Innumerable process and means exist for generating heat essentially based on combustion especially of gas, and on electrical resistance.
Heat is transferred by conduction, convection and radiation, energy being transferred respectively among contiguous molecules, molecules, electromagnetic waves.
In the case of conduction and convection, generally speaking a thermal chain is created that conditions the performance of an installation to a considerable extent.
Combustible gas for example feeds a burner whose flame, transforming energy from the gas into thermal energy, heats the water of a boiler that heats central heating panels which in turn warm the air close to them. As it warms up the air becomes lighter and, in doing so, rises drawing in cold air towards the panels where it in turn becomes heated.
A convective movement of air is thus created which warms the surrounding space.
In the case of radiation the electromagnetic waves, of suitable length, substantially heat objects while the air remains transparent.
This phenomenon, in an accentuated form in microwave ovens, creates considerable advantages not only environmental but also for materials and products generally, dispersal of heat in the air being almost entirely avoided since it is concentrated in the bodies to be heated.
A heating installation that operates by radiation works somewhat like a microwave oven, except that it functions by radiating energy at a lower frequency and on a longer wavelength.
These advantages however are lessened by the fact that present systems are based on use of highly resistant materials becoming heated to very high temperatures with a high concentration of heat when electric current is passed through them.
These temperatures are nearly always much higher than those needed for indoor heating, for ovens and for various appliances.
Receiving heat at very high temperatures these appliances need specially made and costly means of diffusion.
The high temperatures of resistance require supporting means of special materials such as ceramics and the like, that are difficult to construct, as well as fragile and complex structures for insulation and covering that rapidly become obsolete.
Efficiency of such installations compared with that of systems operating on combustible materials is very low.
Bearing in mind the considerable cost of high resistance materials as well, all this makes for high purchasing and running costs.
It is well known in all cases a great deal of the output of a system is lost along the thermal chain from generators to appliances, especially due to the great difference between the temperature of the flame or of the electric heating elements and the temperature to be provided, with the result that actual the amount of energy used is very low when compared with that available and consumed in the process.
The document WO-A-9 522 236 discloses a system for transforming electric energy into thermal energy already diffused by conductor bodies of high conductivity having a thickness measurable in microns, compatible with their formation and with the resistance to stresses during use that may be made from films obtained by electroplating or similar processes.
The purpose of these characteristics is to eliminate the following drawbacks; The high temperatures of the conductors require special means of support of special materials such as ceramic and the like, difficult to construct, fragile, and complex insulating and coating structures
xe2x80x9cThe high temperatures cause these structures to become rapidly obsolete . . . xe2x80x9d and clearly define the field and modes of application of the patent since its purpose is also undoubtedly that of limiting the temperature in the heat generators to substantially low values.
Conductors of micrometric thickness may also be obtained by electroplating cannot in fact withstand high temperatures nor can the supports for conductors for low temperatures used to replace those of ceramic and the like specifically required for high temperatures.xe2x80x9d
Subject invention permits transformation of electric energy into thermal energy already diffused achieving a level of efficiency much greater than that offered by present techniques, this also in the field of the high temperatures that cannot be reached on the basis of the document described, as will be explained here below.
Subject of the invention is a system for transforming electric energy into thermal energy already diffused, at high temperature.
The electric circuit is closed by electric resistances formed of conductors possessing very high electric conduction, such as copper and aluminium, having a very thin constant cross section and a high ratio between width and thickness, applied flat with fixed fastenings, side by side reciprocally insulated, on a support that offers a superior degree of insulation against high temperatures.
A continuous heat-emitting surface is thus obtained and therefore, in relation to the prior art, a drastic increase in surface extension of the resistances with generation of thermal energy already diffused and a far lower thermal and dimensional difference in relation to the bodies and volumes to be heated.
The support is formed of a strongly insulating sheet backed with a thick layer of insulating material covered, on its other face, with a protective sheet of metal or of some other material.
The strongly insulating sheet is preferably of mica.
The fastening means are preferably clips formed of a long thin metal body bent in the shape of a wide xe2x80x9cUxe2x80x9d with an intermediate linear section and shanks bent at 90xc2x0, forced into the insulating support through pairs of holes made in said conductors, of a diameter considerably greater than the width of each shank of the xe2x80x9cUxe2x80x9d in order to ensure sufficient space between each shank and the hole in the conductor.
In another type of execution the clips can be driven into the conductors and into the insulating support even without holes being made in said conductors.
In one type of execution fastening is done by mechanical stapling. Said stapling can hold the conductors and the heavily insulated sheet together or can even fix the conductors to the whole insulating support. The band-shaped conductors are advantageously laid serpentine-wise. A serpentine can also be obtained by making parallel cuts in a sheet, starting first from one edge and then from the opposite edge.
In other types of execution the band-shaped conductors are placed in a spiral that may be circular, square, rectangular or of some other shape. Optimum thickness of the conductors is between 0.1 and 0.5 mm. Along their length the conductors may have a constant or different cross section according to the amount of heat and the temperature level to be reached in the various sections of the length.
Dimensional variations may be gradual or sudden, continuous or discontinuous according to circumstances or needs.
Electric feed may reach the conductors either at their ends or in intermediate areas.
Values of current that feed the ends or intermediate areas may be equal or different.
Optimum temperatures of the generators described vary from 300 to 800xc2x0 C.:
Said generators may advantageously take the form of panels.
In one type of execution said panels are completed by a four-piece frame in the form of a U-shaped channel into which the main parts such as the mica sheet, the insulating plate and rear protective sheet are fixed.
The heat-emitting surfaces of the generators can be placed in the indoor spaces, where greater warmth than ordinary room temperature is required, for the purpose of securing physical or chemical changes in the materials, so creating static, tunnel or ring-shaped furnaces and the like through which materials to be baked or treated generally, such as impregnating means, may pass.
The advantages of the disclosure are evident.
The thermal energy produced by the low voltage electric energy is of a high temperature and simultaneously diffused, and is transmitted by electromagnetic waves of medium length and therefore by radiation.
In spite of the high temperature the system of fastenings, especially using the U-shaped clips fixed into the insulating support through pairs of holes made in the flat conductors, hole diameter being considerably greater than the section of the shanks forming the xe2x80x9cUxe2x80x9d, ensures stability while allowing ample space for dilation of the conductors.
Concentrations of heat and high temperatures that would burn the area round the fastenings, inevitable with other systems, are here avoided. The above advantages are allied to a level of thermal efficiency far higher than that possible with prior art methods since the loss of heat, inevitable especially if conveyed by conduction or convection, is avoided while the cost of construction is much lower than with present generators there being no need for costly supporting bodies requiring strong thermal and electrical insulation.
The compact form of flat panels makes possible a variety of applications not only for heating static or moving bodies, as in present furnaces, but also for environmental heating.
Characteristics and purposes of the invention will be made still clearer by the following examples of its execution illustrated by diagrammatically drawn figure.