ELECTRICITY GENERATOR

Abstract: A device (1) for generating electricity comprises a resonance tube (3) and a pulse combustor (9) for causing oscillations in a gas in the resonance tube (3). The device has a rotor (17) with an associated electrical generator unit (15) remote from the pulse combustor (9). The oscillations in the gas cause the rotor (17) to rotate and drive the electrical generator unit (15).

Description: Electricity generator The present invention relates to a generator of electricity, particularly, although not exclusively suited to use as a self-contained generator for medium sized buildings such as apartment or office blocks or supermarkets. Recently, a need has developed for self-contained on-site electrical generators either as primary electricity sources, particularly .for remote locations, or as secondary (back-up) generators. It is already known to provide discrete back-up generators in buildings, which generators for example comprise an alternator driven by a diesel engine. However, these known generators incur both wear and high maintenance costs during long sustained operation, so that generation costs are high. European Patent specification EP-A-0 368 650 describes a gas resonance device comprising a pulsed combustor located in the middle of a substantially spherical resonance chamber. The device incorporates a zeolite bed gas separator for oxygen enrichment. Alternatively, it may incorporate a plurality of diaphragms each attached to a transducer for converting the mechanical energy of the resonant gas oscillations into electrical energy, which would be AC, single phase, at the resonant frequency of the device. The latter arrangement has significant limitations because it utilises a multiplicity of small generating units in series or parallel, all operating at a frequency governed by the drifting resonance of the excited gas oscillations. European Patent Specification EP-A-0 267 727 describes another gas resonance device comprising a resonance tube at the top end of which is located a pulsed combustor. This device also incorporates a molecular sieve gas separator. A heat pump to provide a low-grade source of heat may also be included but there is no disclosure of incorporating a transducer to convert the mechanical energy of the gas oscillations into electrical energy. If one thought of the possibilities of adapting the tubular device according to EP-A-0 267 727 to a generator of electricity, one might naturally think of using the diaphragm/transducer arrangement of EP-A-0 368 650, rather in the manner of a loudspeaker placed at the bottom of the resonance tube. This is particularly so as in many cases, the oscillations in such a tube will occur in the range of a few tens of Herz. However, such an arrangement has a number of drawbacks. We have now devised an eletriσal generator of the gas resonance type which mitigates or overcomes the disadvantages of the aforementioned hypothetical combination of tubular resonance device with diaphragm and transducer. Our new generator is suitable in a wide range of applications, can produce significant power levels and has a relatively high efficiency. Thus, the present invention provides a device for generating electricity which device comprises a resonance tube and a pulse combustor for causing oscillations in a gas in the resonance tube, wherein the device further comprises a rotor with an associated electrical generator unit positioned remote from the pulse combustor so that the gas oscillations cause the rotor to rotate and drive the electrical generator unit. Preferably, the rotor is a self-rectifying turbine, that is to say it will rotate in the same direction, regardless of the direction from which moving air is incident upon it. This enables it to execute uni-sense rotational motion when subject to the oscillations in the gaseous medium (usually although not exclusively, air) within the resonance tube. One known self-rectifying turbine is described in UK Patent GB 1 595 700. It is especially preferred for the self-rectifying turbine to be a multi-bladed (eg. 4-blade) zero incidence rotor. Preferably, the resonance tube is in the form of a housing with the pulse combustor and the electrical generator unit with associated rotor are situated at substantially opposite ends of the column. The air column defined by the resonance tube may be of any convenient shape but preferably is overall substantially paraboloidal, although the paraboloid may be truncated. This enables the oscillations set-up by the pulse burner to be maintained as a standing wave with a pressure null point at approximately 0.63 x the length of column from the paraboloidal focus. In this form, the incremental density/pressure ratio in the air column is oscillatory with amplitude given by the zero-order Bessel Function of the first kind: J oι where r is the radius and 1 the length of the column. Similarly, the axial displacement amplitude in the column is given by the first order Bessel function of the first kind J l m Plots of these solutions are shown in Figure 1 of the appended drawings. In a preferred embodiment, the pulse combustor is situated at the top of the air column and is gas fired, eg. using natural (methane) gas, or operates by vaporising oil. In the preferred embodiment, a regenerator, preferably comprising a plurality of plates, is situated substantially immediately below the burner jet of the pulse combustor, inside the top of the air column. The combination of the pulse burner with the regenerator and the air column acts as a heat engine which gives rise to the oscillatory air movement. Operation may be explained as follows, with reference to Figure 2. It is generally agreed with respect to heat engines that the ideal thermal efficiency is determined by lower and upper limits of temperature T and T as shown in Figure 2. The Stirling cycle is defined by fixed volume limits, and the requirement for the steτ> T to T , and the corresponding expansion stroke, is that no heat shall be exchanged through the containing walls, heat exchanges being confined to extremes of stroke. If not adiabatic, the compression/expansion strokes can be isothermal with the aid of a regenerator. The latter is suitable for low pressure ratios, and therefore low adiabatic temperatures, in order to obtain high values of the ratio T /T . The ideal efficiency is the Carnot value, η = 1 - , where T ι and To are absolute values. The virtue of a large value of T is simply explained in terms of the inverse ratio between density and absolute temperature at given pressure. The higher the temperature T , the lower the mass per unit volume and therefore, at constant specific heat, the smaller the heat addition to produce a given volume expansion capability, whereby a give amount of mechanical work is produced. In the Atkinson cycle, with rightward extension, as shown in Figure 2, the heated gas is expanded fully to ambient pressure and more work is done. The cycle efficiency in the limit of small heat input at temperature T is give by η= 1 - x ° where is the ratio of specific heats at constant pressure and temperature respectively. The function of the regenerator is to act as an axial heat flow filter without impeding gas flow, and it preferably consists of a stack of closely spaced thin plates with axial alignment. It possesses, in general, a large temperature gradient in the axial direction, but conveys negligible heat by solid conduction in this direction, even if made of metal. The gas inside it takes up the same temperature gradient, increasing in temperature during the leftward compressive oscillation, and vice versa. The rate of heat transfer under these circumstances, again in general, intermittently exceeds the power input and output. The closely spaced plates perform another function, which is to constrain axial heat exchange in the gas by limiting the extent of eddy diffusion. Under these circumstances the heat pumping action maintains the temperature gradient at an equilibrium value which may readily be calculated if the amplitudes of gas displacement and adiabatic temperature change are known. It is preferred for the generator plates to be arranged in a substantially involute configuration in radial section, adjacent involute plates having substantially constant separation. The generator unit may be any suitable dynamo/alternator and possible types will be apparent to those skilled in the art, eg. an alternator or dc shunt generator. However, the preferred embodiment utilises an asynchronous (preferably three phase) generator unit. That is to say, in particular an induction motor coupled to the power source (rotor) mechanically driven beyond synchronous speed. That enables the electrical output to have a frequency corresponding to any power supply it is boosting. The rotor should be attached to the generator unit in such a position as to be driven efficiently by the oscillating air column. Normally, this is best achieved by mounting the rotor on the generator unit drive shaft, directly above the unit and axially symmetric in the housing. In order for the heat engine to function efficiently, the low grade heat transferred beyond the regenerator plates and so to the air column must be conducted away. Economic efficiency of the unit will be improved if this heat energy can be harnessed. Therefore, we prefer to provide a heat exchanger, preferably in or associated with the resonance tube. It is convenient to arrange a heat exchange trickle bed in a cavity in the housing of the resonance tube. The exhaust air from the column can be conducted into the bottom cavity to rise against a counter-current of coolant, for example water, before exiting through an exhaust port at or near the top of the structure. The heated coolant can then be pumped away for use. When the generator is employed to provide electricity for a building, the heated coolant can be used for central heating and, if water, as the hot water supply for the building. The present invention will now be illustrated in more detail by the following description of a preferred embodiment and with reference to the accompanying drawings in which: - Figure 1 shows plots of the incremental density/pressure ratio and axial displacement amplitude in a parabaloidal air column of a generator according to the present invention; Figure 2 shows a pressure vs volume regenerating cycle of a regenerator utilised in a generator according to the present invention; Figure 3 shows a generator according to the present invention. Figure 4 shows a radial cross-section through the zero incidence rotor of the generator shown in Figure 3; Figure 5 shows the shape of the rotor depicted in Figure 4, when viewed from the underside. Figure 6 shows a cross-section VI-VI through a blade of the rotor depicted in Figure 5, viewed in the direction of the arrows; and Figure 7 shows a radial cross-section through the regenerator plates of the generator depicted in Figure 3. As shown in Figure 3, a generator 1 according to the present invention comprises a housing 3 defining an air column 5. The shape of the wall 7 of the housing is such that the air column is a truncated paraboloid. A pulse burner 9 is situated at the top end 11 of the housing. At the bottom end 13 of the housing, there is an asynchronous three-phase squirrel cage generator unit 15 with an associated four-blade zero incidence rotor 17. A rotor shaft 19 connecting the rotor to the generator unit lies along the axis of symmetry of the air column. The blades 21, 23 of the rotor are substantially perpendicular to this axis. Figure 4 shows the zero incidence rotor in radial section. The blades are supported on a collar 25 and capped with a hemispherical spinner 27. The blade tips 29, 31 have angled peripheral surfaces and clear the wall of the housing by approximately by 1 mm. Figure 5 shows the shape of the rotor .in radial cross-section, showing all four blades 21, 23, 33, 35. The blade tips 29, 31, 37, 39 are curved.- The blades narrow progressively inwards towards the collar, in approximately linear fashion. The blade profile is shown i~n Figure 6. The thickness at each fractional chord as marked in Figure 6 is as follows: - Chord 0 0.0125 0.25 0.05 0.075 0.10 0.15 0.25 0.30 Thickness 0 0.206 0.429 0.592 0.694 0.7750.8780.980 1.000 Chord 0.40 C.SO 0.60 0.70 0.80 0.90 0.95 1.0 Thickness 0.980 0.959 0.755 0.612 0.4290.2450.143 0 The overall characteristics of the rotor are a β follow β : - 16 Radius Ratio 1 25 4 Actual:cm 64 41 16 Estimated mass 5Kg. Circumferential Ratio 4- ι ■s— Out-of -balance force Chord Actual: an 29 23.2 14.5 500N/πα eccentricity Thickness Ratio 0.039 0.10 0.25 Peak axial load + 5000N Actual: an 1.12 2.32 3.62 Generator bearing loads not critical Cross-section Ratio 0.61 1 0.98 Area Actual :ca 2 25 42 41 Referring back to Figure 3, the pulse burner has a Bunsen-type gas mixing valve 41 and is mounted on top of the housing. Regenerator plates 43 below the burner and mixing valve are located immediately inside the top of the housing. Figure 7 shows the involute shape of these plates in radial cross -section. A gas igniter 45 and a metering disc 47 for monitoring gas consumption are located between the mixing valve and the regenerator plates . I n use, the gas emerging from mixing valve is ignited and through the agency of the regenerator plates, work is done setting-up a standing oscillatory standing-wave in the column. The air movement causes the rotor to spin which drives the asynchronise generator unit to produce electricity. The housing wall is provided with a cavity 49. Hot exhaust air enters the cavity through a plurality of openings 51, 53 etc situated towards the lower end of the air column near the rotor. As shown in the inserts 55 in Figure 3, the cavity is filled with pea gravel 57 to act as a heat exchange trickle bed. As the exhaust gases rise through the bed and leave through exit port 59, they run counter to a falling stream of water flowing through the bed. This water is thereby heated and can be pumped away to fulfil a useful function such as a hot water supply to a building and/or central heating for same. This generator as described is suitable as an electricity supply unit for many medium sized buildings such as apartment blocks, schools, hospitals, factories, supermarkets and the like. Typically, it has a rated power capacity of about 50W-50KW although the design would be scaled-up quite easily to produce 200W-200KW. In the light of this disclosure, modifications of the aforementioned preferred embodiment as well as other embodiments, all within the scope of the present invention as defined by the claims will now be apparent to persons skilled in the art.

Claims: CLAI MS 1. A device (1) for generating electricity, which device (1) comprises a resonance tube (3) and a pulse combustor (9) for causing oscillations in a gas in the resonance tube (3), characterised in that the device further comprises a rotor (17) with an associated electrical generator unit (15) positioned remote from the pulse combustor (9) so that the gas oscillations cause the rotor (17) to rotate and drive the electrical generator unit (15). 2. A device according to claim 1, wherein the rotor (17) is a self-rectifying turbine. 3. A device according to claim 2, wherein the self-rectifying turbine is a multi-bladed zero incidence rotor. 4. A device according to any preceding claim, wherein the resonance tube (3) is in the form of a housing with the electrical generator unit (15) and associated rotor (17) situated at a substantially opposite end of the column from the pulse combustor (9). 5. A device according to any preceding claim, wherein the air column defined by the resonance tube (3) is substantially parabaloidal. 6. A device according to any preceding claim, wherein the pulse combustor (9) is situated at the top of the resonance tube (3) and is fired by gas or vapourised oil. 7. A device according to any preceding claim, wherein a regenerator (43) is situated substantially immediately below the pulse combustor (9). 8. A device according to claim 7, wherein the regenerator (43) comprises a stack of closely spaced plates having axial alignment. 9. A device according to claim 8, wherein the plates are arranged in a substantially involute configuration in radial section with adjacent involute plates having substantially constant separation. 10. A device according to any preceding claim, wherein the electrical generator unit (15) comprises an asynchronous generator. 11. A device according to any preceding claim, further comprising a heat exchanger (49-59) in or associated with the resonance tube. 12. A device according to claim 11, wherein the heat exchanger (49-59) comprises a trickle bed (57) arranged in a cavity (49) of a housing of the resonance tube.

Inventors: WELLS ALAN ARTHUR, WELLS, ALAN, ARTHUR
Applicants: HASER CO LTD, HASER COMPANY LIMITED
Application year: 1992
Main classification: F02G3
IPC codes: F01D1, F02C3