Heat and Heat Technology

Chapter 10

                                           

                  

How do you get your body warmer?

Temperature

• Temperature: Measures averagekinetic energy; the more kinetic energy the warmer the object

Thermometer•Instrument used to measure temperature•Usually filled with alcohol or mercury•Degree is the unit used to measure temperature

Temperature Scales• Fahrenheit scale commonly used

in the U.S.• Freezing is 32° and boiling is 212°

• Celsius scale is used in science• Freezing is 0° and boiling is 100°

• Kelvin scale is based upon absolute zero, no negative temperatures

• Freezing 273 K and boiling 373 K• Scientist use this scale because 0 K

is the lowest temperature possible, it has never been reached (theoretical)

Temperature Conversions

C is Celsius F is Farenheit C = 5/9 (F-32) F = 9/5 (C+32 Let's try converting 68 degrees Farenheit to celsius 5/9(68-32)Step 1: 68 less 32 is 36Step 2: 5 divided by 9 is 0.5555555555555Step 3: multiply the repeating decimal by 36Step 4: your solution is 20Now, convert 20 degrees Celsius to Farenheit to check your work.9/5C +32Step 1: 9 divided by 5 is 1.8Step 2: 1.8 multiplied by 20 is 36Step 3: 36 plus 32 = 68

C to K C = K + 273

Thermal Expansion•Most substances (all phases) expand when the temperature is increased

•However; water expands as it cools from 4° C to 0° C. Ice becomes less dense than liquid water

Thermostat•Thermostat is used to change temperature of a heater•Bimetallic strip is used inside to sense the change in temperature. Two metals are joined together, each having its own rate of expansion. It coils or uncoils reaction to heat turning the electric circuit on or off

Heat•Is the energy transferred between objects that are at different temperatures

Thermal Energy•The sum of the potential energy and the kinetic energy of all the molecules in an object measured in joules

Heat Transfers: Conduction

•Heat is transferred through a substance by direct contact•Works best in solids because all the atoms are touching

Thermal conductors and thermal insulators

•Conductors- iron, aluminum, copper, and silver•Insulators- wood, plastic, rubber, and air

Convection•Takes place in liquids and gases•It is the up and down movement called convection currents•Heated material rises because it is less dense

Radiation•Heat is transferred through empty space•Ex: heat from the sun, an open fire, or heater

Specific Heat• The amount of heat required to

raise the temperature of 1 gram of a substance by 1° C, expressed as calories/gram

Water 1.00 cal/grAluminum 0.22 cal/grMercury 0.03 cal/gr

Calculating Heat Energy• Heat gained or lost = mass * T * Specific heat ( T change in temperature

either + or -)

How much energy would it take to raise the temperature of 4 grams of aluminum from 0° to 5°?

4g * 5° * 0.22 = 4.4 cal

Phase Changes•A change in phase requires heat energy but temperature does not rise until the phase change is complete

ice melts to water water vaporizes to a gas

• Heat of Fusion from a solid to a liquidFreezing point of water is 0° C and the

melting point of ice is 0°

• Heat of vaporization from a liquid to a gas

Vaporizing point of a liquid in 100° C and the condensation point of a gas

is 100° C

During a phase change there is only a change in energy not temperature

Calories

The scientific "calorie" is spelledwith a lower-case "c".

One "calorie" = 4.184 Joules---------------------------------------------The "dieter's" calorie is spelledwith an upper-case "C".

One "Calorie" = 1000 calories

Calorie is the quantity of heat required to raise the temperature of 1 gram of liquid water 1 degree Celsius1 calorie = 4.2 joules

Heating Systems• Hot water can be used to heat a

room by the heat being radiated through pipes

• Warm air heating, a furnace heats the air and it is circulated through the room

• Solar energy collectors are placed on the roof and collect the energy in water

Heat Engines• External heat engines

• Internal heat engine

• Cooling systems

Sorry…. We are at the end!!!!!!