Refrigeration & Air Conditioning Technology, 8e - 35

35

Unit 2 Matter and Energy
Figure 2.10 An electric heat airstream.

ELECTRIC HEAT COILS
AIR
(758F)

AIR
(858F)

BLOWER

Figure 2.12 (A) If two substances of different temperatures are moved
close to each other, heat from the substance with the higher temperature will flow to the one with the lower temperature. (B) Heat energy is
still available at these low temperatures and will transfer from the warmer
substance to the colder substance.

758F

1008F
HEAT
FLOW

An example of indirect conversion is a fossil-fuel power
plant. Gas may be used in the power plant to produce the
steam that turns a steam turbine generator to produce
electricity. The electricity is then distributed by the local
power company and consumed locally as electric heat,
Figure 2.10.

2.8 CONSERVATION OF ENERGY
The preceding sections in this unit lead to the law of
conservation of energy. This law states that energy is neither
created nor destroyed but can be converted from one form to
another. It can thus be said that all energy can be accounted for.
Most of the energy we use is a result of the sun's support of plant growth for millions of years. Fossil fuels come
from decayed vegetable and animal matter covered by
earth and rock during changes in the earth's surface. This
decayed matter is in various states, such as gas, oil, or coal,
depending on the conditions it was subjected to in the past,
Figure 2.11. The energy stored in fossil fuels is called chemical energy because a chemical reaction is needed to release
the energy.

Figure 2.11 Gas and oil deposits settle into depressions.
EARTH'S
EARTH
S SURFACE

SOIL
ROCK
GRAVEL SAND ROCK
ROCK
GAS
GAS
OIL
OIL
OI

(A)

22008F

23508F
HEAT
FLOW

(B)

2.9 ENERGY CONTAINED
IN HEAT
Temperature is a measure of the degree of heat or the heat
intensity, but not necessarily the amount of heat. Heat is a
form of energy because of the motion of molecules. To be
specific, heat is thermal energy. If two substances of different temperatures are moved close to each other, heat energy
from the substance with the higher temperature will flow to
the one with the lower temperature, Figure 2.12(A). Because
molecular motion does not stop until 2460°F, energy is still
available in a substance even at very low temperatures. In
Figure  2.12(B) a substance at 2200°F is placed next to a
substance at 2350°F. As we discussed earlier, heat travels
from hot to cold, so heat travels from the warmer 2200°F
substance to the colder 2350°F substance.
Most of the heat energy used in homes and industry is provided from fossil fuels, but some comes from electrical energy.
As shown in Figure 2.10, electron flow in high-resistance wire
causes the wire to become hot, thus heating the air. A moving
airstream is then passed over the heated wire, allowing heat
to be transferred to the air by conduction and moved to the
heated space by forced convection (the blower).

2.10 ENERGY IN MAGNETISM
Magnetism is another method of converting electron flow
to usable energy. Electron flow is used to generate magnetic
fields that are, in turn, used to turn motors. The motors turn



Refrigeration & Air Conditioning Technology, 8e

Table of Contents for the Digital Edition of Refrigeration & Air Conditioning Technology, 8e

Contents
Refrigeration & Air Conditioning Technology, 8e - Cover1
Refrigeration & Air Conditioning Technology, 8e - Cover2
Refrigeration & Air Conditioning Technology, 8e - i
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Refrigeration & Air Conditioning Technology, 8e - Contents
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