Aldo Vieira da Rosa

Electron content obtained from Faraday rotation and phase path length variations

Abstract A critical study is made of electron content calculations made by measurements of polarization rotation and phase path length changes. The accuracies of the principal methods are examined for satellites in ‘low’, eccentric and geostationary orbits. Observed variation with local time, latitude, season, solar cycle and in ionospheric storms are summarized. Finally the relevance of these measurements to existing ionospheric problems is discussed.

Chapter 5 – Thermoelectricity

Publisher Summary This chapter focuses on engines that transform heat directly into electricity—the thermoelectric, the thermionic, and the radio-noise converters. The ability of a thermocouple to generate a voltage when there is a temperature difference across it suggests its use as a heat engine capable of producing electricity directly. The unparalleled reliability and simplicity of the thermoelectric generators make them the preferred device in applications in which unattended operation is more important than efficiency. These applications include power supplies for spacecraft that operate too far from the sun to take advantage of photovoltaics, topping cycles for stationary power plants (potentially), generators for oil-producing installations, including ocean platforms, and electric power providers for air-circulating fans in residential heating systems that otherwise would not operate during periods of electric power failures. Thermoelectric devices are silent—a virtue in many cases where noises would be distracting or unacceptable.

Chapter 9 – Fuel Cells

Publisher Summary Mechanical heat engines generally use the heat released by the reaction of a chemical substance (fuel) with oxygen (usually from air). The heat is then upgraded to mechanical energy by means of rather complicated machinery. It is the outcome of the millenarian struggle to control and use fire. Converting chemical energy directly into electricity is more straightforward, especially in view of the electric nature of the chemical bond that holds atoms in a molecule. Devices that convert chemical energy directly into electricity are called voltaic cells, a subgroup of electrochemical cells, which also include devices that use an electric current to promote a chemical reaction. Such devices are called electrolytic cells or electrolyzers. Flashlight batteries, automobile batteries, and fuel cells are examples of voltaic cells. Because voltaic cells transform chemical energy directly into electricity without requiring an intermediate degradation into heat, they are not limited by the Carnot efficiency. The words “cell” and “battery” are, in modern parlance, interchangeable. “Cell” suggests one single unit (although “fuel cell” most frequently consists of a number of series-connected units). “Battery” suggests a number of units, but a single 1.5-V flashlight cell is commonly called a battery.

Mechanical Heat Engines

Publisher Summary The driving agent of a heat engine is a temperature differential. A heat engine must have a source and a sink of heat. The heat source may be direct solar radiation, geothermal steam, geothermal water, ocean water heated by the sun, nuclear energy (fission, fusion, or radioactivity), or the combustion of a fuel. When carbon burns completely in an oxygen atmosphere, the product is carbon dioxide. However, most fuels contain hydrogen, and, thus, when burned, they produce water. The resulting water may leave the engine in liquid or in vapor form. For this reason, hydrogen-bearing fuels can be thought of as having two different heats of combustion: one, called the higher heat of combustion, corresponds to the production of liquid water, whereas the other, corresponding to the formation of water vapor, is called the lower heat of combustion. The higher the order of the hydrocarbon, the larger the relative amount of carbon compared with hydrogen, thus, the smaller the heat of combustion. Methane, the first of the aliphatic hydrocarbons, has the largest heat of combustion, 55.6 MJ/kg.

Ocean Thermal Energy Converters

The most plentiful renewable energy source on the planet is solar radiation. Harvesting this energy is difficult because of its dilute and erratic nature. Large collecting areas and large storage capacities are needed. These two requirements are satisfied by the tropical oceans. Oceans cover 71% of Earths surface. In the tropics, they absorb sunlight, and the top layers heat up to some 25°C. Warm surface waters from the equatorial belt flow poleward, melting both the Arctic and the Antarctic ice. The resulting cold waters return to the equator at great depth, completing a huge planetary thermosyphon. Two basic configurations have been proposed for ocean thermal energy converters (OTECs)—those using hydraulic turbines and those using vapor turbines. The first uses the temperature difference between the surface and bottom waters to create a hydraulic head that drives a conventional water turbine. The advantages of this proposal include the absence of heat exchangers. It is easier to find warm surface water than sufficiently cool abyssal waters, which are not readily available in continental shelf regions. This limits the possible sitings of ocean thermal energy converters.

Radio-Noise Generators

Radiation losses are proportional to the surface area of the heated part while the generated noise power is independent of this area. By reducing the dimensions of the device, it is possible to reduce radiation losses without diminishing the useful power output. It is well known that a resistor generates electric noise owing to the random motion of electrons. The available noise power is proportional to the temperature but is independent of the value of the resistance. If two resistors are connected in parallel and maintained at different temperatures, there is a net flow of electric noise power from the hotter to the colder. This energy can be converted into direct current and used for any desired purpose. The system described converts heat into electricity directly. There is also heat transfer by convection, conduction, and radiation. The crucial question is how much of the input heat is lost by these parasitic processes compared with what is transformed into electricity. By taking appropriate precautions, one can, at least conceptually, eliminate both convection and conduction but not radiation.

Chapter 10 – Hydrogen Production

Publisher Summary Though extremely abundant, hydrogen, unlike fossil fuels, is not a source of energy. Much of the existing hydrogen is in the form of water—hydrogen ash—and considerable energy is required to extract the desired element. Hydrogen is, at best, an excellent vector of energy. It holds great promise as fuel for land and sea vehicles, especially when used in high-efficiency fuel cells, fuel for large air- and spacecraft owing to its high energy-to-weight ratio when in cryogenic form, industrial and domestic fuel for generation of heat and electricity, and a means for transporting large quantities of energy over long distances. The advantages of hydrogen include low pollution—i.e., hydrogen burns cleanly, producing only water. It is true that, depending on the flame temperature when burned in air, small amounts of nitrogen oxides may also be generated. Pollution, however, may be associated with some hydrogen production processes and controllability—i.e., at ambient temperatures, hydrogen reacts extremely slowly with oxygen. Catalysts permit adjusting the reaction speed over a large range from very low-temperature flames to intense ones. Accumulation of hydrogen in high points of equipment or buildings can be prevented by installing catalysts that cause the (relatively) slow oxidation of the gas and its conversion to water. Odorants such as mercaptans can be added to the hydrogen to alert people to any escaping gas.

Chapter 6 – Thermionics

Publisher Summary This chapter illustrates the fundamentals of the emission process, the transport of electrons through a vacuum, the operation of the vacuum diode converter, the creation of cesium plasma, and the behavior of the plasma when present in concentrations low enough to allow disregarding collision ionization. A thermionic converter is a heat engine in which electrons are boiled off a hot surface (emitter) and are collected by a colder one (collector). There is an energy cost in evaporating electrons from a solid, just as there is a somewhat similar cost in evaporating a liquid. The minimum energy necessary to remove an electron from a metal or a semiconductor is called the work function. Thermionics are the basis of radio tubes used in most high-power radio and TV transmitters and of cathode-ray tubes employed in oscilloscopes. Thermionics also play an essential role in most microwave tubes such as klystrons, magnetrons, and traveling-wave tubes.

Chapter 15 – Wind Energy

Publisher Summary The use of wind energy dates back to ancient times when it was employed to propel sailboats. Wind-driven water pumps, cereal grinders, and sawmills aided the development of the American West. These wind machines drove their mechanical loads directly. Modern turbines generate electric energy. Although wind is free, the investment and maintenance of the plant caused the cost of electricity to be much higher than that produced by steam plants. The American interest in wind turbines mirrored the worldwide trend. At the end of 2007, over 94 GW (equivalent to 94 large nuclear plants) were in operation throughout the world, mostly in Germany (22.2 GW), the United States (16.8 GW), and Spain (15.5 GW). It is undeniable that wind energy is now an important player in the generation of electricity. In addition to the growing economic attractiveness of wind energy, there are major ecological arguments for its use—wind-power plants emit absolutely no CO2, the operation of wind turbines leaves behind no dangerous residues as do nuclear plants, decommissioning costs of wind turbines are much smaller than those of many other types of power plants, especially compared with those of nuclear generators, and land occupied by wind farms can find other simultaneous uses such as in agriculture.

Chapter 3 – Mechanical Heat Engines

Publisher Summary The driving agent of a heat engine is a temperature differential. A heat engine must have a source and a sink of heat. The heat source may be direct solar radiation, geothermal steam, geothermal water, ocean water heated by the sun, nuclear energy (fission, fusion, or radioactivity), or the combustion of a fuel. When carbon burns completely in an oxygen atmosphere, the product is carbon dioxide. However, most fuels contain hydrogen, and, thus, when burned, they produce water. The resulting water may leave the engine in liquid or in vapor form. For this reason, hydrogen-bearing fuels can be thought of as having two different heats of combustion: one, called the higher heat of combustion, corresponds to the production of liquid water, whereas the other, corresponding to the formation of water vapor, is called the lower heat of combustion. The higher the order of the hydrocarbon, the larger the relative amount of carbon compared with hydrogen, thus, the smaller the heat of combustion. Methane, the first of the aliphatic hydrocarbons, has the largest heat of combustion, 55.6 MJ/kg.