Environmental Engineering Reference
In-Depth Information
2. Set the final units at the end of a dimensional analysis equation.
3. Check that the problem is set up so that starting units are converted into ending units.
4. Simplify the math, cancel out zeros, and simplify the numbers.
5. Solve the math.
6. Rewrite your answer including the units.
Laws of Thermodynamics
There are four laws of thermodynamics, two of which are especially applicable in natural systems. The
first
law of thermodynamics
states that energy can be changed from one form to another, but it cannot be created
or destroyed. Energy input is equal to energy output. The
second law of thermodynamics
(see the following
figure) deals with order and has many implications including the fact that systems naturally flow from states of
high energy (low entropy), to states of low energy (high entropy). Systems do not naturally move toward high-
er states of order, and when energy flows through the components of a system, some energy is made unavail-
able at each transfer. Think of a food chain: the sun's energy is photosynthesized in plant material, which may
then be eaten by (for example) a deer. However, the deer uses much of this energy for heat and movement,
rather than growth, so when the deer is eaten by a mountain lion, the lion receives only a fraction of the initial
energy provided by the sun.
Energy Consumption
