastic encased in plastic

USE OVEN MITTSUSE OVEN MITTS

Why do we use oven mitts?Why do we use oven mitts? Duh, right? Duh, right? We do not want to burn ourselves We do not want to burn ourselves

when we take hot things out of when we take hot things out of the oven.the oven.

Keeping Yourself Keeping Yourself WarmWarm How do we keep ourselves warm How do we keep ourselves warm

during the winters?during the winters?– We layer up. Just like in insulation.We layer up. Just like in insulation.– Down- when it’s fluffed it holds air in Down- when it’s fluffed it holds air in

placeplace– Layer up when you are going to be Layer up when you are going to be

outside….when you start sweat remove a outside….when you start sweat remove a layer as it will make you colder. This will layer as it will make you colder. This will keep the heat transfer constant, thus keep the heat transfer constant, thus keeping your body at equilibrium.keeping your body at equilibrium.

InuitInuit

Cold days: inner suit is fur next to Cold days: inner suit is fur next to the body which soaks up the body the body which soaks up the body moisture and transfers it to through moisture and transfers it to through the leather. Outer suit is worn with the leather. Outer suit is worn with the fur to the outside. The fur the fur to the outside. The fur around the face warms the air so around the face warms the air so that the air breathed in is warmed. that the air breathed in is warmed. Condensation from the breathing Condensation from the breathing will not cause ice because of the will not cause ice because of the fur. fur.

Hot AreasHot Areas

They wear a lot of clothes to They wear a lot of clothes to minimize heat transfer. minimize heat transfer.

Covering…protects skin from the Covering…protects skin from the sun’s rayssun’s rays

Light coloured clothing…absorbs Light coloured clothing…absorbs less heatless heat

FirefightersFirefighters

Suits contain flame retardant Suits contain flame retardant materials which only chars. materials which only chars.

Inner material absorbs body Inner material absorbs body moisture, keeping firefighter cool.moisture, keeping firefighter cool.

Firefighters can still suffer heat Firefighters can still suffer heat stroke.stroke.

All firefighting gear All firefighting gear mustmust pass pass safety inspection and testing!safety inspection and testing!

DiversDivers

Tight suits prevent cold water Tight suits prevent cold water from cooling the skin by from cooling the skin by conduction (what’s conduction?)conduction (what’s conduction?)

Suits are made of neoprene with Suits are made of neoprene with bubbles of nitrogen trapped in the bubbles of nitrogen trapped in the fabric (keeps body heat inside)fabric (keeps body heat inside)

They have hoods for the same They have hoods for the same reason.reason.