Konversi Temperatur
Thermal Expansion
As its temperature increases, its volume almost always increases.
This phenomenon, known as thermal expansion, has an important
role in numerous engineering applications.
Thermal Expansion
Thermal-expansion joints are used
to separate sections of roadways
on bridges.
Without these joints, the surfaces
would buckle due to thermal
expansion on very hot days or crack
due to contraction on very cold days.
Thermal Expansion
Thermal expansion: The extreme
temperature of a July day in Asbury
Park, NJ, caused these railroad
tracks to buckle and derail the
train in the distance. (AP/Wide
World Photos)
Volume Expansion
V  V0T
∆V = change in volume (m3)
V0 = initial volume (m3)
∆T = change in temperature (oC)
 = coeficient of volume expansion (1/oC)
Liquids generally increase in volume with increasing temperature
Thermal Expansion
Thermal Expansion
A steel railroad track has a length
of 30.000 m when the temperature
is 0.0°C. (a) What is its length
when the temperature is 40.0°C?
L  L0 T
= [11x10-6(0C)-1](30.000 m)(40.0C)
= 0.013 m
If the track is 30.000 m long at 0.0°C,
its length at 40.0°C is 30.013 m.
Additional Question..
(b) Suppose that the ends of the rail
are rigidly clamped at 0.0°C so
that expansion is prevented. What
is the thermal stress set up in the
rail if its temperature is raised to
40.0°C?
F
L
Y
Tensile stress =
A
Li
Because Y for steel is 20x1010 N/m2,
Tensile stress is 8.7x107 N/m2
If the rail has a crossectional-area of
30.0 cm2, the force compression in the
rails 2.6x105 N
Contoh soal
1. Sebuah logam bertambah panjang 1.5 mm saat
suhu bertambah 2 kali semula. Besar
pertambahan panjang yang terjadi jika suhu
bertambah 3 kali semula adalah …. Mm
2. Sebatang balok panjang 10 m ditempatkan pada
temperatur mula-mula 10oC. Berapa gaya
kompresi ketika temperatur mencapai 40oC
ketika daerah kontak antara setiap balok adalah
0.2 m2? (Modulus young balok = 20 x 109 N/m2)
Effect of expansion
BIMETAL = DUA LOGAM
APLIKASI BIMETAL
The Unusual Behavior of Water
How the density of water at atmospheric pressure changes with
temperature. The inset at the right shows that the maximum density of
water occurs at 4°C.
HEAT
Heat is defined as the transfer of energy across the boundary
of a system due to a temperature difference between the
system and its surroundings.
Conduction
Conduction is the transfer of heat within a substance, molecule by molecule. If
you put one end of a metal rod over a fire, that end will absorb the energy from
the flame. The molecules at this end of the rod will gain energy and begin to
vibrate faster. As they do their temperature increases and they begin to bump into
the molecules next to them. The heat is being transfered from the warm end to
the cold end.
Convection
Convection is heat transfer by the mass movement of a
fluid in the vertical (up/down) direction. This type of heat
transfer takes place in liquids and gases. This occurs
naturally in our atmosphere.
Advection
Advection is the transfer of heat in the horizontal (north/east/south/
west) direction. In meteorology, the wind transports heat by
advection. This happens all the time on Earth, heat is transported in
many ways. For example, wind blowing over a body of water will
pick up evaporated water molecules and carry them elsewhere, when
the air with these water molecules cools, the water will condense
Radiation
Radiation allows heat to be transfered through wave energy. These
waves are called Electromagnetic Waves, because the energy travels
in a combination of electric and magnetic waves. This energy is
released when these waves are absorbed by an object. For example,
energy traveling from the sun to your skin, you can feel your skin
getting warmer as energy is absorbed.
Three kinds
of
heat
transfer
UNITY OF HEAT
calorie (cal) is defined as the amount of energy transfer
necessary to raise the temperature of 1 g of water
from 14.5°C to 15.5°C.
1 cal = 4.186 J
1 Cal = 4.186 kJ = 4186 J
Heat transfer
When energy is added to a substance and no work is done, the temperature
of the substance usually rises.
For example, the quantity of energy required to raise the temperature of 1 kg of
water by 1°C is 4186 J, but the quantity of energy required to raise the
temperature of 1 kg of copper by 1°C is only 387 J.
From this de.nition, we can express the energy Q transferred by heat between a
sample of mass m of a material and its surroundings for a temperature change T as
Q  mcT
Q = Energy (J)
m = massa (kg)
c = specific heat (J/kg.oC)
∆T = Temperature (oC)
Specific heats
Latent heats
Different materials store different
amounts of heat energy.
90OC
1 kg of Aluminum
90OC
1 kg of Gold
20OC
20OC
By the time aluminum heats up to 90OC it will have
stored 7 times more calories of heat than the gold did.
Black Principle
To understand the role of latent heat in phase changes, consider the energy required to
convert a 1.00-g block of ice at 30.0°C to steam at 120.0°C. Figue indicates the
experimental results obtained when energy is gradually added to the ice. Let us
examine each portion of the red curve.
Heat Transfer
Part A. On this portion of the curve, the temperature of the ice changes from
30.0°C to 0.0°C. Because the specific heat of ice is 2090 J/kg °C, we can
calculate the amount of energy added by using equation :
QA = miciT = (1.00x 10-3 kg)(2090 J/kg. °C)(30.0C) = 62.7 J
Part B. When the temperature of the ice reaches 0.0°C, the ice –water mixture
remains at this temperature—even though energy is being added—until all the ice
melts. The energy required to melt 1.00 g of ice at 0.0°C is
QB = mLf = (1.00 x 10-3 kg)(3.33 x 105 J/kg) = 333 J
Thus, we have moved to the 396 J = ( 62.7 J + 333 J) mark on the energy axis.
Azas Black
Heat Transfer
Part C. Between 0.0°C and 100.0°C, nothing surprising happens. No phase
change occurs, and so all energy added to the water is used to increase its
temperature. The amount of energy necessary to increase the temperature from
0.0°C to 100.0°C is
QC= mwcw T = (1.00x 10-3 kg)(4.19x 103 J/kg. °C)(100°C) = 419 J
Part D. At 100.0°C, another phase change occurs as the water changes from
water at 100.0°C to steam at 100.0°C. Similar to the ice –water mixture in part
B, the water–steam mixture remains at 100.0°C—even though energy is being
added— until all of the liquid has been converted to steam. The energy required
to convert 1.00 g of water to steam at 100.0°C is
QD = mLv = (1.00 x 10-3 kg)(2.26 x 106 J/kg) = 2.26 x 103 J
Azas Black
Heat Transfer
Part E. On this portion of the curve, as in parts A and C, no phase change occurs;
thus, all energy added is used to increase the temperature of the steam. The
energy that must be added to raise the temperature of the steam from 100.0°C to
120.0°C is
QE = mscs T = (1.00x 10-3 kg)(2.01x 103 J/kg. °C)(20°C) = 40.2 J
The total amount of energy that must be added to change 1 g of ice at 30.0°C
to steam at 120.0°C is the sum of the results from all five parts of the curve,
which is 3.11x103 J. Conversely, to cool 1 g of steam at 120.0°C to ice at
30.0°C, we must remove 3.11x103 J of energy.
QTotal = QA + QB + QC + QD + QE = 3.11x103 J
Conversely, to cool 1 g of steam at 120.0°C to ice at 30.0°C, we must
remove 3.11x103 J of energy.
Geothermal
Heat flows outward from Earth's interior. The crust insulates us from
Earth's interior heat. The mantle is semi-molten, the outer core is liquid
and the inner core is solid.
Geothermal
The deeper you go, the hotter it gets (in Celsius and kilometers).
Geothermal
Geothermal
Earth's crust is broken into huge plates that move apart or push together
at about the rate our fingernails grow. Convection of semi-molten rock in
the upper mantle helps drive plate tectonics.
Geothermal
New crust forms along mid-ocean spreading centers and continental rift
zones. When plates meet, one can slide beneath another. Plumes of magma
rise from the edges of sinking plates.
Geothermal
Many areas have accessible geothermal resources, especially countries along the
circum-Pacific "Ring of Fire," spreading centers, continental rift zones and
other hot spots.
Geothermal
Thinned or fractured crust allows magma to rise to the surface as lava. Most
magma doesn't reach the surface but heats large regions of underground rock.
Geothermal
Rainwater can seep down faults and fractured rocks for miles. After being
heated, it can return to the surface as steam or hot water.
Geothermal
When hot water and steam reach the surface, they can form fumaroles,
hot springs, mud pots and other interesting phenomena.
Geothermal
When the rising hot water and steam is trapped in permeable and porous
rocks under a layer of impermeable rock, it can form a geothermal reservoir.
Geothermal
If a reservoir is discovered, characteristics of the well and the
reservoir are tested by flowing the well.
Geothermal
This photograph shows a vertical geothermal well test
Geothermal
Geothermal
Natural steam from the production wells power the turbine generator. The
steam is condensed by evaporation in the cooling tower and pumped down an
injection well to sustain production.
Geothermal
Like all steam turbine generators, the force of steam is used to spin the trubine
blades which spin the generator, prducing electricity. But with geothermal
energy, no fuels are burned.
Geothermal
Turbine blades inside a geothermal turbine generator.
Geothermal
Turbine blades inside a geothermal turbine generator.
Different materials store different
amounts of heat energy.
90OC
1 kg of Aluminum
90OC
1 kg of Gold
20OC
20OC
By the time aluminum heats up to 90OC it will have
stored 7 times more calories of heat than the gold did.