Introduction
from the high-temperature substance to the low by conduction, a direct
molecular interaction. If you touch a hot stove, your hand is heated by
conduction.
Heat transport by a moving fluid is called convection. The heat is first
transferred to the fluid by conduction; the bulk fluid motion carries away
the heat stored in the fluid. Most home heating systems rely on convection
to heat the air and walls of the house.
Unlike convection and conduction, radiative exchange requires no intervening molecules to transfer energy from one surface to another. A
surface radiates energy at a rate proportional to the fourth power of its
absolute temperature. Both the sun and the earth emit radiation, but because the sun is at a higher temperature the emitted radiant flux density
is much higher for the surface of the sun than for the surface of the earth.
Much of the heat you receive from a campfire or a stove may be by radiation and your comfort in a room is often more dependent on the amount
of radiation you receive from the walls than on the air temperature.
To change from a liquid to a gaseous state at 20" C, water must absorb
about 2450 joules per gram (the latent heat of vaporization), almost 600
times the energy required to raise the temperature of one gram of water by
one degree. Evaporation of water from an organism, which involves the
latent heat required to convert the liquid water to vapor and convection of
this vapor away from the organism, can therefore be a very effective mode
of energy transfer. Almost everyone has had the experience of stepping
out of a swimming pool on a hot day and feeling quite cold until the water
dries from their skin.
1.3 Mass and Momentum Transport
Organisms in natural environments are subject to forces of wind or water
and rely on mass transport to exchange oxygen and carbon dioxide. The
force of wind or water on an organism is a manifestation of the transport
of momentum from the fluid to the organism. Transport of momentum,
oxygen, and carbon dioxide in fluids follow principles similar to those
developed for convective heat transfer. Therefore, just one set ofprinciples
can be learned and applied to all three areas.
1.4 Conservation of Energy and Mass
One of the most powerful laws used in analyzing organism-environment
interaction is the conservation law. It states that neither mass nor energy
can be created or destroyed by any ordinary means. The application of
this law is similar to the reconciliation of your checking account. You
compute the deposits and withdrawals, and the difference is the balance
or storage. As an example, consider the energy balance of a vegetated
surface. We can write an equation representing the inputs, losses, and
from the high-temperature substance to the low by conduction, a direct
molecular interaction. If you touch a hot stove, your hand is heated by
conduction.
Heat transport by a moving fluid is called convection. The heat is first
transferred to the fluid by conduction; the bulk fluid motion carries away
the heat stored in the fluid. Most home heating systems rely on convection
to heat the air and walls of the house.
Unlike convection and conduction, radiative exchange requires no intervening molecules to transfer energy from one surface to another. A
surface radiates energy at a rate proportional to the fourth power of its
absolute temperature. Both the sun and the earth emit radiation, but because the sun is at a higher temperature the emitted radiant flux density
is much higher for the surface of the sun than for the surface of the earth.
Much of the heat you receive from a campfire or a stove may be by radiation and your comfort in a room is often more dependent on the amount
of radiation you receive from the walls than on the air temperature.
To change from a liquid to a gaseous state at 20" C, water must absorb
about 2450 joules per gram (the latent heat of vaporization), almost 600
times the energy required to raise the temperature of one gram of water by
one degree. Evaporation of water from an organism, which involves the
latent heat required to convert the liquid water to vapor and convection of
this vapor away from the organism, can therefore be a very effective mode
of energy transfer. Almost everyone has had the experience of stepping
out of a swimming pool on a hot day and feeling quite cold until the water
dries from their skin.
1.3 Mass and Momentum Transport
Organisms in natural environments are subject to forces of wind or water
and rely on mass transport to exchange oxygen and carbon dioxide. The
force of wind or water on an organism is a manifestation of the transport
of momentum from the fluid to the organism. Transport of momentum,
oxygen, and carbon dioxide in fluids follow principles similar to those
developed for convective heat transfer. Therefore, just one set ofprinciples
can be learned and applied to all three areas.
1.4 Conservation of Energy and Mass
One of the most powerful laws used in analyzing organism-environment
interaction is the conservation law. It states that neither mass nor energy
can be created or destroyed by any ordinary means. The application of
this law is similar to the reconciliation of your checking account. You
compute the deposits and withdrawals, and the difference is the balance
or storage. As an example, consider the energy balance of a vegetated
surface. We can write an equation representing the inputs, losses, and