摘要:

The paperis an effort toexplain the reason why, and the conditions in which, electrical power can be used competitively for the heating of buildings, in spite of the fact that the cost of the crude heat is several times greater than that of any other heating medium. It deals exclusively with the cost of the fuel and the labour inevitablyincurred in handling it, and not with questions of capital cost and allied matters.It details the causes of loss of heat inevitably incurred in the use of any other form of fuel, estimates their respective amounts, and traces the stages by which the heat generated at a central boiler-house is frittered away on its way to the rooms where it is required.The principal features which enable electrical power whensuitably installed to compete withother fuels are its 100 per cent technical efficiency, its instantaneous control, and the very low time-lag and absorption. It is shown that, owing mainly to these features, an amount of heat fully equivalent to the energy of the electrical current used can be delivered at the exact time only when it is required, thereby avoiding the waste caused essentially by the lack of accurate timing inevitably associated with all systems in which heat is generated in and distributed from acentral boiler, whether or not this iselectrically heated. In this sense electricity, locally applied, is the only means by which an overall “efficiency” of 100 per cent can be rationally claimed for an entireinstallation—in the sense thatthe amount of electrical energy used isequal to the bare minimum of theheat physically necessary to secure the desired result.The overall efficiency of the heating process by other media is determined as thecontinuous product of numerousdetailed efficiencies (corresponding tothe various stages of loss), each of which is so defined that their continuous product may be equal to a final “overallefficiency” representingthe ultimate ratio between the heat physicallynecessary for securing the desired result and that in the fuel purchased.Representative maximum, medium, and minimum values are in all cases given of each of these factors where they areliable to wide variation, and the tables are drawn up in such a form that they can readily be corrected for any variation in these assumed values.A close comparison ismade between the features of electricityand gas (herein called the “mobile fuels”) as heating agents; also between the operating characteristics of the “portable fuels”—oil and coke. The labour involved in handling thefuel in each case is considered in detail.A sharp distinction is drawn between the relative costs in the respective cases of continuous and intermittent heating.It is inthe latter that the economy of electric heating showsto greatest advantage; the reasons for this are given. Explanationsare advanced of the reasons why instantaneous control, suchas is only obtainable by electricity, is of great importance in restricting the unnecessary use of heat and at the same time in supplying an adequate amount for main taining comfort conditions during all times of actualoccupation, and onlyduring those times.Numericaltables and diagrams are given showing theprogressive loss of heat in the various stages through which the heat passes, and explanations are given of the details of thecalculations of the heat quantities really necessary for maintaining the required temperatures, as well as of the proportions inevitably dissipated in the process of delivering heat from a central point to the rooms. The ratio between these iscalled the “occupation efficiency”, the incidence of which on the calculated result is fully explained. Finally a table is given in which, assuming fixed prices for the crude heat, average medium values for the various factors involved and theoretical perfection of the heating result for an assumed period, the relative annual costs of heating 1 000 cubic feet of average space by the various media is calculated.It is emphasized that all the factors on which these costs depend are essentially very variable and that no such table of relative costs can conceivably be absolute apart from the factors involved.

DOI:10.1049/jiee-1.1933.0041

出版商:IEE    

年代:1933

数据来源: IET

摘要:

The paper gives a critical summary of the existing knowledge of electronic oscillations and of their production in triode, diode, and magnetron circuits. The application of these oscillations to ultra-wave communication is outlined, and apparatus used in a recent demonstration is briefly described. A general knowledge of ordinary short wave technique is assumed.

DOI:10.1049/jiee-1.1933.0049

出版商:IEE    

年代:1933

数据来源: IET

摘要:

The possible methods of utilizing magnetrons to generate short-wave oscillations are indicated and the more important results of previous workers are described. The theoretical basis of “electronic”and “dynatron”oscillations is discussed, with particular reference to those features which can be investigated experimentally. It is shown that the wavelength of the electronic oscillations is determined mainly, if not entirely, by the electron time of transit. The general expression for the time of transit is given and hence expressions for the wavelength in terms of magnetic field strength are obtained for zero and saturated space-charge conditions. The wavelength is found to be about 36 per cent greater in the latter case. It is shown that initial electron velocity causes an appreciable reduction in wavelength in normal cases. The effect of magnetic field on space charge is considered and is found to lead to a small, possibly negligible, increase in wavelength. It is shown that the space charge is uniformly distributed when the magnetic field strength exceeds the critical value at which the electron orbits just touch the anode surface. This result has been previously stated by Hull, but Hull's deduction that the electrons travel in circular orbits round the cathode is disputed.An attempt to provide a simplified theoretical explanation of the “dynatron”characteristics of a “split anode”magnetron leads to a false result from which it is concluded that no theory will provide an explanation which does not take into account the non-uniformity of the electric fields in the two halves of the valve. The general shape of the static characteristics is indicated by means of Habann's theory, which is, however, not capable of giving proof of the existence of negative resistance in the case of a symmetrical oscillatory circuit, which is the case considered here. A qualitative explanation of the occurrence of negative resistance, i.e. of the greater fraction of the anode current reaching the lower-potential anode segment, is given.The object of the experimental investigation was to discover the nature of the fundamental relations in the electronic and dynatron types of oscillation, to compare these relations with the indications of the theory, and to apply the knowledge obtained to the production of a sufficient amount of power to be technically useful at the shortest possible wavelength.For electronic oscillations it is found that the experimental results are entirely in agreement with the theory in so far as it is applicable. In particular it is confirmed that the strength of the electronic oscillations is greatest at the “critical” relation between anode voltage and magnetic field strength, and that the wavelength of the optimum oscillation is inversely proportional to the magnetic field strength. The actual value of the wavelength and the amount of the wavelength change due to space charge both agree with the theoretical values within experimental accuracy. It is concluded that the effect of magnetic field on space-charge distribution is not great enough to affect the wavelength appreciably. It is shown that apparently anomalous results can be explained by taking into account the stray capacitances, due in particular to the glasswork of the valve, across the oscillatory circuit. Theselead to internal resonance effects which, although often a nuisance to the investigator, sometimes have the advantage of enabling a relatively large output to be obtained at a particular wavelength.The fact that the greatest output is, in general, obtained with the magnetic field not exactly in the direction of the electrode axis, which has been reported by Slutzkin and Steinberg and by Ranzi, was observed independently. The existence of an optimum field angle differing from zero is found to be due to the resultant spiral motion of the electrons balancing out the effect of cathode potential-drop for electrons arriving at part of the anode surface in such a way as to increase the number of oscillating electrons.By making use of an internal resonance effect and suitably adjusting the field angle,'an output of the order of 1–5 watts was obtained at a wavelength of about 24 cm.It is pointed out that the wavelength of the electronic oscillations can be expressed in the same form as the Bark-hausen-Kurz equation for the triode case, and that the existence of an optimum value of anode current (approximately 1/10th of the space-charge saturation value) leads, as in the triode case, to the result that the minimum wavelength obtainable without overloading the valve depends on the anode diameter and decreases with it. For an anode diameter of 3 mm the shortest wavelength at which optimum oscillating conditions can be maintained is of the order of 20 cm. The corresponding figure for the triode case (grid diameter 3 mm) is about 50 cm. The shortest wavelength actually observed was 18 cm. Oscillations of shorter wavelength have not been investigated, owing to the small power obtainable.It is shown that it is possible to obtain dynatron oscillations in a split-anode magnetron by tilting the magnetic field, and that these are distinct from both the electronic and simple dynatron oscillations. Hollmann has investigated the occurrence of oscillations of this kind in the full cylindrical, anode magnetron and found a minimum wavelength of about 20 m. It is shown here that these oscillations can be produced down to about 35 cm wavelength, but at this wavelength the effect of electron inertia is important.In the investigation of the simple dynatron oscillations, static characteristics showing the negative resistance effect are obtained. From these curves the operating characteristics of the valve are calculated and checked by comparison with a. set of measured values (for a relatively low frequency). Good agreement is obtained.It is found that the energy of the dynatron oscillation starts to fall off rapidly at a wavelength which is about 4 times the electronic oscillation wavelength corresponding to the anode voltage used. This leads to a formula for the wavelength limit for dynatron oscillations.The relation between oscillation amplitude and anode voltage is discussed, with particular reference to modulation.It is found that during oscillation the anode current may exceed the original total emission. This is probably due to bombardment of the filament by electrons which return to it with considerable velocity. The exact mechanism of this bombardment is not clear and the effect is being further investigated. By taking steps to reduce this effect it has been possible to obtain an output of 60 watts from a relatively small valve at about 2 m wavelength.The shortest wavelength obtained by means of dynatron oscillations was about 30 cm. At this wavelength the power obtainable was about 0-1 watt. It is concluded that for wavelengths below about 50 cm electronic oscillations give the greater output.

DOI:10.1049/jiee-1.1933.0050

出版商:IEE    

年代:1933

数据来源: IET