Thermal power of electric current and its practical application

The cause of the heating of the conductor lies in the fact that the energy of the electrons moving in it (in other words, the energy of the current) in the course of successive collision of particles with the ions of the molecular lattice of the metallic element is converted into a warm type of energy, or Q, thus the concept of "thermal power" is formed.

The current is measured using the international SI system, applying joules (J) to it, the current is defined as "watt" (W). Departing from the system in practice, can use, among other things, extrasystem units that measure the operation of the current. Among them, watt-hour (W × h), kilowatt-hour (abbreviated kWh). For example, 1 W × h represents the operation of a current with a specific power of 1 Watt and a time duration of one hour.

If the electrons move along the fixed conductor from the metal, in this case all the useful work of the current being generated is distributed to the heating of the metal structure, and, based on the provisions of the energy conservation law, this can be described by the formula Q = A = IUt = I ² Rt = (U ² / R) * t. Such relations accurately express the well-known Joule-Lenz law. Historically, it was first determined experimentally by the scientists D. Joule in the middle of the 19th century, and at the same time, independently of him, by another scientist, E. Lenz. Practical application of thermal power found in technical performance from the invention in 1873 by the Russian engineer A. Ladyginym ordinary incandescent lamp.

The thermal power of the current is used in a number of electrical appliances and industrial installations, namely, in thermal measuring devices, heating type electric stoves, electric welding and inventory equipment, domestic appliances with electric heating effect - boilers, soldering irons, kettles, irons are very common.

It finds a thermal effect in the food industry. With a high share of use, the possibility of electrocontact heating is used, which guarantees thermal power. It is caused by the fact that the current and its thermal power, influencing the food product, which has a certain degree of resistance, causes in it a uniform heating. One can give an example of how sausages are made: through a special dispenser the minced meat enters metallic forms, the walls of which serve simultaneously as electrodes. This ensures a uniform heating uniformity over the whole area and volume of the product, the set temperature is maintained, the optimum biological value of the food product is maintained, together with these factors, the duration of technological work and energy consumption remain the least.

The specific thermal power of the electric current (ω), in other words - the amount of heat that is released per unit volume for a certain unit of time, is calculated as follows. The elementary cylindrical volume of the conductor (dV), with a transverse conductor section dS, a length dl parallel to the current direction, and the resistance form the equations R = p (dl / dS), dV = dSdl.

According to the definitions of the Joule-Lentz law, for a given time (dt) in the volume taken by us, the heat level will be equal to dQ = I ² Rdt = p (dl / dS) (jdS) ² dt = pj ² dVdt. In this case, ω = (dQ) / (dVdt) = pj ² and, using Ohm's law to establish the current density j = γE and the relation p = 1 / γ, we immediately obtain the expression ω = jE = γE ^2. It in the differential Form gives an idea of the law of Joule-Lenz.