Electrical energy from chemicals
Electric energy was significantly obtained using chemical reactions at the end of the eighteenth century. These reactions created powers measured in watts and tens of watts. Before that, significant sparks had been produced in electrostatic machines, but the power developed by electrostatic machines did not exceed fractions
of a watt.
In 1800, A. Volta demonstrated at the National Institute in Paris an electric current obtained by dipping copper and zinc plates into dilute acid. The zinc dissolved in the acid and electrical energy was obtained as a result of this reaction.
Using a battery of many such elements, Russian academician V. V. Petrov obtained an electric arc discharge for the first time. Electromagnets were studied, the telegraph was built for the first time, and the first experiments with incandescent lamps were conducted using chemical elements.
Only a few decades after the appearance of chemical elements, the first designs of electrical machines with a mechanical drive were created. At first, these machines were very crude and imperfect, and many scientists and inventors thought they could have greater success by obtaining electrical energy through chemical reactions. Most experiments with electric lighting were carried out in the middle of the last century using chemical elements.
In the Volta element and most subsequent designs, electrical energy was obtained by oxidizing zinc. But zinc does not occur in nature in its pure form. Zinc must be extracted from ore by reducing its oxides with coal. Thus, a zinc cathode ultimately obtains electrical energy from coal in chemical elements.
One kilowatt-hour of energy obtained using elements with a zinc cathode is significantly more expensive than that obtained from a dynamo rotated by a steam engine.
In modern technology, obtaining electrical energy from chemical energy is often necessary. However, this is done only in small quantities in cases where it is impossible to connect to power station networks.
" Dry elements" are used in pocket flashlights. In them, the zinc cathode is made in the form of a box containing a carbon anode and a portion of electrolyte—a solution of ammonia mixed with thick glue. The same dry elements power radio receivers for remote rural areas. Dry elements are sometimes used in small mobile military radio installations.
Balloons with measuring instruments and small radio transmitters are sent high into the atmosphere for weather reconnaissance. The signals from the transmitters are used to learn about the pressure, temperature, and humidity of the high layers of the atmosphere. Special batteries, especially light, are built to power the transmitters of these radiosondes, but they are designed only for short-term operation.
Some factories produce electrochemical cells. But all this is only "small" energy.
Electricity piggy banks
Secondary elements - batteries - are also chemical current sources. These are electricity piggy banks, although not perfect. If the deposit is not claimed within several months, it will disappear - the battery loses all its energy reserves due to self-discharge. But even if the energy deposited in the battery is consumed several days or even hours after charging, the battery will still give no more than 60-70% of the energy spent on its charge. And it is impossible to claim the entire deposit quickly: the battery operating mode is about 10 hours.
On the other hand, the battery is valuable because it is always ready for action. A well-charged battery will not fail, will not let you down, and will provide current on demand. Millions of batteries work in cars. They start engines, power lighting, horns, and ignition. Small battery carts are convenient for transporting goods over short distances. Power plants have large storage batteries for power signals, relay circuits, and emergency lighting. Telegraph stations always have storage batteries.
Combustion Elements
Many attempts have been made to obtain electricity through cheaper chemical reactions. Naturally, the most tempting seemed to be the reaction of carbon oxidation, obtaining energy by burning coal. At first, using coal as a cathode in an element seemed wild and incredible. Before that, coal in elements was used as a positive pole - an anode that did not change during operation.
Then, working designs of elements with carbon cathodes appeared. Hopes flared up that this was the cheapest and most convenient way to obtain electrical energy. Combustion elements that would produce current directly from burning coal seemed a very tempting idea for a long time.
The famous inventor Yablochkov spent a lot of effort creating powerful chemical generators of electric current. But no one has succeeded in creating industrial designs capable of competing with dynamos connected to steam engines. Combustion elements operate with low energy intensity. They are very bulky; their useful output is lower than that of dynamos. The shortcut turned out to be not the most profitable. Direct conversion of the chemical energy of coal into electrical energy is significantly less economical than a long chain of energy transformations at a modern power plant.
And even today, projects for powerful electrochemical generators still appear occasionally. More often than not, these are the naive ideas of novice inventors who know nothing about the work of their predecessors. But there are also solid scientific treatises on combustion elements. Occasionally, dissertations are written on this issue.
Many inventors have tried to create combustion elements in which gas, not coal, would serve as fuel. Hydrogen was fed into this generator on one side and oxygen on the other. Meeting on a wet porous partition, hydrogen, and oxygen combined, forming water. In this case, a voltage of about 1 V is developed. A series connection of many such elements is used to obtain higher voltages. High purity of the supplied gases is required to operate gas elements successfully. Impurities poison the porous partition, and the reaction stops.
Electrical energy from heat
In a closed circuit consisting of dissimilar conductors, such as a circuit of copper and iron wires, an electric current can be generated if one of the junctions of the dissimilar conductors is heated to a temperature higher than the other junctions.
When the entire circuit is at the same temperature, it has no current. But if one of the junctions of copper and iron (in our example) is heated, say, with a gas burner, then electrons from the copper will begin to move into the iron. This movement of electrons will spread throughout the entire circuit, and an electric current will flow in it.
The current caused by heating one of the junctions of dissimilar conductors is called thermoelectric. The resulting electrical voltage, electromotive force (abbreviated thermo-emf), depends on the materials in contact. Copper and iron are not the best thermocouples. Metals and alloys that produce a higher thermo-emf can be selected.
For any thermocouple, the higher the heating temperature (or the temperature difference between the heated and unheated places—junctions), the greater the developed thermo-emf. But even for the best thermocouples at high heating temperatures, the thermo-emf is measured in only thousandths of a volt (millivolts).
Connecting many thermocouples in series is necessary to build a large thermopile to obtain at least several volts. Thermoelectric phenomena have been known for a very long time, and proposals have been made to use them to get large amounts of energy for a long time. One circumstance prevents this. Along with the flow of electrons from the heated junction, there is also a flow of thermal energy, a harmful leakage of heat from the heated junction to the cold part of the circuit. This heat leakage is tens of times greater than the useful energy of the electric current; the efficiency of a thermoelement made of metal conductors does not exceed fractions of a percent.
Thermobatteries also have valuable properties. They wear out little during operation, and if the heating is constant, they produce a very stable voltage. Georg Simon Ohm used a thermopile when he established his famous law of the dependence of current on voltage and electrical resistance of a circuit—"Ohm's law." To increase a thermoelement's useful output, finding a pair of materials that develop a large thermo-emf and have low thermal conductivity would reduce harmful heat leakage.
What is thermoelectricity good for? Thermoelements are widely used in modern science and technology. We have already mentioned that the voltage developed by a thermoelement is very stable: it depends only on the temperature of the "hot" junction (which is called this in contrast to the second "cold" junction, which is at a constant temperature). Therefore, thermoelements (thermocouples) are readily used for precise temperature measurements. They can register changes in thousandths of a degree and are used in the most accurate physical and biological studies. Still, at the same time, they can also measure very high temperatures. Their readings are easy to transmit over a distance. Chapter 3 of this book discusses using thermocouples to measure high-frequency currents. Thermocouples are widely used in installations with automatic temperature control. In conditions where it is impossible to use the energy of power plants (in non-electrified areas, in geological expeditions), "kerosene thermogenerators" - a combination of a kerosene lamp and a thermopile - have found application for powering radio receivers. The prospects for creating and using effective designs of thermoelements are significant.
Electrons from hot bodies
Hot bodies emit electrons. Coal burns in a stream of oxygen, developing a very high temperature, and the electron radiation of the coal is quite large. If a cold metal plate - a collector - is placed near the hot coal, an electromotive force of up to several volts will arise between the plate and the coal. When the circuit is closed, a current will flow through it.
This experience inspired many inventors to build new electric generators. The mechanism for obtaining energy in such generators is between a combustion element and a thermoelement. All their negative properties—low efficiency and low energy intensity—are evident here, too. Now, ways to get around these difficulties have been found, and so-called thermionic converters are beginning to come into use, primarily for using waste heat from nuclear reactors.
Charge transfer by gas and steam jets
Over a hundred years ago, it was first discovered that a jet of wet steam, striking an insulated body, can charge it to a high voltage.
A steam-electric machine was built in 1845 according to Faraday's design. A boiler about a meter long and half a meter in diameter was mounted on insulating glass legs. It maintained a pressure of six atmospheres. Steam escaped from six parallel nozzles made of hardwood and was cooled from the outside with water. The steam jets were directed to a metal comb connected to a ball mounted on an insulating glass leg.
The ball was charged to several thousand volts, and sparks up to 60 cm long could be extracted from it. Faraday explained the operation of this generator as follows: The nozzles were cooled with water, so the steam was partially condensed, and the output stream contained tiny droplets of water. When rubbing against the wall of the nozzles, the droplets were charged with positive electricity and, falling on the comb, gave it its charge.
The droplets carried positive charges from the boiler, charging the boiler itself to a high negative potential. This steam-electric machine's efficiency was negligible; it operated unstably, and it was not used in practice.
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