Motors Part 18
Artificial power, if we may so term it, is a late development. It is very young when compared with the history of man.
High Character of Motor Study.--The study of motors requires intellect of a high order. It is a theme which is not only interesting and attractive to the boy, but the mastery of the subject in only one of its many details, opens up a field of profit and emoluments.
The Unlimited Field of Power.--It is a field which is ever broadening.
The student need not fear that compet.i.tion will be too great, or the opportunities too limited, and if these pages will succeed, in only a small measure, in teaching the fundamental ideas, we shall be repaid for the efforts in bringing together the facts presented.
CHAPTER XV
THE ENERGY OF THE SUN, AND HOW HEAT IS MEASURED
In the first chapter we tried to give a clear view of the prime factors necessary to develop motion. The boy must thoroughly understand the principles involved, before his mind can fully grasp the ideas essential in the undertaking.
While the steam engine has been the prime motor for moving machinery, it is far from being efficient, owing to the loss of two-thirds of the energy of the fuel in the various steps from the coal pile to the turning machinery.
_First_, the fuel is imperfectly consumed, the amount of air admitted to the burning ma.s.s being inadequate to produce perfect combustion.
_Second_, the mechanical device, known as the boiler, is not so constructed that the water is able to completely absorb the heat of the fuel.
_Third_, the engine is not able to continuously utilize the expansive force of the steam at every point in the revolution of the crankshaft.
_Fourth_, radiation, the dissipation of heat, and condensation, are always at work, and thus detract from the efficiency of the engine.
The gasoline motor, the next prime motor of importance, is still less efficient in point of fuel economy, since less than one-third of the fuel is actually represented in the mechanism which it turns.
The production of energy, in both cases, involves the construction of a multiplicity of devices and accessories, many of them difficult to make and hard to understand.
To produce power for commercial purposes, at least two things are absolutely essential. First, there must be uniformity in the character of the power produced; and, second, it must be available everywhere.
Water is the cheapest prime power, but its use is limited to streams or moving bodies of water. If derived from the air currents no dependence can be placed on the regularity of the energy.
Heat is the only universal power on the globe. The sun is the great source of energy. Each year it expends in heat a sufficient force to consume over sixty lumps of coal, each equal to the weight of the earth.
Of that vast amount the earth receives only a small part, but the portion which does come to it is equal to about one horse power acting continuously over every thirty square feet of the surface of our globe.
The great problem, in the minds of engineers, from the time the steam engine became a factor, was to find some means whereby that energy might be utilized, instead of getting it by way of burning a fuel.
One of the first methods proposed was to use a lens or a series of mirrors, by means of which the rays might be focused on some object, or materials, and thus produce the heat necessary for expansion, without the use of fuel.
Wonderful results have been produced by this method; but here, again, man meets with a great obstacle. The heat of the sun does not reach us uniformly in its intensity; clouds intervene and cut off the rays; the seasons modify the temperature; and the rotation of the globe constantly changes the direction of the beams which fall upon the lens.
The second method consists in using boxes covered with gla.s.s, the interior being blackened to absorb the heat, and by that means transmit the energy to water, or other substances adapted to produce the expansive force.
Devices of this character are so effective that temperatures much above the boiling point of water have been obtained. The system is, however, subject to the same drawbacks that are urged against the lens, namely, that the heat is irregular, and open to great variations.
These defects, in time, may be overcome, in conserving the force, by using storage batteries, but to do so means the change from one form of energy to another, and every change means loss in power.
The great problem of the day is this one of the conversion of heat into work. It is being done daily, but the boy should understand that the _direct conversion_ is what is required. For instance, to convert the energy, which is in coal, into the light of an electric lamp, requires at least five transformations in the form of power, which may be designated as follows:
1. The burning of the coal.
2. The conversion of the heat thus produced into steam.
3. The pressure of the steam into a continuous circular motion in the steam engine.
4. The circular motion of the steam engine into an electric current by means of a dynamo.
5. The change from the current form of energy to the production of an incandescent light in the lamp itself, by the resistance which the carbon film offers to the pa.s.sage of the current. Should an inventor succeed in eliminating only one of the foregoing steps, he would be hailed as a genius, and millions would not be sufficient to compensate the fortunate one who should be able to dispense with three of the steps set forth.
The Measurement of Heat.--To measure heat means something more than simply to take the temperature. As heat is work, or energy, there must be a means whereby that energy can be expressed.
It has been said that the basis of all true science consists in correct definitions. The terms used, therefore, must be uniform, and should be used to express certain definite things. When those are understood then it is an easy matter for the student to grope his way along, as he meets the different obstacles, for he will know how to recognize them.
Before specifically explaining the measurement it might be well to understand some of the terms used in connection with heat. The original theory of heat was, that it was composed of certain material, although that matter was supposed to be subtle, imponderable and pervading everything.
This imponderable substance was called _Caloric_. It was supposed that these particles mutually attracted and repelled each other, and were also attracted and repelled by other bodies, so that they contracted and expanded.
The phenomenon of heat was thus accounted for by the explanation that the expansion and contraction made the heat. This was known as the _Material Theory of Heat_.
But that phase of the explanation has now been abandoned, in favor of what is known as the _dynamical_, or _mechanical_ theory, which is regarded merely as a _mode_ of _motion_, or a sort of vibration, wherein the particles move among each other, with greater or less rapidity or in some particular manner.
Thus, the movements of the atoms may be accelerated, or caused to act in a certain way, by friction, by percussion, by compression, or by combustion. Heat is the universal result of either of those physical movements.
Notwithstanding that the material theory of heat is now abandoned, scientists have retained, as the basis of all heat measurements, the name which was given to the imponderable substance, namely, _Caloric_.
It is generally written _Calorie_, in the text books. A calorie has reference to the quant.i.ty of heat which will raise the temperature of one kilogram of water, one degree Centigrade.
As one kilogram is equal to about two pounds, three and a quarter ounces, and one degree Centigrade is the same as one and two-thirds degrees Fahrenheit, it would be more clearly expressed by stating that a caloric is the quant.i.ty of heat required to raise the temperature of one and one-fifth pound of water one degree Fahrenheit.
This is known as the scientific unit of the thermal or heat value of a caloric. But the engineering unit is what is called the British Thermal Unit, and designated in all books as B. T. U.
This is calculated by the amount of heat which is necessary to raise a kilogram of water one degree Fahrenheit. According to Berthelot, the relative value of calorics and B. T. U. are as follows:
HEATS OF COMBUSTION
--------------------------------------------------- _Substance._ _Calories._ _B. T. U._ --------------------------------------------------- Hydrogen 34,500 62,100 Carbon to carbon dioxide 8,137 14,647 Carbon to carbon monoxide 2,489 4,480 Carbon monoxide 2,435 4,383 Methane 13,343 24,017 Ethylene 12,182 21,898 Cellulose 4,200 7,560 Acetylene 12,142 21,856 Peat 5,940 10,692 Naphthalene 9,690 10,842 Sulphur 2,500 4,500
When it is understood that heat is transmitted in three different ways, the value of a measuring instrument, or a unit, will become apparent.
Thus, heat may be transmitted either by _conduction_, _convection_, or _radiation_.
_Conduction_ is the method whereby heat is transmitted from one particle to another particle, or from one end of a rod, or other material to the other end. Some materials will conduct the heat much quicker than others, but if we have a standard, such as the calorie, then the amount of heat transmitted and also the amount lost on the way may be measured.
_Convection_ applies to the transmission of heat through liquids and gases. If heat is applied to the top or surface of a liquid, the lower part will not be affected by it. If the heat is applied below, then a movement of the gas or liquid begins to take place, the heated part moving to the top, and the cooler portions going down and thus setting up what are called _convection currents_.