Modern Engineering Thermodynamics

water), it seems reasonable that lightning is simply a large-scale
J current A/m 2
manifestation of the viscoelectric effect. The conditions and parameters
necessary to understand its formation can be found from
J mass kg/(s · m 2 )
∇ϕ V/m = kg · m/(s 3 · A)
the viscoelectric coupling coefficients. The development of strategically
placed large lightning capture power plants, which would
∇(p/ρ) N/kg = m/s 2
L ϕϕ
A 2 · s 3 /(m 3 · kg)
rapidly convert the electrical energy of lightning into another
L mm kg · s/m 3
form of energy, would be a practical method of dealing with the
L ϕm A · s 2 /m 3
highly transient nature of lightning. For example, a lightning
L mϕ A · s 2 /m 3 strike could be used to rapidly dissociate water into hydrogen and
Summary 783
Table 19.5 Case Study SI Units
The theoretical basis behind the existance of lightning has been a
source of debate for many years. However, since air is a dielectric
Quantity
Units
fluid that contains small charged particles (dust, ice, and liquid
oxygen. The oxygen could be released into the atmosphere and
thehydrogencouldbeusedtosupplydomesticenergythrough
fuel cells or direct combustion.
Recent satellite data suggest that there are more than 3 million lightning
flashes worldwide per day, or more than 30 flashes per second
on average. An average bolt of lightning can carry a current of
300,000 A, transfers a charge of up to 300 coulombs, has a potential
difference up to 10 GV (10,000 million volts), and lasts for tens or
hundreds of milliseconds. A moderate thunderstorm generates several
hundred megawatts of electrical power, which is enough energy to
supply the entire United States with electricity for 20 min.
Figure 19.11 illustrates where lightning is abundant. The area
on earth with the highest lightning activity is located over
the Democratic Republic of the Congo in Central Africa. This
area has thunderstorms all year round as a result of moistureladen
air masses from the Atlantic Ocean encountering
mountains.
FIGURE 19.11
The average yearly lightning flashes per square kilometer based on data collected by NASA satellites between 1995 and 2002. Places where less
than one flash occurred each year are light gray. The places with the largest number of lightning strikes are black. Much more lightning occurs
over land than ocean because daily sunshine heats up the land surface faster than the ocean. The map also shows that more lightning occurs near
the equator than near the poles.
SUMMARY
In this chapter, we discuss the basic concepts of coupled phenomena. The linear phenomenological equations
are shown to accurately model near equilibrium thermoelectric and thermomechanical coupling. Thermoelectric
coupling is shown to consist of the Seebeck, Peltier, Kelvin, Fourier, Joule, and Ohm effects. Thermomechanical