Title: Insulators vs. Conductors
1Insulators vs. Conductors
- Conductors transfer thermal energy rapidly
(metals) - Insulators reduce the transfer of thermal energy
(wood, foam) - Insulation reduces unwanted transfer of thermal
energy
2R-value of insulating materials
Which materials are the best insulators? What is
insulating glass and how does it differ from flat
glass? How does changing the thickness of
building materials affect insulating
effectiveness?
3(No Transcript)
4Trapped air makes a good insulator
5Cooling System
- A device that transfers energy as heat out of an
object to lower its temperature. - Work must be done against heat flow to transfer
heat from inside air to outside air
62nd law of thermodynamics
- Heat flows from hot to cold
- Heat flows until thermal equilibrium is reached
Temp inside Temp outside - During the summer
- Heat flows from outside your home to inside and
does not stop unless thermal equilibrium is
reached - Refrigerator
- Heat flows from outside the refrigerator to inside
7Air conditioners and Refrigerators
8FUNCTION OF A REFRIGERATOR
Deposit unwanted Thermal Energy on the outside
Remove unwanted Thermal Energy from inside
By condensation of refrigerant
By evaporation of Refrigerant
9- Heat can be made to flow the other way only if
work is done to the system. External effort! - Example air conditioner or refrigerator
10The Function of an air conditioner
11HOW DO AIR CONDITIONERS AND REFRIGERATORS WORK?
- These appliances produce a thermal energy flow by
evaporation and condensation. - Evaporation removes thermal energy.
- Condensation releases thermal energy.
1223.8 Energy and Changes of Phase
- Applications of Phase Changes
A refrigerators cooling cycle uses the changes
of phase of the refrigeration fluid (not water).
1323.8 Energy and Changes of Phase
- Applications of Phase Changes
- Liquid is pumped into the cooling unit, where it
is forced through a tiny opening to evaporate.
1423.8 Energy and Changes of Phase
- Applications of Phase Changes
- It draws heat from the things stored in the food
compartment.
1523.8 Energy and Changes of Phase
- Applications of Phase Changes
- The gas then goes to coils located outside the
cooling unit.
1623.8 Energy and Changes of Phase
- Applications of Phase Changes
- As the gas condenses in the coils, heat is given
off.
1723.8 Energy and Changes of Phase
- Applications of Phase Changes
- The liquid returns to the cooling unit, and the
cycle continues.
18COOLING SYSTEM IS REVERSE HEAT ENGINE
With enough pressure, a gas can condense into a
liquid
MECHANICAL ENERGY IN THERMAL ENERGY OUT
19Air Conditioning and Refrigeration
- Work is done to remove heat that is entering a
house, car or refrigerator - Evaporation removes heat and condensation
releases heat (evaporation inside, condensation
outside) - Analogy Leaky boat
- Water represents heat flow
- Bailing represents removal of thermal energy
- Collecting water in bucket (evaporation of
refrigerant) - Dumping water outside boat (condensation of
refrigerant)
20Evaporation and Condensation
- Evaporation is a cooling process takes heat from
surroundings - Condensation is a warming process releases heat
into surroundings - Uses the property of gases cooling during
expansion and warming during compression - Uses the concept of reverse heat engine to
compress a gas (mechanical energy in thermal
energy out)
21The evaporation-condensation process
Blue is evaporation of refrigerant (draws heat
from inside) Red is condensation of refrigerant
(releases heat to the outside)
22(No Transcript)