WO2010070271A1

WO2010070271A1 - Heat generating apparatus

Info

Publication number: WO2010070271A1
Application number: PCT/GB2009/002879
Authority: WO
Inventors: David John Crouch; Andrew Jonathan Spurr
Original assignee: David John Crouch; Andrew Jonathan Spurr
Priority date: 2008-12-17
Filing date: 2009-12-14
Publication date: 2010-06-24

Abstract

Heat generating apparatus (10) comprising a passageway through which a liquid is passed when the apparatus is in use. The passageway has a first cross sectional area along a first portion (24) of the passageway, and a second cross sectional area along a second portion (26) of the passageway downstream of the said first portion (24) relative to an intended direction of flow of the liquid The second cross sectional area is greater than the first cross sectional area. A cavitation generator (40 or 22) is provided in the region of the said first portion (24) to generate cavitation in the liquid travelling m that portion when the apparatus is m use such as to cause nuclear fusion reactions between particles m the said second portion of the passageway when the apparatus is in use. The invention extends to a method of generating heat using such apparatus.

Description

HEAT GENERATOR APPARATUS

The present invention relates to heat generating apparatus

It has already been proposed to create temperatures of the order 5,000⁰C in a very small region of water, by means of cavitation using ultrasonic waves of a frequency of 20KHz More especially this has been created by positioning two piezoelectric ceramic annuli diametrically opposite one another against a generally spherical glass flask containing water at room temperature and pressure, and applying an electrical voltage to the annuli oscillating at 20KHz This has been found to create a small bubble in the water at the centre of the flask, which grows and diminishes at the same frequency Light has been observed to emanate from this bubble, and this phenomenon has been termed sonolummescence Black body radiation analysis of the light suggests that heat is generated as the bubble collapses to give a temperature of the order of 5,000⁰C It has been estimated that pressures which are generated as the bubble collapses are of the order of IK atmosphere

Because such a temperature creates a plasma withm the liquid in which atoms are stripped of their electrons, the phenomenon has created interest especially from the point of view of whether the phenomenon could be used to trigger nuclear reactions One of the problems encountered from this point of view is that the temperature generated is well below that required to trigger nuclear fusion For deuteπum nuclei this requires a temperature of the order 10^9oC For tritium nuclei the temperature reduces to around 10^7oC, but this is still about one hundred times the temperature believed to be generated in the phenomenon of sonolummescence Whilst it may be suggested that increasing the ambient pressure of the water might increase the temperature achieved, it has been found that an increase in pressure reduces the likelihood that the phenomenon can be produced Furthermore, if the conditions were modified in such a way as would cause nuclear fusion, those conditions would immediately be destroyed by the nuclear reaction itself, so that failure seems inevitable

The present invention seeks to provide a remedy

Accordingly the present invention is directed to heat generating apparatus comprising a passageway through which a liquid is passed when the apparatus is m use, in which a first portion of the passageway has a first cross sectional area, and a second portion of the passageway has a second cross sectional area, the second portion of the passageway being downstream of the said first portion relative to an intended direction of flow of the liquid, in which the second cross sectional area is greater than the first cross sectional area, and in which a cavitation generator is provided m the region of the said first portion to generate cavitation m the liquid travelling m that portion when the apparatus is in use, such as to cause nuclear fusion reactions between particles in the said second portion of the passageway when the apparatus is m use.

Preferably, the transition between the portion of smaller cross section and the portion of larger cross section occurs in a transition portion of the passageway in which portion the rate of change of the size of the cross section of the passageway as a function of distance along the axis thereof in the intended direction of liquid flow increases and then decreases This facilitates laminar flow of the fluid in a region of the passageway in which its cross section changes sharply

In an extreme case, the increase may be from zero to infinity, and the decrease may be from infinity to zero, defining a step transition However, such an abrupt change is likely to lead to turbulence in the liquid flow, so that it is more preferable for the change in the size of the cross section to be smooth.

Preferably, thermahsmg material is located adjacent to at least the said second portion of the passageway. This facilitates conversion of the energy generated in the said second portion m the form of gamma rays and fast moving neutrons into heat energy. More preferably the thermahsmg mateπal surrounds at least the said second portion The thermahsmg material may comprise lithium (which may be in the form of a lithium salt), or it may compπse heavy water (deuterium oxide), or graphite (carbon) Heat conductive filaments, for example copper filaments, may extend through the thermahsmg mateπal to facilitate extraction of heat therefrom.

The passageway may be part of a liquid circuit loop, to recycle the liquid through the passageway The loop may include a reservoir which contains liquid which flows through the passageway when the apparatus is in use. The reservoir may be provided with a heater or other device for degasifymg the liquid The loop may include part of a heat exchanger Alternatively or in addition, at least one fluid conduit other than the said passageway may pass through the thermalismg material, which conduit constitutes part of a heat exchanger

Advantageously the cavitation generator comprises at least one ultrasonic generator to generate ultrasonic waves in the liquid travelling in the said first portion when the apparatus is m use, which in turn create cavitation

Advantageously the or a further ultrasonic generator extends to the transition portion and/or to the said second portion to generate ultrasonic waves m the liquid travelling in the transition region and/or in the said second portion when the apparatus is in use

The passageway may compose a bore through a block of material or it may comprise the intenor bore of a pipe The block or the pipe may comprise stainless steel or carbon fibre or glass

Preferably the passageway is of circular cross section

It is desirable for the surfaces which define the passageway to be smooth, preferably optically smooth to reduce the likelihood of turbulence and to provide laminar flow within the flowing liquid

Whilst the ultrasonic generator could comprise oscillating variations m the cross sectional area of at least the first portion of the passageway as a function of distance progressed along the passageway, this is likely to cause undesirable turbulence in the liquid flow

More preferably therefore the ultrasonic generator compπses an oscillator arranged adjacent to at least the first portion of the passageway The oscillator may comprise piezoelectric material, for example piezoelectric ceramic mateπal This may be connected to electrical circuitry constructed to apply an oscillating voltage to the ceramic material so as to cause the latter to create cylindrical waves within liquid withm the said first portion The piezoelectric mateπal may be in the form of a cylinder for this purpose These waves may be standing waves which provide a maximum in pressure oscillation along a central longitudinal axis of the passageway

The ultrasonic generator or a further ultrasonic generator or generators may generate ultrasonic waves in the transition portion between the said first and second portions The ultrasonic generator or a further ultrasonic generator or generators may generate ultrasonic waves in the said second portion at least where it is adjacent to such a transition portion or to the said first portion It is desirable to have the waves cylindrical m form This enables them to be in phase at least throughout the length of the said first portion of the passageway, more preferably also in the transition portion between the first and second portions, more preferably also m at least a part of the second portion where it is adjacent to the first portion or to the transition region.

To this end the ultrasonic generator may comprise a cylinder of piezoceramic material which extends around the first and second portions of the passageway, and the transition therebetween, with material between the cylinder and the passageway being such as to ensure that acoustic waves generated within the passageway by the cylinder when the apparatus is in use are m phase throughout the length of the passageway.

Preferably, the cavitation generator comprises a further transition portion upstream of the said first portion, in which the cross sectional area of the passageway in the intended direction of liquid flow reduces hi such a construction, it is preferred that the said first portion is m the range from 1 to 10cm in length, this also being the spacing between the two transition portions, so that the cavitation is extinguished or destroyed on or immediately after enteπng the first mentioned transition region and/or the said second region. This length may depend on other variables of the system such as the speed with which the liquid is travelling through any given position along the passageway.

In so far as it is the liquid that provides fusion mateπal, it preferably comprises heavy water (deuteπum oxide), more preferably mixed with tritium oxide This provides material with a relatively low temperature at which nuclear fusion will take place, more especially the temperature at which the hydrogen isotope nuclei will fuse to from helium nuclei_'. The tritium oxide preferably constitutes 5% to 50% of the liquid by volume, and 10% may be a good compromise between the cost of the apparatus and its effectiveness. Glyceπne or the like may be added to the liquid to increase the ease with which sonoluminescent cavities or bubbles are created. The amount of glyceπne may be m the range from 0 01 to 1 per cent by volume, preferably about 0 1 per cent by volume.

In addition or alternatively, in so far as it is a gas or gasses withm the liquid that provides the fusion material, the liquid, which may comprise water, or acetone and/or benzene, may have deuterium and/or tritium gas dissolved in it or injected into degasified liquid as microbubbles so that when cavitation occurs, the mateπal within the cavitation comprises deuterium, tritium or a mixture thereof To this end deuterium and/or tritium gas may be added to the liquid after it has been degasified Thus a gas bubble injector may be provided at a point intended to be upstream of the cavitation generator which serves when the apparatus is in use to inject bubbles of such gas m the liquid The distance by which the injector is upstream of the cavitation generator may be such that by the time such gas has reached the cavitation generator it is dissolved in the liquid. More preferably, however, the distance by which the injector is upstream of the cavitation generator is such that the gas is still travelling m bubbles when it reaches the cavitation generator

A small percentage of a noble gas may also be dissolved in the liquid as this is known m the field to improve the quality of the effect.

The ultrasonic generator or generators is or are advantageously constructed to create ultrasonic waves within the passageway having a frequency in the range from 15KHz to 30KHz, m which range the phenomenon of sonolummescence is most prominent, more especially the frequency is substantially 20KHz (20,000 cycles per second).

With a view to changing the ambient pressure of the liquid swiftly enough between the time a bubble or cavity has a maximum size to the time it is collapsed, the spacing between the passageway where it has the first cross section and the passageway where it has the second cross section is in the range from 0.5mm to 10mm, more preferably substantially 3.0mm. At the same time the transition between the two cross sections is desirably smooth to give laminar flow of the liquid m this region of the passageway 3.0mm is the distance travelled by liquid moving at about 120 msec^"1 in a half cycle of 20KHz frequency If the mean angle of the surfaces which define the passageway relative to its longitudinal axis at the transition is to be about 30°, this requires an overall step m the wall at the transition of about 1 5mm. One combination of values that sets a pressure differential of about 100 atmospheres if the pressure m the said first portion of the passageway is to be about one atmosphere would then be to have the cross sectional area of the second portion of the passageway about 64 mm² and the cross sectional area of the first portion of the passageway about 28 mm² These values correspond to respective diameters for the first and second portions of the passageway if the latter is a bore of circular cross-section for example of about 6mm and 9mm Application of Bernoulli's equation for fluid flow then requires a speed of flow of liquid through the first portion of about 170 msec^"' to give a speed of flow through the second portion of the passageway of about 74 msec^"1. This would provide at least approximately the average speed required at the transition It will be appreciated that there are an infinite number of possible solutions to give the pressures sought, but these provide a convenient set of dimensions.

Thus Bernoulli's equation for the fluid flow reads as follows:

P₂ - P, = p(V,² - V₂ ²)/2g

where P₂ is the pressure in the second portion of the passageway, Pj is the pressure in the first portion of the passageway, p is the density of the liquid, g is the acceleration of a body owing to gravity, V₁ is the speed of the liquid in the first portion of the passageway and V₂ is the speed of the liquid m the second portion of the passageway.

In cgs units, g is about 1000 cmsec^"2 and p is about 1 gm cm^"3. With the values set above, this gives:

P₂ = (p(V₁ ² - V₂ ²)/2g) + P₁

~ (((289-55) x 10⁶)/2 x 10³) + 10³

- 118 atmospheres

It will be appreciated that there are many combinations of passageway dimensions and speed of liquid flow that will give rise to a sufficient increase in liquid pressure m a sufficiently short distance of travel of the liquid. Nonetheless the foregoing shows that the following ranges of values are advantageous: speed of liquid flow m the said first portion: 100msec^"1 to 250msec^"1; mean angle of the side walls of the passageway relative to its longitudinal axis at the transition: 10° to 50°; diameter of the first portion: 3mm to 10mm; diameter of the second portion: 5mm to 15mm; ratio of the pressure in the second portion of the passageway to the pressure m the first portion of the passageway: in the range 10 to 1000, preferably in the range 50 to 200.

Preferably the passageway is m fluid communication with a heat exchanger.

An injector may be provided in an intended upstream position relative to the said first portion of the passageway, for injecting gaseous microbubbles m the stream of liquid, for example microbubbles of air, deuteπum, tritium, noble gasses or a mixture of the aforesaid

The present invention extends to apparatus for generating electricity by means of heat generating apparatus according to one or more of the preceding paragraphs, preferably through the intermediary of a steam turbine.

The present invention extends to a method of generating heat comprising passing a liquid through a passageway which has a first cross sectional area along a first portion of the passageway, and a second cross sectional area along a second portion of the passageway downstream of the said first portion relative to the direction of flow of the liquid, in which the second cross sectional area is greater than the first cross sectional area such as to cause nuclear fusion reactions between particles in the said second portion of the passageway.

Such cavitation may be generated by an ultrasonic generator, or by a narrowing of the passageway.

Such a method may be carried out using heat generating apparatus according to any one or more of the preceding paragraphs.

The present invention extends to a method of generating electricity by means of a method according to one or more of the preceding three paragraphs, with or without the use of a steam turbine

The optional features, values and ranges of values referred to hereinbefore m relation to apparatus embodying the present invention also apply to the foregoing method according to the invention Examples of apparatus embodying the present invention, and methods embodying the invention, will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a fluid circuit diagram of apparatus embodying the present invention;

Figure 2 shows an electrical circuit diagram of electrical circuitry of the apparatus shown in Figure 1 ; Figure 3 shows a fluid circuit diagram of another construction of apparatus embodying the present invention, and Figure 4 shows a fluid circuit diagram of a further construction of apparatus embodying the present invention.

With reference to Figures 1 and 2 heat generating apparatus 10 shown in Figure 1 comprises a reservoir 12 for liquid connected via a duct 14 to a pump 16. An outlet of the latter is connected via a passageway in the form of a smooth bore 18, 20 and 22 of circular uniform cross-section of diameter substantially 9mm to a ventuπ having a smooth bore 24 of circular uniform cross-section of diameter substantially 6mm and of length substantially 60cm. The downstream side of the ventuπ is connected via a further portion of the passageway m the form of a further smooth bore 26, 28 and 30 of circular uniform cross-section of diameter substantially 9mm to a back-pressure device 32, for example a simple oπfice. The fluid circuit proceeds from the device 32 via a duct 34 to a heat exchanger 36, an outlet from which is connected to complete a closed loop circuit to the reservoir 12 via a duct 38.

The bore sections 18 to 30 are defined by stainless steel or carbon fibre pipes.

A second closed fluid circuit that passes through the heat exchanger 36 has an appliance 48 connected to receive heated working fluid from an outlet pipe 50 from the heat exchanger 36, and to return the working fluid to the heat exchanger via a return pipe 52. The appliance may be any one of a range of possibilities To give a few examples, the appliance may comprise one or more domestic radiators, a boiler, or a steam turbine The appliance 48 may comprise an electricity generator,, some of the electricity from which may be used to power the apparatus 10 itself. The bore 18, 20 and 22 comprises a first section 18 connected to a second section 22 via an elbow section 20 which is shown only diagrammatically, but is of sufficiently large radius so as not to upset laminar flow of the liquid withm the bore Similarly for the bore 26, 28 and 30, the section 28 being an elbow section connecting the sections 26 and 30. The sections 22, 24, and 26 are all straight and hoπzontal and are integral with one another, and the sections 22 and 26 are substantially 100cm long to give laminar flow at the ventuπ.

The transitions from the bore section 22 to the bore section 24, and from the bore section 24 to the bore section 26, are smooth transitions so that a longitudinal section through a side wall at both transitions follows a shallow S shape, to maintain laminar flow through the transitions. Each transition is substantially 3mm long.

The bore section 24 is surrounded by a cylinder 40 of piezoelectric ceramic material which is co-axial with the bore section 24 and which extends along the whole of the length of the bore section 24. At least the interior surface thereof is everywhere bonded by adhesive to the outside surface of the wall defining the bore section 24, itself substantially lmm thick. Rings 42 of piezoelectric ceramic mateπal surround respective portions of the transition from the bore section 24 to the bore section 26, and are co-axial therewith. Although two are shown there are preferably a greater number than that, preferably about six. These rings are also bonded to the transition wall, which increases in thickness as it progresses towards the bore section 26 to take account of the progressive increase in the pressure of the liquid. A further relatively short cylinder 44 of piezoelectric ceramic material is bonded to the outside cylindrical wall of the bore section 26 immediately adjacent to the transition between that section and the bore section 24. The cylinder 44 is about 20mm long. The rings 42 and the cylinder 44 enable the apparatus to operate so that the cylindrical ultrasound waves generated in the bore section 24 co-axial therewith extend into the transition between that section and the bore section 26, and a short distance into the latter section.

An extremely narrow pipe 46 extends through the wall of the pipe defining the bore section 22 into the interior thereof at a position close to the elbow section 20, to enable liquid flowing through that section to regain laminar flow by the time it reaches the section 24. The narrow pipe 46 curves through 90° into a short straight section of the pipe 46 which lies on the longitudinal axis of the bore section 22. The free end of the pipe 46 is formed with a hole of diameter about lμm to enable extremely small bubbles of gas to be injected into the bore section 22. In so far as this gas provides fusion material, it preferably compπses deuterium or a mixture of deuteπum and tritium In so far as it is the liquid that provides fusion material, the gas may be air, helium, argon or another noble gas.

In the illustrated apparatus, the injected gas is travelling as bubbles when it reaches the section 24.

A region of the passageway a little upstream and downstream of the transition between the section 24 and the section 26 is surrounded by a jacket 54 comprising lithium. The jacket 54 comprises a housing of stainless steel or other mateπal having good strength and thermal conductivity, such as carbon fibre, with dividers of the same material extending transversely of the housing, the hollow of the housing being filled with lithium to obtain a connection of good thermal conductivity between the lithium and the pipe defining the sections 24 and 26.

The passageway sections 20 to 28 and surrounding parts of the apparatus are encased in a lead surround 56 to ensure that no neutrons or gamma rays escape from the apparatus

The electrical circuitry which is used to operate the ultrasonic parts of the apparatus is shown in Figure 2 It compπses a number of sub-circuits 60, 62, 64 and 66, connected to the cylinder 40, the πngs 42 and the short cylinder 44 respectively. The sub-circuits 62 and 64 may be more in number, corresponding to the number of πngs 42, again preferably about six. The sub-circuits are constructed to generate oscillatory voltages at substantially 20KHz, so that when in operation they cause the cylinders 40 and 44 and the rings 42 to vibrate physically by contracting and expanding towards and away from their common axis at substantially the same frequency. The outputs from the sub-circuits 62 which drive the rings 42 and the sub-circuit 64 which dπves the cylinder 44 have respective phases which bear relationships with that of the sub-circuit 60 for the cylinder 40 to ensure that the cylindrical ultrasonic waves thus generated within the bore section 24 extend smoothly into the transition between the bore section 24 and the bore section 26, and a little way into the latter bore section, so that the waves m all these bore sections are in phase with one another.

When the apparatus is in use, the aforesaid closed loop which includes the bore section 24 is filled with a liquid comprising degasified heavy water or deuteπum oxide mixed with substantially ten percent by volume of tritium oxide and substantially 0.1 per cent by volume of glycerine. This liquid is drawn from the reservoir 12 through the duct 14 and pumped into the bore sections 18 to 22 by the pump 16. The liquid passes through the ventuπ defined by the bore section 24 and through the upstream and downstream transitions at the ends thereof. From the ventuπ the liquid passes along the bore sections 26 to 30, through the back-pressure device 32 and then via the duct 34 to the heat exchanger 36, wherefrom it is returned to the reservoir 12 via the duct 38 The pump 16 and the backpressure device 32 are so constructed and operated as to cause the liquid to flow at about 74 msec ' through the bore sections 22 and 26 and therefore at about 170 msec^"1 through the bore section 24, with a pressure of about 1 atmosphere in the bore section 24 and over 110 atmospheres in the bore sections 22 and 26

The sub-circuits 60 to 64 are powered up to create ultrasonic waves withm the liquid m the sections 24 and 26 and the transition therebetween as descπbed herein.

Micro-bubbles of gas, the possible composition of which have already been descπbed, are injected into the liquid in the bore section 22 through the pipe 46. These facilitate the creation of oscillating sonolummescent cavities or bubbles along the central axis of the bore section 24 as a result of the action of the ultrasonic waves generated by the sub-circuits 60 to 64 and the piezoceramic components 40 to 44 As these pass into the transition between the bore section 24 and the bore section 26, and thence into the upstream end of the bore section 26 itself, they move into a region of much higher pressure. This destroys the cavities or bubbles, but the speed of their collapse is accelerated to such an extent that not only are the atoms of the liquid stripped of their electrons, but also nuclear reactions take place. More especially, collisions between nuclei, more especially the deuterium and tπtium nuclei, result in the creation of helium nuclei with the release of considerable energy. This is thermahsed within the jacket of lithium 54. The liquid passing away from the ventuπ is therefore considerably hotter than it would be merely for having passed through the venturi

The heat thus generated is transferred to be effective in the appliance 48 by means of the heat exchanger 36

Means such as a heater (not shown) may be provided m the reservoir 12 to maintain the liquid in a degasified condition. The ducts 14, 34 and 38 may be of substantially greater cross-section than those of the bore sections 18 to 30, so that the liquid through the ducts 14, 34 and 38 travels at lower speeds than it does through the bore sections 18 to 30.

An alternative construction to that shown in Figure 1 is shown in Figure 3. AU components of the heat generating apparatus shown in Figure 3 which are the same as those m Figure 1 bear the same reference numerals The differences between the constructions are that the ultrasonic generating parts 40,42 and 44 are absent from the Figure 3 construction and the passageway 24 is shorter, being of a length of about 2.5cm

In the Figure 3 embodiment the entrance to the section of smaller cross section 24 from the section of passageway of larger cross section 22, causes cavitation by loweπng the pressure This cavitation is then extinguished or destroyed upon or immediately after enteπng the transition between sections 24 and 26, and or the section 26, where the pressure m the liquid rapidly increases It will be appreciated that the microbubbles injected by the pipe 46 facilitate the cavitation, but also that the pipe 46 may be omitted in the Figure 3 construction since the pressure drop at the entrance to the section 24 will cause cavitation m any case.

In the construction illustrated in Figure 4, the transition between sections 22 and 24 is much more gradual, taking place smoothly over a distance for example in the range from 10mm to 500mm, preferably about 300mm This reduces the likelihood that cavitation will anse at this transition, giving greater control to the arrangement of the pipe 46 in the creation of microbubbles entering the section 24

Numerous variations and modifications may occur to the reader without taking the resulting construction outside the scope of the present invention. For example, for suitably high changes in pressure as the liquid exits the ventuπ, the tritium oxide may be omitted from the liquid. The nngs 42 and the short cylinder 44 may be omitted. The cylinder 40 may comprise a number of shorter cylinders arranged successively along the bore section 24 end to end, connected to one or more sub- circuits to vibrate m phase with one another The length of the bore section 24 may be longer or shorter whilst remaining useful, to mention only one of many of the dimensions given which may be varied The bore sections 18 and 20 may be omitted, the duct 14 extended, and the pump 16 located at the end of the bore section 22 further from the ventuπ, upstream of the pipe 46, so that there is no need for the elbow section 20. This may improve laminar flow of the liquid in the bore section 22.

The hole at the free end of the pipe 46 may be of any dimension in the range from 0 lμm to 50μm, preferably from 0.5μm to 5μm.

The length of the passageway 24 m the Figure 3 embodiment may be any length in the range from 0.5cm to 10cm, preferably in the range from 1.5cm to 4cm.

Further passageways for heat exchanging fluid may extend through the jacket 54.

Further safety against radioactivity may be obtained by encasing the whole of the apparatus m a lead container

The effect of the piezoceramic components 40, 42 and 44 may be obtained with a simpler construction if one cylinder of piezoceramic with the same cross-sectional diameter as the component 44 extends throughout the length of the combination of components 40, 42 and 44, to surround the section 24 of the passageway, as well as a first part of the section 26 and the transition between the sections 24 and 26, the cavity between the one cylinder and the pipe which defines section 24 of the passageway and the transition being filled with the same liquid as flows through the passageway, or with a medium through which sound passes at the same speed as it passes through the liquid which flows through the passageway.

Claims

Claims:

1. Heat generating apparatus comprising a passageway through which a liquid is passed when the apparatus is in use, in which the passageway has a first cross sectional area along a first portion of the passageway, and a second cross sectional area along a second portion of the passageway downstream of the said first portion relative to an intended direction of flow of the liquid, in which the second cross sectional area is greater than the first cross sectional area, and in which a cavitation generator is provided in the region of the said first portion to generate cavitation in the liquid travelling m that portion when the apparatus is in use such as to cause nuclear fusion reactions between particles in the said second portion of the passageway when the apparatus is in use.

2. Heat generating apparatus according to claim 1, in which the transition between the portion of smaller cross section and the portion of larger cross section occurs in a transition portion of the passageway in which portion the rate of change of the size of the cross section of the passageway as a function of distance along the axis thereof in the intended direction of liquid flow increases and then decreases.

3. Heat generating apparatus according to claim 1 or claim 2, in which the change in the size of the cross section is smooth.

4. Heat generating apparatus according to any preceding claim, in which thermalismg material is located adjacent to at least the said second portion of the passageway.

5. Heat generating apparatus according to claim 4, in which the thermalismg mateπal surrounds at least the said second portion.

6. Heat generating apparatus according to claim 4 or claim 5, m which the thermalismg material comprises lithium.

7 Heat generating apparatus according to claim 6, m which the lithium is in the form of a lithium salt.

8. Heat generating apparatus according to claim 5,_' in which the thermalismg material comprises deuterium oxide

9 Heat generating apparatus according to claim 5, in which the thermalismg material comprises carbon in the form of graphite.

10. Heat generating apparatus according to claim 9, m which heat conductive filaments extend through the thermahsing material to facilitate extraction of heat therefrom.

11. Heat generating apparatus according to claim 10, in which the mateπal of the heat conductive filaments comprises copper

12. Heat exchange apparatus according to any one of claims 4 to 11, in which at least one fluid conduit other than the said passageway passes through the thermahsing mateπal, which conduit constitutes part of a heat exchanger.

13. Heat generating apparatus according to any preceding claim, m which the passageway is part of a liquid circuit loop, to recycle the liquid through the passageway.

14. Heat generating apparatus according to claim 12, in which the loop includes a reservoir which contains liquid which flows through the passageway when the apparatus is in use

15. Heat generating apparatus according to claim 13, m which the reservoir is provided with a device for degasifying the liquid.

16. Heat generating apparatus according to any one of claims 12 to 14, in which the loop includes part of a heat exchanger.

17. Heat generating apparatus according to any preceding claim, in which the cavitation generator comprises at least one ultrasonic generator to generate ultrasonic waves in the liquid travelling in the said first portion when the apparatus is in use, which in turn create cavitation.

18. Heat generating apparatus according to claim 17, in which the or a further ultrasonic generator extends to the transition portion and/or to the said second portion to generate ultrasonic waves in the liquid travelling in the transition region and/or in the said second portion when the apparatus is in use.

19. Heat generating apparatus according to any preceding claim, m which the passageway comprises a bore through a block of mateπal.

20. Heat generating apparatus according to any one of claims 1 to 18, m which the passageway comprises the interior bore of a pipe.

21. Heat generating apparatus according to claim 19 or claim 20, m which block or the pipe as the case may be comprises stainless steel.

22. Heat generating apparatus according to claim 19 or claim 20, in which block or the pipe as the case may be comprises carbon fibre or glass.

23. Heat generating apparatus according to any preceding claim, in which the passageway is substantially of circular cross section.

24. Heat generating apparatus according to any preceding claim, in which the surfaces which define the passageway are smooth.

25. Heat generating apparatus according claim 24, in which the surfaces which define the passageway are optically smooth.

26. Heat generating apparatus according to any preceding claim, in which the ultrasonic generator compπses an oscillator arranged adjacent to at least the first portion of the passageway.

27. Heat generating apparatus according to claim 26, m which the oscillator compπses piezoelectric material

28. Heat generating apparatus according to claim 27, in which the piezoelectric mateπal comprises piezoelectric ceramic mateπal.

29. Heat generating apparatus according to claim 28, m which the piezoelectric ceramic material is connected to electrical circuitry constructed to apply an oscillating voltage to the ceramic material so as to cause the latter to create cylindrical waves within liquid at least withm the said first portion.

30. Heat generating apparatus according to claim 29, in which the piezoceramic mateπal is in the form of a cylinder.

31. Heat generating apparatus according to claim 29, in which the waves are standing waves which provide a maximum in pressure oscillation along a central longitudinal axis of the passageway

32. Heat generating apparatus according to claim 17 or claim 18, or to any one of claims 19 to 31 read as appended to claim 17 or claim 18, m which the ultrasonic generator or further ultrasonic generator or generators generate ultrasonic waves in the transition portion between the said first and second portions

33. Heat generating apparatus according to claim 32, in which the ultrasonic generator or further ultrasonic generator or generators generate ultrasonic waves in the said second portion at least where it is adjacent to such a transition portion or to the said first portion.

34. Heat generating apparatus according to claim 33, m which the apparatus is such that the waves are in phase at least throughout the length of the said first portion of the passageway.

35. Heat generating apparatus according to claim 34, in which the waves are also in phase in the transition portion between the first and second portions.

36. Heat generating apparatus according to claim 35, m which the waves are also in phase in at least a part of the second portion where it is adjacent to the first portion or to the transition region.

37. Heat generating apparatus according to claim 36, in which the ultrasonic generator comprises a cylinder of piezoceramic material which extends around the first and second portions of the passageway, and the transition therebetween, with material between the cylinder and the passageway being such as to ensure that acoustic waves generated within the passageway by the cylinder when the apparatus is in use are in phase throughout the length of the passageway.

38. Heat generating apparatus according to any one of claims 1 to 9, in which the cavitation generator comprises a further transition portion upstream of the said first portion, m which the cross sectional area of the passageway in the intended direction of liquid flow reduces.

39. Heat generating apparatus according to claim 38, m which the said first portion is in the range from 1 to 10cm in length, this also being the spacing between the two transition portions, so that the cavitation is extinguished or destroyed on or immediately after entering the first mentioned transition region and/or the said second region.

40. Heat generating apparatus according to any preceding claim, in which the liquid comprises heavy water (deuteπum oxide).

41. Heat generating apparatus according to claim 40, in which the heavy water is mixed with tritium oxide.

42 Heat generating apparatus according to claim 41, m which the tritium oxide constitutes 5% to

50% of the liquid by volume.

43. Heat generating apparatus according to claim 42, m which the tritium oxide constitutes 10% of the liquid by volume.

44 Heat generating apparatus according to any preceding claim, in which glycerine is present m the liquid.

45. Heat generating apparatus according to claim 44, in which glycerine is present m the liquid in the range from 0.01 to 1 per cent by volume.

46. Heat generating apparatus according to claim 45, m which about 0 1 per cent by volume of glycerine is present in the liquid.

47. Heat generating apparatus according to any one of claims 1 to 39, in which the liquid comprises water.

48. Heat generating apparatus according to any one of claims 1 to 39, in which the liquid comprises acetone and/or benzene.

49. Heat generating apparatus according to claim 47 or claim 48, in which deuterium and/or tritium gas is dissolved in it.

50. Heat generating apparatus according to claim 47 or claim 48, m which the liquid is degasifϊed and has microbubbles of deuteπum and/or tritium injected into it so that when cavitation occurs, the material within the cavitation comprises deuterium, tritium or a mixture thereof.

51. Heat generating apparatus according to any preceding claim, in which a gas bubble injector is provided at a point intended to be upstream of the cavitation generator, which injector serves when the apparatus is in use to mject bubbles of gas into the liquid.

52. Heat generating apparatus according to claim 51, in which the distance by which the injector is upstream of the cavitation generator is such that by the time such gas has reached the cavitation generator it is dissolved in the liquid.

53. Heat generating apparatus according to claim 51, in which the distance by which the injector is upstream of the cavitation generator is such that the gas is still travelling m bubbles when it reaches the cavitation generator.

54. Heat generating apparatus according to any one of claims 51 to 53, m which the gas injected by the injector when the apparatus is m use comprises air, deuteπum, tritium, and/or a noble gas

55 Heat generating apparatus according to any preceding claim, m which a small percentage of a noble gas is dissolved in the liquid.

56. Heat generating apparatus according to any preceding claim, m which the ultrasonic generator or generators is or are constructed to create ultrasonic waves within the passageway having a frequency in the range from 15K Hz to 30K Hz.

57. Heat generating apparatus according to claim 56, in which the frequency is substantially 2OK Hz (20,000 cycles per second).

58. Heat generating apparatus according to any preceding claim, in which the spacing between the passageway where it has the first cross section and the passageway where it has the second cross section is in the range from 0.5mm to 10mm.

59. Heat generating apparatus according to claim 58, m which the spacing between the passageway where it has the first cross section and the passageway where it has the second cross section is substantially 3 0mm.

60. Heat generating apparatus according to any preceding claim, m which the transition between the two cross sections is smooth to give laminar flow of the liquid in this region of the passageway.

61. Heat generating apparatus according to any preceding claim, in which this the length of the overall step m the wall at the transition of about 1.5mm.

62. Heat generating apparatus according to any preόedmg claim, in which the pressure m the said first portion of the passageway is substantially one atmosphere.

63. Heat generating apparatus according to any preceding claim, in which the pressure differential between the respective pressures in the first and second portions of the passageway is substantially 100 atmospheres.

64. Heat generating apparatus according to any preceding claim, in which the cross sectional area of the second portion of the passageway is substantially 64 mm² and the cross sectional area of the first portion of the passageway is substantially 28 mm².

65. Heat generating apparatus according to any preceding claim, in which the passageway is of substantially circular cross-section.

66. Heat generating apparatus according to any preceding claim, in which the speed of flow of liquid through the first portion is substantially 170 msec^"1 when the apparatus is m use.

67. Heat generating apparatus according to any preceding claim, in which the passageway is in fluid communication with a heat exchanger when the apparatus is m use.

68. Electricity generating apparatus compπsing heat generating apparatus as claimed in any preceding claim.

69. Electricity generating apparatus according to claim 68, in which electricity is generated by means of the heat generating apparatus through the intermediary of a steam turbine.

70 A method of generating heat compπsing passing a liquid through a passageway which has a first cross sectional area along a first portion of the passageway, and a second cross sectional area along a second portion of the passageway downstream of the said first portion relative to the direction of flow of the liquid, m which the second cross sectional area is greater than the first cross sectional area such as to cause nuclear fusion reactions between particles m the said second portion of the passageway.

71. A method of generating heat according to claim 70, using apparatus as claimed in any one of claims 2 to 67.

72. A method of generating electricity using a method as claimed in claim 70 and apparatus according to claim 68 or claim 69.