This invention relates to the control of the vapour content and temperature in various gaseous atmospheres, and although not limited to any particular application the invention is most particularly directed to air conditioning, medical and chemical processing procedures requiring such control.

BACKGROUND

When water changes state from a liquid to a vapour, an amount of heat energy known as the latent heat of change of state is absorbed from the surrounding atmosphere.

Air may be cooled by evaporation which is known from the typical evaporative air conditioning apparatus . On one hand the typical evaporative air conditioner provides a wanted cooling affect which is balanced against the generally unwanted increase in humidity (effectiveness of cooling being less as ambient relative humidity approaches 100%), while on the other hand, the wanted increase in humidity in a greenhouse environment provides unwanted reduction in temperature which typically is compensated by providing a further heating means and fan for dispersing the heated water vapour produced.

Cooling towers use evaporative cooling techniques and are found to operate more efficiently, when, rather than relying on air passing over the heat exchanger portion of the tower,, a fine spray of water is entrained into the inlet air stream. This arrangement lowers the dry bulb temperature and enhances the air side heat transfer due to droplet vaporisation, without wetting the heat exchanger surface and reducing or eliminating problems with algae and other contaminate build-up on the air side heat exchanger surfaces.

It is also known that heat transfer co-efficients increase with decreasing flow velocity and also decreasing temperature difference between the surface and the air flow.

It is also known to operate an ultrasonic transducer which is submerged in a reservoir of water to induce pressure pulsations of acoustic or hydrodynamic fields which can lead to the pressure in the water being lower than the saturated vapour pressure and thus create a condition suitable for the onset of cavitation. This type of apparatus is typically used for ultrasonic cleaning.

In water, cavitation arises only at considerable pressure reductions which are quantified by the excess of hydrostatic pressure over the saturated vapour pressure, while in other liquids, such as cryogenic liquids cavitation arises more readily with only slight pressure pulsations. The reason is not only the difference between the static pressure and pressure of saturated vapours, but, cryogenic liquids have smaller values of surface tension than water.

Cavitation is known to have a nucleation phase, wherein, cavitation nuclei comprising gas pockets trapped in cracks/ crevices, hydrophobia impurities or icrobubbles stabilised in solution against total dissolution, are activated, and, a second growth phase, wherein microbubbles are formed and expand from the stabilised nuclei.

The uses of the phenomenon of cavitation are well known and include their use as a humidifier wherein an ultrasonic transducer submerged in a reservoir of water promotes the ejection of water molecules from the body of water at its surface interface.

It is also known to apply electrostatic fields to a region containing liquid droplets which creates the condition of individual water droplets accumulating mutually exclusive

charges at opposite sides which interact with the attractive forces between the molecules of the liquid through surface tension and attractive forces between the charged liquid and the charged electrodes creating the electrostatic field which in combination creates a tendency for reducing droplet size in the field. This effect, however, is only significant when the atmosphere carrying the liquid (water for example) is moving at a rate greater than 30 m/s.

Electro-aerodynamic atomisation is a similar means of ato isation to that of the action of an electrostatic field. These processes cause atomisation not vaporisation. Electro- aerodynamic atomisation results from the application of non- static electrical fields to a liquid droplet laden atmosphere. Atomisation results from the opposing effect of the cohesive surface tension forces and the disruptive forces created by the repulsive forces between like charges at molecular level, where it is known, that the electric field necessary to cause disruption in the liquid mass increases as the liquid surface tension increases. In electric fields a droplet of water forms at the crest of the electric waves and it is observed that there is preferential migration of charges to surface protuberances caused by the distortion of the droplets by the electric field. New smaller droplets are formed from the crest of the surface waves, since the maximum concentration of electric charges and minimum value of surface tension will occur at thes-e areas.

A further atomisation process results from vibrating an element over which a controlled depth of fluid is passed (so called sonicating thin film liquids) from which small droplets of liquid are projected. The viscosity of the liquid, the depth of the film, the frequency and amplitude of the vibrating element all determine the size of the droplet produced.

However, it is proposed that the creation of an atmosphere using a working gas carrying water droplets past an ultrasonic energy emitter which imparts its energy thereon can very efficiently vaporise droplets in the working gas. One of the very useful uses of this process is cooling and humidification effects, as described previously for evaporative air-conditioners.

The vaporisation, of water and other liquids which are carried, entrained, suspended or distributed within a working gaseous atmosphere by ultrasonic transducers, enables the temperature and humidity of that gaseous atmosphere to be controlled by the degree of application of the ultrasonic energy.

A transducer means to produce this effect requires that there be a controllable production of mechanical acoustic energy transferred as efficiently as possible to the atmosphere surrounding the liquid in droplet form carried by that atmosphere. It- is understood that vaporisation occurs as a result of creating suitable rarefication and compression waveforms in the atmosphere surrounding small liquid droplets such as to distort the droplet shape and impart sufficient energy so as to overcome the cohesive forces of the liquid molecules.

A variety of transducer apparatus are considered suit¬ able for this purpose, typically but not exclusively, having magneto, electrostriσtive or peizostrictive characteristics. That is the transducer material changes its dimensions due to magnetization, electrostatic or electric forces applied to the material. These forces may produce linear and volumetric changes in dimensions in the transducer material at a variety of frequencies.

Typical magnetostrictive materials are iron, nickel, cobalt, ferrites, and alloys thereof, eg. Ni-Fe as well as

ceramic compositions and exhibit a variety of Joule magnetostriction (length change) quantities as a function of the applied magnetic field strength. The electromagnetic coupling factor, k, of these magneto strictive materials is affected by eddy current loss factors (reduced by considering construction, geometry) and their polarization state and stress configuration as well as the materials heat capacity, thermal conductivity and both static and dynamic tensile strength and the efficiency of the application of the requisite magnetic flux density to the material under predetermined mechanical stresses.

In an un-polarized state magnetostrictive transducers are non-linear, however, in a polarized state (achieved by the use of permanent magnets, direct current or operation at remanance) they are linear (i.e. piezomagnetic) .

Properly arranged magnetostrictive transducers can achieve radiated ultrasonic (acoustic) powers up to several kilowatts with efficiencies of 50%, however, operating frequencies are usually limited to frequencies below 100 kHz.

Typically electrostatic transducers comprise a fixed conductive plate having one electric charge and a moveable conductive plate (diaphragm) to which is applied a variable (amplitude) attractive or repulsive electric charge. The resulting force on the diaphragm produces a mechanical energy which is transferred to the surrounding atmosphere.

Typical piezoelectric transducers use crystals or polycrystalline ceramic materials and in their simplest form are arranged to form an expansion-contraction region along the axis between the electrodes when an alternating voltage, also typically a very low current is applied. These materi¬ als may be operated in various modes, two of those modes be¬ ing the 33-mode where the stress, strain and electric field are in the same direction and the 31-mode where the stress

and strain are in the same direction but orthogonal to the electric field. For the example of piezoelectric ceramics their properties vary as a function of time, static stress, stress cycling and electric field strength.

The electro magnetic coupling factor, k, of these materials is an important measure of the effectiveness of the energy conversion mechanism and is a function of mutual elastic and dielectric energy density, elastic self energy density and dielectric self energy density.

A benefit of piezo electric transducers of the polymeric film type is the adaptability of their physical form to the shape required in the application. They are pliant, flexible, tough and light weight. These materials are based on a polyvinylidene flouride (PVDF) which show typically the highest piezo and pyroelectric activities of most polymers and is capable of being produced in a variety of thickness and configurations of shape and active area.

Additional characteristics of this material comprise the ability to produce patterned transducer arrays, high piezoelectric sensitivity in planar and hydrostatic modes g which can produce volts into 10 ohm resistance, broad band

_3 frequency response from 10 Hz to GHz providing also a wide

—8 6 dynamic response over 286 dB (10 to 10 psi) (utorr to

Mbar) , elastic compliance, high dielectric strength (up to 75V/um) , high mechanical strength 10 9-1010 Pascal modulus and importantly high stability particularly in high moisture, high temperature (100'C), chemical, oxidant and UV affected atmospheres. Low mechanical and electric impedance allows efficient transfer of energy to air or other gasses.

BRIEF DESCRIPTION OF THE INVENTION

In an aspect of the invention a method for atomizing a liquid at temperatures and pressures below the boiling point

of the liquid (evaporation) comprises the steps of; a) providing a working atmosphere comprising a mixture of gas and suspended liquid droplets, and, b) subjecting said working atmosphere to ultrasonic energy which reduces the size of said liquid droplets .

In a further aspect of the invention a method for converting liquid into a vapour at temperatures and pressures below the boiling point of the liquid (evaporation) comprises the steps of; a) providing a working atmosphere that is to be cooled, comprising a mixture of gas and suspended liquid droplets, and, b) subjecting said working atmosphere to ultrasonic energy which partially evaporates said liquid droplets, thereby inducing absorption of latent heat of evaporation from the said working atmosphere thereby cooling the atmosphere.

In yet a further aspect of the invention a method for converting liquid into a vapour at temperatures and pressures below the boiling point of the liquid (evaporation) comprises the steps of; a) providing a working atmosphere comprising a mixture of gas and suspended liquid droplets, and, b) subjecting said working atmosphere to ultrasonic energy which evaporates said liquid droplets, thereby inducing absorption of latent heat of evaporation from the said working atmosphere thereby cooling the atmosphere.

In another aspect of the invention a method of evaporation according to the method described above comprises the further step of c) circulating a portion of the working atmosphere so as to be subjected to step b) again and thereby further cool the working atmosphere.

Yet another aspect of the invention is a method of evaporation comprising the further step of g) using a predetermined ultrasonic energy frequency and amplitude which selectively vaporizes a selected liquid.

In yet a further aspect of the invention a method of conditioning air comprises the steps of; a) creating a flow of air through a passage, b) distributing droplets of liquid in said flowing air, c) applying ultrasonic energy into said flowing air containing liquid droplets, and thereby inducing absorption of latent heat of evaporation from said flowing air to cool said air.

A further aspect of the invention is an air-conditioning apparatus for conditioning an air atmosphere comprising an air flow passage for passing an air atmosphere therethrough, liquid droplet distribution means to distribute droplets of liquid in said air flow, and an ultrasonic energy emitter means arranged and adapted so as to emit ultrasonic energy into said air flow 'passage containing air and liquid droplets to thereby induce absorption of latent heat of evaporation from said flowing air to cool said air.

In an aspect of the invention a bacterial reduction apparatus comprising an air flow passage for passing an air atmosphere therethrough, liquid droplet distribution means to distribute droplets of liquid containing bacteriological matter into said air flow, and an ultrasonic energy emitter means arranged and adapted so as to emit ultrasonic energy into said air flow passage containing air and said liquid droplets o thereby evaporate said liquid droplets destroying said

bacteriological matter, inducing absorption of latent heat of evaporation from the said air and cooling the air and in combination reducing the incidence of live bacteriological matter in said air/vapour atmosphere passing from said flow passage.

In a further aspect a bacterial reduction apparatus comprises an ultrasonic energy emitter adapted to have its field of effect directed to the internal volume of a pipe containing a working atmosphere that is to be cooled comprising a mixture of gas and liquid droplets containing bacteriological matter, and, an ultrasonic energy emitter means arranged and adapted so as to emit ultrasonic energy into said working atmosphere to thereby evaporate said liquid droplets to induce an absorption of the latent heat of evaporation from the said working atmosphere thereby cooling the atmosphere and reducing the incidence of live bacteriological matter in said air/vapour atmosphere passing from said flow passage.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, wherein

Fig. 1 depicts a schematic of an air conditioning system incorporating the method and apparatus of the invention,

Fig. 2 depicts a schematic of an air-conditioning apparatus using a heat exchanger means incorporating the method and means of the invention, and

Fig. 3 depicts a schematic of a closed pipe work system incorporating the method and means of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It will be understood that the following descriptions relating to typical embodiments of the present invention are given for the purpose of illustration only and that this invention includes all modifications and equivalents with lie within the scope of the invention.

In an air-conditioning example, as depicted schematically in Fig. 1, incoming atmosphere 10 is a mixture of air and water vapour to which is added by ato ization means 11, a spray of water droplets 12 which can be carried by the air flow denoted by arrows 13.

In this particular atmospheric condition ultrasonic energy is most advantageously applied.

In this embodiment the air, vapour, and water droplet mixture is directed into an air flow passage 14 by a negative pressure fan 15 (located coaxial with the air flow passage) . Within the air flow passage is preferably located an ultrasonic energy emitter means 16 arranged to direct its energy emission into the air flow passage.

The physical configuration of such an energy emitter means could take many forms. In this embodiment the emitter is formed integral with a grid like form work 17 located in the air flow path within the air flow passage. The emitter is required to create an environment in the air, vapour, water droplet air flow, which leads to the evaporation of the water droplets.

In this embodiment piezo film 18 is adhered to the grid like frame work 17. The framework is designed to minimize friction to the air flow and to space the active (piezo film) ultrasonic emission areas within the air flow such that the field in which evaporation takes place is confined to the air flow passage in the vicinity of the grid like framework.

In an alternative embodiment schematically depicted in Fig. 2 the framework may be arranged as an array of passages 19 and 20 in which the piezo film is placed in passageways 19 such that its field of effect envelopes the volume of the passageway. Other passages 20 for communicating dry air to be cooled are arranged to lie orthogonal to the first said passages as in a heat exchanger configuration. Thus the other passages can act as the dry side of the heat exchanger and as latent heat of evaporation is drawn from the atmosphere within the first of said passages, heat will also be drawn from the other passages. Thus the air 20 flowing in the dry side of the heat exchanger looses heat and its temperature reduces. This arrangement may be suitable for use in an air-conditioning apparatus to provide cool dry air to which can be added moisture if desired.

It is a property of the above process while in use, that the vapour pressure of the air flowing in the passages acted upon by the ultrasonic energy emitter means is increased, therefore, a means to condense the acquired water vapour 21 (refer to Fig. 1) may be used to reduce the vapour pressure (relative humidity) of the air flow exiting from the first of said air flow passages. Since condensing water releases its latent heat of phase change, this heat if not used by the apparatus, may be released to the atmosphere and the condensed water 22 used in the evaporation process as a source of the water to be atomised. Typically, also, the condensed water is relatively cool and assists the cooling effect caused first by the atomised spray vaporising and then by the further vaporisation induced by the ultrasonic means.

in a further adaption of the alternative embodiment described above, moisture loaded air flow produced by the ultrasonic emitters can be injected into the wet side of a heat exchanger configuration wherein, upon condensation of the water in the air flow passages, latent heat of phase change is drawn from the air flow on the dry side of the heat

exchanger.

The preceding embodiments are an example of a open ended atmospheric application of the processes of the invention used typically in the control of temperature and humidity in domestic and industrial air conditioning.

The embodiment as depicted in Fig. 3 relates to a closed application of the process of the invention, although self contained in its configuration, this particular arrangement may be used to enhance the operation of a conventional open ended air conditioning system.

Fig. 3 depicts a cross-section of a single bore pipe 23 having an internal wall 24 and an internal atmospheric condition A, initially comprising atomized liquid in gaseous suspension. The atomised liquid may be water, alcohol or other suitable liquid which has a change of state temperature at or below the pressure internal of the pipe, while the working or transport, gas used therein may be air, an inert gas or other suitable gas typically although not necessarily at atmospheric or lower pressure.

On the internal surface of the wall 24 there is located an ultrasonic energy emitter 25, preferably of the piezo film type. A further embodiment not shown may provide for a portion of the pipe to be constructed of a suitable transducer material. Alternatively, the film may be located in a grid like configuration within the pipe and/or the film may still be able to exert its field of effect into the pipe although it is attached or adhered to the outside of the pipe. It the latter case it could be that the mechanical resonance of the pipe could be chosen to match the ultrasonic frequencies required for the purposes of advantageously af¬ fecting the contents of the pipe. Furthermore, the internal surface of the pipe may be advantageously shaped or profiled so as to promote the desired effect occurring within the

pipe .

When the piezo film is energized in a required zone of the pipe, the atmosphere condition A will change to a state Al, in which the liquid droplets suspended in the pipe volume are evaporated. This process draws latent heat of change of state from the gas atmosphere Al in the pipe as well as the region outside the pipe or as in this embodiment atmosphere B which exist outside the pipe. The efficiency of this arrangement being of course dependant on the heat transfer characteristics of the pipe as determined by its material and surface profile and the characteristics of the region external of the pipe.

Schematically, as depicted in Fig. 3 the vaporised atmosphere Al is pumped to a location 26 for condensation and then for insertion again into the atmosphere at A and the latent heat of phase change from vapour to liquid occurring at 26 may be drawn off for heating purposes or vented to atmosphere.

Fig. 3 also depicts schematically the disposition of an atmosphere B surrounding the pipe which may advantageously made a part of the air flow of an open ended air conditioning apparatus. In this case, the atmosphere B will be in the vicinity of the pipe and leave the vicinity at a cooler temperature because there will be. a loss of energy as the latent heat of change of state taking place within the pipe will be drawn from the passing air flow denoted as atmosphere B.

However, further assistance to the process of cooling atmosphere B maybe provided by locating additional piezo film adjacent or upon the pipe, whereby, the field of influence of an ultrasonic energy field may also impinge on the atmosphere B flowing past the pipe. It is anticipated that in such an arrangement any droplets (atomized liquid) suspended in

atmosphere B may be acted upon in such a way that evaporation is induced and further latent heat of phase change is drawn from atmosphere B to thereby produce cool moist (i.e. high vapour pressure) atmosphere.

It will be appreciated that the gas, liquid mixture used in the pipe could be different from the typically air/water mixture used external to the pipe and advantageously so when the pipe mixture is capable of producing temperature reduc¬ tions at temperatures below O'C.

Indeed, in the case of below water freezing temperatures any water that condenses on the pipe would be almost immediately re-evaporated and its latent heat of change of state typically taken from the atmosphere B while the latent heat of condensation lost into the pipe system.

It is further possible to appreciate that the air/water mixture of the atmosphere B can be controlled in respect to its temperature and .vapour pressure by the controlled action of the piezo film both within and external to the pipe. Control is possible by way of varying one or more of a number of driving forces applied to the piezo film. These forces include the frequency of operation, the level of the signal applied and the duration of its application. Therefore, although there may be a number of controlled variables, it is possible using appropriate control means, to make it easy for the operator to adjust one indicator for temperature and one indicator for relative humidity.

The embodiment schematically depicted in Figs. 2 and 3 may form the basis for an arrangement of a plurality of such pipes, arranged so that a large volume of gas, liquid or atmosphere may be drawn past the pipes in quantities sufficient to control the temperature and humidity of larger volumes of atmosphere as may be required in domestic and industrial environments.

Although not depicted, the environment in the vicinity of the cooling coils of a typical Reverse Cycle Air- Conditioner (RC A/C) may be controlled using the field of an ultrasonic emitter. For example, piezo film, as an example of the ultrasonic emitter, could be placed adjacent or upon the cooling coils of the RC A/C and it will be found that there will be beneficial effect by the improvement of the efficiency of heat transfer.

Using the abovementioned arrangement any liquid contained within the atmosphere passing within the field of effect of the emitter will be evaporated thus reducing its temperature of the atmosphere adjacent its placement.

It is thought, that as long as the vapour pressure in the passing atmosphere is below saturation, this process can continue to produce benefits since moist atmosphere will a) assist the cooling effect of the RC A/C apparatus, and b) beneficially add moisture to the RC A/C air being produced which typically is dried by the A/C apparatus.

The tendency for the cooling coils to accumulate by way of condensation, water from the atmosphere being passed through them, provides the ideal environment for the application of the process of the invention. Evaporation of the water produced not only balances the loss of any latent heat of condensation but should assist the generally cooling effect of the cooling coils by promoting evaporation when the effect of the ultrasonic emitters is added to the process.

A further embodiment of the invention not depicted is that of adjusting the frequency and/or amplitude of the ultrasonic energy to selectively vaporize a liquid which has been entrained by any suitable atomisation means into an atmosphere as previously described. In this example, there may exist a number of fluids in a mixture and after atomisation the application of a particular ultrasonic energy

will separate from the atmosphere in vapour form the desired fluid. Alternatively, the resulting atmosphere may be used in a particular chemical process to advantage as a result of the vaporization of the desired liquid.

VAPOUR COMPRESSION REFRIGERATION

Conventional refrigeration processes depend on the vaporisation of refrigerant generally in a closed system evaporator. Vaporising refrigerant extracts from the evaporator the necessary heat to supply the latent heat of vaporisation of the refrigerant and the evaporator, in turn draws the necessary heat from its surroundings thus cooling the enclosed refrigerator space.

The vaporisation process takes place at the entrance to the evaporator, which, typically comprises an isenthalpic nozzle arranged to create a two phase (liquid/vapour) atmosphere which is cooled in the process but the droplets do not always totally vaporise.

Therefore, ultrasonic induced vaporisation with little extra energy expenditure to create the ultrasonic environment, will increase the amount of vaporisation, enhance the cooling effect of the evaporator and increase the quantity of heat drawn from the surroundings of the evaporator thus further cooling the enclosed refrigerator space. This may occur by way of the action of ultrasonic energy on the gaseous atmosphere itself and may advantageously induce sympathetic resonant vibrations in the mechanical structure of the evaporator apparatus.

With the advantageous use of such an arrangement, not only will current CFC based refrigerants work more efficiently but more environmentally friendly refrigerants which previously worked less efficiently in traditional arrangements may work in the new arrangement with increased

efficiency to rival current CFC based refrigerants.

ABSORPTION REFRIGERATION

Absorption refrigeration for domestic use has generally been abandoned for a number of reasons, namely, high running costs, they are expensive to build, poisonous refrigerant (ammonia) is typically used and because of the corrosive nature of the refrigerant a 10 year life time is typical. The three latter reasons have become lesser concerns as, manufacturing techniques, handling and alternative refrigerants and planned obsolescence, measures improve. However, with the use of a low cost ultrasonic vaporisation process which greatly enhances heat exchange efficiency, the economics of running such a refrigerator become more affordable. Add to this the improvements of technology which provides alternative energy especially in remote areas and small absorption refrigeration system which uses little energy becomes an even more economic proposition for these areas.

BACTERIA REDUCTION IN GASEOUS ENVIRONMENTS

Although not described in detail hereinbefore, it is believed that, even though the use of ultrasonic emitters to reduce or eliminate bacteriological organisms in liquid is well known, the use of ultrasonic emitters in a liquid vapour, liquid droplet and gaseous atmosphere to reduce or eliminate bacteriological organisms is not known.

The parameters of the environment required to produce this desired result comprise a suitable field flux of ultrasonic energy at an appropriate frequency of operation and an appropriate exposure period of the mixture within the field.

A variety of applications of this aspect of the invention are described herein. One example is the use of such an environment in the operation of a cooling tower as is typically used in commercial air-conditioning plants. The incidence of Legionella bacteria in its many forms has been cause for great concern to health officials. Therefore, it will be clearly apparent that, either the direct treatment of the water towers' water reservoir, or, treatment of the environment about the water tower cooling apparatus would be advantageous in this regard.

Placement of a suitable ultrasonic emitter in one or more of these locations would be beneficial by a) reducing or eliminating harmful bacteriological organisms and b) reducing the temperature by inducing further vaporisation.

In a further example it may be seen that domestic hot water systems may be kept at lower temperatures than are typically the case. Generally, hot water services are kept at temperatures greater than 60"C for the express reason of providing an environment non-conducive to unwanted bacteriological growth, however, a lower temperature say between 50 ^* C and 55 ^* C would still suffice for domestic hot water purposes.

Therefore, by providing an efficient , reliable and safe in-line ultrasonic emitter device which adequately eliminates bacteria at the outlet of the hot water service, the thermostatically controlled hot water service temperature may be kept at more economical and safer temperatures.

A bacteriological barrier as generally proposed herein, could also be adapted to fit at the outlets of air-condition¬ ing systems of any type, so that, the air, vapour, and suspended moisture mixture of the gasses being supplied to the room, operating theatre, etc, can be adequately treated to eliminate or reduce the level of airborne contaminants

which would otherwise possibly be harmful to the room oc¬ cupants.

An embodiment of such a barrier could be in much the same configuration as that depicted and described in regards to the grid framework shown in Fig. 1.