Adiabatic Change and Cloud Formation
An adiabatic change is a reversible change that happens in a system
when the total amount of energy in the system stays the same. Volume and
temperature can change in an adiabatic change. The amount of heat energy
does not change. However, work is done on or done by the system.
The following web site describes adiabatic processes and lapse rate:
http://daphne.palomar.edu/jthorngren/adiabatic_processes.htm
The following web site provides illustrations of adiabatic heating and cooling.
http://www3.uakron.edu/geography/lrb/physf97/lectures/stability/sld001.htm
Make an Adiabatic Cloud Machine
An adiabatic change happens in the atmosphere as a parcel of air rises or
sinks. That parcel of are may be referred to as “the system”. When the parcel of
air is close to Earth's surface, the air is more compressed. When that same
parcel of air rises into the upper atmosphere, the air expands. This can be
demonstrated with a 2-liter soda bottle.
1.
2.
3.
4.
Obtain a clear 2-liter soda bottle.
Place some warm water into the bottle and close the cap.
Shake the bottle to create a humid atmosphere inside the bottle.
Squeeze the bottle.
Question 1: What do you think happens to the number of air molecules inside
the bottle when you squeeze it?
Question 2: What do you think happens to the distance between air molecules
inside the bottle when it is squeezed?
Question 3: What do you think happens to the air pressure inside the bottle
when you squeeze it?
Question 4: What do you think happens to the temperature inside the bottle
when you squeeze it?
Adiabatic Phase Change
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5. Remove the cap from the bottle.. Light a strip of filter paper or “touch” paper
and blow out the flames of the match (and the paper if necessary) . Caution:
Keep hair and clothing away from an open flame.
6. Allow some smoke from the paper to enter the soda bottle.
7. Put the cap back on the bottle. Squeeze the bottle hard and observe what
happens as you release the pressure. You may need to repeat the squeezing
and letting go several times before the effect of changes in pressure and volume
are observable.
8. Record your observations as you repeatedly squeeze and release the soda
bottles.
Question 5: What do you think happens to the number of air molecules inside
the bottle when you let the bottle expand?
Question 6: What do you think happens to the distance between air molecules
inside the bottle when you let the bottle expand?
Question 7: What do you think happens to the air pressure inside the bottle
when you let the bottle expand?
Question 8: What do you think happens to the temperature inside the bottle
when you let the bottle expand?
Question 9: Why would the water vapor change into condensation when the
bottle is expanded?
Question 10: What purpose do you think that the particles of smoke serve?
(Hint: What happens to water vapor the atmosphere of a bathroom when you
are taking a hot shower?)
Question 11: Why would a parcel of air expand or compress as it rises or sinks
in the atmosphere?
Try This Web Site
Meteorologists sometimes mention “environmental lapse rate”. Here is a web
site that gives you a chance to predict the environmental lapse rate.
http://daphne.palomar.edu/jthorngren/adiabi.htm
Adiabatic Phase Change
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Isothermal Processes
The temperature of a container of a gas or air is kept constant in an
isothermal process. Boyle’s Law describes the relationship between the volume
and pressure of a gas in a closed container. It states that the pressure of a gas
is inversely proportional to the volume of a gas when if the temperature and
number of gas molecules remains constant.
Question 12: Why is the adiabatic formation of clouds not a demonstration of
Boyle’s Law?
Condensation Nuclei
Many people assume that only a bathroom mirror is covered with
condensed water vapor when the air in a bathroom becomes saturated and the
temperature of the mirror is below the dew point. Since all of the surfaces in a
room are at approximately the same temperature, all of the surfaces in a
bathroom are condensing surfaces.
Question 13: Why does water vapor condense on cool surfaces?
Question 14: What purpose do the particles of smoke serve in the adiabatic
cloud maker?
Dust storms, forest fires, and the incomplete combustion of fuels are
several examples of sources of condensation nuclei in the atmosphere. Small
particles of salt enter the atmosphere as water evaporates from small droplets of
seawater as ocean waves crash on beaches. Volcanic eruptions also generate
condensation nuclei. The following web sites provide information about one
recent volcanic eruption that increased the number of condensation nuclei in the
atmosphere.
http://www.giss.nasa.gov/research/intro/hansen_02/
http://academic.emporia.edu/aberjame/remote/space/pinatub2.htm
Adiabatic Phase Change
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E. The Affect of Volcanic Eruptions on Climate
It has been suspected that large volcanic eruptions might have a
significant influence on Earth’s climate. The 1993 Mississippi Flood of 1993
occurred a year after the eruption of Mt. Penatubo in the Philippines. An
example of a web site that describes the extent of that flooding is:
http://umbc7.umbc.edu/~tbenja1/baumann/baumann.html
The following web site can be used to answer Question 15.
http://www.bluehill.org/
Question 15: Was there a significant increase in snowfall during the winters that
followed the Penatubo eruption?
E. Heat Pumps
The Second Law of Thermodynamics states the thermal energy naturally
flows from warmer matter to colder matter. Air conditioners and refrigerators are
examples of heat pumps that move thermal energy from a cooler environment to
a warmer environment. The following are examples of web sites can be used to
answer Questions 16 and 17.
http://www.howstuffworks.com/question49.htm
http://www.heatpumpcentre.org/tutorial/home.htm
http://www.nrel.gov/clean_energy/geoheatpumps.htm
Question 16: How do heat pumps move thermal energy from a cooler
environment to a warmer environment and still obey the Second Law of
Thermodynamics.
Question 17: How can heat pumps be used to heat homes in cold weather
climates?